Abstract: In one aspect, a dual tunnel magnetoresistance (TMR) element structure includes a first TMR element and a second TMR element. The TMR element structure also includes a conducting layer that is disposed between the first TMR element and the second TMR element and is in direct contact with the first TMR element and the second TMR element.

Abstract: A process is disclosed for using an iron oxide and alumina catalyst with no more than more than about 55 wt % of the alumina in the diaspore phase or in the alpha phase in SHC. Alpha alumina is less effective catalyst component for slurry hydrocracking in terms of TIOR conversion. Drying procedures should avoid more than about 51 wt % of the alumina change to the alpha phase. The SHC catalyst is for converting heavy hydrocarbon feed into lighter hydrocarbon products.

Abstract: A method for using an extended-life settable composition is disclosed. The method includes providing an extended-life settable composition comprising red mud, calcium hydroxide, water, and a cement set retarder. The method further includes activating the extended-life settable composition. The method additionally includes introducing the extended-life settable composition into a subterranean formation and allowing the extended-life settable composition to set in the subterranean formation.

Abstract: A process for producing alumina trihydrate includes a digestion step, a separation step, and a precipitation step the separation step including: b1) pretreating a slurry from the digestion step by adding a flocculant to said slurry and mixing the flocculant and the slurry, b2) settling the resulting flocculated slurry in a gravity settler vessel, b3) determining a measured value representative of the concentration of solid particles in the resulting clarified liquor, b4) comparing the measured value with a predetermined threshold, b5) feeding said clarified liquor directly to the precipitation step, while the measured value is less than said predetermined threshold, and b6) redirecting said clarified liquor to the pre-treatment step b1), when the measured value is more than said predetermined threshold. An installation may be configured for operating said process.

Abstract: The present invention relates to a method for preparing high-purity aluminum, the method comprising: a mother liquor preparing step for preparing a mother liquor by dissolving and aging ordinary aluminum hydroxide; a refining step for adding pulp to absorb impurities from the prepared mother liquor after the mother liquor preparing step; and an obtaining step for obtaining high-purity alumina by adding a seed into the mother liquor and precipitating a precipitate, and filtering, washing, and recrystallizing the precipitate, and calcining the precipitate. Thus, the present invention enables an environmentally-friendly and low-cost preparation of high-purity alumina.

Abstract: A process for neutralization is provided which can maintain a high solid content of a bauxite dissolution residual substance slurry even after a neutralization treatment is completed and the stabilize pH within a short time of the neutralization treatment. Such a process for neutralizing a bauxite dissolution residual substance containing a desiliconizing product which is generated in the production process of aluminum hydroxide using Bayer process, includes: mixing a bauxite dissolution residual substance or a bauxite dissolution residual substance slurry with sulfuric acid in an amount ranging from 0.6 to 1.2 equivalence to the total amount of sodium contained in the bauxite dissolution residual substance or a bauxite dissolution residual substance slurry, such that the solid content after mixing becomes 400 to 700 g/l to gelate the mixture, and thereafter obtaining a bauxite dissolution residual substance neutralized slurry.

Abstract: The present disclosure is directed to a method of improving the transfer of slurry in a Bayer process through the addition of one or more chemical species to a Bayer process, wherein said chemical species is selected from the group consisting of: non-ionic surfactants, polyglycols, polyglycol ethers, anionic surfactants, anionic polymers, and a combination thereof. The present invention is also directed to a method of deaerating a slurry in a Bayer process through the addition of an effective amount of one or more chemical species to a Bayer process, wherein said chemical species is selected from the group consisting of: non-ionic surfactants, polyglycols, polyglycol ethers, anionic surfactants, anionic polymers, and a combination thereof.

