CN111072052A - Method and system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater - Google Patents
Method and system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater Download PDFInfo
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- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 title claims abstract description 144
- VTHJTEIRLNZDEV-UHFFFAOYSA-L magnesium dihydroxide Chemical compound [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 title claims abstract description 86
- 239000000347 magnesium hydroxide Substances 0.000 title claims abstract description 86
- 229910001862 magnesium hydroxide Inorganic materials 0.000 title claims abstract description 86
- 239000002351 wastewater Substances 0.000 title claims abstract description 82
- 229910000019 calcium carbonate Inorganic materials 0.000 title claims abstract description 71
- 239000011777 magnesium Substances 0.000 title claims abstract description 58
- 229910052749 magnesium Inorganic materials 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims abstract description 25
- 238000006243 chemical reaction Methods 0.000 claims abstract description 41
- 238000002425 crystallisation Methods 0.000 claims abstract description 38
- 230000008025 crystallization Effects 0.000 claims abstract description 38
- 239000013078 crystal Substances 0.000 claims abstract description 33
- 238000011084 recovery Methods 0.000 claims abstract description 33
- 229910001385 heavy metal Inorganic materials 0.000 claims abstract description 24
- 125000001741 organic sulfur group Chemical group 0.000 claims abstract description 19
- 235000008733 Citrus aurantifolia Nutrition 0.000 claims abstract description 16
- 235000011941 Tilia x europaea Nutrition 0.000 claims abstract description 16
- 239000004571 lime Substances 0.000 claims abstract description 16
- 239000008267 milk Substances 0.000 claims abstract description 15
- 210000004080 milk Anatomy 0.000 claims abstract description 15
- 235000013336 milk Nutrition 0.000 claims abstract description 15
- 238000001914 filtration Methods 0.000 claims abstract description 14
- 239000000706 filtrate Substances 0.000 claims abstract description 13
- 238000003756 stirring Methods 0.000 claims abstract description 13
- 239000002244 precipitate Substances 0.000 claims abstract description 10
- 239000007788 liquid Substances 0.000 claims abstract description 9
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims abstract description 7
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 claims abstract description 6
- 239000012065 filter cake Substances 0.000 claims abstract description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 claims abstract description 6
- 239000012295 chemical reaction liquid Substances 0.000 claims abstract description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 86
- 229910001868 water Inorganic materials 0.000 claims description 85
- 239000012528 membrane Substances 0.000 claims description 33
- 229910052500 inorganic mineral Inorganic materials 0.000 claims description 19
- 239000011707 mineral Substances 0.000 claims description 19
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical group [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 claims description 16
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical group [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 15
- 229910001424 calcium ion Inorganic materials 0.000 claims description 13
- BHPQYMZQTOCNFJ-UHFFFAOYSA-N Calcium cation Chemical compound [Ca+2] BHPQYMZQTOCNFJ-UHFFFAOYSA-N 0.000 claims description 12
- 239000013505 freshwater Substances 0.000 claims description 9
- 229910000029 sodium carbonate Inorganic materials 0.000 claims description 8
- 239000002245 particle Substances 0.000 claims description 7
- 238000004519 manufacturing process Methods 0.000 claims description 6
- 239000000047 product Substances 0.000 claims description 5
- 238000001035 drying Methods 0.000 claims description 4
- 238000005406 washing Methods 0.000 claims description 4
- 229910021532 Calcite Inorganic materials 0.000 claims description 3
- 230000001174 ascending effect Effects 0.000 claims description 3
- 238000011049 filling Methods 0.000 claims description 3
- 230000035484 reaction time Effects 0.000 claims description 3
- 230000001105 regulatory effect Effects 0.000 claims description 3
- 235000019738 Limestone Nutrition 0.000 claims description 2
- 239000006028 limestone Substances 0.000 claims description 2
- NYVOYAFUSJONHU-UHFFFAOYSA-K trisodium;1,3,5-triazine-2,4,6-trithiolate Chemical group [Na+].[Na+].[Na+].[S-]C1=NC([S-])=NC([S-])=N1 NYVOYAFUSJONHU-UHFFFAOYSA-K 0.000 claims description 2
- 239000000243 solution Substances 0.000 description 19
- 238000006477 desulfuration reaction Methods 0.000 description 12
- 230000023556 desulfurization Effects 0.000 description 12
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 9
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 8
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 8
- 239000011575 calcium Substances 0.000 description 8
- 229910052791 calcium Inorganic materials 0.000 description 7
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 description 6
- 229910001425 magnesium ion Inorganic materials 0.000 description 6
- 238000001556 precipitation Methods 0.000 description 6
- 230000000052 comparative effect Effects 0.000 description 5
- 238000001704 evaporation Methods 0.000 description 5
