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WO2019074444A1 - Procédé de traitement de flux de déchets contenant des résidus de bauxite - Google Patents

Procédé de traitement de flux de déchets contenant des résidus de bauxite Download PDF

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Publication number
WO2019074444A1
WO2019074444A1 PCT/SG2018/050511 SG2018050511W WO2019074444A1 WO 2019074444 A1 WO2019074444 A1 WO 2019074444A1 SG 2018050511 W SG2018050511 W SG 2018050511W WO 2019074444 A1 WO2019074444 A1 WO 2019074444A1
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Prior art keywords
hydroxide
tailings
aluminum
solution
alkali metal
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PCT/SG2018/050511
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English (en)
Inventor
Charles Dean JAQUAYS
John Franklin SMALL
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Ecologistics Pte Ltd
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Ecologistics Pte Ltd
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Publication of WO2019074444A1 publication Critical patent/WO2019074444A1/fr
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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
    • C01F11/00—Compounds of calcium, strontium, or barium
    • C01F11/18—Carbonates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D1/00—Oxides or hydroxides of sodium, potassium or alkali metals in general
    • C01D1/04—Hydroxides
    • C01D1/20—Preparation by reacting oxides or hydroxides with alkali metal salts
    • C01D1/22—Preparation by reacting oxides or hydroxides with alkali metal salts with carbonates or bicarbonates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D7/00—Carbonates of sodium, potassium or alkali metals in general
    • 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
    • C01F11/04—Oxides or hydroxides by thermal decomposition
    • C01F11/06—Oxides or hydroxides by thermal decomposition of carbonates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F7/00—Compounds of aluminium
    • C01F7/02—Aluminium oxide; Aluminium hydroxide; Aluminates
    • C01F7/04—Preparation of alkali metal aluminates; Aluminium oxide or hydroxide therefrom
    • C01F7/06—Preparation of alkali metal aluminates; Aluminium oxide or hydroxide therefrom by treating aluminous minerals or waste-like raw materials with alkali hydroxide, e.g. leaching of bauxite according to the Bayer process
    • C01F7/066—Treatment of the separated residue
    • 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
    • C01F7/141—Aluminium oxide or hydroxide from alkali metal aluminates from aqueous aluminate solutions by neutralisation with an acidic agent
    • C01F7/142—Aluminium oxide or hydroxide from alkali metal aluminates from aqueous aluminate solutions by neutralisation with an acidic agent with carbon dioxide
    • 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
    • C01F7/46—Purification of aluminium oxide, aluminium hydroxide or aluminates
    • 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
    • C04B14/00—Use of inorganic materials as fillers, e.g. pigments, for mortars, concrete or artificial stone; Treatment of inorganic materials specially adapted to enhance their filling properties in mortars, concrete or artificial stone
    • C04B14/02—Granular materials, e.g. microballoons
    • C04B14/26—Carbonates
    • C04B14/28—Carbonates of calcium
    • 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
    • C04B2/005—Lime, magnesia or dolomite obtained from an industrial by-product
    • 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
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/141—Feedstock

Definitions

  • the invention relates generally to a chemical process for utilizing bauxite tailings, and more specifically, to a process for treating waste streams containing bauxite tailings to recover alkali metal hydroxide(s) present as refined mineral values such as aluminum hydroxide.
  • the Bayer process is an industrial process for refining bauxite to produce alumina (aluminium oxide). Over 95% of the alumina produced globally is a product of the Bayer process. Bauxite, the ore of aluminium and starting material in the process, contains 30-60% aluminium oxide (AI2O3). The remainder is a mixture of silica, various iron oxides, and titanium dioxide. The aluminium oxide must be purified before it can be refined to aluminium metal.
  • bauxite ore is heated in a pressure vessel along with a sodium hydroxide solution.
  • the aluminum is penetrated as sodium aluminate in an extraction process.
  • the aluminum compounds in the bauxite can be present as gibbsite (AI(OH)s), boehmite (AIHO2) or diaspore (AIO(OH)).
  • gibbsite aluminium hydroxide
  • AIO(OH) diaspore
  • Bauxite tailings are a by-product in the production of alumina (aluminium oxide). For every ton of alumina produced, approximately 1 to 1 .5 tons of bauxite tailings/residue are also produced. The aluminum industry generates more than a hundred million tons of this waste per year. The tailings are both a source of pollution and a waste of a potentially valuable mineral resource.
