TREATMENT OF PHOSPHATE TAILINGS CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No.

62/536, 170, filed 24 July 2017, the entire disclosure of which is hereby incorporated by reference herein.

TECHNICAL FIELD

[0002] The present disclosure relates to dewatering and consolidation of phosphate tailings.

BACKGROUND

[0003] Phosphate containing ores are a valuable source of fertilizer. The ores contain sand, clay and other minerals that must be separated from the phosphate rich component. In Florida, USA, for example, phosphate ores are almost equal parts sand, clay and phosphate minerals.

[0004] In order to hydro-transport the phosphate ore from the mine site to an extraction or beneficiation plant, the mined ore is mixed with water to form a slurry. Washing, screening, desliming and flotation operations then raise the phosphate grade to fertilizer production requirements.

[0005] There are various waste streams produced by these processes and these introduce a number of environmental problems. In Florida, about one ton each of waste sand and clay is produced for each ton of final phosphate product. Approximately 100,000 tons a day of phosphatic clays in the form of tailings slurries are generated, which are stored in slime or clay ponds.

[0006] Clay ponds or settling areas are contained by above-grade dam walls. A tailings clay slurry with a solids content of about 3% is pumped into these containment ponds and surface water runs off through spill ways. Over time, the clays consolidate to a material with the consistency of toothpaste, with a 15-18% solids content. Further evaporation of water is limited by the formation of a surface crust and it can take decades to get to a solids content of just 25- [0007] In Florida, every acre mined is required to be reclaimed for productive use.

Because the clays have high shrink-sweil characteristics, low mechanical strength and low hydraulic conductivity, options for reclamation and restoration of clay ponds have been limited. As a result, about 40% of mined land has been left as unstable clay settling areas.

[0008] One option that has been explored is the use of sand-clay mixtures. See Beavers and Hanlon et ai., 2015, Publication SL423, Sand-Clay Mix in Phosphate Mine Reclamation: Characteristics and Land Use, UF/IFAS Extension at http://edis.ifas. ufl.edu/ss636. Sand was mixed with clay tailings slurries to give a tailings slurry with a solids content of about 28% and sand-clay solids ratios of 2: 1. This slurry must still be contained by dams, but over a period of about 4 years can reach a solids content of about 71%. The dam walls can then be pushed in, but form an over-layer that is not as nutrient rich if the recovered land is to be used for agriculture. However, there is a problem with sand-clay segregation and the land is still difficult to traverse with farm equipment. It cannot support the weight of buildings and roads. Higher sand-clay ratios (about 4: 1) improve the physical properties of the reclaimed land, but there is not sufficient sand available to use at these levels.

[0009] Current landscape restoration priorities seek to maximize developable land, so at present there are no new sand-clay mix areas planned for Florida, See Hanlon et ai, cited above. The clay or slime ponds thus remain a significant environmental problem, not only in Florida, but also in other regions of the world where phosphates are mined,

[0010] There is a clear need for a technology that can produce tailings mixtures with improved physical properties including a relatively fast dewatering with low segregation of solids.

SUMMARY OF THE DISCLOSURE

[001 1] Advantages of the present disclosure include processes to dewater aqueous waste compositions from phosphate mining and extraction operations, e.g., phosphate tailings, to produce high solids content materials. Such phosphate tailings result from washing, screening, deliming and flotation of phosphate mining and extraction operations,

[0012] These and other advantages are satisfied, at least in part, by a process of consolidating solids in the phosphate tailings. The process comprises treating a phosphate tailings, which can include solids, some or all of which are sized as fines, and process water. Advantageously, the process can include treating the phosphate tailings with the at least one highly water soluble salt or solution thereof. Optionally, the process can further include treating the phosphate tailings with either or both of at least one polymer flocculant or solution thereof and/or coarse particles, e.g., sand, to form a treated tailings. The treated tailings can include a consolidated material in the process water. The process water can then be advantageously separated from the consolidated material. The consolidated solids can then be placed in lined landfills or used as a source of building materials or valuable minerals.

[0013] Implementations of the process of the present disclosure include, for example, (i) treating phosphate tailings with at least one highly water soluble salt to form a treated tailings including a consolidated material in the process water, (ii) treating phosphate tailings with at least one highly water soluble salt and at least one polymer flocculant to form a treated tailings including a consolidated material in the process water, (iii) treating phosphate tailings with at least one highly water soluble salt thereof, and coarse particles to form a treated tailings including a consolidated material in the process water, and (iv) treating phosphate tailings with at least one highly water soluble salt, at least one polymer flocculant and coarse particles to form a treated tailings including a consolidated material in the process water. Each of these implementations can include aqueous solutions of the salt and/or polymer flocculant to treat the tailings. Each of these implementations can include separating the process water from the consolidated material.

[0014] Embodiments of the processes include one or more of the following features individually or combined. For example, the tailings can include rare earth elements. In still other embodiments, the at least one highly water soluble salt can have a solubility in water (a salt/water solubility) of at least about 5 g/100 g at 20 °C, e.g., at least about 10 g/100 g at 20 °C, In other embodiments, the at least one highly water soluble salt is a non-hydrolyzing salt. In still further embodiments, the at least one highly water soluble salt can have a monovalent cation and can include an ammonium based salt, a phosphate based salt, or a sulfate based salt, or combinations thereof.