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 4
- 230000008020 evaporation Effects 0.000 description 4
- 238000001223 reverse osmosis Methods 0.000 description 4
- 239000012266 salt solution Substances 0.000 description 4
- 239000011780 sodium chloride Substances 0.000 description 4
- 229910052938 sodium sulfate Inorganic materials 0.000 description 4
- 235000011152 sodium sulphate Nutrition 0.000 description 4
- 239000000292 calcium oxide Substances 0.000 description 3
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium oxide Inorganic materials [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 238000000926 separation method Methods 0.000 description 3
- 238000004065 wastewater treatment Methods 0.000 description 3
- RNFJDJUURJAICM-UHFFFAOYSA-N 2,2,4,4,6,6-hexaphenoxy-1,3,5-triaza-2$l^{5},4$l^{5},6$l^{5}-triphosphacyclohexa-1,3,5-triene Chemical compound N=1P(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP(OC=2C=CC=CC=2)(OC=2C=CC=CC=2)=NP=1(OC=1C=CC=CC=1)OC1=CC=CC=C1 RNFJDJUURJAICM-UHFFFAOYSA-N 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- BRPQOXSCLDDYGP-UHFFFAOYSA-N calcium oxide Chemical compound [O-2].[Ca+2] BRPQOXSCLDDYGP-UHFFFAOYSA-N 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 239000003063 flame retardant Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000001728 nano-filtration Methods 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 239000000779 smoke Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000000725 suspension Substances 0.000 description 2
- 229920002994 synthetic fiber Polymers 0.000 description 2
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 238000000889 atomisation Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 238000003889 chemical engineering Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 239000006071 cream Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000005342 ion exchange 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 compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 231100000956 nontoxicity Toxicity 0.000 description 1
- 239000003973 paint Substances 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
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- 229920000642 polymer Polymers 0.000 description 1
- 239000002861 polymer material Substances 0.000 description 1
- 230000008092 positive effect Effects 0.000 description 1
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- 230000002265 prevention Effects 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 239000010802 sludge Substances 0.000 description 1
- 239000006228 supernatant Substances 0.000 description 1
- 230000001502 supplementing effect Effects 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 229920006305 unsaturated polyester Polymers 0.000 description 1
- 238000003911 water pollution Methods 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/18—Carbonates
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/14—Magnesium hydroxide
- C01F5/22—Magnesium hydroxide from magnesium compounds with alkali hydroxides or alkaline- earth oxides or hydroxides
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F9/00—Multistage treatment of water, waste water or sewage
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/66—Treatment of water, waste water, or sewage by neutralisation; pH adjustment
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/20—Heavy metals or heavy metal compounds
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/18—Nature of the water, waste water, sewage or sludge to be treated from the purification of gaseous effluents
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2209/00—Controlling or monitoring parameters in water treatment
- C02F2209/06—Controlling or monitoring parameters in water treatment pH
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2209/00—Controlling or monitoring parameters in water treatment
- C02F2209/10—Solids, e.g. total solids [TS], total suspended solids [TSS] or volatile solids [VS]
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2301/00—General aspects of water treatment
- C02F2301/08—Multistage treatments, e.g. repetition of the same process step under different conditions
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Abstract
The invention discloses a method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, which comprises the following steps: heavy metal and suspended matter removing step: adding lime milk and organic sulfur into the high-magnesium wastewater to enable the pH value of the high-magnesium wastewater to be 8-9 and generate heavy metal sulfide precipitate, and filtering to remove the heavy metal sulfide precipitate and suspended matters generated in the high-magnesium wastewater to obtain clear liquid; calcium carbonate recovery step: introducing the clear liquid into a circulating crystallization fluidized bed, and then adding a carbonate solution for reaction to obtain calcium carbonate crystals and reaction liquid overflowing from the circulating crystallization fluidized bed; and (3) magnesium hydroxide recovery step: adding a soluble hydroxide solution into the reaction solution, adjusting the pH value to 11-11.5, reacting while stirring, and then filtering and separating to obtain a magnesium hydroxide filter cake and a filtrate. The invention can recover high-purity calcium carbonate and magnesium hydroxide, and meets the requirement of circular economy.
