WO2014005226A1 - Neutralisation de résidu de bauxite avec capture des gaz améliorée par enzymes - Google Patents

Neutralisation de résidu de bauxite avec capture des gaz améliorée par enzymes Download PDF

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Publication number
WO2014005226A1
WO2014005226A1 PCT/CA2013/050513 CA2013050513W WO2014005226A1 WO 2014005226 A1 WO2014005226 A1 WO 2014005226A1 CA 2013050513 W CA2013050513 W CA 2013050513W WO 2014005226 A1 WO2014005226 A1 WO 2014005226A1
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ion
solution
rich
depleted
neutralisation
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PCT/CA2013/050513
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English (en)
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Jonathan Andrew CARLEY
Jingui HUANG
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Co2 Solutions Inc.
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Publication of WO2014005226A1 publication Critical patent/WO2014005226A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/14—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by absorption
    • B01D53/1456—Removing acid components
    • B01D53/1475—Removing carbon dioxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/46—Removing components of defined structure
    • B01D53/62—Carbon oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
    • B09B1/00—Dumping solid waste
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
    • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/60—Inorganic bases or salts
    • B01D2251/606—Carbonates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/80—Type of catalytic reaction
    • B01D2255/804—Enzymatic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/02—Other waste gases
    • B01D2258/025—Other waste gases from metallurgy plants
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/40—Capture or disposal of greenhouse gases of CO2
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/20—Waste processing or separation

Definitions

  • the present invention generally relates to bauxite residue neutralisation and more particularly to the neutralisation of bauxite residue integrated with enzymatically enhanced gas capture.
  • Bauxite residue is a by-product of processing bauxite which is aluminum ore that can be transformed into aluminum.
  • bauxite processing the aluminum ore is usually refined and heated in a pressure vessel along with sodium hydroxide to promote dissolution of aluminate.
  • Red mud which is a ferruginous material also called bauxite residue (BR)
  • BR bauxite residue
  • BR contains a mixture of minerals including iron and titanium oxides, silica, calcium carbonate, unrecovered alumina, as well as some caustic sodium hydroxide. BR thus is highly alkaline.
  • BR neutralisation by sea water treatment will largely depend on location. This type of treatment is preferred where the sea water can be easily and cheaply sourced, which is, however, not the case in many aluminium refineries.
  • BR treatment by C0 2 injection could be affected by a number of factors such as location of a suitable C0 2 source and costs for the requested C0 2 concentration level. Furthermore, in a gaseous injection form, loss of C0 2 into the atmosphere would also be a concern.
  • BR Management of BR poses a number of economic, environmental and technical challenges. BR has also been relatively undervalued and may be treated to extract and recover valuable compounds including metal and/or rare earth elements (US 4,464,347; US 5,030,424). BR may be integrated into various industries for more useful applications, such as building materials, absorbents for gas and water treatment (US 20050087107; US 7,077,963) and other products. SUMMARY OF INVENTION
  • processes for neutralising bauxite residues with an ion-rich solution including bicarbonate ions that are derived from enzymatic C0 2 absorption from the gases derived from aluminum processing operations use enzymatically accelerated capture of significant quantities of C0 2 from smelter, refinery or other aluminum production operations, to produce a solution in effective amounts to neutralise bauxite residues.
  • a process for neutralising bauxite residues with an ion-rich solution including bicarbonate ions that are derived from enzymatic absorption of C0 2 from a C0 2 -containing gas resulting of aluminum processing operations is provided.
  • a process for neutralising bauxite residues with gaseous C0 2 derived from the desorption of an ion-rich solution including bicarbonate ions derived from the desorption of an ion-rich solution including bicarbonate ions.
  • the ion-rich solution may be derived from absorption of C0 2 in presence of an enzyme.
  • the enzyme may be separated from the ion-rich solution before the desorption step.
  • the desorption of the ion-rich solution may be performed in presence of an enzyme.
  • the enzyme may be carbonic anhydrase or analogues thereof.
  • a process for neutralisation of a bauxite residue the process including:
  • the process may include recycling the ion- depleted solution as at least part of the aqueous absorption solution.
  • the process may include recycling a portion of the ion-rich solution for contacting the ion-depleted solution for further neutralisation.
  • step (a) may be performed in a packed reactor. Further optionally, the step (a) may be performed in a spray reactor, in a fluidized bed or in a bubble reactor. Optionally, the step (b) may be performed in a cell that is open to the atmosphere.
  • the carbonic anhydrase in step (a), may be provided free in the aqueous absorption solution; dissolved in the aqueous absorption solution; immobilized on the surface of supports that are mixed in the aqueous absorption solution and flow therewith; immobilized on the surface of supports that are fixed within an absorption reactor; entrapped or immobilized by or in porous supports that are mixed in the aqueous absorption solution; entrapped or immobilized by or in porous supports that are fixed within the absorption reactor; as cross-linked enzyme aggregates (CLEA); and/or as cross linked enzyme crystals (CLEC); or a combination thereof.
