COAL WASTE

CROSS-REFERENCE TO RELATED APPLICATIONS

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

62/536179, filed 24 July 2017, the entire disclosure of which is hereby incorporated by reference herein,

TECHNICAL FIELD

10002] The present disclosure relates to dewatering and consolidation of aqueous coal waste compositions which can include fines and process water.

BACKGROUND

[0003] Remediation of waste materials from coal cleaning and power plant operations is a significant environmental and safely concern. One type of coal waste is coal ash, a residue of combustion that includes several components (fly ash, bottom ash, coal combustion residuals, coal combustion by-products, etc.). More than 100 million tons of coal ash are generated in the U.S. every year and larger amounts are generated in China and India. The ash contains heavy metals, including contaminants such as arsenic, mercury, cadmium and selenium. These can pollute water sources if not properly managed. There are dry- methods of disposal and coal ash can also be recycled into building material, but for economic reasons the wet disposal of ash into ash ponds has been common practice.

[0004] Another coal waste product that is a major concern is a product of coal preparation plants, where soil and rock are removed from run-of-mine coal to lower its ash content and increase its value. This is accomplished by washing with water or other aqueous liquids. However, coal cleaning processes produce a reject stream in the form of slurry. This slurry contains ver ' fine coal particles together with various types of rock, mud, clay, mineral matter, etc. Such slurries can also contain toxic heavy metals. It is very difficult to dewater coal wash slurries economically using standard methods. Such coal wash slurries are sometimes referred to as waste coal and coal refuse.

[0005] Most coal wastes (ash and wash slurries) are stored in unlined wet impoundments or ponds contained by dams, often near waterways. Various studies have detected groundwater contamination near impoundment sites. In addition, in many cases dam design was not performed by professional engineers. In some states, regulation of coal ash dams and landfills is minimal. It is now well-known that many impoundment ponds have dangerously weak walls and failures have occurred periodically. Some of these failures have been catastrophic, leading to loss of life and serious environmental damage. For example, in the year 1972 at Buffalo Creek in West Virginia, coal waste was dumped in the river, which was dammed to form a "pond". After days of heavy rain the dams failed, killing 118 people, injuring more than a 1000 and leaving 4000 people homeless. In Marin Count} ⁷ , Kentucky, a coal ash spill released 306 million gallons of slurry, which the EPA called ^" 'one of the worst environmental disasters in the Southeastern United States". In 2008, a dam failure at Kingston, Tennessee occurred. Although a much larger spill, this time there was fortuitously no loss of life, but to this day the creek remains flooded with waste. The TVA has spent more than $1 billion on clean-up work.

10006] In addition to these catastrophic failures, contaminated water has leached from ash ponds throughout the coal mining regions of Appalachia and in other coal producing regions. One incident occurred at the E. W. Brown Power Station near Danville, Kentucky, where water contaminated with arsenic and selenium leached into groundwater and Herrington Lake. Although Louisville Gas and Electric (LG&E) and Kentucky Utilities (KU) have taken remedial measures, aquatic life in the lake has been poisoned. In Jefferson County, Kentucky, a hidden camera operation revealed that the Mill Creek Generating Station has discharged ash slurry directly into the Ohio River. In Pennsylvania, The Bruce Mansfield Power Station's Little Blue Run Impoundment covers 1 ,000 acres and is the largest unlined coal ash pond in the United States. A high hazard earthen dam separates it from the Ohio River. Discharges to groundwater from the pond have exceeded federal drinking water standards for arsenic and other contaminants in multiple neighboring residential drinking wells.

10007] There are numerous sites that have been identified by the U.S. EPA as problematic. The total number of impoundment ponds in the U.S. does not seem to be known with any precision, but the estimates are large. As of 2001, there were over 700 coal washing waste impoundments, mostly in the Appalachian coal mining region. According to the U.S. EPA there are not only more than 600 coal ash ponds, but also hundreds of retired or abandoned sites. The impoundments can be as large as 50 acres in size and contain billions of gallons of toxic sludge. [0008] There is a clear need for the development and deployment of technology that can dewater coal waste such as those generated in processing coal and/or stored in impoundment ponds. The dewatered solids could then be stored in lined landfills or dedicated disposal areas, or more usefully used as a source of building materials. Many coal ash and waste solids also contain valuable minerals such as rare earth elements and could be a source of such materials. An added environmental benefit would accrue if the technology also produced cl ean water as a resul t of treating aqueous coal waste.