Description
Technical Field
The invention belongs to the field of wastewater treatment, and particularly relates to a method and a system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater.
Background
With the release of the national water pollution prevention and control plan, higher requirements are put forward on water use and drainage of a thermal power plant, and the construction of a thermal power plant wastewater zero-discharge system becomes a development trend of power plant wastewater treatment. Various waste water discharged by a power plant is most difficult to treat by high-salinity waste water and desulfurization waste water generated by an ion exchange regeneration system, and the waste water has high hardness, high suspended matters, high salinity, stronger corrosivity and larger water quality and water quantity fluctuation.
At present, the main processes for zero discharge of power plant wastewater include: pretreatment, membrane concentration, evaporative crystallization, pretreatment, flue evaporation, mechanical atomization and evaporation and the like. The pretreatment, membrane concentration and evaporative crystallization technologies can recover industrial salt and more than 90% of fresh water, and the method is one of the technologies with development prospects in zero discharge of wastewater. Mg in high-magnesium wastewater2+The concentration can reach 5000-2+And Mg2+However, this method has problems of large amount of precipitate formation, consumption of softener and excessive cost for high magnesium desulfurization waste water. Meanwhile, magnesium ions and calcium in the wastewaterIons are a precious resource and are converted into sludge through softening treatment, so that the dosing cost of wastewater treatment is increased, and calcium and magnesium resources in water are wasted.
Magnesium hydroxide is an inorganic additive type flame retardant, the thermal decomposition temperature of the magnesium hydroxide reaches 350 ℃, bound water is released when the magnesium hydroxide is heated and decomposed, a large amount of latent heat is absorbed, the surface temperature of a synthetic material filled with the magnesium hydroxide in flame is reduced, the magnesium hydroxide has the effects of inhibiting the decomposition of a polymer and cooling generated combustible gas, magnesium oxide generated by the decomposition is a good refractory material, the fire resistance of the synthetic material can be improved, and simultaneously water vapor released by the magnesium hydroxide can be used as a smoke inhibitor. The magnesium hydroxide has the advantages of low smoke, no toxicity, good thermal stability and the like, and is widely applied to high polymer materials such as rubber, chemical engineering, building materials, plastics, electronics, unsaturated polyester, paint, coating and the like.
Disclosure of Invention
In view of the shortcomings and drawbacks of the prior art, an object of the present invention is to provide a method for recovering calcium carbonate and magnesium hydroxide from high magnesium wastewater.
The invention also aims to provide a system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater.
The technical scheme adopted by the invention for solving the technical problem is as follows:
a method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater comprises the following steps:
heavy metal and suspended matter removing step: adding lime milk and organic sulfur into the high-magnesium wastewater to enable the pH value of the high-magnesium wastewater to be 8-9 and generate heavy metal sulfide precipitate, and filtering to remove the heavy metal sulfide precipitate and suspended matters generated in the high-magnesium wastewater to obtain clear liquid;
calcium carbonate recovery step: introducing the clear liquid into a circulating crystallization fluidized bed, and then adding a carbonate solution for reaction to obtain calcium carbonate crystals and reaction liquid overflowing from the circulating crystallization fluidized bed;
and (3) magnesium hydroxide recovery step: adding a soluble hydroxide solution to the reaction solution, adjusting the pH value to 11-11.5 (for example, 11.1, 11.2, 11.3 and 11.4), reacting while stirring, and then filtering and separating to obtain a magnesium hydroxide cake and a filtrate.