  • a small amount of the sodium hydroxide used in the process remains with the tailings, causing the material to have a high pH/alkalinity (usually >12). The tailings have a high concentration of iron oxide which gives the product a characteristic red colour.
  • scientists in the aluminum industry have attempted to recycle the
  • the tailings are a major source of pollution. They are typically dumped into storage pounds where they gradually seep into water supplies or the ocean.
  • tailings were often discharged into rivers, estuaries, or the oceans via pipelines or barges. In some instances the residue was shipped out to sea in deep ocean trenches offshore. It was also common to pump the tailings into lagoons or ponds sometimes created in former bauxite mines or depleted quarries. In other operations, impoundments were constructed with dams, levees or valleys for long-term storage areas of the tailings.
  • tailings are thickened to a high density slurry (48-55% solids or higher), and then deposited in a way that it consolidates and dries.
  • the invention relates to a process for treating waste streams containing bauxite tailings to recover alkali metal hydroxide(s) and obtain them as refined mineral values such as aluminum hydroxide that will increase the efficiency of the Bayer process. The results are improved yields and efficiency. Further, the process yields an environmentally beneficial finished calcium carbonate product that can be incorporated into building materials and/or filtration media. Building materials such as bricks can be produced with enhanced properties. Filtration systems can have improved heavy metal and other contaminant uptake properties. The invention further relates to enhanced building materials containing tailing material treated in accordance with the process of the invention.
  • the invention includes a process for recovering aluminum oxide from a slurry containing bauxite tailings comprising the steps of (a) washing and/or rinsing the slurry with a basic solution, (b) removing a supernatant fluid from the slurry, (c) exposing the supernatant fluid to acidic gas, thereby lowering the pH of the solution to form an acidic salt and an alkali metal hydroxide, (d) extracting the alkali metal hydroxide and (f) filtering the extracted alkali metal hydroxide.
  • the acidic gas can be carbon dioxide; the acidic salt can be sodium bicarbonate; and the alkali metal hydroxide can be aluminum hydroxide.
  • the aluminum hydroxide can be recycled to an Aluminum refiner.
  • the invention also includes a process for recovering calcium carbonate from bauxite tailings comprising the steps of (a) adding water to bauxite tailings to form a slurry, (b) washing and/or rinsing the slurry with a basic solution, (c) removing a supernatant fluid from the slurry, (d) exposing the supernatant fluid to acidic gas, thereby lowering the pH of the solution to form an acidic salt and an alkali metal hydroxide, (e) allowing the alkali metal hydroxide to settle and then extracting the alkali metal hydroxide and (f) recovering calcium carbonate from the supernatant.
  • the acidic gas can be carbon dioxide; the acidic salt can be sodium bicarbonate; and the alkali metal hydroxide can be aluminum hydroxide.
  • the process can also include the step of the treating calcium carbonate for use in filtration media and/or treating the calcium carbonate to form a component of building material (e.g. a brick or cementitious material).
  • a component of building material e.g. a brick or cementitious material
  • a first aspect of the invention is a method of recovering aluminum and sodium hydroxide from bauxite tailings.
  • a second aspect of the invention is a method of converting bauxite tailings into useful industrial compounds.
  • a third aspect of the invention is a method of reducing the toxicity of bi-products of the Bayer process.
  • a fourth aspect of the invention is a method of isolating aluminum oxide from bauxite ore with zero effluent.
  • FIG. 1 is a flowchart that depicts the steps involved in the Bayer process.
  • FIG. 2 is a flowchart that depicts the steps involved in treating red mud according to one aspect of the invention.
  • FIG. 3 is a flowchart that depicts the processes used in a preferred method of treating red mud according to one aspect of the invention.
  • embodiment/aspect means that a particular feature, structure, or characteristic described in connection with the embodiment/aspect is included in at least one embodiment/aspect of the disclosure.
  • aluminum or "aluminium” refers to a chemical element with symbol Al and atomic number 12. It is the most widely used non-ferrous metal. Aluminum is the most widely used non-ferrous metal.