SUMMARY OF THE DISCLOSURE

[0009] Advantages of the present disclosure include processes to dewater aqueous compositions including coal waste, e.g., coal ash and/or coal wash slurries, to produce high solids content materials.

[0010] These and other advantages are satisfied, at least in part, by a process of consolidating solids in the aqueous coal waste composition. The process comprises treating an aqueous coal waste composition, which can include solids, some or all of which are sized as fines, and process water. Advantageously, the process can include treating the composition with at least one highly water soluble salt or solution thereof to form a treated composition. Optionally the process can further include treating the composition with either or both of (i) at least one polymer flocculant or solution thereof and/or (ii) optionally coarse particles, e.g. , sand, to form the treated composition. The treated composition can include a consolidated material in the process water, which can then be advantageously separated from the process water. The consolidated material can then be placed in lined landfills or used as a source of building materials or valuable minerals.

[0011] Implementations of processes 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 composition with at least one highly water soluble salt and at least one polymer flocculant to form a treated composition including a consolidated material in the process water, (iii) treating the composition with at least one highly water soluble salt and coarse particles to form a treated composition including a consolidated material in the process water, and (iv) treating the composition with at least one highly water soluble salt, at least one polymer flocculant and coarse particles to form a treated composition 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 composition. Each of these implementations can include separating the process water from the consolidated material. Advantageously, the consolidated material can have a density greater than the process water.

[0012] Embodiments of the processes include one or more of the following features individually or combined. For example, the aqueous coal waste composition can include coal waste fines. In some embodiments, the coal waste includes 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.

[0013] In certain embodiments, the treated composition can have a salt-composition 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 polyacrylamide or co-polymer thereof. The treated composition can have a polymer-composition 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%. In other embodiments, the composition is 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 about 0.5: 1 or between about 2.25: 1 to about 0.75: 1. 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.

[0014] In various embodiments, treating the aqueous coal waste composition can include combining the composition with a solution including the at least one highly water soluble salt and the at least one polymer flocculant. In some embodiments, treating the composition can include combining a stream of the aqueous coal waste composition, 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 composition can include combining a stream of the aqueous coal waste composition 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 composition or stream thereof and/or to arty or all of the solution streams. Advantageously, the streams can be mixed inline and/or with the aid of an inline mixer. In certain embodiments, treating the aqueous coal waste composition can be carried out at ambient temperature, e.g., no more than about 2 °C to about 5 °C above ambient temperature. In other embodiments, treating the aqueous coal waste composition 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 hypersalme water or sourced from a brine waste stream.

[0015] 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.

[0016] 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) recy cling at least a portion of recovered separated process water to treat additional aqueous coal waste compositions; (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 aqueous coal waste compositions.

[0017] Yet another aspect of the present disclosure includes recovering valuable materials from the aqueous coal waste composition. The valuable materials can include rare earth elements (REE) associated with solids such as clays in the compositions. Therefore, in practicing certain aspects of the processes of the present disclosure and the various embodiments thereof, the aqueous coal waste compositions can further include rare earth element materials which can be recovered by treating the composition with at least one highly water soluble salt, e.g., an ammonium based salt such as ammonium sulfate, to form a treated composition including REE 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 from the separated process water and/or the consolidated materials.

[0018] Advantageously, the processes of the present disclosure ca consolidate the solids of the composition 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.

[0019] In practicing certain aspects of the processes of the present disclosure and the various embodiments thereof, the consolidated material formed in the treated composition according to certain embodiments can result in a high solids content after mixing and/or dewatering the treated composition 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.

[0020] 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

[0021] Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent similar elements throughout and wherein:

[0022] Figure 1A schematically illustrates a process of consolidating an aqueous composition including coal waste in accordance with aspects of the present disclosure. [0023] Figure IB schematically illustrates another process of consolidating an aqueous composition including coal waste in accordance with aspects of the present disclosure.

10024] Figure 2 shows pictures of coal slurry as received (left) and a sample poured into a vial (right).

[0025] Figure 3 shows pictures of vials containing waste coal slurry treated according to an embodiment of the present disclosure. The pictures show coal slurry after adding an ionic solution (left), then centrifuging (middle) and after removal of supernatant solution (right).