Abstract: Process for manufacturing alumina trihydrate by alkaline attack of bauxite, following the general steps of the Bayer process, and during which, after settling and before decomposition, the aluminate liquor undergoes a filtration, known as security filtration, so that at the end of the filtration it contains less than 10 mg/l of insoluble particles, characterized in that, during said security filtration, a filtration device is used that comprises a zone in which the liquor is subjected, after passing through said filtration media, to a pressure greater than 2 bar, preferably greater than 3 bar. Preferably, this device also comprises a zone in which the liquor is subjected, before passing through the filtration media, to a pressure greater than 5 bar, preferably greater than 6, typically in the vicinity of 7 bar. In this way, the aluminate liquor can be kept at a high temperature during the security filtration, typically greater than 130° C., preferably greater than 140° C.

Abstract: The invention provides a method of inhibiting the accumulation of DSP scale in the liquor circuit of Bayer process equipment. The method includes adding one or more particular silane based small molecules to the liquor fluid circuit. These scale inhibitors reduce DSP scale formation and thereby increase fluid throughput, increase the amount of time Bayer process equipment can be operational and reduce the need for expensive and dangerous acid washes of Bayer process equipment. As a result, the invention provides a significant reduction in the total cost of operating a Bayer process.

Abstract: The invention provides methods and compositions for improving the production of alumina trihydrate. The invention involves adding one or more cross-linked polysaccharides to a filter used to separate solids from liquid in the Bayer process. The one or more polysaccharides can be a cross-linked polysaccharide (such as cross-linked dextran or cross-linked dihydroxypropyl cellulose). The cross-linked polysaccharides can impart a number of advantages including greater flow rate and lower residual moisture in the resulting cake.

Abstract: Discolored organic compounds (DOC) may be extracted from a medium using a sorbent composition derived by sulfidation of red mud, which contains hydrated ferric oxides derived from the Bayer processing of bauxitic ores. In some aspects, the sorbent composition is slurried with the medium. In other aspects, the sorbent composition is formed into pellets or the like, which are contacted with the medium. The red mud (along with adsorbed contaminants) is then separated from the water using any suitable technique, such as filtration, sedimentation, or centrifugation.

Abstract: Toxic substances such as heavy metals are extracted from a medium using a sorbent composition. The sorbent composition is derived by sulfidation of red mud, which contains hydrated ferric oxides derived from the Bayer processing of bauxite ores. Exemplary sulfidizing compounds are H2S, Na2S, K2S, (NH4)2S, and CaSx. The sulfur content typically is from about 0.2 to about 10% above the residual sulfur in the red mud. Sulfidized red mud is an improved sorbent compared to red mud for most of the heavy metals tested (Hg, Cr, Pb, Cu, Zn, Cd, Se, Th, and U). Unlike red mud, sulfidized red mud does not leach naturally contained metals. Sulfidized red mud also prevents leaching of metals when mixed with red mud. Mixtures of sulfidized red mud and red mud are more effective for sorbing other ions, such as As, Co, Mn, and Sr, than sulfidized red mud alone.

Abstract: The invention provides methods and compositions for improving the production of alumina hydrate. The invention involves adding one or more polysaccharides to liquor or slurry in the fluid circuit of the production process. The one or more polysaccharides can be a cross-linked polysaccharide (such as cross-linked dextran or cross-linked dihydroxypropyl cellulose). The various polysaccharides can impart a number of advantages including at least some of: greater flocculation effectiveness, increasing the maximum effective dosage, faster settling rate. The production process can be a Bayer process.

Abstract: A method and composition for flocculation and separation of suspended solids from an industrial process stream containing suspended solids is provided. The method includes the steps of adding to the stream a water-in-oil-in-water emulsion polymer in an amount effective to flocculate the suspended solids and separating the flocculated solids therefrom. The composition is a water-in-oil-in-water emulsion of a water-soluble polymer in which the continuous phase is an aqueous solution of a water-soluble salt.