  • alumina is a chemical compound of aluminium and oxygen with the chemical formula Al 2 0 3 . It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium(lll) oxide.
  • bauxite refers to a rock formed from a laterite soil that has been severely leached of silica and other soluble materials in a wet tropical or subtropical climate. It is the primary ore of aluminum and is mixture of hydrated aluminium oxides and compounds of other elements such as iron.
  • the term "bauxite tailings” refers to a by-product in the production of alumina (aluminium oxide) by the Bayer Process.
  • the tailings have a high concentration of iron oxide which gives the product a characteristic red color.
  • a small residual amount of the sodium hydroxide remains with the tailings, causing the material to have a high pH/alkalinity.
  • furnace refers to a steel cylinder that rotates inside a heated furnace and performs indirect high-temperature processing (550-1 150 °C, or 1000-2100 °F) within a controlled atmosphere.
  • austicize refers to a process of making a solution caustic, and more particularly, to converting (alkaline carbonate) into a hydroxide by the use of lime.
  • HasAIFe cryolite
  • CasAIFe calcium fluoride
  • the liquid aluminum metal sinks to the bottom of the solution and is tapped off, and usually cast into large blocks called aluminum billets for further processing.
  • Carbon dioxide is produced at the carbon anode: 2 O 2" + C ⁇ CO2 + 4 e-
  • the term "polishing” refers to a process that removes small (usually microscopic) particulate material, or removes very low concentrations of dissolved material from a liquid or water.
  • the term "sodium aluminate” refers to an important commercial inorganic chemical. It works as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as NaAIO2 or NaAI(OH) 4 (hydrated).
  • sodium hydroxide also known as lye and caustic soda, refers to an inorganic compound with formula NaOH. It is a white solid ionic compound consisting of sodium cations Na+ and hydroxide anions OH-.
  • red mud refers to a toxic byproduct of the industrial process that refines bauxite, raw aluminum ore, into aluminum oxide, or alumina.
  • the main constituents of the residue after the extraction of the aluminium component are unreacted metallic oxides. The percentage of these oxides produced by a particular alumina refinery will depend on the quality and nature of the bauxite ore and the extraction conditions.
  • thixotropy refers to a time-dependent shear thinning property. Certain gels or fluids that are thick, or viscous, under static conditions will flow (become thin, less viscous) over time when shaken, agitated, sheared or otherwise stressed (time dependent viscosity).
  • the invention includes a process for the conversion of a mining industry's operation to become fully sustainable, with zero effluent, while at the same time, creating the opportunity to remediate other industrial mining sites to make those water supplies that were once rendered toxic, suitable for repopulation of the affected bio- system and put back on the path to natural rehabilitation.
  • FIG. 1 depicts the steps involved in the Bayer process.
  • Bauxite ore 105 is a mixture of hydrated aluminium oxides and compounds of other elements such as iron.
  • the bauxite ore is heated in a pressure vessel 110 with a sodium hydroxide solution 105.
  • the soluble part of the bauxite ore is dissolved using sodium hydroxide under conditions of high temperature and pressure.
  • the insoluble part of the bauxite (the residue) is removed, giving rise to a solution of sodium aluminate, which is then seeded and allowed to cool and aluminium hydroxide precipitates from the solution.
  • Sodium aluminate (NaAI02) is soluble in strongly alkaline water and the other components of the ore are not. Sometimes lime is added to precipitate the silica as calcium silicate. The solution is clarified by filtering off the solid impurities, commonly with a rotary sand trap and with the aid of a flocculant such as starch, to remove the fine particles.
  • the undissolved waste after the aluminium compounds are extracted (i.e. red mud) 120 contains iron oxides, silica, calcia, titania and some unreacted alumina
  • the aluminum is penetrated as sodium aluminate in an extraction process. After separation of the residue by filtering, gibbsite (aluminium hydroxide) is precipitated when the liquid is cooled and then seeded with fine-grained aluminium hydroxide, (AI(OH)s) 125.
  • gibbsite aluminium hydroxide
  • the aluminum hydroxide seeds stimulate the precipitation/crystallization of solid aluminum hydroxide crystals 130.
  • the aluminum hydroxide settles at the bottom of the tank and is removed.
  • the aluminum hydroxide is washed 135 of any remaining caustic soda and heated to remove excess water 140.