[0026] Figure 4 shows pictures of the dewatered coal slurry from Figure 3 after removal from the vial (left) and subsequent hand-pressing between paper towels.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0027] The present disclosure relates to treating aqueous compositions of coal waste, which includes solids, some or all of which are sized as fines, and process water, to consolidation and dewatering the compositions. As used herein coal waste refers to coal ash and/or coal wash waste. As described in the background section, coal ash and coal wash waste are a waste by-product of coal combustion and coal cleaning operations, respectively.

[0028] Such aqueous coal waste compositions contain various solid particles such as rocks, clays, ash, fines, such as coal fine particles, mineral matter, etc. The fraction of solids in aqueous coal waste compositions varies with the nature of the source of the coal waste the process producing such waste. In addition, the fraction of solids in impoundment ponds containing such aqueous coal waste varies from site to site and is poorly documented. Certain coal processes finely grind coal prior to combustion to more readily liberate pyrite (a sulfur based compound) and hence reduce sulfur emissions upon combustion of the ground coal. Such processes can produce fine coal particles as well as other fine mineral or mineral matter in the aqueous composition that are difficult to capture and use.

[0029] The particulate solids in the aqueous compositions 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 (μηι). Sand is considered solid particles with sizes greater than 44 μπι. 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, and can also include coal fines from certain coal washing processes. Aqueous coal waste compositions can have various solids contents and various amounts of fines as its solids content. The aqueous coal waste compositions treated according to embodiments of the present disclosure can include a significant amount of fines by weight (>5 wt%) as their solids content. Such compositions can include at least about 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%, 70 wt% or higher fines as their solids content.

[0030] Advantageously, the process of the present disclosure can consolidate the solids of an aqueous coal waste composition to produce solids content initially in excess of about 45% by weight, e.g., a solids content of greater than about 50%, 60 wt% or 70 wt%, or higher than about 75% by weight.

[0031 ] The terms coagulation and fiocculation are often used interchangeably in the literature. As used herein, however, coagulation means particle aggregation brought about by the addition of hydrolyzing salts, whereas fiocculation 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 fiocculation, 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.

[0032] In practicing aspects of the present disclosure, an aqueous coal waste composition can be consolidated by treating the composition with one or more highly water soluble salt(s) or an aqueous solution thereof to destabilize and consolidate solids in the composition, e.g., to destabilize and consolidate fines in the composition. Aggregation induced by the addition of highly soluble 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 composition is an aqueous coal waste composition that includes a suspension of particulate solids including fines in an aqueous liquid. The process includes treating the composition with the highly water soluble salt(s) or an aqueous solution thereof to form a treated composition including a consolidated material, e.g., consolidated solids and/or fines, in process water. The process water can then be separated from the consolidated material. Advantageously, the consolidated material has a solids content of at least 45% by weight, e.g. , a solids content of greater than about 50% and higher than about 60%, 65%, 70% and 75% by weight.

10033 ] 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 tha 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.

[0034] 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 coal waste compositions 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.

10035 ] 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.

[0036] 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 (NH4C2H ₃ O2), ammonium chloride (NH4CI), ammonium bromide (NH ₄ Br), ammonium carbonate ((NKU^CCh), ammonium bicarbonate (NH4HCO3), ammonium nitrate (NH4NO3), ammonium sulfate ((NH ₄ ) ₂ S04), ammonium hydrogen sulfate (NH4HSO4), ammonium dihydrogen phosphate (NH4H2PO4), ammonium hydrogen phosphate ((ΝΗ ₄ ) ₂ ΗΡ0 ₄ ), ammonium phosphate ((NH ) ₃ P0 ₄ ), etc. Mixtures of such salts can also be used.

[0037] 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 coal waste compositions 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 disclosui'e, the highly water soluble salt or salts used in the processes of the present disclosui'e can preferably be non-toxic and beneficial to plant life to aid in environmental remediation and the restoration of mine sites.

[0038] In one aspect of the present disclosure, treating the aqueous coal waste compositions of the present disclosui'e with a highly water soluble salt destabilizes and consolidates solids in the composition. Such a process can include mixing the composition, 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.

