Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F11/00—Treatment of sludge; Devices therefor
  • C02F11/12—Treatment of sludge; Devices therefor by de-watering, drying or thickening
  • C02F11/14—Treatment of sludge; Devices therefor by de-watering, drying or thickening with addition of chemical agents
  • C02F11/148—Combined use of inorganic and organic substances, being added in the same treatment step
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
  • C02F1/441—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by reverse osmosis
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
  • C02F2103/10—Nature of the water, waste water, sewage or sludge to be treated from quarries or from mining activities
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P10/00—Technologies related to metal processing
  • Y02P10/20—Recycling

Definitions

• the present disclosure relates to dewatering and consolidating aqueous compositions including solids such as tailings.
• aqueous compositions including solids such as tailings.
• tailings result from processing ore such as metal, phosphate and coal-based ores.
• tailings stream characterized as a slurry of particulate matter in water.
• These tailings often contain components that are hazardous and cannot be discharged directly into rivers and streams.
• a common practice is to store tailings in ponds, which can be very large or encompass numerous sites. For example, it has recently been estimated that Canadian oil-sands tailings ponds cover an area of about 200 square kilometers.
• the Environmental Protection Agency has identified more than 500 ash and coal slurry ponds, mostly in the Appalachian coal mining region.
• phosphate mining results in the production of approximately 100,000 tons a day of phosphatic clays in the form of a slurry that is also stored in ponds.
• fines are defined as particles having a diameter equal to or less than 44 pm. They are part of a waste stream that settles much more slowly than coarse sand, leaving a layer of water with some entrained fines near the surface of the ponds. This water is reused in the bitumen extraction process. Initially, most of the fines (mainly silica and clay particles) form an intermediate layer of so-called fluid fine tailings (FFT). This fluid has a low solids content, between 15% and 30% and is also referred to as thin fine tailings (TFT).
• FFT fluid fine tailings
• MFT mature fine tailings
• So-called impoundment ponds are used to store two types of waste from coal handling and combustion.
• Coal ash that is a residue of combustion is one such material and includes several components (fly ash, bottom ash, etc.).
• the second type of impoundment pond for coal processing wastes stores material that 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.
• this coal cleaning process produces a reject stream in the form of a sludge or slurry.
• This slurry contains very fine coal particles together with other material (such as clays) and, as with the tailings streams mentioned above, is very difficult to dewater economically using standard methods.
• the impoundments can be as large as 50 acres in size and contain billions of gallons of toxic sludge. This material represents both an economic cost in terms of the loss of a valuable resource (in the form of coal fines) and a major environmental hazard.
• the Washington Post (April 24, 2013) reported that a study by the Office of Surface Mining Reclamation and Enforcement found that many sludge impoundment walls are weak and are known to leak. Historically, a number of catastrophic failures of ash and sludge ponds have occurred, resulting in significant loss of life and environmental devastation. With the coal industry in decline and mining companies filing for bankruptcy, the impoundment ponds, both those that remain in use and those that have been abandoned, are a significant and growing problem.
• Advantages of the present disclosure include processes to dewater aqueous compositions including suspended solids, e.g., tailings, to produce high solids content materials.
• the process comprises treating tailings with a highly water soluble salt.
• the process can include treating tailings with at least one highly water soluble salt or solution thereof and can optionally include either or both of (i) at least one polymer flocculant or solution thereof and/or (ii) optionally coarse particles, e.g., sand, to form a treated tailings.
• the treated tailings can include a consolidated material in the process water, which can then advantageously be separated from the consolidated material.
• Implementations of the process of the present disclosure include, for example, (i) treating tailings with at least one highly water soluble salt to form a treated tailings including a consolidated material in the process water, (ii) treating 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 tailings with at least one highly water soluble salt and coarse particles to form a treated tailings including a consolidated material in the process water, and (iv) treating 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 tailings.
• Each of these implementations can include separating the process water from the consolidated material.
• the consolidated materials can have a density greater than the process water.
