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WO2009039592A1 - Procédé pour la précipitation de boehmite à partir d'une pré-précipitation de liqueur de bayer - Google Patents

Procédé pour la précipitation de boehmite à partir d'une pré-précipitation de liqueur de bayer Download PDF

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Publication number
WO2009039592A1
WO2009039592A1 PCT/AU2008/001447 AU2008001447W WO2009039592A1 WO 2009039592 A1 WO2009039592 A1 WO 2009039592A1 AU 2008001447 W AU2008001447 W AU 2008001447W WO 2009039592 A1 WO2009039592 A1 WO 2009039592A1
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Prior art keywords
precipitation
liquor
precipitation liquor
boehmite
precipitating
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PCT/AU2008/001447
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English (en)
Inventor
John Besida
Dean Ilievski
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Alcoa of Australia Ltd
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Alcoa of Australia Ltd
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Priority claimed from AU2007905354A external-priority patent/AU2007905354A0/en
Application filed by Alcoa of Australia Ltd filed Critical Alcoa of Australia Ltd
Publication of WO2009039592A1 publication Critical patent/WO2009039592A1/fr
Anticipated expiration legal-status Critical
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    • 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
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/04—Preparation of alkali metal aluminates; Aluminium oxide or hydroxide therefrom
    • C01F7/14—Aluminium oxide or hydroxide from alkali metal aluminates
    • C01F7/144—Aluminium oxide or hydroxide from alkali metal aluminates from aqueous aluminate solutions by precipitation due to cooling, e.g. as part of the Bayer process

Definitions

  • the present invention relates to a method for precipitating boehmite from a pre- precipitation Bayer liquor.
  • the Bayer process is widely used for the production of alumina from alumina- containing ores such as bauxite.
  • the process involves contacting alumina- containing ores with recycled caustic aluminate solutions at elevated temperatures in a process commonly referred to as digestion. Solids are removed from the resulting slurry and the solution cooled to induce a state of supersaturation and provide a 'pre-precipitation liquor', also known as green liquor or pregnant liquor.
  • Aluminium hydroxide is added to the pre-precipitation liquor as seed to induce precipitation of aluminium hydroxide therefrom.
  • the precipitated aluminium hydroxide is separated from the caustic aluminate solution (known as spent liquor), with a portion of aluminium hydroxide being recycled to be used as seed and the remainder recovered as product.
  • the remaining caustic aluminate solution is recycled for further digestion of alumina-containing ore.
  • the precipitation reaction can be generally represented by the following chemical equation:
  • AI(OH) 4 " (aq) + Na + (aq) ⁇ AI(OH) 3 (s) + OH " (aq) + Na + (aq)
  • A represents the alumina concentration, expressed as gl_ ⁇ 1 L of AI 2 O 3
  • TC represents total caustic concentration, (concentration of sodium hydroxide plus sodium aluminate; expressed as gl_ "1 sodium carbonate).
  • A/TC concentration of sodium hydroxide plus sodium aluminate
  • the TC and TA in Bayer liquors are determined by the conditions in a number of processing steps including digestion and causticisation.
  • the precipitation of gibbsite from Bayer liquors is induced and driven by first seeding the liquor with gibbsite and progressively cooling the suspension.
  • the TC and TA are both changed during precipitation due to the changes in the liquor arising from the removal of the alumina from solution to form the aluminium hydroxide solid precipitate.
  • Carbonation of Bayer liquors has also been used to induce precipitation of alumina. This step reduces the TC but does not affect the TA of the liquor. Further, carbonation results in loss of sodium hydroxide which must be recovered, and the steps associated therewith are costly and time consuming.
  • the alumina in most aluminium-containing ores is in the form of an alumina hydrate.
  • the alumina is generally present as a trihydrate, i.e., AI 2 O 3 -SH 2 O or AI(OH) 3 , or as a monohydrate, i.e., AI 2 O 3 -H 2 O or AIO(OH).
  • the trihydrate termed gibbsite, dissolves or digests more readily in the aqueous alkali solution than the monohydrate, termed boehmite.
  • boehmite dissolves or digests more readily in the aqueous alkali solution than the monohydrate
  • US4595581 teaches a process for precipitating substantially pure boehmite by heating a seeded sodium aluminate suspension to a temperature between about 115 0 C to 145 0 C and separating the boehmite precipitate from the suspension.
