CN117164153A - Method and system for recycling inorganic salt by fractional crystallization of salt-containing wastewater - Google Patents
Method and system for recycling inorganic salt by fractional crystallization of salt-containing wastewater Download PDFInfo
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- CN117164153A CN117164153A CN202311206310.4A CN202311206310A CN117164153A CN 117164153 A CN117164153 A CN 117164153A CN 202311206310 A CN202311206310 A CN 202311206310A CN 117164153 A CN117164153 A CN 117164153A
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- 150000003839 salts Chemical class 0.000 title claims abstract description 208
- 238000000034 method Methods 0.000 title claims abstract description 113
- 239000002351 wastewater Substances 0.000 title claims abstract description 77
- 238000001640 fractional crystallisation Methods 0.000 title claims abstract description 37
- 229910017053 inorganic salt Inorganic materials 0.000 title claims abstract description 36
- 238000004064 recycling Methods 0.000 title claims description 39
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 claims abstract description 256
- 238000002425 crystallisation Methods 0.000 claims abstract description 226
- 230000008025 crystallization Effects 0.000 claims abstract description 224
- 239000012528 membrane Substances 0.000 claims abstract description 128
- 238000000926 separation method Methods 0.000 claims abstract description 121
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 claims abstract description 113
- 239000012452 mother liquor Substances 0.000 claims abstract description 113
- 229910000019 calcium carbonate Inorganic materials 0.000 claims abstract description 54
- 238000001035 drying Methods 0.000 claims abstract description 27
- 239000010802 sludge Substances 0.000 claims abstract description 23
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims abstract description 21
- 239000002910 solid waste Substances 0.000 claims abstract description 18
- 238000005342 ion exchange Methods 0.000 claims abstract description 15
- 238000010612 desalination reaction Methods 0.000 claims abstract description 14
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 283
- 239000013078 crystal Substances 0.000 claims description 187
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 154
- 239000000047 product Substances 0.000 claims description 128
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims description 117
- 239000002245 particle Substances 0.000 claims description 83
- 229910052938 sodium sulfate Inorganic materials 0.000 claims description 82
- 235000011152 sodium sulphate Nutrition 0.000 claims description 82
- 238000001728 nano-filtration Methods 0.000 claims description 80
- 239000012267 brine Substances 0.000 claims description 73
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 claims description 73
- 239000011780 sodium chloride Substances 0.000 claims description 72
- 238000001704 evaporation Methods 0.000 claims description 61
- RSIJVJUOQBWMIM-UHFFFAOYSA-L sodium sulfate decahydrate Chemical compound O.O.O.O.O.O.O.O.O.O.[Na+].[Na+].[O-]S([O-])(=O)=O RSIJVJUOQBWMIM-UHFFFAOYSA-L 0.000 claims description 57
- 238000001471 micro-filtration Methods 0.000 claims description 54
- 238000001223 reverse osmosis Methods 0.000 claims description 49
- 239000000243 solution Substances 0.000 claims description 40
- 239000011777 magnesium Substances 0.000 claims description 38
- 239000000347 magnesium hydroxide Substances 0.000 claims description 38
- 229910001862 magnesium hydroxide Inorganic materials 0.000 claims description 38
- 239000002244 precipitate Substances 0.000 claims description 37
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 35
- 229910052749 magnesium Inorganic materials 0.000 claims description 35
- VTHJTEIRLNZDEV-UHFFFAOYSA-L magnesium dihydroxide Chemical compound [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 claims description 35
- 239000002253 acid Substances 0.000 claims description 32
- 239000003795 chemical substances by application Substances 0.000 claims description 31
- 230000008014 freezing Effects 0.000 claims description 25
- 238000007710 freezing Methods 0.000 claims description 25
- 239000003513 alkali Substances 0.000 claims description 24
- 239000003456 ion exchange resin Substances 0.000 claims description 24
- 229920003303 ion-exchange polymer Polymers 0.000 claims description 24
- 230000008569 process Effects 0.000 claims description 22
- 230000008018 melting Effects 0.000 claims description 21
- 238000002844 melting Methods 0.000 claims description 21
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 claims description 18
- 238000007599 discharging Methods 0.000 claims description 18
- 238000002156 mixing Methods 0.000 claims description 17
- 239000011575 calcium Substances 0.000 claims description 16
- 229910052782 aluminium Inorganic materials 0.000 claims description 14
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 14
- 239000000391 magnesium silicate Substances 0.000 claims description 14
- 229910052919 magnesium silicate Inorganic materials 0.000 claims description 14
- 235000019792 magnesium silicate Nutrition 0.000 claims description 14
- 239000007787 solid Substances 0.000 claims description 14
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 claims description 13
- 150000001768 cations Chemical class 0.000 claims description 13
- 229910001425 magnesium ion Inorganic materials 0.000 claims description 13
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 12
- 229910052791 calcium Inorganic materials 0.000 claims description 12
- 239000012153 distilled water Substances 0.000 claims description 12
- 239000007788 liquid Substances 0.000 claims description 12
- 239000000203 mixture Substances 0.000 claims description 12
- 239000002455 scale inhibitor Substances 0.000 claims description 12
- 239000010413 mother solution Substances 0.000 claims description 11
- 239000013049 sediment Substances 0.000 claims description 9
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 claims description 8
- 239000001110 calcium chloride Substances 0.000 claims description 8
- 229910001628 calcium chloride Inorganic materials 0.000 claims description 8
- 239000000378 calcium silicate Substances 0.000 claims description 8
- 229910052918 calcium silicate Inorganic materials 0.000 claims description 8
- OYACROKNLOSFPA-UHFFFAOYSA-N calcium;dioxido(oxo)silane Chemical compound [Ca+2].[O-][Si]([O-])=O OYACROKNLOSFPA-UHFFFAOYSA-N 0.000 claims description 8
- 150000002500 ions Chemical class 0.000 claims description 8
- 238000011084 recovery Methods 0.000 claims description 8
- 239000002699 waste material Substances 0.000 claims description 8
- 230000009471 action Effects 0.000 claims description 7
- 229910001385 heavy metal Inorganic materials 0.000 claims description 7
- 229910000323 aluminium silicate Inorganic materials 0.000 claims description 6
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 claims description 6
- 230000002195 synergetic effect Effects 0.000 claims description 6
- 239000006004 Quartz sand Substances 0.000 claims description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 5
- 230000007935 neutral effect Effects 0.000 claims description 5
- 238000010992 reflux Methods 0.000 claims description 5
- 239000002223 garnet Substances 0.000 claims description 4
- 238000012958 reprocessing Methods 0.000 claims description 3
- ZADYMNAVLSWLEQ-UHFFFAOYSA-N magnesium;oxygen(2-);silicon(4+) Chemical compound [O-2].[O-2].[O-2].[Mg+2].[Si+4] ZADYMNAVLSWLEQ-UHFFFAOYSA-N 0.000 claims 3
- 239000000758 substrate Substances 0.000 claims 2
- 239000002920 hazardous waste Substances 0.000 abstract description 5
- 230000009467 reduction Effects 0.000 abstract description 5
- 235000002639 sodium chloride Nutrition 0.000 description 247
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 42
- 230000008020 evaporation Effects 0.000 description 33
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 24
- 239000010703 silicon Substances 0.000 description 24
- 229910052710 silicon Inorganic materials 0.000 description 24
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 22
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 15
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 14
- 235000011121 sodium hydroxide Nutrition 0.000 description 14
- 238000006243 chemical reaction Methods 0.000 description 13
- HCWCAKKEBCNQJP-UHFFFAOYSA-N magnesium orthosilicate Chemical compound [Mg+2].[Mg+2].[O-][Si]([O-])([O-])[O-] HCWCAKKEBCNQJP-UHFFFAOYSA-N 0.000 description 11
- 238000001556 precipitation Methods 0.000 description 10
- 229910001415 sodium ion Inorganic materials 0.000 description 10
- FKNQFGJONOIPTF-UHFFFAOYSA-N Sodium cation Chemical compound [Na+] FKNQFGJONOIPTF-UHFFFAOYSA-N 0.000 description 9
- 239000012141 concentrate Substances 0.000 description 9
- 239000011734 sodium Substances 0.000 description 9
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 8
- TWRXJAOTZQYOKJ-UHFFFAOYSA-L Magnesium chloride Chemical compound [Mg+2].[Cl-].[Cl-] TWRXJAOTZQYOKJ-UHFFFAOYSA-L 0.000 description 8
- 238000005119 centrifugation Methods 0.000 description 8
- 230000001965 increasing effect Effects 0.000 description 8
- 229910000029 sodium carbonate Inorganic materials 0.000 description 8
- 238000000108 ultra-filtration Methods 0.000 description 8
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 7
- 238000005516 engineering process Methods 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 239000002994 raw material Substances 0.000 description 7
- 239000000126 substance Substances 0.000 description 7
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 6
- 229910002651 NO3 Inorganic materials 0.000 description 6
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 6
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 6
- 239000002585 base Substances 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 238000005189 flocculation Methods 0.000 description 6
- 230000016615 flocculation Effects 0.000 description 6
- 229910052708 sodium Inorganic materials 0.000 description 6
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 5
- 235000019738 Limestone Nutrition 0.000 description 5
- 235000011941 Tilia x europaea Nutrition 0.000 description 5
- 238000000909 electrodialysis Methods 0.000 description 5
- 238000001914 filtration Methods 0.000 description 5
- 239000010440 gypsum Substances 0.000 description 5
- 229910052602 gypsum Inorganic materials 0.000 description 5
- 239000012535 impurity Substances 0.000 description 5
- 239000004571 lime Substances 0.000 description 5
- 239000006028 limestone Substances 0.000 description 5
- 229940088417 precipitated calcium carbonate Drugs 0.000 description 5
- 235000017550 sodium carbonate Nutrition 0.000 description 5
- 229910004298 SiO 2 Inorganic materials 0.000 description 4
- 230000033558 biomineral tissue development Effects 0.000 description 4
- 239000001569 carbon dioxide Substances 0.000 description 4
- 229910002092 carbon dioxide Inorganic materials 0.000 description 4
- 229920001429 chelating resin Polymers 0.000 description 4
- 238000005262 decarbonization Methods 0.000 description 4
- 238000006477 desulfuration reaction Methods 0.000 description 4
- 230000023556 desulfurization Effects 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 238000004090 dissolution Methods 0.000 description 4
- 239000010842 industrial wastewater Substances 0.000 description 4
- 229910001629 magnesium chloride Inorganic materials 0.000 description 4
- 239000008267 milk Substances 0.000 description 4
- 210000004080 milk Anatomy 0.000 description 4
- 235000013336 milk Nutrition 0.000 description 4
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 3
- 230000001174 ascending effect Effects 0.000 description 3
- 239000004566 building material Substances 0.000 description 3
- 239000006227 byproduct Substances 0.000 description 3
- NKWPZUCBCARRDP-UHFFFAOYSA-L calcium bicarbonate Chemical compound [Ca+2].OC([O-])=O.OC([O-])=O NKWPZUCBCARRDP-UHFFFAOYSA-L 0.000 description 3
- 229910000020 calcium bicarbonate Inorganic materials 0.000 description 3
- 229910001424 calcium ion Inorganic materials 0.000 description 3
- 159000000007 calcium salts Chemical class 0.000 description 3
- 125000004122 cyclic group Chemical group 0.000 description 3
- 239000013505 freshwater Substances 0.000 description 3
- 230000006698 induction Effects 0.000 description 3
- 239000006247 magnetic powder Substances 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 230000000630 rising effect Effects 0.000 description 3
- 159000000000 sodium salts Chemical class 0.000 description 3
- 229910021578 Iron(III) chloride Inorganic materials 0.000 description 2
- MKPXGEVFQSIKGE-UHFFFAOYSA-N [Mg].[Si] Chemical compound [Mg].[Si] MKPXGEVFQSIKGE-UHFFFAOYSA-N 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- -1 containing Chemical class 0.000 description 2
- 230000018044 dehydration Effects 0.000 description 2
- 238000006297 dehydration reaction Methods 0.000 description 2
- 230000001687 destabilization Effects 0.000 description 2
- 230000000368 destabilizing effect Effects 0.000 description 2
- 239000008233 hard water Substances 0.000 description 2
- RBTARNINKXHZNM-UHFFFAOYSA-K iron trichloride Chemical compound Cl[Fe](Cl)Cl RBTARNINKXHZNM-UHFFFAOYSA-K 0.000 description 2
- 238000003973 irrigation Methods 0.000 description 2
- 230000002262 irrigation Effects 0.000 description 2
- QWDJLDTYWNBUKE-UHFFFAOYSA-L magnesium bicarbonate Chemical compound [Mg+2].OC([O-])=O.OC([O-])=O QWDJLDTYWNBUKE-UHFFFAOYSA-L 0.000 description 2
- 229910000022 magnesium bicarbonate Inorganic materials 0.000 description 2
- 235000014824 magnesium bicarbonate Nutrition 0.000 description 2
- 239000002370 magnesium bicarbonate Substances 0.000 description 2
- 239000010446 mirabilite Substances 0.000 description 2
- 238000005457 optimization Methods 0.000 description 2
- 239000011347 resin Substances 0.000 description 2
- 229920005989 resin Polymers 0.000 description 2
- 238000007790 scraping Methods 0.000 description 2
- 235000012239 silicon dioxide Nutrition 0.000 description 2
- 238000001694 spray drying Methods 0.000 description 2
- 230000001502 supplementing effect Effects 0.000 description 2
- 239000004902 Softening Agent Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 238000012271 agricultural production Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 230000000903 blocking effect Effects 0.000 description 1
- 230000003139 buffering effect Effects 0.000 description 1
- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 1
- 239000000920 calcium hydroxide Substances 0.000 description 1
- 235000011116 calcium hydroxide Nutrition 0.000 description 1
- 229910001861 calcium hydroxide Inorganic materials 0.000 description 1
- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-N carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 description 1
- 238000005341 cation exchange Methods 0.000 description 1
- 239000003518 caustics Substances 0.000 description 1
- 239000013043 chemical agent Substances 0.000 description 1
- 238000009388 chemical precipitation Methods 0.000 description 1
- 238000005352 clarification Methods 0.000 description 1
- 238000005345 coagulation Methods 0.000 description 1
- 230000015271 coagulation Effects 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 239000000084 colloidal system Substances 0.000 description 1
- 238000009833 condensation Methods 0.000 description 1
- 230000005494 condensation Effects 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000011033 desalting Methods 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000003651 drinking water Substances 0.000 description 1
- 235000020188 drinking water Nutrition 0.000 description 1
- 239000003814 drug Substances 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 238000004043 dyeing Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 238000005194 fractionation Methods 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 239000003621 irrigation water Substances 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 239000000395 magnesium oxide Substances 0.000 description 1
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 1
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical group [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000005374 membrane filtration Methods 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 238000005065 mining Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 238000002203 pretreatment Methods 0.000 description 1
- 238000007639 printing Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000008213 purified water Substances 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000013535 sea water Substances 0.000 description 1
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 1
- 239000001488 sodium phosphate Substances 0.000 description 1
- 229910000162 sodium phosphate Inorganic materials 0.000 description 1
- 239000002689 soil Substances 0.000 description 1
- 238000009270 solid waste treatment Methods 0.000 description 1
- 238000007711 solidification Methods 0.000 description 1
- 230000008023 solidification Effects 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 239000006228 supernatant Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- RYFMWSXOAZQYPI-UHFFFAOYSA-K trisodium phosphate Chemical compound [Na+].[Na+].[Na+].[O-]P([O-])([O-])=O RYFMWSXOAZQYPI-UHFFFAOYSA-K 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 238000004065 wastewater treatment Methods 0.000 description 1
Abstract
A method and a system for recovering inorganic salt by fractional crystallization of salt-containing wastewater, wherein the method comprises the following steps: the method comprises the steps of (1) primary calcium carbonate crystallization, (2) primary membrane separation, (3) membrane concentration desalination, (4) calcium sulfate crystallization, (5) secondary calcium carbonate crystallization, (6) secondary membrane separation and collaborative desilication, (7) ion exchange deep hardness removal, (8) carbonate alkalinity removal, (9) salt separation and crystallization, (10) mixed salt crystallization, and (11) mother liquor drying. The method and the system can perform fractional crystallization on the salt-containing wastewater, so that various inorganic salt products in the salt-containing wastewater can be recycled, the 'source emission reduction' is realized, the solid waste and the hazardous waste yield of mixed salt of sludge are reduced, and the 'secondary pollution' is reduced.