The control of the pH value in the magnesium hydroxide recovery step can ensure that the recovery rate of magnesium ions reaches more than 95 percent and the purity of the magnesium hydroxide is high.
In the above method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, as a preferred embodiment, in the heavy metal and suspended matter removal step, the pH of the high-magnesium wastewater is 8 to 8.8 (e.g., 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, 8.7). The pH value control of the desulfurization wastewater in the step has important influence on the recovery rate and purity of calcium carbonate and magnesium hydroxide. Higher pH will precipitate the doped magnesium hydroxide and reduce the recovery of the final magnesium hydroxide.
In the above method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, as a preferred embodiment, in the heavy metal and suspended matter removal step, the lime milk is added in the form of an aqueous solution, the mass concentration of the aqueous solution of the lime milk (i.e. the mass content of CaO) is 5% -10%, the addition amount of the organic sulfur is 10-20mg/L, preferably, the organic sulfur is trimercapto-s-triazine trisodium salt, and the addition amount of the organic sulfur is determined according to the concentration of heavy metal ions in the high-magnesium wastewater, and is usually 10-20 mg/L; the filtration is performed through a tubular membrane.
In the above method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, as a preferred embodiment, in the calcium carbonate recovery step, the circulating crystallization fluidized bed is filled with mineral seeds; preferably, the particle size of the mineral seed crystal is 0.05-0.1mm, which can ensure that the mineral seed crystal is in a suspension state in the fluidized bed, and is beneficial to the adhesion of calcium carbonate on the seed crystal, and the mineral seed crystal is preferably one or more of calcite, limestone and/or aragonite; the mineral seed crystal filling height is 1/5-1/4, preferably 22-23% of the height of the circulating crystallization fluidized bed; preferably in terms of CO3 2-：Ca2+The molar ratio is 1.0-1.2: 1 adding the carbonate solutionSaid Ca2+Is the calcium ion concentration in the clear solution; more preferably, the carbonate is sodium carbonate; preferably, the ascending flow velocity in the circulating crystallization fluidized bed is 60-100m/h (such as 70 m/h, 75m/h, 80m/h, 85m/h, 90 m/h and 95 m/h), if the flow velocity is too high, the crystal seeds overflow, and if the flow velocity is too low, the suspension state of the crystal seeds cannot be ensured. As the calcium carbonate generated by the reaction grows on the surface of the mineral seed crystal, the calcium carbonate crystal is discharged when the crystal particle grows to 2-4mm (2.5 mm, 2.8mm, 3.0mm, 3.2mm, 3.5mm, 3.8 mm), and the mineral seed crystal with the same discharge amount is supplemented so that the height of the mineral seed crystal in the circulating crystallization fluidized bed reaches 1/5-1/4, preferably 22-23%, and the same amount of the mineral seed crystal is reached again. By adopting the calcium carbonate recovery method, the magnesium hydroxide precipitation is less and the magnesium hydroxide grows slowly on the seed crystal, so that the purity of the calcium carbonate can be well ensured to reach more than 95 percent.
In the above method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, as a preferred embodiment, in the magnesium hydroxide recovery step, the hydroxide is sodium hydroxide; preferably, the stirring speed is 100-200r/min (120 r/min, 140r/min, 160r/min, 180 r/min), and the reaction time is 1-2 h; preferably, washing and drying the magnesium hydroxide filter cake to obtain a magnesium hydroxide product; preferably, the filtrate is concentrated by a membrane to recover fresh water.
A system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, comprising in the direction of wastewater flow:
a heavy metal and suspended matter removing unit, a calcium carbonate recovery unit and a magnesium hydroxide recovery unit; the calcium carbonate recovery unit comprises a circulating crystallization fluidized bed, one end of the circulating crystallization fluidized bed is communicated with the heavy metal and suspended matter removal unit, and the other end of the circulating crystallization fluidized bed is communicated with the magnesium hydroxide recovery unit.