[0039] Highly water soluble salts that ca be used in practicing the present process can also include salts having multivalent cations. Such salts include, for example, divalent cation salts such as calcium and magnesium cation salts, such as calcium chloride (( ^' <!( ^" ! >). calcium bromide (CaBr ₂ ), calcium nitrate (Ca N0 ₃ ) ₂ ), magnesium chloride (MgCl?), magnesium bromide (MgBr ₂ ), magnesium nitrate (Mg(N0 ₃ ) ₂ ), magnesium sulfate (MgS0 ₄ ); and trivalent cation salts such as aluminum and iron (III) cation salts, e.g., aluminum chloride (AICI ₃ ), aluminum nitrate (A1(N03)¾), aluminum sulfate (A1 ₂ (S0 ₄ ) ₃ ), iron (III) chloride (FeCl ₃ ), iron (III) nitrate i ! ^; ei\0 ; ) ;}. iron (111) sulfate (Fe ₂ (SQ ₄ ) ₃ , etc. As explained above, the highly water soluble salts used in the processes of the present disclosure are preferably non-hydrolyzing. Many of the multivalent cation salts are hydrolyzing and thus less preferred for the reasons stated above. Moreover, experimentation with multivalent salts showed increased fouling of containers and formation of less cohesive consolidated materials as compared to highly water soluble salts having monovalent cations. In addition, some multivalent salts, such as FeCl ₃ and Fe ₂ (S0 ₄ )3, are particularly corrosive and Fe ₂ (S0 ₄ )3 s formed from oxidizing pyrite and results in acid mine run-off, which make such salts less preferable for use in processes of the present disclosure.

[0040] When a sufficiently high concentration of the highly water soluble salt is included in the treated composition, the salt can destabilize and consolidate solids in the composition. For a relatively short process times with a relatively low energy input, the salt- composition 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-composition concentration" as used herein refers to the concentration of the highly water soi uble salt(s) in the treated composition 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 composition and any water used to dilute the salt(s). For example, combining 1 part undiluted (i.e., neat) salt to 99 parts composition by weight results in a salt-composition concentration of 1 wt%. Alternatively, treating compositions with an equal weight of a 2 wt% solution of the salt also results in a salt- composition concentration of 1 wt% in the treated compositions.

[0041 J The highly water soluble salt(s) can be used to treat compositions of the present disclosure as a solid, e.g., combining the salt as a powder with the composition. Alternatively, the salt can be used to treat as a solution, e.g., combining an aqueous salt solution with the compositions. 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. The composition and salt solution or slurry should be mixed at a ratio sufficient to destabilize the composition to cause consolidation of the solids therein. In one aspect of the present disclosure, the composition 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 composition to salt solution.

[0042] 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 sal ts 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.

[0043] In other embodiments of the present processes, it can be advantageous to use a bnne produced in desalmization of salt water such as process water as a source of a highly soluble salt(s). The brine can be used alone as a source of a highly soluble salt(s) or in combination with another source of a highly soluble salt(s) such as seawater.

[0044] After treating the aqueous coal waste composition with at least one highly water soluble salt, the solids in the composition can be consolidated such as by mixing followed by gravity sedimentation in a settling tank or by 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.

[0045] Although highly water soluble salts can destabilize and consolidate solids in the aqueous coal waste composition 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. [0046] The one or more polymer flocculants(s) can be added concurrent with or subsequent to treating an aqueous coal waste composition with the at least one highly water soluble salt to form the treated composition. The one or more polymer flocculants(s) can also be added prior to treating the composition with the at least one highly water soluble salt but it appeared more effective to add flocculant concurrent with or subsequent with the at least one highly water soluble salt to form the treated composition. It was also found that the present processes can be useful for consolidating aqueous coal waste that have already been treated with flocculating polymer to partially consolidate solids therein such as a thickener underflow stream. Such a thickener underflow streams typically include solids, some of which may be in the size of non-consolidated fines, process water and polymer flocculant. The solids content of thickener underflow can range from about 20 wt% to about 50 wt%, for example, and the solids can be further consolidated to high solids content of above 60 wt% such as above 70 wt%, for example by treatment with a highly soluble salt and polymer flocculant.