Description
Technical Field
The invention belongs to the field of water treatment, and particularly relates to a method and a system for recovering inorganic salt by fractional crystallization of salt-containing wastewater.
Background
The production way of the salt-containing wastewater is wide, and the salt-containing wastewater is mainly derived from the production and processing processes of industries such as chemical industry, petrochemical industry, medicine, printing and dyeing industry, papermaking industry, metallurgy industry, electric power industry, mining industry and the like, and the wastewater with high inorganic salt component concentration generated in the treatment process of unconventional water sources such as sea water desalination, wastewater recycling and the like. These waste waters contain, in addition to organic contaminants, also a large amount of inorganic salts, mainly containing, for example, chloride ions (Cl) - ) Sulfate radical (SO) 4 2- ) Heavy Carbonate (HCO) 3 - ) Sodium ion (Na) + ) Calcium ion (Ca) 2+ ) And magnesium ion (Mg) 2+ ) An inorganic salt composed of plasma. At present, the salt-containing wastewater is a popular method, and is not accurately defined. Referring to the related literature, the concentration of salt (TDS) in water is divided into five types of water quality: the salt content (TDS) is less than 1g/L and is fresh water; the salt content (TDS) is 1-3g/L of brackish water; the salt content (TDS) is 3-10 g/L; the salt content (TDS) is 10-50 g/L; brine with a salt content (TDS) of more than 50 g/L. Fresh water or brackish water can be used for farmland irrigation, the salt water can be used for irrigation after a certain technical measure is adopted, and the salt water and brine can not be used as irrigation water. If the salt-containing wastewater is directly discharged without treatment, the salt-containing wastewater will have great harm to water body organisms, domestic drinking water and industrial and agricultural production water, and will have great harm to the ground surfaceThe water, the underground water and the soil cause serious pollution and destroy the ecological environment. Therefore, the wastewater with the salt content of more than 3g/L is generally called as salt-containing wastewater, and the wastewater with the salt content of more than 10g/L is generally called as high-salt wastewater. Regarding the technology of salt-containing wastewater treatment, many researches and application reports are made, such as the technology of evaporation, chemical precipitation, ion exchange, reverse osmosis, electrodialysis and the like and the combined process thereof. However, the method has the problems of high consumption of chemicals, high solid waste yield, low recycling rate of inorganic salt, low treatment efficiency, high running cost and the like.
For the wastewater, the combined flow of pretreatment-membrane concentration-evaporative crystallization is adopted, the hardness, silicon, suspended matters and other impurities in the water are removed through pretreatment methods such as chemical softening clarification, ion exchange and the like, membrane treatment technologies such as ultrafiltration, reverse osmosis, nanofiltration, electrodialysis and the like are adopted to recycle water and concentrate salt, the concentrated and reduced high-salt brine is treated through evaporative crystallization, inorganic salt in the high-salt brine is recovered through fractional crystallization, or the inorganic salt and other impurities in the brine are crystallized and solidified through mixed salt crystallization and evaporative drying, so that the aim of zero emission of the wastewater is finally realized, and the risk of environmental pollution is controlled.
CN 103508602A discloses a process of zero emission of high salinity industrial wastewater integrated with membrane and evaporation crystallization, specifically discloses a process of delivering industrial wastewater to a reverse osmosis process through a high pressure pump after ultrafiltration pretreatment, recycling water after osmosis measurement, carrying out electrodialysis treatment on concentrated solution after filtration for many times, evaporating and crystallizing materials after electrodialysis concentration, and obtaining salt mud and condensed water. The invention couples the membrane and the evaporation crystallization, not only can recover high-quality purified water from high-salt-concentration industrial wastewater, but also can realize zero emission of the high-salt wastewater, but the material of the invention only can obtain a mixture of salt mud after final evaporation crystallization, and the finally obtained salt mud cannot be fully reused, and the high-concentration salt concentrated solution obtained after the industrial wastewater is subjected to ultrafiltration pretreatment and reverse osmosis and electrodialysis treatment contains various components including sodium chloride, sodium sulfate and the like, so that great waste is caused by direct abandonment or emission, and the formed solid dangerous waste also produces certain pollution to the environment.
CN 105523676A discloses a method for separating salt from high-salt wastewater by zero-emission evaporation crystallization, specifically discloses a method for separating salt from high-concentration salt concentrated solution after pretreatment and deep concentration sequentially through an evaporation crystallization device, a freezing nitrate crystallization device and a salt evaporation crystallization device according to the separation sequence of sodium sulfate, sodium chloride or sodium chloride and sodium sulfate, wherein the nitrate evaporation crystallization device and the salt evaporation crystallization device are connected with a cooling water system through a vapor compressor by referring to the temperature required by freezing nitrate crystallization under the condition of respectively utilizing the vapor compressor to extract and compress secondary steam, and utilize a cooler and/or the temperature required by the inside of the freezing nitrate crystallization device of a refrigerator, so that the solvent recycling and the full separation of solute of the high-concentration salt concentrated solution are realized. The sodium sulfate and commercial salt separated by the high-salt wastewater zero-emission evaporation crystallization salt fractionation method are used as industrial recoverable raw materials, and water resources are recycled, but before the salt concentrated solution is subjected to the fractional separation, the hardness ions such as heavy metal ions, calcium and magnesium in the wastewater are required to be effectively removed by adopting a chemical method, lime or sodium hydroxide, sodium carbonate, PAC and PAM are sequentially added into a high-density pond for coagulation and softening reactions, the generated precipitated sludge is dehydrated into mud cakes by sludge and is treated, the problems of large solid waste sludge amount, large chemical consumption and the like exist, the solid waste treatment difficulty is increased, the fractional crystallization treatment salt amount is increased, and the treatment cost is high.
CN 109179743A discloses a wastewater pretreatment system and method with high calcium sulfate mineralization degree, specifically discloses a pretreatment system comprising a destabilizing flocculation precipitation system, a softening precipitation system, a mechanical filter, an ultrafiltration and post-treatment system, sludge treatment equipment and a magnetic powder separator, and also provides a method for wastewater pretreatment by using the system, which comprises the steps of destabilizing crystallization, flocculation precipitation, softening, flocculation precipitation, precipitation separation and filtration. The technical scheme provided by the invention can be used for pretreatment of coal mine water containing high calcium and high sulfate radical mineralization degree, high salt-containing wastewater and the like, the mineralization degree content after pretreatment is greatly reduced, and the water quality requirement of the Ultrafiltration (UF) system can be met. The calcium sulfate crystallization is promoted by the destabilization crystallization of the waste water with high calcium sulfate mineralization degree, the filter residue gypsum product is separated by flocculation precipitation separation and dehydration, the operation cost is reduced, but the hardness content of the water discharged by the destabilization flocculation precipitation system is still high, the water quality requirement of the water inflow in the ultrafiltration and post-treatment process cannot be met, the softening agent such as quicklime-sodium carbonate method or caustic soda + soda or slaked lime + soda + sodium phosphate is still needed to be added by the softening precipitation system, and meanwhile, the magnetic powder is added, and the problems of large solid waste amount of the softened sludge, large additive amount of chemicals and magnetic powder and high operation cost still exist after the process of loading flocculation precipitation and filtration treatment and the subsequent ultrafiltration and post-treatment process.
In summary, inorganic salts in salt-containing wastewater are generally mainly composed of sodium chloride, sodium sulfate, calcium bicarbonate, magnesium bicarbonate, calcium sulfate and the like. In the prior art, the softening of lime-sodium carbonate or the softening of caustic soda-sodium carbonate and the advanced hard removal pretreatment of cation exchange are commonly adopted, divalent or more multivalent cations such as calcium, magnesium and the like in water are replaced by sodium ions, carbonate alkalinity is removed by adding acid, finally inorganic salt of salt-containing wastewater is converted into a water salt system with sodium chloride and sodium sulfate as absolute dominant components, and then crystallization mixed salt or quality-separated salt is formed by membrane concentration and evaporative crystallization technology. The treatment process has the problems of high consumption of chemical agents, large solid waste sludge, low recovery rate of byproduct inorganic salt and the like. At present, the problem is not solved well.
Disclosure of Invention
The first aim of the invention is to provide a fractional crystallization recovery method of salt-containing wastewater, which can recycle various inorganic salt products in the salt-containing wastewater, realize 'source emission reduction', reduce solid waste and hazardous waste yield of mixed salt of sludge and reduce 'secondary pollution';
the second aim of the invention is to provide a fractional crystallization recovery system of the salt-containing wastewater, which can be used in the fractional crystallization recovery method of the salt-containing wastewater, so that various inorganic salt products in the salt-containing wastewater are recycled, the emission reduction of the source is realized, the solid waste and the dangerous waste yield of mixed salt are reduced, and the secondary pollution is reduced.
In order to achieve the first object of the present invention, the following technical solutions are adopted:
a method for recovering inorganic salt by fractional crystallization of salt-containing wastewater comprises the following steps:
(1) Primary calcium carbonate crystals
Adding alkali into the salt-containing wastewater to adjust the pH value to 9.5-11.5, then delivering the salt-containing wastewater into a primary induced crystallization fluidized bed reactor, adding a first seed crystal into the primary induced crystallization fluidized bed reactor for induced crystallization, separating out calcium carbonate crystal particles, and outputting magnesium hydroxide precipitate along with effluent;
(2) Primary membrane separation
Adding alkali and/or magnesium agent into the effluent of the step (1) to convert magnesium ions in the effluent into magnesium hydroxide precipitate and/or magnesium silicate complex, then sending the magnesium hydroxide precipitate and/or magnesium silicate complex to primary microfiltration membrane equipment along with water for microfiltration treatment, discharging sludge comprising magnesium hydroxide precipitate and/or magnesium silicate and calcium silicate precipitate, and outputting effluent comprising sodium chloride, sodium sulfate and calcium sulfate;
(3) Membrane concentration desalination
Adding acid into the effluent from the step (2) to adjust the pH value to be neutral, adding a scale inhibitor, sending the mixture to a membrane group system along with the water to perform concentration and desalination treatment under the action of the scale inhibitor, outputting produced water for recycling, and outputting concentrated water obtained by concentrating calcium sulfate to supersaturation;
(4) Calcium sulfate crystal
Delivering the concentrated water obtained in the step (3) into a seed crystal circulating fluidized bed, adding calcium sulfate seed crystals into the concentrated water for induced crystallization, separating out calcium sulfate crystal particles, discharging large-particle-size calcium sulfate crystal particles from the bottom, discharging small-particle-size calcium sulfate crystal particles from the middle upper part, and overflowing overflow water containing calcium sulfate and calcium chloride from the upper part; wherein, the grain diameter of the large-grain-diameter calcium sulfate crystal grains is 0.3-2mm, and the grain diameter of the small-grain-diameter calcium sulfate crystal grains is 0.05-0.3mm;
(5) Secondary calcium carbonate crystals
Adding alkali into the overflow water outlet part in the step (4) to adjust the pH value to 10.5-12, then sending the overflow water outlet part into a secondary induced crystallization fluidized bed reactor, adding the first seed crystal into the overflow water outlet part to carry out induced crystallization, separating out calcium carbonate crystal particles, and outputting magnesium hydroxide precipitate along with the water outlet;
(6) Secondary membrane separation synergistic desilication
Adding an aluminum agent into the effluent of the step (5), then sending the effluent to a secondary microfiltration membrane device for microfiltration separation, discharging sludge containing aluminosilicate sediment and silica-magnesium hydroxide sediment, and outputting desilication effluent;
(7) Ion exchange depth hardness removal
Adding acid into the desilication effluent from the step (6) to adjust the pH value to 7-9, then sending the desilication effluent to ion exchange resin for ion exchange so as to remove divalent or more multivalent cations such as heavy metal ions, calcium, magnesium and the like, and outputting effluent from the bottom;
(8) Carbonate alkalinity removal
Adding acid to the effluent from the step (7) to adjust the pH value to below 4.3, and then sending the effluent to a decarbonizer fan to convert CO from residual carbonate in the water 2 Removing, and outputting effluent water containing sodium chloride and sodium sulfate;
(9) Salt separation and crystallization
Separating and crystallizing sodium chloride and sodium sulfate from the effluent, outputting sodium chloride products and sodium sulfate products, and outputting mother liquor;
(10) Mixed salt crystal
Evaporating and crystallizing the mother solution in the step (9) to separate out mixed salt crystals, and outputting supersaturated mixed salt crystal particles; then, carrying out centrifugal separation on the supersaturated mixed salt crystal particles, and outputting solid mixed salt and third centrifugal mother liquor;
(11) Drying the mother liquor
And (3) drying the third centrifugal mother liquor output in the step (10) to output solid waste and tail gas.
