WO2021055477A1

WO2021055477A1 - Chemical compositions for improving the rheology of red mud slurry in the alumina extraction process

Info

Publication number: WO2021055477A1
Application number: PCT/US2020/051071
Authority: WO
Inventors: Renata VINHAS; Airong Song
Original assignee: Cytec Industries Inc.
Priority date: 2019-09-20
Filing date: 2020-09-16
Publication date: 2021-03-25
Also published as: WO2021055477A8

Abstract

Methods and compositions that can significantly reduce the viscosity of a red mud slurry in the Bayer process, by adding an effective amount of a viscosity-reducing agent. In certain aspects, a sodium allyl sulfonate maleic add copolymer (e.g., a copolymer comprising monomers of formula (!) and (!!)), and/or a styrene maleic anhydride copolymer (e.g., a copolymer of formula (III)) may be used as the viscosity- reducing agent. The viscosity-reducing agent may be added during the Bayer process, e.g., after flocculation of the red mud slurry, at one or more washing tanks, and/or at the feed to a press filter. These methods and compositions allow alumina refinery plants to increase alumina production and reduce energy consumption by improving throughput of red mud processing and disposal, reducing energy consumption used to pump the red mud slurry, and reducing the operational costs of press filters.

Description

CHEMICAL COMPOSITIONS FOR IMPROVING THE RHEOLOGY OF RED

MUD SLURRY IN THE ALUMINA EXTRACTION PROCESS

Field of the Invention

[0001] This invention relates to chemical compositions for improving the rheology, (e.g., reducing the viscosity) of a red mud slurry in the alumina extraction process.

Background

[0002] Bauxite is the basic raw material for almost all manufactured aluminum compounds. In the course of production of aluminum compounds, bauxite can be refined to aluminum hydroxide and subsequently to alumina, e.g., using the Bayer process, the Sinter process, as well as combinations or variations thereof. The mineralogical composition of bauxite can impact the method of processing. [0003] Bauxite is the generic name for naturally occurring ores that are rich in hydrated aluminium oxides. The ores are composed of gibbsite (Al₂O₃.3H₂O), boehmite (y-AIO(OH)) and diaspore (a-AIO(OH)), combined with iron oxides, such as goethite (FeO(OH)) and hematite (Fe₂O₃), as well as other impurities such as kaolinite clays. [0004] The Bayer process is a hydrometallurgical system for refining naturally occurring bauxite ores into anhydrous alumina, Al₂O₃. First proposed in 1888 by Karl Josef Bayer, it is currently the leading industrial means of alumina production. It is a multi-step, continuous process, comprising of grinding, pre-desilication, digestion, decantation, filtration, precipitation and calcination.

[0005] In the Bayer process, mined bauxite is first ground to fine solids, and then typically, pre-desilicated to convert most of the clays to sodalite. During the digestion the bauxite is treated with caustic soda (NaOH), known as the Bayer liquor, at high temperature and pressure to produce dissolved sodium aluminate. The solid-liquid separation or decantation occurs in the settler, where high concentrated solid slurry (30 to 50%) settles in the bottom of the settling tank, while the supernatant liquor, containing low concentration of mud remains in the top layer of the settler.

[0006] The settled slurry (also known as red mud) is subsequently pumped to a series of decanters (e.g., washers), in order to recover the residual caustic soda in the mud that has been settled. The poor viscosity and high solids concentration of this settled slurry can cause operation difficulties, such as pumpability, and high specific energy consumption from these pumps.

[0007] Specifically, the high viscosity of the red mud slurry causes great power consumption by the pumps, which decreases the overall productive capacity of the plant for obtaining alumina . Further, the presence of highly viscous red mud slurry inside the tanks and pumps dirties the aforesaid machinery, making it necessary to perform numerous cleaning operations on the vessels, pipelines, and the pumps. In addition, the presence of highly viscous red mud slurry inside pumps produces rapid wear to said pumps.

[0008] To facilitate pumping and to reduce pumping pressure, or to obtain a lower consistency of the red mud slurry, water has often been added. However, the addition of water is not a satisfactory solution For example, water is a diluent that must eventually be removed, which adds processing steps and overall expense of the process. Also, the waste water may contain impurities, such that disposal may require further processing steps, or require that it be pumped back to the plant for treatment.

[0009] Thus, there remains a need for methods and compositions that reduce the viscosity of a red mud slurry, such as those that also minimize or eliminate the need for addition of water as a means to increase flowability.

Summary of the Invention

[0010] In the present specification red mud is red mud bauxite residues generated as a waste product during the production of alumina , for example in the Bayer process. [0011] Described herein are compositions that can significantly reduce the viscosity of red mud, which can allow alumina refinery plants to increase throughput of red mud disposal, reduce energy consumption used to pump the red mud slurry, reduce maintenance and wear on equipment, and increase mud solids for press filtration so as to reduce the operational costs of press filters. For example, increased mud solids for press filtration reduces the operational costs of press filters because to filter the same amount of red mud, the increased mud solids in the feed flow of press filters can lead to reduced operational time.

[0012] In accordance with the invention, described herein are methods of treating a Bayer process red mud slurry by adding to the slurry a viscosity-reducing agent which may be one or more of the compounds as described herein, which is effective to reduce the viscosity of the slurry.

[0013] Described herein are compositions that can significantly reduce the viscosity of red mud slurry, which allow alumina refinery plants to increase throughput, resulting in increased alumina production, reduced energy consumption or a combination of both.

[0014] Certain aspects relate to a method of treating a red mud slurry comprising: adding a viscosity-reducing agent to a red mud slurry, in an effective amount to reduce the viscosity of the red mud slurry, wherein the viscosity-reducing agent is selected from the group consisting of a styrene maleic anhydride copolymer or salt thereof, a sodium allyl sulfonate maleic acid copolymer or salt thereof, and mixtures thereof.

[0015] In one aspect, described herein is a process to improve the viscosity (e.g., lowering the viscosity) of a red mud slurry in a Bayer process comprising: adding an effective amount of a viscosity-reducing agent to the red mud slurry, wherein the viscosity-reducing agent comprises a sodium allyl sulfonate maleic acid copolymer or salt thereof, and mixtures thereof.

[0016] In one aspect, described herein is a process to improve the viscosity of a red mud slurry in a Bayer process comprising: adding an effective amount of a viscosity- reducing agent to the red mud slurry, wherein the viscosity-reducing agent comprises a co-polymer comprising: a monomeric unit according to formula (I)

and

a monomeric unit according to formula (II)

wherein:

R¹ is no group, O, C₁-C₁₀ alkyl, C₁-C₁₀ aryl, or C₁-C₁₀ arylalkyl;

M⁺ is a group I metal ion or N(R⁴)4⁺;

R⁴ is hydrogen or an optionally substituted hydrocarbyl radical comprising from about 1 to about 20 carbons; n is an integer from 1-300; and m is an integer of from 1-300.

[0017] Typically, n is an integer from 1-1000; or an integer from 1-500, or an integer of from 1-300, or preferably an integer of from 1-10.

[0018] Typically, m is an integer of from 1-1000, or an integer of from 1-500, or an integer of from 1-300, or preferably an integer of from 1-10.