[0047] In addition, the processes of the present disclosure can also include treating aqueous compositions with coarse particles, e.g., particles with sizes greater than 44 μηι, such as sand, to increase the solids content. Mixing with sand is appropriate for aqueous compositions that have solids mostly as fines, as the fine particles can sit in the voids between the coarse particles, enhancing packing and solids content. It was found, however, that for certain coal waste the addition of sand was not needed to achieve a high solids content, as there were sufficient coarse particles present in the coal waste to give a high solids content material.

[0048] Hence, implementations of the process of the present disclosure include, for example, (i) treating an aqueous coal waste 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 composition with at least one highly water soluble salt and at least one polymer flocculant to form a treated composition including a consolidated material in the process water, (lii) treating the composition with at least one highly water soluble salt, and coarse particles to form a treated composition including a consolidated material in the process water, and (iv) treating the composition with at least one highly water soluble salt, at least one polymer flocculant and coarse particles to form a treated composition 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 composition. Each of these implementations can include separating the process water from the consolidated material. The process water can then he 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 dewatering consolidated material such as a centrifuge, decanting centrifuge, dewatering screw, hydrocyclone, vacuum belt filter, industrial filter press, e.g., a plate and frame press, recessed plate and frame filter presses, automatic filter presses, 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 compositions.

10049] Polymers that are useful in practicing the present disclosure include water soluble flocculating polymers such as a nonionic polyacrylamide, an anionic poly aery lamide (APAM) such as a polyacrylamide-co-acrylic acid, and a cationic polyacrylamide (CP AM), which can contain co-monomers such as acryloxyethyltrimethyl ammonium chloride, methaciyloxyethyltrimethyl ammonium chloride, dimethyldiallyammonium chloride (DMDAAC), etc. Other water soluble flocculating polymers useful for practicing the present disclosure include a poly amine, such as a poly amine or quaternized form thereof, e.g., polyacrylamide-co-dimethylaminoethylacrylate in quaternized form, a polyethyleneimine, a polydialiyldimethyl ammonium chloride, a polydicyandiamide, or their copolymers, a polyamide-co-amine, poly electrolytes 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 fioccuiants 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. [0050] The amount of polymer(s) used to treat aqueous coal waste compositions of the present disclosure should preferably be sufficient to flocculate the solids in the composition and any added sand. The amount of polymer(s) used to treat aqueous coal waste compositions can be characterized as a concentration based on the total weight of the composition or as a dosage based on the weight percent of the solids in the composition.

[0051 ] In some embodiments of the present disclosure, the concentration of the one or more polymer flocculant(s) in the treated composition has a polymer-composition concentration of 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-composition concentrations no less than about 0.04 wt%. The term "polymer-composition concentration" as used herein refers to the concentration of the flocculating poiymer(s) in the treated composition 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 composition and any water used to dissolve the polymer(s). For example, combining 1 part undiluted (i.e., neat) polymer to 9999 parts composition by weight results in a polymer- composition concentration of 0.01 wt%. Alternatively, treating the composition an equal weight of a 0.02 wt% solution of the polymer also results in a polymer-composition concentration of 0.01 wt%. In certain embodiments, aqueous coal waste compositions are treated with at least one polymer flocculant to yield a polymer-composition concentration of up to about 0.02 wt%, such as up to about 0.03 wt%, 0.04 wt%, 0.05 wt%, and even up to 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 .

[0052] In some embodiments of the present disclosure, the concentration of the one or more polymer flocculant(s) in the treated composition has a dosage (weight of the flocculantis) to weight of the solids in the composition, e.g., composition) 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%.

[0053] The amount of polymer flocculant can be reduced if the salt-composition concentration is increased. While the reason for this effect is not clear, a very low polymer- composition concentration of up to about 0,001 wt%, e.g., up to 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 composition if the salt-composition concentration is increased.

[0054] Coarse particles useful for practicing certain processes according to the present disclosure are preferably sand and when used in treating compositions 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 about 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 coal waste composition 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.

[0055] Treating an aqueous composition of coal waste including solids, some or all of which are 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 fiocculant and/or optionally sand can be carried out in a number of ways, in certain embodiments, treating the composition includes combining and/or mixing the various components. In addition, the at least one salt can be added directly to the composition either as an undiluted solid in powder form or as a solution; the at least one polymer fiocculant can be added directly to the composition either as an undiluted material or as a solution, and optionally coarse particles (e.g., sand) can be added to the composition 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 composition. The order of combining the salt, polymer and sand to the composition can give equivalent results and optimization of the process will depend on the type of composition, and the scale and equipment used in the process.