• the tailings subject to treatment can resulting from processing a metal-based ore, phosphate-based ore, or coal based ore.
• the at least one highly water soluble salt can have a solubility in water (a salt/water solubility) of at least about 5 g/lOO g at 20 °C, e.g., at least about 10 g/lOO g at 20 °C.
• the at least one highly water soluble salt is a non-hydrolyzing salt.
• 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.
• the treated 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 0.70 wt%, such as at least about 1 wt%, 1.25 wt %, 1.5 wt%, 1.75 wt%, 2 wt% and even at least about 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, etc. of the at least one highly water soluble salt.
• the at least one polymer flocculant is a polyacrylamide or co-polymer thereof.
• the treated 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%.
• tailings are treated with coarse particles, e.g., sand, at a sand to fines ratio of less than 4: 1, e.g., including about 2.5: 1.0 to about 0.5: 1 or including about 2.25: 1 to about 0.75 : 1.
• 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.
• treating tailings can include combining tailings with a solution including the at least one highly water soluble salt and the at least one polymer flocculant.
• treating tailings can include combining a stream of tailings, e.g., tailings from processing metal ore such as copper ore, 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.
• treating tailings can include combining a stream of 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 can also be added to tailings or stream thereof and/or to any or all of the solution streams.
• the streams can be mixed inline and/or with the aid of an inline mixer.
• treating tailings can be carried out at ambient temperature, e.g., no more than about 2 °C to about 5 °C above ambient.
• treating tailings can be carried out a temperature of no more than about 50 °C, e.g., no more than about 40 °C or 30 °C.
• treating tailings 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.
• 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.
• 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, etc.. Once separated, the consolidated material can be transferred for further dewatering or disposal.
• 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 tailings; (iii) purifying at least a portion of recovered process water; 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 tailings.
• Yet another aspect of the present disclosure includes recovering valuable materials from the aqueous composition of fines, e.g., tailings.
• the valuable materials can include rare earth elements (REE) associated with solids such as clays in tailings from various types of aqueous fines such as tailings stream. Therefore, in practicing certain aspects of the processes of the present disclosure and the various embodiments thereof, the aqueous compositions can further include rare earth element materials which can be recovered by treating 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 in the process water and/or in the consolidated materials.
• 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.
• the processes of the present disclosure can consolidate the solids of 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.
• 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.
• 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.
• the aqueous solution includes a highly water soluble ammonium based salt and a polymer flocculant, e.g., a water soluble polymer.
• Embodiments include, together or individually, an aqueous solution of one or more of the highly water soluble salt(s) and having a concentration of no less than about 1 wt%, e.g., at least about 2 wt%, 5 wt%, 10 wt%, 20 wt%, 30 wt% and even as great as a 40 wt% or as an aqueous salt slurry.
• the aqueous solution can also include one or more of the polymer flocculant(s) and having a concentration of not less than zero and 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.
• Figure 1 A schematically illustrates a process of consolidating a tailings stream in accordance with aspects of the present disclosure.
• Figure 1B schematically illustrates another process of consolidating a tailings stream in accordance with aspects of the present disclosure.
• Figure 2 are 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).
• Figure 3 are pictures of the dewatered coal slurry from Figure 2 after removal from the vial (left) and subsequent hand-pressing between paper towels.
• Figure 4 shows pictures of vials containing mature fine tailings from oil sands processing treated with an ammonium salt solution including a polyacrylamide flocculant at the concentrations indicated in the figure.
• Figure 5 shows pictures of vials containing mature fine tailings treated with an ammonium salt and a polyacrylamide flocculant and illustrate effects of increasing salt concentration and reducing polymer concentration under the conditions tested.
• Figure 6 shows a picture of vials containing mature fine tailings from oil sands processing treated with seawater which included varying amounts of a polyacrylamide flocculant.
• Figures 7A, 7B and 7C show picture of treating tailings generated from processing copper ore.
• the present disclosure relates to treating tailings and other aqueous compositions which include solids to consolidate and dewater the tailings.