Abstract: Materials and methods are provided whereby polymers with least 0.5 mole % of the pendant group or end group containing —Si(OR?)3 are used to control aluminosilicate scaling in an industrial process having an alkaline process stream such as a pulping mill process stream or a high level nuclear waste processing plant. When materials of the present invention are added to the alkaline process stream, they reduce and even completely prevent formation of aluminosilicate scale on equipment surfaces such as evaporator walls and heating surfaces. The present materials are effective at treatment concentrations that make them economically practical.

Abstract: A process in which material comprising an aqueous liquid with dispersed particulate solids is transferred as a fluid to a deposition area, then allowed to stand and rigidify, and in which rigidification is improved while retaining the fluidity of the material during transfer, by combining with the material an effective rigidifying amount of aqueous solution of a water-soluble polymer. The process is particularly suitable for the treatment of the tailings underflow resulting from a mineral processing operation and the co-disposal of fine and coarse tailings fractions. In addition, liquor released during the rigidification step is of high clarity.

Abstract: A process in which a suspension comprising dispersed particulate material in an aqueous medium is transferred as a fluid to a deposition area, then allowed to stand and rigidify, and in which rigidification is improved whilst retaining the fluidity of the suspension during transfer, by combining with the suspension during transfer a rigidifying amount of a treatment system which comprises i) a water-soluble synthetic polymer and ii) a water-soluble natural or seminatural polymer. Improved rigidification can be achieved, including dose efficiency especially in regard to the amount of synthetic polymer required. In addition improvements in the clarity of liquor released from the suspension can be achieved.

Abstract: The invention relates to a method for transesterification of at least one component comprising at least one ester group with at least one component comprising at least one hydroxyl group, wherein the red mud produced in the Bayer process used for producing aluminum is added to the method as a reaction-promoting component. The invention also relates to the use of carboxylic acid salts produced during the transesterification method as plant treating agents and as detergents in cleaning and washing agents. The invention also relates to the use of dealkalized red mud obtained by means of the method according to the invention as the iron-contributing component of an iron fertilizer which can be used in particular in agriculture and to which limestone can also be added.

Abstract: The invention relates to a process for alkaline hydrolysis of carboxylic acid derivatives, especially carboxylic esters, to carboxylic acids, wherein, for the alkaline hydrolysis of the carboxylic acid derivatives, red mud which is produced by the Bayer process used for aluminum production is used as a reaction-promoting component, especially as a hydroxide ion source.

Abstract: A Bayer process is disclosed. The Bayer process includes a step of treating any one or more of: (a) Bayer liquor or liquors produced in the process, (b) precipitated aluminium trihydrate particles produced in the process, and (c) other solids added to or produced in the process, with ultrasonic energy and destroying organics in the liquor or liquors, on the precipitated aluminium trihydrate particles, and on the other solids.

Abstract: A process for the production of alumina trihydrate by alkaline digestion of bauxite using the Bayer process in which aluminate liquor and insoluble residues are separated using a solid/liquid separation device (E; W2; DC) characterised in that the said slurry (21a; 41; 230?) is at least partially passed through a hydrocyclone (H1; H21; H22; H3) to improve and accelerate the separation of the sodium aluminate liquor from the insoluble residues in the slurry (21a; 41; 230?) containing the said liquor and the said residues and that supplies or is derived from the said liquid-solid separation device. In a first embodiment, at least one hydrocyclone is used at the upstream side of the settler-thickener, as clarifier of the pregnant liquor. In a second embodiment, at least one hydrocyclone is used as a thickener of insoluble residue mud. In a third embodiment, a hydrocyclone is used in combination with the causticisation settler.

Abstract: The present invention relates ways to increase the output of a high quality product from the aluminum hydroxide recovery processes such as the Bayer process. The invention is a method of increasing the size of precipitated aluminum hydroxide while not reducing the total production amounts. The invention relates to the use of a crystal growth modifier compositions added to the precipitation liquor to increase the particle size distribution of the precipitated alumina trihydrate.

