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EP3820820A1 - Procédé d'obtention de particules d'aluminate tricalcique calibrées en taille et utilisation de telles particules dans un procédé de raffinage d'alumine - Google Patents

Procédé d'obtention de particules d'aluminate tricalcique calibrées en taille et utilisation de telles particules dans un procédé de raffinage d'alumine

Info

Publication number
EP3820820A1
EP3820820A1 EP19736758.4A EP19736758A EP3820820A1 EP 3820820 A1 EP3820820 A1 EP 3820820A1 EP 19736758 A EP19736758 A EP 19736758A EP 3820820 A1 EP3820820 A1 EP 3820820A1
Authority
EP
European Patent Office
Prior art keywords
calcium hydroxide
suspension
particles
particle size
size
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP19736758.4A
Other languages
German (de)
English (en)
Inventor
Chris Du Plessis
Hugues LAMBERT
Robert GÄRTNER
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Lhoist Recherche et Developpement SA
Original Assignee
Lhoist Recherche et Developpement SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Lhoist Recherche et Developpement SA filed Critical Lhoist Recherche et Developpement SA
Publication of EP3820820A1 publication Critical patent/EP3820820A1/fr
Pending legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/16—Preparation of alkaline-earth metal aluminates or magnesium aluminates; Aluminium oxide or hydroxide therefrom
    • C01F7/164—Calcium aluminates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/02—Oxides or hydroxides
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2/00—Lime, magnesia or dolomite
    • C04B2/02—Lime
    • C04B2/04—Slaking
    • C04B2/06—Slaking with addition of substances, e.g. hydrophobic agents ; Slaking in the presence of other compounds
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer

Definitions

  • the present invention is related to a process for obtaining size-calibrated tri calcium aluminate (TCA) particles comprising the steps of providing a process liquor containing sodium aluminate, then providing a suspension of coarse calcium hydroxide particles and mixing said selected suspension of calcium hydroxide particles with said process liquor to allow them to react to obtain the said tri-calcium aluminate particles.
  • TCA tri calcium aluminate
  • the present invention is related to the use of such coarse tri calcium aluminate particles in a process of purifying alumina process liquors.
  • Bayer process alumina refineries typically make use of a filtration process step to remove fine suspended particulate impurities prior to the alumina precipitation step, where the so-called “green liquor” or “process liquor” containing mainly sodium aluminate is precipitated as alumina Al 2 0 3 product.
  • the filtration step to remove suspended impurities typically fine Fe and/or Si containing solids
  • This impurity removal step is typically referred to as “security filtration”, “impurity filtration” or “solution polishing” and is conducted in well-known pressure filtration systems (e.g.
  • the filter aid is typically tri-calcium aluminate (Ca 3 [AI(OH) 6 ] 2 ), hereinafter abbreviated as TCA, which is produced by reacting a portion of the process liquor, containing sodium aluminate NaAI(OH) 4 with Ca(OH) 2 , in a molar ratio suited for the plant operation, generally from 0.5:1 to 3:1 but is specific to plant conditions.
  • TCA tri-calcium aluminate
  • the Ca(OH) 2 reagent is typically added to the reactor as a slaked lime slurry, also called milk of lime, or suspension, with a solids content ranging from 12-25 % w/w. Slaking occurs when quicklime, CaO, is reacted with excess water to form a suspension of Ca(OH) 2 .
  • the process feed liquor temperature is typically in the range of 95-105 °C.
  • the slaked lime slurry is preferably at a similar temperature, or as high as practically possible, generally in the range of 70-95 °C.
  • the TCA filter aid generation reaction is typically conducted at 95-98 °C. Although some plants use quicklime, CaO, directly in this process step, the CaO still undergoes hydration to Ca(OH) 2 , before reacting with sodium aluminate to form TCA:
  • TCA filter aid rather than the filter cloth that performs the filtration duty.
  • the properties of the TCA filter aid are, therefore, critical to filtration performance. If the TCA particles are too fine, the filtration bed voids might be too small, thus slowing down the filtration process and increasing filtration backpressure. Operationally, this requires frequent back-flushing to prevent clogging, therefore causing a plant throughput bottleneck. If the TCA particles are too coarse, the voids between the particles may be too large and the suspended impurities are not sufficiently removed during the filtration process.
  • the ideal TCA filter aid particle size and distribution is different for each alumina refinery and is dependent upon a number of process and equipment factors, such as: the throughput rate required, the suspended impurity particle load and size, the type of filter, filtration conditions and filter cloth, membrane or screen type used.
  • alumina refineries are restricted in their use of a lime reagent to that which provides acceptable TCA filter aid properties, even if said lime reagent other properties are sub-optimal. This is particularly problematic for alumina refineries that require coarse TCA filter aid, i.e. with a d50 larger than 20 pm. Depending on the plant installations and/or on the ore compositions, some refineries will require specific particle size distribution of TCA used as a filter aid.
  • the present invention is related to a process for obtaining size-calibrated tri-calcium aluminate (TCA) particles comprising the steps of:
  • Tri-calcium aluminate (Ca 3 [AI(OH) 6 ] 2 ) is hereinhafter referred to as TCA.
  • Sodium aluminate is hereinafter used to describe 2NaAI(OH) 4 .
  • size-calibrated tri-calcium aluminate particles is meant according to the invention tri-calcium aluminate particles with an optimal particle size distribution for use as a TCA filter aid in a process of alumina refining.
  • the optimal TCA particles size is a compromise between too fine and too coarse, to provide an efficient filtration of suspended impurities while minimizing filter clogging, backpressure and throughput issues.
  • the particle size distribution is expressed as the d50 measured by granulometry laser diffraction in methanol after sonication.
  • Size-calibrated tri-calcium aluminate particles may vary according to the requirements of the plant, for example Size-calibrated tri-calcium aluminate particles may have a d50 of larger than 5 pm, preferably larger than 10 pm, more preferably larger than 15 pm, more preferably larger than 20 pm. In another embodiment of the invention the d50 of the size-calibrated tri-calcium aluminate particles may be lower than 200 pm, preferably lower than 100 pm, even more preferably less then 50 pm.
  • size-calibrated calcium hydroxide particles is meant according to the invention calcium hydroxide particles having an optimal particle size distribution being a compromise between too fine and too coarse for obtaining optimal size-calibrated TCA particles.
  • the particle size distribution of TCA particles obtained by the process according to the invention is linked to the particle size distribution of the calcium hydroxide particles by a generally linear relationship.
  • the slope of the linear relationship is specific to the particular conditions, including: the solution composition, the molar ratio of Ca(OH) 2 to NaAI(OH) 4 , the temperature of both the Ca(OH) 2 reagent and the alumina refinery liquor, the tip speed of agitation (i.e. shear force), the hydraulic residence time, the particle residence time, the extent of precipitate seeding and seed recycling.
  • the relationship is also dependent on the quicklime properties used to produce the Ca(OH) 2 , including its reactivity (as measured by its reaction rate with water) and its chemical composition. For all of these reasons, the precise relationship between particle size distribution of the Ca(OH) 2 and the TCA may be determined for each particular plant scenario. The determination of the relationship is based on generating a range of Ca(OH) 2 reagents with increasing particle size distributions (meaning the d25, d50 and d90 are increased), and observing the impact of using these reagents on the particle size distribution of the resulting TCA.