• Tailings are typically produced when mining and processing ores such as metal-based ores, e.g., aluminum, copper, zinc, lead, iron, gold, silver, molybdenum, lithium, etc., non-metal based ores, e.g., phosphate ore, nitrate ore, iodine ore, oil sands, etc.
• Aqueous compositions of fines can also be produced when processing coal. For example, certain 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 an aqueous composition that are difficult to recapture and reuse.
• Particulate solids in the tailings or aqueous compositions of the present disclosure can be minerals and mineral like materials, i.e., mineral matter, clays, slit, 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 (pm). Sand is considered solid particles with sizes greater than 44 pm.
• 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. Tailings can have various solids contents and various amounts of fines as its solids content.
• the tailings treated according to embodiments of the present disclosure can include a significant amount of fines by weight (>5 wt%) as their solids content.
• Such tailings 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.
• the process of the present disclosure can consolidate the solids of tailings to produce 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.
• 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.
• tailings, and other an aqueous composition of solids and process water can be consolidated by treating the tailings with one or more highly water soluble salt(s) or an aqueous solution thereof to destabilize and consolidate solids in the tailings, e.g., to destabilize and consolidate coarse solids and fines in 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.
• tailings e.g., a suspension of particulate solids, which can include fines, in process water are treated.
• Such tailings that can be treated include tailings streams from processing metal- based ores, non-metal based ores, or a coal slurry.
• the process includes treating the tailings with a highly water soluble salt(s) or an aqueous solution thereof to form a treated tailings 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.
• 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.
• 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/l00g) at 20 °C.
• the highly water soluble salt has a water solubility of at least about 5 g/lOO g at 20 °C, e.g., at least about 10 g/lOO g of salt/water at 20 °C.
• 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 tailings in continuous or semi-continuous processes.
• 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.
• 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.
• 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.
• alkali halide salts such as sodium chloride, potassium chloride
• 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.
• ammonium based salts such as ammonium acetate (NH4C2H3O2), ammonium chloride (NH 4 Cl), ammonium bromide (MUBr), ammonium carbonate ((NH4)2C03), ammonium bicarbonate (NH4HCO3), ammonium nitrate (NH4NO3), ammonium sulfate ((NHI)2S04), ammonium hydrogen sulfate (NH4HSO4), ammonium dihydrogen phosphate (NH4H2PO4), ammonium hydrogen phosphate ((NH4)2HP04), ammonium phosphate ((NH4)3P04), etc.
• ammonium based salts such as ammonium acetate (NH4C2H3O2), ammonium chloride (NH 4 Cl), ammonium bromide (MUBr), ammonium carbonate ((NH4)2C03), ammonium bicarbonate (NH4HCO3), ammonium nitrate (NH4NO3), am
• 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 fines, e.g., tailings, can be beneficial to plant life.
• 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.
• 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.
• Highly water soluble salts that can 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 (CaCb), calcium bromide (CaBn), calcium nitrate (Ca(NCb)2), magnesium chloride (MgCb), magnesium bromide (MgBn), magnesium nitrate (Mg(NCb)2), magnesium sulfate (MgSCri); and trivalent cation salts such as aluminum and iron (III) cation salts, e.g., aluminum chloride (AlCb), aluminum nitrate (Al (NC>3)3), aluminum sulfate (Ab(S0 4 )3), iron (III) chloride (FeCb), iron (III) nitrate (Fe(N03)3), iron (III) sulfate (Fe2(S0 4 )3, etc
• 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.
• 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.
• some multivalent salts such as FeCb and Fe2(S0 4 )3, are particularly corrosive and Fe2(S0 4 )3 is 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.
• 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 0.70 wt%, such as at least about 1 wt%, 1.25 wt %, 1.5 wt%, 1.75 wt%, 2 wt% and even at least about 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, etc.
• salt-tailings concentration 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.
• 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 tailings.
• the salt can be used to treat as a solution, e.g., combining an aqueous salt solution with tailings.
• 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%, 5 wt%, 10 wt%, 20 wt%, 30 wt% and even as great as a 40 wt% or as an aqueous salt slurry.