Abstract: A Bayer process comprises grinding and then digestion of bauxite by bringing it into contact with a sodium aluminate liquor. Digestion consists of forming a slurry that is then treated to separate insoluble residues from the sodium aluminate liquor. The liquor is then crystallized and recycled back to green liquor after having been separated from the alumina trihydrate precipitated during crystallization. The process comprises a predesilication treatment during which the ground bauxite, before digestion, is brought into contact with an aqueous sodic solution that has a content of carbonates, sulphates and possibly chlorides which, expressed as a percentage related to the caustic concentration, has less than half of the corresponding impurities content of the spent liquor. Preferably, the pure caustic soda used to compensate for caustic soda losses in the Bayer circuit, previously injected just after evaporation, is now added in the aqueous sodic solution for the predesilication treatment.

Abstract: A process for removing anionic impurities from a caustic aluminate solution having aqueous tetrahydroxy aluminate ions is described. A caustic aluminate solution is obtained such that anionic impurities are partially or substantially substituted into tetrahydroxy aluminate ions to form substituted aluminate ions. A suitable calcium compound, such as quicklime, is reacted in a conventional slaker (10) with a slaking solution, for example water, and stored in an agitated storage tank (12). The resulting slurry is pumped to a reaction vessel (14) where it is reacted with a caustic aluminate solution under appropriate conditions such that the calcium compound is converted into tricalcium aluminate (TCA) precipitate. Upon reaction substituted aluminate ions are substantially incorporated within the TCA precipitate to form a substituted TCA precipitate enabling the anionic impurities to be removed from the solution via the substituted TCA precipitate for disposal or recovery.

Abstract: A process for recovering alumina values from a first liquor having an initial concentration of aluminate ions and hydroxyl ions in solution is described. The first liquor is treated with a hydroxide of a metal other than aluminium to form an aluminium-bearing layered double hydroxide and produce a treated stream of first liquor, the treated stream of first liquor having a final concentration of aluminate ions less than the initial concentration of aluminate ions. The aluminium-bearing layered double hydroxide is separated from the treated stream of first liquor. Thereafter the clarified treated stream of first liquor is returned to a first location within an alumina refinery. The separated aluminium-bearing layered double hydroxide is contacted with a solution containing carbonate ions to form a slurry comprising an insoluble salt of the metal other than aluminium and a second liquor comprising aluminate ions released from the aluminium-bearing layered double hydroxide.

Abstract: Process for the treatment of bauxite (10) by alkaline digestion, typically using the Bayer process in order to obtain alumina hydrate, characterized in that ground bauxite (11, 15) is added directly into an alkaline solution (21a) that is drawn off and that will be reinserted into the Bayer aluminate liquor circuit (20), the said alkaline solution (21a) being heated at a temperature such that after the said ground bauxite (11, 15) and the said alkaline solution have been brought into contact, the temperature of the slurry resulting from this mix is greater than a temperature close to the boiling temperature at atmospheric pressure, in other words typically greater than 95° C. and preferably greater than or equal to the boiling temperature at atmospheric pressure.

Abstract: The invention provides methods for purifying caustic feed streams using membranes that comprise polysulfonamide matrices.

Abstract: The inventive method for producing refractory high-strength spherical granules consists in separately presintering kaolin and bauxite in a rotational furnace, jointly sintering said components in order to produce a charging material, granulating, drying and screening said charging material, sintering said granules in the rotational furnace and screening the sintered granules. Said sintered kaoline is produced by sintering at a temperature ranging from 1400 to 1500 DEG C so far as a water absorption of 5% is attained for kaoline containing 40-45 mass % and a free quartz in a quantity equal to or greater than 60 mass %. The Al2O3:SiO2 ratio in the charging material is equal to 1:1 at the following charging material component ratio: 36-67 mass % sintered kaolin and the rest being sintered bauxite.

Abstract: This invention relates to a process for reducing the contaminants in condensate resulting from the conversion of bauxite to alumina.