  • alumina aluminum oxide
  • the process converts the aluminium oxide in the ore to soluble sodium aluminate (NaAI02). This treatment also dissolves silica, but the other components of bauxite do not dissolve.
  • the solution is clarified by filtering off the solid impurities, commonly with a rotary sand trap and with the aid of a flocculant such as starch, to remove the fine particles.
  • the undissolved waste after the aluminium compounds are extracted i.e. bauxite tailings
  • a process for treating waste streams containing bauxite tailings to render them suitable for incorporation into useful materials, such as bricks and filtration media that are formed using classic concrete formulations or sintering to form ceramic materials.
  • the invention further provides an improved building material in which bauxite tailings which have been treated with an alkaline solution to remove previously fugitive alkali metal hydroxides currently lost by the Bayer-based alumina refining industry, and rendering the resultant tailings environmentally benign and concurrently creating a cost and performance enhancing adjunct for building materials and filtration media.
  • This new by-product can then be combined with concrete based materials and cured to provide superior construction materials.
  • the treated tailings can also be incorporated into ceramic formulations that result in cost and performance enhancements of ceramic building materials and even be utilized as a filtration media with unparalleled sorbent characteristics.
  • water and all or a portion of the alkali metal salts native to classic Bayer processes are removed.
  • the tailings while they do contain a small amount of "free sodium hydroxide," the reality is that, in the Bayer process, the aluminum present in the ore body has been leached out using concentrated caustic soda (sodium hydroxide) which forms aqueous sodium aluminate NaAI(OH) 4 when contacted with the aluminum rich bauxite ore.
  • Sodium aluminate only remains stable at high pH levels.
  • the refiners usually recover some of that liquid as that represents the means by which the aluminum values are separated from the solid remnant of the ore.
  • the liquid is separated from the ore by filtration, or sedimentation and then is allowed to cool in its supersaturated condition, often times "seeded” with some nucleation material (aluminum hydroxide) harvested from previous batches to stimulate and accelerate the precipitation of aluminum hydroxide from the solution.
  • nucleation material aluminum hydroxide
  • the aluminum hydroxide is allowed to settle, is drawn off the bottom of the settling tank and is then filtered and washed in preparation to be further processed into aluminum oxide using thermal decomposition by the refiner.
  • the depleted bauxite is pumped out to catchment ponds where any surplus liquid is drawn off the surface and recycled back into the process. The loss of value occurs when one considers the volume of liquid that is required to make one ton of dry bauxite fluid enough to pump.
  • a 50% humidity content in bauxite tailings represents a dry friable solid that is neither plastic nor fluid.
  • the typical humidity content of concentrated depleted bauxite tailings that have had days or weeks to settle in containment ponds is between 60% - 70%. This means that for every tonne of depleted bauxite sent to the containment pond, there are about three tonnes of liquid trapped in those tailings that can hold as much as 18% by weight of sodium aluminate, plus some "free" unbound sodium hydroxide.
  • the invention takes advantage of a little-known attribute of sodium hydroxide, that being, "a little bit goes a long way" and the fact that sodium aluminate will spontaneously "break” during the rinsing process of a slurry if plain water is used and the pH of the slurry being washed falls below nine.
  • the sodium aluminate is still comingled with the tailings slurry, (which it invariably is) the aluminum hydroxide will precipitate out of solution as a solid and will form a colloidal suspension.
  • the slurry will spontaneously transition from a fluid slurry to a thixotropic gel resembling a red hydroscopic and plastic clay. At this point it becomes very difficult to remove those three parts liquid from the one part of tailings, the minimum amount needed to render the suspension, fluid enough to pump and or filter, further confounding the dewatering process.
  • the new process displaces the basic sodium aluminate using a displacement solution that has been raised to a pH of at least 10 by adding about 100 PPM of sodium hydroxide to the rinse water solution.
  • displacement volumes are used to wash the tailings using a filtration means that allows for a rinsing step to be incorporated in the dewatering process.
  • the sodium aluminate is prevented from "breaking" while “in situ” with the ore, so that the aluminum, while still in its soluble state during the filtration and rinsing process, is simply displaced by the rinsing solution, which allows for the recovery of those values from the displaced liquid (once it has been filtered) and recovery of those values at a high degree of purity (99.9%) and at a very high rate of recovery (99.9%).