  • CLSA cross-linked enzyme aggregates
  • CLEC cross linked enzyme crystals
  • the process may include a separation step, prior to step (b), wherein at least a portion of the carbonic anhydrase is removed from the ion-rich solution.
  • the separation step may include removing the at least a portion of the carbonic anhydrase by filtration, by centrifugal methods or any equivalents thereof.
  • a remaining portion of the carbonic anhydrase is present in step (b).
  • the carbonic anhydrase may be completely removed from the ion-rich solution during the separation step.
  • the separation step may be performed in a separation unit comprising a settler and another separation device which is a membrane, a hydrocyclone separator, a centrifugal decanter or any combination thereof.
  • the at least a portion of the carbonic anhydrase which is removed from the ion-rich solution may be recycled back into the step (a).
  • the process may include monitoring neutralisation properties of the neutralised bauxite and adjusting operation of step (a) to achieve given neutralisation properties.
  • the step of adjusting operation of step (a) may include regulating a concentration of the ion-rich solution to achieve a given neutralisation reactivity in step (b).
  • the process may further include treating the ion-depleted solution prior to recycling a treated solution back into step (a).
  • the treating of the ion-depleted solution may include removing fine particulate material from the ion-depleted solution.
  • the treating of the ion-depleted solution may include filtering the ion-depleted solution.
  • the treating of the ion-depleted solution may include a pH adjustment of the ion-depleted solution.
  • the process may include adding fresh carbonic anhydrase to the aqueous absorption solution prior to step (a).
  • a process for neutralisation of bauxite residue including: (a) contacting a C0 2 -containing gas derived from a smelter, a refinery or a plant in an aluminum manufacturing operation, with an aqueous absorption solution, in the presence of carbonic anhydrase, to promote the hydration reaction of C0 2 into bicarbonate and hydrogen ions and produce a C0 2 -depleted gas and an ion-rich solution;
  • the process may include removing the carbonic anhydrase from the ion-rich solution prior to subjecting the ion-rich solution to the desorption.
  • the process may include removing the carbonic anhydrase from the ion-rich solution after subjecting the ion-rich solution to the desorption.
  • a system for neutralisation of bauxite residue including:
  • an absorption unit for contacting a C0 2 -containing gas derived from a smelter, a refinery or a plant in an aluminum manufacturing operation, with an aqueous absorption solution, in the presence of enzymes, to promote the hydration reaction of C0 2 into bicarbonate and hydrogen ions and produce a C0 2 -depleted gas and an ion-rich solution;
  • a neutralisation unit for contacting the ion-rich solution with the bauxite residue to produce a neutralised bauxite stream and an ion-depleted solution
  • a separation unit arranged in between the absorption unit and the neutralisation unit, for removing at least some of the enzymes and produce an enzyme-depleted stream and an enzyme-rich stream.
  • the enzyme-depleted stream may be supplied to the neutralisation unit and the enzyme rich stream may be recycled, in whole or in part, to the absorption unit.
  • the separation unit may include one or more separators in series or parallel.
  • the separators may include filters or other types of separators, depending on the removal characteristics for the enzymes and the form of the enzymes or particles.
  • an absorption unit for contacting a C0 2 -containing gas derived from a smelter, a refinery or a plant in an aluminum manufacturing operation, with an aqueous absorption solution, in the presence of enzymes, to promote the hydration reaction of C0 2 into bicarbonate and hydrogen ions and produce a C0 2 -depleted gas and an ion-rich solution;
  • a desorption unit for subjecting the ion-rich solution to desorption for promoting release of bicarbonate ions from the ion-rich solution and producing a C0 2 gas stream and an ion-depleted solution; and a neutralisation unit for injecting the C0 2 gas stream into the bauxite residue to produce a neutralised bauxite stream;
  • the system may include a separation unit arranged in between the absorption unit and the neutralisation unit, for removing at least some of the enzymes and produce an enzyme-depleted stream and an enzyme-rich stream.
  • the separation unit may be arranged in between the absorption unit and the desorption unit.
  • the enzymes may be carbonic anhydrase or analogues thereof.
  • the carbonic anhydrase may be provided free in the aqueous absorption solution; dissolved in the aqueous absorption solution; immobilized on the surface of supports that are mixed in the aqueous absorption solution and flow therewith; immobilized on the surface of supports that are fixed within an absorption reactor; entrapped or immobilized by or in porous supports that are mixed in the aqueous absorption solution; entrapped or immobilized by or in porous supports that are fixed within the absorption reactor; as cross-linked enzyme aggregates (CLEA); and/or as cross linked enzyme crystals (CLEC); or a combination thereof.
  • CLSA cross-linked enzyme aggregates
  • CLEC cross linked enzyme crystals
  • any one of the above mentioned optional aspects of each process of bauxite neutralisation may be combined with any other of the aspects thereof, unless two aspects clearly cannot be combined due to their mutually exclusivity.
  • the various operational steps and/or structural elements of the process including a separation step as described herein-above, herein-below and/or in the appended Figures may be adapted to any of the process including a desorption step as appearing herein-above, herein-below and/or in the appended Figures.