[0019] Typically M⁺ is Li⁺, Na⁺ or K⁺. Preferably M⁺ is Na⁺. [0020] In one aspect, described herein is a process to improve the viscosity (e.g., lowering the viscosity) of a red mud slurry in a Bayer process comprising: adding an effective amount of a viscosity-reducing agent to the red mud slurry, wherein the viscosity-reducing agent comprises a styrene maleic anhydride copolymer (known also as Poly(Styrene-co-Maleic Anhydride)), or salt thereof.

[0021] Preferably the Poly(Styrene-co-Maleic Anhydride) viscosity-reducing agent has a structure according to formula (III):

wherein:

R² is H, C₁-C₅ alkyl, C₁-C₁₀ alkyl, C₁-C₅ aryl, C₁-C₁₀ aryl, or C₁-C₁₀ arylalkyl; q is an integer from 1-300; r is an integer of from 1-300; and p is an integer from 1-300.

[0022] Typically, “q" is an integer from 1-200. Typically, “r" is an integer from 1-200.

Preferably, “q" is an integer from 1-100. Preferably, “r" is an integer from 1-100.

Typically, "p” is an integer from 1-300. Preferably, "p” is an integer from 1-100.

[0023] The viscosity-reducing agent may comprise a hydrolyzed form of formula (III).

The viscosity-reducing agent may comprise a hydrolyzed form of formula (III) having a counterion of Li⁺, Na⁺ or K⁺. Preferably, the viscosity-reducing agent comprises an aqueous solution of the sodium salt of the styrene maleic anhydride copolymer according to formula (III) herein. [0024] Typically, the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 30%, 20%, or 10% as compared to the viscosity of a red mud slurry absent the viscosity-reducing agent.

[0025] Optionally, the viscosity-reducing agent can further comprise an anionic surfactant, a non-ionic surfactant, an amphoteric surfactant, a zwitterionic surfactant or a combination thereof. Thus, compositions of the invention may have the presence or absence of surfactant, or any one or more of anionic surfactant, non-ionic surfactant, amphoteric surfactant, zwitterionic surfactant or combination thereof.

Brief Description of the Drawing

[0026] FIG. 1 shows a general overview of the Bayer process, including the production of red mud.

[0027] FIG. 2 is a simplified schematic showing an embodiment of the red-mud washer section of a Bayer process plant.

Detailed Description of Invention and Preferred Embodiments

[0028] The present invention broadly relates to methods for treating a red mud slurry formed in the Bayer process by adding thereto a viscosity-reducing agent, effective to reduce the viscosity of the red mud. The present invention also relates to red mud compositions resulting thereof.

[0029] The methods and compositions described herein can significantly reduce the viscosity of a red mud slurry, which can allow alumina refinery plants to increase throughput of mud disposal, reduce energy consumption used to pump the red mud slurry, and to increase mud solids for press filtration so as to reduce the operational costs of press filters.

[0030] The Bayer process for obtaining alumina from bauxite is a multi-step. continuous process, comprising grinding, pre-desilication, digestion, decantation, filtration, precipitation and calcination. A general overview of the Bayer process is shown in FIG. 1. During the digestion, the bauxite 2 is ground in a grinding mill 12. The ground bauxite 14 then passes to a desilication unit 16. The desilicated bauxite 18, steam 20, and concentrated caustic soda stream 22 (for example 15-25 wt.% sodium hydroxide), known as Bayer liquor, are fed to a digestion unit 24 where the desilicated bauxite 18 is digested with the caustic soda at high temperature and pressure to produce dissolved sodium aluminate (Na-AI(OH)₄).

[0031] The dissolved sodium aluminate discharges as sodium aluminate-containing stream 26 from the digestion unit 24 and feeds a settling/ thickening tank 30 where it is treated with settler flocculant 32. Typically, the solid liquid separation or decantation occurs in the settling/ thickening tank 30, where high concentrated solid slurry (30 to 50% solids) settles in the bottom of the settling/ thickening tank 30 and discharges as red mud stream 34. The settled slurry is known as "red mud" and is subsequently pumped as red mud stream 34 to the washer section 40. Meanwhile the supernatant liquor, containing low concentration of mud remains in the top layer of the settling/ thickening tank 30 and discharges as supernatant liquor stream 35.

[0032] The supernatant liquor stream 35 is filtered by a filter 36 to produce a cleaned supernatant liquor stream 37 (which contains caustic soda and dissolved sodium aluminate) and a red mud-containing stream 39 which passes to the washer section 40. [0033] The red mud stream 34 and red mud-containing stream 39 are washed in the washer section 40 with flocculant stream 42, additive 43 and wash water 44 to recover the caustic soda from the mud that had been settled. The additive 43 is added as a separate stream to the washer section 40. In the alternative the additive 43 can be added directly into the underflow (U/F) red mud layer in the tank 30 or into the U/F red mud discharge line 34. The additive 43 may be a viscosity-reducing agent. The cleaned red mud discharges as a red mud containing stream 46, which may pass to a mud press filter 50 which produces a cleaned caustic soda containing stream 52 and a red mud stream 53. In the alternative the plant does not have a mud press filter, in this case, the red mud from the last washer is disposed directly into a lake, usually called a mud lake. The cleaned caustic soda containing stream 52 and the cleaned supernatant liquor 37 feed a liquor cooler 70. The red mud stream 53 goes to mud storage 54. Recovered wash water after use discharges from washer section 40 as effluent wash water stream 45 which may be also feed the liquor cooler 70.

[0034] This liquor cooler 70 produces a cooled liquor stream 72 which feeds a precipitator 74. A sodium hydroxide stream 75 also feeds precipitator 74 where solids precipitate. The precipitated solids discharge as a precipitated solids stream 76 which feeds a classifier 78 to contact a hydrate flocculant 80. The classifier 78 produces a spent liquor stream 82, a precipitated solids slurry stream 84, and a seed stream 86. [0035] The seed stream 86 passes through a seed filter 90 and is recycled to the precipitator 74.

[0036] The precipitated solids slurry stream 84 feeds a filter washer unit 94 where it is washed with condensate 97 from an evaporator 98. This forms a purified stream of sodium aluminate 100 which feeds a calcination unit 102 to form alumina 110.

[0037] The spent liquor stream 82 feeds the evaporator 98 where it is heated with steam 112 to recover a strong liquor stream 99 and the condensate 97.

[0038] The strong liquor stream 99 is fed to a test tank 113 and then a portion 114 of the strong liquor stream feeds the desilication unit while another portion 116 of the strong liquor stream feeds the digestion unit 24.

[0039] As shown in FIG. 2 the washer section 40 is a series of decanters, also named washing tanks 200, 202, 204. The high solids concentration of the “red mud” settled slurry in red mud streams 34 and 39 can cause operation difficulties, such as pumpability, and high specific energy consumption from these pumps (not shown) used to pump red mud in streams 34 and 39.

[0040] In particular, after the bauxite is initially digested (e.g., with caustic soda) to extract alumina (as dissolved sodium aluminate) in the Bayer process liquor, the particulate residues (known as red mud) are separated from the Bayer process liquor and collected in a concentrated slurry for transport to a storage or disposal site, while the process liquor is subjected to decomposition to precipitate alumina trihydrate, which is then calcined to recover the desired alumina product.