[0056] 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 composition. In certain embodiments, an aqueous solution of one or more highly water soluble salt(s) can be prepared having a concentration of no less than about 0.5 wt% or 1 wt%, e.g., at least about 2 wt%, 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 slum' for use in treating the composition. The one or more polymer floccuiant(s) can also be included in the aqueous solution of the salt(s) and can have a concentration of up to about 0.005 wt%, e.g., up to 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 soluble salt(s) and polymer flocculant(s) can be used to treat the composition and can be combined with such compositions at a ratio of between 5.0; 1 .0 and 1.0:5.0, e.g., at a ratio between 1.5: 1.0 to 1.0: 1.5 of composition to aqueous solution. Optionally, sand can be combined with the composition before, during, or after combining the composition with the aqueous solution of salt and/or polymer flocculant.

[0057] Because highly water soluble salts and polymer flocculants that are preferably water soluble are used in the process of the present disclosure, the temperature of the treated aqueous coal waste compositions need not be elevated above ambient temperature to practice the process. In certain embodiments, treating the aqueous coal waste composition can be carried out at ambient temperature, e.g., no more than about 2 °C to about 5 °C above ambient. In other embodiments, treating the aqueous coal waste composition 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.

[0058] in practicing aspects of the present disclosure, aqueous coal waste compositions, which include fines and process water, can be consolidated by treating the compositions with at least one highly water soluble salt or aqueous solutions thereof and can optionally include either or both of at least one polymer flocculant, e.g., a water-soluble flocculating polymer, or aqueous solutions thereof, and/or optionally coarse particles, e.g., sand to form a treated composition. Treating compositions in this manner can cause destabilization and consolidation of the solids, e.g., fines and coarse panicles, in the treated composition to form a consolidated material, which can aggregate relatively quickly, in the process water. The process water can then be readily separated from the consolidated material.

[0059] The treated compositions 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 compositions can be separated from the process water by any one or more of decanting, filtering, e.g., electrofiltering, cross-flow filtering, 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, industrial filter press, e.g., a plate and frame press, recessed plate and frame filter presses, automatic filter presses, 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 composition through a cross-flow filter, e.g., a porous or slotted pipe, which filters and dewaters the treated composition stream to separate the process water from the consolidated material. The process water can then be readily separated 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 composition, e.g., within about two weeks or within about one week of gravity draining after treating the composition. 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.

[0060] The consolidated material formed in the treated compositions 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 compositions according to certain embodiments can result in a high solids content after mixing and/or dewatering the treated compositions in a short period. 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 after mixing and/or dewatering. In certain embodiments a solids content of at least about 70 % is achieved within about one month of gravity draining after treating the composition, e.g., within about two weeks or within about one week of gravity draining after treating the composition.

[0061] In an embodiment of the present disclosure, the process includes mixing the composition 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 about 2.25: 1 to about 0.75: 1 to form a treated composition 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, depending on the dewatering method used.

[0062] Another advantage of the processes of the present disclosure is the recover}' of materials from aqueous coal waste compositions that include rare earth elements. For example, certain coal waste 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).

[0063 J REE in coal waste are typically 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. Coal ash and coal cleaning wastes can contain rare earth elements. Fire clay coal ash has unusually high concentrations of Y ttrium and zirconium.

10064] The processes of the present disclosure are useful in recovering REE. It is believed that in some aqueous coal waste compositions, REEs absorb on the surface of clays in compositions. In other compositions, REEs are included also among the solids of the compositions 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 coal waste composition can be obtained by leaching the solids with acid followed by extraction and precipitation or by caustic decomposition followed by acid leaching.

10065] Another aspect of processes of the present disclosure includes consolidating an aqueous composition of coal waste, which include REE materials, by treating the composition with at least one highly water soluble salt, e.g., an ammonium based salt such as ammonium sulfate, to form a treated composition 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 composition consolidates 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 composition consolidates the fines and REEs are among the consolidated materials. 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.

[0066] In addition, the composition can be treated with at least one polymer fiocculant and optionally sand to form the treated composition. The treated composition can have a salt-composition 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.