• the tailings and salt solution or slurry should be mixed at a ratio sufficient to destabilize the tailings to cause consolidation of the solids therein.
• the tailings and the salt solution can be mixed at a ratio of tailings to salt solution at a range of about 80: 1 to 1 : 1, e.g., 70: 1 to 1 : 1, 50: 1 to 1 : 1, 30: 1 to 1 : 1, 20: 1 to 1 : 1, 15: 1 to 1 : 1, 10: 1 to 1 : 1, 5: 1 to 1 : 1, and/or about 2: 1 to 1 : 1 tailings to salt solution.
• 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.
• 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%.
• seawater in the world’s oceans has a salinity of about 3.5% (35 g/L, 599 mM).
• Seawater includes of 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.
• a brine produced in desalinization of salt 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.
• Seawater has been used in grinding and flotation processes of mining copper ore. See Moreno et al.,“The use of seawater as process water at Las Luces copper- molybdenum beneficiation plant in Taltal (Chile)”, Minerals Engineering 2011 :24:852-858. However, use of seawater requires increased capital and maintenance costs to combat the corrosive effects of seawater. Id.
• tailings from ore processes can be treated with a waste brine from desalinization as a source of the at least one highly water soluble salt, with or without other sources of highly soluble salt(s) such as seawater.
• the solids in the tailings can be consolidated such as by mixing followed by gravity sedimentation in a settling tank or by mechanically consolidation such as by pressing or centrifugation to increase the rate of forming a consolidated material in the treated tailings.
• the consolidated material can be separated from the process water by decanting, filtering, electrofiltration, cross-flow filtering, vacuuming, and/or by mechanical dewatering, i.e., applying an external force to the consolidated material. Once separated, the consolidated material can be transferred for further dewatering or disposal.
• the one or more polymer flocculants(s) can be added concurrent with or subsequent to treating the tailings with the at least one highly water soluble salt to form the treated tailings.
• the one or more polymer flocculants(s) can also be added prior to treating the tailings with the at least one highly water soluble salt but it appeared more effective to add flocculant, even with tailings already containing polymer flocculant such as thickener underflow tailings, concurrent with or subsequent with the at least one highly water soluble salt to form the treated tailings.
• the processes of the present disclosure can also include treating aqueous fines with coarse particles, e.g., particles with sizes greater than 44 pm, such as sand, to significantly increase the solids content.
• coarse particles e.g., particles with sizes greater than 44 pm, such as sand
• sand is appropriate for aqueous fines 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 compositions such as coal slurry and metal ore tailings, the addition of sand was not needed to achieve a high solids content, as there were sufficient coarse particles present in the tailings to give a high solids content material within a short period of time.
• implementations of the process of the present disclosure include, for example, (i) treating tailings with at least one highly water soluble salt to form a treated tailings including a consolidated material in the process water, (ii) treating 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 tailings with at least one highly water soluble salt and coarse particles to form a treated tailings including a consolidated material in the process water, and (iv) treating 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 consolidated material has a density greater than the process water.
• 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 dewatering consolidated material such as a centrifuge, decanting centrifuge, dewatering screw, hydrocyclone, vacuum belt filter, filter press or pressing devices, etc.
• the separated consolidated material can be disposed or deposited in a containment structure which allows removal of released water from the consolidated material.
• the process water separated from the treated tailings can be cycled back to treat additional tailings.
• Polymers that are useful in practicing the present disclosure include water soluble flocculating polymers such as polyacrylamides or copolymers thereof such as a nonionic polyacrylamide, an anionic polyacrylamide (APAM) such as a polyacrylamide-co-acrylic acid, and a cationic polyacrylamide (CPAM), which can contain co-monomers such as acryloxyethyltrimethyl ammonium chloride, methacryloxyethyltrimethyl ammonium chloride, dimethyldiallyammonium chloride (DMDAAC), etc.
• APAM anionic polyacrylamide
• CPAM cationic polyacrylamide
• 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 polydiallyldimethyl 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.
