METHOD FOR CONTROLLING THE SEDIMENTATION OF A MINING DERIVATIVE

Abstract

The invention relates to a method for controlling the sedimentation of an aqueous mineral suspension of a mining derivative by means of the gravimetric concentration of the aqueous suspension in the presence of a flocculating agent and a polymer (P) which has a GPC-measured molecular mass Mw of between 2000 and 20000 g/mol and is prepared using at least one free radical polymerisation reaction of at least one anionic monomer (M).

The invention also relates to the resulting suspension, which has a Brookfield viscosity of less than 1 800 mPa.Math.s or a yield point of less than 80 Pa.

Claims

1. A method for controlling a settling of an aqueous mineral suspension comprising a flocculating agent and with a dry solids content that is greater than 10% by weight of the aqueous mineral suspension, selected from the group consisting of: an aqueous metal ore residue, an aqueous suspension of metal ore and an aqueous suspension of useable metal or of a useable metal derivative and derived from metal ore, the method comprising gravimetrically concentrating the aqueous suspension in the presence of at least one polymer (P) with a molecular mass Mw, measured by GPC, ranging from 2,000 to 20,000 g/mol and prepared by at least one radical polymerisation reaction, at a temperature greater than 50° C., of at least one anionic monomer (M) comprising a polymerisable olefinic unsaturation and a carboxylic acid group or one of its salts, in the presence of at least one radical-generating compound selected from the group consisting of hydrogen peroxide, benzoyl peroxide, acetyl peroxide, laurel peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, ammonium persulphate, an alkaline metal persulphate, an azo compound and their respective combinations or associations with an ion selected from the group consisting of Fe.sup.II, Fe.sup.III, Cu.sup.I, Cu.sup.II and mixtures thereof.

2. The method according to claim 1, wherein the aqueous mineral suspension has a dry solids content: greater than 15% by weight; greater than 10% by weight and less than 20% by weight; and ranging from 10 to 50% by weight.

3. The method according to claim 1, wherein the gravimetrically concentrating comprises separating a supernatant phase and a settling bed.

4. The method according to claim 1, wherein the gravimetrically concentrating comprises separating a supernatant phase and a settling bed that has: a Brookfield viscosity, measured at 100 rpm and at 25° C., of less than 1,800 mPa.Math.s or a flow threshold measured at a temperature of 25° C. using a rheometer with imposed shearing, equipped with a bladed spindle, for a particular torsional loading, of less than 80 Pa or a Brookfield viscosity, measured at 100 rpm and at 25° C., of less than 1,800 mPa.Math.s and a flow threshold, measured at a temperature of 25° C. using a rheometer with imposed shearing, equipped with a bladed spindle, for a particular torsional loading, of less than 80 Pa.

5. The method according to claim 1, wherein the gravimetrically concentrating comprises separating a supernatant phase and a settling bed that has: a flow threshold of less than 70 Pa; a flow threshold greater than 10 Pa; a flow threshold greater than 10 Pa and less than 70 Pa a viscosity of less than 1,500 mPa.Math.s.

6. The method according to claim 1, wherein the gravimetrically concentrating comprises separating a supernatant phase with a dry solids content of less than 5% by weight and a settling bed with a dry solids content greater than 40% by weight.

7. The method according to claim 1, wherein the aqueous mineral suspension comprises from 0.01 to 2% by weight of polymer (P) (dry/dry relative to the ore residue).

8. The method according to claim 1, further comprising adding one, two or three different polymer(s) (P) or adding at least one compound selected from the group consisting of a lignosulphonate derivative, a silicate, an unmodified polysaccharide and a modified polysaccharide.

9. The method according to claim 1, wherein: the metal ore is selected from the group consisting of lithium, strontium, lanthanide, actinide, uranium, rare earth, titanium, zirconium, vanadium, niobium, chromium, molybdenum, tungsten, manganese, iron, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, gold, zinc, cadmium, tin and lead ores; the metal ore comprises a metal oxide, a metal sulphide or a metal carbonate; the metal ore residue comprises a residual amount of metal of less than 2,000 g per tonne (dry/dry) relative to an amount of metal ore residue.

10. The method according to claim 1, wherein: the gravimetrically concentrating is carried out using at least one device selected from the group consisting of a conventional thickener, a high-density thickener, a high yield thickener, or in which: the polymer (P) is added: before the gravimetrically concentrating; during the gravimetrically concentrating; simultaneously with an addition of the flocculating agent; in parallel to the addition of the flocculating agent; during the gravimetrically concentrating and simultaneously with the addition of the flocculating agent, or during the gravimetrically concentrating and in parallel to the addition of the flocculating agent.

11. The method according to claim 1, wherein: the polymerisation reaction is carried out in the presence of at least one compound comprising phosphorus in the oxidation I state; the polymerisation reaction is also carried out in the presence of at least one compound comprising a bisulphite ion; the polymerisation reaction is carried out in the presence of at least one compound comprising phosphorus in the oxidation III state; the polymerisation reaction is also carried out in the presence of from 0.05 to 5% by weight, relative to the total amount of monomers, of at least one compound selected from the group consisting of a xanthate derivative, a mercaptan compound and a compound of formula (I): ##STR00003## wherein: X independently represents H, Na or K and R independently represents a C.sub.1-C.sub.5-alkyl group, preferably a methyl group, particularly a compound of formula (I) which is disodic diisopropionate trithiocarbonate (DPTTC); the polymerisation reaction is carried out at a temperature ranging from 50 to 98° C.; the polymerisation reaction is carried out in water, in a solvent, alone or in a mixture with water; the polymer (P) has a molecular mass Mw, measured by GPC, ranging from 2,200 to 10,000 g/mol; the polymer (P) is completely or partially neutralised; the polymerisation reaction uses: 100% by weight of anionic monomer (M) or from 70% to 99.5% by weight of anionic monomer (M) and from 0.5% to 30% by weight of at least one other monomer.