[0067] The process of the present disclosure allows for large scale treatment of aqueous coal waste compositions in a continuous or semi-continuous process with further recovering, recycling and purifying at least a portion of the process water in the aqueous coal waste composition 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 composition can advantageously include a significant amount of the one or more highly water soluble salt(s) initially used to treat the composition. 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 aqueous coal waste compositions; 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 salts(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 aqueous coal waste compositions.

10068] In other embodiments, the separated process water includes REE materials and the process further includes recovering at least a portion of the separated process water and recovering the REE materials.

[0069] Figure 1A schematically illustrates such an exemplary continuous or semi- continuous process. As shown in the figure, aqueous coal waste compositions including fines and process water are treated with one or more highly water soluble sait(s), and optionally one or more polymer flocculant(s) and optionally coarse panicles (sand) by combining a stream of the salt(s) ( 1 01 a), which can be an aqueous solution with a stream of the composition (103a). Optionally, the composition 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 composition stream (103a). Alternatively, the salts(s) and flocculant(s) can be combined together as a solution to treat the composition as a stream thereof. Coarse particles (sand) can also be added to the composition or stream thereof and/or to any or all of the solution streams.

[0070] The solution streams of salt(s) and polymer(s) can be sourced from storage areas 101 and 102, respectively, and the streams of coal waste and sand can be sourced from storage areas such as tanks or ponds 103 and 105, respectively. Alternatively, the coal waste can be sourced directly from a coal waste generating operation.

[0071] For this embodiment, the stream of salt(s) (101a) and polymer(s) (102a) and coal waste stream (103a) are carried to mixing device 107 and the combination mixed. (A stream of sand optionally can be added to the streams of salt(s) and polymer(s) (105a) or to coal waste composition 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 101a, 102a, 103a and optionally 105a. For this embodiment, the coal waste composition is combined with the sait(s) followed by polymer(s) and as solutions. However, the coal waste composition can be treated with an aqueous solution including both the salt(s) and polymer(s). In some implementations of the process, the combination of the streams in a line can cause sufficient mixing, e.g., inline mixing, to eliminate the need for a separate mixing device and the combined streams can be carried directly to a mechanical dewatering device to separate consolidated material from process water.

[0072] As shown in the embodiment of Figure lA, after mixer 107, the treated aqueous coal waste composition, which include a consolidated material and process water, is transferred to a solids/liquid separator 109 to separate the process water from the consolidated material. Such devices include, for example, one or more of a decanting, filtering, electrofilteriiig, cross-flow filtering, 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, industrial filter press, e.g., a plate and frame press, recessed plate and frame filter presses, automatic filter presses, etc. or combinations thereof.

10073] A stream of separated process water (1 1 1 ) can be recovered and collected in a tank or pond and separated consolidated material (1 13) can be recovered. For this embodiment, the process water (111) includes the process water from the aqueous coal waste composition and from stream 10 la 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). If the aqueous coal waste composition includes REE materials, the stream of process water (111) can also include REE materials. There can also be highly water soluble salts that are constituents of the original aqueous coal waste composition and these become part of the recovered process water (111). The recovered process water (111) can then be transferred to a water purifying system 115 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 (1 19), which includes the one or more highly water soluble salt(s) and highly water soluble salts from stream 101a and potentially highly water soluble salt(s) that are constituents of the original coal waste 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 holding source 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.

[0074] 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.

10075] 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. The process of the present disclosure can also include steps to recover coal particles from the coal waste compositions. Coal washing slurries typically include coal fine particles that could be separated from coarse mineral particles by taking advantage of their density differences.

[0076] Figure IB schematically illustrates another exemplary continuous or semi- continuous process in accordance with certain aspects of the present disclosure. For this embodiment, a stream of an aqueous coal waste composition that has been thickened with polymer ilocculant, e.g., a thickener underflow coal waste stream, is illustrated. Such a stream can include about 20 wt% to about 50 wt% solids and a polymer ilocculant. Such thickener underflow streams can still benefit from treatment with a highly water soluble salt and optionally additional polymer ilocculant to further consolidate solids in accordance with processes of the present disclosure.