  • US4595581 reports boehmite precipitation experimental results from a range of liquors with compositions characteristic of Bayer refinery pre-precipitation liquors. The liquors were seeded with boehmite and the tests conducted at 125 °C. Both crystalline and non-crystalline boehmite was tested as seed. Yields after 6 hr precipitation were reported in the range from 11.3 to 32 gl_ "1 as AI 2 O 3 .
  • US4595581 recommends the preferred seed material to be amorphous boehmite gel rather than crystalline boehmite on the basis of higher yields achieved. Separating and recycling boehmite gel as part of the seeding circuit for a continuous commercial scale Bayer operation introduces significant operating difficulties and possibly a new classification technology when compared to using large crystalline aluminium hydroxide as seed. US4595581 reports yields of less than 20 gl_ "1 when crystalline boehmite seed is used. Whilst US4595581 teaches the precipitation of boehmite, the author fails to recognise that increased yields may be obtained by treating the liquor to drive the precipitation reaction.
  • boehmite is a thermodynamically more stable phase than gibbsite, with a lower solubility and, hence a higher theoretical yield potential, and its precipitation instead of gibbsite would provide energy saving, it is not considered to be a commercially viable alternative.
  • pre-precipitation liquor shall be understood to indicate any liquor in the Bayer circuit post digestion and prior to aluminium hydroxide precipitation.
  • solution or variations such as “solutions”, will be understood to encompass slurries, suspensions and other mixtures containing undissolved and/or dissolved solids.
  • a method for precipitating boehmite from a pre-precipitation Bayer liquor comprising the steps of:
  • the step of treating the pre-precipitation liquor to decrease both the total caustic concentration and the total alkalinity of the pre-precipitation liquor favours the precipitation of alumina and should result in increased alumina yields.
  • boehmite precipitation from Bayer liquors is inhibited not only by the concentration of free hydroxide but also by the presence of sodium ions.
  • removing sodium ions from the pre-precipitation liquor should have a positive effect on boehmite precipitation.
  • boehmite is precipitated from the treated pre- precipitation liquor at a temperature of at least 105 0 C and a pressure greater than atmospheric pressure.
  • boehmite is precipitated from the treated pre-precipitation liquor at a temperature of at least 120 0 C.
  • the boehmite is precipitated from the treated pre-precipitation liquor at a pressure greater than atmospheric pressure.
  • the method comprises the steps of:
  • Pre-precipitation liquors that have been clarified and filtered may be known in the art by various terms including green liquors and pregnant liquors.
  • the combination of the treated pre-precipitation liquor and untreated pre- precipitation liquor may contain the liquors in any ratio. It will be appreciated that the ratio will depend on many factors including Bayer circuit throughput, treated pre-precipitation liquor properties (e.g. A, TC, TA) and untreated pre-precipitation liquor properties (e.g. A, TC, TA).
  • the method of the present invention maybe performed as a batch process or a continuous process.
  • the present invention reduces hydroxide concentrations in Bayer liquors and reduces both the TC and TA of the Bayer process liquor. Further, the present invention increases the A/TC of the Bayer process liquor, thereby increasing the precipitation efficiency of boehmite.
  • the method may comprise a plurality of treatment steps to decrease both the total caustic concentration and the total alkalinity of the pre-precipitation liquor.
  • the method comprises the further step of:
  • gibbsite co-precipitation with boehmite is reduced or eliminated by the addition to the pre-precipitation Bayer liquor of the gibbsite precipitation inhibitor.
  • pre-precipitation liquor may contain calcia, which is known to affect the induction time of gibbsite precipitation. Without being limited by theory, it is believed that calcia does not affect the precipitation of boehmite to the same extent as gibbsite.
  • the method may comprise the further step of:
  • the gibbsite precipitation inhibitor is provided in the form of organic compounds such as gluconate and tartrate. Certain organic compounds are believed to inhibit gibbsite precipitation by reducing the number of active sites on the seed surface. As the crystal structure of boehmite is different to that of gibbsite, it is believed that boehmite precipitation will be less affected by organic compounds than gibbsite precipitation.
  • the method comprises the further step of:
  • the optimal seeding rate will depend on many factors, including the seed and liquor properties and the design of the precipitation circuit, and may be anywhere in the range of 50 to 1300 gl_ "1 .
  • boehmite seed is recycled from the Bayer precipitation circuit.
  • boehmite seed particle characteristics may affect the particle characteristics of the precipitated boehmite.
  • the particle characteristics of the precipitated boehmite will make them suitable for classification by commercially available bulk processing technologies such as cyclones, thickeners and classifiers.
  • the extractant is provided in the form of a weak acid.