  • Fig. 1 is a process diagram according to an optional aspect of the present invention.
  • Fig. 2 is a process diagram according to another optional aspect of the present invention.
  • Fig. 3 is a process diagram according to another optional aspect of the present invention.
  • Fig. 4 is a process diagram according to another optional aspect of the present invention.
  • Bauxite residue is issued from the digestion of bauxite with caustic liquor so as to further produce alumina, according to the well-known Bayer process. After crushing and milling the bauxite to enhance extraction, the bauxite is mixed with a caustic liquor to form another liquor, also referred to as the Bayer liquor. The Bayer liquor is then filtered for separation into a solid slurry (bauxite residue, also referred to as red mud) and an alkaline solution.
  • bauxite residue also referred to as red mud
  • Bauxite residue consists of both solid and liquid phases, with solid concentration varying from 28% (for instance BR in Jamaica) to 65% (filtered mud cake) of the total weight of freshly produced BR.
  • Solids of BR include sodalite [Na 6 (AISi0 4 ) 6 ⁇ 2NaOH] and cancrinite [Na 6 (AISi0 4 ) 6 ⁇ 2CaC0 3 ], that are characteristic solids produced during the pre-desilication and digestion steps of the Bayer process.
  • the solid components of BR may also contain unextracted minerals from the treated bauxite such as hematite [Fe 2 0 3 ], boehnite [ ⁇ - ⁇ ] and gibbsite [AI(OH) 3 ] , and some calcium-bearing byproducts that are formed during the process.
  • hematite Fe 2 0 3
  • boehnite boehnite
  • gibbsite gibbsite
  • One of the main calcium compounds in BR is tricalcium aluminate [3Ca(OH) 2 -2AI(OH) 3 ].
  • the aqueous phase of BR is essentially a diluted solution of the Bayer liquor, includingcaustic soda (NaOH), sodium aluminate (NaAI(OH) 4 ), and sodium carbonate (Na 2 C0 3 ), along with smaller amounts of sodium salt impurities such as sulfate, chloride, and fluoride, as well as traces of heavy metals.
  • BR is a highly alkaline residue (with a pH value of 13 or higher) due to its content in alkaline anions in solution OH " , C0 3 2 7HC0 3 " , AI(OH) 4 7AI(OH) 3(aq) and H 2 Si0 4 2 7H 3 Si0 4 ⁇ .
  • the present invention relates to a process for neutralising BR.
  • neutralising BR refers to reducing the alkalinity of the BR and producing a neutralised residue.
  • the neutralised residue may have a pH between 8 and 10.5.
  • BR may be neutralised by addition of a solution which is rich in bicarbonate ions.
  • the bicarbonate ion-rich solution is issued from a C0 2 absorption process using aqueous absorption solution in presence of an enzyme.
  • BR neutralization with a sodium bicarbonate solution could be described by the following reactions.
  • the caustic soda (NaOH) and the sodium aluminate (NaAI(OH) 4 ) included in the liquid phase of the BR could quickly react with the sodium bicarbonate (NaHC0 3 ) to form a sodium carbonate (Na 2 C0 3 ) solution and dawsonite (NaAI(OH) 2 C0 3 ) according to following reactions 1 and 2.
  • the overall system includes a C0 2 capture system 10 and a bauxite neutralisation system 1 1.
  • the C0 2 capture system 10 enables to capture C0 2 from a C0 2 containing gas 12 while producing a bicarbonate solution which may be used for neutralising a bauxite residue (BR) in the bauxite neutralisation system 1 1.
  • BR bauxite residue
  • the C0 2 capture system and the bauxite neutralisation system may be operated in series so as to recycle various streams of the bauxite neutralisation system into the C0 2 capture system.
  • Each of the C0 2 capture system and bauxite neutralisation system may further respectively include a plurality of C0 2 capture systems operated in parallel and a plurality of bauxite neutralisation system operated in parallel.
  • the source of C0 2 -containing gas may be a smelter, a refinery or another type of plant in an aluminum manufacturing operation.
  • the C0 2 -containing gas 12 is supplied to an absorption unit 14, which is also fed with an aqueous absorption solution 16 for contacting the C0 2 -containing gas 12 and absorbing the C0 2 therein.
  • the C0 2 -containing gas 12 may be fed into the absorption unit through a gas inlet port near the bottom of the absorption unit 14.
  • the absorption unit 14 may be of various types, such as a packed reactor, a spray reactor, a fluidized bed, or a bubble column type reactor. There may be one or more reactors that may be provided in series or in parallel.
  • the aqueous absorption solution 16 may include sodium carbonate (Na 2 C0 3 ) or other carbonate salts such as potassium carbonate, ammonium carbonate or a combination thereof.
  • the production of the sodium bicarbonate is enhanced in the presence of an enzyme.
  • the enzyme may include carbonic anhydrase or analogs thereof. Carbonic anhydrase catalyses the hydration reaction of C0 2 into bicarbonate and hydrogen ions (equation 6) and thus a C0 2 - depleted gas 18 and an ion-rich solution 20, including sodium bicarbonate, are produced.