In the above system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, as a preferred embodiment, the heavy metal and suspended matter removal unit comprises a regulating tank, a first reaction water tank, a tubular membrane and a first intermediate water tank which are sequentially communicated in the flowing direction of the wastewater; preferably, a stirring device, a lime milk dosing device, an organic sulfur dosing device and a pH monitor are arranged in the first reaction water tank.
In the system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, as a preferred embodiment, a sodium carbonate distribution region is arranged in the circulating crystallization fluidized bed; preferably, the calcium carbonate recovery unit further comprises a second intermediate water tank disposed between the circulating crystallization fluidized bed and the magnesium hydroxide recovery unit.
In the above system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, as a preferred embodiment, the magnesium hydroxide recovery unit comprises a second reaction water tank, a filter and a third intermediate water tank which are communicated in sequence along the wastewater flowing direction; preferably, the second reaction water tank is connected with the second intermediate water tank; preferably, the second reaction water tank is provided with a stirring device, a hydroxide dosing device and a pH monitor.
In the above system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, as a preferred embodiment, the system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater further comprises a membrane concentration unit and a water production tank, the membrane concentration unit is connected with a water outlet of the third intermediate water tank, and water produced by the membrane concentration unit enters the water production tank.
The high-magnesium wastewater firstly enters an adjusting tank, the adjusting tank is connected with a first reaction water tank through a pipeline, lime milk and organic sulfur are added into the first reaction water tank through a dosing device, the PH value of the wastewater is adjusted, heavy metal ions form precipitates, a water outlet of the first reaction water tank is connected with a water inlet of a tubular membrane, the effluent of the tubular membrane enters a first intermediate water tank, the water of the first intermediate water tank enters a crystallization fluidized bed through an addition pump, the overflow of the crystallization fluidized bed enters a second intermediate water tank, an outlet of the second intermediate water tank is connected with an inlet of a second reaction water tank, an outlet of the second reaction water tank is connected with a filter, the filtrate of the filter enters a third intermediate water tank, the water of the third intermediate water tank enters a membrane concentration system, and the produced water of the membrane concentration system enters a product water tank.
Compared with the prior art, the invention has the following positive effects:
(1) the method converts calcium and magnesium ions in the desulfurization wastewater into calcium carbonate and magnesium hydroxide with the purity of more than or equal to 95 percent, so that the calcium carbonate and the magnesium hydroxide are separated, and the obtained calcium carbonate and magnesium hydroxide have high purity and high recovery rate. Fresh water is recovered through the membrane concentration system, calcium carbonate returns to a desulfurization system of a power plant, magnesium hydroxide is used as a raw material for producing a flame retardant, and the fresh water is recycled, so that the reclamation of water, calcium and magnesium in the desulfurization wastewater is realized, and the requirement of circular economy is met;
(2) by adopting the circulating crystallization fluidized bed technology, the generated calcium carbonate particles are large, easy to separate and high in purity.
Drawings
FIG. 1 is a system diagram of the present invention for recovering calcium carbonate and magnesium hydroxide from high magnesium waste water.
Detailed Description
In order to highlight the objects, technical solutions and advantages of the present invention, the present invention is further illustrated by the following examples, which are presented by way of illustration of the present invention and are not intended to limit the present invention. The technical solution of the present invention is not limited to the specific embodiments listed below, and includes any combination of the specific embodiments.
Referring to the attached figure 1, the invention provides a system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater, which comprises the following components in the flowing direction of the wastewater: the system comprises a regulating tank 1, a first reaction water tank 2, a tubular membrane 3, a first intermediate water tank 4, a circulating crystallization fluidized bed 5, a second intermediate water tank 6, a second reaction water tank 7, a filter 8, a third intermediate water tank 9, a membrane concentration system 10 and a water production tank.