[0041] As used herein, the terms “Bayer process red mud slurry," “red mud solids” or

“red mud slurry" will be used interchangeably to refer to the alkaline aqueous red mud slurries that are formed from the Bayer process, which are also known in the art as “red sludge" or “Bauxite tailings.”

[0042] Red mud is composed of a mixture of solid and metallic oxides, including iron oxides, which comprise up to 60% of the mass and provide the red colour. Chemically, it comprises in varying amounts (depending upon the composition of the starting bauxite), oxides of iron and titanium, sodalite, silica, unleached residual alumina , and minor quantities of other metal oxides. TABLES 1 and 2 below show the composition ranges for common chemical constituents and components, although the actual values may vary widely:

TABLE 1 : Composition Ranges for common chemical constituents in Red Mud

TABLE 2: Exemplary Components and amounts in Red Mud

[0043] As mentioned above, FIG. 1 shows an example of a Bayer process in which the bauxite is digested in aqueous caustic NaOH to extract alumina from the bauxite as sodium aluminate, leaving undissolved the red mud slurry. The sodium aluminate- containing stream 26 is discharged from the digestion unit 24 and feeds the settling/ thickening tank 30 where it is treated with settler flocculant 32. Although not shown in FIG. 1 , after digestion in the digestion unit 24 on route to the settling/ thickening tank 30 the sodium aluminate-containing stream 26 may be processed in a series of flash tanks, then fed to a blow off tank, and then to the settling/ thickening tank 30 where the red mud is separated from the liquor. The liquor is further processed (e.g., cooling, precipitation, seeding, etc.) as explained above.

[0044] The settling/ thickening tank 30 is typically a High Rate Thickener or a settling tank. Conventional Thickeners and Alcan Deep Thickeners are also examples of other common thickener designs used in the Alumina industry. High Rate Thickeners are designed specifically to operate with flocculants and hence optimizes flocculant consumption as known in the art. For example, a high rate thickener may be designed to have feed dilution to ensure proper mixing of flocculant with incoming feed and facilitate proper floe formation, as well as have a rake mechanism designed to operate at sufficiently high torque levels to handle high slurry throughput. For example, High Rate Thickeners may provide immediately reusable process water and recover approximately 85% of the water from an effluent feed. This high level of water recovery keeps water consumption at sustainable levels, as well as drastically reduces the slurry volume reporting to waste ponds. Typical high rate thickeners are described at The High Rate Thickener, URL:<http://www.solidliquid- separation.com/Thickeners/High%20Rate/highrate.htm> retrieved from the Internet July 30, 2019.

[0045] High-Rate thickeners may be used with the sedimentation line of equipment. Thickeners occupy large spaces which may be saved by introducing high-rate machines. Furthermore, they are normally positioned far away from the center of the plant so to allow gravity feed and thus save pumping costs their distance is influenced by the hydraulic gradient for the large flows. This factor determines the elevation of the entire plant and consequently has a substantial impact on capital investment. One advantages of the high-rate thickener is the smaller volume of the tank so it speeds up startups or shutdowns and less volume is required for storing the product in the event that the tank has to be emptied. Likewise, high-rate thickeners consume substantially less flocculants with savings up to 60%. High-rate thickeners may replace conventional thickeners and depending on the application they are capable of delivering a throughput that is 5-10 higher than with a conventional machine of equal size. This prompted a tendency to retrofit existing installations at a substantial saving in capital investment when increased capacity was required.

[0046] High-rate thickeners that are built as dedicated machines are available in sizes up to 40 meter diameter but retrofits of conventional thickeners are often larger in size. When viewed from the outside high-rate thickeners look very much like conventional machines except that their tanks have a greater height to diameter ratio. Their height is derived from test work by calculating retention time and the reduced area as obtained for the increased throughput. A high rate thickener typically has an internal rise rate from 4 to 10 metres per hour, and has a diameter ranging from 10 to 60 metres. The feedwell is the most common point for flocculants addition. Proper feedwell design and flocculation addition location is typically applied in order to maximize the effectiveness of the flocculation. A thickener of this type requires a flocculant and generally utilizes a deep feedwell. A mud bed of up to 5 metres in height is created, and such thickeners are capable of processing from 12 to 19 tons per square metre per day. As to the internals, there are several approaches to the mechanism of high-rate thickening. There are design options such as deep feedwells with progressive flocculation along the incoming stream route, direct injection into the feedwell or recirculation of liquid from the clear zone to enhance settling rate by diluting the feed internally. There are also concepts that resemble sludge-blanket clarifiers with feedwells that are submerged in the sludge bed and provide an additional benefit of trapping the fines to produce a clear effluent.

[0047] Typically, the at least partial separation of the red mud solids from pregnant liquor at elevated temperatures by settling or by filtration is expedited by the use of a flocculant. This initial clarification of the pregnant liquor into a clarified liquor phase is referred to as the primary settler stage which occurs in the settling/ thickening tank 30. The red mud slurry 26 is settled in the settling/ thickening tank 30 with the help of flocculants 32 to give two layer: overflow (O/F) supernatant liquor 35 and underflow (U/F) red mud 34. Flocculating agents 32 improve the separation of insolubles by increasing the rate at which the solids settle, by reducing the amount of residual solids suspended in the liquor, and by decreasing the amount of liquor in the settled solids phase. Flocculation performance is important in the primary settlement stages. Generally, red mud may be comprised of very fine particles, which hinder the desired rapid and clean separation of red mud particles from the solubilized alumina liquor. [0048] The overflow supernatant liquor 35 is sent to filter press 36 to further reduce the solid content in the liquor. The red mud filter cake is either disposed or returned to digestion or the red mud settler.

[0049] The underflow red mud layer 34 is pumped by at least one pump (not shown) to the washer section 40 which comprises a series of mud washing tanks 200, 202, 204 to be washed by water to reduce the residual liquor in the red mud. The washing tanks may be any suitable for washing red mud. Typical suitable washing tanks are deep cone washing tanks. Typically the washer section 40 has a countercurrent flow arrangement in which the underflow red mud of each washer is pumped by at least one pump (not shown) to the next washer downstream for further washing, and the overflow supernatant liquid of each washer is sent to the previous (upstream) washer to wash the mud. [0050] FIG. 2 shows this washing circuit of washer section 40 in which after the settling stage in the settling/ thickening tank 30, the red mud slurry (underflow red mud solids) 34 and the red mud stream 39 are fed to a washing circuit of washer section 40. This washing circuit includes a series of washing tanks 200, 202, 204 (e.g., conventional mud washers). For example, FIG. 2 shows the red mud washed in these tanks in a countercurrent washing circuit having a series of cascading washing tanks 200, 202, 204 to remove most of the caustic soda (carried with the red mud from the starting liquor).

