WO2020233558A1 - Process for purifying a sodium sulfate residue - Google Patents

Process for purifying a sodium sulfate residue Download PDF

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Publication number
WO2020233558A1
WO2020233558A1 PCT/CN2020/090982 CN2020090982W WO2020233558A1 WO 2020233558 A1 WO2020233558 A1 WO 2020233558A1 CN 2020090982 W CN2020090982 W CN 2020090982W WO 2020233558 A1 WO2020233558 A1 WO 2020233558A1
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Prior art keywords
sodium
mother liquor
sodium sulfate
aqueous solution
salt
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PCT/CN2020/090982
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English (en)
French (fr)
Inventor
Michael Wood
Yan Wang
Sabrina BEDEL
Claude Criado
Aiping Wang
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Solvay Sa
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Application filed by Solvay Sa filed Critical Solvay Sa
Priority to CN202311265402.XA priority Critical patent/CN117326574A/zh
Priority to KR1020217041435A priority patent/KR20220034732A/ko
Priority to CN202080037986.3A priority patent/CN113874322B/zh
Priority to EP20809363.3A priority patent/EP3972936A4/en
Publication of WO2020233558A1 publication Critical patent/WO2020233558A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
    • C01D5/16—Purification
    • 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
    • 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
    • C01P2006/82—Compositional purity water content

Definitions

  • the present invention relates to a sodium sulfate recovery plant from sodium sulfate residue comprising sodium sulfate, sodium carbonate or sodium bicarbonate, and insoluble matter.
  • Many processes produce flue gases containing sulfur oxides and other organics. Most of said flue gases are generated by the combustion of carbonaceous products such as: coal, coke, oil, or organic material such as wood or agriculture wastes, paper wastes, municipal and industrial wastes. Most of those flue gases contain also heavy metals, in particular the ones that are volatile at high temperatures of combustions (such as above 800°C or above 1100°C) .
  • sodium alkaline compounds is one of those uses that is developing fast, as very efficient.
  • dry-sorbent injection (DSI) using trona or sodium bicarbonate is an interesting way to mitigate acidic gases as it produces less vapor clouds and dryer gases when released to atmosphere, compared to wet mitigation processes, and less residues byproducts compared to calcium alkaline compounds.
  • trona or sodium bicarbonate are injected directly in the flue gas at temperatures of more than 100°C generally, and preferably at temperatures of more than 140°C, alone or with co-sorbents such as active carbon or lignite-coke. With hot fumes, trona or sodium bicarbonate are transformed into high specific porous sodium carbonate particles that react rapidly with acidic gas. The generated salts such as sodium sulfate (SO2 and SO3 mitigation) or sodium chloride (HCl mitigation) , are then recovered on electrostatic filters or preferably on bag filters, constituting sodium sulfate residues.
  • SO2 and SO3 mitigation sodium sulfate
  • HCl mitigation sodium chloride
  • US5135734 discloses a sodium sulfate residue treatment process wherein sodium sulfate is reacted with calcium chloride to generate calcium sulfate that is stored underground in salt cavity, and co-generating sodium chloride that can be valorize in ammonia soda ash plant to produce sodium carbonate. Though the amounts of volume of calcium sulfate exceeds the volume of sodium sulfate residues, and so does not solve the problem linked to the disposals and leaks.
  • US6180074 discloses a process using a sodium sorbent made of sodium bicarbonate and sodium ammonium compounds.
  • the sodium sulfate residues from flue gas mitigation is dissolved, optionally treated with reactants to precipitate heavy metals on the main streams, but is silent on other compounds that built up in the circuits and how to decrease the purge volumes.
  • some of the ammonium compounds form complex with specific heavy metals such as copper and give blue coloration on the produced sodium sulfate that is then hardly accepted by other industrial users.
  • the inventors of present invention have discovered that sodium sulfate residues, in particular those for flue gas SOx mitigation, may effectively be processed and purified, while minimizing the purge to obtain salable sodium sulfate, and minimizing the amount of final wastes to be disposed of, that represents a noticeable progress compared to existing technologies.
  • the present invention relates to a sodium sulfate recovery plant and to a sodium sulfate recovery process from sodium sulfate residue, said sulfate residue comprising sodium sulfate, sodium carbonate and/or sodium bicarbonate, insoluble matter, and optionally: organics, sodium sulfite, and/or sodium nitrite, said recovery plant comprising:
  • a separation equipment such as: a filter, a decanter, or a centrifuge, for separating insoluble matter by filtration, decantation, or centrifugation from the first aqueous suspension for obtaining:
  • an alkalinizing reactor (C3) having a feeding inlet for an alkali solid or an alkaline solution such as sodium carbonate solid or solution, or sodium hydroxide solid or solution, for alkalinizing to a pH of about 7 or more the aqueous solution exiting the acidifying reactor (C1) or the optional oxidizing reactor (C2) ;
  • an evaporator-crystallizer for removing at least part of the water from the alkalinized aqueous solution exiting the alkalinizing reactor (C3) and to obtain a mother liquor and to crystallize sodium sulfate particles within said mother liquor;
  • a recycling mean such as a gravity pipe outlet or a pump, for recycling at least part of the non-purged mother liquor in at least one of the devices (A) to (D) ;
  • the purge mean (F) provides a purge weight ratio of the purged separated mother liquor to the non-purged separated mother liquor of at least 0.005 t/t and at most 0.20 t/t.