[0015] In certain embodiments, the treated phosphate tailings can have a salt-tailings concentration of at least 0.5 wt% of the at least one highly water soluble salt and preferably no less than about 1 wt%, such as at least about 2 wt% and even greater than about 3 wt%, 4 wt%, 5 wt%, etc. of the at least one highly water soluble salt. In some embodiments, the at least one polymer flocculant is a poly acryl amide or co-polymer thereof. The treated phosphate tailings can have a polymer-tailings concentration of the at least one polymer flocculant of not less than zero and up to about 0.001 wt%, e.g., up to about 0.003 wt%, 0.005 wt%, 0.01 wt% or 0.04 wt%. Advantageously, when added, the polymer flocculant can form high density floes, e.g., having a density greater than the process water, which facilitates separation and dewatering of the consolidated materials. In other embodiments, the tailings also can be treated with coarse particles, e.g., sand, at a sand to fines ratio of less than 4: 1, e.g., between about 2.5: 1.0 to 0.5: 1 or between about 2.25: 1 to about 0.75: 1 .

[0016] In various embodiments, treating the phosphate tailings can include combining the phosphate tailings with a solution including the at least one highly water soluble salt and the at least one polymer flocculant. In some embodiments, treating the phosphate tailings can include combining a stream of the tailings with a stream of a solution including the at least one highly water soluble salt and a separate stream of a solution including the at least one polymer flocculant. Alternatively, or in combination, treating the phosphate tailings can include combining a stream of the tailings with a stream of a solution including both the at least one highly water soluble salt and the at least one polymer flocculant. Coarse particles (sand) can also be added to the phosphate tailings or stream thereof and/or to any or all of the salt(s) and/or polymer(s) solution streams. Advantageously, the streams can be mixed inline and/or with the aid of an inline mixer. In certain embodiments, treating the tailings can be earned out at ambient temperature, e.g., no more than about 2 °C to about 5 °C above ambient temperature. In other embodiments, treating phosphate tailings can be carried out at a temperature of no more than about 50 °C, e.g., no more than about 40 °C or 30 °C. In still further embodiments, the aqueous coal waste composition includes using a solution of one or more highly soluble salts sourced from a natural or existing source such as seawater or a body of hypersaline water or sourced from a brine waste stream.

[0017] In still further embodiments, the process water can be separated from the consolidated material by any one or more of decanting, filtering, vacuuming, gravity draining, electrofiltering, etc. or combinations thereof. In various embodiments, separating the process water from the consolidated material can include mechanically dewatering the consolidated material, e.g., mechanically dewatering the consolidated material by a dewatering screw industrial filter press, e.g., a plate and frame press, recessed plate and frame filter presses, automatic filter presses, etc. Once separated, the consolidated material can be transferred for further dewatering or disposal,

[0018] In practicing aspects of the processes of the present disclosure and the various embodiments thereof, the separated process water can include the at least one highly water soluble salt and the process can further comprise one or more of: (i) recovering at least a portion of the separated process water; (ii) recycling at least a portion of recovered separated process water to treat additional phosphate tailings; (iii) purifying at least a portion of recovered process water; and/or (iv) concentrating the at least one highly water soluble salt in recovered process water to form a brine and using the brine to treat additional phosphate tailings.

[0019] Yet another aspect of the present disclosure includes recovering valuable materials from the phosphate tailings. The valuable materials can include rare earth elements associated with solids such as clays in the tailings. Therefore, in practicing certain aspects of the processes of the present disclosure and the various embodiments thereof, the phosphate tailings can further include rare earth element materials which can be recovered by treating the tailings with at least one highly water soluble salt, e.g., an ammonium based salt such as ammonium sulfate, to form a treated tailings including REE materials in the process water and/or in the consolidated materials. In some embodiments, the process further includes separating the process water from the consolidated material and recovering the REE materials from the separated process water and/or the consolidated materials.

[0020] Advantageously, the processes of the present disclosure can consolidate the solids of the phosphate tailings to produce a consolidated material having a solids content in excess of about 45% by weight, e.g., a solids content of greater than about 50% and higher than about 60%, 65%, 70% and 75% by weight,

[0021] In practicing certain aspects of the processes of the present disclosure and the various embodiments thereof, the consolidated material formed in the treated tailings can result in a high solids content after mixing and/or dewatering the treated tailings in a short period of time. In some embodiments, the consolidated material can have a solids content of greater than about 50% and at least about 60%, 65%, 70%, 75% and 80% by weight after mixing and/or dewatering.

[0022] Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent similar elements throughout and wherein:

[0024] Figure I schematically illustrates an exemplary embodiment of a process of consolidating phosphate tailings.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0025] The present disclosure relates to treating aqueous waste compositions from phosphate mining and extraction operations such as phosphatic clay tailings and slimes or any other aqueous waste stream from phosphate mining, hereinafter phosphate tailings or tailings. The processes of the present disclosure are applicable to phosphate tailings generated during mining operations and phosphate tailings deposited in ponds or other containment areas. As described in the background section, phosphate tailings including phosphatic clay slurries are a waste by-product of phosphate mining and extraction and include process water, solids, some of which are sized as fines, e.g., fine clay particles, and small amounts of other particles. The fraction of solids in the phosphate tailings varies, but is typically of the order of 3 wt% in the initial tailings and in the range of 15-30 wt% for material stored in clay or slime ponds.