Those skilled in the art will appreciate that if access is relevant
Preferably, step (9) comprises method one and/or method two; wherein,
the method one comprises the following steps:
i. nanofiltration salt separation
Separating the effluent from the step (8) by using a nanofiltration membrane to output nanofiltration membrane produced water enriched with sodium chloride as nanofiltration produced water and outputting nanofiltration concentrated water enriched with sodium sulfate;
ii. Sodium sulfate crystal
Carrying out sodium sulfate crystallization on the nanofiltration concentrated water obtained in the step i to obtain second brine containing sodium sulfate crystals; centrifugally separating the second brine to output a sodium sulfate product and a second centrifugal mother liquor;
iii, crystallization of sodium chloride
Evaporating and crystallizing the nanofiltration produced water in the step i, outputting distilled water as reuse water, and outputting supersaturated sodium chloride concentrated solution as first brine; centrifugally separating the first brine to output sodium chloride industrial salt products and first centrifugal mother liquor;
iv, mixing the second centrifugal mother liquor of step ii and the first centrifugal mother liquor of step iii as the mother liquor of step (9);
the second method comprises the following steps:
i. reverse osmosis concentration
Carrying out reverse osmosis concentration on the effluent from the step (8), outputting reverse osmosis concentrated water enriched with sodium chloride and sodium sulfate, and recycling reverse osmosis produced water;
ii. Sodium sulfate crystal
Freezing and crystallizing the reverse osmosis concentrated water obtained in the step i to obtain second brine containing sodium sulfate decahydrate crystals; centrifugally separating the second brine, and outputting a sodium sulfate decahydrate product and a second centrifugal mother liquor containing sodium chloride; then melting the obtained sodium sulfate decahydrate product, and sequentially carrying out evaporative crystallization and centrifugal separation to output an anhydrous sodium sulfate product;
iii, crystallization of sodium chloride
Evaporating and concentrating the second centrifugal mother liquor obtained in the step ii, outputting distilled water as reuse water, and outputting supersaturated sodium chloride concentrated solution as first brine; centrifugally separating the first brine to output sodium chloride industrial salt products and first centrifugal mother liquor;
iv, taking the first centrifugal mother liquor in the step iii as the mother liquor in the step (9).
In one embodiment, in method one of step (9), the specific steps of step ii are as follows: freezing and crystallizing the nanofiltration concentrated water obtained in the step i to separate out a sodium sulfate decahydrate product, and outputting second brine containing the sodium sulfate decahydrate product; then, carrying out centrifugal separation on the second brine, and outputting a sodium sulfate decahydrate product and a second centrifugal mother solution; and then melting the obtained sodium sulfate decahydrate product, and sequentially carrying out evaporative crystallization and centrifugal separation to output an anhydrous sodium sulfate product.
In one embodiment, in method one of step (9), the specific steps of step ii are as follows: evaporating and crystallizing the nanofiltration concentrated water in the step i to obtain a concentrated solution supersaturated with sodium sulfate; then, carrying out centrifugal separation on the concentrated solution supersaturated with sodium sulfate, and outputting an anhydrous sodium sulfate product and primary centrifugal mother liquor; then, freezing and crystallizing the obtained primary centrifugal mother liquor to separate out a sodium sulfate decahydrate product, and outputting second brine containing the sodium sulfate decahydrate product; then carrying out centrifugal separation on the second brine, and outputting a sodium sulfate decahydrate product and outputting a secondary centrifugal mother liquor as a second centrifugal mother liquor; the obtained sodium sulfate decahydrate product is preferably returned to the front end of the evaporative crystallization for reprocessing after hot melting.
In one embodiment, in method one of step (9), the specific steps of step ii are as follows: evaporating and crystallizing the nanofiltration concentrated water in the step i, and outputting supersaturated sodium sulfate concentrated solution as second brine; and then carrying out centrifugal separation on the second brine, and outputting an anhydrous sodium sulfate product and a second centrifugal mother solution.
Preferably, in the first method of step (9), in step ii, the second centrifuged mother liquor is partially returned to step (6) for microfiltration separation.
Preferably, in the first method of step (9), in step ii, the second centrifuged mother liquor is partially returned to step i for sodium chloride crystallization.
Preferably, in the first method of the step (9), in the step iii, the solid mixed salt is returned to the step (6) for microfiltration separation after being dissolved in water.
Preferably, in the first method of step (9), in step i, the nanofiltration membrane produced water is subjected to reverse osmosis concentration, and the reverse osmosis concentrated water is output as nanofiltration produced water and recycled water.
Preferably, in step (9) of the first process, step iii, the first centrifuged mother liquor fraction is returned to the front end of its evaporative crystallisation.
Preferably, in the second method of step (9), in step ii, the second centrifuged mother liquor is partially returned to step (6) for microfiltration separation.
Preferably, in the step (1), the particle size of the first seed crystal is 0.1-0.3mm; preferably the first seed crystal comprises quartz sand and/or garnet.
Preferably, in the step (4), small-particle-size calcium sulfate crystal particles are subjected to cyclone separation, the obtained calcium sulfate fine crystals are returned to the step (4) to be used as seed crystals for recycling, and the obtained clear liquid effluent is combined with the overflow effluent.
Preferably, in step (4), the supersaturation degree of calcium sulfate in the overflow effluent is not more than 1.2 times the solubility product of calcium sulfate.
Preferably, in step (4), the overflow effluent is partially recycled to step (3), preferably by controlling the reflux ratio, so that the concentration of calcium sulfate in the feed water to the membrane module system is not higher than 0.9 times the solubility product of calcium sulfate.
In order to achieve the second object, the invention also provides a system for the method for recovering inorganic salt by fractional crystallization of the salt-containing wastewater.
The invention has the beneficial effects that:
(1) The method and the system for recycling the inorganic salt by fractional crystallization of the salt-containing wastewater can crystallize a plurality of inorganic salts such as calcium salt, sodium salt and the like in the salt-containing wastewater in a fractional crystallization mode, and selectively separate to obtain inorganic salt products such as calcium carbonate, calcium sulfate, sodium chloride and the like, thereby recycling the plurality of inorganic salt products in the salt-containing wastewater, realizing 'source emission reduction', reducing the solid waste and the hazardous waste yield of mixed salt of sludge, reducing 'secondary pollution', and reducing the influence on ecological environment pollution;
(2) According to the method and the system for recycling inorganic salt through fractional crystallization of the salt-containing wastewater, in the process of recycling fresh water from the salt-containing wastewater, calcium salt and sodium salt in the salt-containing wastewater can be selectively separated to obtain and recycle valuable byproducts such as calcium carbonate, calcium sulfate, sodium sulfate and sodium chloride through fractional crystallization, so that the purposes of water recycling and inorganic salt recycling are achieved, and the treatment cost is effectively reduced;
(3) According to the method and the system for recycling inorganic salt through fractional crystallization of the salt-containing wastewater, disclosed by the invention, calcium carbonate crystals are selectively separated out through configuration of a crystallization fluidized bed reactor carrier induced crystallization technology, wherein the purity of the calcium carbonate is more than 90%, and the standards of desulfurization limestone and the like can be met to be used as raw materials for recycling;
(4) According to the method and the system for recycling inorganic salt through fractional crystallization of the salt-containing wastewater, disclosed by the invention, calcium sulfate in the salt-containing wastewater is enriched to form calcium sulfate crystal particles by configuring a coupling process technology of membrane concentration and calcium sulfate seed crystal circulating fluidized bed induction crystallization, wherein the purity of the calcium sulfate reaches 90% or more, and the calcium sulfate reaches the standard of a calcium sulfate dihydrate (gypsum) related product, so that the calcium sulfate can be used as a building material raw material for recycling;
(5) According to the method and the system for recycling inorganic salt through fractional crystallization of the salt-containing wastewater, the high-salt water is finally converted into a water salt system taking sodium chloride and sodium sulfate as absolute dominant components after impurity removal treatment and induced crystallization recovery of calcium carbonate (limestone) and calcium sulfate (gypsum), and then the water salt system is subjected to membrane denitration salt separation or frozen crystallization salt separation or thermal salt co-production salt separation and combined salt separation process treatment to obtain anhydrous sodium sulfate (anhydrous sodium sulfate) and sodium chloride (industrial salt) products, wherein the purity of the anhydrous sodium sulfate (anhydrous sodium sulfate) products can meet the GB/T6009 quality standard requirements, and the purity of the sodium chloride (industrial salt) products can meet the GB/T5462 quality standard requirements, so that recycling is performed;
(6) According to the method and the system for recycling the inorganic salt through fractional crystallization of the salt-containing wastewater, disclosed by the invention, through the integrated optimization of the whole system treatment flow, the flow optimization measures such as the regeneration waste liquid return treatment, the centrifugal mother liquid reflux, the mixed salt dissolution and the like, the byproduct inorganic salt recovery rate can be improved, the chemical consumption is reduced, the hazardous waste yield of mixed salt is reduced, and the treatment cost and the influence on the ecological environment are further effectively reduced.
Drawings
FIG. 1 is a process flow diagram of the aforementioned method for fractional crystallization of salt-containing wastewater to recover inorganic salts in a first embodiment;
FIG. 2 is a process flow diagram of the aforementioned method for fractional crystallization of salt-containing wastewater to recover inorganic salts in a second embodiment;
FIG. 3 is a process flow diagram of the aforementioned method for fractional crystallization of salt-containing wastewater to recover inorganic salts in a third embodiment;
FIG. 4 is a process flow diagram of the aforementioned method for fractional crystallization of salt-containing wastewater to recover inorganic salts in a fourth embodiment.
Detailed Description
The technical scheme and effects of the present invention are further described below with reference to specific embodiments. The following embodiments/examples are only for illustrating the contents of the present invention, and the present invention is not limited to the following embodiments or examples. Simple modifications of the invention using the inventive concept are within the scope of the invention as claimed.
The method for recovering inorganic salt by fractional crystallization of the salt-containing wastewater is shown in fig. 1-4, and comprises the following steps:
the method comprises the steps of (1) primary calcium carbonate crystallization, (2) primary membrane separation, (3) membrane concentration desalination, (4) calcium sulfate crystallization, (5) secondary calcium carbonate crystallization, (6) secondary membrane separation and collaborative desilication, (7) ion exchange deep hardness removal, (8) carbonate alkalinity removal, (9) salt separation and crystallization, (10) mixed salt crystallization, and (11) mother liquor drying. The method comprises the following steps:
(1) Primary calcium carbonate crystals
The salt-containing wastewater is added with alkali to adjust the pH value to 9.5-11.5, such as 9, 9.5, 10, 10.5 and 11, then is sent into a primary induced crystallization fluidized bed reactor 101, and is added with a first seed crystal for induced crystallization, calcium carbonate crystal particles are separated out, and magnesium hydroxide precipitate is output along with effluent.
In the step (1), in the presence of a first seed crystal and at a pH of 9.5-11.5, calcium bicarbonate and magnesium bicarbonate in the salt-containing wastewater are respectively converted into calcium carbonate crystals and magnesium hydroxide precipitates; wherein, calcium bicarbonate is crystallized by seed crystal induction to generate calcium carbonate crystallization, and can be attached to the surface of the seed crystal to form crystallization particles, and the crystallization particles are induced to the fluidized bed reactor 101 at one time along with the water discharge by utilizing the principle that magnesium hydroxide sediment is not easy to adsorb deposition on the surface of the seed crystal at high flow rate and exists in a dispersed and superfine form of suspension; the crystallized particles are generally spherical, have the particle size of 1-5mm and can be discharged periodically; the hardness (temporary hardness) of carbonate in the brine waste can be removed through the step (1), the formed crystal particles and magnesium hydroxide precipitate are selectively separated through the carrier induced crystallization of the primary induced crystallization fluidized bed reactor 101 and the washing of suspended matters which are not easy to precipitate at a high flow rate, and the formed crystal particles are mainly calcium carbonate crystals, and in one embodiment, the purity of the calcium carbonate in the crystal particles is more than 90 percent, so that the calcium carbonate can be used as a raw material of the desulfurization limestone for recycling.