  • a first advantage of the present invention is that the purge is reduced by a factor 4 to 10 compared to previous technology processing such residues.
  • a second advantage of the present invention is that the solids to be disposed of, for instance in underground mines, is also reduced by a factor 4 to 10 compared to previous known technology.
  • a third advantage of the present invention is that it enables to reduce equipment size by treating mother liquors where impurities are concentrated rather than treating the main stream after dissolution of sodium sulfate residues.
  • a forth advantage of present invention is that it enables the production of high purity sodium sulfate with a low content in organics and heavy metals, in particular when the sodium sulfate residues are from DSI of steel industry, coke industry and sinter plants, and particularly suitable for the detergent industries and textile industries, while minimizing purge volumes.
  • Figure 1 shows a representative scheme of the sodium sulfate recovery plant according one embodiment of present invention.
  • vol. % refers to "percent by weight” and the sign “vol. %” refers to “percent by volume” .
  • vol. % refers in present application to dry gas concentrations (therefore without water vapor content) .
  • a range of values for a variable defined by a bottom limit, or a top limit, or by a bottom limit and a top limit, also comprises the embodiments in which the variable is chosen, respectively, within the value range: excluding the bottom limit, or excluding the top limit, or excluding the bottom limit and the top limit.
  • soluble′′ and ′′insoluble′′ used herein means soluble or insoluble in aqueous solution, unless indicated otherwise.
  • soluble denotes salts having solubility in water of equal to more than 0.05 g/liter at 20°C.
  • insoluble denotes salts having solubility in water of less than 0.05 g/liter at 20°C.
  • the different embodiments of the present invention related to a sodium sulfate recovery plant (items 1 to 13) and related to a process for purifying a sodium sulfate residue (items 101 and subsequent items) , are defined hereafter. All Items 1 to 13 and 101 to 123 of present invention are combinable together.
  • a sodium sulfate recovery plant from sodium sulfate residue comprising sodium sulfate, sodium carbonate and/or sodium bicarbonate, insoluble matter, and optionally: organics, sodium sulfite, and/or sodium nitrite, said recovery plant comprising:
  • a separation equipment such as: a filter, a decanter, or a centrifuge, for separating insoluble matter by filtration, decantation, or centrifugation from the first aqueous suspension for obtaining:
  • an alkalinizing reactor (C3) having a feeding inlet for an alkali solid or an alkaline solution such as sodium carbonate solid or solution, or sodium hydroxide solid or solution, for alkalinizing to a pH of about 7 or more the aqueous solution exiting the acidifying reactor (C1) or the optional oxidizing reactor (C2) ;
  • an evaporator-crystallizer for removing at least part of the water from the alkalinized aqueous solution exiting the alkalinizing reactor (C3) and to obtain a mother liquor and to crystallize sodium sulfate particles within said mother liquor;
  • a recycling mean such as a gravity pipe outlet or a pump and pipes, for recycling at least part of the non-purged mother liquor in at least one of the devices (A) to (D) ;
  • the purge mean (F) provides a purge weight ratio of the purged separated mother liquor to the non-purged separated mother liquor of at least 0.005 t/t and at most 0.20 t/t.
  • Item 2 The sodium sulfate recovery plant of item 1, characterized in that the purge mean (F) provides a purge weight ratio of the purged separated mother liquor to the non-purged separated mother liquor of at most 0.10 t/t.
  • the purge mean (F) provides a purge weight ratio of the purged separated mother liquor to the non-purged separated mother liquor of at most 0.10 t/t.
  • Item 3 The sodium sulfate recovery plant of item 2 characterized in that the purge outlet mean (F1) provides a purge weight ratio of the purged separated mother liquor to the non-purged separated mother liquor of at most 0.05 t/t.
  • the purge outlet mean (F1) provides a purge weight ratio of the purged separated mother liquor to the non-purged separated mother liquor of at most 0.05 t/t.
  • Item 4 The sodium sulfate recovery plant of any one of preceding items, suitable for treating sodium sulfate residue comprising a residual salt from flue gas SO x mitigation, said flue gas being selected from: a coke plant, a sinter plant, a steel plant, a cement plant, a glass plant, an oil refinery, a petro-chemical plant, a power plant, a lime kiln, a waste incinerator, preferably selected from: a coke plant, a sinter plant, a steel plant, more preferably from: a coke plant.