[0051] In this way, the red mud slurry is thickened or filtered to a high solids concentration (high solids consistency, typically about 10-70% by weight solids) for delivery to a storage or disposal site. The percentage of solids depends on the granulometry of the bauxite and of the red mud. For very finely divided red mud, such as obtained from Jamaica bauxite, the solids content is between 15 and 30%; for coarser bauxite and red mud, such as obtained from African bauxite, the solids content can range from 60 to 70%. The aqueous vehicle of this slurry still has significant alkalinity, e.g., a concentration of NaOH (expressed as Na₂CO₃) of 1 to 40 g/L, but more usually from 4 to 25 g/L. Such high-solids, alkaline red mud slurries underflow the mud thickeners and mud filters of Bayer process plants, and are usually pumped therefrom (ordinarily with high pressure positive displacement pumps) over relatively long distances to storage or disposal sites. The underflow red mud solids 46 of the last washer 204 is pumped to one or more pressure filters 50 (one shown) for dewatering, and the resulting filter cake 53 is disposed to mud storage 54 (seen in FIG. 1).

[0052] In the washing tanks 200, 202, 204 of FIG. 2, the aqueous wash liquor from the slurry is pumped upstream through the circuit, to the previous washer to wash the mud, while the red mud solids travel downstream to the next washing tank for further washing. Thus, the red mud stream 39 and red mud stream 34 feed the first washing tank 200 to contact additive stream 243 and wash liquid 203. The cleaned solids stream 207 from the first washing tank 200 passes to the second washing tank 202 where it contacts additive stream 143 and wash liquid 205. The cleaned solids stream 207 from the second washing tank 202 passes to the third washing tank 204 where it contacts additive stream 43, flocculant stream 42, and wash water 44.

[0053] Ultimately, the underflow mud 46 of the last washing tank 204 is pumped to the mud press filter 50 for dewatering, where the Bayer liquor 52 may be recovered, and the resulting filter cake 53 may be disposed to the mud storage area 54.

[0054] FIG. 2 shows countercurrent flow, but other flow arrangements may be employed. For example, an alternative arrangement (not shown) could have independent separate wash water streams to each washing tank.

[0055] The viscosity-reducing additive agent may be added at any convenient point during the processing of the red mud. For example, it may be added to the underflow mud slurry from the settling tank 30, preferably after a flocculation step has already been completed. It may be added to the discharge of any one of the washing tanks, which may be pumped to the previous washer to wash the red mud. It may be added at the entry point of the pressed filtrate (feed).

[0056] Thus, in the invention the viscosity-reducing agent may be added at one or more of the following points during the process: (i) to the red mud solids after the flocculation step, or prior to the washing circuit (e.g., added to the underflow red mud solids from the settling tank), (ii) to one or more washing tanks, e.g., in certain aspects, could be added to the wash water, or to one or more of the overflow aqueous wash liquor (e.g., discharge from one washing tank in the washing circuit) to one or more washing tanks, and (iii) the entry point of the pressed filtrate (e.g., the feed to the press filter).

[0057] The viscosity-reducing agent may be added several times during the process, either sequentially or at the same time. The total dosage of the viscosity-reducing agent may be divided, and added in more than one portion during the process.

[0058] For example, FIG. 2 shows the viscosity-reducing additive agent added as additive stream 243 to washing tank 200, additive stream 143 to washing tank 202, and additive stream 43 to washing tank 202. Wash water 44 and flocculent stream 42 are also fed to washing tank 204. It may also be added as additive stream 343 to underflow red mud solids stream 46 discharged from washing tank 204. [0059] Typically, the viscosity of the red mud slurry is monitored, and the viscosity- reducing agent is added as needed throughout the process, for example, sequentially in one or more steps of the Bayer process, to achieve the desired decrease in viscosity of the red mud slurry.

[0060] Viscosity-reducing agents

[0061] The invention typically uses an effective amount to reduce the viscosity of the red mud slurry, either neat (e.g., as a dry powder or solid), or dissolved in an appropriate vehicle (e.g., water, etc.) to provide a solution, suspension, or slurry.

[0062] As used herein, the terminology "effective amount" in reference to the relative amount of a red mud composition means the relative amount of a viscosity-reducing agent that is effective to lower viscosity of the red mud slurry at a given application rate as compared to the red mud slurry in the absence of the viscosity-reducing agent.

[0063] It is therefore understood that the term “viscosity-reducing agent" is not meant as a limitation regarding step, i.e., the term is not limiting as to any step during the

Bayer process (e.g., adding the composition only during the grinding step) but can be used in any step according to several embodiments as described herein.

[0064] The viscosity-reducing agents as described herein are capable of reducing the viscosity of the red mud slurry when added in an effective amount. In one embodiment, the quantity of the viscosity-reducing agent added to the red mud slurry is between about 5 ppm to about 10,000 ppm. In another embodiment, the quantity of the viscosity-reducing agent added to the red mud slurry is between about 10 ppm to about 5000 ppm. In another embodiment, the quantity of the viscosity-reducing agent added to the red mud slurry is between about 25 ppm to about 4000 ppm. In yet another embodiment, the quantity of the viscosity-reducing agent added to the red mud slurry is between about 50 ppm to about 3000 ppm. In another embodiment, the quantity of the viscosity-reducing agent added to the red mud slurry is between about 75 ppm to about 1000 ppm. In yet another embodiment, the quantity of the viscosity-reducing agent added to the red mud slurry is between about 90 ppm to about 750 ppm. In yet another embodiment, the quantity of the viscosity-reducing agent added to the red mud slurry is between about 100 ppm to about 500 ppm. [0065] Typically, the total quantity of the viscosity-reducing agent added to the red mud slurry has a lower limit of 10 ppm, or 20 ppm, or 50 ppm, or 75 ppm, or 100 ppm, or 150 ppm, or 175 ppm, or 200 ppm, or 250 ppm, or 300 ppm, or 400 ppm, or 500 ppm, or 800 ppm, or 1000 ppm, or 1500 ppm, or 2000 ppm, or 2500 ppm or 3000 ppm. [0066] Typically, the quantity of the viscosity-reducing agent added to the red mud slurry has an upper limit of 10,000 ppm, or 7500 ppm, or 5000 ppm or 4500 ppm or 4000 ppm, or 3500 ppm, or 3000 ppm, or 2500 ppm, or 2000 ppm, or 1500 ppm, or 1000 ppm, or 900 ppm, or 800 ppm, or 700 ppm, or 600 ppm, or 500 ppm or 400 ppm. [0067] The presence of the viscosity-reducing agent may reduce the viscosity of the red mud slurry compared with the viscosity that said red mud slurry would have in the absence of the viscosity-reducing agent as described herein. The presence of the viscosity-reducing agent may reduce the viscosity of the red mud slurry 10 to 90%, more typically 20 to 60%, compared with the viscosity that the red mud slurry would have in the absence of the viscosity-reducing agent as described herein.

[0068] The viscosity can be measured using a suitable method used in the art. For example, a Brookfield DV-3T Rheometer with V-73 vane spindle may be used to measure viscosity. The viscosity profile measurement may be measured as demonstrated in the examples, where the viscosity of the slurry may be determined at spindle speeds and shear rates for a specific duration of time, employing a vane spindle (V-73) connected to a rheometer. Typically tested at one or more RMP values from 10 to 250. In certain aspects, the viscosity is measured at a shear rate of about 2.14 1/s, a shear rate of about 16.05 1/s or a shear rate of about 53.5 1/s. The viscosity reduction is measured with reference to a blank. The blank is usually a red mud sample without the additive (e.g., the viscosity-reducing agent).