In this step (1), in one embodiment, the base comprises a NaOH solution or lime milk (Ca (OH) 2 ). The concentration of the base has little effect on the results, such as NaOH solution concentrations of 5-32%, such as 10%, 15%, 20%, 25% and 30%; such as lime milk, in a concentration of 5-20%, such as 10% and 15%.
In this step (1), in one embodiment, the first seed crystals have a particle size of 0.1 to 0.3mm, such as 0.2mm; preferably the first seed crystal comprises quartz sand and/or garnet; in one embodiment, the first seed crystal is added in an amount of 0.2 to 2.5mg/L water, such as 0.5mg/L water, 1mg/L water, 1.5mg/L water, and 2mg/L water.
In this step (1), in one embodiment, the water ascending flow rate in the primary crystallization-inducing fluidized bed reactor 101 is 50 to 100m/h, such as 60m/h, 70m/h, 80m/h, and 90m/h.
In this step (1), in one embodiment, the brine waste is first sent to an adjustment tank where alkali is added to adjust the pH.
(2) Primary membrane separation
Adding alkali and/or magnesium agent into the effluent of the step (1) to convert magnesium ions in the effluent into magnesium hydroxide sediment and/or magnesium silicate complex, then sending the magnesium hydroxide sediment and/or magnesium silicate and calcium silicate complex to the primary microfiltration membrane device 202 along with the water for microfiltration treatment, discharging sludge comprising magnesium hydroxide sediment and/or magnesium silicate and calcium silicate sediment, and outputting effluent comprising sodium chloride, sodium sulfate and calcium sulfate.
After softening and clarifying at the high pH value in the step (1) and membrane filtration and separation in the step (2), most of the temporary hardness and magnesium ion hardness in the salt-containing wastewater can be removed, and the salt-containing wastewater can be converted into permanent hard water quality mainly comprising calcium hardness. The salt in the effluent of the step (2) mainly comprises sodium chloride, sodium sulfate and calcium sulfate, wherein the calcium sulfate is in an unsaturated state.
In step (2), in one embodiment, alkali is added to the effluent of step (1) to adjust the pH to 11-12, such as 11.5, to convert residual magnesium ions in the incoming water to magnesium hydroxide precipitate; preferably, the base comprises NaOH solution or lime milk (Ca (OH) 2 ). The concentration of the base has little effect on the results, such as NaOH solution concentrations of 5-32%, such as 10%, 15%, 20%, 25% and 30%; such as lime milk, in a concentration of 5-20%, such as 10% and 15%. In the step (2), in one embodiment, a magnesium agent is added into the effluent of the step (1) to cooperatively remove silicon, and the silicon-magnesium complex and Mg (OH) are fully utilized 2 Generating adsorption effect on silicon, thereby achieving the aim of effectively and cooperatively removing silicon; mg (OH) 2 The surface of the particles of (a) is adsorbed with a silicic acid compound to form indissolvable magnesium silicate, and condensation of silicic acid colloid and formation of calcium silicate also occur to some extent; preferably, the magnesium agent is magnesium oxide and/or magnesium chloride; preferably, the Silicon (SiO) is added according to the water (i.e. the effluent from step (1) 2 ) The magnesium agent is added according to the content and the magnesium-silicon ratio data, and in one embodiment, the magnesium agent is added according to the magnesium agent and SiO 2 The mass ratio of (4-10) is 1, adding magnesium agent, wherein the magnesium agent is calculated by MgO. For example, magnesium and SiO 2 The mass ratio of (2) is 5:1, 6:1, 7:1, 8:1 and 9:1. The magnesium agent is calculated as MgO and means, if the magnesium agent is other magnesium agent than MgO such as magnesium chloride, it is calculated as mass of MgO containing the same amount of magnesium as the amount of magnesium. In one embodiment, the primary microfiltration membrane device 202 of step (2) employs bag-type microfiltration and/or tube-type microfiltration, preferably bag-type microfiltration.
In step (2), in one embodiment, the effluent from step (1) is first fed into a primary mixing reactor 201 for alkali and/or magnesium addition to effect magnesium ion conversion.
(3) Membrane concentration desalination
And (3) adding acid into the effluent from the step (2) to adjust the pH value to be neutral, adding a scale inhibitor, sending the added scale inhibitor to the membrane group system 302 along with the water to perform concentration and desalination treatment under the action of the scale inhibitor, recycling output produced water, and concentrating the output calcium sulfate into supersaturated concentrated water.
In this step (3), in one embodiment, the acid comprises hydrochloric acid and/or sulfuric acid. The concentration of the acid has little influence on the result, for example, the concentration of the hydrochloric acid is 5-31%, such as 10%, 15%, 20%, 25% and 30%, and 31% hydrochloric acid can be directly added for convenience; for example, sulfuric acid may be added directly to a concentration of 10-98%, such as 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90%, for convenience. The scale inhibitor is a mainstream product of companies such as PWT, nalco and Shenmei technology, which are commonly used in the field, and is commercially available. Such as Titan ASDTM 200SC, titan ASDTM150 SC from PWT corporation. In one embodiment, the membrane module system 302 includes a reverse osmosis membrane module and/or a nanofiltration membrane module. In one embodiment, the supersaturation of calcium sulfate in the concentrate water is 1.5 to 4 times, such as 2 times, 2.5 times, 3 times, and 3.5 times, the solubility product of calcium sulfate. Under the action of scale inhibitor, concentrating calcium sulfate to supersaturation, and controlling the solubility product (Ksp) of calcium sulfate within 1.5-4 times.
In this step (3), in one embodiment, the effluent from step (2) is sent to a membrane concentrate feed tank 301 for acid addition to adjust the pH.
(4) Calcium sulfate crystal
Delivering the concentrated water in the step (3) to a seed crystal circulating fluidized bed 401, adding calcium sulfate seed crystals into the concentrated water for induced crystallization, separating out calcium sulfate crystal particles, discharging large-particle-size calcium sulfate crystal particles from the bottom, discharging small-particle-size calcium sulfate crystal particles from the middle upper part, and overflowing overflow water containing calcium sulfate and calcium chloride from the upper part; wherein the large-size calcium sulfate crystal particles have a particle size of 0.3 to 2mm, such as 0.5mm, 0.8mm, 1mm, 1.3mm and 1.8mm; the small-size calcium sulfate crystal particles have a particle size of 0.05 to 0.3mm, such as 0.1mm, 0.15mm, 0.2mm and 0.25mm.
In the step (4), water (concentrated water in the step (3)) is added to contact and react with calcium sulfate seed crystals in a fluidized bed, and calcium and sulfate ions which begin to crystallize and deactivate are attached to the pre-added calcium sulfate seed crystals under the induction action of the seed crystals, so that calcium sulfate crystal particles are formed.
In this step (4), in one embodiment, the upward flow rate of the water flow in the seed circulating fluidized bed 401 is 40-80m/h, such as 50m/h, 60m/h and 70m/h, so that the supersaturated calcium sulfate in the water is adsorbed by the seed to gradually grow to form calcium sulfate crystal particles, the calcium sulfate crystal particles form different particle size distributions along the bed layer of the seed circulating fluidized bed 401, the large-particle-size calcium sulfate crystal particles gradually sink to the bottom of the fluidized bed, and the small-particle-size calcium sulfate crystal particles are suspended in the upper middle of the fluidized bed. In one embodiment, the upward flow rate of the water flow at the top of the seed crystal circulating fluidized bed 401 is not higher than 20m/h, preferably, the upward flow rate of the water path at the top of the seed crystal circulating fluidized bed 401 is controlled to be not higher than 20m/h by increasing the water flow section at the upper part of the seed crystal circulating fluidized bed 401, so that 'mud-water' separation is realized, and clear liquid overflows and water is discharged.
In the step (4), the large-particle-size calcium sulfate crystal particles are periodically discharged through a bottom discharge pipeline, and in one embodiment, the large-particle-size calcium sulfate crystal particles are dehydrated and separated to recover a calcium sulfate dihydrate crystal particle product (gypsum), and the purity of the obtained calcium sulfate crystal particles can reach 90% or more, so that the calcium sulfate crystal particles can be used as building material raw materials for recycling.
In the step (4), small-size calcium sulfate crystal particles are led out through a pipeline at the middle upper part, in one embodiment, the small-size calcium sulfate crystal particles are subjected to cyclone separation, and the obtained calcium sulfate fine crystals (the particle size of the calcium sulfate fine crystals is 0.05-0.3mm, such as 0.1mm, 0.15mm, 0.2mm and 0.25 mm) are returned to the seed crystal circulating fluidized bed 401 to be recycled as seed crystals, and the obtained clear liquid effluent is combined with overflow effluent of the seed crystal circulating fluidized bed 401 and sent to subsequent processes for treatment. In one embodiment, the cyclonic separation is performed within cyclone separation 402.
In this step (4), in one embodiment, the supersaturation level of calcium sulfate in the overflow effluent is reduced to not more than 1.2 times the solubility product of calcium sulfate; preferably, the overflow effluent portion is returned to step (3) and the concentration of calcium sulfate in the feed water to the membrane module system 302 is controlled to be no greater than 0.9 times the solubility product of calcium sulfate by controlling the reflux ratio.
After the treatment in the step (3) and the step (4), the salt concentration in the overflow effluent is increased, and the corresponding hardness content is also increased. At this time, the hardness in water is mainly the permanent hardness in the form of calcium sulfate and calcium chloride, and a small amount of magnesium hardness remains.
(5) Secondary calcium carbonate crystals
And (3) adding alkali into the overflow effluent part in the step (4) to adjust the pH to 10.5-12, such as 11 and 11.5, then sending the overflow effluent part into a secondary induced crystallization fluidized bed reactor 501, adding the first seed crystal into the overflow effluent part to perform induced crystallization, separating out calcium carbonate crystal particles, and outputting magnesium hydroxide precipitate along with effluent.
Calcium sulfate (CaSO) 4 ) Slightly soluble in water, calcium chloride (CaCl) 2 ) Is easy to dissolve in water, and in order to meet the requirements of subsequent salt separation step, ensure product quality and prevent scaling and blocking, in said step (5), it is necessary to firstly use alkali to convert the permanently hard and residual small quantity of magnesium hardness of calcium sulfate and calcium chloride into less-soluble calcium carbonate (CaCO) respectively 3 ) And magnesium hydroxide precipitate to soften hard water.
In this step (5), in one embodiment, the base comprises NaOH solution and/or sodium carbonate (Na 2 CO 3 ) So as to convert the permanent hardness and the magnesium hardness in the water into calcium carbonate and magnesium hydroxide precipitates respectively. The concentration of the base has little effect on the results, such as NaOH solution concentrations of 5-32%, such as 10%, 15%, 20%, 25% and 30%; such as sodium carbonate solutions, at concentrations of 5-20%, such as 10% and 15%.
In this step (5), in one embodiment, the water ascending flow rate within the secondary induced crystallization fluidized bed reactor 501 is 50-100m/h, such as 60m/h, 70m/h, 80m/h, and 90m/h.
In the step (5), calcium carbonate crystals are generated by seed crystal induced crystallization and are adhered to the surface of the seed crystal to form calcium carbonate crystal particles, and the magnesium hydroxide precipitate is generated in a dispersed and superfine form of suspended matters by utilizing the principle that the magnesium hydroxide precipitate is not easy to adsorb and deposit on the surface of the seed crystal at a high flow rate, and is washed out of the fluidized bed reactor along with effluent. The calcium carbonate crystal particles are generally spherical, have the particle size of 1-5mm, such as 2mm, 3mm and 4mm, can be discharged through a bottom discharge pipeline at regular intervals, are mainly composed of calcium carbonate, have the purity of more than 90%, and can be used as a raw material of desulfurization limestone for recycling.
(6) Secondary membrane separation synergistic desilication
And (3) adding an aluminum agent into the effluent of the step (5), then sending the effluent to a secondary microfiltration membrane device 602 for microfiltration separation, discharging magnesium hydroxide precipitated sludge containing aluminosilicate precipitate and adsorbed silicon, and outputting desilication effluent.
The effluent from step (5) contains Silicon (SiO) 2 ) And magnesium hydroxide precipitate, in the step (6), silicon (SiO) in the effluent according to the step (5) 2 ) Adding aluminum agent into the mixture and reacting to form aluminosilicate precipitate, and adsorbing Si with the magnesium hydroxide precipitate carried out in the effluent from step (5) to reach the aim of synergistic Si removal. The precipitated sludge at the bottom of the secondary microfiltration membrane device 602 is periodically discharged, and is properly disposed or utilized after sludge dewatering.
In this step (6), in one embodiment, the secondary microfiltration membrane device 602 is an alkali resistant microfiltration device, preferably a bag type microfiltration device and/or a tube type microfiltration device.
In this step (6), in one embodiment, the aluminum agent comprises any one or a combination of more of sodium metaaluminate, polyaluminum chloride, and polyaluminum ferric chloride.
In the step (6), in one embodiment, the aluminum agent is added in an amount corresponding to the amount of Silicon (SiO) in the effluent of the step (5) 2 ) The mass ratio of (3) is as follows: (0.5-3): 1, such as 1:1, 1.5:1, 2:1, and 2.5:1.
In the step (6), in one embodiment, the effluent from the step (5) is fed to the secondary mixing reaction tank 601 and an aluminum agent is added.
(7) Ion exchange depth hardness removal
Adding acid to the desilication effluent from the step (6) to adjust the pH to 7-9, such as 7.5, 8 and 8.5, then sending to the ion exchange resin 702 for ion exchange to remove divalent and more multivalent cations such as heavy metal ions, calcium, magnesium and the like, and outputting the effluent from the bottom.
In this step (7), in one embodiment, the desilication effluent from step (6) is sent to a cation bed feed tank 701 for acid addition to adjust the pH.
