WO2019170697A1

WO2019170697A1 - Process for treating an aqueous slurry and composition for use therein

Info

Publication number: WO2019170697A1
Application number: PCT/EP2019/055488
Authority: WO
Inventors: Stephen John Adkins; Melissa LOAN; Lewis UTTING
Original assignee: Basf Se
Priority date: 2018-03-07
Filing date: 2019-03-06
Publication date: 2019-09-12

Abstract

The present invention relates to a process for treating an aqueous slurry comprising particulate mineral material, the process comprising the steps of: (a) providing a stream of the aqueous slurry in which the solids content is from 10% to 80% by weight of the aqueous slurry; (b) adding to the aqueous slurry a flocculant system comprising components: (i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multi valent or monovalent counter ion; and (ii) a polyethylene oxide; (c) mixing the components (i) and (ii) and the aqueous slurry to provide a mixture; and (d) discharging the mixture in a deposition area, in which the proportion of component (ii) employed in the flocculant system is up to 20% polymer content by weight of the total active polymer content of the flocculant system. The invention also includes a aqueous composition comprising (i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multi valent or monovalent counterion; and (ii) a polyethylene oxide, in which the proportion of component (ii) is up to 20% active polymer content by weight of the total active polymer content of the aqueous composition. The inventive process and composition are useful in the treating of aqueous slurries containing particulate mineral material. The invention provides effective dewatering in terms of rheology of deposited solids, volume of liquor release and turbidity of liquor released.

Description

Process for Treating an Aqueous Slurry and Composition for Use Therein Background of the Invention Field of the Invention

In one of its aspects, the present invention relates to a process for treating an aqueous slurry such as a tailings stream from a mineral processing operation. Said process employs a flocculant system that includes (i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer; and (ii) a polyethylene oxide. In another of its aspects, the present invention relates to an aqueous composition containing (i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer; and (ii) a polyethylene oxide.

Description of the Prior Art

Processes of treating mineral ores, coal or oil sands in order to extract mineral values or in the case of oil sands to extract hydrocarbons, or coal will normally result in waste material from the beneficiation processes. Often the waste material is an aqueous slurry or sludge comprising particulate mineral material, for instance clay, shale, sand, great, oil sand tailings, metal oxides etc. admixed with water.

In some cases the waste material such as mine tailings can be conveniently disposed of in an underground mine to form backfill. Generally, waste comprises a high proportion of coarse large sized particles together with other smaller sized particles and is pumped into the mine as a slurry, occasionally with the addition of a pozzolan, where it is allowed to dewater leaving a sedimented solid in place. It is common practice to use flocculants to assist this process by flocculating the fine material to increase the rate of sedimentation. However, in this instance, the coarse material will normally sediment at a faster rate than the flocculated fines, resulting in a heterogeneous deposit of coarse and fine solids.

For other applications it may not be possible to dispose of the waste in a mine. In these instances it is common practice to dispose of this material by pumping the aqueous slurry to lagoons, heaps or stacks and allowing it to dewater gradually through the actions of sedimentation, drainage and evaporation. In these instances it is common practice to dispose of this material above ground, or into open mine voids, or even purpose-built dams or containment areas. This initial placement of the mining waste into the disposal area may be as a free-flowing liquid, thickened paste or the material may be further treated to remove much of the water, allowing it to be stacked and handled as a solid-like material. The mining waste is allowed to further dewater gradually through the actions of sedimentation, drainage and evaporation.

For example, in the case whereby the tailings are sent to the disposal area in a liquid and fluid form, it must be contained in a lagoon by dams or similar impoundment structures. The tailings may have been pretreated by adding flocculating agents and thickened in a gravity thickener to remove and recover some of the water content, but the overall solids content is such that the fluid has no, or a low yield stress, and hence the material behaves largely as a liquid on deposition. These lagoons may be relatively shallow, or very deep, depending upon how much land is available, the method for building the impoundment area and other geotechnical factors within the vicinity of the mine site. Dependent upon the nature of the solid particles in the waste, often the particles will gradually settle from the aqueous slurry and form a compact bed at the bottom of the deposition area. Released water may be recovered by pumping or is lost to the atmosphere through evaporation, and to groundwater through drainage. It is desirable to remove the aqueous phase from the tailings whereby the geotechnical moisture content is below the liquid limit of the tailings solids, in order to manage the remaining tailings in a form that have a predominantly solid or semi solid handling characteristics. Numerous methods can be employed to achieve this, the most common, when the material properties of the tailings allows, is self weight consolidation in a tailings dam, whereby the permeability of tailings is sufficient enough to overcome the filling rate of the dam and water can be freely released from the tailings. Where the permeability of the tailings is not sufficient for water to escape freely, polymers are typically used to improve permeability thereby making the tailings suitable for a self weight consolidation process. Eventually it may be possible to rehabilitate the land containing the dewatered solids when they are sufficiently dry and compact. However, in other cases, the nature of the waste solids will be such that the particles are too fine to settle completely into a compacted bed, and although the slurry will thicken and become more concentrated over time, it will reach a stable equilibrium whereby the material is viscous but still fluid, making the land very difficult to rehabilitate. It is known that flocculants are sometimes used to treat the tailings before depositing them into the disposal area, in order to increase the sedimentation rate and increase the release of water for recovery or evaporation.

In an alternative method of disposal, the tailings may be additionally thickened, often by the treatment with polymeric agents, such that the yield stress of the material increases so that the slurry forms heaps or stacks when it is pumped into the deposition area.

Specialised thickening devices such as Paste Thickeners or Deep Cone Thickeners may be used to produce an underflow with the required properties. Alternatively, polymeric agents may be added to the tailings slurry during transfer or discharge into the disposal area, in order to render the material less mobile and achieve the required yield stress. This heaped geometry aids more rapid dewatering and drying of the material to a solid like consistency as the water is removed and recovered more rapidly through run-off and drainage, and the compaction of the solids may occur more rapidly through the increased weight and pressure of the solids when formed into a heap or a stack. In some instances, the deposition of the solids is controlled to build up relatively narrow bands of tailings, which can also dewater quickly through evaporation, prior to adding a new layer of treated waste material on top. This method has been widely used to dispose of red mud tailings from alumina processing for a number of years. Air drying of tailings can be used to great effect where the environment has some evaporation potential and there is enough area to spread the tailings thinly enough for this process to be effective. Where the area for evaporation is limited it is possible for polymers to be added to the tailings in order to improve this process. The addition of the polymer is able to increase the permeability of the tailings whereby typically about 20% by weight of the water can be allowed to drain, while another 20% of the water that is typically more associated with the particle surfaces and the clay matrix can be removed through evaporation.

It is often useful for the tailings pond or dam to be of limited size in order to minimise the impact on the environment. In addition, providing larger tailings ponds can be expensive due to the high costs of earthmoving and the building of containment walls. These ponds tend to have a gently sloping bottom which allows any water released from the solids to collect in one area and which can then be pumped back to the plant. A problem that frequently occurs is when the size of the tailings pond and dam are not large enough to cope with the output of tailings from the mineral processing operation. Another problem that frequently occurs is when fine particles of solids are carried away with the run-off water, thus contaminating the release water and having a detrimental impact on recycling and subsequent uses of the water.

Another method for disposal of the mine tailings is to use mechanical dewatering devices such as filters and centrifuges, in order to remove a significant amount of the water from the aqueous minerals slurry, such that the waste material may be deposited in the disposal area directly with a solids like consistency. In many cases, it is necessary to treat the tailings with polymeric flocculating agents immediately prior to the mechanical dewatering step, to enable this equipment to perform efficiently and achieve the degree of dewatering required.