  • the said suspension of size-calibrated calcium hydroxide particles is obtained from slaking quicklime, said quicklime having an available lime content greater than 82 %, preferably greater than 85 %, preferably greater than 90 %, more preferably greater than 92 %, more preferably greater than 95 %, measured according to EN459-2:2010 standard.
  • Quicklimes having an available lime content greater than 90 % are also generally referred as "high quality quicklime”.
  • Size-calibrated calcium hydroxide can be produced from high quality quicklime having a content of available lime greater than 85% as measured according to EN459-2 standard, and generally presents a high reactivity with water.
  • the use of such high quality quicklime and milk of lime derived from high quality quicklime is also advantageous for use in other components of the alumina refining process, other than TCA filter aid generation, by reducing lime reagent consumption.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime in the presence of a coarsening additive causing a coarsening effect on the particle size distribution of the calcium hydroxide particles obtained by said process of slaking.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking formulated quicklime, prepared from quicklime to which a coarsening additive has been added by spraying a solution containing a coarsening additive onto quicklime.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime in the presence of 2 w% or less, preferably, 0.1 to 1.5 w%, preferably, 0.15 to 0.8 w% and more preferably from 0.2 to 0.65 w% of a coarsening additive relative to the weight of quicklime, wherein said coarsening additive is selected among alkaline sulfates or alkaline earth sulfates.
  • the said coarsening additive is sodium sulfate.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process wherein
  • a concentrated aqueous solution of coarsening additive in particular sodium sulfate, is provided by dissolving an amount of a coarsening additive of at least 10 w%, preferably at least 30 w% in water at a temperature of dissolution adapted to dissolve such an amount of coarsening additive;
  • said concentrated aqueous solution of coarsening additive at the said temperature of dissolution is sprayed onto quicklime with an amount comprised of between 5 dm 3 and 30 dm 3 , preferably between 10 dm 3 and 20 dm 3 per dry metric ton of said quicklime to obtain a formulated quicklime;
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime with an amount of water such that the solid content in the milk of lime solids content comprises between 10 and 45 % in weight of the total weight of the milk of lime preferably with a solid content in the milk of lime up to 40 %, preferably up to 35 %, more preferably up to 30 %, more preferably up to 25 % in weight of the total weight of the milk of lime.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking partially pre-hydrated quicklime particles having a superficial layer, at least partially superficial, of hydrated lime and a core of quicklime.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime in a reactor cooled at a temperature lower than or equal to 60 °C.
  • the particles of hydrated lime obtained in such conditions are generally coarser than particles of hydrated lime obtained in conditions of temperatures comprised between 60 °C and 95 °C.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime in a reactor at a temperature greater or equal to 95 °C.
  • the particles of hydrated lime obtained in such conditions are generally coarser than particles of hydrated lime obtained in conditions of temperatures comprised between 60 °C and 95 °C.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime to obtain a first suspension of calcium hydroxide followed by a step of particle size selection of said first suspension to remove particles of calcium hydroxide that have a particle size under a predetermined particle size and to retain the calcium hydroxide particles larger than a predetermined particle size for obtaining, possibly after dilution, said suspension of size-calibrated calcium hydroxide particles.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime to obtain a first suspension of calcium hydroxide followed by:
  • a first step of particle size selection of said first suspension to remove particles of calcium hydroxide having a particle size smaller than a first predetermined particle size and to retain calcium hydroxide particles larger than a first predetermined particle size for obtaining, possibly after dilution, a second suspension of calcium hydroxide particles
  • a second step of particle size selection of said second suspension of calcium hydroxide particles to remove particles of calcium hydroxide having a particle size larger than a second predetermined particle size greater than the said first predetermined particle size and to retain the remaining calcium hydroxide particles having a particle size comprised between said first predetermined particle size and said second predetermined particle size for obtaining, possibly after dilution said suspension of size-calibrated calcium hydroxide particles.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slurrying hydrated lime where the hydrated lime was prepared by dry hydration and its particle size was controlled by grinding and sieving to obtain the targeted size.
  • said size-calibrated calcium hydroxide particles have a particle size distribution predetermined for obtaining TCA particles with a desired particle size distribution on basis of a calibration curve obtained by realizing the said steps a) to c) with at least three suspensions of calcium hydroxide of different predetermined particle size distribution.
  • the present invention is related to the use of coarse tri-calcium aluminate particles obtained by the process as disclosed herein above in a process of refining alumina from an ore comprising aluminum minerals.
  • the present invention is related to the use of coarse tri-calcium aluminate particles obtained by the process as disclosed above in a process of manufacturing TCA filter aid.
  • the figure 1 presents an image obtained by Scanning Electron Microscopy of the TCA particles obtained according to the process of invention.
  • the present invention is related to a process for obtaining size- calibrated tri-calcium aluminate (TCA) particles comprising the steps of:
  • the said suspension of size-calibrated calcium hydroxide is obtained from slaking quicklime, said quicklime having an available lime content greater than 82 %, preferably greater than 85 %, preferably greater than 90 %, more preferably greater than 92 %, more preferably greater than 95 %, measured according to EN459-2:2010 standard.