  • the ion-rich solution 20 may be collected near the bottom of the absorption unit 14, and the C0 2 -depleted gas stream 18 may be discharged to the atmosphere near the top of the absorption unit 14.
  • the aqueous absorption solution 16 may be supplied from an absorption solution make-up tank 22.
  • the enzyme is provided directly as part of a formulation or solution.
  • the carbonic anhydrase may be in a free or soluble state in the formulation or immobilized on or in particles or as aggregates, chemically modified or stabilized, within the formulation.
  • enzyme used in a free state may be in a pure form or may be in a mixture including impurities or additives such as other proteins, salts and other molecules coming from the enzyme production process.
  • Immobilized enzyme free flowing in the solutions could be entrapped inside or fixed to a porous coating material that is provided around a support that is porous or non-porous.
  • the enzymes may be immobilized directly onto the surface of a support (porous or non-porous) or may be present as cross linked enzyme aggregates (CLEAs) or cross linked enzyme crystals (CLECs).
  • CLA include precipitated enzyme molecules forming aggregates that are then cross-linked using chemical agents.
  • the CLEA may or may not have a 'support' or 'core' made of another material which may or may not be magnetic.
  • CLEC include enzyme crystals and cross linking agent and may also be associated with a 'support' or 'core' made of another material.
  • a support When a support is used, it may be made of polymer, ceramic, metal(s), silica, alumina, solgel, chitosan, nylon, cellulose, alginate, polyacrylamide, magnetic particles, titanium oxide, zirconium oxide and/or other materials known in the art to be suitable for immobilization or enzyme support.
  • the enzymes are immobilized or provided on particles, such as micro-particles, the particles are preferably sized and provided in a particle concentration such that they are pumpable with the solution throughout the process.
  • the micro-particles may be sized in a number of ways.
  • the micro-particles may be sized to facilitate separation of the micro-particles from the ion-rich mixture.
  • the micro-particles may be sized to have a diameter above about 1 ⁇ or above about 5 ⁇ .
  • the micro-particles may also be sized to have a catalytic surface area including the biocatalysts having an activity density so as to provide an activity level equivalent to a corresponding activity level of soluble biocatalysts above about 0.05 g biocatalyst /L, optionally between about 0.05 g biocatalyst /L and about 2 g biocatalyst /L.
  • the absorption solution and the C0 2 form a reactive liquid film having a thickness and the micro-particles may be sized so as to be within an order of magnitude of the thickness of the reactive liquid film.
  • the micro-particles may also be sized so as to be smaller than the thickness of the reactive liquid film.
  • the thickness of the reactive liquid film may be about 10 ⁇ .
  • the micro-particles are sized between about 0.2 ⁇ and about 100 ⁇ . It should also be noted that precipitates may be formed in the ion-rich solution and the micro-particles may be sized to be larger or heavier than the precipitates or to be easily separable therefrom. In some optional aspects of the process, the particles may be sized so as to be nano-particles. The micro-particles may also be provided in the absorption solution at a maximum particle concentration of about 40% w/w.
  • the maximum micro-particle concentration may be 35% w/w, 30% w/w, 25% w/w, 20% w/w, 15% w/w, 10% w/w, or 5% w/w.
  • the micro-particles may be composed of support material(s) that is at least partially composed of nylon, cellulose, silica, alumina, silica gel, chitosan, polystyrene, polymethylmetacrylate, alginate, polyacrylamide, magnetic material, titanium oxide, zirconium oxide or a combination thereof.
  • the support may preferably be composed of nylon or polystyrene.
  • the density of the support material may be between about 0.6 g/cm 3 and about 4 g/cm 3 .
  • Carbonic anhydrase is a very efficient catalyst that enhances the reversible reaction of C0 2 to HC0 3 " .
  • Carbonic anhydrase is not just a single enzyme form, but a broad group of metalloproteins that exists in three genetically unrelated families of isoforms, ⁇ , ⁇ and ⁇ .
  • Carbonic anhydrase (CA) is present in and may be derived from animals, plants, algae, bacteria, etc.
  • the human variant CA II, located in red blood cells, is the most studied and has a high catalytic turnover number.
  • the carbonic anhydrase includes any analogue, fraction and variant thereof and may be alpha, gamma or beta type from human, bacterial, fungal or other organism origins, having thermostable or other stability properties, as long as the carbonic anhydrase can be provided to function in the C0 2 capture or desorption processes to enzymatically catalyse the reaction:
  • carbonic anhydrase or analogues thereof as used herein includes naturally occurring, modified, recombinant and/or synthetic enzymes including chemically modified enzymes, enzyme aggregates, cross-linked enzymes, enzyme particles, enzyme-polymer complexes, polypeptide fragments, enzyme-like chemicals such as small molecules mimicking the active site of the carbonic anhydrase enzyme and any other functional analogue of the enzyme carbonic anhydrase.
  • the aqueous absorption solution may be a carbonate-based solution, such as potassium carbonate solution, sodium carbonate solution, ammonium carbonate solution, promoted potassium carbonate solutions, promoted sodium carbonate solutions or promoted ammonium carbonates; or mixtures thereof.