[0069] The % viscosity reduction of treated samples is calculated according to the following equation for each shear rate condition applied:

% viscosity reduction =

100% x (average blank viscosity - sample viscosity) / average blank viscosity. [0070] The presence of the viscosity-reducing agent may reduce the viscosity of the red mud slurry by more than 70% compared with the viscosity that said red mud slurry would have in the absence of the viscosity-reducing agent as described herein.

[0071] The viscosity-reducing agent may reduce the viscosity of the red mud slurry by more than 60% compared with the viscosity that said red mud slurry would have in the absence of the viscosity-reducing agent as described herein.

[0072] The viscosity-reducing agent reduces the viscosity of the red mud slurry by more than 50% compared with the viscosity that said red mud slurry would have in the absence of the viscosity-reducing agent as described herein.

[0073] The viscosity-reducing agent reduces the viscosity of the red mud slurry by more than 40% compared with the viscosity that said red mud slurry would have in the absence of the viscosity-reducing agent as described herein.

[0074] The viscosity-reducing agent reduces the viscosity of the red mud slurry by more than 30% compared with the viscosity that said red mud slurry would have in the absence of the viscosity-reducing agent as described herein.

[0075] The viscosity-reducing agent reduces the viscosity of the red mud slurry by more than 20% compared with the viscosity that said red mud slurry would have in the absence of the viscosity-reducing agent as described herein.

[0076] The viscosity-reducing agent reduces the viscosity of the red mud slurry by more than 10% compared with the viscosity that said red mud slurry would have in the absence of the viscosity-reducing agent as described herein.

[0077] The reduction of viscosity makes the red mud slurry more flowable, facilitating the passage thereof during pumping operations. The viscosity-reducing agent as described herein also allow for a reduction in the electric energy consumption of pumps conveying the red mud slurry. In some embodiments, the energy saving can be up to 10%, or up to 15%, or up to 20%, or up to 25% or up to 30%.

[0078] Viscosity Reducing Agent Structures

[0079] Any of the viscosity-reducing agents listed in TABLE 3 may be selected either alone or in various combinations, for treating the red mud slurry. TABLE 3: Examples of viscosity-reducing agents to be used in the methods and compositions described herein

[0080] Typically, the viscosity-reducing agent comprises a Sodium allyl Sulfonate maleic acid copolymer comprising a monomeric unit according to formula (I): and

a monomeric unit according to formula (II):

wherein:

M+ is a group I metal ion or N(R⁴)4⁺;

R⁴ is hydrogen or an optionally substituted hydrocarbyl radical comprising from about 1 to about 20 carbons; n is an integer of from 1-300; and m is an integer of from 1-300.

[0081] Typically, the co-polymer comprising the monomeric unit according to formula (I) and formula (II) is a sodium allyl sulphonate maleic acid copolymer.

[0082] Typically, R⁴ is hydrogen or an optionally substituted C₁-C₂₀ alkyl, C₁-C₂₀ aryl, C₁-C₂₀ arylalkyl, C₁-C₁₀ alkyl, C₁-C₁₀ aryl, or C₁-C₁₀ arylalkyl.

[0083] Typically, n is an integer from 1-1000; or an integer from 1-500, or an integer of from 1-300, or preferably an integer of from 1-10.

[0084] Typically, m is an integer of from 1-1000, or an integer of from 1-500, or an integer of from 1-300, or preferably an integer of from 1-10. [0085] Typically, M⁺ is Li⁺, Na⁺ or K⁺. In one embodiment, M⁺ is Na⁺.

[0086] Preferably, the viscosity-reducing agent comprises a Styrene maleic anhydride copolymer of formula (III):

wherein:

R² is H, C₁-C₅ alkyl, C₁-C₁₀ alkyl, C₁-C₅ aryl, C₁-C₁₀ aryl, or C₁-C₁₀ arylalkyl; p is an integer from 1-300; q is an integer from 1-300; and r is an integer of from 1-300.

[0087] Typically “q" is an integer from 1 to 200 preferably 1 to 150, more preferably from 1 to 100, most preferably from 1 to 75 or from 25 to 75.

[0088] Typically "r" is an integer from 1 to 200 preferably 1 to 150, more preferably from 1 to 100, most preferably from 1 to 75 or from 25 to 75.

[0089] Preferably, R² is a hydrogen, q=1 , r=1 , and p is an integer from 1 to 300.

More preferably, R² is a hydrogen, q=1 , r=1, and p is an integer from 10 to 100. Most preferably, R² is a hydrogen, q=1 , r=1 , and p is an integer from 20 to 40.

[0090] The viscosity-reducing agent composition is a hydrolyzed form of formula (III).

Typically the viscosity-reducing agent comprises a hydrolyzed form of formula (III) having a counterion of Li⁺. Na⁺ or K⁺. Typically the viscosity-reducing agent comprises an aqueous solution of the sodium salt of the styrene maleic anhydride copolymer according to formula (III) herein. [0091] The viscosity-reducing agent may comprise the copolymer comprising the monomeric unit according to formula (I) and the monomeric unit according to formula

(II), as described herein.

[0092] The viscosity-reducing agent may comprise, consist of, or consist essentially of the copolymer comprising the monomeric unit according to formula (I) and the monomeric unit according to formula (II), as described herein.

[0093] To facilitate a better understanding of the present invention, the following examples of preferred or representative embodiments are given. In no way should the following examples be read to limit, or to define, the scope of the invention.

EXAMPLES

[0094] Henan red mud and Almatis red mud were tested in the following experiments. A Brookfield DV-3T Rheometer with V-73 vane spindle was used to measure viscosity. The red mud slurry compositions were tested in the following examples.

[0095] The solids concentration in the last washer underflow red mud was as follows:

Henan: 37%

Almatis: 46%

[0096] Materials:

-125ml HOPE bottles -Syringes -Micropipettes -Micropipettes tips -100 mL plastic beakers -Oven or Hot Water Bath

-Brookfield DV-3T Rheometer with V-73 vane spindle

[0097] Sample preparation for Henan and Almatis Mud was as follows:

1. The required amount of LWUM (Last Washer Underflow Mud) was mixed in a bucket. 2. The rotatory water bath or rotatory oven was preheated to a temperature of 70

°C.

3. A 100 g sample of mud slurry was poured into 125 ml plastic bottles.

4. The required dosages of reagents were applied to each bottle.

5. The bottle caps were tightened and the bottles were placed in the rotatory water bath or oven.

6. The bottles were allowed to mix in the rotatory water bath or oven for at least 30 minutes before the first measurement is taken.

General testing procedure for Henan bauxite and Almatis bauxite. viscosity profile measurement

[0098] The viscosity profile measurement involved measuring the viscosity of the slurry at spindle speeds and shear rates for a specific duration of time as specified in

TABLE 4 employing a vane spindle (V-73) connected to a rheometer.

