SEPARATION OF SUSPENSIONS OF SOLIDS EMPLOYING WATER SOLUBLE POLYMER AND A CHEMICAL AGENT

Abstract

A process of separating a suspension of particulate solids dispersed in an aqueous liquid into a liquid portion and a solids portion by transferring the suspension by flowing it to a deposition area, subjecting the suspension to a treatment system during the transfer, and at the deposition area allowing the suspension to separate into the liquid portion and the solids portion, in which the treatment system contains (a) a water soluble polymer; and (b) a chemical agent selected from at least one of an oxidising agent, a reducing agent, and/or a free radical agent.
The treatment system enables a solids portion to be deposited and formed by an initial rigidification of the solids accompanied by an initial release of fluid, followed by a further consolidation of the rigidified solids with the further release of liquid.

Claims

1. A process of separating a suspension comprising particulate solids dispersed in an aqueous liquid into a liquid portion and a solids portion comprising transferring the suspension by flowing it to a deposition area, subjecting the suspension to a treatment system during the transfer, and at the deposition area allowing the suspension to separate into the liquid portion and the solids portion, wherein the treatment system comprises, (a) a water soluble polymer; and (b) a chemical agent selected from at least one of an oxidising agent, a reducing agent, and/or a free radical agent.

2. The process according to claim 1 in which the water soluble polymer is formed from at least one ethylenically unsaturated water-soluble monomer.

3. The process according to claim 1 in which the water-soluble polymer is formed from at least one monomer selected from the group consisting of (meth) acrylic acid (or a salt thereof), allyl sulphonic acid (or a salt thereof), and 2-acrylamido-2-methyl propane sulphonic acid (or a salt thereof), optionally in combination with at least one comonomer selected from the group consisting of (meth) acrylamide, hydroxy alkyl esters of (meth) acrylic acid, N-vinyl pyrrolidone, vinyl amides, and vinyl carboxylates.

4. The process according to claim 1 in which the water soluble polymer is formed from at least one monomer selected from the group consisting of (meth) acrylamide, hydroxy alkyl esters of (meth) acrylic acid, N-vinyl pyrrolidone, vinyl amides, and vinyl carboxylates.

5. The process according to claim 1 in which the water soluble polymer is formed from at least one monomer selected from the group consisting of dimethyl amino ethyl (meth) acrylate-methyl chloride, (DMAEA.MeCl) quat, diallyl dimethyl ammonium chloride (DADMAC), trimethyl amino propyl (meth) acrylamide chloride (ATPAC) optionally in combination with non-ionic co-monomers, selected from the group consisting of (meth) acrylamide, hydroxy alkyl esters of (meth) acrylic acid, N-vinyl pyrrolidone, vinyl amides, and vinyl carboxylates.

6. The process according to claim 1 in which the water soluble polymer is added to the suspension in the form of an aqueous solution.

7. The process according to claim 1 in which the chemical agent is selected from the group consisting of peroxides, ozone, hypochlorites, peracetates, perborates, percarbonates, persulphates, bromates, bisulphites, sulphites, ferrous ammonium sulphate, ammonium persulphate, and ceric ammonium nitrate.

8. The process according to claim 1 in which the water soluble polymer and the chemical agent are both added to the suspension substantially simultaneously.

9. The process according to claim 1 in which the water soluble polymer and the chemical agent are both added to the suspension after a pumping stage.

10. The process according to claim 1 in which the dispersed particulate solids are mineral.

11. The process according to claim 1 in which the dispersed particulate solids are derived from tailings from a mineral sands process, coal fines tailings, oil sands tailings, or red mud.

12. The process according to claim 1 in which the dispersed particulate solids have particles sizes less than 100 m.

13. The process according to claim 1 in which the dispersed particulate solids have a bimodal distribution of particle sizes comprising a fine fraction and a coarse fraction, in which the fine fraction peak is less than 25 m and a coarse fraction peak is greater than 75 m.

14. The process according to claim 1 in which the suspension has a solids content in the range of 15% to 80% by weight of total suspension.

15. The process according to claim 1 in which the suspension 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 which is removed from the vessel as the underflow.

16. The process according to claim 1 in which the suspension is transferred along a conduit employing at least one pump to an outlet of the conduit from which the suspension exits into the deposition area.

17. The process according to claim 15 in which coarse particles are added to the underflow from the vessel either before or during the addition of the treatment system.

18. The process according to claim 1 in which the suspension is transferred to a holding vessel before being pumped to the deposition area.

19. The process according to claim 1 in which the solids portion forms a layer in the deposition area.

20. The process according to claim 1 in which the liquid portion which separates from the suspension in the deposition area flows away from the separated solids portion which remains as a layer in the deposition area.

21. The process according to claim 1 in which the solids portion has a higher yield stress than the suspension prior to separation.

22. The process according to claim 1 in which the solids portion forms a layer over the surface of one or more layers of previously solids portion.

23. The process according to claim 1 in which the solids portion is formed by an initial release of liquid and rigidification of the solids followed by a subsequent consolidation of the rigidified solids with further release of liquid.

24. The process according to claim 22 in which the layers of the solids portion forms a stack comprising multiple layers of the solids portion in which each layer of solids portion is formed by an initial release of liquid and rigidification of the solids and in which a subsequent consolidation of each layer of solids occurs with further release of liquid.

Description

EXAMPLE 1

[0093] A slurry of coal tailings is provided from the underflow of a thickener vessel of a coal processing operation.

[0094] The slurry of coal tailings is flowed along a conduit towards a deposition zone. An aqueous solution of an anionic polyacrylamide at a concentration of 0.5% is dosed into the flowing slurry at a dose of 350 grams per tonne (active polymer on dry solids of the slurry) about 12 m from the deposition zone end of the conduit. 2 m after the polymer is dosed into the flowing slurry a hydrogen peroxide solution at 30% concentration is dosed into the flowing slurry at a dose to provide a ratio of polymer to hydrogen peroxide of 1:65.

[0095] On exiting the conduit at the deposition zone, the so treated mineral sands slurry pours onto a beach in the deposition zone where the flow of the solids ceases and liquid component of the slurry quickly flows from the deposited solids. A reduction in the volume of tailings deposited is accompanied by increased solids density, increased hydraulic conductivity and increase yield stress over a period of several weeks from three hours after deposition.

EXAMPLE 2

[0096] A slurry of mineral sands tailings is provided from the underflow of a thickener vessel of a mineral sands processing operation. The solids content of the slurry is typically between 50 and 55% (wt/wt) of which, between 10 and 12% (wt/wt) have a particle size of less than 75 m. Typically, the specific gravity is in the region of about 1.5 g/cm.sup.3.

[0097] The slurry of mineral sands tailings is flowed along a conduit towards any depositions zone. At 5 m from the depositions zone end of the conduit an aqueous solution of an anionic polyacrylamide at a concentration of 0.05% w/v is dosed into the flowing slurry at a dose of 50 g per tonne (active polymer on dry solids of the slurry) at the same time as dosing into the slurry an aqueous solution of hydrogen peroxide (at a concentration of 30%). The ratio of polymer to hydrogen peroxide added to the slurry is 1:50.

[0098] The so treated mineral sands slurry exits the conduit at the depositions zone onto a surface where the flow of the solids stops and the liquid component of the slurry quickly flows from the deposited solids. A reduction in the body of tailings deposited is accompanied by increased solids density, increased hydraulic conductivity and increase yield stress over a period of several weeks from three hours from deposition.