  • carbonate-based solutions may be promoted with one or more of the above-mentioned chemical compounds.
  • the ion-rich solution may contain from about 0.1 M to 10 M of bicarbonate ions.
  • the carbonate loading of the solution will depend on the operating conditions, reactor design and the chemical compounds that are added. For instance, when potassium or sodium bicarbonate compounds are used in the absorption solution, the ion-rich solution may contain from about 0.2 M to 1 .5 M of bicarbonate ions.
  • the ion-rich solution When the ion-rich solution is highly loaded with carbonate/bicarbonate ions, it may become much more viscous which can have a detrimental effect on mass transport within the solution.
  • the presence of carbonic anhydrase flowing with the solution further enhances the mass transport along with the enzymatic reaction, thus improving the overall C0 2 capture, for instance by supersaturating the solution with bubbles of gaseous C0 2 .
  • the C0 2 capture system 10 may include a separation unit arranged in between the absorption unit 14 and the bauxite neutralisation system 1 1 , for removing at least some and possibly all of the biocatalyst in the event the enzyme is flowing with the ion-rich solution 20, e.g. when the enzyme is free in solution or provided with respect to particles.
  • the ion-rich solution 20 may be a suspension of solid particles including heavier solid particles, such as the immobilized biocatalyst particles and/or aggregates.
  • the separation unit separates the ion-rich solution into a sodium bicarbonate rich liquid stream 32 and an enzyme rich stream 52.
  • the sodium bicarbonate rich liquid stream 32 may be supplied to the bauxite neutralisation system 1 1.
  • the bauxite neutralisation system 1 1 may include a neutralisation unit 36 receiving a portion 33 of the sodium bicarbonate rich liquid stream 32 for contact and reaction with supplied BR 38.
  • the neutralisation unit 36 aims at decreasing the pH of the alkaline BR by washing the BR with sodium bicarbonate to extract as much sodium hydroxide (NaOH) as possible while forming sodium carbonate (Na 2 C0 3 ) (equation 1).
  • a neutralised bauxite stream 37 and a sodium carbonate rich stream 40, also referred to as BR liquor 40 may thus be released from the neutralisation unit 36.
  • BR liquor 40 may be recycled to the C0 2 capture system 10.
  • the neutralised bauxite stream 37 may be sent to downstream storage sites or used as a construction material.
  • the neutralised bauxite may be discharged safely and have a minimized impact on environment comparing to untreated bauxite residue.
  • the bauxite neutralisation system 1 1 may also include a separate neutralisation tank 42 which is supplied with a sodium carbonate rich stream 40, also referred to as BR liquor, that may be pumped from the neutralisation unit 36.
  • the sodium carbonate rich stream 40 is further neutralised with an aqueous solution of sodium bicarbonate which may be a recycled portion 44 of the sodium bicarbonate rich liquid stream 32 from the C0 2 capture system 10.
  • a neutralised solution 46 is thereby formed and may be recycled from the neutralisation tank 42 to the absorption solution make-up tank 22.
  • the temperature in the bauxite neutralisation tank 42 may increase due to exothermal reaction of sodium hydroxide (remained in the BR liquor 40) and sodium bicarbonate (contained in the sodium bicarbonate rich liquid stream 32 and the bicarbonate solution 44).
  • a cold water cooling system may be combined to the bauxite neutralisation system.
  • a cold water cooling system may be adapted to the neutralisation tank 42.
  • the neutralised solution 46 is guided to the absorption solution make-up tank 22.
  • the separation unit may include one or more separators in series or parallel. The separators may be filters or other types of separators, depending on the removal characteristics for the enzymes and the form of the enzymes or particles.
  • the separation unit may include a settler 24 which is supplied with the ion-rich solution 20 so as to precipitate heavier solid particles and separate them from the solution 20. Upon settling, the heavier particles may be collected near the bottom of the settler 24 as an enzyme rich stream 26 that may be recycled, in whole or in part, to the absorption unit 16, through the absorption solution make-up tank 22 for example. An enzyme- depleted stream 28 may be collected near the top of the settler 24.
  • the separation unit may further include a membrane filtration system 30 which separates the enzyme-depleted stream 28 into a permeate 32 and a retentate 34.
  • the membrane filtration system 30 may optionally be an ultrafiltration system.
  • the membrane filtration system 30 may optionally be a microfiltration system that is capable of removing fine particles from the system.
  • the permeate 32 is rich in sodium bicarbonate (NaHC0 3 )
  • at least a portion 33 thereof may be supplied to the bauxite neutralisation system 1 1.
  • the neutralisation unit 36 may receive the portion 33 of the permeate 32 for contact and reaction with BR 38.
  • a main portion 50 of the enzyme rich stream 26 and the retentate 34 from the membrane filtration system 30 are combined and recycled back as stream 52 to the absorption solution make-up tank 22. Additionally, some aggregates from the settler 24 can be partially removed out of the system, as a minor part of the enzyme rich stream 26.
  • the absorption solution make-up tank 22 receives the neutralised solution 46 and recycled enzymes in stream 52.