  • flue gas being selected from: a coke plant, a sinter plant, a steel plant, a cement plant, a glass plant, an oil refinery, a petro-chemical plant, a power plant, a lime kiln, a waste incinerator, preferably selected from: a coke plant, a sinter plant, a steel plant, more preferably from: a coke
  • the sodium sulfate recovery plant of any one of preceding items suitable for treating sodium sulfate residue obtained from flue gas mitigation using a dry sodium sorbent injection, such as: sodium bicarbonate dry sorbent injection or trona dry sorbent injection.
  • TOC total organic carbon
  • Item 7 The sodium sulfate recovery plant of item 6, comprising an adsorption device (H1) for adsorbing at least part of organics from the non- purged separated mother liquor before being recycled in at least one of the devices (A) to (G) , and wherein said adsorption device (H1) comprises active carbon.
  • H1 adsorption device for adsorbing at least part of organics from the non- purged separated mother liquor before being recycled in at least one of the devices (A) to (G) , and wherein said adsorption device (H1) comprises active carbon.
  • Item 8 The sodium sulfate recovery plant of any one of the preceding items, further comprising:
  • an hydroxide salt such as: hydrated lime (Ca (OH) 2 ) , or caustic soda (NaOH) ;
  • silicate such as sodium silicate or sodium metasilicate
  • a calcium salt such as one chosen among: lime (CaO) , portlandite (Ca (OH) 2 ) , calcium sulfate (CaSO 4 ) anhydrous or hydrated (in particular: calcium sulfate hemihydrate or calcium sulfate dihydrate ie.: gypsum) , calcium chloride (CaCl 2 ) , calcium nitrate (Ca (NO 3 ) 2 ) ;
  • a sulfide salt such as sodium sulfide (Na 2 S) or an organic sulfide compound such as TMT15;
  • ferrous salt such as ferrous sulfate (FeSO 4 )
  • ferric salt such as ferric sulfate (Fe 2 (SO 4 ) 3 )
  • a phosphate salt such an alkaline metal phosphate salt or an alkaline earth metal phosphate salt; advantageously in combination with a calcium salt as listed above;
  • a lead salt such as lead carbonate (PbCO 3 ) ;
  • heavy metals or chemical elements such as aluminum (Al) , arsenic (As) , boron (B) , barium (Ba) , cadmium (Cd) , chromium (Cr) , iron (Fe) , manganese (Mn) , mercury (Hg) , nickel (Ni) , lead (Pb) , antimony (Sb) , selenium (Se) , titanium (Ti) , vanadium (V) , or zinc (Zn) , from the non-purged separated mother liquor.
  • heavy metals or chemical elements such as aluminum (Al) , arsenic (As) , boron (B) , barium (Ba) , cadmium (Cd) , chromium (Cr) , iron (Fe) , manganese (Mn) , mercury (Hg) , nickel (Ni) , lead (Pb) , antimony (Sb)
  • Item 9 The sodium sulfate recovery plant of item 8, wherein the separation equipment (B) is suitable for separating heavy metal precipitates or chemical element precipitates generated by the addition mean (I) of the at least one reactant when said reactant is added to the dissolver (A) and/or added to the non-purged separated mother liquor before being recycled in at least one of the devices (A) to (H2) .
  • Item 10 The sodium sulfate recovery plant of any one of the preceding items, wherein the evaporator-crystallizer (D) is of a forced circulation evaporator-crystallizer type, or is of a draft-tube baffled evaporator-crystallizer type, and preferably equipped with a mechanical vapor recompression device, preferably also operating under vacuum, and generally operating at temperatures from 50°C to 120°C.
  • the evaporator-crystallizer (D) is of a forced circulation evaporator-crystallizer type, or is of a draft-tube baffled evaporator-crystallizer type, and preferably equipped with a mechanical vapor recompression device, preferably also operating under vacuum, and generally operating at temperatures from 50°C to 120°C.
  • Item 12 The sodium sulfate recovery plant of item 11, wherein the weight ratio or the volume ratio of the purged separated mother liquor to the non-purged separated mother liquor is controlled so that the weight ratio of sodium chloride to sodium sulfate in the purged separated mother liquor is at least 1.5 and at most 6, preferably at least 2.5 and at most 4.
  • Item 13 The sodium sulfate recovery plant of any items 1 to 11, wherein the purged separated mother liquor volume or flow is controlled so that the concentration of at least one of the following salt: sodium chloride, sodium nitrate, sodium borate, sodium phosphate, is maintained in a defined range of salt concentration in the mother liquor or in the sodium sulfate particles.