A further method for disposal of the mine waste is through filtration in a Geotube® whereby the aqueous slurry is pumped into a permeable geotextile bag which retains the solids particles and some of the water is released through a filtration process, escaping through the walls of the geotextile bag. In some cases, where the starting permeability of the mine tailings is low, it may be desirable to add a flocculating agent in order to increase the filtration rate, and improve the retention of fine particles within the Geotube®.

For example, in oil sands processing, the ore is processed to recover the hydrocarbon fraction, and the remainder, including both process material and the gangue, constitutes the tailings that are to be disposed of. In oil sands processing, the main process material is water, and the gangue is mostly sand with some silt and clay. Physically, the tailings consist of a solid part (sand tailings) and a more fluid part (sludge). The most satisfactory place to dispose of the tailings, is of course in the existing excavated hole in the ground. It turns out, however, that the sand tailings alone from the one cubic foot of ore occupy just about one cubic foot. The amount of sludge is variable, depending on the or quality and process conditions, but average about 0.3 cubic feet. The tailings simply will not fit into the hole in the ground.

In a typical mineral or oil sands processing operation, waste solids are separated from solids that contain mineral valuables in an aqueous process. The aqueous suspensions of waste solids often contain clays and other minerals, and are usually referred to as tailings. These solids are often concentrated by a flocculation process in a gravity thickener to give a higher density underflow and to recover some of the process water. It is usual to pump the underflow to a surface holding area, often referred to as a tailings pit or dam or more usually a tailings pond in the case of oil sands. Once deposited at this surface holding area, water will continue to be released from the aqueous suspension resulting in further concentration of the solids over a period of time, as described in the paragraphs above. Once a sufficient volume of water has been collected this is usually pumped back to the mineral or oil sands processing plant.

Within the oil sands industry, there are a number of different types of process tailings streams which may require treatment with polymeric agents. One example is "fine fluid tailings" (FFT) which is the fines fraction (mainly silt and clay) from the process after the hydrocarbon content has been removed, and the sand fraction has been largely removed, usually by passing the "whole tailings" (WT) through a cyclone. The solids content of the fine fluid tailings may vary significantly, depending upon whether or not the material has been thickened by gravity sedimentation.

Another example is "combined tails" (CT) in which all the particle size ranges are present (sand, silt and clay). This may be the whole tailings, prior to the removal of the sand, or other tailings streams which may be formed by subsequent mixing of fine tailings with sand fractions, to varying degrees. A further example is "mature fines tailings" (MFT) which are formed after storage of fluid fine tailings, or in some cases combine tailings, in a tailings pond for several years.

In the oil sands tailings pond, the process water, and residual hydrocarbons and minerals settle naturally to form different strata. The upper stratum can be predominantly water that may be recycled as process water to the extraction process. The lower strata can contain settled residual hydrocarbon and minerals which are predominantly fines, usually clay. It is usual to refer to this lower stratum as mature fines tailings. It is known that mature fines tailings consolidate extremely slowly and may take many hundreds of years to settle into a consolidated solid mass. Consequently, mature fines tailings and the ponds containing them are a major challenge to tailings management and the mining industry.

The composition of mature fines tailings tends to be variable. The upper part of the stratum may have a mineral content of about 10% by weight but at the bottom of the stratum the mineral content may be as high as 50% by weight. The variation in the solids content is believed to be as a result of the slow settling of the solids and consolidation occurring over time. The average mineral content of the MFT tends to be of about 30% by weight. MFT behaviour is typically dominated by clay behaviour, with the solids portion of the MFT behaving more as a plastic-type material than that of a coarser, more friable sand.

The MFT frequently comprises a mixture of sand, fines and clay. Generally, the sand may refer to siliceous particles of any size greater than 44 pm and may be present in the MFT in an amount of up to 50% by weight. The remainder of the mineral content of the MFT tends to be made up of a mixture of clay and fines (silts). Generally, the fines refer to mineral particles no greater than 44 pm. The clay may be any material traditionally referred to as clays by virtue of its mineralogy and will generally have a particle size of below 2 pm. Typically, the clays tend to be a blend of kaolin, illite, chlorite and water swelling clays, such as montmorillonites.

Additional variations in the composition of MFT may be as a result of the residual hydrocarbon which may be dispersed in the mineral ore and may segregate into mat layers of hydrocarbon. The MFT in a pond not only has a wide variation of compositions distributed from top to bottom of the pond but there may also be pockets of different compositions at random locations throughout the pond.

In all cases, in addition to mineral-based particulate material, it is usual for tailings from the oil sands mining operation also to contain some residual bitumen (hydrocarbon) material as it is not possible to completely recover all of the hydrocarbon from the mined raw ore feed to the plant.

It has been known to treat aqueous slurry such as tailings through the use of polymer flocculants. See, for example, any of:

EP-A-388108;

WO 96/05146;

WO 01/92167;

WO 04/060819; WO 97/0611 1.

Canadian patent 2,803,904 teaches the use of high molecular weight multi valent anionic polymers for clay aggregation. Specifically, a polymer comprising an anionic water-soluble multivalent cation-containing acrylate copolymer is described.

Canadian patent 2,803,025 teaches a polymer similar to the polymer taught in Canadian patent 2,803,904 with the proviso that the polymer has an intrinsic viscosity of less than 5 dl/gm.

WO 2017/084986 describes a multivalent cation containing copolymer derived from one or more ethylenically unsaturated acids. The copolymer has the following characteristics: (a) an intrinsic viscosity of at least about 3 dl/g when measured in 1 M NaCI solution at 25°C; (b) the copolymer is derived from a monomer mixture comprising an ethylenically unsaturated acid and at least one comonomer, the ethylenically unsaturated acid present in an amount in the range of from about 5% to about 65% by weight; and (c) a residual comonomer content of less than 1000 ppm when the comonomer is an acrylamide. The copolymer, inter-alia, is useful as a flocculant for treating an aqueous slurry comprising particulate material, preferably tailings from a mining operation.

There is a desire to improve upon the treatment of aqueous slurrys comprising particulate material. This is particularly so in dewatering operations where it would be desirable to improve upon the net water release and/or slump height of separated solids. It is alternatively or additionally desirable to improve upon the turbidity of the released water.

Summary of the Invention

Accordingly, in one of its aspects, the present invention provides a process for treating an aqueous slurry comprising particulate mineral material, the process comprising the steps of:

(a) providing a stream of the aqueous slurry in which the solids content is from 10% to 80% by weight of the aqueous slurry;

(b) adding to the aqueous slurry a flocculant system comprising components: (i) a

copolymer comprising repeating units of (meth)acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multivalent or monovalent counterion; and (ii) a polyethylene oxide;

(c) mixing the components (i) and (ii) and the aqueous slurry to provide a mixture; and (d) discharging the mixture in a deposition area, in which the proportion of component (ii) employed in the flocculant system is up to 20% polymer content by weight of the total polymer content of the flocculant system.

In a further aspect of the present invention, we provide an aqueous composition comprising (i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multivalent or monovalent counterion; and

(ii) a polyethylene oxide, in which the proportion of component (ii) is up to 20% active polymer content by weight of the total active polymer content of the aqueous composition. In a further embodiment of the aforementioned aqueous composition, said composition further comprises:

(iii) an aqueous slurry comprising particulate mineral material having a solids content from 10% to 80% by weight of the aqueous slurry.

Detailed Description By (meth)acrylamide we mean either methacrylamide or acrylamide.