[0077] For the process flow illustrated in Figure IB, the aqueous salt solution also includes at least one polymer ilocculant. As shown in Figure IB, aqueous coal waste stream 203 is combined with an aqueous solution stream including the at least one highly water soluble salt and the at least one polymer ilocculant (202a) to produce a treated tailings stream 207. For this embodiment, aqueous salt/polymer solution stream 202a and coal waste stream 203 are mixed in-line to produce the treated composition 207. Combining the streams (202a and 203) produces a treated composition that includes a consolidated material in process water.

[0078] Although not illustrated, the aqueous coal waste composition could have been treated with separate streams of the salt(s) and flocculant(s). The aqueous streams of sait(s) and polymer floccuiant(s) can be sourced from storage 202. In certain embodiments, seawater is used as the source of the highly water soluble salt as a make-up source of the salt in 220. In other, embodiments, brine from a reverse osmosis system is used as the source of the highly water soluble salt as a make-up source of the salt in 220 and in still further embodiments, both seawater and brine are used as the source of the highly water soluble salt as a make-up source of the salt in 220.

10079] For this embodiment, the treated tailings are carried to a solids/liquid separator

(209). The S/L separator separates the process water of the treated composition from the consolidated material. Such S/L separators include, for example, one or more of a centrifuge, decanting centrifuge, dewatering screw, hydrocyclone, vacuum belt filter, industrial filter press, e.g., a plate and frame press, recessed plate and frame filter presses, automatic filter presses, etc. or combinations thereof. S/L separator 209 generates a stream of consolidated material 213 and a stream of separated process water 21 1. Process water stream 21 1 includes the process water from coal waste stream 203 diluted and water from aqueous solution stream 202a 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). At least a portion, if not all, of process water stream 211 ca be recovered and purified with a reverse osmosis system 215. Reverse osmosis system 215 can concentrate the at least one highly soluble salt in the recovered portion of separated process water 21 1 to form brine 219. At least a portion, if not all, of the brine 219 can be cycled back to salt / polymer flocculant storage 202 to treat additional coal waste stream 203. Reverse osmosis system 215 can concentrate the at least one highly soluble salt to a concentration of greater than 2 wt% such as greater than 4 wt%, 5 wt%, 6 wt%, 7wt% and higher such that the salt-composition concentration in salt /polymer flocculant storage can be at an equilibrium of 2wt% to 7 wt%, and values therebetween, or higher. To reduce the quantity of water subject to reverse osmosis, a stream of some of the process water 212 optionally can be cy cled back to salt / polymer flocculant storage 202 without being subject to reverse osmosis. Thus, the salt- composition concentration of the highly water soluble salt in storage 202 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 215 and the amount cycled back to storage 202 without being subject to reverse osmosis. The aqueous solution stream including the at least one highly water soluble salt and the at least one polymer flocculant (202a) can be combined with the coal waste stream 203 stream 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.

EXAMPLES

[0080] The following examples are intended to further illustrate certain preferred embodiments of the invention and are not limiting in nature. Those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances and procedures described herein.

[0081 J Coal Ash Slurry Consolidation

[0082] A sample of a coal wash slurry is shown in Figure 2 as received (left) and a sample poured into a vial (right). An initial sample of a coal waste slurry was analyzed by infrared spectroscopy to determine the content of solids content. Further, the sample was estimated to have 30% or more coal fines present, i.e., a mixture of fine coal particles and fine mineral particles. Approximately 5 g of the coal slurry was placed in a vial and an equal weight of an aqueous ionic solution was added and the diluted slurry shaken to mix the components. The ionic solution was composed of water, 10 wt% ammonium sulfate and 0.1 wt% polyacrylamide (PAM). Settling started immediately, as can be seen in the picture on the left in Figure 3. The vial was then centrifuged for 30 seconds at 3000 rpm and the particles consolidated into a compact mass, as shown in the picture in the center of Figure 3. The supernatant liquid appeared to be clear, with no visible suspended particles. Upon removal of the liquid it was found that the compacted solids have enough cohesive strength to hold their shape when the vial was inverted, as can be seen in the picture on the right in Figure 3.

[0083] The material was removed from the vial (Figure 4, left) and a portion dried.

The consolidated material had an initial solids content of 54%. Some of the remainder was pressed (by hand) between paper towels (Figure 4, right). This pressed material had a solids content of 74%. [0084] 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.