TABLE 4: Viscosity Testing Settings

[0099] In the Examples the blanks were red mud without the additive. The viscosity of two untreated samples (blanks) for every shear rate condition applied (as shown above) is measured in each experiment, to determine the average blank viscosity. The blank final viscosity for each shear rate condition applied is the result of the average of the first and the second runs. In the examples, the average % viscosity reduction of treated samples is calculated according to the following equation for each shear rate condition applied:

Average % viscosity reduction =

100% x (average blank viscosity - sample viscosity) / average blank viscosity.

[0100] Then, the reported average% viscosity reduction from each sample tested is obtained by calculating the average of the viscosity results from each shear rate condition applied (from equation above).

[0101] The viscosity reduction agents of the examples were aqueous solution of the sodium salt of Styrene maleic anhydride or Sodium allyl sulphonate maleic acid copolymer. The aqueous solution of the sodium salt of Styrene maleic anhydride (SMA- 1000) was hydrolyzed in 2% NaOH to make a 5 wt% polymer solution before being tested.

Experiment 1

[0102] Substrate: Henan Mud.

[0103] Sodium salt styrene maleic anhydride copolymer (SMA) and sodium allyl sulphonate maleic acid copolymer of Table 3 were tested as viscosity reduction additives.

[0104] Viscosity reduction additive dosage amounts tested: 500 and 1000 PPM [0105] TABLE 5 shows results of blank testing. TABLE 5: Blank measurements

[0106] TABLE 6 shows results of testing compositions of the invention.

TABLE 6: Experimental results using treated samples

Experiment 2

[0107] Substrate: Henan Mud

[0108] Sodium salt styrene maleic anhydride copolymer (SMA) and sodium allyl sulphonate maleic acid copolymer were tested as viscosity reduction additives. [0109] Dosage amounts tested: 100, 250, and 1000 PPM

[0110] TABLE 7 shows the results of testing the blank. The blank was the red mud without the additive.

TABLE 7: Blank measurements

[0111] TABLE 8 shows the results of testing the compositions of the invention. TABLE 8: Experimental results using treated samples

Experiment 3

[0112] Substrate: Almatis Mud

[0113] Sodium salt styrene maleic anhydride copolymer (SMA) and sodium allyl sulphonate maleic acid copolymer were tested as viscosity reduction additives.

[0114] Dosage amounts tested: 100 and 1000 PPM [0115] TABLE 9 shows the results of testing the blank.

TABLE 9: Blank measurements

[0116] TABLE 10 shows the results of testing the compositions of the invention.

TABLE 10: Experimental results using treated samples

[0117] Unless indicated otherwise, concentrations of the compositions as described herein are expressed on a "real” basis (i.e., the concentrations reflect the amount of active ingredient in solution). Unless indicated otherwise, concentration units are on a weight/volume basis (i.e., percent (%) is on a g/100 mL basis, and per million (ppm) is on a weight/weight basis, g/ton of bauxite).

[0118] As used herein, the terms “a” and “an” do not denote a limitation of quantity, but rather the presence of at least one of the referenced items. “Or” means “and/or" unless clearly indicated to the contrary by the context. Recitation of ranges of values are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, and each separate value is incorporated into this specification as if it were individually recited, Thus each range disclosed herein constitutes a disclosure of any sub-range falling within the disclosed range. Disclosure of a narrower range or more specific group in addition to a broader range or larger group is not a disclaimer of the broader range or larger group. All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. “Comprises” as used herein includes embodiments “consisting essentially of" or “consisting of" the listed elements. [0119] As used herein, the term "alkyl" means a saturated straight chain, branched chain or cyclic hydrocarbon radical, such as for example, methyl, ethyl, n-propyl, iso- propyl, n-butyl, sec-butyl, t-butyl, pentyl, n-hexyl, cyclohexyl, which, in the case of cyclic alkyl groups, may be further substituted on one or more carbon atoms of the ring with a straight chain or branched alkyl group and wherein any two of such substituents may be fused to form a polyalkylene group that bridges the two ring carbon atoms to which they are attached.

[0120] As used herein, the term "aryl" or “aromatic” means a monovalent unsaturated hydrocarbon radical containing one or more six-membered carbon rings in which the unsaturation may be represented by three conjugated double bonds, which may be substituted one or more of carbons of the ring with hydroxy, alkyl, alkenyl, halo, haloalkyl, or amino, such as, for example, phenoxy, phenyl, methylphenyl, dimethylphenyl, trimethylphenyl, chlorophenyl, trichloromethylphenyl, aminophenyl, and tristyrylphenyl.

[0121] As used herein, the terminology "(C_m-C_n)" in reference to an organic group, wherein “m” and “n” are each integers, indicates that the group may contain from m carbon atoms to n carbon atoms per group.

[0122] Embodiments disclosed herein include various methods of treating a red mud slurry comprising adding a viscosity-reducing agent to a red mud slurry, in an effective amount to reduce the viscosity of the red mud slurry, as well as compositions thereof.

[0123] In certain embodiments, the viscosity-reducing agent comprises a sodium allyl sulfonate maleic acid copolymer. In certain aspects, the sodium allyl sulfonate maleic acid copolymer is a copolymer comprising monomers of formula (I) and (II), as described herein. In certain aspects, M⁺ in formula (I) is Na⁺.

[0124] In certain embodiments, the viscosity-reducing agent comprises a styrene maleic anhydride copolymer. In certain aspects, the styrene maleic anhydride copolymer is a copolymer of formula (III), as described herein. In certain aspects, the viscosity-reducing agent comprises a hydrolyzed form of the copolymer according to formula (III). [0125] CLAUSES OF THE INVENTION

[0126] The following clauses describe various aspects of the invention.

[0127] Clause 1. A method of treating a red mud slurry comprising: adding a viscosity-reducing agent to a red mud slurry, in an effective amount to reduce the viscosity of the red mud slurry, wherein the viscosity-reducing agent is selected from the group consisting of a styrene maleic anhydride copolymer or salt thereof, a sodium allyl sulfonate maleic acid copolymer or salt thereof, and mixtures thereof.

[0128] Clause 2. The method of clause 1, wherein the viscosity-reducing agent is a styrene maleic anhydride copolymer or salt thereof comprising a copolymer according to formula (III):

wherein R² is H, C₁-C₅ alkyl, C₁-C₁₀ alkyl, C₁-C₅ aryl, C₁-C₁₀ aryl, or C₁-C₁₀ arylalkyl; q is an integer from 1-300; r is an integer of from 1-300; and p is an integer from 1-300. [0129] Clause 3. The method of clause 2, wherein the viscosity-reducing agent comprises a hydrolyzed form of the copolymer according to formula (III).

[0130] Clause 4. The method of clause 1, wherein the viscosity-reducing agent is a sodium allyl sulfonate maleic acid copolymer or salt thereof, comprising a monomeric unit according to formula (I)

and a monomeric unit according to formula (II)

wherein

M⁺ is a Group I metal ion or N(R⁴)4⁺;

R⁴ is hydrogen or an optionally substituted hydrocarbyl radical comprising from about 1 to about 20 carbons; n is an integer from 1 to 300; and m is an integer of from 1-300.