• 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 Hoc to below the density of the process water from which they are separated.
• 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.
• the amount of polymer(s) used to treat tailings should preferably be sufficient to flocculate the solids in tailings and any added coarse particles, e.g., sand.
• the amount of polymer(s) used to treat tailings can be characterized as a concentration based on the total weight of tailings or as a dosage based on the weight percent of the solids in tailings.
• the concentration of the one or more polymer flocculant(s) in the treated tailings has a polymer-tailings 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%.
• a polymer-tailings 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%.
• consolidation of the solids can be obtained at polymer-tailings concentrations of no less than about 0.04 wt%.
• polymer-tailings concentration 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 tailings with an equal weight of a 0.02 wt% solution of the polymer also results in a tailings concentration of 0.01 wt%.
• tailings are treated with at least one polymer flocculant to yield a polymer- tailings 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, at high concentrations it becomes difficult to dissolve the flocculant, the solution becomes too viscous, and the process is less economical.
• 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%.
• 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 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 tailings, if the salt-tailings concentration is increased.
• 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., including about 2.5: 1.0 to about 0.5: l or including about 2.25: 1 to about 0.75: 1.
• SFR ratio is calculated by determining the amount of sand added to an estimated amount of solid fines in the aqueous fines 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.
• Treating tailings e.g., tailings from metal ore and non-metal ore processes, 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.
• treating the tailings includes combining and/or mixing the various components.
• the at least one salt can be added directly to the tailings either as an undiluted solid in powder form or as a solution;
• the at least one polymer flocculant can be added directly to the tailings either as an undiluted material or as a solution, and optionally coarse particles (e.g., sand) can be added to the 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 tailings.
• the order of combining the salt, polymer, and optionally sand, to the tailings can give equivalent results and optimization of the process will depend on the nature of tailings, and the scale and equipment used in the process.
• 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 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 10 wt%, 15 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 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 tailings and can be combined with such tailings at a ratio of tailings to salt solution at a range of about 80: 1 to 1 : 1, e.g., 70: 1 to 1 : 1, 50: 1 to 1 : 1, 30: 1 to 1 : 1, 20: 1 to 1 : 1, 15: 1 to 1 : 1, 10: 1 to 1 : 1, 5: 1 to 1 : 1, and/or about 2: 1 to 1: 1 tailings to salt solution.
• sand can be combined with the tailings before, during, or after combining the tailings with the aqueous solution of salt and/or polymer flocculant.
• the temperature of the treated tailings need not be elevated above ambient temperature to practice the process.
• treating the tailings according to the various embodiments herein can be carried out at about ambient temperature or no more about 2 to about 5 °C above ambient temperature.
• 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.
• tailings e.g., tailings from metal ore and non-metal ore processes
• tailings can be consolidated by treating such tailings 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 tailings.
• Treating tailings in this manner can cause destabilization and consolidation of the solids, e.g., fines and coarse solids, in the treated tailings to form a consolidated material, which can aggregate relatively quickly, in the process water.
• 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.
• 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 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, etc.
• 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. The process water can then be readily separated from the consolidated material.
• 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.
• the consolidated material can be further dewatered after separating from the treated tailings by depositing the separated consolidated material in a thin lift deposition.
• 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.
• 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.
• 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.
• a solids content of at least about 70 % is achieved within about one month of gravity draining after treating tailings, e.g., within about two weeks or within about one week of gravity draining after treating tailings.
• 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 about 2.25: 1 to about 0.75: 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, depending on the dewatering method used.
• a highly water soluble salt e.g., an ammonium based salt
• a water soluble polymer e.g., a polyacrylamide
• 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 tailings including a consolidated material having a high solids
• a rare earth element as defined by EJPAC, 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).
• REE in aqueous fines are typically in the form of an ion or oxide.
• zirconium can be present as zircon
• ZrSiCri titanium can be present as the minerals ilmenite, leucoxene and rutile.