The stream of the aqueous slurry should have a solids content of from 10% to 80% by weight of the aqueous slurry. The aqueous slurry to be treated may already have a solids content within this range. Typically, however, an aqueous slurry may have undergone some sort of initial thickening stage where an amount of the aqueous liquid may have been removed. Such an initial thickening stage may, for instance, be a sedimentation stage, such as in a thickening or sedimentation vessel or in a pit. Alternatively, the thickening stage may include a belt thickener or a centrifuge. Other means of bringing the solids content to within the required range may also be possible.

By particulate mineral solids we mean that the solids include mineral or mining solids, typically from a mining or mineral processing operation. The particulate solids in the slurry may, for instance, contain filter cake solids or tailings. Often, the particulate mineral material comprises tailings. Suitably, the aqueous slurry may comprise phosphate slimes, gold slimes or wastes from diamond processing. Typically, the particulate mineral material is selected from the group consisting of coal fines tailings, mineral sands tailings, red mud (alumina Bayer process tailings), oil sands tailings, mature fines tailings, zinc ore tailings, lead ore tailings, copper ore tailings, silver ore tailings, uranium ore tailings, nickel ore tailings and iron ore tailings.

The copolymer containing a multivalent or monovalent counterion (i) may be added to the aqueous slurry in any suitable form. This may, for instance, be by addition of the copolymer in the form of a solid, typically in particulate form, for example as polymeric beads, granular particles, agglomerates, pellets or powder. In this form of addition the solid polymer would hydrate and dissolve in the aqueous slurry. It may also be desirable to add the copolymer to the aqueous slurry in the form of a dispersion. This may, for instance, be as an aqueous dispersion containing particles of the copolymer suspended in an aqueous medium, for instance a suspension of the copolymer such that the copolymer particles are prevented from dissolving in the aqueous medium by the presence of dissolved copolymer or other dissolved compounds, such as dissolved inorganic salts or other polymers. Nevertheless, preferably the copolymer containing a multivalent or monovalent counterion (i) is added to the aqueous slurry in the form of an aqueous solution. Typically, the copolymer would be dissolved into water at the site where the aqueous solution is intended for use. Dissolution of the copolymer may be achieved by any suitable technique and employing equipment well-known in the art and described in the patents and literature. Suitable equipment for dissolving the copolymer includes the Auto Jet Wet® apparatus and Aerowet® apparatus, both of which are available from BASF.

Desirably this copolymer may be added to the aqueous slurry at any suitable concentration of aqueous solution. It may be desirable to employ a relatively concentrated solution, for instance up to 10% or more, based on the weight of the polymer, in order to minimise the amount of water introduced into the aqueous slurry.

The copolymer containing a multivalent or monovalent counterion (i) may be added to the aqueous slurry at a concentration of from 0.01 % to 10%, based on the weight of the polymer. Desirably, the concentration may be from 0.05% to 5%, based on the weight of the polymer, typically from 0.1 % to 4%, frequently from 0.2% to 3%, often from 0.25% to 2%, usually from 0.3% to 1 %.

The polyethylene oxide (ii) may be added to the aqueous slurry in any suitable form. This may, for instance, be by addition of the copolymer in the form of a solid, typically in particulate form, for instance as granular particles, polymeric beads, agglomerates, pellets or powder. In this form of addition the solid particles would hydrate and dissolve in the aqueous slurry. It may also be desirable to add the polyethylene oxide to the aqueous slurry in the form of a dispersion, for instance as a dispersion of polyethylene oxide particles suspended in an aqueous liquid which may contain a dissolved water-soluble polymer, for instance dissolved polyethylene oxide, which would prevent the solid particles from dissolving completely. Alternatively, the polyethylene oxide may be added as a dispersion of polyethylene oxide particles suspended in the form of a dispersion in an aqueous salt solution. Typically, the salt solution may be a solution of an alkali metal or alkaline earth metal salt of a strong acid, for instance as the chloride or sulphate. Preferably, the salt may be of an alkali metal chloride or an alkali metal sulphate, particularly sodium chloride, sodium sulphate, potassium chloride or potassium sulphate. As a further alternative, the polyethylene oxide may be added as a dispersion of polyethylene oxide particles in a non-aqueous liquid, for instance in anhydrous polyethylene glycol (PEG), polyethylene glycol derivatives (such as methyl terminated polyethylene glycol) or propylene oxide-ethylene oxide (PO-EO) copolymers that are liquid at ambient temperature i.e. 25°C. Suitably, such PEG, PEG derivatives or PO-EO copolymers may have a molecular weight of below 1000 g/mole. Preferably, the molecular weight may be below 800 g/mole, for instance a molecular weight of from 100 to 650 g/mole, such as PEG 400 or PEG 300. Nevertheless, preferably the polyethylene oxide (ii) is added to the aqueous slurry in the form of an aqueous solution. Typically, the polyethylene oxide would be dissolved into water at the site where the aqueous solution is intended for use. Dissolution of the polyethylene oxide may be achieved by any suitable technique and employing equipment well-known in the art and described in the patents and literature. Suitable equipment for dissolving the polyethylene oxide may be analogous to the aforementioned equipment used for dissolving the copolymer containing a multi valent or monovalent counterion (i), for instance the Auto Jet Wet® apparatus and

Aerowet®, available from BASF.

Desirably the polyethylene oxide may be added to the aqueous slurry at any suitable

concentration of aqueous solution. It may be desirable to employ a relatively concentrated solution, for instance up to 10% or more, based on the weight of the polyethylene oxide, in order to minimise the amount water introduced into the aqueous slurry.

Specifically, the polyethylene oxide (ii) may be added to the aqueous slurry at a concentration of 0.01 % to 10%, based on the weight of the polyethylene oxide. Desirably, the concentration may be from 0.05% to 7%, based on the weight of the polymer, typically from 0.01 % to 5%, frequently from 0.2% to 4%, often from 0.25% to 2%, usually from 0.5% to 1.5%.

In the process of the present invention the flocculant system may be added to the aqueous slurry in the form of an aqueous composition. Such an aqueous composition may comprise, (i) a copolymer comprising (meth)acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multi valent or monovalent counterion; and

(ii) a polyethylene oxide, in which the proportion of component (ii) is up to 20% active polymer content by weight of the total active polymer content of the aqueous composition.

The aqueous composition may be formed by combining an aqueous solution of the copolymer containing a multi valent or monovalent cation (i) with an aqueous solution of the polyethylene oxide (ii). Alternatively, the aqueous composition may be formed by dissolving a mixture of solid particles of the two polymers together into an aqueous liquid. In a further alternative the aqueous composition may be formed by forming an aqueous solution of either the copolymer containing a multi valent or monovalent cation (i) or the polyethylene oxide (ii) first and then dissolving the other component into said aqueous solution.

Desirably, in the process of the present invention the components of the flocculant system may be added to the aqueous slurry separately. This separate addition of the components of the flocculant system may be simultaneous addition or sequential addition.

The copolymer containing a multivalent or monovalent counterion comprises repeating units of (meth)acrylamide and an ethylenically unsaturated anionic monomer. The reference to ethylenically unsaturated anionic monomer means any ethylenically unsaturated monomer which bears and anionic group. Typically, such an anionic group would be an acid group or an acid radical group which is in ionic association with the multi valent or monovalent counterion. Typical ethylenically unsaturated anionic monomers include acrylic acid (or salts thereof), methacrylic acid (or salts thereof), itaconic acid (or salts thereof), maleic acid (or salts thereof), fumaric acid (or salts thereof), styrene sulphonic acid (or salts thereof), allyl sulphonic acid (or salts thereof), vinyl sulphonic acid (or salts thereof), 2-acrylamido-2-methyl propane sulphonic acid (or salts thereof) and vinyl phosphonic acid (or salts thereof).