Wherein the first reaction water tank 2 is provided with a stirring device, a lime cream dosing device, an organic sulfur dosing device and a pH monitor;
a sodium carbonate distribution region is arranged in the circulating crystallization fluidized bed 5;
the second reaction water tank 7 is provided with a stirring device, a sodium hydroxide dosing device and a pH monitor;
the high-magnesium wastewater firstly enters an adjusting tank 1, the adjusting tank 1 is connected with a first reaction water tank 2 through a pipeline, lime milk and organic sulfur are respectively added into a first reaction water tank 2 through a lime milk dosing device and an organic sulfur dosing device, the PH value of wastewater is adjusted, and heavy metal ions form precipitation, a water outlet of the first reaction water tank 2 is connected with a water inlet of a tubular membrane 3, water discharged from the tubular membrane 3 enters a first intermediate water tank, water in the first intermediate water tank 4 enters a circulating crystallization fluidized bed 5 through an addition pump, overflow of the circulating crystallization fluidized bed 5 enters a second intermediate water tank 6, an outlet of the second intermediate water tank 6 is connected with an inlet of a second reaction water tank 7, an outlet of the second reaction water tank 2 is connected with a filter 8, filtrate of the filter 8 enters a third intermediate water tank 9, water in the third intermediate water tank 9 enters a membrane concentration system 10, and produced water in the membrane concentration system 10 enters a production water tank.
The following is a detailed description of an embodiment of the method for recovering calcium carbonate and magnesium hydroxide from high magnesium wastewater according to the present invention.
Example 1
The chemical composition of the high-magnesium wastewater of a certain power plant is shown in Table 1, the concentration of calcium ions is 580mg/L, and the concentration of magnesium ions is 4650 mg/L.
Table 1 chemical composition of desulfurization waste water from a certain power plant.
A method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater comprises the following steps:
(1) adding lime milk solution with mass concentration of 5% (namely the content of calcium oxide is 5%) and organic sulfur into the high-magnesium wastewater, so that the pH value of the desulfurization wastewater is 8.2-8.8, the addition amount of organic sulfur TMT15 is 16mg/L, filtering and separating through a tubular membrane to remove heavy metals and suspended matters in the high-magnesium wastewater, and enabling the tubular membrane produced water to enter a middle water tank;
(2) and (3) recovering calcium carbonate: pumping the clear liquid obtained by the tubular membrane separation in the step (1) into a circulating crystallization fluidized bed, wherein mineral seed crystals are filled in the bed, the particle size of the seed crystals is 0.05-0.1mm, the mineral seed crystals are calcite, the filling height of the seed crystals is 1/4 of the height of the fluidized bed, and the clear liquid is obtained by CO3 2-：Ca2+(removal of heavy matters)Concentration of calcium ions in the supernatant after filtration of the metal and suspended matter) in a molar ratio of 1.0 to 1.1: 1, adding a sodium carbonate solution, allowing the ascending flow velocity in a fluidized bed to be 60-80m/h, allowing calcium carbonate generated along with the reaction to grow on the surface of a mineral seed crystal, allowing the crystal particle to grow to 2-4mm, discharging the calcium carbonate crystal, and simultaneously supplementing the seed crystal with the same amount;
(3) recovering magnesium hydroxide: overflowing the crystallization fluidized bed in the step (2) to enter a reaction water tank, adding a sodium hydroxide solution into the reaction water tank, adjusting the pH value of the reaction solution to 11-11.5, reacting for 1-2h, stirring at a speed of 100r/min, filtering and separating by using a filter after the reaction is finished to obtain a magnesium hydroxide filter cake, washing and drying to obtain a magnesium hydroxide product, concentrating the filtrate by using a membrane, performing nanofiltration to separate salt, performing reverse osmosis concentration on a monovalent salt solution mainly containing sodium chloride, recovering fresh water, and performing evaporative crystallization on the concentrated solution to obtain industrial sodium chloride; the divalent salt solution mainly containing sodium sulfate is subjected to reverse osmosis concentration, fresh water is recovered, and the concentrated solution is subjected to evaporation crystallization to obtain the industrial sodium sulfate.