  • fresh biocatalyst such as carbonic anhydrase or analogues thereof, may be added to stream 52.
  • the absorption solution make-up tank 22 aims at adjusting the concentration of the aqueous absorption solution 16 in enzymes and absorption compounds. The aqueous absorption solution 16 is then supplied to the absorption unit 14
  • the separation unit may include one or more membrane filtration system, also referred to as filtration modules. It is known that an average of about 40 kg of C0 2 per ton of BR by dry mass may be used for BR neutralisation into carbonates. Accordingly, the total C0 2 needed at any single alumina refinery site may be generally generated by C0 2 emissions of a 20 MW equivalent power plant. For example, according to an embodiment of the present invention, for a 20 MW equivalent power plant, an ion-rich solution flow rate of approximately 800 m 3 /h may be needed.
  • the separation unit includes membrane filtration systems that may have an average membrane flux of 400 LMH (liter per meter square per hour) for an ultrafiltration (UF) and 600 LMH for a microfiltration (MF), the total membrane filtration area needed would respectively be 2000 m 2 , and 1333 m 2 for the UF and MF.
  • the separation unit would have to respectively include 10 to 20 filtration modules for an UF filtration and 7 to13 filtration modules for a MF system with a membrane module size of 100-200 m 2 /per filtration module, so as to filtrate an ion-rich solution with a flow rate of 800 m 3 /h.
  • the membrane filtration system may include membranes made of polypropylene (PP), polyamide (PA), polysulfone (PS), polyethersulfone (PES), polyvinylidene difluoride (PVDF), polyetherimide (PEI), polyimide (PI), polyvinylpyrrolidone or combination thereof. It should be understood that any membrane used for water and wastewater treatment could be used in the separation unit.
  • the separation unit may include a settler and a hydrocyclone separator.
  • the separation unit may benefit from the advantages of the solid/liquid (S/L) separation in hydrocyclone separators.
  • Hydrocyclone separators have a system configuration which is relatively simple and generally requires little maintenance. Additionally, the separation of the ion-rich solution may take place very quickly, with a residence time inferior to two seconds.
  • the hydrocyclone separator may be suited when the C0 2 absorption is enhanced by enzymes immobilized on particles which size is superior to 10 ⁇ .
  • mini-hydrocyclones having a diameter ranging from 10 to 13 mm may be used.
  • the ion-rich solution 20 is separated into three streams, the enzyme rich stream 26, the enzyme-depleted stream 28 and intermediate enzyme-containing stream 53. At least a portion 50 of the enzyme rich stream 26 may be recycled to the absorption solution make-up tank 22. The remaining portion of the enzyme rich stream 26 may be removed from the system as discharge or sent to be regenerated, depending on the state of the biocatalysts being used.
  • the enzyme-containing stream 53 is collected from an intermediate portion of the settler 24, and includes biocatalysts particles which have not yet settled.
  • the enzyme-containing stream 53 is sent to a hydrocyclone separator 54 to be further separated into an enzyme-depleted liquid stream 55 collected at the top of the hydrocyclone separator 54, and an enzyme - concentrated stream 56 collected near the bottom of the hydrocyclone separator 54.
  • the enzyme-depleted streams 28 and 55 include a high concentration of bicarbonate ions (HC0 3 ⁇ ), a portion 33 of which may be supplied to the neutralisation unit and another portion 44 of which may be supplied to the neutralisation tank 42.
  • the number and configuration of hydrocyclone separator included in the separation unit may vary according to the flow rate of ion-rich solution to be treated.
  • the feed capacity of a mini-hydrocyclone of 12,7 mm diameter may be about 0.7 GPM (2.65 L/min); each mini-hydrocyclone may occupy a surface area with an equivalent diameter of 20 mm; and for a given separation unit, the occupation density of the mini-hydrocyclones may be 80%.
  • N the maximum small hydrocyclones (N) that may be installed is calculated according to the following equation:
  • the separation unit may include a settler and a centrifugal device.
  • the use of the centrifugal device may be suited for biocatalysts having particle sizes of 10 ⁇ or larger.
  • the biocatalysts may be separated from the ion-rich solution and recovered for reuse in the aqueous absorption solution by a centrifugal device including a decanter.
  • the decanter may be used to further separate the enzyme rich stream collected from the settler into an enzyme-concentrated stream and a liquid stream.
  • the ion-rich solution 20 collected near the bottom of the absorption unit 14 is pumped into the settler 24, where the heavier biocatalyst particles are precipitated and settled.
  • the enzyme rich stream 26 is collected near the bottom of the settler 24 and pumped for supply to a centrifugal decanter 60.
  • the decanter 60 separates the enzyme rich stream 26 into an enzyme- concentrated stream 62 and an enzyme-depleted liquid stream 64.
  • the enzyme- concentrated stream 62 includes solid particles of enzyme. At least a portion 63 of the enzyme-concentrated stream 62 may be re-dispersed into the absorption solution make-up tank 22, the remaining portion being discharged for regeneration or replacement when needed.