  • the extractant is provided in the form of a weak acid
  • the extraction of a sodium ion into the substantially water-immiscible solution will be accompanied by the transfer of a proton from the substantially water-immiscible solution into the pre-precipitation liquor.
  • the weak acid extractant comprises at least one polar group with an ionisable proton with a pKa of between about 9 and about 13.
  • the extractant is preferably a straight chain, branched chain or cyclic hydrocarbon, a halogenated hydrocarbon, an aliphatic or aromatic ether or alcohol with more than 6 carbon atoms.
  • the extractant comprises an alcohol or phenol functional group.
  • Suitable extractants include 1 H,1 H-perfluorononanol,
  • (alpha,alpha-dimethylbenzyl)phenol (4-cumylphenol), 2,3,6-trimethylphenol, 2,4-di-terf-butylphenol, 3,5-di-ferf-butylphenol, 2,6-di-ferf-butylphenol, 2,4-di-terf- pentylphenol (2,4-di-fert-amylphenol), 4-sec-butyl-2,6-di-terf-butylphenol, 2,4,6-tri- - - -
  • terf-butylphenol 2,4-bis(alpha,alpha-dimethylbenzyl)phenol (2,4-dicumylphenol) and other alkylated phenols or mixtures thereof.
  • substantially water-immiscible solution may form the extractant.
  • the acidic form of the extractant is substantially insoluble in water.
  • the deprotonated form of the extractant is substantially insoluble in water.
  • the extractant concentration will depend on a number of factors including the intended amount induced supersaturation which will in turn be influenced by the temperature at which precipitation is initiated.
  • the degree of deprotonation in the extraction step will depend on the acidity of the ionisable proton, as well as the pH and salt content of the Bayer liquor.
  • phase transfer catalysts may enhance extractions rates.
  • Suitable phase transfer catalysts may be selected from lipophilic quaternary ammonium or phosphonium salts or organic macrocycles such as crown ethers, calixarenes, calixarene-crown ethers, spherands and cryptands.
  • the substantially water-immiscible solution is an organic liquid, a combination of organic liquids or an ionic liquid. _ (
  • the organic liquid is substantially non-polar.
  • the organic liquid is a high boiling organic liquid with a low vapour pressure at Bayer process temperatures.
  • the organic liquid has a flash point above process temperature.
  • the organic liquid is a alkaline stable.
  • the organic liquid is preferably a straight chain, branched chain or cyclic hydrocarbon, a halogenated hydrocarbon, an aliphatic or aromatic ether or alcohol with more than 4 carbon atoms.
  • Suitable solvents include benzene, toluene, xylene, stilbene, 1-octanol, 2-octanol, 1-decanol, /so-octyl alcohol (such as that commercially available as Exxal 8 from ExxonMobil), iso-nonylalcohol (such as that commercially available as Exxal 9 from ExxonMobil), /so-decanol, iso- tridecanol, 2-ethyl-1-hexanol, kerosene and other hydrocarbons commercially available under the names Escaid 100, Escaid 110, Escaid 240, Escaid 300, lsopar L, lsopar M, Solvesso 150, Exxsol D110
  • partitioning of the organic solvent and the extractant in the pre-precipitation liquor is minimal.
  • partitioning of the pre- precipitation liquor in the organic solvent is minimal.
  • the organic solvent solvates the extractant in both its acid and sodium salt forms.
  • volume of substantially water-immiscible solution relative to the volume of the pre-precipitation liquor may vary according to the manner in which both the Bayer liquor and the substantially water-immiscible solution are contacted and the loading of the extractant in the substantially water- immiscible solution.
  • the contact time between the pre-precipitation liquor and the organic phase should be sufficient for reaction to occur between the extractant and the sodium cations to form a sodium cation-depleted aqueous phase and a hydrogen ion-depleted organic phase.
  • Said contact time will be influenced by many factors including the pKa of the ionisable proton on the extractant, the pH of the aqueous phase, the volumes of the aqueous and organic phases, the temperature, the concentration of the extractant and sodium ions, the total alkalinity, the total caustic concentration, the extent of agitation and the presence of other species in the pre-precipitation liquor.
  • the volumes of the pre-precipitation liquor and the substantially water-immiscible solution need not be the same. It should be appreciated that where the method is performed as a countercurrent flow or continuous processing, volumes of the phases are less critical than with batch methods.
  • the method comprises the further step of:
  • the step of separating the pre-precipitation liquor and the substantially water-immiscible solution may be performed by any method known in the art including centrifugation.