In this step (7), in one embodiment, the ion exchange resin 702 is a sodium cation resin, including any one or more combinations of strong acid sodium ion exchange resin, weak acid sodium ion exchange resin, and chelating resin; specifically, the concentration of salt in the water (silicon-removing effluent in the step (6)) can be selected according to the concentration of salt, for example, chelating resin is selected when the concentration of salt is high (TDS is more than or equal to 30000 mg/L), strong acid sodium ion exchange resin is selected when the concentration of salt is low (TDS is less than or equal to 5000 mg/L), and weak acid sodium ion exchange resin is selected when the concentration of salt is low. Preferably, the ion exchange resin 702 is regenerated step by using hydrochloric acid and sodium hydroxide; preferably, the regenerated waste liquid is returned to the step (3) for treatment.
In this step (7), in one embodiment, the total hardness of the effluent of the ion exchange resin 702 is measured as CaCO 3 The total weight is less than or equal to 1mg/L, so that divalent or more multivalent cations such as heavy metal ions, calcium, magnesium and the like in water are replaced by sodium ions.
After the treatment, part of carbonate ions still remain in the effluent of the step (7).
(8) Carbonate alkalinity removal
Adding acid to the effluent from the step (7) to adjust the pH to below 4.3, and then sending the effluent to the decarbonizer fan 801 to convert CO from residual carbonate in the water 2 And removing, and outputting effluent water containing sodium chloride and sodium sulfate.
In this step (8), in one embodiment, the acid added is hydrochloric acid and/or sulfuric acid. The concentration of the acid has little influence on the result, for example, the concentration of the hydrochloric acid is 5-31%, such as 10%, 15%, 20%, 25% and 30%, and 31% hydrochloric acid can be directly added for convenience; for example, sulfuric acid having a concentration of 10-98%, such as 20%, 30%, 40%, 50%, 60%, 70%, 80% and 90%, may be added directly with 95-98% sulfuric acid for convenience.
In the step (8), the purpose of adjusting the pH to 4 or less by adding an acid is to enter water (effluent from the step (7))All remaining carbonate ions are converted to carbonic acid, which is now almost completely present in the water in the form of carbon dioxide, and can be easily removed by the decarbonizer fan 801. The decarbonizer fan 801 blows air to maintain the air-water ratio of 15-40m 3 (air)/m 3 (Water), e.g. 20m 3 (air)/m 3 (Water), 25m 3 (air)/m 3 (Water), 30m 3 (air)/m 3 (Water) and 35m 3 (air)/m 3 And (3) removing the carbon dioxide from the water, wherein the content of the carbon dioxide in the effluent water of the step (8) after treatment can be less than 5mg/L, and the pH value can be increased to be more than 6, so that the carbonate in the water is almost completely converted into chloride or sulfate.
(9) Salt separation and crystallization
And (3) separating and crystallizing sodium chloride and sodium sulfate from the effluent, outputting sodium chloride products and sodium sulfate products, and outputting mother liquor.
In one embodiment, step (9) comprises method one and/or method two; wherein,
the method one comprises the following steps:
i. nanofiltration salt separation
Separating the effluent from the step (8) by using a nanofiltration membrane to output nanofiltration membrane produced water enriched with sodium chloride as nanofiltration produced water and outputting nanofiltration concentrated water enriched with sodium sulfate;
in the step, nanofiltration salt separation mainly utilizes the difference of ionic radius or charge characteristics of chloride ions and sulfate ions, etc., sulfate radicals are efficiently intercepted by a nanofiltration membrane, and nitrate-enriched high-salt brine mainly containing sodium sulfate salt is formed by enrichment on the concentrated water side of the nanofiltration membrane, so that monovalent salt and divalent salt are separated and enriched in the nanofiltration membrane separation process;
ii. Sodium sulfate crystal
Carrying out sodium sulfate crystallization on the nanofiltration concentrated water obtained in the step i to obtain second brine containing sodium sulfate crystals; centrifugally separating the second brine to output a sodium sulfate product and a second centrifugal mother liquor;
iii, crystallization of sodium chloride
Evaporating and crystallizing the nanofiltration produced water in the step i, outputting distilled water as reuse water, and outputting supersaturated sodium chloride concentrated solution as first brine; centrifugally separating the first brine to output sodium chloride industrial salt products and first centrifugal mother liquor;
iv, mixing the second centrifugal mother liquor of the step ii and the first centrifugal mother liquor of the step iii to output as the mother liquor of the step (9);
the second method comprises the following steps:
i. reverse osmosis concentration
Carrying out reverse osmosis concentration on the effluent from the step (8), outputting reverse osmosis concentrated water enriched with sodium chloride and sodium sulfate, and recycling reverse osmosis produced water;
ii. Sodium sulfate crystal
As shown in fig. 4, the reverse osmosis concentrated water in the step i is subjected to freezing crystallization to obtain second brine containing sodium sulfate decahydrate crystals; centrifugally separating the second brine, and outputting a sodium sulfate decahydrate product and a second centrifugal mother liquor containing sodium chloride; then melting the obtained sodium sulfate decahydrate product, and sequentially carrying out evaporative crystallization and centrifugal separation to output an anhydrous sodium sulfate product;
iii, crystallization of sodium chloride
Evaporating and concentrating the second centrifugal mother liquor obtained in the step ii, outputting distilled water as reuse water, and outputting supersaturated sodium chloride concentrated solution as first brine; centrifugally separating the first brine to output sodium chloride industrial salt products and first centrifugal mother liquor;
iv, outputting the first centrifugal mother liquor in the step iii as the mother liquor in the step (9).
In one embodiment, as shown in fig. 1, in a first method of step (9), the specific steps of step ii are as follows: firstly, freezing and crystallizing the nanofiltration concentrated water in the step i to separate out a sodium sulfate decahydrate product (mirabilite), and outputting second brine containing the sodium sulfate decahydrate product; then, carrying out centrifugal separation on the second brine, and outputting a sodium sulfate decahydrate product and a second centrifugal mother solution; and then melting the obtained sodium sulfate decahydrate product, and then sequentially carrying out evaporative crystallization and centrifugal separation to output an anhydrous sodium sulfate product (anhydrous sodium sulfate).
In one embodiment, as shown in fig. 2, in a method one of the step (9), the specific steps of the step ii are as follows: evaporating and crystallizing the nanofiltration concentrated water in the step i to obtain a concentrated solution supersaturated with sodium sulfate; then, carrying out centrifugal separation on the concentrated solution supersaturated with sodium sulfate, and outputting an anhydrous sodium sulfate product and primary centrifugal mother liquor; then, freezing and crystallizing the obtained primary centrifugal mother liquor to separate out a sodium sulfate decahydrate product, and outputting second brine containing the sodium sulfate decahydrate product; then carrying out centrifugal separation on the second brine, and outputting a sodium sulfate decahydrate product and outputting a secondary centrifugal mother liquor as a second centrifugal mother liquor; the obtained sodium sulfate decahydrate product is preferably returned to the front end of the evaporative crystallization for reprocessing after hot melting.
In one embodiment, as shown in fig. 3, in the method one of the step (9), the specific steps of the step ii are as follows: evaporating and crystallizing the nanofiltration concentrated water in the step i, and outputting supersaturated sodium sulfate concentrated solution as second brine; and then carrying out centrifugal separation on the second brine, and outputting an anhydrous sodium sulfate product and a second centrifugal mother solution.
In one embodiment, in step (9) of the first method, in step ii, the second centrifuged mother liquor fraction is returned to step (6) for microfiltration separation.
In one embodiment, in process one of step (9), in step ii, the second centrifuged mother liquor fraction is returned to step i for sodium chloride crystallization.
In one embodiment, in the first method of step (9), in step iii, the solid mixed salt is added with water for dissolution and then returned to step (6) for microfiltration separation.
In one embodiment, in the first method of step (9), in step i, the nanofiltration membrane produced water is subjected to reverse osmosis concentration, and the reverse osmosis concentrated water is output as nanofiltration produced water and the reuse water is output.
In one embodiment, in method one of step (9), in step iii, the first centrifuged mother liquor fraction is returned to the front end of its evaporative crystallization.
In one embodiment, in a second method of step (9), in step ii, the second centrifuged mother liquor fraction is returned to step (6) for microfiltration separation.
(10) Mixed salt crystal
Evaporating and crystallizing the mother solution in the step (9) to separate out mixed salt crystals, and outputting supersaturated mixed salt crystal particles; and then carrying out centrifugal separation on the supersaturated mixed salt crystal particles, and outputting solid mixed salt and third centrifugal mother liquor.
Those skilled in the art will appreciate that in the relevant steps, MVR evaporative crystallization or single-effect evaporative crystallization or multiple-effect evaporative crystallization may be employed.
In one embodiment, the obtained solid mixed salt is returned to the step (6) for microfiltration separation after being dissolved in water.
(11) Drying the mother liquor
And (3) drying the third centrifugal mother liquor output in the step (10) to output solid waste and tail gas.
In the step (11), the third centrifugal mother liquor may be subjected to drying treatment, and impurities such as impurity salts and organic matters which are enriched in the third centrifugal mother liquor and cannot be recycled may be solidified by a drying technique. The dried solid formed after drying and solidification is disposed as solid waste. The third centrifugal mother liquor can be dried by adopting drying techniques such as roller scraping plate drying, spray drying, vacuum rake drying and the like, and preferably roller scraping plate drying is adopted. The tail gas output by drying can reach the relevant atmospheric emission standard to be discharged after passing through environmental protection treatment facilities such as dust removal and the like.
The method for recycling inorganic salt by fractional crystallization of the salt-containing wastewater can crystallize a plurality of inorganic salts such as calcium salt, sodium salt and the like in the salt-containing wastewater in a fractional crystallization mode, and selectively separate to obtain inorganic salt products such as calcium carbonate, calcium sulfate, sodium chloride and the like, thereby recycling a plurality of inorganic salt products in the salt-containing wastewater, realizing 'source emission reduction', reducing solid waste and hazardous waste yield of mixed salt of sludge and reducing 'secondary pollution'.
In each step of the application, the temperature of freezing crystallization and evaporating crystallization is a conventional design condition, and can be reasonably selected according to different application scenes. In one embodiment, the temperature of the freeze crystallization is-5-10 ℃, such as 0 ℃ and 5 ℃, in each step; and/or the temperature of the evaporative crystallization is 70-110 ℃, such as 80 ℃, 90 ℃ and 100 ℃.
The application also provides a system for the method for recovering inorganic salt by fractional crystallization of the salt-containing wastewater.