[0026] The particulate solids in the tailings of the present disclosure can be minerals and mineral like materials, i.e., mineral matter, clays, silt, and in sizes ranging from fines to coarse solids. The term fines as used herein is consistent with the Canadian oil sands classification system and means solid particles with sizes equal to or less than 44 microns (μτη). The composition of the fines depends on the source of the materials, but generally fines are comprised mostly of silt and clay material and sometimes minerals or mineral matter, depending on the ore. Sand is considered solid particles with sizes greater than 44 μπι. The tailings from phosphate mining and extraction operations can also include a significant amount of fines by weight (>5 wt%) as their solids content.

[0027] Advantageously, the process of the present disclosure can consolidate the solids of phosphate tailings to produce solids content initially in excess of about 35% by weight, e.g., solids content of greater than about 40 wt%, 50 wt%, 60 wt¾ or 70 wt%, or higher.

[0028] The terms coagulation and flocculation are often used interchangeably in the literature. As used herein, however, coagulation means particle aggregation brought about by the addition of hydrolyzing salts, whereas flocculation means particle aggregation induced by flocculating polymers. Hydrolyzing salts undergo hydrolysis when added to water to form metal hydroxides, which precipitate from the solution, trapping fines and other minerals in the coagulating mass. Hydrolyzing salts typically have low solubility in water and are used as coagulants. Aggregation induced by flocculation, in contrast, is believed to be the result of the polymer binding to the particles thereby tying the particles together into a so called floe causing aggregation of the particles.

[0029] In practicing aspects of the present disclosure, phosphate tailings can be consolidated by treating the tailings with one or more highly water soluble sait(s) or an aqueous solution thereof to destabilize and consolidate solids in the tailings, e.g., to destabilize and consolidate fines in the tailings. Aggregation induced by the addition of salts is believed to be the result of destabilizing the particles suspended in the fluid by an alteration or a shielding of the surface electrical charge of the particles to reduce the inter-particle repulsive forces that prevent aggregation. In certain embodiments, the tailings includes a suspension of particulate solids including fines in an aqueous liquid. The process includes treating the phosphate tailings with the highly water soluble salt(s) or an aqueous solution thereof to form a treated tailings including a consolidated material, e.g. consolidated fines, in process water. The process water can then be separated from the consolidated material. [0030] Salts that are useful in practicing the present disclosure include salts that are highly soluble in water. A highly water soluble salt as used herein is one that has a solubility in water of greater than 2 g of salt per 100 g of water (i.e., a salt/water solubility of 2g/100g) at 20 °C. Preferably the highly water soluble salt has a water solubility of at least about 5 g/100 g at 20 °C, e.g., at least about 10 g/100 g of salt/water at 20 °C.

[003 ] In addition, the highly water soluble salts used in the processes of the present disclosure are preferably non-hydrolyzing. Hydrolyzing salts undergo hydrolysis when added to water to form metal hydroxides, which precipitate from the solution. Such hydrolyzing salts are believed to form open floes with inferior solids content and cannot be readily recycled for use with additional phosphate tailings in continuous or semi-continuous processes. In addition, hydrolyzing salts typically have low solubility in water and are used at elevated temperatures to ensure sufficient solubility for aggregation, which is an energy intensive process. See US 4,225,433 which discloses the use of lime as a coagulating agent at a temperature of 75 °C.

[0032] Further, the highly water soluble salts are preferably not carboxylate salts since such organic acid salts tend to be more expensive than inorganic salts and can be deleterious to plant and/or animal life.

[0033] Highly water soluble salts that are not hydrolyzing and useful in practicing processes of the present disclosure include salts having a monovalent cation, e.g., alkali halide salts such as sodium chloride, potassium chloride; also salts with monovalent cations such as sodium nitrate, potassium nitrate, sodium and potassium phosphates, sodium and potassium sulfates, etc. are useful in practicing processes of the present disclosure. Other monovalent cationic salts useful in practicing processes of the present disclosure include ammonium based salts such as ammonium acetate (XI 1 1 X)-X ammonium chloride (NH ₄ C1), ammonium bromide (NH ₄ Br), ammonium carbonate i | ). ( s), ammonium bicarbonate (NH ₄ HC0 ₃ ), ammonium nitrate ( H ₄ NO ₃ ), ammonium sulfate ((NH ₄ ) ₂ S0 ₄ ), ammonium hydrogen sulfate (NH ₄ HSO ), ammonium dihydrogen phosphate ( H ₄ H ₂ PO ₄ ), ammonium hydrogen phosphate ((NH ₄ ) ₂ HP0 ), ammonium phosphate ((NH ₄ ) ₃ P0 ₄ ), etc. Mixtures of such salts can also be used.

[0034] Ammonium based salts are useful for practicing the present disclosure since residual ammonium based salts on the consolidated material after combining the salt with the aqueous phasphate tailings can be beneficial to plant life. In fact, many of the ammonium based salts are useful as fertilizers, e.g., ammonium chloride, ammonium nitrate, ammonium sulfate, etc. Many of the monovalent sulfate and phosphate salts are also useful as fertilizers. In certain embodiments of the present disclosure, the highly water soluble salt or salts used in the processes of the present disclosure can preferably be non-toxic and beneficial to plant life to aid in environmental remediation and the restoration of mine sites.

[0035] In one aspect of the present disclosure, treating phosphate tailings with a highly water soluble salt destabilizes and consolidates solids in the tailings. Such a process can include mixing the phosphate tailings, which includes fines and process water, with a highly water soluble salt to consolidate the fines, and separating the process water from the consolidated fines to produce a high solids content, e.g., at least 45% by weight. In certain embodiments, the highly water soluble salt is an ammonium based salt.