  • the method comprises the further steps of:
  • the stripping solution may be provided in the form of water or a Bayer process stream including condensate or lake water.
  • the stripping solution has a pH of at least 5.
  • the method comprises the further steps of:
  • the substantially water-immiscible solution after contact with the stripping solution may be re-used in subsequent extraction steps.
  • the aqueous solution of sodium hydroxide may be re-used in other stages of the Bayer circuit. Depending on the concentration of sodium hydroxide, the aqueous solution may need to be pre-treated prior to subsequent use.
  • precipitation liquor is an anolyte and wherein an ion permeable membrane is provided between the first region and the second region;
  • the pre-precipitation liquor is not directed to the second region.
  • a relatively pure caustic stream may be produced from the second region.
  • a stream could be used within the Bayer circuit for, for example, washing bauxite (to extract impurities) or any other application where clean caustic is useful.
  • the Bayer process liquor, after a precipitation step may be used elsewhere in the Bayer circuit. For example, it would have a lower TC/TA content and a lower alumina content than normal spent liquor which should enable more efficient causticisation with lime.
  • the ion permeable membranes will preferably be substantially coplanar such that adjacent ion permeable membranes will preferably permit the transfer of oppositely charged ions.
  • an anion permeable membrane and a cation permeable membrane are provided.
  • a plurality of ion permeable membranes wherein the plurality of ion permeable membranes comprise a electrodialysis unit.
  • a bipolar membrane there may further be provided a bipolar membrane. - -
  • the transfer of the sodium ion from one region to another region will encompass the transfer of more than one sodium ion from the first region to the second region.
  • one region is provided with an anode and another region is provided with a cathode.
  • the transfer of the cation from one region to another region will either be accompanied by a concomitant neutralisation of hydroxide ions within the Bayer process liquor and generation of hydroxide ion in the second region or, in the case of an electrodialysis unit, the transfer of hydroxide from one region to another region, and in the opposite direction to the cation transfer to maintain solution charge balance.
  • the present invention offers distinct advantages over methods employing carbonation to reduce hydroxide concentrations in Bayer process solutions, as carbonation reduces TC without affecting TA, but the present invention reduces both the TC and TA of the Bayer process liquor. Further, the present invention increases the A/TC of the Bayer process liquor, thereby increasing the precipitation efficiency of alumina.
  • the ion permeable membrane should be substantially resistant to corrosion or degradation under the electrolytic conditions.
  • ion permeable membrane will be dependant on many factors including the selectivity of ion transport, including the selectivity of sodium ion transport. Further factors include the conductivity and rate of ion transport, the mechanical, dimensional and chemical stability, resistance to fouling and poisoning and membrane lifetime.
  • the cation permeable membranes may comprise perfluorinated polymers such as a sulfonated tetrafluorethylene copolymer, carboxylate polymer, polystyrene based polymer, divinylbenzene polymer, or sodium conducting ceramics such as beta-alumina or combinations thereof.
  • perfluorinated polymers such as a sulfonated tetrafluorethylene copolymer, carboxylate polymer, polystyrene based polymer, divinylbenzene polymer, or sodium conducting ceramics such as beta-alumina or combinations thereof.
  • the cation permeable membrane is a Nafion 115, Nafion 117, Nafion 324, Nafion 440, Nafion 350, Nafion 900 series, Fumatech FKB, Fumatech FKL membrane, Astom CMB or Astom CMX membrane.
  • Perfluorinated membranes are known to have a high resistance to chemical attack under conditions of high pH.
  • the stability and favourable physical properties are believed to be due to the substantially inert and strong backbone of the polymer which contains regular side chains ending with ionic groups.
  • the choice of the ionic groups is important as they affect interactions with the migrating ions, the pK a of the ion exchange polymer, the solvation of the polymer and the nature and extent of interactions between the fixed ionic groups.
  • the anion permeable membrane is preferably a Neosepta AHA membrane or a Fumatech FAP membrane.
  • the electrode material should exhibit high conductivity and low electrical resistance and be substantially resistant to corrosion under the electrolytic conditions.
  • Pre-precipitation liquor is highly caustic but H + is produced at the anode. It will be appreciated that choice of electrode material will be within the ability and knowledge of the skilled addressee. Since pre-precipitation liquor contains anions such as fluoride, sulphate etc. the production of hydrofluoric acid, sulfuric acid etc. occurs at the interface between anode and solution (even though the solution is highly caustic).
  • Suitable anode materials include platinum coated niobium, platinum coated titanium or Monel.
  • cathode material may be wider than anode material.