Preferably, the ethylenically unsaturated anionic monomer is a salt of acrylic acid.

Preferably, the (meth)acrylamide is acrylamide.

The term "copolymer containing multivalent or monovalent counterion" as used throughout the specification is intended to mean that the multivalent or monovalent counterion is contained as part of the copolymer. Typically, the multivalent or monovalent counterion containing copolymer would be the multivalent or monovalent salt of the copolymer. Suitably, the multivalent counterion may be formed from alkaline earth metals, group Ilia metals, transition metal etc. Preferable multivalent counterions include magnesium ions, calcium ions, aluminium ions etc. Desirably, the monovalent counterion may be formed from alkali metals or ammonium.

Preferable monovalent counterions include lithium ions, sodium ions, potassium ions, ammonium ions etc. Suitable copolymers containing multivalent counterions may include repeating units of magnesium diacrylate, calcium diacrylate and aluminium triacrylate. Suitable copolymers containing monovalent counterions include lithium acrylate, sodium acrylate, potassium acrylate and ammonium acrylate.

Desirably, the copolymer comprising repeating units of (meth)acrylamide and an ethylenically unsaturated anionic monomer contains a sodium counterion, a potassium counterion, an ammonium counterion, a calcium counterion or a magnesium counterion. Preferably, the copolymer contains a calcium counterion. More preferably, the copolymer is of acrylamide and an ethylenically unsaturated anionic monomer containing a calcium counterion.

Suitably, component (i) of the flocculant system is a copolymer comprising repeating units of (meth)acrylamide, especially acrylamide, and as the ethylenically unsaturated anionic monomer at least one of the group consisting of sodium acrylate, potassium acrylate, ammonium acrylate, calcium diacrylate and magnesium acrylate. Preferably the component (i) is a copolymer comprising repeating units of acrylamide and calcium diacrylate.

Typically, the multivalent or monovalent counterion is contained in the copolymer (i) in a significant amount relative to the amount of repeating units of the ethylenically unsaturated anionic monomer. Normally, the molar equivalent of multivalent or monovalent counterion to repeating anionic monomer units is at least 0.10:1. Suitably, the molar ratio equivalent may be from 0.15:1 to 1.6:1 , normally from 0.20:1 to 1.2:1 , preferably from 0.25:1 to 1 :1.

The multivalent or monovalent counterion containing copolymer (i) may be obtainable by copolymerisation of ethylenically unsaturated anionic monomer which is already in association with the multivalent or monovalent counterion, for instance multivalent or monovalent cation salts of ethylenically unsaturated anionic monomer with (meth)acrylamide.

Thus, the multivalent or monovalent counterion containing copolymer (i) may be derived from a monomer mixture comprising a multivalent or monovalent cation salt of an ethylenically unsaturated anionic monomer and (meth)acrylamide. The ethylenically unsaturated anionic monomer salt may be present in an amount in the range of from 5% to 95% by weight, based on the total weight of the monomers. Desirably, the amounts of the respective monomers used to form the copolymer (i) may be, for instance, from 5% to 95% by weight of multivalent or monovalent cation salt of an ethylenically unsaturated anionic monomer; and from 5% to 95% by weight of (meth) acrylamide.

Preferably, the amount of multivalent or monovalent cation salt of the ethylenically unsaturated anionic monomer may be from 5% to 85% by weight, such as from 5% to 70% by weight, typically from 10% to 60% by weight, often from 15% to 50% by weight, desirably from 20% to 45% by weight, for instance from 25% to 40% by weight; and the amount of (meth)acrylamide may be from 50% to 95% by weight, such as 30% to 95% by weight, typically from 40% to 90% by weight, often from 50% to 85% by weight, desirably from 55% to 80% by weight, for instance from 60% to 75% by weight.

Preferably, polymerisation is effected by reacting the aforementioned monomer mixture using redox initiators and/or thermal initiators. Typically redox initiators include a reducing agent such as sodium sulphite, sodium metabisulphite, sulphur dioxide and an oxidising compound such as ammonium persulphate or a suitable peroxy compound, such as tertiary butyl hydroperoxide etc. Redox initiation may employ up to 10,000 ppm (based on weight of aqueous monomer) of each component of the redox couple. Preferably though, each component of the redox couple is often less than 1000 ppm, typically in the range from 1 to 100 ppm, normally in the range from 4 to 50 ppm. The ratio of reducing agent to oxidising agent may be from 10:1 to 1 :10, preferably in the range from 5:1 to 1 :5, more preferably from 2:1 to 1 :2 for instance around 1 :1.

The polymerisation of the monomer mixture may be conducted by employing a thermal initiator alone or in combination with other initiator systems, for instance redox initiators. Thermal initiators would include suitable initiator compound that releases radicals at an elevated temperature, for instance azo compounds, such as azobisisobutyronintrile (AIBN), 4,4'-azo bis- (4-cyanovalereic acid) (ACVA). Typically, thermal initiators are used in an amount of up to 10,000 ppm, based on weight of aqueous monomer. In most cases, however, thermal initiators are used in the range from 100 to 5000 ppm, preferably from 200 to 2000 ppm, more preferably from 300 to 700 ppm, usually around from 400 to 600 ppm, based on the weight of the aqueous monomer mixture.

Typical methods of preparation of the multivalent or monovalent counterion containing copolymer (i) are given in WO 2017084986.

The multivalent or monovalent counterion containing copolymer (i) desirably has an intrinsic viscosity of at least about 3 dl/g, when measured in 1 M NaCI solution at 25°C.

Intrinsic viscosity of the copolymer may be determined by first preparing a stock solution. This may be achieved by placing 1.0 g of copolymer in a bottle and adding 199 ml of deionised water. This mixture may then be mixed for 4 hours, for instance on a tumble wheel, at ambient temperature (25°C). Diluted solutions may then be prepared by, for instance, taking O.Og, 4.0 g, 8.0 g, 12.0 g and 16.0 g, respectively, of the aforementioned stock solution and placing each into 100 ml volumetric flasks. In each case, 50 ml of sodium chloride solution (2 M) should then be added by pipette and the flask then filled to the 100 ml mark with deionised water and in each case the mixtures shaken for five minutes until homogenous. In each case, the respective diluted copolymer solutions are in turn transferred to an Ubbelohde viscometer and the measurement carried out at 25°C with the capillary viscometer Lauda iVisc. As such, the reduced specific viscosity of each of the dilute solution may be calculated and then extapolated to determine the intrinsic viscosity of the polymer, as described in the literature.

Suitably, the multivalent or monovalent counterion containing copolymer (i) may have an intrinsic viscosity in the range of from 3 to 30 dl/g, desirably from 4 to 25 dl/g, such as from 5 to 20 dl/g, for instance from 7 to 20 dl/g, often from 9 to 19 dl/g, typically from 10 to 18 dl/g, normally from 12 to 18 dl/g.

In one preferred form, the multivalent or monovalent counterion containing copolymer (i) is water-soluble. By water-soluble we mean that the copolymer has a gel content measurement of less than 50% gel. The gel content measurement is described below.