  • Item 14 The sodium sulfate recovery plant of item 13, wherein the defined range of salt concentration is defined with a lower concentration limit and an upper concentration limit of said salt (s) .
  • Item 15 The sodium sulfate recovery plant of items 13 or 14, wherein the lower concentration limit of said salt (s) multiply by the flow of the purged separated mother liquor is at least 60%, preferably at least 80%, of the flow of said salt entering the sodium sulfate recovery plant by the sodium sulfate residue.
  • a dryer such as a spray dryer, for drying the purged separated mother liquor into a salt powder.
  • Item 17 The sodium sulfate recovery plant of any one of the preceding items, wherein the evaporator-crystallizer (D) comprises a condenser (L) for condensing at least part of the water removed from the alkalinized aqueous solution as vapor into a condensate, and the condenser (L) comprises a pipe (M) for hydraulic connection to dissolver (A) , for recycling at least part or totally the condensate to the dissolver (A) for dissolving the sodium sulfate residue.
  • the evaporator-crystallizer (D) comprises a condenser (L) for condensing at least part of the water removed from the alkalinized aqueous solution as vapor into a condensate
  • the condenser (L) comprises a pipe (M) for hydraulic connection to dissolver (A) , for recycling at least part or totally the condensate to the dissolver (A) for dissolving the sodium sulf
  • a process for purifying a sodium sulfate residue comprising: sodium sulfate, sodium carbonate and/or sodium bicarbonate, and sodium chloride, and optionally insoluble matter, said process comprising :
  • step (c3) alkalinizing the acidified second aqueous solution obtained at step (c1) to a pH of about 7 or more, using an alkali or an alkaline solution such as sodium hydroxide or part of the second aqueous solution obtained at step (b) ;
  • step (f) purging at least part of the mother liquor and recycling at least part of the non-purged mother liquor in at least one of the steps (a) to (d) , characterized in that the weight ratio of the purged separated mother liquor to the non-purged separated mother liquor is at most 0.20, preferably at most 0.10, more preferably at most 0.05 t/t, or at most 0.005 t/t.
  • Item 102 The process of Item 101 wherein the sodium sulfate residue comprises:
  • Item 103 The process of Item 101 or Item 102 wherein the sodium sulfate residue comprises:
  • ppm part per million
  • step (a) is operated per batch operation or in a continuous or semi continuous operation, and when operated in continuous operation is preferably operated in at least two dissolver devices in series.
  • Item 108 The process of any one of the preceding Items wherein steps (c1) and (c2) are both operated in a same device.
  • Item 109 The process of any one of the preceding Items wherein the weight ratio of the purged separated mother liquor to the non-purged separated mother liquor is at least 0.001, preferably at least 0.002 t/t.
  • Item 110 The process of any one of the preceding Items, wherein the sodium sulfate residue comprises a residual salt from flue gas SO x mitigation, said flue gas being selected from: a coke plant, a sinter plant, a steel plant, a cement plant, a glass plant, an oil refinery, a petro-chemical plant, a power plant, a lime kiln, a waste incinerator.
  • flue gas being selected from: a coke plant, a sinter plant, a steel plant, a cement plant, a glass plant, an oil refinery, a petro-chemical plant, a power plant, a lime kiln, a waste incinerator.
  • Item111 The process of the preceding Item, wherein the sodium sulfate residue comprises a residual salt from flue gas SO x mitigation, said flue gas being from: a coke, or a steel plant or a sintering plant, preferably from a coke plant.
  • Item112 The process of any one of the preceding Items, wherein the sodium sulfate residue is a salt residue obtained from a flue gas mitigation using a dry sodium sorbent injection, such as sodium bicarbonate dry sorbent injection or trona dry sorbent injection.
  • a dry sodium sorbent injection such as sodium bicarbonate dry sorbent injection or trona dry sorbent injection.
  • Item 113 The process of the preceding Item, wherein the the flue gas mitigation uses sodium bicarbonate dry sorbent injection wherein the sodium bicarbonate dry sorbent has a particle size distribution so that at least 90%in weight of the particles have a particle size of less than 30 ⁇ m, preferably less than 20 ⁇ m, more preferably less than 15 ⁇ m.
  • Item114 The process of any one of the preceding Items, wherein the sodium sulfate residue is a salt residue obtained from a flue gas mitigation using a dry sodium sorbent injection, using a sodium sorbent injection operating at temperatures between 150°C and 400°C, preferably between 160 and 270°C, more preferably between 170 and 220°C.
  • Item 115 The process of any one of the preceding Items, wherein the sodium sulfate residue comprises from 0.05 to 10wt. %sodium sulfite, and wherein step (c2) is performed so that to oxidize at least part of sodium sulfite into sodium sulfate.