The purity of the calcium carbonate recovered by the method is about 95.8 percent, and the calcium carbonate is returned to a desulfurization system of a power plant; the purity of the recovered magnesium hydroxide was about 96.1%. In the filtrate obtained after calcium carbonate and magnesium hydroxide are recovered, the concentration of calcium ions in the wastewater is about 28mg/L, the concentration of magnesium ions is about 26.5mg/L, the recovery rate of calcium in the wastewater is about 92.2 percent, and the recovery rate of magnesium is about 99.4 percent.
Comparative example 1
The high magnesium wastewater described below is the same as the power plant high magnesium wastewater in example 1.
A method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater comprises the following steps:
(1) adding lime milk solution with the mass concentration of 5% (namely the mass concentration of the calcium oxide in the lime milk solution is 5%) and organic sulfur into the high-magnesium wastewater, so that the pH value of the desulfurization wastewater is 8.2-8.8, the addition amount of the organic sulfur TMT15 is 16mg/L, filtering and separating through a tubular membrane to remove heavy metals and suspended matters in the high-magnesium wastewater, and enabling the tubular membrane produced water to enter a middle water pool;
(2) and (3) recovering calcium carbonate: according to CO3 2-：Ca2+Mole ofThe ratio is 1.0-1.05: 1, adding a sodium carbonate solution into the clear liquid obtained by the tubular membrane separation in the step (1), and precipitating and filtering to obtain calcium carbonate and filtrate;
(3) recovering magnesium hydroxide: the filtrate obtained in the step (2) enters a reaction water tank, a sodium hydroxide solution is added into the reaction water tank, the pH value of the reaction solution is adjusted to be 11-11.5, the reaction time is 1-2 hours, the stirring speed is 100r/min, a filter is adopted for filtering and separating after the reaction is finished, a magnesium hydroxide filter cake is obtained, a magnesium hydroxide product is obtained after washing and drying, the filtrate is subjected to membrane concentration and nanofiltration separation, a monovalent salt solution mainly containing sodium chloride is subjected to reverse osmosis concentration, fresh water is recovered, and industrial sodium chloride is obtained by evaporating and crystallizing the concentrated solution; the divalent salt solution mainly containing sodium sulfate is subjected to reverse osmosis concentration, fresh water is recovered, and the concentrated solution is subjected to evaporation crystallization to obtain the industrial sodium sulfate.
According to the comparative example method, the recovery rate of calcium in the wastewater is only about 64%, and the recovered calcium carbonate has very low purity and is not suitable for recycling and returning to a desulfurization system of a power plant because the common precipitation mode has poor precipitation effect and simultaneously can precipitate a small amount of magnesium hydroxide. The purity of the recovered magnesium hydroxide is low, and because the calcium precipitation effect in the step (2) is not ideal, the calcium ion concentration in the filtrate obtained in the step (2) is high, so that the magnesium hydroxide recovered in the step (3) is doped with a large amount of calcium.
Comparative example 2
In the comparative example, the pH value of the desulfurized wastewater of only the step (1) after adjustment is different from that of the example 1, and the other process steps are the same as those of the example 1. The pH value of the desulfurization wastewater is adjusted to 9.5-10 by lime milk.
In the comparative example, a small amount of magnesium hydroxide and heavy metals are precipitated in the step (1) due to the high pH value in the step (1), and importantly, the high pH value in the step (1) causes the higher pH value of the wastewater after the sodium carbonate is added in the step (2), the precipitation of the magnesium hydroxide is increased, the step (2) cannot separate the magnesium hydroxide from the calcium carbonate well, the purity of the obtained calcium carbonate is low, and the recovery rate of the magnesium hydroxide in the step (3) is low.
Claims (9)
1. A method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater is characterized by comprising the following steps:
heavy metal and suspended matter removing step: adding lime milk and organic sulfur into the high-magnesium wastewater to enable the pH value of the high-magnesium wastewater to be 8-9 and generate heavy metal sulfide precipitate, and filtering to remove the heavy metal sulfide precipitate and suspended matters generated in the high-magnesium wastewater to obtain clear liquid;
calcium carbonate recovery step: introducing the clear liquid into a circulating crystallization fluidized bed, and then adding a carbonate solution for reaction to obtain calcium carbonate crystals and reaction liquid overflowing from the circulating crystallization fluidized bed;
and (3) magnesium hydroxide recovery step: adding a soluble hydroxide solution into the reaction solution, adjusting the pH value to 11-11.5, reacting while stirring, and then filtering and separating to obtain a magnesium hydroxide filter cake and a filtrate.