  • Quicklimes having an available lime content than 90 % is generally also referred as "high quality quicklime”.
  • a typical alumina refinery process is described in the document "The chemistry of CaO and Ca(OH) 2 ", B.l. Whittington, Hydrometallurgy 43 (1996) 13-35.
  • An ore containing high amounts of aluminum such as bauxite is crushed and milled.
  • the resulting product is transferred into a first tank for a pre-desilication step wherein the crushed ore is put in contact with milk of lime under agitation at temperatures about 100 °C before being transferred to a digestion tank wherein highly concentrated solution of NaOH and milk of lime is injected.
  • This digestion step occurs under high pressure and high temperature.
  • the resulting mud obtained after digestion is cooled and sent to a sedimentation tank to settle out the solid fraction from the liquid fraction hereby called process liquor.
  • the solid fraction is washed with water, in a series of counter current decantation washers.
  • One of the washer overflow eluents is sent to a tank for causticization wherein milk of lime is added to increase alkalinity by converting sodium carbonate to sodium hydroxide.
  • milk of lime also referred to as a suspension of calcium hydroxide particles
  • tri-calcium aluminate particles which are used as a filter aid to filter the remaining process liquor.
  • the filtered process liquor is then cooled and settled to precipitate aluminum trihydroxide in a precipitation tank.
  • the precipitate is calcined after washing to obtain a purified Al 2 0 3 Alumina product.
  • the process of refining alumina comprises different steps involving the use of milk of lime
  • the use of a milk of lime derived from high quality quicklime is advantageous for use in other components of the alumina refining process, other TCA filter aid generation, by reducing lime reagent consumption.
  • quicklime can be slaked in the presence of a coarsening additive causing a coarsening effect on the particle size distribution of the calcium hydroxide particles obtained by said process of slaking.
  • the said coarsening additive is selected among alkaline sulfate such as sodium sulfate as a non-limitative example or alkaline earth sulfates such as calcium sulfate as a non- limitative example.
  • alkaline sulfate such as sodium sulfate as a non-limitative example
  • alkaline earth sulfates such as calcium sulfate as a non- limitative example.
  • the coarsening additive can be added to quicklime before the step of slaking for example by spaying the said coarsening additive onto quicklime and then the step of slaking is performed with sufficient amount of water to obtain a suspension of calcium hydroxide particles.
  • the coarsening additive can be added during the step of slaking, for example in the slaking water.
  • the step of slaking quicklime is realized in presence of less than 2 w%, preferably 0.1 to 1.5 w%, preferably, 0.15 to 0.8 w% and more preferably from 0.2 to 0.65 w% of a coarsening additive relative to the weight of quicklime.
  • a minimum amount of coarsening additive is required to provide the coarsening effect on calcium hydroxide particles and a maximum amount of coarsening additive is set up to keep the suspension of calcium hydroxide particles over a certain degree of purity and to prevent the formation of too coarse calcium hydroxide particles.
  • a suspension of size-calibrated calcium hydroxide particles is obtained from a process wherein:
  • a concentrated aqueous solution of sodium sulfate is provided by dissolving an amount of sodium sulfate of at least 10 w%, preferably at least 35 w% in water at a temperature of dissolution adapted to dissolve such an amount;
  • said concentrated solution of sodium sulfate at the said temperature of dissolution is sprayed onto quicklime with an amount comprised of between 5 dm 3 and 30 dm 3 , preferably between 10 dm 3 and 20 dm 3 of said concentrated solution per ton of said quicklime to obtain a formulated quicklime; said formulated quicklime is slaked with water to provide said suspension of size- calibrated calcium hydroxide particles.
  • the amount of water is adapted to provide a suspension of calcium hydroxide (or milk of lime) wherein the solid content in the milk of lime is comprised between 10 and 45 % in weight of the total weight of the milk of lime, preferably with a solid content in the milk of lime up to 40 %, preferably up to 35 %, more preferably up to 30 %, more preferably up to 25 % in weight of the total weight of the milk of lime.
  • a minimum amount of solid content is required to provide sufficient amount of calcium hydroxide in a minimum volume of suspension and a maximum amount of solid content is preferably set up to minimize the volume of the suspension while keeping a good flowability and pumpability of the suspension.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking partially pre-hydrated quicklime particles having a superficial layer, at least partially superficial, of hydrated lime and a core of quicklime.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime in a reactor cooled at a temperature lower than or equal to 60 °C.
  • the particles of hydrated lime obtained in such conditions are generally coarser than particles of hydrated lime obtained in conditions of temperatures comprised between 60 °C and 95 °C.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime in a reactor at a temperature greater or equal to 95 °C.
  • the particles of hydrated lime obtained in such conditions are generally coarser than particles of hydrated lime obtained in conditions of temperatures comprised between 60 °C and 95 °C.
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime to obtain a first suspension of calcium hydroxide followed by a step of particle size selection of said first suspension to remove particles of calcium hydroxide that have a particle size under a predetermined particle size and to retain the calcium hydroxide particles larger than a predetermined particle size for obtaining, possibly after dilution, said suspension of size-calibrated calcium hydroxide particles.
  • This step of particle size selection can be done for example by cutting the said first suspension with a sieve selected from the commercially available sieves having sieve openings inferior to 125 pm (120 mesh), preferably inferior to 105 pm (140 mesh), more preferably inferior to 88 pm (170 mesh), more preferably inferior to 74 pm (200 mesh), more preferably inferior to 63 pm (230 mesh).