• Coal ash and coal cleaning wastes contain rare earth elements. Fire clay coal ash has unusually high concentrations of Yttrium and zirconium. Oil sands tailings also contain REE.
• REEs absorb on the surface of clays in tailings.
• REEs are predominately included 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 tailings can be obtained by leaching the solids with acid followed by extraction and precipitation or by caustic decomposition followed by acid leaching.
• tailings which include REE materials
• at least one highly water soluble salt e.g., an ammonium based salt such as ammonium sulfate
• 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.
• the treated tailings consolidate 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.
• acid e.g., nitric acid, sulfuric acid, etc.
• 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.
• the tailings which include REE materials 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 wt% of the at least one highly water soluble salt and preferably no less than about 0.70 wt%, such as at least about 1 wt%, 1.25 wt %, 1.5 wt%, 1.75 wt%, 2 wt% and even at least about 2.5 wt%, 3 wt%, 4 wt%, 5 wt%, etc. of the at least one highly water soluble salt.
• the process of the present disclosure allows for large scale treatment of 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.
• 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.
• 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 tailings; and/or (iii) purifying at least a portion of recovered process water.
• the recovered separated process water which includes the highly soluble salts(s)
• 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 tailings.
• the separated process water includes REE materials salt and the process further includes recovering at least a portion of the separated process water and recovering the REE materials and/or purifying at least a portion of the recovered process water.
• FIG. 1A schematically illustrates an exemplary continuous or semi-continuous process.
• tailings are treated with one or more highly water soluble salt(s), and optionally one or more polymer flocculant(s) and optionally coarse particles (sand) by combining a stream of the salt(s) (10 la), which can be an aqueous solution with a stream of the tailings (l03a).
• tailings can also be treated with one or more polymer flocculant(s) by combining a stream of the flocculants(s) (l02a), which can be as an aqueous solution, with the tailings stream (l03a).
• the salts(s) and flocculant(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.
• the solution streams of salt(s) and polymer(s) can be sourced from holding tanks
• the streams of tailings and sand can be sourced from holding tanks or ponds 103 and 105, respectively.
• the tailings can be sourced directly from an ore extraction process.
• the stream of salt(s) (lOla) and polymer(s) (l02a) and tailings stream (103 a) are carried to mixing device 107 and the combination mixed.
• a stream of sand (l05a) can be optionally added).
• Mixing device 107 can be an inline mixer, a mixing tank, ribbon mixer or other mixing device that can mix streams lOla, l02a, l03a and, optionally l05a.
• the tailings are combined with the salt(s) followed by polymer(s) and as solutions. However, the tailings can be treated with an aqueous solution including both the salt(s) and polymer(s).
• 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 tailings pond or a mechanical dewatering device to separate consolidated material from process water.
• a separate mixing device e.g., inline mixing
• the treated tailings which include a consolidated material and process water
• Solid/Liquid separator 109 to separate the process water from the consolidated material.
• Such devices include, for example, one or more of a decanting, filtering, electrofiltering, 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, filter press or pressing devices, etc. or combinations thereof.
• a stream of recovered process water (111) includes the process water from the tailings diluted with stream lOla 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) as well as components from tailings. If the tailings include REE materials, the recovered stream of process water (111) and/or the consolidated material (113) can also include REE materials.
• the recovered process water (111) can be transferred to a water purifying system (115) to purify at least a portion of the recovered process water 117 which can be recycled in the mining process.
• 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 or brine which includes the highly water soluble salts from stream lOla and potentially highly water soluble salt(s) that are constituents of the original tailings, (119) can be recycled back to the treatment process.
• At least a portion of the non-purified recovered process water can be recycled back to holding tank 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 containers 121 and 122.
• 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.
• the consolidated solids can be recovered.
• the recovered consolidated solids can include residual highly water soluble salt(s) from the treatment of the tailings.
• the salt used in treating the tailings are beneficial to plant life, such as an ammonium based salt or sulfate based salt or phosphate based salt
• the residual salt can act as a fertilizer with the consolidated solids.