  • the aluminum hydroxide will immediately begin to form crystals that will precipitate out of the solution, and if left to settle, will accumulate at the bottom of the reactor vessel in which it is contained.
  • the aluminum hydroxide can then be drawn off the bottom of the vessel, filtered and rinsed with distilled water to yield 99.9% pure aluminum hydroxide.
  • FIG. 2 depicts the steps involved in treating red mud according one aspect of the invention.
  • the process can be used to convert red mud 120 to obtain 99.9% pure Aluminum Hydroxide (AI(OH3)) 180.
  • the bauxite tailings (red mud 120) are delivered to the process usually suspended in (roughly) three to four parts of water by an alumina refinery. Slurry is delivered directly to a filtration means that allows for a washing or rinsing cycle to occur during the filtration and dewatering process to produce a filter cake. This step is depicted at 150.
  • the filtration means may be one or more of a pressure filter, polishing filter, red mud filter or any combination thereof.
  • the filter cake is washed with an aqueous solution of water and sodium hydroxide with a pH of 10-12 using a volume of the solution sufficient to displace the resident liquor that remains entrained within the dewatered slurry 155.
  • the filter cake should be simultaneously dewatered and rinsed. Once the filter cake has been sufficiently depleted of its hydroxide(s) rich liquid, the filtrate cake is rejected from the dewatering/filtration system 200 and termed as depleted red mud.
  • the hydroxide(s) rich liquid or supernatant fluid is then re-filtered using a microfiltration system to remove any microparticles of the "red mud" from the solution (not shown).
  • the fluid which is now rich with sodium aluminate is sent to a contacting platform. In the platform, the fluid is exposed to CO2 160 that, on contact with the free water in the solution, will form carbonic acid 165. As the acid is formed it lowers the pH of the solution, and ultimately, selectively forms sodium bicarbonate and aluminum hydroxide.
  • the aluminum hydroxide is insoluble in water and so precipitates out of solution 170.
  • the mixture is transferred to a conical settling tank where the aluminum hydroxide is allowed to settle to bottom of the tank, is extracted as a suspended slurry and sent to a filtration means that allows the filtrate to be rinsed so it is free from sodium bicarbonate impurities 180.
  • the rinsed dry cake of 99.9% aluminum hydroxide can then be recycled back to the refiner so that it can be calcined along with refiner's "hydrate” to supplement their production of aluminum oxide "alumina” 185.
  • the remaining sodium bicarbonate solution 190 can then be "causticized” by using classic causticizing means typically found on-site at Bayer-based alumina refineries.
  • the by-products of this reaction are sodium hydroxide and calcium carbonate 195.
  • the calcium carbonate is also insoluble in water and so precipitates out of solution. That mixture can once again be sent to a conical settling tank where the calcium carbonate is allowed to settle to the bottom of the tank, where it is extracted as a slurry, sent to a filtration means that also provides rinsing capabilities to provide a 99.9% pure filter cake of calcium carbonate that is then used for decomposition back into calcium oxide and gaseous carbon dioxide that get recycled back into the carbonization and caustization process respectively.
  • the filtrate, a dilute solution of sodium hydroxide can then be recycled back to the refiner. It can be used at the front end of the process where it is added with the raw material to reach the required pH required during the preliminary grinding and digestion process.
  • the calcium ion exchanges places with the sodium ion to form calcium carbonate.
  • the hydroxyl ion exchanges places from the calcium ion to the sodium ion to form sodium hydroxide.
  • the calcium carbonate is relatively insoluble and so therefore precipitates out of the solution to settle to the bottom of the reactor vessel. That material can then be drawn off the bottom of the vessel, washed with clean (or distilled water) to yield up to 99.9% pure precipitated calcium carbonate.
  • the material can be dried, bagged and sold as an industrial chemical that has a myriad of applications. In the alternative, it can be recycled back into the process by thermally decomposing the calcium carbonate, back into two of the primary reagents used in the process (calcium oxide & carbon dioxide) to close the loop of the process.