[0036] In other aspects of the present disclosure, a salt that serves to inhibit swelling of the clays in aqueous suspensions, such as highly water soluble salts containing potassium ions (K ⁺ ), should preferably be used. Water soluble quaternary ammonium salts, such as choline chloride, can also be used to inhibit clay swelling.

[0037] When a sufficiently high concentration of the highly water soluble salt is included in the treated tailings, the salt can destabilize and consolidate solids in the tailings. For a relatively short process times with a relatively low energy input, the salt-tailings concentration of the at least one highly water soluble salt should preferably be at least 0.5 wt% and preferably no less than about 1 wt%, such as at least about 2 wt% and even at least about 3 wt%, 4 wt%, 5 wt%, etc. The term "salt-tailings concentration" as used herein refers to the concentration of the highly water soluble salt(s) in the treated tailings and is determined by taking the percentage of the mass of highly water soluble salt(s) divided by the combined mass of the salt(s) plus the tailings and any water used to dilute the salt(s). For example, combining 1 part undiluted (i.e., neat) salt to 99 parts tailings by weight results in a salt-tailings concentration of 1 wt%. Alternatively, treating tailings with an equal weight of a 2 wt% solution of the salt also results in a salt-tailings concentration of 1 wt% in the treated tailings.

[0038] The highly water soluble salt(s) can be used to treat phosphate tailings of the present disclosure as a solid, e.g., combining the salt as a powder with the tailings. Alternatively, the salt can be used to treat as a solution, e.g., combining an aqueous salt solution with the tailings. In some aspects of the present disclosure, an aqueous solution of the highly water soluble salt can be prepared having a concentration of no less than about 1 wt%, e.g., greater than about 2 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, 20 wt%, 30 wt% and even as great as a 40 wt% or as an aqueous salt slurry.

[0039] In some embodiments of the present processes, it can be more advantageous to use a natural source of a highly soluble salt or salts such as in a natural body of water including such salts in sufficiently high concentration such as at least about 2 wt% and even at least about 3 wt% or greater. For example, ocean or seawater can be used as a source of highly soluble salts, which can significantly improve the economics of the process under certain conditions. The vast majority of seawater has a salinity of between 31 g/kg and 38 g/kg, that is, 3, 1 -3.8%. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g 'L, 599 mM). Seawater includes a mixture of salts, containing not only sodium cations and chlorine anions (together totaling about 85% of the dissolved salts present), but also sulfate anions and calcium, potassium and magnesium cations. There are other ions present (such as bicarbonate), but these are the main components. Another natural source of highly soluble salts that can be used as a source of highly soluble salts includes a hypersaline body of water, e.g., a hypersaline lake, pond, or reservoir. A hypersaline body of water is a body of water that has a high concentration of sodium chloride and other highly soluble salts with saline levels surpassing ocean water, e.g., greater than 3.8 wt% and typically greater than about 10 wt%. Such hypersaline bodies of water are located on the surface of the earth and also subsurface, which can be brought to the surface as a result of ore mining operations.

[0040] In other embodiments of the present processes, it can be advantageous to use a brine produced in desalinization of salt water as a source of a highly water soluble salt(s). The brine can be used alone as a source of a highly water soluble salt(s) or in combination with another source of a highly water soluble salt(s) such as seawater.

[0041] The phosphate tailings and aqueous salt solution or slurry should be mixed at a ratio sufficient to destabilize the tailings to cause consolidation of the solids therein. In one aspect of the present disclosure, the tailings and the salt solution are mixed at a ratio within a range of about 5.0: 1.0 to about 1.0:5.0, e.g., mixed at a ratio within a range of about 3 : 1 to about 1 :3, such as about 1.5: 1.0 to about 1.0: 1.5 tailings to salt solution. [0042] After treating the phosphate tailings with at least one highly water soluble salt, the solids in the tailings can be consolidated such as by mixing followed by gravity sedimentation in a settling tank or pond, or mechanical dewatering, i.e., applying an external force to the consolidated material, to increase the rate of forming a consolidated material in the treated composition. The consolidated material can be separated from the process water by decanting, filtering, electrofiltration, cross-flow filtering, vacuuming, a dewatering screw, an industrial filter press, e.g., a plate and frame press, recessed plate and frame filter presses, automatic filter presses, etc, or any combination thereof. Once separated, the consolidated material can be transferred for further dewatering or disposal.

[0043] Although highly water soluble salts can destabilize and consolidate solids in the phosphate tailings including fines, it was found that the process could be significantly improved by adding one or more polymer flocculant(s). The addition of a polymer flocculant to the highly water soluble salt significantly reduced the time for consolidation of fines. In addition, the processes of the present disclosure can also include treating phosphate tailings with coarse particles, e.g., particles with sizes greater than 44 μιη, such as sand, to increase the solids content. Mixing with sand is appropriate for phosphate tailings that have solids mostly as fines, as the fine particles can sit in the voids between the coarse particles, enhancing packing and solids content. For certain tailings the addition of sand is not needed to achieve a high solids content, as there can be sufficient coarse particles present in the tailings to give a high solids content material.