• the recovered consolidated solids can include REE materials which can be separated from the consolidated solids as explained elsewhere.
• FIG. 1B schematically illustrates another exemplary continuous or semi- continuous process.
• tailings from a metal ore such as tailings from copper ore processing are illustrated.
• flotation cells or concentrator (201) generates tailings 203.
• Many processes of metal and even non-metal ore include a concentration step in which valuable minerals are concentrated by flotation in an aqueous mixture including various agents. The valuable minerals are separated and tailings stream is produced.
• the tailings can be a thickener underflow tailings stream.
• Such thickener underflow streams can still benefit from treatment with a highly water soluble salt and optionally additional polymer flocculant to further consolidate solids in accordance with processes of the present disclosure.
• the tailings stream is treated with a stream of an aqueous solution including at least one highly water soluble salt.
• the aqueous solution also includes the at least one polymer flocculant.
• tailings stream 203 is combined with an aqueous solution stream including the at least one highly water soluble salt and the at least one polymer flocculant (202a) to produce a treated tailings stream 207.
• aqueous solution stream 202a and tailings 203 are mixed in-line to produce treated tailings 207. Combining the streams (202a and 203) produces treated tailings that include a consolidated material in process water.
• the tailings could have been treated with separate streams of the salt(s) and flocculant(s).
• the aqueous streams of salt(s) and polymer flocculant(s) can be sourced from storage 202.
• seawater is used as the source of the highly water soluble salt as a make-up source of the salt in 220.
• 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.
• the treated tailings are carried to a solids/liquid separator
• the S/L separator separates the process water of the treated tailings 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, filter press or pressing devices, etc. or combinations thereof.
• S/L separator 209 generated a stream of consolidated material 213 and a stream of separated process water 211.
• Process water stream 211 includes the process water from tailings stream 203 diluted with 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 can 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 211 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 tailings 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%, 7 wt%, 8 wt%, 9 wt%, 10 wt% and higher such that the salt-composition concentration in salt /polymer flocculant storage can be at an equilibrium of about 2 wt% to about 10 wt%, and values therebetween, or higher.
• 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 tailings stream 203 stream at a ratio range of tailings to salt solution including about 30: 1 to 1 : 1, 20: 1 to 1 : 1, 15: 1 to 1 : 1, 10: 1 to 1 : 1, 5: 1 to 1 : 1, and/or about 2: 1 to 1 : 1 tailings to salt solution.
• Reverse osmosis system 215 can also be used to generate desalted water 240 from seawater 250 in which desalted water 240 is used in other processes of the mining operation. Waste brine from system 215 can be used as a source of the highly soluble salt to treat tailings thereby improving efficiency of the overall operation and reducing the adverse environmental impact of discharging brine into the environment.
• seawater can be used as a source of the highly water soluble salt to treat tailings such as providing seawater in make-up source 250.
• 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 2.
• the supernatant liquid appeared to be clear, with no visible suspended particles.
• ETpon 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 2.
• the material was removed from the vial ( Figure 3, 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 3, right). This pressed material had a solids content of 74%.
• Table 1 Solids content of MFT treated with an equal weight of a salt/P AM solution without the addition of sand and after centrifugation.
• Table 2 Solids content of MFT treated with an equal weight of a salt/P AM solution with the addition of sand (SFR ratio 1 : 1) after centrifugation.
• the salt-tailings concentration was about 5 wt%.
• the salt-tailings concentration was about 2.5 wt%
• the salt-tailings concentration was about 1 wt%.
• Table 1 reports the solids content of dried consolidated material following treating of MFT with the various salt/polymer solutions without sand. After centrifugation for just 30 seconds, the highly water soluble salts gave solids contents for the consolidated materials in a range between about 3 l%-37%. However, the use of highly water soluble salts having a multivalent cation such as the aluminum and ferric cations appeared to cause fouling of the vial walls and gave a less cohesive consolidated material as compared to highly water soluble salts having a monovalent cation under the tested conditions. In some tests using salt concentrations of 10%, the clarified water sitting on top of the consolidated materials were removed using a pipette and the wet solids pressed between paper towels.