  • the solution of sodium hydroxide that results from the "causticizing" step will also be of high purity ( ⁇ 99.9%) and can be recycled back to the refiner. This allows the recovery of the fugitive component of the refiner's process flow and radically reduces the recurring cost of replacing the lost sodium hydroxide that is at the root of the safe bauxite tailings storage and recycling challenge that faces the industry.
  • tailings having now been effectively “scrubbed” of the valuable remnants of caustic and alumina. They also now have a comparatively neutral at a pH (-10) which is low enough to be used "as is” for some recycling applications like building materials and acidic water run-off remediation from other mining efforts that use acids for the enrichment of their ores.
  • the pH can be lowered further to 7, if an application requires it, by simple titration with any other mineral acid or additional carbonic acid.
  • the finished modified tailings product has enhanced efflorescence resistance that is superior to the resistance levels of concrete products not incorporating untreated bauxite tailings as well as those that do.
  • FIG. 3 further depicts the steps involved in treating red mud according one aspect of the invention.
  • Red mud waste material 120 is obtained from a final settling tank by any conventional refinery plant for use in the process described herein ("the process"). Transport water is added to the red mud waste to form a red mud suspension for the purpose of transport to the process, via a pipeline for example.
  • the red mud waste material 120 is obtained from a final settling tank by any conventional refinery plant for use in the process described herein ("the process"). Transport water is added to the red mud waste to form a red mud suspension for the purpose of transport to the process, via a pipeline for example.
  • the red mud waste material 120 is obtained from a final settling tank by any conventional refinery plant for use in the process described herein ("the process"). Transport water is added to the red mud waste to form a red mud suspension for the purpose of transport to the process, via a pipeline for example.
  • the red mud mud waste material 120 is obtained from a final settling tank by any conventional refinery plant for use in the process described herein ("the process"). Transport water is added to
  • suspension is composed of approximately 40% solids, which contains Na, Al, and O, plus Fe and other leftover components. Filtration - Step 2
  • the red mud suspension is subjected to pressure filtration 205, potentially through the use of a hyperbaric mechanism.
  • the filtration further includes a washing step that utilizes a mild caustic solution of water and sodium hydroxide to displace the sodium aluminate that is in suspension. This step results in the red mud solids being separated from the liquid suspension components. The solids are separated out as a dry waste component referred to as depleted red mud 200.
  • the liquid (supernatant) sodium aluminate solution is filtered and is then exposed to carbon dioxide within a contacting platform, such as a carbonation reactor where the carbon dioxide, once exposed to the free water, forms carbonic acid 210.
  • the carbonic acid then changes the pH of the solution and causes the sodium aluminate to react with the acid to form sodium bicarbonate and aluminum hydroxide.
  • the aluminum hydroxide which is not water soluble, precipitates out as a solid.
  • the aluminum hydroxide solids are sent to a filter press for filtration 215 to squeeze all the liquids out of the aluminum hydroxide, which are also rinsed with distilled water, for the sake of providing a pure product of aluminum hydroxide.
  • the rinsing water having a remnant of sodium bicarbonate forms a liquid (supernatant) sodium bicarbonate solution.
  • the liquid (supernatant) sodium bicarbonate solution is then subjected to caustization 220.
  • the supernatant solution is exposed to a suspended solution of calcium hydroxide.
  • the calcium hydroxide with the sodium bicarbonate produce a metathesis reaction (i.e. dual ion exchange reaction) whereby the calcium ion bonds to the carbonate ion, and the hydroxyl ion bonds to the sodium ion.
  • a calcium carbonate forms that is insoluble and precipitates out of the mixed solution, to leave an aqueous solution of sodium hydroxide 240.
  • the calcium carbonate 235 is filtered and washed 230 with distilled water for the sake of purifying the calcium carbonate product.
  • the calcium carbonate product is set aside and reserved to be recycled back into the process by thermal decomposition in a calciner to form calcium oxide and carbon dioxide to perpetuate the process at the appropriate stage and step.
  • the dilute sodium hydroxide is recycled back to the host facility to be admixed to the refiner's primary grinding, which is the initial digestion step in the alumina refining process.