[0044] Hence, implementations of the process of the present disclosure include, for example, (i) treating the composition with at least one highly water soluble salt to form a treated composition including a consolidated material in the process water, (ii) treating the tailings with at least one highly water soluble salt and at least one polymer flocculant to form a treated tailings including a consolidated material in the process water, (iii) treating the tailings with at least one highly water soluble salt thereof, and coarse particles to form a treated tailings including a consolidated material in the process water, and (iv) treating the tailings with at least one highly water soluble salt, at least one polymer flocculant and coarse particles to form a treated tailings including a consolidated material in the process water. Each of these implementations can include aqueous solutions of the salt and/or polymer flocculant to treat the tailings. Each of these implementations can include separating the process water from the consolidated material . The process water can then be readily separated from the consolidated material as, for example, by one or more of decanting, filtering, gravity draining, electrofiltering, cross-flow filtering, vacuuming and other evaporating techniques, etc. and/or by one or more of a device for dewateiing consolidated material such as a centrifuge, decanting centrifuge, dewatering screw, hydrocyclone, vacuum belt filter, filter press or pressing devices, etc. In addition, the separated consolidated material can be disposed or deposited in a containment structure which allows removal of released water from the consolidated material . In addition, the process water separated from the consolidated material can be concentrated and cycled back to treat additional phosphate tailings.

[0045] Polymers that are useful in practicing the present disclosure include water soluble flocculating polymers such as a nonionic polyacrylamide, an anionic polyacrylamide (APAM) such as a polyacryl amide-co-acrylic acid, and a cationic polyacrylamide (CP AM), which can contain co-monomers such as acryloxyethyltrimethyl ammonium chloride, methacryloxyethyltrimethyl ammonium chloride, dimethyldiallyammonium chloride (DMDAAC), etc. Other water soluble flocculating polymers useful for practicing the present disclosure include a polyamine, such as a polyamine or quaternized form thereof, e.g., polyacrylamide-co-dimethylaminoethylacrylate in quaternized form, a polyethyleneimine, a polydial lyldimethyl ammonium chloride, a polydicyandiamide, or their copolymers, a polyamide-co-amine, polyelectrolytes such as a sulfonated polystyrenes can also be used. Other water soluble polymers such as polyethylene oxide and its copolymers can also be used. The polymer flocculants can be synthesized in the form of a variety of molecular weights (MW), electric charge types and charge density to suit specific requirements. Advantageously, the flocculating polymer used in practicing processes of the present disclosure do not include use of activated polysaccharides or activated starches, i.e., polysaccharides and starches that have been heat treated, in sufficient amounts to lower the density of the floe to below the density of the process water from which they are separated. Such activated polysaccharides and activated starches when used in sufficiently high dosages tend to form low density floes which rise to the surface of an aqueous composition, which can hinder removal of solids in large scale operations involving high solids content and can also hinder dewatering of consolidated material. [0046] The amount of polymer(s) used to treat phosphate tailings of the present disclosure should preferably be sufficient to flocculate the solids in the tailings and any added sand. The amount of polymer(s) used to treat phosphate tailings can be characterized as a concentration based on the total weight of the tailings or as a dosage based on the weight percent of the solids in the tailings,

[0047] In some embodiments of the present disclosure, the concentration of the one or more polymer flocculant(s) in the treated tailings has a polymer-tailings concentration of no less than zero and up to about 0.001 wt%, e.g., up to about 0.003 wt%, 0,005 wt% or up to about 0.01 wt%. For relatively short processing times, consolidation of the fines/sand mixture can be obtained at polymer-tailings concentrations no less than about 0.04 wt%. The term "polymer- tailings concentration" as used herein refers to the concentration of the flocculating polymer(s) in the treated tailings and is determined by taking the percentage of the mass of the polymer(s) divided by the combined mass of the polymer(s) plus the tailings and any water used to dissolve the polymer(s). For example, combining 1 part undiluted (i.e., neat) polymer to 9999 parts tailings by weight results in a polymer-tailings concentration of 0.01 wt%. Alternatively, treating the tailings an equal weight of a 0.02 wt% solution of the polymer also results in a polymer-tailings concentration of 0.01 wt%. In certain embodiments, phoasphate tailings are treated with at least one polymer flocculant to yield a polymer-tailings concentration of up to about 0,02 wt%, such as no less than about 0.03 wt%, 0.04 wt%, 0.05 wt%, and even at least about 0.07 wt%, 0.09 wt%, 0.1 wt%, 0.2 wt%, etc. The amount of polymer flocculant can be used in greater concentrations. However, after certain high concentrations it becomes difficult to dissolve the flocculant, the solution becomes too viscous and the process is less economical.

[0048] In some embodiments of the present disclosure, the concentration of the one or more polymer flocculant(s) in the treated tailings has a dosage (weight of the flocculant(s) to weight of the solids in the tailings) of no less than zero and up to about 0.005 wt%, e.g., up to about 0.01 wt% and in some implementations up to about 0,015 wt%, 0.020 wt%, 0,025 wt%, 0.03 wt%, or 0.04 wt%.

[0049] The amount of polymer flocculant can be reduced if the salt-tailings concentration is increased. While the reason for this effect is not clear, a very low polymer-tailings concentration of no less than about 0.001 wt%, e.g. no less than about 0.003 wt%, 0,005 wt%, 0,01 wt%, 0,02 wt%, 0.03 wt%, 0,04 wt%, 0,05 wt %, for example, can achieve reasonably fast consolidation of solids in the tailings if the salt-tailings concentration is increased.