Abstract: A method for producing aluminum hydroxide includes a step of elevating a temperature of a slurry of aluminum hydroxide suspended in a sodium aluminate solution from 70° C. or lower to 85° C. or higher, and a step of applying a centrifugal force to the slurry. The aluminum hydroxide constituting the slurry is obtained beforehand through the Bayer's process.

Abstract: A process for the removal and causticisation of sodium oxalate and/or sodium sulphate from a Bayer process liquor containing sodium carbonate and one or both of sodium oxalate and sodium sulphate in an alumina refinery is described. The process is based on the observation that to efficiently causticise sodium oxalate solutions, it is first necessary to remove the aluminate ion from solution, optionally with recovery of the aluminate ion in some later step. This is effected by removing aluminate ions from the Bayer liquor through the formation of a carbonate bearing hydrocalumite and/or sulpha-bearing hydrocalumite. The liquor may then be treated with sufficient lime to remove and causticise any residual carbonate ions and some or all of the oxalate ions present so that any reacted lime solids thus formed can be separated and safely disposed of.

Abstract: A method for the production of aluminum from bauxites containing aluminum monohydate of the diaspore or boehmite type which may contain more than 1.5% by weight of calcium carbonates. The ore is digested by producing feeding a suspension produced from milled bauxite ore and concentrated aluminate liquor to a plant with a series of autoclaves and a series of regulators supplying tubular reheaters across the autoclaves with steam. The suspension first travels across the series of autoclaves, and on exiting, the digestion of the ore is practically complete, and the suspension then travels across the series of regulators. The condensation water from the steam coming from the regulator and feeding the reheater is collected in a purge pot. Within the series of regulators, the suspension is diluted on entering a regulator with the water coming from the condensation of the steam from one or several upstream regulators.

Abstract: In a BAYER circuit, a process for controlling precipitation in which particle size quality of alumina hydrate produced in the circuit and circulating in feed tanks is monitored utilizing a calibration step and a control step. In the calibration step, cumulative percentage of alumina hydrate particles circulating in the feed tanks in the circuit that are finer than X2 ?m, defined as CPFT X2, is measured vs. time and cumulative percentage of alumina hydrate particles circulating in the feed tanks in the circuit that are finer that X1 ?m, defined as CPFT X1 vs. time, is measured, where X1 and X2 are predetermined particles sizes and X1 is smaller than X2. A relationship R between CPFT X1 and later changes in CPFT X2, is determined and upper and lower trigger thresholds of CPFT X1 which correspond to maximum permissible variation in CPFT X2 are defined. In the control step, CPFT X1 and CPFT X2 are regularly measured, and R and the correlation between CPFT X2 and the particle size of hydrate produced are updated.

Abstract: A process in which material comprising an aqueous liquid with dispersed particulate solids is pumped as a fluid then allowed to stand and rigidify and the rigidification is improved whilst retaining the pump ability of the material by combining polymeric particles with the material during or prior to pumping the material, wherein the polymeric particles comprise water soluble polymer which has an intrinsic viscosity of at least 3 dl/g. The process of the invention more effectively minimises the area taken up by a stack of the material of given volume whilst maintaining the pumpability of the material. This invention is particularly suited to material that comprises red mud from the Bayer alumina process.

Abstract: Materials and a process are provided whereby polymers with the pendant group or end group containing —Si(OR″)3 (where R″ is H, an alkyl group, Na, K, or NH4) are used to control aluminosilicate scaling in a Bayer process. When materials of the present invention are added to the Bayer liquor before the heat exchangers, they reduce and even completely prevent formation of aluminosilicate scale on heat exchanger walls. The present materials are effective at treatment concentrations that make them economically practical.

Abstract: A formulation for use as a treating agent in the Bayer process is disclosed. The formulation comprises a blend of 200-300 ppm of starch and up to 10 ppm of another polysaccharide. When added to a liquor derived from the digestion of bauxite ore in a caustic solution to extract alumina, the formulation may result in increased filterability of the liquor. The formulation may also be used in conjunction with a filter aid in the filtration of a caustic sodium aluminate solution.