The gel content may be determined by filtering a stock solution (preparation of a stock solution is described above in the method of measuring intrinsic viscosity) through a sieve with a 190 pm mesh size. The residue which stays in the filter is washed, recovered, dried (1 10°C) and weighed, and the percentage of undissolved polymer is calculated (weight of dry residue from the filter [g] /weight of dry polymer before filtration [g]). Where necessary, this provides a quantifiable confirmation of the visual solubility evaluation.

Polyethylene oxide and polyethylene glycol are terms that refer to polyethers with the general formula H0-(CH2-CH2-0-)_nH in which n is an integer greater than 1. Generally, polyethylene glycol refers to oligomers or polymers with a molecular weight of less than 20,000 g/mol.

Polyethylene oxide, on the other hand, refers to polymers with a molecular weight of at least 20,000 g/mol, and generally of considerably higher molecular weight. In the process of the present invention it is preferred that the average molecular weight of the polyethylene oxide component (ii) is at least 1 million g/mol (grams per mole). Suitably, the polyethylene oxide may have an average molecular weight in the range of from 1 million g/mol to 15 million g/mol, desirably from 2 million g/mol to 12 million g/mol, for instance from 4 million g/mol to 11 million g/mol, such as from 5 million g/mol to 10 million g/mol. Suitable polyethylene oxide products include those available commercially from Dow Chemical Co under the trademark Polyox™ such as WSR-308™ and Ucarfloc Polymer 309™, both of which exhibit a molecular weight of approximately 8 million g/mol. In the treatment system according to the present invention the proportion of the polyethylene oxide i.e. component (ii) is up to 20 weight % polymer content by weight of the total polymer content of the flocculant system, i.e both components (i) and (ii). Suitably, the proportion of component (ii) on the total polymer content of the flocculant system is below this, for instance from 0.01 weight % to 15 weight % polymer content, usually from 0.02 weight % to 10 weight %, frequently from 0.04 weight % to 5 weight %, typically from 0.07 weight % to 2 weight %, such as from 0.1 weight % to 1 weight %. The desired precise proportion of the polyethylene oxide to the total flocculant system may depend on the particular aqueous slurry, for instance the particular particulate mineral material contained therein.

Typical doses of the multi valent or monovalent counterion containing copolymer comprising repeating units of (meth) acrylamide and ethylenically unsaturated anionic monomer

(component (i)) may range from 20 to 2000 g of polymer per tonne of solids content of the aqueous slurry. Desirably, this may be from 40 or 50 to 1500 g per tonne, suitably from 75 to 1000 g per tonne, often from 90 to 750 g per tonne, usually from 100 to 500 g per tonne.

Typical doses of the polyethylene oxide (component (ii)) may range from 0.1 to 500 g polymer per tonne of solids content of the aqueous slurry, suitably from 0.1 to 100 g per tonne, such as 0.1 to 50 g per tonne, for instance 0.1 to 20 g per tonne, desirably from 0.15 to 10 g per tonne, for instance from 0.25 to 7 g per tonne, suitably from 0.5 to 5 g per tonne, for instance from 1 to 2.5 g per tonne.

The exact doses of each of the two components may depend on the particular aqueous slurry, including the particular particulate mineral material of the slurry and the solids content of the slurry. Nevertheless, the amount of component (ii) in terms of polymer content should not exceed 20% of the total polymer content of the flocculant system.

The flocculant system of the present invention should be applied to the stream of aqueous slurry during transfer as it flows towards the deposition area into which it is discharged. This can be achieved by addition of both the multivalent or monovalent counterion containing anionic copolymer (component (i)); and the polyethylene oxide (component (ii)) to the aqueous slurry. As given above, the two components of the flocculant system may be added as a composition containing both components or the two components may be added separately. Separate addition may be sequential or simultaneous.

When the two components of the flocculant system are added sequentially, the polyethylene oxide may be added to the aqueous slurry and then the multivalent or monovalent counterion containing anionic polymer may be added subsequently. Alternatively, the multivalent or monovalent counterion containing anionic copolymer may be added to the aqueous slurry first and then the polyethylene oxide may be added afterwards. Desirably, where the polyethylene oxide is added before the multivalent or monovalent counterion containing anionic copolymer, the polyethylene oxide may be added at any convenient point before the addition of the multivalent or monovalent counterion containing anionic polymer. This may, for instance, be a considerable distance before, such as at least 100 m before. In some cases, however, in may be desirable to add the polyethylene oxide less than 100 m before the point at which the multivalent or monovalent counterion containing anionic polymer is added. This may be from 1 m to less than 100 m before, for instance from 2 m to 80 m before, such as from 3 m to 10 m before. On the other hand, it may be is desirable to add the polyethylene oxide less than 5 m before the addition of the multivalent or monovalent counterion containing anionic polymer, for instance less than 3 m before, or less than 2 m before, or even less than 1 m before.

Although it is more desirable that the polyethylene oxide be either added before or

simultaneously with the addition of multivalent or monovalent counterion containing anionic polymer, it may alternatively be desirable that the multivalent or monovalent counterion containing anionic polymer be added before the addition of the polyethylene oxide.

In general, the aqueous slurry comprising the particulate mineral material would normally be transferred to the deposition area by the employment of at least one pumping stage. In some cases, it may be desirable to add the flocculant system, comprising addition of both the polyethylene oxide and multivalent or monovalent counterion containing anionic polymer, prior to a pumping stage. This may allow the flocculant system to fully integrate into the aqueous slurry of particulate solids. Alternatively, it may be desirable to add one of the components of the flocculant system, for instance either the polyethylene oxide or the multivalent or monovalent counterion containing anionic polymer before a pumping stage and the other component after a pumping stage. Preferably, the flocculant system, including both the polyethylene oxide and the multivalent or monovalent counterion containing anionic polymer after a pumping stage. Preferably, the flocculant system, including both the polyethylene oxide and the multivalent or monovalent counterion containing anionic polymer, is added after a pumping stage. In the case where there is only one pumping stage it is preferred that the flocculant system, including both the polyethylene oxide and the multivalent or monovalent counterion containing anionic polymer, be added after that pumping stage. In the case where there is more than one pumping stage employed to transfer the aqueous slurry to the deposition area, it is more preferred that the flocculant system, comprising both the polyethylene oxide and the multivalent or monovalent containing anionic polymer, be added after the last pumping stage. This is particularly case where the multivalent or monovalent counterion containing anionic polymer added to the aqueous slurry comprising particulate mineral material is in the form of an aqueous solution or aqueous composition. Typically, the aqueous slurry is transferred by pumping along a conduit to a deposition area.

The conduit can be any convenient means for transferring the aqueous slurry to the deposition area and may, for instance, be a pipeline or even a trench. The deposition area may be a tailings dam or lagoon or may be adjacent to a tailings dam or lagoon.

Normally the aqueous slurry would be transferred continuously to the deposition area i.e.

without interruption of the flow. However, in some cases it may be desirable to transfer the aqueous slurry first to a holding vessel before being transferred to the deposition area.

Suitably, the aqueous slurry is transferred to the deposition area through a conduit, for instance a pipeline. Normally, such a conduit, for instance pipeline, would have an outlet from which the aqueous slurry exits as it flows to the deposition area. Typically, the outlet of the conduit, for instance pipeline, is at the deposition area or may be close to the deposition area, for instance less than 20 m, usually less than 10 m and desirably less than 5 m from the deposition area. In such cases where the conduit or more specifically pipeline is close to the deposition area, the aqueous slurry should be able to flow into the deposition area.