[0050] Coarse particles useful for practicing certain processes according to the present disclosure are preferably sand and when used in treating tailings the amount of such particles are preferably in a sand to fines ratio (SFR ratio) of less than 4: 1, e.g., between about 2,5: 1.0 to 0.5: 1 or between about 2.25: 1 to about 0.75: 1. The SFR ratio is calculated by determining the amount of sand added to an estimated amount of solid fines in the phosphate tailings on a weight basis. It is believed that the use of coarse particles facilitates packing of the consolidated fines which advantageously increases the solids content and can even form a jammed structure of consolidated solids, i.e. a structure in which generally individual particles of the consolidated solid can no longer move freely relative to other particles.

[0051] Treating phosphate tailings including solids, some of which can be sized as fines, and process water with at least one highly water soluble salt and optionally with either or both of at least one polymer flocculant and/or optionally sand can be carried out in a number of ways. In certain embodiments, treating the phosphate tailings includes combining and/or mixing the various components. In addition, the at least one salt can be added directly to the phosphate tailings either as an undiluted powder or as a solution, the at least one polymer flocculant can be added directly to the phosphate tailings either as an undiluted material or as a solution, and the sand can be added to the phosphate tailings directly or with the salt and/or polymer or solutions thereof. The salt and polymer can be combined in a single solution, with or without sand, and combined with the phosphate tailings. The order of combining the salt, polymer and sand to the phosphate tailings can give equivalent results and optimization of the process will depend on the character of the tailings, and the scale and equipment used in the process.

[0052] However, it tends to be more convenient to use one or more solutions including the one or more highly water soluble salt(s) and the one or more polymer flocculant(s) followed by combining the one or more solutions with the tailings and sand. In certain embodiments, an aqueous solution of one or more highly water soluble salt(s) can be used having a concentration of no less than about 0.5 wt% or 1 wt%, e.g., at least about 2 wt¾, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 10 wt%, 20 wt%, 30 wt% and even as great as a 40 wt% or as an aqueous salt slurry for use in treating the tailings. The one or more polymer flocculant(s) can also be included in the aqueous solution of the salt(s) and can have a concentration of no less than about 0.005 wt%, e.g. no less than about 0.01 wt%, 0.04 wt%, 0.05 wt %, 0.1 wt%, 0.2 wt%, 0.4 wt%, for example. The aqueous solution of the highly water solubl e salt(s) and polymer flocculant(s) can be used to treat the tailings and can be combined with such tailings at a ratio of between about 5.0: 1.0 and about 1.0:5.0, e.g., at a ratio between about 3 : 1 to about 1 :3 and about 1.5: 1.0 to about 1.0: 1.5 of tailings to aqueous solution. Sand can be combined with the tailings before, during, or after combining the tailings with the solutions.

[0053] Because highly water soluble salts and polymer fiocculants that are preferably water soluble are used in the process of the present disclosure, the temperature of the treated phosphate tailings need not be elevated above ambient temperature to practice the process. In certain embodiments, treating the tailings according to the various embodiments herein can be carried out at ambient temperature, e.g., no more than about 2 °C to about 5 °C above ambient temperatures. In other embodiments, treating the phosphate tailings can be carried out at a temperature of no more than 50 °C, e.g., no more than about 40 °C or 30 °C.

[0054] In practicing aspects of the present disclosure, phosphate tailings, which include solids and process water, can be consolidated by treating the tailings with at least one highly water soluble salt or aqueous solutions thereof and can optionally include either or both of (i) at least one polymer floccuiant, e.g., a water-soluble flocculating polymer, or aqueous solutions thereof, and/or optionally coarse particles, e.g., sand to form a treated tailings. Treating tailings in this manner can cause destabilization and consolidation of the solids, e.g., fines and sand, in the treated tailings to form a consolidated material, which can settle under gravity relatively quickly, in the process water. The process water can then be readily separated from the con sol i dated materi al .

[0055] The treated tailings and/or consolidated material can be further dewatered to further separate the process water from the consolidated material and, in some instances, further consolidate the solids. In some embodiments, the consolidated material formed in the treated tailings can be separated from the process water by any one or more of decanting, filtering, e.g., electrofiltering, cross-flow filtration, gravity draining, vacuuming and other evaporating techniques, etc. and/or by any one or more of a mechanical dewatering, i.e., applying an external force to the consolidated material, with a device for dewatering consolidated material such as by applying a centrifuge, decanting centrifuge, dewatering screw, hydrocyclone, filter press, pressing device, etc. or combinations thereof. In one aspect of the processes of the present disclosure, the process water can be separated from the consolidated material by passing a stream of treated tailings through a cross-flow filter, e.g., a porous or slotted pipe, which filters and dewaters the treated tailings stream to separate the process water from the consolidated material. In another aspect of the processes of the present disclosure, the process water can be separated from the consolidated material by gravity draining to achieve a solids content of at least about 70% within about a month after treating the tailings, e.g., within about two weeks or within about one week of gravity draining after treating the tailings. In still further aspect of the processes of the present disclosure, the consolidated material can be further dewatered after separating from the treated tailings by depositing the separated consolidated material in a thin lift deposition or in one or more dewatering tubes.

[0056] The consolidated material formed in the treated tailings can advantageously have a high solids content, e.g., a solids content of greater than about 50% and at least about 60%, 65%>, 70% and 75% by weight. In addition, the consolidated material formed in the treated tailings according to certain embodiments can result in a high solids content after mixing and/or dewatering the treated tailings in a short period, e.g., less than about 10 minutes. In embodiments of the present disclosure, the consolidated material can have a solids content of greater than about 50% and at least about 60%, 65%, 70%, 75% and 80% by weight in less than about 5 minutes, such as less than about 2 minutes and preferably less that about 1 minute after mixing and/or dewatering.