  • Item 116 The process of any one of the preceding Items, wherein the sodium sulfate residue comprises from 0.01 to 10wt. %sodium nitrite, and wherein step (c2) is performed so that to oxidize at least part of sodium nitrite into sodium nitrate.
  • Item 117 The process of any one of the preceding Items, wherein after acidifying step (c1) or during aerating step with oxygen or air (c2) or after step (c2) , an oxidant selected among: hydrogen peroxide, ozone and sodium hypochlorite, or mixture thereof, is (are) added to the acidified second aqueous solution, and then after alkalization step (c3) of pH about 7 or more, the alkalized aqueous solution is filtered to discolor (decrease the aqueous solution coloration measured with ASTM D1209 standard) or to improve the transparency of the aqueous solution.
  • an oxidant selected among: hydrogen peroxide, ozone and sodium hypochlorite, or mixture thereof, is (are) added to the acidified second aqueous solution, and then after alkalization step (c3) of pH about 7 or more, the alkalized aqueous solution is filtered to discolor (decrease the aqueous solution coloration measured with ASTM D1209 standard) or to improve
  • Item 118 The process of the preceding Item, wherein the acidified second aqueous solution after step (c1) has an APHA color measured with ASTM D1209 standard of at least 100, and wherein after filtration the aqueous solution comprising sodium sulfate has an APHA value of less than 60, preferably less than 20.
  • Item 119 The process of any one of the preceding Items, wherein the non-purged separated mother liquor, before being recycled to any one of steps (a) to (d) is treated with at least one of the following treatments:
  • an oxidant selected among: hydrogen peroxide, ozone, sodium hypochlorite, or mixture thereof, is (are) added to mother liquor at acidic pH of less than 6, preferably at pH about 3 to 4 and then the obtained mother liquor is alkalized to pH about 7 or more with an alkaline solution, such as of sodium hydroxide or of calcium hydroxide, to obtain an alkalized mother liquor, and the alkalized mother liquor is filtered to discolor (decrease the aqueous solution coloration measured with ASTM D1209 standard) and/or to improve the transparency of the aqueous solution, and/or decrease total organic carbon (TOC) content, and/or decrease the chemical oxygen demand (COD) .
  • an oxidant selected among: hydrogen peroxide, ozone, sodium hypochlorite, or mixture thereof
  • Item 120 The process of any one of the preceding Items, wherein the the first aqueous suspension on step (a) , or the second aqueous solution from any steps (b) to (c3) , or the mother liquor from any step (d) to (f) , or the non-purged separated mother liquor before or when being recycled to any one of steps (a) to (d) , is treated with at least one of the following chemical agent in solid form or in solution:
  • an hydroxide salt such as: hydrated lime (Ca (OH) 2 ) , or caustic soda (NaOH) ;
  • silicate such as sodium silicate or sodium metasilicate
  • a calcium salt such as lime (CaO) , calcium hydroxide (Ca (OH) 2 ) , calcium sulfate (CaSO 4 ) anhydrous or hydrated (such as: calcium sulfate hemihydrate or calcium sulfate dihydrate ie.: gypsum) , calcium chloride (CaCl 2 ) , calcium nitrate (Ca (NO 3 ) 2 ) ;
  • a sulfide salt such as sodium sulfide (Na 2 S) or an organic sulfide compound such as: trimercapto-s-triazine, trisodium salt (such as TMT15 from ) ;
  • ferrous salt such as ferrous sulfate (FeSO 4 )
  • ferric salt such as: ferric sulfate (Fe 2 (SO 4 ) 3 ) or iron chloride (FeCl 3 )
  • FeSO 4 ferrous sulfate
  • FeCl 3 iron chloride
  • a phosphate salt such an alkaline metal phosphate salt or an alkaline earth metal phosphate salt, preferably in presence of calcium salt listed above;
  • a calcium phosphate solid chosen among: hydroxyapatite, apatite, tricalciumphosphate, whitlockite, phosphate octacalcium, brushite, monetite, preferably: apatite;
  • a lead salt such as lead carbonate (PbCO 3 ) ;
  • heavy metals or chemical residue elements such as: aluminum (Al) , arsenic (As) , boron (B) , barium (Ba) , cadmium (Cd) , chromium (Cr) , cobalt (Co) , iron (Fe) , manganese (Mn) , mercury (Hg) , molybdenum (Mo) , nickel (Ni) , lead (Pb) , antimony (Sb) , selenium (Se) , titanium (Ti) , vanadium (V) , or zinc (Zn) , or mixtures thereof, from the non-purged separated mother liquor.
  • Item 121 The process of the preceding Item, wherein the treatment with at least one of the chemical agent selected from: the silicate salt, the calcium salt, the sulfide salt, the ferrous salt, the phosphate salt, the calcium phosphate solid, and mixtures thereof is operated at a pH of 7 to 13, or more preferably at a pH 8 to 10.5.