• Table 2 reports the solids content of dried consolidated material following treating
• the salt-tailings concentration in treated MFT can be achieved in a number of ways. For ease of handling in the foregoing vial tests, it was convenient to combine equal weights of salt/polymer solutions to MFT. However, smaller amounts of salt/polymer solutions with higher concentrations thereof to give the same salt-tailings concentration give equivalent results of consolidated materials.
• salt-tailings concentrations in excess of 0.5 wt% and preferably no less than about 0.70 wt%, such as at least about 1 wt%, should be used to achieve reasonably fast consolidation of the solids in the tailings.
• a degree of consolidation of the fmes/sand mixture is obtained at polymer-tailings concentrations as low as 0.01 wt% for relatively short processing times, superior results are obtained at polymer- tailings concentrations of 0.05% and higher.
• the top set of vials in Figure 4 shows results obtained by adding 5 g of a 2 wt% ammonium sulfate ((NH 4 )2S04) solution containing PAM to 5 g of MFT. Sand was also added to give a sand-to-fmes ratio of 1 : 1 (i.e., 1.5 g of sand was added). The amount of PAM in the solutions was varied between 0.1% (by weight) and 0.02% (by weight). The bottom set of vials show what is observed when a 1 wt% of the ammonium sulfate was used. The vials were centrifuged at 3000 rpm for 30 seconds to accelerate settling.
• a 2 wt% ammonium sulfate ((NH 4 )2S04) solution containing PAM
• Sand was also added to give a sand-to-fmes ratio of 1 : 1 (i.e., 1.5 g of sand was added).
• Figure 4 was determined by drying, i.e., the centrifuged consolidated material was separated from its supernatant liquid, the wet mass weighed, dried and reweighed to determine a solids content.
• the solids content of the consolidated materials for the sets of vials are summarized in Table 3.
• Table 3 The solids content of centrifuged ammonium sulfate/P AM treated MFT as determined by separating and drying consolidated material.
• Treating MFT with an equal weight of the (NH 4 )2S0 4 / polymer solutions resulted in a salt-tailings concentration of about 1 wt% for each of vials A4-E4, and for vial A4, a polymer-tailings concentration of about 0.05 wt% PAM, for vial B4 a polymer-tailings concentration of about 0.04 wt% PAM, for vial C4 a polymer-tailings concentration of about 0.03 wt% PAM, for vial D4 a polymer-tailings concentration of about 0.02 wt% PAM, and for vial E4 a polymer-tailings concentration of about 0.01% PAM.
• the solids content was very variable, reflecting the problems with segregation of coarse and fine particles in the consolidated materials in these experiments.
• the treated mixtures were first stirred and then the vials were centrifuged at 3000 rpm for 30 seconds to accelerate settling.
• the results are shown in the picture of Figure 6. From left to right, the seawater used to treat the MFT included about 0.1 wt%, 0.08 wt%, 0.06 wt%, 0.04 wt% and 0.02 wt% of the polymer flocculant, respectively.
• a sample of tailings generated from processing copper ore was combined with an approximate equal amount of an aqueous ionic solution in a 500 ml beaker.
• the aqueous ionic solution comprised water, a highly water soluble salt and flocculant (polyacrylamide (PAM)).
• PAM polyacrylamide
• the solids started to consolidate almost immediately. After standing for just a few minutes, the sold aggregated and settled to the bottom with a clarified water layer above the consolidated solids. See Figure 7A. The consolidated solids were also cohesive. Consolidated material taken from the beaker was readily compressed by hand to form a ball (see Figure 7B).
• a step test in which the hand compacted ball shown in Figure 7B was placed between paper towels and stepped on by a tester, showed that the consolidated material does not foul paper towels (See Figure 7C).
• Such a test is an indication of how readily the consolidated material can be filtered and mechanically dewatered in which a low fouling indicates good filterability and mechanical dewatering.
• the solids content of the pressed tailings was measured to be about 75%.

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