  • Suitable cathodes include stainless steel or a gas diffusion electrode (oxygen depolarized cathode).
  • the current density must be controlled as increasing the current density will increase the rate of product formation but it will also increase the energy consumption. For higher current densities, less membrane area may be required for a given quantity of caustic extracted.
  • the preferred current density may be between 20 mA/cm 2 and 600 mA/cm 2 . More preferably, the current density is between 150 mA/cm 2 and 350 mA/cm 2 .
  • the catholyte is a caustic solution. Whilst it is advantageous to have the catholyte caustic concentration as high as possible, if it is too high, the current efficiency may be compromised due to back diffusion of ions from the catholyte to the anolyte.
  • the caustic solution may be sourced from the Bayer circuit. It will be appreciated that where the caustic solution is sourced from the Bayer circuit, the solution should have a caustic concentration below that of the Bayer process liquor. Non-limiting examples include Bayer lake water or condensate.
  • the catholyte caustic concentration is not greater than about 8M NaOH or 25% NaOH catholyte. It will be appreciated that if the caustic concentration is too low then the current density may drop due to lower conductivity.
  • the catholyte has a maximum alumina concentration of 20 gl_ "1 as AI 2 O 3 .
  • the method of the present invention may be performed as a batch process wherein the first region is provided in the form of a first compartment and the second region is provided in the form of a second compartment and the ion permeable membrane is provided between the first compartment and the second compartment.
  • the pre-precipitation liquor anolyte is introduced into the first compartment and the catholyte is introduced into the second compartment and a potential is applied between the first compartment and the second compartment for a set period of time, after which the pre-precipitation liquor, depleted in sodium - -
  • the method of the present invention may be performed as a continuous process wherein the first region is provided in the form of a first compartment and the second region is provided in the form of a second compartment and the ion permeable membrane is provided between the first compartment and the second compartment.
  • Pre-precipitation liquor anolyte is continuously introduced into the first compartment and catholyte is continuously introduced into the second compartment with a potential continuously applied between the first compartment and the second compartment.
  • Treated pre- precipitation liquor, depleted in sodium ions and in hydroxide ions is continuously removed from the first compartment and catholyte with an increased sodium hydroxide concentration is continuously removed from the second compartment.
  • the method of the present invention may be performed as a continuous process with many compartments in a cell with adjacent compartments being alternately separated by cation permeable membranes and anion permeable membranes. Every second region contains a feed solution of pre-precipitation liquor anolyte and instead of hydroxide being neutralized by production of protons at the anode, it is removed from the feed solution through an anionic membrane to form pure caustic (sodium ions come in from the opposite side via a cationic membrane).
  • the method is believed to consume less energy than electrolysis with a single ion permeable membrane because the amount of water that is electrolysed to form protons and hydroxide, with concomitant formation of hydrogen and oxygen, is minimized.
  • the arrangement could include bipolar membranes which split water directly, to produce hydroxide ions and protons, with no hydrogen or oxygen formation.
  • the solid support comprising an exchangeable ion is an ion exchange resin.
  • Ion exchange resins are high molecular weight polymeric materials containing many ionic functional groups per molecule.
  • Cation-exchange resins can be either a strong-acid type containing sulfonic acids groups (RSO 3 ' H + ) or a weakly-acidic type such as those containing carboxylic acid (RCOOH) or phenolic (ROH) groups.
  • Anion exchange resins contain basic amine functional groups attached to the polymer molecule. Strong-base exchangers are quaternary amines (RN(CH 3 ) 3 + OH " ) and weak-base types contain secondary or tertiary amines.
  • the ion exchange resin is a cation exchange resin and in highly preferred forms of the invention, the cation exchange resin is a weakly-acidic cation exchange resin.
  • the exchangeable ion on the solid support is a proton. It will be appreciated that the exchange of the sodium ion present in the pre- precipitation liquor with a proton on the extractant will encompass the exchange of more than one sodium ion and more than one proton.
  • the solid support has a pKa of about 9-13.
  • the exchange of a cation present in the pre-precipitation liquor with a proton on the resin will be accompanied by a concomitant neutralisation of hydroxide ions in the pre-precipitation liquor according to the following equation where RH represents the hydrogen form of the resin.
  • the solid support and the extractant are provided in the form of an ion aqueous biphasic extraction chromatography resin.
  • this type of resin are ABEC-2000 and ABEC-5000.
  • Such resins contain polyethylene glycol (PEG) chains tethered to a polymer backbone, such as polystyrene divinylbenzene backbone. As the PEG chains are not endowed with ion-exchange capability, the expected extraction mechanism is by transfer of NaOH ion pairs into the resin.