  • the chemical agent selected from: the silicate salt, the calcium salt, the sulfide salt, the ferrous salt, the phosphate salt, the calcium phosphate solid, and mixtures thereof is operated at a pH of 7 to 13, or more preferably at a pH 8 to 10.5.
  • Item 122 The process of Item 120, wherein the treatment of the first aqueous suspension on step (a) , or of the second aqueous from steps (b) or (c3) , or of the mother liquor from any step (d) to (f) , or of the non-purged separated mother liquor is done with an hydroxide salt and is operated at a pH of at least 12, and is followed by a separation step of insoluble matter so that to discolor (decrease the aqueous solution coloration measured with ASTM D1209 standard) corresponding solution after said separation step.
  • Item 123 The process of the preceding Item, wherein the treatment of the first aqueous suspension on step (a) , or of the mother liquor from any step (d) to (f) , or of the non-purged separated mother liquor with the hydroxide salt operated at a pH of at least 12 is done at step (a) so that to discolor the second aqueous solution from step (b) .
  • Item 124 The process of Items 123 or 124, wherein the pH is at most 13.
  • Item 125 The process of any Items 120 to 124, wherein the treatment with the hydroxide salt, the silicate salt, the calcium salt, the sulfide salt, the ferrous salt, the phosphate salt, the calcium phosphate solid, and mixtures thereof is operated before or when recycling the non-purged mother liquor at step (a) or (b) .
  • Item126 The process of any Items 120 to 125, wherein the treatment with at least one of the chemical agent selected from: the hydroxide salt, the silicate salt, the calcium salt, the sulfide salt, the ferrous salt, the phosphate salt, and mixture thereof is performed before or when recycling at step (a) or (b) , and preferably at a pH of 7 to 13, or more preferably at a pH 8 to 10 (pH 8 to 10 being particularly preferred when the solutions comprise more than 2 ppm Pb) .
  • the chemical agent selected from: the hydroxide salt, the silicate salt, the calcium salt, the sulfide salt, the ferrous salt, the phosphate salt, and mixture thereof is performed before or when recycling at step (a) or (b) , and preferably at a pH of 7 to 13, or more preferably at a pH 8 to 10 (pH 8 to 10 being particularly preferred when the solutions comprise more than 2 ppm Pb) .
  • Item 127 The process of any Items 120 to 125, wherein the treatment with at least one of the chemical agent selected from: the ferric salt, or the lead salt is the hydroxide salt, the silicate salt, the calcium salt, the sulfide salt, the ferrous salt, the phosphate salt, and mixture thereof is performed before or when recycling at step (c) or (d) , and preferably at a pH of 3 to 7, more preferably at a pH of 4 to 6.
  • Item 128 The process of any one of the preceding Items, wherein the purged mother liquor has a sodium sulfate concentration of at most 15 wt%, preferably at most 10 wt%, more preferably at most 8 wt%.
  • Item 129 The process of any one of the preceding Items, wherein the purged mother liquor has a sodium chloride concentration of at least 5 wt%, preferably at least 10 wt%, or at least 15 wt%.
  • Item 130 The process of any one of the preceding Items, wherein the purged mother liquor has a sodium chloride concentration of at most 28 wt%, preferably at most 25 wt%, or at most 20 wt%.
  • Item 131 The process of any one of the preceding Items, wherein the purged mother liquor is then sprayed-dried.
  • Item 133 The process of any one of the preceding Items, wherein the sodium sulfate particles obtained at step (d) is anhydrous sodium sulfate.
  • Item 134 The process of any one of Items 101 to 131, wherein the sodium sulfate particles obtained at step (d) is sodium sulfate decahydrate crystals.
  • Item 135. The process of any one of the preceding Items, wherein the sodium sulfate particles are further used in a soda ash plant as a sodium raw material.
  • Item 136 The process of the preceding Item, wherein the sodium sulfate particles are further dissolved and reacted with residual distillation liquid comprising calcium chloride from an ammonia soda ash process, to produce sodium chloride and calcium sulfate, and said sodium chloride is further recycled to produce sodium carbonate or sodium bicarbonate.
  • Item 137 Use of the sodium sulfate particles obtained from steps (e) or (f) of any one of the preceding Items, in detergent powder or detergent tablet.
  • Item 138 Use of the sodium sulfate particles obtained from steps (e) or (f) of any one Items 101 to 136, in glass furnace.
  • Item 139 Use of the sodium sulfate particles obtained from steps (e) or (f) of any one Items 101 to 136, in dyeing and/or textile processes.
  • FIG. 1 illustrates an embodiment of the sodium sulfate recovery plant of present invention.