[0131] Clause 5. The method of clause 4, wherein M⁺ is Na⁺.

[0132] Clause 6. The method of clause 1, wherein the red mud slurry is characterized by a solids concentration of about 10% to about 70%. [0133] Clause 7. The method of clause 1, wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 10% as compared to the viscosity of the red mud slurry absent the viscosity-reducing agent.

[0134] Clause 8. The method of clause 1, wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 20% as compared to the viscosity of the red mud slurry absent the viscosity-reducing agent.

[0135] Clause 9. The method of clause 1, wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 30% as compared to the viscosity of the red mud slurry absent the viscosity-reducing agent.

[0136] Clause 10. The method of clause 1, wherein an effective amount of the viscosity-reducing agent is added to the red mud slurry after flocculation of the red mud slurry.

[0137] Clause 11. The method of clause 1, wherein an effective amount of the viscosity-reducing agent is added to the red mud slurry at one or more washing tanks. [0138] Clause 12. The method of clause 1, wherein an effective amount of the viscosity-reducing agent is added to the red mud slurry at the feed to a press filter.

[0139] Clause 13. The method of clause 1, wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 100 ppm.

[0140] Clause 14. The method of clause 1 , wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 250 ppm.

[0141] Clause 15. The method of clause 1 , wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 1000 ppm.

[0142] Clause 16. The method of clause 1 , wherein the effective amount of the viscosity-reducing agent is in the range of about 10 ppm to about 5000 ppm.

[0143] Clause 17. The method of clause 1 , wherein the effective amount of the viscosity-reducing agent is in the range of about 50 ppm to about 3000 ppm.

[0144] Clause 18. The method of clause 1, wherein the effective amount of the viscosity-reducing agent is in the range of about 100 ppm to about 500 ppm.

[0145] Clause 19. The method of clause 1, wherein the red mud slurry is fed to a washing unit comprising one washing tank or a plurality of washing tanks arranged in series, wherein washing liquor comprising wash water is fed to the washing unit to wash the red mud slurry, wherein the viscosity reducing agent is added to the red mud slurry discharged from the washing unit.

[0146] Clause 20. The method of clause 19, wherein the plurality of washing tanks comprises at least a first washing tank and a last washing tank, and optionally one or more intermediate washing tanks between the first washing tank and last washing tank, wherein the red mud slurry passes in countercurrent flow to the washing liquor through the plurality of washing tanks such that the red mud slurry is fed to the first washing tank and travels in sequence from the first washing tank to the last washing tank to discharge from the last washing tank, and the washing liquor is fed to the last washing tank and travels in sequence from the last washing tank to the first washing tank to discharge from the first washing tank, wherein the viscosity reducing agent is added to the red mud slurry discharged from the last washing tank.

[0147] Clause 21. The method of clause 1, wherein the red mud is produced in a process for alumina production, wherein the red mud slurry is fed to a first washer in a series of washers, wherein washing liquor is fed to a last washer in the series of washers, wherein the red mud slurry passes in a succession through the series of washers in countercurrent flow to the washing liquor, wherein the viscosity-reducing agent is added to the red mud slurry discharged from the last washer in the series of washers, wherein the viscosity-reducing agent is provided in the effective amount to reduce the viscosity of the red mud slurry, and wherein the viscosity-reducing agent is selected from the group consisting of the styrene maleic anhydride copolymer or salt thereof, the sodium allyl sulfonate maleic acid copolymer or salt thereof, and mixtures thereof.

[0148] Clause 22. The method of clause 1, wherein the viscosity is measured at a shear rate of about 2.14 1/s.

[0149] Clause 23. The method of clause 1, wherein the viscosity is measured at a shear rate of about 16.05 1/s.

[0150] Clause 24. The method of clause 1 , wherein the viscosity is measured at a shear rate of about 53.50 1/s.

[0151] Clause 25. A red mud slurry composition comprising (i) a red mud slurry and (ii) a viscosity-reducing agent, wherein the viscosity-reducing agent is present in an effective amount to reduce the viscosity of the red mud slurry, and wherein the viscosity-reducing agent is selected from the group consisting of a styrene maleic anhydride copolymer or salt thereof, a sodium allyl sulfonate maleic acid copolymer or salt thereof, and mixtures thereof.

[0152] Clause 26. The red mud slurry composition of clause 25, wherein the viscosity-reducing agent is a styrene maleic anhydride copolymer or salt thereof, according to formula (III):

wherein R² is H, C₁-C₅ alkyl, C₁-C₁₀ alkyl, C₁-C₅ aryl, C₁-C₁₀ aryl, or C₁-C₁₀ arylalkyl; q is an integer from 1-300; r is an integer of from 1-300; and p is an integer from 1-300.

[0153] Clause 27. The red mud slurry composition of clause 25, wherein the viscosity-reducing agent is a sodium allyl sulfonate maleic acid copolymer or salt thereof, comprising a monomeric unit according to formula (I):

and a monomeric unit according to formula (II):

wherein

M⁺ is a Group I metal ion or N(R⁴)4⁺;

[0154] Clause 28. The red mud slurry composition of clause 27, wherein M⁺ is Na⁺.

[0155] Clause 29. The red mud slurry composition of clause 25, wherein the red mud slurry is characterized by a solids concentration of about 10% to about 70%.

[0156] Clause 30. The red mud slurry composition of clause 25, wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 10% as compared to the viscosity of the red mud slurry absent the viscosity- reducing agent.

[0157] Clause 31. The red mud slurry composition of clause 25, wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 20% as compared to the viscosity of the red mud slurry absent the viscosity- reducing agent.

[0158] Clause 32. The red mud slurry composition of clause 25, wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 30% as compared to the viscosity of the red mud slurry absent the viscosity- reducing agent. [0159] Clause 33. The red mud slurry composition of clause 25, wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 100 ppm.

[0160] Clause 34. The red mud slurry composition of clause 25, wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 250 ppm.

[0161] Clause 35. The red mud slurry composition of clause 25, wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 1000 ppm.

[0162] Clause 36. The red mud slurry composition of clause 25, wherein the effective amount of the viscosity-reducing agent is in the range of about 10 ppm to about 5000 ppm.

[0163] Clause 37. The red mud slurry composition of clause 25, wherein the effective amount of the viscosity-reducing agent is in the range of about 50 ppm to about 3000 ppm.

[0164] Clause 38. The red mud slurry composition of clause 25, wherein the effective amount of the viscosity-reducing agent is in the range of about 100 ppm to about 500 ppm.

[0165] Clause 39. The red mud slurry composition of clause 25, wherein the viscosity is measured at a shear rate of about 2.14 1/s.

[0166] Clause 40. The red mud slurry composition of clause 25, wherein the viscosity is measured at a shear rate of about 16.05 1/s.

[0167] Clause 41. The red mud slurry composition of clause 25, wherein the viscosity is measured at a shear rate of about 53.50 1/s.

[0168] By way of non-limiting example, exemplary combinations applicable to the embodiments described in this application may include any combination with one or more of Clauses 1-41, described above.