  • agitating the pre-precipitation liquor and the solid support by any means known in the art including shaking, stirring, rolling and sparging.
  • the contact time between the pre-precipitation liquor and the solid support should be sufficient for ion exchange to occur. Said contact time will be influenced by many factors including the pKa of the ionisable proton on the solid support, the pH of the aqueous phase, the volumes of the aqueous and solid phases, the temperature, the concentration of the sodium ions, the total alkalinity, the total caustic concentration, the extent of agitation and the presence of other species in the liquor.
  • the method comprises the further step of:
  • step of separating the Bayer process solution and the solid support may be performed by any method known in the art including filtering and centrifugation.
  • the method comprises the further steps of:
  • the stripping solution may be provided in form of water or a Bayer process liquor including condensate or lake water or an acidic solution.
  • the pH of the stripping solution will be influenced by the type of resin employed.
  • carboxylic acid ion exchange resins may require a stripping solution of pH ⁇ 3
  • a stripping solution of pH 5 or higher should be sufficient.
  • the pKa of the ion exchange resin will influence the step of exchanging a metal cation present in the Bayer process solution with an ion on the solid support.
  • the ion exchange resin has a pKa of about 9-13.
  • the weak-acid cation exchange resin comprises a phenolic group or a hydroxyl group attached to an aromatic ring. _ ⁇ _
  • the step of separating the stripping solution and the solid support may be performed by any method known in the art including filtering and centrifugation.
  • the stripping solution after contact with the substantially water- immiscible solution can be re-used in subsequent steps in the Bayer process or in subsequent stripping steps.
  • the aqueous solution may need to be pre-treated prior to subsequent use.
  • Figure 1 is a schematic flow sheet of a Bayer Process circuit
  • Figure 2 is a schematic flow sheet showing how a method in accordance with an embodiment of the present invention may be utilised in a Bayer Process circuit
  • Figure 3 is an example of an X-ray diffraction pattern of the product from the experiment shown in Table 5.
  • the invention focuses on the precipitation of boehmite from a pre-precipitation Bayer liquor by treating the pre-precipitation liquor to reduce the total alkalinity and total caustic concentration of the spent liquor.
  • Figure 1 shows a schematic flow sheet of the Bayer process circuit for a refinery using a single digestion circuit 10 comprising the steps of:
  • At least a portion 30 of the pre-precipitation liquor 20 is contacted in a solvent extraction apparatus 32 with a solution of an organic solvent 34 comprising an extractant.
  • a solution of an organic solvent 34 comprising an extractant.
  • Up to 100 % of the pre-precipitation liquor 20 may be processed in the extraction apparatus 32.
  • the aqueous layer 36 and the organic layer 38 are separated and the aqueous layer 36 combined with the portion of the untreated pre-precipitation liquor 40 and seeded 24 to induce boehmite precipitation 22.
  • solvent extraction apparatus 32 may be replaced with an ion exchange apparatus or an electrolytic membrane apparatus or other apparatus to remove sodium ions from the process stream.
  • the spent liquor stream 42 may be recycled back through the Bayer circuit or recontacted with a further solvent extraction step to include further precipitation of aluminium hydroxide. It will be appreciated that there may be provided a number of solvent extract apparatus 32 operating in series. Notably, the precipitation of aluminium hydroxide does not need rely on changes in temperature to induce states of supersaturation. - -
  • the organic layer 38 is contacted 44 with an aqueous solution 46 to back extract sodium ions from the organic layer 38 to the aqueous solution 46.
  • the aqueous solution of increased causticity 48 may then be used in the causticisation of further bauxite or in other places in the circuit as appropriate such as, for example, as a pre-treatment step in the washing of bauxite before digestion to remove impurities or in the washing of seed or oxalate.
  • Back extraction of the organic layer 38 results in regeneration of the protonated form of the extractant.
  • the extractant may then be re-used in further extraction steps.
  • Example 1 Treatment of pre-precipitation liquor using ion exchange resins
  • Soda extraction tests were performed using Amberlite IRC86 - hydrogen form - CAS#211811 -37-9, weakly acidic resin 20-50 mesh, sourced from Sigma-Aldrich.
  • Bayer pre-precipitation liquors also known as green liquor or pregnant liquor
  • the filtered green liquor (a sub-sample was analysed by titration) was heated to 80 0 C and contacted with the water-conditioned resin at various concentrations ranging from 100 to 200 gL "1 as shown in Table 1.