It may be desirable in some cases to add one or both components of the flocculant system, i.e. the multivalent or monovalent counterion containing anionic polymer and/or polyethylene oxide, to the aqueous slurry as it exits the conduit for instance pipeline . In other cases, it may be desirable to add both components of the flocculant system prior to the aqueous slurry exiting the outlet of the conduit, or more specifically pipeline, for instance less than 20 m, less than 10 m and desirably less than 5 m from the outlet.

Suitably, the particulate solids of the aqueous slurry comprises mineral solids. Typically, the particulate solids may for instance contain filter cake solids or tailings. Often, the aqueous slurry may be an underflow from a gravimetric thickener, a thickened plant waste stream or alternatively may be an unthickened plant waste stream. For instance, the aqueous slurry may comprise phosphate slimes, gold slimes or wastes from diamond processing. Typical aqueous slurries include slurries of mineral sands tailings, zinc ore tailings, lead ore tailings, copper ore tailings, silver ore tailings, uranium ore tailings, nickel ore tailings, iron ore tailings, coal fines tailings, oil sands tailings or red mud. The aqueous slurry suitable for treatment in accordance with the present invention may include the concentrated suspension from the final thickener or wash stage of a mineral processing operation. Thus, the aqueous slurry may desirably result from a mineral processing operation. Preferably, the suspension comprises tailings. Suitably, the particulate solids contained in the aqueous slurry may comprise at least some solids which are hydrophilic, for instance water swelling clays. More preferably, the particulate solids of the aqueous slurry may be derived from tailings from a mineral sands process, coal fines tailings, oil sands tailings or red mud. The particulate solids of the aqueous slurry will depend upon the particular material, for instance the particular type of tailings. In the case of fine tailings, typically substantially all of the particles would tend to be less than 100 pm, frequently below 50 pm, often less than 25 pm, for instance about 95% by weight of the solids being less than 20 pm and about 75% being less than 10 pm. In some cases, the particulate solids of the aqueous slurry have bimodal distribution of particle sizes, comprising a fine fraction and a coarse fraction, in which the fine fraction peak is less than 25 pm and a coarse fraction peak which is greater than 75 pm.

The concentration of the aqueous slurry will tend to vary according to the particular type of substrate. In general, the aqueous slurry can often be a slurry of thickened tailings, for instance a thickened tailings suspension flowing as an underflow from a thickener, for instance a gravimetric thickener, or other stirred sedimentation vessel. Suitably, the aqueous slurry may have a solids content in the range of from 15 to 80% by total weight of aqueous slurry, for instance from 45% to 65% by weight. Preferably, the solids content of the aqueous slurry will often be from 15 to 50%, frequently from 20 to 45% by total weight of the aqueous slurry.

Preferably, the aqueous slurry containing the particulate mineral material is an underflow stream which flows from a sedimentation vessel in which a first a first suspension of the particulate mineral material is separated into a supernatant layer comprising an aqueous liquor and a thickened layer which is removed from the vessel as an underflow. It would be this underflow which would be subjected to the treatment according to the present invention. It would not be possible to achieve the objectives of the invention by adapting the separation in a conventional sedimentation vessel such that the thickened layer was concentrated enough to form a stack of dewatered solids in the deposition area. On the contrary, in order for such a highly

concentrated thickened layer to be stackable, the yield stress of the thickened layer would be so high that it would be impossible to stir the thickened layer or remove the thickened layer from the conventional sedimentation vessel as an underflow. Furthermore, such solids would not be able to flow as an underflow from the vessel.

Thus, in one embodiment of the present invention the aqueous slurry of particulate mineral material is an underflow stream which flows from a sedimentation vessel in which a first suspension is separated into a supernatant layer comprising an aqueous liquor and a thickened layer, in which the thickened layer is removed from the vessel as an underflow. Subsequently, the flocculant system would be added to said underflow stream in accordance with the present invention. Suitably, the aforementioned first suspension may be treated by addition of at least one flocculant within the sedimentation vessel or prior to the first suspension entering into the sedimentation vessel. Preferably, the at least one flocculant is (i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multivalent or monovalent counterion. In a still preferred feature of this embodiment, the at least one flocculant includes (i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multivalent or monovalent counterion; and (ii) a polyethylene oxide.

In some cases, it may be desirable to add coarse particles to the underflow from the thickener or other sedimentation vessel. This may be done at any convenient point prior to the discharge at the deposition area. Desirably, the coarse particles may be added to the underflow from the vessel either before or during the addition of the flocculant system. When the aqueous slurry containing the fine and coarse particles of being combined for the purposes of co-disposal, the flocculant system, comprising the multivalent or monovalent counterion containing anionic polymer and the polyethylene oxide, should normally be added during or after the mixing of the fine and coarse particles streams. Generally, such mixing of different waste streams, in this case of fine and coarse particles streams, the resulting mixture would be a homogenous slurry.

Desirably, the aqueous slurry, to which the flocculant system has been added, is transferred, preferably by the action of at least one pump, along a conduit, for instance a pipeline, to an outlet of the conduit from which the suspension exits into the deposition area. Suitably, the so treated aqueous slurry at the deposition area is allowed to separate into a liquid portion and a solids portion. The liquid portion would tend to flow from the deposited solids from the aqueous slurry. In general, the deposited solids portion would have a higher yield stress than the aqueous slurry containing the particulate mineral material prior to separation. Typically, the deposited solids portion should form a layer in the deposition area.

In general, as the liquid portion separates from the suspension it would flow away from the deposited separated solids. Further, the aqueous slurry may be allowed to flow over the surface of one or more layers of previously separated deposited solids portions and then itself separate into a deposited solids portion with the release of a liquid portion. Thus, it is desirable that the solids portion forms a layer over the surface of one or more layers of previously solid portion (s).

Separation of the aqueous slurry into the solid portion and liquid portion generally occurs when the flow of the flocculant system treated aqueous slurry slows and the suspension substantially stops flowing to form a layer of deposited solids. Suitably, further so treated aqueous slurry will then be allowed to flow over the surface of the the previously deposited solids and then allowed to separate into a further layer of deposited solids and a liquid portion in an analogous way. Repeating this process of building up deposited layers of solids over previous layers will form a stack comprising multiple layers of deposited solids. The inventors have discovered that the employment of the flocculant system in the present invention can bring about improvements in the height of deposited solid material (sometimes referred to as slump height) and/or the net water release and/or turbidity of the separated liquid.

Desirably, the deposited solids resulting from the treatment of the present invention would form a beach of deposited solids. The beach allows run-off and collection of the release water, and the increasing the "self weight" compressional forces which aid the dewatering process. The angle of the beach slope will depend upon the particular solids, for instance type of tailings, deposited at the deposition area. In the case of coal tailings the angle of the beach may desirably be quite significant, for instance a beach slope of about 8%. In the case of

suspensions of other types of solid particles, for instance tailings from processing hard rock ores, the beach slope may desirably be more subtle, for instance between 2 and 3% beach slope. In order to maximise the ulitilization of the available deposition area generally it would be important to also control the deposition of geometry, i.e. beach slope angle according to the substrate (i.e. type of solids in the aqueous slurry) and size of the depostion area.

Since the deposited solids are generally waste materials which are being disposed of at the deposition area, it is generally important that the deposited solids occupy as small an area as possible. The process of the present invention enables the formation of stacks of multiple layers of deposited solids which facilitate reduced area for disposal.