[0057] In an embodiment of the present disclosure, the process includes mixing the tailings with a highly water soluble salt, e.g., an ammonium based salt, a water soluble polymer, e.g., a polyacrylamide, and optionally sand, such as in a sand to fines ratio of between 0.75: 1 and 2.25: 1 to form a treated tailings including a consolidated material having a high solids content, e.g., a solids content of greater than about 50% by weight, e.g., at least about 60%, 65%, 70 wt% or higher in less than 10 minutes, e.g., less than 5 minutes and even less than 2 minutes, depending on the dewatering method used.

[0058] Another advantage of the processes of the present disclosure is the recovery of materials from phosphate tailings that include rare earth elements. For example, certain phosphate tailings can include valuable minerals that include rare earth elements. A rare earth element (REE), as defined by IUPAC, is one of a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides, as well as scandium and yttrium. Scandium and yttrium are considered rare earth elements because they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties. Many of the REE are used in electronic devices, magnets, high performance coatings. Such REE include cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb) and yttrium (Y).

[0059] REE in phosphate tailings can be in the form of an ion or oxide. For example, zirconium can be present as zircon, ZrSi0 ₄ , titanium can be present as the minerals ilmenite, leucoxene and rutile. Phosphate tailings can contain rare earth elements.

[0060] The processes of the present disclosure are useful in recovering REE. It is believed that in some phosphate tailings, REEs absorb on the surface of clays in tailings. In other compsitions, REEs are included also among the solids of the tailings but can also be in the process water. Absorbed REEs can be exchanged with the highly water soluble salts of the present disclosure, e.g., ammonium based salts due to an exchange of ammonium ions for the REE ions. REEs from the solids of the phosphate tailings can be obtained by leaching the solids with acid followed by extraction and precipitation or by caustic decomposition followed by acid leaching.

[0061] Another aspect of processes of the present disclosure includes consolidating phosphate tailings, which include REE, by treating the tailings with at least one highly water soluble salt, e.g., an ammonium based salt such as ammonium sulfate, to form a treated tailings including a consolidated material in process water which includes the REE materials in the process water and/or among the consolidated materials. In one aspect of the present disclosure, the treated tailings consolidate the fines and also separates REE materials from the solids and into the process water. The process water can then be separated from the consolidated material and the REE materials can be recovered from the separated process water. The REE materials can be recovered from the process water by precipitation, e.g., using oxalic acid, or extraction. Other methods for recovering REE from the process water include mineral processing and physical beneficiation, deep eutectic solvents/ionic liquids extraction, acid dissolution, high temperature phase separations, use of REE selective sorbents, photophoresis, in-situ brine injection and extraction, reactive grinding, etc. In other aspect of the present disclosure, the treated tailings include a consolidated material and REEs are among the consolidated material. The process water can then be separated from the consolidated material. The consolidated material can then be leached with acid, e.g., nitric acid, sulfuric acid, etc., followed by extraction with solvent and/or ion exchange resins and precipitated. Alternatively, the consolidated material can then be treated with a caustic reagent such as sodium hydroxide to decompose certain of the materials to form hydroxides of the REEs followed by leaching in acid, e.g., HC1.

[0062] In addition, the phosphate tailings can be treated with at least one polymer flocculant and optionally sand to form the treated tailings. The treated tailings can have a salt- tailings concentration of at least 0.5 wt¾ of the at least one highly water soluble salt and preferably no less than about 1 wt%, such as at least about 2 wt% and even greater than about 3 w†%, 4 wt%, 5 wt%, etc. of the at least one highly water soluble salt.

[0063] The process of the present disclosure allows for large scale treatment of phosphate tailings in a continuous or semi-continuous process with further recovering, recycling and purifying at least a portion of the process water in the tailings and optionally recovering REE materials. When non-hydrolyzing, highly water soluble salts are used in the processes of the present disclosure, the process water separated from an initial treated tailings can advantageously include a significant amount of the one or more highly water soluble salt(s) initially used to treat the tailings. In practicing aspects of the processes of the present disclosure and the various embodiments thereof, the separated process water can include the at least one highly water soluble salt and the process can further comprise one or more of: (i) recovering at least a portion of the separated process water; (ii) recycling at least a portion of recovered, separated process water to treat additional phosphate tailings: and/or (iii) purifying at least a portion of recovered process water. In some implementations, the recovered, separated process water, which includes the highly soluble saits(s), can be processed to concentrate the highly soluble salts(s) in the water. For example, a reserve osmosis system, which generates desalted water and a waste brine, can be used to generate a brine including the highly soluble salts(s) from recovered separated process water from the treated phosphate tailings. [0064] In other embodiments, the separated process water includes REE materials and the process further includes recovering at least a portion of the separated process and recovering the REE materials.

[0065] Figure 1 schematically illustrates such an exemplary continuous or semi- continuous process. As shown in the figure, phosphate tailings including fines and process water are treated with one or more highly water soluble salt(s), and optionally one or more polymer flocculant(s) and optionally sand by combining a stream of the salt(s) (101a), which can be an aqueous solution with a stream of the tailings (103a). Optionally, the tailings can also be treated with one or more polymer flocculant(s) by combining a stream of the flocculants(s) (102a), which can be as an aqueous solution, with the tailings stream (103a). Alternatively, the salts(s) and floccuiant(s) can be combined together as a solution to treat the tailings as a stream thereof. Coarse particles (sand) can also be added to the tailings or stream thereof and/or to any or all of the solution streams..