Abstract: The claimed invention is a method for separating Bayer process red mud from a Bayer process liquor which comprises adding to a Bayer process liquor containing red mud an effective amount of a water soluble synthetic flocculant, dextran and starch combination. The flocculant is added anywhere in the slurry containing the red mud suspended in Bayer process liquor, or in a liquor slurry containing bauxite prior to or during digestion. Once the flocculant combination is added, it is mixed sequentially with the Bayer process liquor and the red mud contained in the Bayer process liquor is removed by sedimentation, centrifugation or filtration.

Abstract: In order to provide a method for effectively separating red mud generated during alumina-extraction treatment of an alumina ore containing goethite as an iron component, the alumina ore containing goethite as an iron component is treated with an alkaline solution at 110-160° C., to thereby take up alumina components through extraction, and a settling aid formed of a water-soluble polymer including, as an effective component, a copolymer containing, as a monomer component, a vinylhydroxamic acid compound or a salt thereof (A) and having an average molecular weight of at least 2,000 is added to the resultant extract, to thereby settle the red mud for separation thereof.

Abstract: A process is disclosed for the treatment of an alumina process feedstock prior to transferring the treated feedstock to an alumina process for extracting refined alumina from the treated feedstock. The treatment process includes the following steps: (a) heating the alumina process feedstock to a temperature of 400C. to 650C. by direct contact with combustion gases, and (b) cooling the heated feedstock to a temperature at which it can be handled and fed to the alumina process. The treatment process is characterised by controlling the contact time of the solid alumina process feedstock at temperatures in the above range in step (a) to less than 5 minutes.

Abstract: The present invention provides an improved process for the production of alumina trihydrate crystals. Through the addition of a hydroxamated polymer at various stages of the process for production of these alumina trihydrate crystals, an upward shift in the particle size distribution of the alumina trihydrate crystals occurs. In one embodiment, the hydroxamated polymer is added to a filtered aqueous solution, which comprises no more than about 10 mg of insoluble solids per liter. In another embodiment, the hydroxamated polymer is added to an aqueous solution comprising insoluble solids after precipitation of alumina trihydrate crystals has commenced. Optionally, alumina trihydrate seed crystals may be added to the aqueous solution to initiate or encourage crystal formation.

Abstract: A process is provided for the treatment of an alumina process feedstock prior to transferring the treated feedstock to an alumina process for extracting refined alumina from the treated feedstock. The treatment process includes: (a) heating the alumina process feedstock to a temperature of 400° C. to 650° C. by direct contact with combustion gas, and (b) cooling the heated feedstock to a temperature at which it can be handled and fed to the alumina process. The treatment process also includes controlling the contact time of the alumina process feedstock at temperatures in step (a) to ensure decomposition of alumina trihydrate and alumina monohydrate. The process also includes: (i) limiting the maximum temperature of incoming gas to a stage of the process in which the alumina process feedstock reaches the above temperature range of 400° C. to 650° C.

Abstract: A process for the removal of organic impurities in a Bayer process liquor in which wet and dry oxidation processes are linked together in a complementary way, such that the weaknesses of each individual organic removal process become a strength of the combined process. An organics-rich liquor stream is fed to a wet oxidation process to produce a first processed liquor which is depleted in organic compounds, but enriched in sodium carbonate and/or sodium oxalate. A feed slurry is fed to the dry oxidation process, typically including a liquor burner, where sodium compounds react to produce a discharge product. The first processed liquor and discharge product are directed into a leach tank, resulting in the formation of precipitated products including sodium carbonate and/or sodium oxalate. The precipitated products are separated from the leach tank and recycled in a mix tank providing the feed slurry to the liquor burner.