In one embodiment, as shown in fig. 1-4, the system comprises a primary precipitated calcium carbonate crystallization unit, a primary membrane separation unit, a membrane concentration desalination unit, a calcium sulfate crystallization unit, a secondary precipitated calcium carbonate crystallization unit, a secondary membrane separation synergistic desilication unit, an ion exchange depth hardness removal unit, a carbonate alkalinity removal unit, a salt separation and crystallization unit, a mixed salt crystallization unit and a mother liquor drying unit which are connected by pipelines; wherein,
a primary precipitated calcium carbonate crystallization unit comprising a primary induced crystallization fluidized bed reactor 101 for feeding brine wastewater from the bottom and adding alkali and a first seed crystal thereto for induced crystallization, wherein precipitated calcium carbonate crystal particles are discharged from the lower part, and the discharged water is discharged from the upper part;
The primary membrane separation unit comprises a primary mixing reaction tank 201 and a primary microfiltration membrane device 202 which are sequentially connected; the primary mixing reaction tank 201 is connected to the water outlet of the primary induced crystallization fluidized bed reactor 101, and is used for introducing the effluent of the primary induced crystallization fluidized bed reactor 101 and supplementing alkali and/or magnesium agent to the effluent to convert magnesium ions into magnesium hydroxide precipitate and/or magnesium silicate complex; the primary micro-filtration membrane device 202 is used for feeding the discharged material of the primary mixing reaction tank 201 and filtering the discharged material by micro-filtration membranes, discharging magnesium hydroxide precipitated sludge or magnesium silicate and calcium silicate precipitated sludge from the bottom, and outputting discharged water comprising sodium chloride, sodium sulfate and calcium sulfate from the top;
the membrane concentration desalination unit comprises a membrane concentration water retracting tank 301 and a membrane group system 302 which are connected in sequence; the feeding pipeline of the membrane concentration water retracting tank 301 is connected to the water outlet of the primary micro-filtration membrane device 202, and is provided with an acid feeding port, and the membrane concentration water retracting tank 301 is used for feeding after adding acid to the effluent of the primary micro-filtration membrane device 202 to adjust the pH of the system to be neutral; the membrane group system 302 is used for feeding the effluent water of the membrane concentration water tank 301, concentrating and desalting the effluent water under the action of a scale inhibitor, concentrating the calcium sulfate to supersaturation, obtaining concentrated water from the top, and recycling the produced water from the bottom;
A calcium sulfate crystallization unit comprising a seed circulating fluidized bed 401; the feed line of the seed crystal circulating fluidized bed 401 is connected to the concentrated water port of the membrane module system 302, and is provided with a calcium sulfate seed crystal feed pipe for feeding concentrated water of the membrane module system 302 and adding calcium sulfate seed crystal into the concentrated water for induced crystallization, calcium sulfate crystals are separated out, large-particle-size calcium sulfate crystals are discharged from a first outlet at the lower part, small-particle-size calcium sulfate crystals are discharged from a second outlet at the middle upper part, and overflow water is discharged from the upper part; preferably, the calcium sulfate crystallization unit further comprises a cyclone separation 402; an inlet of the cyclone separator 402 is connected to a second outlet of the seed crystal circulating fluidized bed 401, and is used for introducing and cyclone separating the small-particle-size calcium sulfate crystals, outputting the calcium sulfate crystals from the bottom, and outputting clear liquid from the top; preferably, the bottom outlet of the cyclone separator 402 is connected to the calcium sulfate seed feed tube for recycling the calcium sulfate seed; preferably, the top outlet of the cyclone separation 402 is connected to the feed line of the seed circulating fluidized bed 401 for calcium sulfate recycle crystallization of its supernatant effluent; preferably, the calcium sulfate crystallization unit further comprises a concentrate tank 403, wherein the concentrate tank 403 is arranged on a feed line of the seed crystal circulating fluidized bed 401 and is used for buffering the concentrate of the membrane group system 302; preferably, the bottom outlet of the cyclone separator 402 is connected to the water inlet of the concentrate tank 403; preferably, an upper outlet of the seed crystal circulating fluidized bed 401 is connected to a water inlet of the membrane concentration water inlet tank 301 for delivering a clear liquid outlet portion of the seed crystal circulating fluidized bed 401 to the membrane concentration desalination unit (3) for circulation;
A secondary precipitated calcium carbonate crystallization unit, comprising a secondary induced crystallization fluidized bed reactor 501, wherein a feed line of the secondary induced crystallization fluidized bed reactor 501 is connected to a top outlet of the seed crystal circulating fluidized bed 401, and is used for feeding at least part of clear liquid effluent of the seed crystal circulating fluidized bed 401 from the bottom and supplementing alkali (such as NaOH solution or sodium carbonate) and the first seed crystal into the clear liquid effluent for induced crystallization, converting calcium ions into calcium carbonate for crystallization precipitation, converting magnesium ions into magnesium hydroxide precipitate, discharging the magnesium hydroxide precipitate from the lower part, and discharging the effluent from the upper part;
the secondary membrane separation cooperated silicon removal unit comprises a secondary mixing reaction tank 601 and a secondary micro-filtration membrane device 602 which are connected in sequence; the secondary mixing reaction tank 601 is connected to the water outlet of the secondary induced crystallization fluidized bed reactor 501, and is used for introducing the water discharged from the secondary induced crystallization fluidized bed reactor 501 and adding an aluminum agent (such as sodium metaaluminate) into the water to adsorb silicon in the water and convert the silicon into aluminosilicate precipitate; the secondary micro-filtration membrane device 602 is used for feeding the discharged material of the secondary mixing reaction tank 601 and filtering the discharged material by micro-filtration membranes, discharging precipitated sludge from the bottom and outputting water from the top; preferably, the secondary microfiltration membrane device 602 is an alkali resistant microfiltration device, preferably a bag type microfiltration device and/or a tube type microfiltration device;
The ion exchange depth hardness removal unit comprises a cation bed water inlet tank 701 and an ion exchange resin 702 which are connected in sequence; the inlet of the cation bed water inlet tank 701 is connected to the top outlet of the secondary micro-filtration membrane device 602, and is used for feeding the effluent of the secondary micro-filtration membrane device 602 from the top and adding acid (such as hydrochloric acid and/or sulfuric acid) into the effluent to adjust the pH of the effluent to 7-9; the ion exchange resin 702 is used for feeding the effluent of the cation bed water inlet tank 701 from the upper part to perform ion exchange on the effluent so as to remove divalent or more multivalent cations such as heavy metal ions, calcium, magnesium and the like in the effluent, and outputting the effluent from the bottom; preferably, the ion exchange resin 702 is a sodium type cation resin, including any one or a combination of a strong acid sodium type ion exchange resin, a weak acid sodium type ion exchange resin, and a chelating resin; preferably, the total hardness of the effluent of the ion exchange resin 702 is CaCO 3 The weight of the mixture is less than or equal to 1mg/L;
a carbonate alkalinity removing unit comprising a decarbonizer fan 801, the decarbonizer fan 801 being connected to a water outlet of the ion exchange resin 702 for introducing the effluent of the ion exchange resin 702 and adding an acid (such as hydrochloric acid and/or sulfuric acid) thereto to adjust the pH thereof to below 4.3 to convert residual carbonate in the water into CO 2 Removing, namely outputting effluent water containing sodium chloride and sodium sulfate from the lower part;
the salt separation and crystallization unit comprises a salt separation device and a crystallization device, and is used for separating and crystallizing sodium chloride and sodium sulfate from the effluent of the carbonate alkalinity removing unit, outputting sodium chloride products and sodium sulfate products and outputting mother liquor;
in one embodiment, the salt separation and crystallization unit comprises:
the nanofiltration salt separation unit comprises a nanofiltration membrane structure 9101, wherein a water inlet of the nanofiltration membrane structure 9101 is connected to a water outlet of the decarbonization device fan 801, and is used for separating sodium chloride and sodium sulfate in the effluent of the decarbonization device fan 801 by a nanofiltration membrane, and outputting nanofiltration membrane produced water enriched with sodium chloride from the top as produced water of the nanofiltration salt separation unit and nanofiltration concentrated water enriched with sodium sulfate from the bottom; preferably, the nanofiltration salt separation unit further comprises a reverse osmosis membrane device 9102, the reverse osmosis membrane device 9102 is connected to a water outlet of the nanofiltration membrane structure 9101, and is used for feeding nanofiltration produced water of the nanofiltration membrane structure 9101 to perform reverse osmosis concentration on the nanofiltration produced water, and outputting concentrated produced water from the top as produced water of the nanofiltration salt separation unit and outputting recycled water from the bottom;
A sodium sulfate crystallization unit comprising a second crystallization device 9301 and a second centrifugation device 9302; the second crystallization device 9301 is connected to a water outlet of the nanofiltration membrane structure 9101, and is configured to crystallize nanofiltration concentrated water from the nanofiltration membrane structure 9101, and output second brine containing sodium sulfate; the second centrifugal device 9302 is connected to a crystallization mother liquor outlet of the second crystallization device 9301, and is used for centrifugally separating second brine from the second crystallization device 9301, and outputting sodium sulfate products and second centrifugal mother liquor; in one embodiment, the second crystallization device 9301 comprises a freeze crystallization device and/or an evaporative crystallization device; in one embodiment, the second crystallization device 9301 comprises a freezing crystallization device, a melting device, and an evaporation crystallization device in this order, and the freezing crystallization device, the second centrifugation device, the melting device, and the evaporation crystallization device are connected end to end in this order; the freezing and crystallizing device is connected to a concentrated water outlet of the nanofiltration membrane structure 9101, and is used for freezing and crystallizing nanofiltration concentrated water from the nanofiltration membrane structure 9101 to separate out a sodium sulfate decahydrate product, and outputting second brine containing the sodium sulfate decahydrate product; the melting device melts the sodium sulfate decahydrate product from the second centrifugal device 9302; the evaporation crystallization device is used for evaporating and crystallizing a molten sodium sulfate decahydrate product to obtain anhydrous sodium sulfate serving as a sodium sulfate product; in one embodiment, the second crystallization device 9301 comprises an evaporative crystallization device and a freeze crystallization device, the evaporative crystallization device, the primary centrifugation device, the freeze crystallization device, and the secondary centrifugation device are connected end to end in sequence, and the evaporative crystallization device is connected to the produced water outlet of the nanofiltration membrane structure 9101; the evaporation crystallization device is used for evaporating and concentrating nanofiltration concentrated water from the nanofiltration membrane structure 9101, outputting distilled water as reuse water and outputting supersaturated sodium sulfate concentrated solution; the primary centrifugal device is used for carrying out centrifugal separation on supersaturated sodium sulfate concentrated solution from the evaporation crystallization device, and outputting sodium sulfate products and primary centrifugal mother liquor; the freezing and crystallizing device is used for freezing and crystallizing the primary centrifugal mother liquor from the primary centrifugal device to separate out a sodium sulfate decahydrate product and outputting second brine containing the sodium sulfate decahydrate product; the secondary centrifugal device is used for carrying out centrifugal separation on the second brine from the freezing and crystallizing device and outputting a sodium sulfate decahydrate product; after hot melting, the mixture is sent to the evaporation crystallization device for re-evaporation crystallization; in one embodiment, the second crystallization device 9301 further comprises a hot melting device and a second return line, wherein the hot melting device is connected to the sodium sulfate decahydrate product outlet of the secondary centrifugal device and is used for performing hot melting treatment on the sodium sulfate decahydrate product from the secondary centrifugal device to obtain a molten sodium sulfate decahydrate product; one end of the second return pipeline is connected to an outlet of the hot melting device, and the other end of the second return pipeline is connected to a feed inlet of the evaporation crystallization device and is used for conveying a molten sodium sulfate decahydrate product from the hot melting device to the evaporation crystallization device for cyclic treatment; in one embodiment, the second crystallization device 9301 includes an evaporation crystallization device for evaporating and concentrating nanofiltration concentrated water from the nanofiltration membrane structure 9101, outputting distilled water as reuse water, and outputting supersaturated sodium sulfate concentrate as crystallization mother liquor; in one embodiment, the sodium sulfate crystallization unit further comprises a third return pipeline, one end of the third return pipeline is connected to the second centrifugal mother liquor outlet of the sodium sulfate crystallization unit, and the other end of the third return pipeline is connected to the secondary membrane separation collaborative desilication unit, and is used for returning the second centrifugal mother liquor from the sodium sulfate crystallization unit to the secondary membrane separation collaborative desilication unit for cyclic treatment; preferably the other end of the third foldback line is connected to the feed inlet of the secondary microfiltration membrane device 602 in the secondary membrane separation co-desilication unit;
A sodium chloride crystallization unit comprising a first crystallization device 9201 and a first centrifugation device 9202 connected in sequence; the first crystallization device 9201 is an evaporation crystallization device, and is connected to a water outlet of the nanofiltration salt separation unit, and is used for evaporating and concentrating the water produced by the nanofiltration salt separation unit, outputting distilled water as reuse water, and outputting supersaturated sodium chloride concentrated solution as first brine; the first centrifugal device 9202 is used for performing centrifugal separation on the first brine from the first crystallization device 9201, and outputting sodium chloride industrial salt products and first centrifugal mother liquor; preferably, the evaporation device is a mechanical vapor compression cycle evaporation crystallization device or a single-effect evaporation crystallization or multiple-effect evaporation crystallization device; preferably, the sodium chloride crystallization unit further comprises a first return line, one end of which is connected to the first centrifugal mother liquor outlet of the first centrifugal device 9202, and the other end of which is connected to the feed inlet of the first crystallization device 9201, for returning the first centrifugal mother liquor portion into the first crystallization device 9201 for circulation treatment;
in one embodiment, the salt separation and crystallization unit comprises:
the reverse osmosis concentration unit comprises a reverse osmosis membrane device 9102, wherein the reverse osmosis membrane device 9102 is connected to a water outlet of the decarbonization device fan 801 and is used for carrying out reverse osmosis concentration on sodium chloride and sodium sulfate in the effluent of the decarbonization device fan 801, outputting reverse osmosis concentrated water enriched with sodium chloride and sodium sulfate, and recycling reverse osmosis produced water;
A sodium sulfate crystallization unit comprising a second crystallization device 9301 and a second centrifugation device 9302; the second crystallization device 9301 is connected to a reverse osmosis concentrated water outlet of the reverse osmosis membrane device 9102, and is used for crystallizing the reverse osmosis concentrated water from the reverse osmosis membrane device 9102 to obtain second brine containing sodium sulfate crystals; the second centrifugal device 9302 is connected to a crystallization mother liquor outlet of the second crystallization device 9301, and is used for centrifugally separating second brine from the second crystallization device 9301, and outputting sodium sulfate products and second centrifugal mother liquor containing sodium chloride; in one embodiment, the second crystallization device 9301 comprises a freeze crystallization device and/or an evaporative crystallization device; in one embodiment, the second crystallization device 9301 comprises a freeze crystallization device, a melting device, and an evaporative crystallization device, which are connected end to end in sequence; the freezing and crystallizing device is connected to a reverse osmosis concentrated water outlet of the reverse osmosis membrane device 9102, and is used for freezing and crystallizing the reverse osmosis concentrated water from the reverse osmosis membrane device 9102 to separate out a sodium sulfate decahydrate product, and outputting second brine containing the sodium sulfate decahydrate product; the melting device is used for melting the sodium sulfate decahydrate product from the second centrifugal device 9302; the evaporation crystallization device is used for sequentially carrying out evaporation crystallization and centrifugal separation on a molten sodium sulfate decahydrate product to obtain anhydrous sodium sulfate serving as a sodium sulfate product; in one embodiment, the sodium sulfate crystallization unit further comprises a third return pipeline, one end of the third return pipeline is connected to the second centrifugal mother liquor outlet of the sodium sulfate crystallization unit, and the other end of the third return pipeline is connected to the secondary membrane separation collaborative desilication unit, and is used for returning the second centrifugal mother liquor from the sodium sulfate crystallization unit to the secondary membrane separation collaborative desilication unit for cyclic treatment; preferably the other end of the third foldback line is connected to the feed inlet of the secondary microfiltration membrane device 602 in the secondary membrane separation co-desilication unit;
A sodium chloride crystallization unit comprising a first crystallization device 9201 and a first centrifugation device 9202 connected in sequence; the first crystallization device 9201 is an evaporation crystallization device, and is connected to a second centrifugal mother liquor outlet of the sodium sulfate crystallization unit, and is used for evaporating and concentrating the second centrifugal mother liquor from the sodium sulfate crystallization unit, outputting distilled water as reuse water, and outputting supersaturated sodium chloride concentrated solution as first brine; the first centrifugal device 9202 is used for performing centrifugal separation on the first brine from the first crystallization device 9201, and outputting sodium chloride industrial salt products and first centrifugal mother liquor; preferably, the evaporation device is a mechanical vapor compression cycle evaporation crystallization device or a single-effect evaporation crystallization or multiple-effect evaporation crystallization device; preferably, the sodium chloride crystallization unit further comprises a first return line, one end of the first return line is connected to the first centrifugal mother liquor outlet of the first centrifugal device 9202, and the other end of the first return line is connected to the feed inlet of the first crystallization device 9201, so that the first centrifugal mother liquor is partially returned to the first crystallization device 9201 for circulation treatment.