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  • Ceramic Engineering (AREA)
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Abstract

L'invention apporte une solution aux problèmes rencontrés par les boues rouges classiques produites par le procédé Bayer. L'invention comprend un procédé de traitement de flux de déchets contenant des résidus de bauxite pour récupérer de l'(des) hydroxyde(s) de métal alcalin présent(s), pour les obtenir en tant que minéraux raffinés tels que l'hydroxyde de sodium et l'hydroxyde d'aluminium qui augmenteront l'efficacité du procédé Bayer. En outre, le procédé conduit à un produit de carbonate de calcium bénéfique pour l'environnement qui peut être incorporé dans des matériaux de construction ou des milieux de filtration.
PCT/SG2018/050511 2017-10-11 2018-10-09 Procédé de traitement de flux de déchets contenant des résidus de bauxite Ceased WO2019074444A1 (fr)

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CN110482821A (zh) * 2019-08-13 2019-11-22 昆明理工大学 一种含硫尾矿对赤泥的循环水式脱碱系统及脱碱方法
CN116460981A (zh) * 2023-06-06 2023-07-21 安徽建筑大学 一种高流动性饰面超高性能混凝土制备工艺及其设备
EP4261299A1 (fr) * 2022-04-12 2023-10-18 Dubai Aluminium PJSC Procédé de traitement de résidus de bauxite issus du processus bayer et produit minéral obtenu par ledit procédé
CN116924740A (zh) * 2023-07-18 2023-10-24 济南大学 一种赤泥-石墨尾矿道路基层材料及其制备方法和应用
WO2025106538A1 (fr) * 2023-11-13 2025-05-22 Aeon Blue Technologies, Inc. Capture de carbone et production de dioxyde de carbone

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US2398425A (en) * 1943-04-27 1946-04-16 Elnathan H Steinman Process for treating alunite ores and the like
GB941900A (en) * 1961-08-21 1963-11-13 Kaiser Aluminium Chem Corp Improvements in or relating to calcium carbonate
US20090311154A1 (en) * 2003-06-16 2009-12-17 Urquhart-Dykes & Lord Llp Extraction process for reactive metal oxides
CN102757060A (zh) * 2011-09-16 2012-10-31 东北大学 一种消纳拜耳法赤泥的方法
CN105197973A (zh) * 2015-09-09 2015-12-30 洛阳国兴矿业科技有限公司 利用低品铝土矿制取氧化铝的方法
CN106044813A (zh) * 2016-05-26 2016-10-26 宜宾学院 一种粉煤灰制备活性氧化铝的清洁化工艺

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US2398425A (en) * 1943-04-27 1946-04-16 Elnathan H Steinman Process for treating alunite ores and the like
GB941900A (en) * 1961-08-21 1963-11-13 Kaiser Aluminium Chem Corp Improvements in or relating to calcium carbonate
US20090311154A1 (en) * 2003-06-16 2009-12-17 Urquhart-Dykes & Lord Llp Extraction process for reactive metal oxides
CN102757060A (zh) * 2011-09-16 2012-10-31 东北大学 一种消纳拜耳法赤泥的方法
CN105197973A (zh) * 2015-09-09 2015-12-30 洛阳国兴矿业科技有限公司 利用低品铝土矿制取氧化铝的方法
CN106044813A (zh) * 2016-05-26 2016-10-26 宜宾学院 一种粉煤灰制备活性氧化铝的清洁化工艺

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110482821A (zh) * 2019-08-13 2019-11-22 昆明理工大学 一种含硫尾矿对赤泥的循环水式脱碱系统及脱碱方法
EP4261299A1 (fr) * 2022-04-12 2023-10-18 Dubai Aluminium PJSC Procédé de traitement de résidus de bauxite issus du processus bayer et produit minéral obtenu par ledit procédé
CN116460981A (zh) * 2023-06-06 2023-07-21 安徽建筑大学 一种高流动性饰面超高性能混凝土制备工艺及其设备
CN116460981B (zh) * 2023-06-06 2024-06-07 安徽建筑大学 一种高流动性饰面超高性能混凝土制备工艺及其设备
CN116924740A (zh) * 2023-07-18 2023-10-24 济南大学 一种赤泥-石墨尾矿道路基层材料及其制备方法和应用
WO2025106538A1 (fr) * 2023-11-13 2025-05-22 Aeon Blue Technologies, Inc. Capture de carbone et production de dioxyde de carbone

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