  • a sieve selected from the commercially available sieves having sieve openings inferior to 125 pm (120 mesh), preferably inferior to 105 pm (140 mesh), more preferably inferior to 88 pm (170 mesh), more preferably inferior to 74 pm (200 mesh), more preferably inferior to 63 pm (230 mesh).
  • said suspension of size-calibrated calcium hydroxide particles is obtained from a process of slaking quicklime to obtain a first suspension of calcium hydroxide followed by:
  • the first step of particle size selection can be done for example by cutting the said first suspension with a sieve selected from the commercially available sieves having sieve openings inferior to 125 pm (120 mesh), preferably inferior to 105 pm (140 mesh), more preferably inferior to 88 pm (170 mesh), more preferably inferior to 74 pm (200 mesh), more preferably inferior to 63 pm (230 mesh).
  • a sieve selected from the commercially available sieves having sieve openings inferior to 125 pm (120 mesh), preferably inferior to 105 pm (140 mesh), more preferably inferior to 88 pm (170 mesh), more preferably inferior to 74 pm (200 mesh), more preferably inferior to 63 pm (230 mesh).
  • the second step of particle selection can be done by cutting the said second suspension with a sieve selected from the commercially available sieves having sieve openings greater than the ones of the sieve utilized in the first step of particle selection, such as sieves having openings greater than 105 pm (140 mesh), preferably greater than 125 pm (120 mesh), more preferably greater than 149 pm (100 mesh), more preferably greater than 177 pm (80 mesh).
  • a sieve selected from the commercially available sieves having sieve openings greater than the ones of the sieve utilized in the first step of particle selection such as sieves having openings greater than 105 pm (140 mesh), preferably greater than 125 pm (120 mesh), more preferably greater than 149 pm (100 mesh), more preferably greater than 177 pm (80 mesh).
  • the said size- calibrated calcium hydroxide particles have a particle size distribution predetermined for obtaining TCA particles with a desired particle size distribution on the basis of a calibration curve obtained by realizing the said steps a) to c) with at least three suspensions of calcium hydroxide of different predetermined particle size distribution.
  • calcination of limestone into quicklime can also be realized by using fuels (such as high sulfur content coal, or petroleum coke, also called petcoke) that would impart a high sulfur content (typically in the form of a sulfate or other oxidized form of sulfur) onto the quicklime product.
  • fuels such as high sulfur content coal, or petroleum coke, also called petcoke
  • a high sulfur content typically in the form of a sulfate or other oxidized form of sulfur
  • size-calibrated particles of calcium hydroxide preferably obtained from quicklime having an available lime content of more than 82 %, or even higher, can be used in different stages of the process including the step of formation of tri-calcium aluminate. Therefore, the method of manufacturing TCA particles provides not only a control method for the particle size distribution of TCA particles but also provides the possibility of using a high quality quicklime, with a CaO available content equal or greater than 82 %, to generate high quality milk of lime, thereby increasing the utilization efficiency of this reagent in all process units of the alumina refining process where it is used. Examples
  • Synthetic Bayer liquor can be prepared in an autoclave by heating at 180°C under stirring an aqueous mixture containing 6 mol/dm 3 of NaOH, 2.2 mol/dm 3 of AI(OH) 3 , and 0.4 mol/dm 3 of Na 2 C0 3 .
  • Three samples of formulated quicklime are prepared by mixing quicklime having the properties listed in table 1 with respectively 0.3 w%, 0.5 w% and 0.7 w% of Na 2 S0 4 in weight of said quicklime.
  • the three said samples of formulated quicklime were crushed to ⁇ 5 mm and then slaked in water at room temperature in a slaker for 20 minutes with an amount of water to obtain about 16 w% of solid content in the milk of lime.
  • the particle size distribution d 50 for those three milks of lime obtained are measured by granulometry laser diffraction in methanol after sonication.
  • the d 50 of the calcium hydroxide particles of the three milks of lime obtained increases substantially linearly with the amount of Na 2 S0 4 in the formulated quicklime.
  • the measured d 50 of calcium hydroxide particles are provided in table 2.
  • Three samples of tri-calcium aluminate are prepared from 200 ml of the synthetic Bayer process liquor as prepared above and from an appropriate amount of one of the three samples of milk of lime as prepared above such that the molar ratio of calcium to aluminum expressed in equivalent CaO to Al 2 0 3 is of 1 to 9.
  • 200 cm 3 of synthetic Bayer process liquor is heated to 80°C in a vessel preferably made of a high-strength, corrosion-resistant nickel chromium material, also known commercially as INCONEL ® .
  • the appropriated amount of the respective milk of lime is added in the vessel under agitation with a stirrer at 250 RPM.
  • the slurry reaches 95 °C, the slurry is allowed to react for 90 minutes at the same stirring rate.
  • the slurry is then cooled to 70 °C for filtration.
  • the figure 1 presents an image obtained by Scanning Electron Microscopy of the TCA particles obtained according to the process of invention. It can be seen that the TCA particles are formed of aggregated crystals of dimensions below 5 pm, and that those TCA particles are larger than 15 pm, as often required for effective operation of pressure static vertical leaf filters.
  • the d 50 of each of the tri-calcium aluminate samples are measured by granulometry laser diffraction in methanol without sonication.
  • the d 50 of the tri-calcium aluminate particles increases substantially linearly with the d 50 of the calcium hydroxide particles of the milk of lime utilized.
  • d 50 for the tri-calcium aluminate particles and the respective values of d 50 of the calcium hydroxide particles utilized for the preparation of those TCA particles are presented in table 2.
  • the amount of milk of lime utilized in the process of preparation of TCA particles is further included in table 2.
  • This example shows that by the process according to the present invention, it is possible to control the particle size distribution of the tri-calcium aluminate particles by adding a coarsening agent and then using calcium hydroxide particles of calibrated particle size distribution to obtain size-calibrated TCA
  • the content of sulfur was relatively low (smaller than to 0.04 % in weight of the quicklime).