[0169] While typical embodiments have been set forth for the purpose of illustration, the foregoing descriptions should not be deemed to be a limitation on the scope herein. Accordingly, various modifications, adaptations, and alternatives can occur to one skilled in the art without departing from the spirit and scope herein.

Claims

Claims What is claimed is:

1. A method of treating a red mud slurry produced in a process for alumina production comprising: adding a viscosity-reducing agent to a red mud slurry, in an effective amount to reduce the viscosity of the red mud slurry, wherein the viscosity- reducing agent is selected from the group consisting of a styrene maleic anhydride copolymer or salt thereof, a sodium allyl sulfonate maleic acid copolymer or salt thereof, and mixtures thereof.

2. The method of claim 1 , wherein the viscosity-reducing agent is a styrene maleic anhydride copolymer or salt thereof comprising a copolymer according to formula (III):

3. The method of claim 2, wherein the viscosity-reducing agent comprises a hydrolyzed form of the copolymer according to formula (III).

4. The method of claim 1, wherein the viscosity-reducing agent is a sodium allyl sulfonate maleic acid copolymer or salt thereof, comprising a monomeric unit according to formula (I)

and a monomeric unit according to formula (II)

wherein

M⁺ is a Group I metal ion or N(R⁴)4⁺;

5. The method of claim 4 wherein M⁺ is Na⁺.

6. The method of claim 1 , wherein the red mud slurry is characterized by a solids concentration of about 10% to about 70%.

7. The method of claim 1 , wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 10% as compared to the viscosity of the red mud slurry absent the viscosity-reducing agent.

8. The method of claim 1, wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 20% as compared to the viscosity of the red mud slurry absent the viscosity-reducing agent.

9. The method of claim 1 , wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 30% as compared to the viscosity of the red mud slurry absent the viscosity-reducing agent.

10. The method of claim 1 , wherein an effective amount of the viscosity-reducing agent is added to the red mud slurry after flocculation of the red mud slurry.

11. The method of claim 1 , wherein an effective amount of the viscosity-reducing agent is added to the red mud slurry at one or more washing tanks.

12. The method of claim 1 , wherein an effective amount of the viscosity-reducing agent is added to the red mud slurry at the feed to a press filter.

13. The method of claim 1 , wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 100 ppm.

14. The method of claim 1 , wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 250 ppm.

15. The method of claim 1 , wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 1000 ppm.

16. The method of claim 1 , wherein the effective amount of the viscosity-reducing agent is in the range of about 10 ppm to about 5000 ppm.

17. The method of claim 1 , wherein the effective amount of the viscosity-reducing agent is in the range of about 50 ppm to about 3000 ppm.

18. The method of claim 1 , wherein the effective amount of the viscosity-reducing agent is in the range of about 100 ppm to about 500 ppm.

19. The method of claim 1 , wherein the red mud slurry is fed to a washing unit comprising one washing tank or a plurality of washing tanks arranged in series, wherein washing liquor comprising wash water is fed to the washing unit to wash the red mud slurry, wherein the viscosity reducing agent is added to the red mud slurry discharged from the washing unit.

20. The method of claim 19, wherein the plurality of washing tanks comprises at least a first washing tank and a last washing tank, and optionally one or more intermediate washing tanks between the first washing tank and last washing tank, wherein the red mud slurry passes in countercurrent flow to the washing liquor through the plurality of washing tanks such that the red mud slurry is fed to the first washing tank and travels in sequence from the first washing tank to the last washing tank to discharge from the last washing tank, and the washing liquor is fed to the last washing tank and travels in sequence from the last washing tank to the first washing tank to discharge from the first washing tank, wherein the viscosity reducing agent is added to the red mud slurry discharged from the last washing tank.

21. The method of claim 1 , wherein the red mud slurry is fed to a first washer in a series of washers, wherein the washing liquor is fed to a last washer in the series of washers, wherein the red mud slurry passes in a succession through the series of washers in countercurrent flow to the washing liquor, wherein the viscosity-reducing agent is added to the red mud slurry discharged from the last washer in the series of washers, wherein the viscosity-reducing agent is provided in the effective amount to reduce the viscosity of the red mud slurry, and wherein the viscosity-reducing agent is selected from the group consisting of the styrene maleic anhydride copolymer or salt thereof, the sodium allyl sulfonate maleic acid copolymer or salt thereof, and mixtures thereof.

22. The method of claim 1 , wherein the viscosity is measured at a shear rate of about 2.14 1/s.

23. The method of claim 1 , wherein the viscosity is measured at a shear rate of about 16.05 1/s.

24. The method of claim 1 , wherein the viscosity is measured at a shear rate of about 53.50 1/s.

25. A red mud slurry composition comprising (i) a red mud slurry and (ii) a viscosity- reducing agent, wherein the viscosity-reducing agent is present in an effective amount to reduce the viscosity of the red mud slurry, and wherein the viscosity-reducing agent is selected from the group consisting of a styrene maleic anhydride copolymer or salt thereof, a sodium allyl sulfonate maleic acid copolymer or salt thereof, and mixtures thereof.

26. The red mud slurry composition of claim 25, wherein the viscosity-reducing agent is a styrene maleic anhydride copolymer or salt thereof, according to formula (III):

27. The red mud slurry composition of claim 25, wherein the viscosity-reducing agent is a sodium allyl sulfonate maleic acid copolymer or salt thereof, comprising a monomeric unit according to formula (I):

and a monomeric unit according to formula (II):

wherein

M⁺ is a Group I metal ion or N(R⁴)4⁺;

28. The red mud slurry composition of claim 27, wherein M⁺ is Na⁺.

29. The red mud slurry composition of claim 25, wherein the red mud slurry is characterized by a solids concentration of about 10% to about 70%.

30. The red mud slurry composition of claim 25, wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 10% as compared to the viscosity of the red mud slurry absent the viscosity-reducing agent.

31. The red mud slurry composition of claim 25, wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 20% as compared to the viscosity of the red mud slurry absent the viscosity-reducing agent.

32. The red mud slurry composition of claim 25, wherein the viscosity-reducing agent is capable of reducing the viscosity of the red mud slurry by at least 30% as compared to the viscosity of the red mud slurry absent the viscosity-reducing agent.

33. The red mud slurry composition of claim 25, wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 100 ppm.

34. The red mud slurry composition of claim 25, wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 250 ppm.

35. The red mud slurry composition of claim 25, wherein the effective amount of the viscosity-reducing agent is equal to or greater than about 1000 ppm.

36. The red mud slurry composition of claim 25, wherein the effective amount of the viscosity-reducing agent is in the range of about 10 ppm to about 5000 ppm.

37. The red mud slurry composition of claim 25, wherein the effective amount of the viscosity-reducing agent is in the range of about 50 ppm to about 3000 ppm.

38. The red mud slurry composition of claim 25, wherein the effective amount of the viscosity-reducing agent is in the range of about 100 ppm to about 500 ppm.

39. The red mud slurry composition of claim 25, wherein the viscosity is measured at a shear rate of about 2.14 1/s.

40. The red mud slurry composition of claim 25, wherein the viscosity is measured at a shear rate of about 16.05 1/s.

41. The red mud slurry composition of claim 25, wherein the viscosity is measured at a shear rate of about 53.50 1/s.