The system further comprises:
the salt mixing crystallization unit comprises a third crystallization device 1001 and a third centrifugation device 1002 which are connected in sequence; the third crystallization device 1001 is connected to a mother liquor outlet of the salt separation and crystallization unit, and is used for evaporating and concentrating mother liquor from the salt separation and crystallization unit as mother liquor of the salt separation and crystallization unit, outputting distilled water as reuse water, and outputting supersaturated mixed salt crystallization particles; the third centrifugal device 1002 is configured to centrifugally separate supersaturated mixed salt crystal particles from the third crystallization device 1001, and output solid mixed salt and a third centrifugal mother liquor; preferably, the mixed salt crystallization unit further comprises a fourth return pipeline, one end of the fourth return pipeline is connected to a solid mixed salt outlet of the mixed salt crystallization unit, and the other end of the fourth return pipeline is connected to the secondary membrane separation collaborative desilication unit, and is used for returning the solid mixed salt from the mixed salt crystallization unit to the secondary membrane separation collaborative desilication unit for carrying out dissolution and circulation treatment;
The mother liquor drying unit comprises a drying device 1101, wherein the drying device 1101 is connected to a third centrifugal mother liquor outlet of the mixed salt crystallization unit and is used for drying the third centrifugal mother liquor from the mixed salt crystallization unit and outputting solid waste and tail gas; preferably, the drying apparatus 1101 includes any one or more of roller blade drying, spray drying, and vacuum rake drying.
Those skilled in the art will appreciate that a pump is also provided in the system for providing power during the material transport process.
In the invention, the evaporation crystallization device is a device commonly used in the field, and comprises a vapor compressor, an evaporation crystallizer, a circulating pump,
Example 1
The process for fractional crystallization and recovery of inorganic salt from the salt-containing wastewater of the present invention is carried out as shown in the flow chart of FIG. 1, wherein,
the treatment capacity of the salt-containing wastewater as the inlet water is 400m 3 /h; the main indexes of the water quality of the inlet water comprise: the salt content (TDS) is 9187mg/L; total hardness (as CaCO) 3 Meter) is 2849mg/L; total alkalinity (CaCO) 3 Meter) is 51.94mg/L; sulfate (in SO) 4 2- Meter) is 2845mg/L; chloride (in Cl) - Calculated) is 2603mg/L; nitrate (in NO) 3 - Calculated) is 539mg/L; calcium ion (in Ca) 2+ Calculated as 9483mg/L; magnesium ion (in Mg) 2+ Calculated) to be 117mg/L; sodium ion (in Na + Calculated) was 1822mg/L.
The method comprises the following steps:
(1) Primary calcium carbonate crystals
Adding alkali (NaOH) into the salt-containing wastewater to adjust the pH value to 10.5-11, then sending the salt-containing wastewater into a primary induced crystallization fluidized bed reactor 101, controlling the rising flow rate of water flow in the primary induced crystallization fluidized bed reactor 101 to be about 60m/h, adding a first seed crystal (garnet seed crystal with the particle size of 0.1 mm) into the primary induced crystallization fluidized bed reactor to perform induced crystallization, separating out calcium carbonate crystal particles, and outputting magnesium hydroxide precipitate along with effluent; obtaining about 17kg/h of calcium carbonate crystal particles with purity of more than 90%; wherein the adding amount of the first seed crystal is 1mg/L water;
(2) Primary membrane separation
Feeding the effluent from the step (1) into a primary mixing reaction tank 201, adding alkali (10% NaOH solution) to adjust the pH to 11-12, converting magnesium ions in the effluent into magnesium hydroxide precipitate, feeding the magnesium hydroxide precipitate to a primary microfiltration membrane device 202 (a bag type microfiltration device) along with the water for microfiltration treatment, discharging sludge comprising the magnesium hydroxide precipitate, and outputting effluent comprising sodium chloride, sodium sulfate and calcium sulfate;
(3) Membrane concentration desalination
After the effluent from the step (2) is sent into a membrane concentration water inlet tank 301 and added with acid (hydrochloric acid) to adjust the pH value to be neutral, a scale inhibitor (Titan ASDTM 200SC of PWT company) is added and sent to a membrane group system 302 (a reverse osmosis and nanofiltration membrane group system) along with the water to carry out concentration and desalination treatment under the action of the scale inhibitor, the desalted produced water is output for recycling, and the calcium sulfate is output to concentrate to supersaturated concentrated water with the supersaturation degree of 3 times of calcium sulfate solubility;
(4) Calcium sulfate crystal
The concentrated water in the step (3) is sent to a seed crystal circulating fluidized bed 401, calcium sulfate seed crystals are added into the seed crystal circulating fluidized bed 401 for induced crystallization, the rising flow speed of water flow in the seed crystal circulating fluidized bed 401 is controlled to be about 40m/h, calcium and sulfate ions deactivated by crystallization are attached to the calcium sulfate seed crystals, calcium sulfate crystal particles are separated out, the rising flow speed is reduced to about 20m/h by increasing the water cross section at the upper part of the seed crystal circulating fluidized bed 401, mud-water separation is realized, large-particle-diameter calcium sulfate crystal particles are discharged from the bottom at regular intervals, calcium sulfate dihydrate (gypsum) crystal particle products are recovered by dehydration separation, the yield of the calcium sulfate crystal particles can reach 1217kg/h, the purity can reach more than 90%, and the calcium sulfate crystal particles are used as building material for recycling; small-particle-size calcium sulfate crystal particles are discharged from the middle upper part, then the calcium sulfate fine crystals separated by cyclone separation are returned to the fluidized bed to be used as seed crystals for recycling, clear liquid effluent from cyclone separation is mixed with overflow effluent from the upper part of the seed crystal circulating fluidized bed 401, and the mixture is sent to subsequent processes for treatment; overflow effluent water containing calcium sulfate and calcium chloride overflows from the upper part; wherein, the grain diameter of the large-grain diameter calcium sulfate crystal grain is 0.3-2mm; the grain diameter of the small-grain-diameter calcium sulfate crystal grains is 0.05-0.3mm; the overflow effluent part is returned to the step (3), and the concentration of calcium sulfate in the inflow water of the membrane group system 302 is controlled to be not higher than 0.9 times of the solubility product of the calcium sulfate by controlling the reflux ratio;
(5) Secondary calcium carbonate crystals
Adding alkali (sodium carbonate solution with the concentration of 10% and NaOH solution with the concentration of 32%) into the overflow water part in the step (4) to adjust the pH value to 10.5-11, then sending the mixture into a secondary induced crystallization fluidized bed reactor 501, adding the first seed crystal into the mixture to carry out induced crystallization, separating out calcium carbonate crystal particles, and outputting magnesium hydroxide precipitate along with the water; wherein the water ascending flow rate in the secondary induced crystallization fluidized bed reactor 501 is controlled to be about 60m/h; the main component of the calcium carbonate crystal particles is calcium carbonate, the purity is more than 90%, the yield is 11kg/h, and the calcium carbonate crystal particles can be used as a raw material of desulfurization limestone for recycling;
(6) Secondary membrane separation synergistic desilication
Delivering the effluent from the step (5) to a mixing reaction tank, adding an aluminum agent (sodium metaaluminate), delivering to a secondary microfiltration membrane device 602 (an alkali-resistant bag-type microfilter) for microfiltration separation, discharging sludge containing aluminosilicate precipitate and adsorbed silica-magnesium hydroxide precipitate, and outputting desilication effluent; silicon removal of SiO in effluent 2 The concentration is below 30 mg/L; wherein the addition amount of the aluminum agent is equal to that of Silicon (SiO) in the effluent of the step (5) 2 ) The mass ratio of (2) to (1);
(7) Ion exchange depth hardness removal
Delivering the desilication effluent from the step (6) to a cation bed water inlet tank 701, adding acid to adjust the pH to 7-9, delivering to an ion exchange resin 702 (weak acid sodium ion exchange resin) for ion exchange to remove divalent or more multivalent cations such as heavy metal ions, calcium, magnesium and the like, and outputting effluent from the bottom; the total hardness of the discharged water is CaCO 3 The weight of the mixture is less than or equal to 1mg/L; the ion exchange resin 702 is regenerated step by adopting hydrochloric acid and sodium hydroxide;
(8) Carbonate alkalinity removal
Adding acid to the effluent from the step (7) to adjust the pH to below 4.3, and then sending the effluent to the decarbonizer fan 801 to convert CO from residual carbonate in the water 2 Removing, and outputting effluent water containing sodium chloride and sodium sulfate; wherein, the air-water ratio is maintained to be about 40m in the decarburization fan 801 3 (air)/m 3 (water); the content of carbon dioxide in the effluent is less than 5mg/L, the pH value can be increased to more than 6, and the carbonate in the water is almost completely converted into chloride or sulfate;
(9) Salt separation and crystallization
Separating and crystallizing sodium chloride and sodium sulfate from the effluent, outputting sodium chloride products and sodium sulfate products, and outputting mother liquor; wherein,
step (9) adopts a method I:
i. nanofiltration salt separation
Separating the effluent from the step (8) by a nanofiltration membrane to output nanofiltration membrane produced water enriched with sodium chloride salt and nanofiltration concentrated water enriched with sodium sulfate; then carrying out reverse osmosis concentration on the nanofiltration membrane produced water, and outputting reverse osmosis concentrated water as nanofiltration produced water and output reuse water; wherein the reverse osmosis concentrated water is high-salt brine with a salt content (TDS) of more than 5%;
ii. Sodium sulfate crystal
Firstly, freezing and crystallizing the nanofiltration concentrated water in the step i to separate out a sodium sulfate decahydrate product (mirabilite), and outputting second brine containing the sodium sulfate decahydrate product; then, carrying out centrifugal separation on the second brine, and outputting 884.4kg/h of sodium sulfate decahydrate product and second centrifugal mother liquor; then melting the obtained sodium sulfate decahydrate product, sequentially carrying out evaporative crystallization and centrifugal separation, and outputting 390kg/h of anhydrous sodium sulfate product (anhydrous sodium sulfate);
The second centrifugal mother liquor part is returned to the step (6) for microfiltration separation;
iii, crystallization of sodium chloride
Evaporating and crystallizing the nanofiltration produced water in the step i, outputting distilled water as reuse water, and outputting supersaturated sodium chloride concentrated solution as first brine; centrifugally separating the first brine, and outputting 1163kg/h of sodium chloride industrial salt product and first centrifugal mother liquor;
iv, mixing the second centrifugal mother liquor of the step ii and the first centrifugal mother liquor of the step iii to output as the mother liquor of the step (9);
(10) Mixed salt crystal
Evaporating and crystallizing the mother solution in the step (9) to separate out mixed salt crystals, and outputting supersaturated mixed salt crystal particles; then, carrying out centrifugal separation on the supersaturated mixed salt crystal particles, and outputting solid mixed salt and third centrifugal mother liquor; and (3) adding water into the obtained solid mixed salt for re-dissolution, and returning to the step (6) for micro-filtration separation.
(11) Drying the mother liquor
Drying the third centrifugal mother liquor output in the step (10) to output 475kg/h of solid waste and tail gas; wherein,
in each step, the temperature of freezing crystallization is 0 ℃; the temperature of the evaporative crystallization was 100 ℃.
Example 2
The fractional crystallization of salt-containing wastewater to recover inorganic salts was performed as in example 1, and the only difference from example 1 was that:
The method for recovering inorganic salt by fractional crystallization of the salt-containing wastewater is carried out according to the flow shown in figure 2;
in the step (1), the upward flow speed of water flow in the step (101) is about 70m/h, and the first seed crystal is quartz sand seed crystal with the particle size of 0.3 mm; the adding amount of the first seed crystal is 0.2mg/L water; the pH is 11-11.5;
in the step (2), the effluent from the step (1) is sent to a primary mixing reaction tank 201 and magnesium (MgO) is added, so that magnesium ions in the effluent are converted into magnesium silicate and calcium silicate precipitates; and according to magnesium and SiO 2 Adding a magnesium agent (MgO) according to the mass ratio of 7:1;
in step (3), the membrane module system 302 is a reverse osmosis membrane module system; the supersaturation degree of calcium sulfate in the concentrated water is 3 times of the solubility product of the calcium sulfate;
in the step (5), adding alkali into the overflow water part obtained in the step (4) to adjust the pH to 11-12, and then conveying the mixture into a secondary induced crystallization fluidized bed reactor 501;
in the step (6), the aluminum agent is polyaluminum chloride; the addition amount of the aluminum agent and the Silicon (SiO) in the effluent of the step (5) 2 ) The mass ratio of (2) is 3:1;
in step (7), the ion exchange resin 702 is a chelating resin;
in the step (8), the air-water ratio is maintained at about 30m 3 (air)/m 3 (water);
step (9) adopts a method I: and the specific steps of step ii are as follows: evaporating and crystallizing the nanofiltration concentrated water in the step i to obtain a concentrated solution supersaturated with sodium sulfate; then, carrying out centrifugal separation on the concentrated solution supersaturated with sodium sulfate, and outputting an anhydrous sodium sulfate product and primary centrifugal mother liquor; then, freezing and crystallizing the obtained primary centrifugal mother liquor to separate out a sodium sulfate decahydrate product, and outputting second brine containing the sodium sulfate decahydrate product; and then carrying out centrifugal separation on the second brine, and outputting a sodium sulfate decahydrate product and outputting a secondary centrifugal mother liquor as a second centrifugal mother liquor.