  • An aqueous solution of fresh enzymes and bicarbonate ions may optionally be introduced into absorption solution make-up tank 22.
  • the enzyme-depleted stream 28 (from the settler 24) and the enzyme lean liquid stream 64 (from the decanter 60) are combined so as to be recycled back for reuse.
  • a liquid portion 33 of the combined streams 28 and 64 may be supplied to the neutralisation unit 36, and another liquid portion 44 may be supplied to the neutralisation tank 42.
  • the remaining liquid portion maybe sent for use in other neutralisation systems or for other application purposes.
  • This liquid portion may also be periodically sent to any BR storage pond or tank for neutralising the extracted BR during the storage process.
  • the decanter may be of GN Solids, LWF series (Tangshan Guanneng Machinery Equipment Co., Ltd. Hebei, China) that can separate particles with a particle separation point of 2-7 ⁇ .
  • the separation unit may include one or more decanters according to the flow rate of the ion-rich solution to be treated.
  • the ion-rich solution entering the settler may have a flow rate of 800 m 3 /h and includes 10% (by volume) of biocatalyst particles.
  • the enzyme rich stream collected from the settler may therefore be 80 m 3 /h. With a total particles concentration in the enzyme rich stream of 50% by volume, two decanters with a capacity of 60-80 m 3 /h and a particle separation point of 2-7 ⁇ would be suited to recover and recycle the biocatalyst particles contained in the ion-rich solution.
  • the biocatalyst may be provided in a number of ways.
  • carbonic anhydrase may be provided to the aqueous absorption solution which flows through the absorption unit.
  • the carbonic anhydrase may be introduced into the overall C0 2 capture system via an absorption solution make-up stream, which may be mixed with the recycled enzyme rich solution.
  • the carbonic anhydrase may also be added to the absorption units via multiple enzyme feed streams.
  • the carbonic anhydrase may be introduced at a given point in the process and spent enzyme may be replaced at a given point in the process.
  • the process may include periodic or continuous removal of denatured enzyme or reduced-activity enzyme, which may be done as part of an absorption solution reclaiming or make-up technique.
  • the particle size of the enzymes contained in the ion-rich solution may be between 0.05 ⁇ and 200 ⁇ , preferably between 0.2 ⁇ and 20 ⁇ .
  • the enzyme concentration of the ion-rich solution may be between 0.02 g/L and 2.0 g/L, preferably between 0.2 g/L and 1.0 g/L, on free enzyme basis or equivalent free enzyme basis for the immobilized particles.
  • the particle concentration of the enzyme rich stream may be between 0.2 (v/v)% and 20 (v/v)%, preferably between 1 (v/v)% and 10 (v/v)%.
  • the particle concentration of the enzyme-depleted liquid stream may be inferior to at most 0.01 (v/v)%.
  • the neutralisation unit may be a large open pond or cell.
  • the neutralisation unit may be a constructed vessel. It should be noted that there may be several different neutralised bauxite streams withdrawn from different locations of the neutralisation unit.
  • At least a portion of sodium bicarbonate rich stream may be added to an underflow stream of a last wash thickener of the Bayer process to neutralise BR online.
  • At least a portion of sodium bicarbonate rich stream may be periodically sent to BR storage ponds or tanks to neutralise the extracted BR during the storage process. Indeed, due to strongly alkaline buffered system of the BR, the pH of the storage ponds or tanks may increase after sometime.
  • another portion of the sodium bicarbonate rich stream may be used for some other applications such as cleaning agent, bio-pesticides, pH level adjustment for garden ponds, or neutralisation of the acidic gases (e.g. HCI, HF, and S0 2 from the aluminum smelter) or other flue gas streams that need to be treated.
  • the overall process combining C0 2 capture and BR neutralisation may be operated in a continuous mode.
  • the system may also include various other treatment units for preparing the ion- rich solution for the neutralisation unit and/or for preparing the ion deplete unit for recycling into the absorption unit.
  • treatment units for preparing the ion- rich solution for the neutralisation unit and/or for preparing the ion deplete unit for recycling into the absorption unit.
  • There may be pH adjustment units or various monitoring units.
  • the system may also include a measurement device for monitoring neutralisation properties of the neutralised bauxite and adjusting operation of the absorption unit to achieve desired neutralisation properties.
  • the step of adjusting may include regulating the concentration of the ion-rich solution to achieve the desired neutralisation reactivity, e.g. by increasing or decreasing the amount of bicarbonate in the ion-rich solution. This could be done by various methods including adjusting the liquid and/or gas flow rates, for example.
  • the present invention relates to a process for neutralising a bauxite residue by injecting a C0 2 gas stream into the bauxite residue.
  • the C0 2 gas stream may be produced from desorption of an ion-rich solution including bicarbonate ions.
  • the desorption may be performed in presence of an enzyme, such as carbonic anhydrase or analogues thereof.
  • the ion-rich solution may be derived from an enzymatic C0 2 capture system.
  • the overall system includes a C0 2 capture system 10 and a bauxite neutralisation system 1 1.