The rheological characteristics of the aqueous slurry containing the particulate mineral material so treated according to the present invention as it flows through the conduit, for instance pipeline, to the deposition area is important, since any significant reduction in flow

characteristics may seriously impair the efficiency of the process. It is important that there is no significant settling of the solids during flow, as this could result in a blockage, which may mean that the plant has to be closed in order to allow the blockage to be cleared. In addition, it is important that there is no significant reduction in flow characteristics since this could drastically impair the flow ability of the suspension. Such a deleterious effect could result in significantly increased energy costs as pumping becomes harder and the likelihood of increased where on the pumping equipment. The addition of the flocculant system according to the present invention does not appear to induce any disadvantageous flow characteristics by comparison to the addition of other treatment systems.

Desirably, the process of the invention will facilitate the formation of deposited solids of a suitable height. Particularly as multiple layers of deposited solids are formed the overall height of the deposited solids may be increased significantly. As the height of the deposited solids is increased so does the angle from the edge of the deposited solids to the highest point of the solids. Deposited solids in which there is a greater height under or adjacent to the intial discharge point compared to the edge of the deposit may be regarded as a heap. In some cases it is preferred that the deposited solids be in the form of a heap, which may be referred to as a heaped geometry.

Deposited solids of significant height, for instance stacks of multiple layers of deposited solids or deposited solids with a heaped geometry, tend to have a higher downward compaction pressure on underlying solids which seems to be responsible for enhancing the rate of dewatering. This can be found to provide a higher volume of waste per surface area, which is both environmentally and economically beneficial.

Where the process of the present invention involves treating an aqueous slurry resulting from an industrial process, for instance a mineral processing operation, the liquor can be returned to that industrial process thus reducing the volume of imported water required and therefore it is important that the liquor released is clear and substantially free of contaminants, especially migrating particulate fines. Suitably, the liquor may, for instance, be recycled to the mining or mineral processing operation, for instance oil sands operation from which the suspension originates. Alternatively, the liquor can be recycled to the spirals or other processes within the same plant.

Description of Drawings

Figure 1 Graph of Net Water Release at different PEO doses and 107 g/tonne Polymer Figure 2 Graph of Release Water Turbidity at different PEO doses and 107 g/tonne Polymer Figure 3 Graph of Net Water Release at different PEO doses and 161 g/tonne Polymer

Figure 4 Graph of Release Water Turbidity at different PEO doses and 161 g/tonne Polymer Figure 5 Graph of Net Water Release at different PEO doses and 215 g/tonne Polymer Figure 6 Graph of Release Water Turbidity at different PEO doses and 215 g/tonne Polymer Figure 7 Graph of Net Water Release at different PEO doses and 269 g/tonne Polymer Figure 8 Graph of Release Water Turbidity at different PEO doses and 269 g/tonne Polymer Figure 9 Graph of Net Water Release at different PEO doses and 322 g/tonne Polymer Figure 10 Graph of Release Water Turbidity at different PEO doses and 322 g/tonne Polymer

The following examples illustrate, but do not limit, the invention. Examples

The following experimentation was carried out to examine the effect on treating china clay and silica containing slurries at different solids contents using flocculant systems according to the present invention comprising multivalent or monovalent counterion containing anionic polymer and polyethylene oxide by comparison to a flocculant treatment employing only multivalent or monovalent counterion containing anionic polymer. The slump height of the deposited separated mineral solids, the net water release and the turbidity of the released water was measured in a drainage test described below.

Additives Employed Polymer A Calcium diacrylate (50 weight %) / acrylamide (50 weight %) copolymer; Intrinsic

Viscosity 9.9 dl/g; polymer powder product prepared by gel polymerisation.

Polymer B Calcium diacrylate (40 weight %) / acrylamide (60 weight %) copolymer; Intrinsic

Viscosity 15 dl/g; polymer powder product prepared by gel polymerisation.

Polymer C Calcium diacrylate (30 weight %) / acrylamide (70 weight %) copolymer; Intrinsic

Viscosity 17.6 dl/g; polymer powder product prepared by gel polymerisation.

Polymer D Calcium diacrylate (10 weight %) / acrylamide (90 weight %) copolymer; Intrinsic

Viscosity 12.8 dl/g; polymer powder product prepared by gel polymerisation.

Polymer E Sodium acrylate (30 weight %) / acrylamide (70 weight %) copolymer; Intrinsic

Viscosity 17 dl/g; polymer powder product prepared by gel polymerisation. PEO 25% suspension of Polyethylene oxide; molecular weight 8 million Daltons.

Preparation of aqueous polymer solutions of Polymers A to E

Solutions of Polymers prepared in deionised water @ 0.5% without dilution prior to dosing

0.5 weight/volume % aqueous solutions of Polymers A to E were prepared by first adding 0.5 g of each respective polymer into a bottle followed by introducing 5 ml of acetone to wet and disperse the polymer particles. To this mixture 95 ml of deionised water was added. The bottle containing the mixture was shaken vigourously until the polymer was fully dispersed throughout the solution and has swelled followed by tumbling the bottle on a tumbling wheel for 90 minutes. In each case the respective polymer solutions were left to stand overnight. Preparation of diluted aqueous solutions of PEO

PEO prepared in deionised water @ 0.25% active, diluted to 0.1 % prior to dosing

495 ml of water was placed in a 1000 ml beaker and placed under an overhead stirrer with anchor paddle followed by setting the stirrer to 500 rpm. 5 ml of the PEO suspension was injected into the side of the vortex. After 30 seconds stirring at 500 rpm the stirrer speed was adjusted to 100 rpm and mixing was continued for a further 10 minutes. After 10 minutes of stirring the 0.25 active % volume/volume stock solution of PEO, it was transferred to a storage container for use.

Substrate employed in the test work - synthetic high clay tailings comprising of: kaolin clay 13.5% wt silt (silica < 44pm) 19.8% wt fine sand 11.7% wt water (2000 ppm NaCI) 55.0 % wt

The synthetic substrate was prepared in bulk by mixing at high speed for 30 mins with a suitably sized propeller type impellor to disperse the solids, and then left to stand for at least 24 hours to allow the clays to hydrate. The slurry is homogenised again with a bucket plunger prior to sampling for individual tests.

Description of Test Work

Substrate conditioning: 300 ± 10 ml of substrate in a 400ml beaker, mechanically agitated using a flat blade Paddle impellor at 300 rpm.

The dilute PEO solution is added and mixed for 10 secs prior to the addition of the secondary polymer.

The mixing time for the secondary polymer is varied (recorded in data table, as measured from the final polymer addition). Test operator visually assesses the conditioning and stops the mixer when optimal flocculation is achieved.

Drainage test:

• Quickly transfer the contents of the beaker (ie treated substrate) on to the sieve (1 mm

mesh) fitted with a drainage collection pan. • Immediately record the central height of the resulting slumped solids on the sieve (note - un-flocculated & poorly flocculated slurry will pass through the sieve and give zero as the slump height)

• leave solids to stand/ drain on the sieve for 10 mins · measure the volume of water collected under the sieve

• measure the turbidity of the water collected under the sieve (turbidity meter - units NTU) Note max reading is 999 NTU so anything above this (off scale) is simply shown as > 1000

• based on the initial solids content of the substrate and the volume of water released, calculate the moisture content of the drained solids and net water released from the substrate. Net water is based on the total amount of water collected minus the amount of water added with the polymer(s) solutions, as a percentage of the total amount of water contained in the substrate

The results of the test work are presented in the following tables

Table 1

Table 2

Table 3

Table 4

Table 5

The results appear to indicate an overall performance benefit in terms of slump height and/or net water release and/or turbidity of water released in the treatments containing both the multivalent or monovalent counterion containing anionic polymer and polyethylene oxide by comparison to the multivalent or monovalent counterion containing anionic polymer in the absence of the polyethylene oxide, especially when considering the overall amount of polymer used in the treatment of the tailings material. For example, comparing 5 g/t PEO and 107 g/t of Polymer C, the performance overall is better than any treatment using Polymer C alone at all the dosage rates tested, up to 322 g/t of Polymer C. Silmilar trends can been seen for all the other Polymers tested. The lowest dosage of Polymer C in combination with 5 g/t PEO gave similar or improved performance when compared to all the higher dosages of the same Polymer used alone.