[0066] The solution streams of salt(s) and polymer(s) can be sourced from storage areas

101 and 102 and the streams of tailings and sand can be sourced from storage areas such as tanks or ponds 103 and 105, respectively. Alternatively, the phosphate tailings can be sourced directly from a phosphate mining or extraction operation.

[0067] For this embodiment, the stream of salt(s) (101a) and polymer(s) (102a) and phosphate tailings stream (103a) are carried to mixing device 107 added and the combination mixed. (Optionally, a stream of sand can be added to the streams of salt(s) and poiymer(s) (105a) or to phosphate tailings stream (105b), for example). Mixing device 107 can be an inline mixer, a mixing tank, ribbon mixer or other mixing device that can mix streams 01a, 102a, 103a and 105a. For this embodiment, the phosphate tailings are combined with the salt(s) and polymer(s) as solutions followed by addition of sand to treat the tailings. However, the order can be changed, e.g., the sand can be combined with tailings (105b) followed by mixing with the salt(s) and polymer(s) solutions. The sand can be added as a wet or dry stream. In some embodiments, the combination of the streams in a line can cause sufficient mixing to eliminate the need for a separate mixing device, e.g., inline mixing, and the combined streams can be carried directly to a mechanical dewatering device to separate consolidated material from process water. [0068] As shown in the embodiment of Figure 1, after mixer 107, the treated tailings, which include a consolidated material and process water, is transferred to a solids/liquid separator 109, e.g., a dewatering device, to separate the process water from the consolidated material. Such devices include, for example, one or more of a decanting, filtering, electrofiltering, cross-flow filtration, gravity draining, or vacuuming device or combination thereof and/or by one or more of a device for dewatering consolidated material such as a centrifuge, decanting centrifuge, dewatering screw, hydrocyclone, vacuum belt filter, filter press or pressing devices, etc. or combinations thereof.

[0069] A stream of separated process water (11 1) can be recovered and collected in a tank or pond and a stream of separated consolidated material (113) can be recovered. For this embodiment, the recovered process water (111) includes the process water from the phosphate tailings and from stream 101a and thus includes residual salt(s) from the one or more highly water soluble salt(s) and can possibly include residual polymer(s) from the one or more polymer flocculant(s). There are also highly water soluble salts that are constituents of the original tailings and these become part of the recovered process water. In some embodiments, the recovered process water (111) can then be transferred to a water purifying system 1 15 to purify at least a portion of the recovered process water (1 17) which can be used for other operations or discharged. Water purifying systems that can be used for embodiments of the processes of the present disclosure include reverse osmosis systems, vacuum distillation systems, electrodialysis, filtration systems, etc. The remaining, non-purified recovered process water (119), which includes the one or more highly water soluble salt(s) from stream 101 a and potentially highly water soluble salt(s) that are constituents of the original phosphate tailings ( 103), can be recycled back to the treatment process. For this embodiment, at least a portion of the non-purified recovered process water can be recycled back to storage 101 and deficiency in the concentration of the salt(s) or polymer(s) can be corrected by adding additional highly water soluble salt(s) or polymer flocculant(s) from one or more make-up tanks such as make-up tanks 121 and 122.

[0070] In certain implementations of the process of the present disclosure, at least a portion, if not all, of recovered process water stream 1 1 1 can be recovered and purified with a reverse osmosis system. Such a system can concentrate the at least one highly soluble salt in the recovered portion of separated process water 1 1 1 to form a brine. At least a portion, if not all, of the brine can be cycled back to salt / polymer flocculant storage 101 and/or 102 to treat additional tailings. Such a reverse osmosis system can concentrate the at least one highly soluble salt to a concentration of greater than about 2 w†% such as greater than about 4 wt%, 5 wt%, 6 wt%, 7wt% and higher such that the salt-tailings concentration in salt /polymer flocculant storage containers can be at an equilibrium of about 2wt% to about 7 wt%, and values therebetween, or higher. Thus, the salt concentration of the highly water soluble salt in storage 101 can be maintained at a range of about 2 wt % to about 7 wt%, and values therebetween, depending on the amount of process water subject to reverse osmosis system and cycled back to the process. The aqueous solution stream including the at least one highly water soluble salt and the at least one polymer flocculant can be combined with the phosphate tailings stream 103a at a ratio within a range of about 5.0: 1.0 to about 1.0:5.0, e.g., combined at a ratio within a range of about 3 : 1 to about 1 :3, such as about 1.5: 1.0 to about 1.0: 1.5.

[0071] The process of the present disclosure can also include recovering REE materials from recycled separated process water or from the consolidated solids. The REE materials can be recovered from the process water by precipitation, e.g., using oxalic acid, or extraction. Other methods for recovering REE from the process water include mineral processing and physical beneficiation, deep eutectic solvents/ionic liquids extraction, acid dissolution, high temperature phase separations, use of REE selective sorbents, photophoresis, in-situ brine injection and extraction, reactive grinding, etc. The process of the present disclosure can also include recovering REE materials from the consolidated solids by acid leaching or caustic decomposition,

[0072] In addition, the consolidated solids can be recovered. The consolidated solids can be placed in lined landfills or used as a source of building materials or valuable minerals. The recovered consolidated solids can include REE materials which can be separated from the consolidated solids.

[0073] Only the preferred embodiment of the present invention and examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. Thus, for example, those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances, procedures and arrangements described herein. Such equivalents are considered to be within the scope of this invention, and are covered by the following claims.