Abstract: The process according to the invention to raise simultaneously to an optimum level the temperature and concentration of an aqueous medium intended for use in bauxite ore digestion in an alumina production plant according to the Bayer process, which includes successive phases (a) to (f) in which: a) the aqueous medium coming from digestion containing pregnant liquor is cooled and evaporated in a multiple staged flash evaporation zone; b) the sterile residue is separated, the aluminium trihydroxide is precipitated and the aqueous medium, consisting of spent liquor, intended for use in digestion is recovered; c) if need be, the required quantity of water, additional to that already evaporated in phase (a) is eliminated by evaporation in a specific evaporation section; d) the aqueous medium intended for use in digestion is heated in several stages; e) the flash vapour generated in each of the stages of the evaporation phase (a) is used in each of the stages of the heating phase (d); f) the aqueous medium in

Abstract: A process in which alumina is extracted from bauxite with an aqueous alkali solution, and a desilication product is precipitated such that the product is not contained in a bauxite residue and does not form a complex. The desilication product is mixed with a calcium compound, and the mixture is calcined, to thereby solubilize and recover an alkali component of the product. In addition, an alkali component is removed from a residue (a solid product), and the residue is effectively used as a resource.

Abstract: A method of flocculating suspended solids in a Bayer process liquor comprising adding to the liquor an effective amount of a polymer comprising salicylic acid groups.

Abstract: A process for producing alumina from bauxite is described in which bauxite is treated with an alkali to form a mixture comprising a solution of aluminum-containing ions and alumina trihydrate is precipitated from the solution. The process comprises treatment of the solution before or after the precipitation step with a layered double hydroxide in order to remove impurities from the solution by intercalation into the layers in the double hydroxide. The double hydroxide may contain layers of the formula: [LiAl2(OH)6]+.

Abstract: An improvement in the Bayer process for producing alumina trihydrate in which bauxite ore is digested in a mixture with a digestion sodium aluminate liquor to produce a slurry, the slurry is settled to remove undigested residues therefrom and produce a pregnant liquor of sodium aluminate and alumina trihydrate is precipitated from the pregnant liquor in the presence of alumina trihydrate recycled as seed. When beginning the precipitation, an aliquot of the pregnant liquor with recycled alumina trihydrate is removed, subjected to mechanical action of an intensity and for a time sufficient to cause formation of seeds, and returned with the formed seeds to the beginning of the precipitation.

Abstract: The present invention comprises a method for reducing the viscosity of the settled mud or underflow of a raked thickener thereby reducing the torque necessary to move the rake blade through the settled mud. The method includes the step of delivering a viscosity modifier to the settled mud and in front of the rake blade by pumping the viscosity modifier down the rake arm to an area in front of the rake blade. The method also includes an improved rake mechanism that includes a means for delivering viscosity modifier to the settled mud and in front of the rake blade. The present invention also includes a method for increasing the rate of consolidation of flocculated solids in a slurry.

Abstract: A process for the removal of reactive silica from a feedstock to the digestion step of the Bayer process for the manufacture of alumina, in which (a) the feedstock is contacted with a caustic liquor under process conditions which result in dissolving and stabilizing at least 50% of the silica into solution at a level of at least 3 gpL and without significant precipitation from solution of dissolved silica, (b) the silica bearing liquor is separated from solid residue of step (a) under conditions which do not promote significant precipitation of the silica; and (c) aluminosilicates are precipitated from the separated silica bearing liquor from step (b), to form a solid aluminosilicate product which is free of a majority of all other components of the feedstock.

Abstract: To recycle a residue after treatment of bauxite completely and effectively. To recover alkali which is used for the treatment. When alumina is extracted from bauxite with an alkali aqueous solution, a desilication product is precipitated such that the product is not contained in a bauxite residue and does not form a complex. The desilication product is mixed with a calcium compound, and the mixture is calcined, to thereby solubilize and recover an alkali component of the product. In addition, an alkali component is removed from a residue (a solid product), and the residue is effectively used as a resource.