For all the treatments of 107 to 322 g/t Polymer and PEO dose of 5.00 g/t overall the most effective polymer was Polymer B at a dose of 322 g/t without the addition of any PEO exhibited a slump height of 14 mm, net water release of 29.3% and a turbidity of 71 NTU. By comparison Polymer B at a dose of 269 g/t and 5.00 g/t PEO provided a slump height of 26, net water release of 31.9% and a turbidity of 13 NTU. This demonstrates that by reducing the Polymer B from 322 to 269 g/t and including 5.00 g/t PEO that the slump height, net water release and turbidity is actually improved.

The multivalent counterion containing Polymer C may be compared against the monovalent counterion containing Polymer E because both polymers contain 30 weight % anionic monomer.

At a Polymer dose of 107 g/t and PEO dose of 5.00 g/t the slump height and net water release after 10 minutes was approximately the same for both Polymers C and E. However, the turbidity measurement was 663 NTU for Polymer C compared with 697 NTU for Polymer E. Thus, the turbidity result for Polymer E is about 5% worse than for Polymer C.

At a Polymer dose of 161 g/t and PEO dose of 5.00 g/t the comparison of slump height and net water release for Polymer C and E was approximately the same but with the turbidity improved i.e. 143 NTU as opposed to 229 NTU respectively, such that Polymer E was about 60% worse than for Polymer C.

At a Polymer dose of 215 g/t and PEO dose of 5.00 g/t the slump height was slightly better for Polymer E than for Polymer C but the turbidity for Polymer E was worse at 153 NTU compared to 54 NTU i.e. 183% worse.

At a Polymer dose of 269 g/t and PEO dose of 5.00 g/t Polymer E gave better results than for Polymer C with analogous slump heights, slightly better net water release of 31.5% compared to 29.8% but improved turbidity of 20 NTU compared to 26 NTU making Polymer C about 30% worse than for Polymer E.

At a Polymer dose of 322 g/t and PEO dose of 5.00 g/t Polymer C gave a better slump height of 25 mm by comparison to 20 mm for Polymer E and analogous net water release and turbidity.

Claims

1. A process for treating an aqueous slurry comprising particulate mineral material, the process comprising the steps of:

copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multi valent or monovalent counter ion; and (ii) a polyethylene oxide;

(c) mixing the components (i) and (ii) and the aqueous slurry to provide a mixture; and

(d) discharging the mixture in a deposition area, in which the proportion of component (ii) employed in the flocculant system is up to 20% polymer content by weight of the total active polymer content of the flocculant system.

2. A process according to claim 1 in which the particulate mineral material comprises tailings.

3. A process according to claim 1 or claim 2 in which the particulate mineral material is selected from the group consisting of coal fines tailings, mineral sands tailings, red mud (alumina bayer process tailings), oil sands tailings, mature fines tailings, zinc ore tailings, lead ore tailings, copper ore tailings, silver ore tailings, uranium ore tailings, nickel ore tailings, iron ore tailings.

4. A process according to any one of claims 1 to 3 in which the copolymer containing a multivalent or monovalent counter ion (i) is added to the aqueous slurry in the form of an aqueous solution.

5. A process according to any one of claims 1 to 4 in which the polyethylene oxide (ii) is added to the aqueous slurry in the form of an aqueous solution.

6. A process according to any one of claims 1 to 5 in which the flocculant system added to the aqueous slurry is in the form of an aqueous composition comprising

(i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multi valent or monovalent counterion; and

7. A process according to any one of claims 1 to 6 in which the ethylenically unsaturated anionic monomer is a salt of acrylic acid.

8. A process according to any one of claims 1 to 7 in which the copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer contains a calcium counter ion.

9. A process according to any one of claims 1 to 8 in which component (i) is a copolymer comprising acrylamide and calcium diacrylate.

10. A process according to any one of claims 1 to 9 in which component (i) exhibits an intrinsic viscosity of at least 3 dl/g.

11. A process according to any one of claims 1 to 10 in which the average molecular weight of the polyethylene oxide is at least 1 million g/mol (grams per mole).

12. A process according to any one of claims 1 to 11 in which the particulate mineral material comprises particles having particle sizes less than 100 pm.

13. A process according to any one of claims 1 to 11 in which the particulate mineral material has a bimodal distribution of particle sizes comprising a fine fraction and a coarse fraction, in which the fine fraction peak is less than 25 pm and the coarse fraction peak is greater than 75 pm.

14. A process according to any one of claims 1 to 13 in which the slurry of particulate mineral material has a solids content in the range of 15% to 80% by weight of total suspension.

15. A process according to any one of claims 1 to 14 in which the slurry of particulate mineral material is an underflow stream which flows from a sedimentation vessel in which a first suspension is separated into a supernatant layer comprising an aqueous liquor and a thickened layer, in which the thickened layer is removed from the vessel as the underflow.

16. A process according to claim 15 in which the first suspension is treated by addition of at least one flocculant within the sedimentation vessel or prior to the first suspension enters into the sedimentation vessel.

17. A process according to claim 16 in which the at least one flocculant is (i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multi valent or monovalent counterion.

18. A process according to claim 16 in which the at least one flocculant includes (i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multivalent or monovalent counterion; and (ii) a polyethylene oxide.

19. A process according to any one of claims 1 to 18 in which the slurry of particulate mineral material is transferred along a conduit employing at least one pump to an outlet of the conduit from which the slurry exits into the deposition area.

20. A process according to any one of claims 1 to 19 in which coarse particles having a peak particle size is greater than 75 pm are added to the aqueous slurry either before or during the addition of the flocculant system.

21. A process according to any one of claims 1 to 20 in which the slurry of particulate mineral material is transferred to a holding vessel before being pumped to the deposition area.

22. A process according to any one of claims 1 to 21 in which the slurry of particulate mineral material forms a layer of particulate solids in the deposition area.

23. A process according to any one of claims 1 to 22 in which liquid separates from the slurry of particulate mineral material deposited in the deposition area.

24. A process according to any one of claims 1 to 23 in which the particulate mineral material deposited in the deposition area has a higher yield stress than the slurry prior to deposition.

25. A process according to any one of claims 1 to 24 in which a stack of deposited particulate mineral material solids are formed in the deposition area by allowing successive layers of the particulate mineral material to form over a first layer.

26. A process according to any one of claims 1 to 25 in which the components of the flocculant system are added to the slurry of particulate mineral material as a blended composition.

27. A process according to any one of claims 1 to 25 in which the components of the flocculant system are added to the slurry of particulate mineral material sequentially.

28. A process according to any one of claims 1 to 25 in which the (i) copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multi valent or monovalent counterion is added to the slurry of particulate mineral material after the addition of the (ii) a polyethylene oxide.

29. An aqueous composition comprising (i) a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer, said copolymer containing a multi valent or monovalent counterion; and

30. An aqueous composition according to claim 29 in which the aqueous composition further comprises:

31. An aqueous composition according to claim 29 or claim 30 in which the component (i) is a copolymer comprising acrylamide and an ethylenically unsaturated anionic monomer containing a calcium ion.