Wherein, the step (1) obtains about 16kg/h calcium carbonate crystal particles with purity more than 90%;
the yield of the calcium sulfate crystal particles obtained in the step (2) can reach 1198kg/h, and the purity is 92%;
the yield of the calcium carbonate crystal particles obtained in the step (5) is 12kg/h, and the purity is more than 90%;
in the step (9), the yield of the obtained anhydrous sodium sulfate product is 385kg/h; the yield of the obtained sodium sulfate decahydrate product is 85kg/h; the yield of the obtained sodium chloride industrial salt product is 1165kg/h;
the yield of the solid waste obtained in the step (10) was 480kg/h.
Example 3
The fractional crystallization of salt-containing wastewater to recover inorganic salts was performed as in example 1, and the only difference from example 1 was that:
the method for recovering inorganic salt by fractional crystallization of the salt-containing wastewater is carried out according to the flow shown in figure 3;
in the step (1), the first seed crystal is quartz sand seed crystal with the grain diameter of 0.2 mm; the pH is 10-11;
in the step (2), the effluent from the step (1) is sent to a primary mixing reaction tank 201 and a magnesium agent (magnesium chloride) is added, so that magnesium ions in the effluent are converted into magnesium silicate and calcium silicate to be precipitated; and according to magnesium and SiO 2 Adding a magnesium agent (magnesium chloride) according to the mass ratio of 4:1;
in step (3), the membrane group system 302 is a nanofiltration membrane group system; the supersaturation degree of calcium sulfate in the concentrated water is 4 times of the solubility product of the calcium sulfate;
In the step (5), adding alkali into the overflow water part obtained in the step (4) to adjust the pH to 10.5-11, and then conveying the mixture into a secondary induced crystallization fluidized bed reactor 501;
in the step (6), the aluminum agent is polyaluminum ferric chloride; the addition amount of the aluminum agent and the Silicon (SiO) in the effluent of the step (5) 2 ) The mass ratio of (2) is 5:1;
in step (7), the ion exchange resin 702 is a strong acid sodium ion exchange resin;
in the step (8), the air-water ratio is maintained at about 15m 3 (air)/m 3 (water);
step (9) adopts a method I: and the specific steps of step ii are as follows: evaporating and crystallizing the nanofiltration concentrated water in the step i, and outputting supersaturated sodium sulfate concentrated solution as second brine; and then carrying out centrifugal separation on the second brine, and outputting an anhydrous sodium sulfate product and a second centrifugal mother solution.
Wherein, the step (1) obtains about 17kg/h of calcium carbonate crystal particles with purity more than 90%;
the yield of the calcium sulfate crystal particles obtained in the step (2) can reach 1220kg/h, and the purity is 90%;
the yield of the calcium carbonate crystal particles obtained in the step (5) is 10kg/h, and the purity is more than 90%;
in the step (9), the yield of the anhydrous sodium sulfate product is 380kg/h; the yield of the obtained sodium chloride industrial salt product is 1170kg/h;
the yield of the solid waste obtained in the step (10) was 478kg/h.
Example 4
The fractional crystallization of salt-containing wastewater to recover inorganic salts was performed as in example 1, and the only difference from example 1 was that:
the method for recovering inorganic salt by fractional crystallization of the salt-containing wastewater is carried out according to the flow shown in figure 4;
and step (9) adopts a second method.
Wherein, the step (1) obtains about 17kg/h of calcium carbonate crystal particles with purity more than 90%;
the yield of the calcium sulfate crystal particles obtained in the step (2) can reach 1217kg/h, and the purity is 90%;
the yield of the calcium carbonate crystal particles obtained in the step (5) is 11kg/h, and the purity is more than 90%;
in the step (9), the yield of the obtained anhydrous sodium sulfate product is 395kg/h; the yield of the obtained sodium sulfate decahydrate product is 895.7kg/h; the yield of the obtained sodium chloride industrial salt product is 1168kg/h;
the yield of the solid waste obtained in the step (10) was 465kg/h.
Claims (10)
1. A method for recovering inorganic salt by fractional crystallization of salt-containing wastewater, which is characterized by comprising the following steps:
(1) Primary calcium carbonate crystals
Adding alkali into the salt-containing wastewater to adjust the pH value to 9.5-11.5, then delivering the salt-containing wastewater into a primary induced crystallization fluidized bed reactor, adding a first seed crystal into the primary induced crystallization fluidized bed reactor for induced crystallization, separating out calcium carbonate crystal particles, and outputting magnesium hydroxide precipitate along with effluent;
(2) Primary membrane separation
Adding alkali and/or magnesium agent into the effluent of the step (1) to convert magnesium ions in the effluent into magnesium hydroxide precipitate and/or magnesium silicate complex, then sending the magnesium hydroxide precipitate and/or magnesium silicate complex to primary microfiltration membrane equipment along with water for microfiltration treatment, discharging sludge comprising magnesium hydroxide precipitate and/or magnesium silicate and calcium silicate precipitate, and outputting effluent comprising sodium chloride, sodium sulfate and calcium sulfate;
(3) Membrane concentration desalination
Adding acid into the effluent from the step (2) to adjust the pH value to be neutral, adding a scale inhibitor, sending the mixture to a membrane group system along with the water to perform concentration and desalination treatment under the action of the scale inhibitor, outputting produced water for recycling, and outputting concentrated water obtained by concentrating calcium sulfate to supersaturation;
(4) Calcium sulfate crystal
Delivering the concentrated water obtained in the step (3) into a seed crystal circulating fluidized bed, adding calcium sulfate seed crystals into the concentrated water for induced crystallization, separating out calcium sulfate crystal particles, discharging large-particle-size calcium sulfate crystal particles from the bottom, discharging small-particle-size calcium sulfate crystal particles from the middle upper part, and overflowing overflow water containing calcium sulfate and calcium chloride from the upper part; wherein, the grain diameter of the large-grain-diameter calcium sulfate crystal grains is 0.3-2mm, and the grain diameter of the small-grain-diameter calcium sulfate crystal grains is 0.05-0.3mm;
(5) Secondary calcium carbonate crystals
Adding alkali into the overflow water outlet part in the step (4) to adjust the pH value to 10.5-12, then sending the overflow water outlet part into a secondary induced crystallization fluidized bed reactor, adding the first seed crystal into the overflow water outlet part to carry out induced crystallization, separating out calcium carbonate crystal particles, and outputting magnesium hydroxide precipitate along with the water outlet;
(6) Secondary membrane separation synergistic desilication
Adding an aluminum agent into the effluent of the step (5), then sending the effluent to a secondary microfiltration membrane device for microfiltration separation, discharging sludge containing aluminosilicate sediment and silica-magnesium hydroxide sediment, and outputting desilication effluent;
(7) Ion exchange depth hardness removal
Adding acid into the desilication effluent from the step (6) to adjust the pH value to 7-9, then sending the desilication effluent to ion exchange resin for ion exchange so as to remove divalent or more multivalent cations such as heavy metal ions, calcium, magnesium and the like, and outputting effluent from the bottom;
(8) Carbonate alkalinity removal
Adding acid to the effluent from the step (7) to adjust the pH value to below 4.3, and then sending the effluent to a decarbonizer fan to convert CO from residual carbonate in the water 2 Removing, and outputting effluent water containing sodium chloride and sodium sulfate;
(9) Salt separation and crystallization
Separating and crystallizing sodium chloride and sodium sulfate from the effluent, outputting sodium chloride products and sodium sulfate products, and outputting mother liquor;
(10) Mixed salt crystal
Evaporating and crystallizing the mother solution in the step (9) to separate out mixed salt crystals, and outputting supersaturated mixed salt crystal particles; then, carrying out centrifugal separation on the supersaturated mixed salt crystal particles, and outputting solid mixed salt and third centrifugal mother liquor;
(11) Drying the mother liquor
And (3) drying the third centrifugal mother liquor output in the step (10) to output solid waste and tail gas.
2. The method of claim 1, wherein the step of determining the position of the substrate comprises,
step (9) comprises a first method and/or a second method; wherein,
the method one comprises the following steps:
i. nanofiltration salt separation
Separating the effluent from the step (8) by using a nanofiltration membrane to output nanofiltration membrane produced water enriched with sodium chloride as nanofiltration produced water and outputting nanofiltration concentrated water enriched with sodium sulfate;
ii. Sodium sulfate crystal
Carrying out sodium sulfate crystallization on the nanofiltration concentrated water obtained in the step i to obtain second brine containing sodium sulfate crystals; centrifugally separating the second brine to output a sodium sulfate product and a second centrifugal mother liquor;
iii, crystallization of sodium chloride
Evaporating and crystallizing the nanofiltration produced water in the step i, outputting distilled water as reuse water, and outputting supersaturated sodium chloride concentrated solution as first brine; centrifugally separating the first brine to output sodium chloride industrial salt products and first centrifugal mother liquor;
iv, mixing the second centrifugal mother liquor of step ii and the first centrifugal mother liquor of step iii as the mother liquor of step (9);
the second method comprises the following steps:
i. reverse osmosis concentration
Carrying out reverse osmosis concentration on the effluent from the step (8), outputting reverse osmosis concentrated water enriched with sodium chloride and sodium sulfate, and recycling reverse osmosis produced water;
ii. Sodium sulfate crystal
Freezing and crystallizing the reverse osmosis concentrated water obtained in the step i to obtain second brine containing sodium sulfate decahydrate crystals; centrifugally separating the second brine, and outputting a sodium sulfate decahydrate product and a second centrifugal mother liquor containing sodium chloride; then melting the obtained sodium sulfate decahydrate product, and sequentially carrying out evaporative crystallization and centrifugal separation to output an anhydrous sodium sulfate product;
iii, crystallization of sodium chloride
Evaporating and concentrating the second centrifugal mother liquor obtained in the step ii, outputting distilled water as reuse water, and outputting supersaturated sodium chloride concentrated solution as first brine; centrifugally separating the first brine to output sodium chloride industrial salt products and first centrifugal mother liquor;
iv, taking the first centrifugal mother liquor in the step iii as the mother liquor in the step (9).
3. The method of claim 2, wherein the step of determining the position of the substrate comprises,
in the method one of the step (9), the specific steps of the step ii are as follows: freezing and crystallizing the nanofiltration concentrated water obtained in the step i to separate out a sodium sulfate decahydrate product, and outputting second brine containing the sodium sulfate decahydrate product; then, carrying out centrifugal separation on the second brine, and outputting a sodium sulfate decahydrate product and a second centrifugal mother solution; then melting the obtained sodium sulfate decahydrate product, and sequentially carrying out evaporative crystallization and centrifugal separation to output an anhydrous sodium sulfate product; and/or
In the method one of the step (9), the specific steps of the step ii are as follows: evaporating and crystallizing the nanofiltration concentrated water in the step (9) to obtain a sodium sulfate supersaturated concentrated solution; then, carrying out centrifugal separation on the concentrated solution supersaturated with sodium sulfate, and outputting sodium sulfate products and primary centrifugal mother liquor; then, freezing and crystallizing the obtained primary centrifugal mother liquor to separate out a sodium sulfate decahydrate product, and outputting second brine containing the sodium sulfate decahydrate product; then carrying out centrifugal separation on the second brine, and outputting a sodium sulfate decahydrate product and outputting a secondary centrifugal mother liquor as a second centrifugal mother liquor; preferably, the obtained sodium sulfate decahydrate product is returned to the front end of the evaporative crystallization for reprocessing after being hot melted; and/or
In the method one of the step (9), the specific steps of the step ii are as follows: evaporating and crystallizing the nanofiltration concentrated water in the step (9), and outputting supersaturated sodium sulfate concentrated solution as second brine; and then carrying out centrifugal separation on the second brine, and outputting an anhydrous sodium sulfate product and a second centrifugal mother solution.
4. A method according to claim 2 or 3, characterized in that,
in the first method of the step (9), in the step ii, the second centrifugal mother liquor part is returned to the step (6) for microfiltration separation;
Preferably, in the first method of step (9), in step ii, the second centrifuged mother liquor is partially returned to step i for sodium chloride crystallization;
preferably, in the first method of the step (9), in the step iii, the solid mixed salt is returned to the step (6) for microfiltration separation after being dissolved in water.
5. The method according to any one of claims 2 to 4, wherein,
in the first method of the step (9), in the step i, reverse osmosis concentration is carried out on the nanofiltration membrane produced water, and the reverse osmosis concentrated water is output as nanofiltration produced water and the reverse osmosis produced water is output as reuse water;
preferably, in step (9) of the first process, step iii, the first centrifuged mother liquor fraction is returned to the front end of its evaporative crystallisation.
6. The method according to any one of claims 2 to 5, wherein,
in the second method of the step (9), in the step ii, the second centrifugal mother liquor part is returned to the step (6) for microfiltration separation.
7. The method according to any one of claims 1 to 6, wherein,
in the step (1), the particle size of the first seed crystal is 0.1-0.3mm; preferably the first seed crystal comprises quartz sand and/or garnet.
8. The method according to any one of claims 1 to 7, wherein,
In the step (4), small-particle-size calcium sulfate crystal particles are subjected to cyclone separation, the obtained calcium sulfate fine crystals are returned to the step (4) to be used as seed crystals for recycling, and preferably, the obtained clear liquid effluent is combined with the overflow effluent.
9. The method according to any one of claims 1 to 8, wherein,
in the step (4), the supersaturation degree of calcium sulfate in the overflow effluent is not higher than 1.2 times of the solubility product of the calcium sulfate;
preferably, in step (4), the overflow effluent is partially recycled to step (3), preferably by controlling the reflux ratio, so that the concentration of calcium sulfate in the feed water to the membrane module system is not higher than 0.9 times the solubility product of calcium sulfate.
10. A system for a method for fractional crystallization recovery of inorganic salts from a brine waste according to any one of claims 1-9.
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