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Ceramic Engineering (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)

Abstract

La présente invention concerne un procédé d'obtention de particules d'aluminate tricalcique (TCA) étalonnées en taille comprenant les étapes consistant à fournir une liqueur de procédé contenant de l'aluminate de sodium ; fournir une suspension de particules d'hydroxyde de calcium calibrées en taille ; mélanger ladite suspension sélectionnée de particules d'hydroxyde de calcium calibrées en taille avec ladite liqueur de procédé pour leur permettre de réagir pour obtenir lesdites particules d'aluminate tricalcique calibrées en taille.
EP19736758.4A 2018-07-11 2019-07-11 Procédé d'obtention de particules d'aluminate tricalcique calibrées en taille et utilisation de telles particules dans un procédé de raffinage d'alumine Pending EP3820820A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP18182967 2018-07-11
PCT/EP2019/068757 WO2020011952A1 (fr) 2018-07-11 2019-07-11 Procédé d'obtention de particules d'aluminate tricalcique calibrées en taille et utilisation de telles particules dans un procédé de raffinage d'alumine

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EP3820820A1 true EP3820820A1 (fr) 2021-05-19

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EP (1) EP3820820A1 (fr)
AU (1) AU2019300344B2 (fr)
BR (1) BR112020026329A2 (fr)
WO (1) WO2020011952A1 (fr)

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CN111871360A (zh) * 2020-07-15 2020-11-03 杭州科创有色金属研究有限公司 一种用于制备氧化铝生产中的助滤剂的方法和装置

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AUPQ889100A0 (en) 2000-07-20 2000-08-10 Worsley Alumina Pty Ltd Improved process for filter aid production in alumina refineries
US7326400B2 (en) * 2005-08-11 2008-02-05 Chemical Lime Company Treatment of high sulfate containing quicklime
BE1021522B1 (fr) * 2012-09-12 2015-12-07 S.A. Lhoist Recherche Et Developpement Composition de lait de chaux de grande finesse
WO2017152960A1 (fr) * 2016-03-08 2017-09-14 S.A. Lhoist Recherche Et Developpement Procédé de fabrication d'un lait de chaux éteinte de grande finesse et lait de chaux de grande finesse obtenu par ce procédé avec de l'eau de traitement

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AU2019300344B2 (en) 2025-03-27
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