2. The method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater according to claim 1, wherein in the heavy metal and suspended matter removing step, the lime milk has a mass concentration of 5% -10%, the organic sulfur is added in an amount of 10-20mg/L, preferably the organic sulfur is trimercapto-s-triazine trisodium salt, and the organic sulfur is preferably added in an amount of 10-20 mg/L; preferably, the filtration is performed by a tubular membrane.
3. The method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater according to claim 1, wherein in the calcium carbonate recovery step, the circulating crystallization fluidized bed is filled with mineral seeds; preferably, the particle size of the mineral seed crystal is 0.05-0.1mm, and preferably, the mineral seed crystal is one or more of calcite, limestone and/or aragonite; the mineral seed crystal filling height is 1/5-1/4%, preferably 22-23%, preferably according to CO3 2-：Ca2+The molar ratio is 1.0-1.2: 1 adding the carbonate solution, wherein Ca2+For calcium ion in the clear liquidMore preferably, the carbonate is sodium carbonate; preferably, the ascending flow velocity in the circulating crystallization fluidized bed is 60-100m/h, as the calcium carbonate generated by the reaction grows on the surface of the mineral seed crystal, the calcium carbonate crystal is discharged when the crystal particle grows to 2-4mm, and simultaneously, the equivalent amount of the mineral seed crystal is supplemented and discharged so that the height of the mineral seed crystal in the circulating crystallization fluidized bed reaches 1/5-1/4, preferably 22-23% of the height of the circulating crystallization fluidized bed again.
4. The method for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater according to claim 1, wherein in the magnesium hydroxide recovering step, the hydroxide is sodium hydroxide; preferably, the stirring speed is 100-200r/min, and the reaction time is 1-2 h; preferably, washing and drying the magnesium hydroxide filter cake to obtain a magnesium hydroxide product; preferably, the filtrate is concentrated by a membrane to recover fresh water.
5. A system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater is characterized by comprising the following components in the flowing direction of the wastewater:
a heavy metal and suspended matter removing unit, a calcium carbonate recovery unit and a magnesium hydroxide recovery unit; the calcium carbonate recovery unit comprises a circulating crystallization fluidized bed, one end of the circulating crystallization fluidized bed is communicated with the heavy metal and suspended matter removal unit, and the other end of the circulating crystallization fluidized bed is communicated with the magnesium hydroxide recovery unit.
6. The system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater according to claim 5, wherein the heavy metal and suspended matter removal unit comprises a regulating reservoir, a first reaction water reservoir, a tubular membrane and a first intermediate water reservoir which are communicated in sequence along the wastewater flowing direction; preferably, a stirring device, a lime milk dosing device, an organic sulfur dosing device and a pH monitor are arranged in the first reaction water tank.
7. The system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater according to claim 5, characterized in that a sodium carbonate distribution area is arranged in the circulating crystallization fluidized bed; preferably, the calcium carbonate recovery unit further comprises a second intermediate water tank disposed between the circulating crystallization fluidized bed and the magnesium hydroxide recovery unit.
8. The system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater according to claim 5, wherein the magnesium hydroxide recovery unit comprises a second reaction water tank, a filter and a third intermediate water tank which are communicated in sequence along the wastewater flowing direction; preferably, the second reaction water tank is connected with the second intermediate water tank; preferably, the second reaction water tank is provided with a stirring device, a dosing device and a pH monitor.
9. The system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater as claimed in claim 5, wherein the system for recovering calcium carbonate and magnesium hydroxide from high-magnesium wastewater further comprises a membrane concentration unit and a water production pond, the membrane concentration unit is connected with a water outlet of the third intermediate water pond, and the water produced by the membrane concentration unit enters the water production pond.
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