  • the liquor- resin slurry was filtered to produce the "treated green” liquor.
  • Sub-samples were titrated for alumina concentration (A), the total caustic concentration (TC) and the total alkali concentration (TA).
  • A alumina concentration
  • TC total caustic concentration
  • TA total alkali concentration
  • the stability of the treated green liquor may be prolonged by the addition of gibbsite precipitation inhibitors such as calcia, sodium gluconate, or other inhibitors.
  • gibbsite precipitation inhibitors such as calcia, sodium gluconate, or other inhibitors.
  • Table 2 presents the results of further soda extraction tests on a different Bayer pre-precipitation liquor using Amberlite IRC86 resin.
  • the liquor was contacted with the resin at 80 ° C for 2 min.
  • Gluconate (5 drops per 10 ml_) was added to stabilize the treated liquor. All the treated liquors were stable at room temperature.
  • TC, TA and A/TC changes after contacting a refinery green liquor with Amberlite IRC86. Note: the moisture content of the conditioned resin is 50 to 60% by weight.
  • Contacting can be conducted at other temperatures, including higher temperatures with suitable contacting and separation equipment. It will be appreciated that the contact temperature may impact on the choice of resin.
  • Example 2 Boehmite precipitation from a combined liquor comprising treated and untreated refinery pre-precipitation liquor
  • the treated green liquor at 95 ° C was injected into a 1 L autoclave containing boehmite seed (324 gl_ "1 ), calcia and untreated green liquor at 145 ° C and under pressure.
  • the temperature control setting on the autoclave was reset to 125 ° C and the temperature of the mixture rapidly adjusted to this value.
  • Boehmite seed was prepared by a hydrothermal conversion of a commercial gibbsite to boehmite in a sealed, pressurised reactor at 200 ° C using de-ionized water.
  • the material produced was analysed by XRD, TGA and DSC and found to be almost pure boehmite with about 0.2 % gibbsite. This boehmite seed was used for all the experiments reported below.
  • the refinery green liquor was filtered through a Pall A/B glass filter paper; calcium hydroxide added (5 gl_ '1 ) and held for 30 min at 80 ° C in a rotating water bath before adding to the autoclave.
  • the treated green liquor was prepared using water conditioned Amberlite IRC86 at 80 C in a single stage of contacting as described above.
  • the filtrate was heated to 95 ° C and added to a sealed cylinder connected to an autoclave.
  • the cylinder containing the treated green liquor was pressurized with argon and the contents injected into the autoclave containing the boehmite slurry at temperature and pressure and the temperature controller set to 125 ° C.
  • the contents were stirred at 300 rpm for 6 hr at 125 C.
  • the autoclave was rapidly cooled to -80 0 C and contents filtered through Pall A/B glass filter paper.
  • the filtrate was sampled, gluconate added and titrated at 25 C for the alumina concentration (A), TC and TA.
  • the solids were washed thoroughly with hot Dl water and dried for 24 hr in a 60 C laboratory oven.
  • the solids were analysed by XRD.
  • the run was repeated using another green liquor sample from the same refinery. The normal variation in refinery liquor composition with time resulted in slightly different but comparable liquor compositions for the two runs.
  • the yield from an isothermal boehmite precipitation circuit with a combined treated and untreated green liquor feed of the same composition as Table 5 would be ⁇ 69 gl_ "1 (as AI 2 O 3 ), ignoring scale and solids overflow losses. This is comparable to commercial gibbsite precipitation circuits using similar refinery liquor.
  • the theoretical yield in this case is ⁇ 78 gl_ "1 , as AI 2 O 3 . If - O -
  • the product was filtered through a 0.45 ⁇ m membrane and washed with hot deionised water. The filtrate was titrated for A, TC and TA values. The solid was dried overnight in an oven (60 0 C) and characterized by XRD and DCS-TGA.
  • a range of precipitation temperatures (105 ° C to 160 ° C) and liquor compositions were tested.
  • the liquors were prepared so as to allow comparison between equivalent refinery green liquor and various combinations of a treated green liquor and untreated green liquor.
  • the equivalent treated and untreated liquors were prepared to match the compositions for the 0 gl_ "1 and 200 gl_ "1 resin charges in Table 1 , respectively. All tests were of 7 hr duration and charged with 500 gl_ "1 boehmite seed from the same batch.