  • the ratio of the recycling mother liquor 13 to the evaporator-crystallizer (D) to the non-purged separated mother liquor (13 + 14) is 0.2 to 1.0 t/t in weight. Preferably this ratio is 0.6 to 0.98 t/t in weight.
  • the recycled mother liquor 13 to the evaporator-crystallizer (D) to the recycled mother liquor 14 to the dissolver (A) is 1.5 to 49 t/t in weight, more preferably 4 to 10 t/t in weight;
  • This enables to make part of secondary impurities treatment (aside sodium chloride impurity that is generally controlled by the purge flow 12 for removing NaCl and for removing other soluble salts such as: NaF, NaBr, NaI, NaNO 2 , NaNO 3 ) when removed in dissolver (A) with additives to make them precipitate as insoluble salts with one of the reactant listed in Item 120, and to remove them on a filtration step b) of above described process.
  • samples used here after have been selected from 3 different steel and coke plants using dry sorbent injection flue gas mitigation, using technical grade sodium bicarbonate.
  • the sulfate residues belongs to inorganic residue and most of the content in the residue is Na 2 SO 4 . There is still 10 to 15%of Na 2 CO 3 in the residue due to insufficient reaction. However, to change the Na 2 CO 3 to Na 2 SO 4 acid attack with H 2 SO 4 , is operated and thus obtaining a Na 2 SO 4 content higher than 95%.
  • Dissolution ⁇ filtration ⁇ acidification ⁇ crystallization ⁇ drying The sodium sulfate residue is dissolved in water first and form a yellow liquid with black insoluble particles (ie first aqueous suspension) .
  • the solution concentration was 25 wt%in salts, close to saturation at room temperature and included Na 2 CO 3 , Na 2 SO 4 , NaCl and insoluble particles.
  • the filtration step was performed on lab filter to remove insoluble particles, so the resultant solution (ie. ‘second aqueous solution’ ) included Na 2 CO 3 , Na 2 SO 4 , and NaCl.
  • H 2 SO 4 was added into the solution at a pH value under 3.7 in order to change all the Na 2 CO 3 to Na 2 SO 4 , and then NaOH was added to adjust pH value back to 7-8 so that after acidification and neutralization process the solution has its sodium carbonate transformed in sodium sulfate, and thus includes mainly Na 2 SO 4 , NaCl.
  • the second aqueous solution was injected into flask for the crystallization process.
  • the crystallization process was kept at 50 °C and under the pressure of 100 mbar.
  • the evaporation rate was 100 g water/h. During the evaporation, the Na 2 SO 4 crystallized when saturation is reached.
  • COD Chemical Oxygen Demand
  • Na 2 SO 3 was low in the solution due to its oxidation at acidic pH into Na 2 SO 4 .
  • the COD content in solution before crystallization was 150-300 ppm of equivalent carbon.
  • the COD from organics does not evaporate in the crystallization step, therefore it accumulates when recycling the mother liquors of the crystallization to dissolve again sodium sulfate residues.
  • the purge is oxidized with H 2 O 2 or hypochlorite at pH , to remove part of the organics (measured as COD or as TOC) . And part of this treated mother liquor is recycled back to the dissolution of sodium sulfate residues according the present invention.
  • the obtained purified sodium sulfate is non-colored, as when the purge from crystallizer is not treated the obtained sodium sulfate particles become more and more brownish.
  • the treatment of the purge enables to decrease sensitively the purge volume, and increases the yield for recovering the sodium sulfate from the residues, and decrease the purge brine to be disposed of.
  • the final crystallized sodium sulfate meets Chinese national standard (Class II first grade) .
  • the residues are Na 2 SO 4 -enriched solid wastes.
  • the incomplete reaction between the flue gases to be treated and the injected sodium bicarbonate explains the remaining amount of Na 2 CO 3 (resulting from the thermal activation of NaHCO 3 ) and NaHCO 3 .
  • these salts can be easily transformed into Na 2 SO 4 by means of a treatment of pH adjustment.
  • the mixture of residues (1200 g) were dissolved in water (5000 g) at 25°C, forming a yellow liquid with black insoluble materials (i.e. the first aqueous suspension) .
  • the liquid comprised 20 wt%of soluble salts (close to the saturation at room temperature of sodium sulfate and other soluble salts from the sodium sulfate residues (i.e.
  • pH of the suspension was 10.5.
  • the rise of the pH to 12.5 had the advantage to decrease sensitively the color of the second aqueous solution obtained after filtration.
  • Sulfuric acid (167 g) was then added to the second aqueous solution to reach a pH value of 3.8.
  • the acidified solution was bubbled with compressed air during 30 minutes to ease the stripping of the carbon dioxide gas (therefore reacting on sodium carbonate to produce sodium sulfate, water and CO 2 gas) , using an air flow of about 8 liters of air per minute and per liter of the aqueous solution to bubbled.