  • the C0 2 capture system 10 includes an absorption unit 14 enabling to capture C0 2 from a C0 2 -containing gas 12 while producing an ion-rich solution 20.
  • the C0 2 capture system 10 also includes a desorption unit 66 enabling to produce gaseous C0 2 68 and a C0 2 -depleted solution 70, from the ion-rich solution 20.
  • the enzymes contained in the ion-rich solution 20 exiting the absorption unit 14 may or may not be removed from the ion-rich solution 20. Enzymes may be removed from the ion-rich solution 20 before sending the ion-rich solution 20 to the desorption unit 66. Any of the above-mentioned separation system may be used to remove enzymes from the ion-rich solution 20: membrane filters, hydrocyclones, decanters, or any combination thererof, depending on the enzyme characteristics and configuration (e.g. free enzymes or immobilized enzymes on a particle support) according to above-described embodiments, may be applied.
  • the desorption may be performed in presence of enzymes, such as carbonic anhydrase or analogues thereof.
  • the gaseous C0 2 68 exiting near the top of the desorption unit 66 is then sent to the neutralisation unit 36 for neutralising the bauxite residue (BR) 38.
  • the gaseous C0 2 is injected into the neutralisation unit 36 through an injection system 72 that bubbles through the BR 38.
  • the neutralized BR liquor 40 issued from the neutralization unit 36 is rich of carbonate ions, it may be recycled to the absorption solution make-up tank 22 to produce the absorption solution 16.
  • the C0 2 -depleted solution 70 may also optionally be recycled to the absorption solution make-up tank 22 so as to be mixed with the neutralized BR liquor 40 and a freshly introduced aqueous solution of enzymes and bicarbonate ions (stream 23).
  • the C0 2 -depleted solution 70 may optionally be used to pre-heat the ion-rich solution 20 through a heat-exchanger 74 before entering the desorption unit 66.
  • Known BR treatment by C0 2 injection may be affected by a number of factors such as location of a suitable C0 2 source and costs for the requested C0 2 concentration level.
  • the present invention provides a suitable source of highly concentrated gaseous C0 2 derived from enzymatic C0 2 absorption-desorption system or enzymatic ion-rich solution desorption system.

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Abstract

L'invention concerne des procédés et un système pour neutraliser un résidu de bauxite, consistant à mettre en contact un gaz contenant du CO2 provenant d'une fonderie, d'une raffinerie ou d'une usine lors d'une opération de fabrication d'aluminium, avec une solution d'absorption aqueux, en présence d'anhydrase carbonique, pour favoriser la réaction d'hydratation du CO2 dans les ions bicarbonates et hydrogènes et à produire un gaz appauvri en CO2 et une solution riche en ions; puis à mettre en contact la solution riche en ions avec le résidu de bauxite pour produire un flux de bauxite neutralisée et une solution appauvrie en ions. La solution riche en ions peut également être soumise à une désorption pour favoriser la libération des ions bicarbonates de la solution riche en ions et produire un flux de gaz CO2 et une solution appauvrie en ions. Le flux de gaz CO2 peut ensuite être injecté dans le résidu de bauxite pour produire un flux de bauxite neutralisée.
PCT/CA2013/050513 2012-07-03 2013-07-03 Neutralisation de résidu de bauxite avec capture des gaz améliorée par enzymes WO2014005226A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10589214B2 (en) 2016-02-02 2020-03-17 University Of Kentucky Research Foundation CO2 mass transfer enhancement of aqueous amine solvents by particle additives

Citations (4)

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Publication number Priority date Publication date Assignee Title
US20100144521A1 (en) * 2008-05-29 2010-06-10 Brent Constantz Rocks and Aggregate, and Methods of Making and Using the Same
US20120049114A1 (en) * 2009-03-02 2012-03-01 William Randall Seeker Gas stream multi-pollutants control systems and methods
WO2012055035A1 (fr) * 2010-10-29 2012-05-03 Co2 Solution Inc. Capture de co2 améliorée par des enzymes et procédés de désorption
WO2012167388A1 (fr) * 2011-06-10 2012-12-13 Co2 Solutions Inc. Techniques de capture de co2 enzymatiques améliorées selon le pka de la solution, la température et/ou le caractère de l'enzyme

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Publication number Priority date Publication date Assignee Title
US20100144521A1 (en) * 2008-05-29 2010-06-10 Brent Constantz Rocks and Aggregate, and Methods of Making and Using the Same
US20120049114A1 (en) * 2009-03-02 2012-03-01 William Randall Seeker Gas stream multi-pollutants control systems and methods
WO2012055035A1 (fr) * 2010-10-29 2012-05-03 Co2 Solution Inc. Capture de co2 améliorée par des enzymes et procédés de désorption
WO2012167388A1 (fr) * 2011-06-10 2012-12-13 Co2 Solutions Inc. Techniques de capture de co2 enzymatiques améliorées selon le pka de la solution, la température et/ou le caractère de l'enzyme

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10589214B2 (en) 2016-02-02 2020-03-17 University Of Kentucky Research Foundation CO2 mass transfer enhancement of aqueous amine solvents by particle additives

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