  • Table 7 compares the results from laboratory boehmite precipitation experiments at 125 ° C for three different liquors: (1) a control, i.e. equivalent to a refinery green liquor; (2) an equivalent to a 50:50 treated and untreated green liquor and (3) - -
  • Table 8 compares the results from laboratory boehmite precipitation experiments at 105 ° C for a control liquor (i.e. equivalent to a refinery green liquor) and a 100% treated green liquor.
  • XRD and DCS-TGA identified the product solids as boehmite.
  • Table 9 compares the precipitation yields at different temperatures from a low soda Bayer liquor, i.e. treated liquor. The results indicate that the kinetic temperature benefit, for the precipitation and extraction conditions investigated, plateaus between 115 C and 140 ° C and drops slightly by 160 C. It will be appreciated that the temperature-yield profile will vary depending on factors such as the extraction temperature, initial liquor composition and other process variables. The decision on the optimal precipitation temperature and temperature profile should primarily be made on the basis of overall circuit yield, energy efficiency and optimizing the plant energy balance.

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  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Inorganic Chemistry (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

Abstract

La présente invention concerne un procédé pour la précipitation de boehmite à partir d'une pré-précipitation préalable de liqueur de Bayer, le procédé comprenant les étapes suivantes: le traitement de la liqueur de pré-précipitation pour réduire la concentration caustique totale et l'alcalinité totale de la liqueur de pré-précipitation; et la pré-précipitation de boehmite à partir de la liqueur de pré-précipitation, au moins une partie du boehmite étant précipitée à une température égale ou supérieure à 105°C.
PCT/AU2008/001447 2007-09-28 2008-09-26 Procédé pour la précipitation de boehmite à partir d'une pré-précipitation de liqueur de bayer Ceased WO2009039592A1 (fr)

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AU2007905354A AU2007905354A0 (en) 2007-09-28 Method for Precipitating Boehmite from Pre-precipitation Bayer Liquors
AU2007905354 2007-09-28

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106673037A (zh) * 2015-11-11 2017-05-17 中国石油化工股份有限公司 一种拟薄水铝石的制备方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4581207A (en) * 1982-12-27 1986-04-08 Aluminum Company Of America Recovery of aluminum from spent liquor
WO1994003396A1 (fr) * 1992-07-29 1994-02-17 Alcan International Limited Dispositif et procede ameliores de digestion de la bauxite
WO1998058876A1 (fr) * 1997-06-24 1998-12-30 National Technical University Of Athens (Ntua) Procede de production de d'oxyde d'aluminium hydrate a partir de solutions d'aluminates sursaturees
US6322702B1 (en) * 1999-09-23 2001-11-27 U.T. Battlle, Llc Solvent and process for recovery of hydroxide from aqueous mixtures

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4581207A (en) * 1982-12-27 1986-04-08 Aluminum Company Of America Recovery of aluminum from spent liquor
WO1994003396A1 (fr) * 1992-07-29 1994-02-17 Alcan International Limited Dispositif et procede ameliores de digestion de la bauxite
WO1998058876A1 (fr) * 1997-06-24 1998-12-30 National Technical University Of Athens (Ntua) Procede de production de d'oxyde d'aluminium hydrate a partir de solutions d'aluminates sursaturees
US6322702B1 (en) * 1999-09-23 2001-11-27 U.T. Battlle, Llc Solvent and process for recovery of hydroxide from aqueous mixtures

Non-Patent Citations (5)

* Cited by examiner, † Cited by third party
Title
LOH, J. ET AL.: "Boehmite vs Gibbsite Precipitation", LIGHT METALS, 2005, pages 203 - 208 *
PANIAS, D. ET AL.: "Boehmite process - a new approach in alumina production", ERZMETALL, vol. 56, no. 2, 2003, pages 75 - 81, XP001143779 *
PANIAS, D. ET AL.: "Boehmite process: An alternative technology in alumina", LIGHT METALS, 2001, pages 97 - 103 *
PANIAS, D.: "Boehmite process - a new approach in alumina production", TRAVAUX DU COMITE INTERNATIONAL POUR L'ETUDE DES BAUXITES, DE L'ALUMINE ET DE L'ALUMINIUM, vol. 29, no. 33, 2002, pages 94 - 104 *
SKOUFADIS, C. ET AL.: "Kinetics of boehmite precipitation from supersaturated sodium aluminate solutions", HYDROMETALLURGY, vol. 68, 2003, pages 57 - 68, XP004409421, DOI: doi:10.1016/S0304-386X(02)00165-2 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106673037A (zh) * 2015-11-11 2017-05-17 中国石油化工股份有限公司 一种拟薄水铝石的制备方法

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