  • the acidified second aqueous solution had the following composition: 21.4 wt%Na 2 SO 4 , 0 wt%Na 2 CO 3 &NaHCO 3 , 0.8 wt%NaCl and 0.03 wt%NaNO 3 and a COD value of 0.03 wt%.
  • the formed Na 2 SO 4 crystals were separated from the mother liquor by a filtration step performed thanks to a stainless filter (paper membrane) coupled with a vacuum pump.
  • the mother liquor after separation of the sodium sulfate crystals had the following composition: 25.1 wt%Na 2 SO 4 and 2.1 wt%NaCl, and 0.06 wt%NaNO 3 and 0.05 wt%COD.
  • the first mother liquor obtained after filtration was mixed back with a part of part of remaining pretreated solution (a sufficient quantity of the pretreated solution was prepared for five crystallization cycles) to simulate the recycling of mother liquors and the resulting solution was adjusted before each crystallization cycle by keeping the quantity of the solution and the concentration of Na 2 SO 4 constant (addition of water) .
  • a washing step of the wet cake with a Na 2 SO 4 saturated solution was carried out to simulate a better removal of mother liquors (i.e. be close to the efficiency of a centrifuge) .
  • a second filtration step was achieved by means of a stainless filter (paper membrane) coupled with a vacuum pump to recover the washed wet cake that was dried in an oven at 100°C to produce purified Na 2 SO 4 .
  • the sodium chloride content in the dried crystals raised gradually to the following values: 0.09 wt%, 0.15 wt%, 0.12 wt%, 0.16 wt%, 0.31 wt%.
  • the NaNO 3 content in the dried crystals raised gradually to the following values: 0.016 wt%to 0.025 wt%.
  • the COD content in the dried crystals raised gradually from 0.08 wt%to 0.017 wt%.
  • the crystals of Na 2 SO 4 resulting from each crystallization cycle meet the intended quality of the final product in terms of purity (including insoluble matter and metals) and whiteness according to *GB/T 6009-2014 Chinese specifications regarding anhydrous sodium sulfate (Whiteness to be >82%for standard II 1rst grade) .
  • Said active carbon were from Calgon Carbon Corporation: Filtrasorb F300D and IPGX. They were tested at 5 different concentrations reported to the weight of the aqueous solution at 0.01%, 0.05%, 0.10%, 1.0%, 2.0%.
  • step (b) of the process of present invention Starting from a second aqueous solution (after step (b) of the process of present invention) , similar as in the test 3.1, O 3 generated by an ozone generator, providing 30 mg O 3 per min and introduced in 50 mL of the same aqueous solution, it was observed that the strong yellow color (APHA value of 213) the value with O 3 injection raised to 451 APHA, with a precipitate. After filtration on a 0.2 ⁇ m membrane, the APHA value went down to a value of 12, and COD content decreases from 100 ppm to 50 ppm, but with a strong efficacy on the color reduction (factor 18) , even if the COD content was reduced by only a factor 2.
  • ozone is effective when used in combination with a filtration on said aqueous solution.
  • the APHA value was measured with platinum/cobalt scale according ASTM standard, expanded to compare the intensity of yellow-tinted samples, using an HACH DR3900 at a wavelength of 465nm.
  • the color decrease of the 100 ppm H 2 O 2 treated solution was as effective as the 500 ppm H 2 O 2 treated solution: the APHA color index went down from 139 in initial solution to less than 10 for both 100 ppm and 500 ppm H 2 O 2 treated solutions. Therefore even at low concentration (100 ppm) H 2 O 2 action at acidic pH, with then a filtration step is effective to discolor the sodium sulfate solution with impurities.
  • step (c3) acidifying with H 2 SO 4 down to pH 3.8 (step (c3) with air injection to strip CO 2 for 30 minutes) and then pH was adjusted to pH 12-13 with NaOH and then filtrated and
  • Both methods 1 and 2 were efficient to discolor the aqueous solution before evaporation and crystallization (respective APHA values of 52 and 33 from a starting point of initial aqueous solution at 139) , even though the COD content remains at same value or range (97-110 ppm) .

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PCT/CN2020/090982 2019-05-22 2020-05-19 Process for purifying a sodium sulfate residue WO2020233558A1 (en)

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CN114261978A (zh) * 2021-12-22 2022-04-01 四川省洪雅青衣江元明粉有限公司 一种硝水的高效净化方法
CN115350500A (zh) * 2022-08-23 2022-11-18 宁夏日盛高新产业股份有限公司 一种发泡剂生产中副产物综合利用系统

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CN115350500B (zh) * 2022-08-23 2023-10-13 宁夏日盛高新产业股份有限公司 一种发泡剂生产中副产物综合利用系统

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