12. The method according to claim 1, wherein the anionic monomer (M) comprises one or two carboxylic acid groups.

13. The method according to claim 1, wherein the polymerisation reaction also uses at least one other monomer selected from the group consisting of: another anionic monomer; 2-acrylamido-2-methylpropanesulphonic acid, a salt of 2-acrylamido-2-methylpropanesulphonic acid, 2-(methacryloyloxy)ethanesulphonic acid, a salt of 2-(methacryloyloxy)ethanesulphonic acid, sodium methallyl sulphonate, styrene sulphonate and combinations or mixtures thereof; a non-ionic monomer comprising at least one polymerisable olefinic unsaturation; and a monomer of formula (II): ##STR00004## wherein: R.sup.1 and R.sup.2, identical or different, independently represent H or CH.sub.3, L.sup.1 independently represents a group selected from the group consisting of C(O), CH.sub.2, CH.sub.2—CH.sub.2 and O—CH.sub.2—CH.sub.2—CH.sub.2—CH.sub.2, L.sup.2 independently represents a group selected from the group consisting of (CH.sub.2—CH.sub.2O).sub.x, (CH.sub.2CH(CH.sub.3)O).sub.y, (CH(CH.sub.3)CH.sub.2O).sub.z and combinations thereof and x, y and z, identical or different, independently represent an integer or decimal comprised in a range from 0 to 150 and the sum of x+y+z is comprised in a range from 10 to 150.

14. The method according to claim 1, wherein the flocculating agent is selected from the group consisting of polyacrylamide and a polyacrylamide derivative.

15. An aqueous mineral suspension, comprising a flocculating agent and with a dry solids content that is greater than 10% by weight of the aqueous mineral suspension, selected from the group consisting of: an aqueous metal ore residue, an aqueous suspension of metal ore and an aqueous suspension of useable metal or of a useable metal derivative and derived from metal ore, comprising at least one polymer (P) with a molecular mass Mw, measured by GPC, ranging from 2,000 to 20,000 g/mol and prepared by at least one radical polymerisation reaction, at a temperature greater than 50° C., of at least one anionic monomer (M) comprising at least one polymerisable olefinic unsaturation and at least one carboxylic acid group or one of its salts, in the presence of at least one radical-generating compound selected from the group consisting of hydrogen peroxide, benzoyl peroxide, acetyl peroxide, laurel peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, ammonium persulphate, an alkaline metal persulphate, an azo compound, and their respective combinations or associations with an ion selected from the group consisting of Fe.sup.II, Fe.sup.III, Cu.sup.I, Cu.sup.II and mixtures thereof.

16. The aqueous mineral suspension according to claim 15: obtained by gravimetric concentration of the aqueous mineral suspension in the presence of at least one polymer (P).

Description

EXAMPLES

[0123] The following examples illustrate the various aspects of the invention.

[0124] A polymer used in the method according to the invention is prepared.

[0125] Polymer (P1) is prepared by placing 212 g water and 0.08 g of iron sulphate heptahydrate into a one-litre glass reactor with mechanical stirring and oil bath heating.

[0126] 303 g of acrylic acid at 100% by weight and 15 g of water are weighed into a 500 mL beaker fitted with a dosing pump.

[0127] 25.6 g of sodium hypophosphite monohydrate diluted with 30 g of water are weighed into a 100 mL test tube fitted with a dosing pump.

[0128] 21 g of hydrogen peroxide at 130 V and 35 g of water are weighed into a 100 mL test tube fitted with a dosing pump.

[0129] The reactor is heated to 95° C. and the monomer, the hypophosphite solution and the hydrogen peroxide solution are added in parallel in 120 min while keeping the temperature of the reaction medium at 95° C.

[0130] Lastly, the pumps are rinsed with water.

[0131] The medium is heated again for 60 min at 95° C.

[0132] The solution is then neutralised using 50% by weight of sodium hydroxide in water until it reaches pH 8 and then diluted to a solids content of 42% by weight. Polymer (P1) is obtained, with a molecular mass Mw, measured by GPC, of 4,500 g/mol.

[0133] The raw material used for this series of tests is an aqueous metal ore residue from a Chilean copper mine located in the north of the country. This is waste resulting from the separation of the ore containing the useable metal from the rock extracted from the mine.

[0134] This aqueous copper ore residue is in the form of a water-based suspension.

[0135] Various measures were taken beforehand on the aqueous residue in the absence of the polymer according to the invention: [0136] particle size distribution using a Mastersizer 2000 laser granulometer (Malvern): D(80) of 243.1 μm and [0137] solids content using a Mettler-Toledo dry balance: 63.5%.

[0138] A test is then performed to assess the effectiveness of the polymer on the settling of a suspension of aqueous copper ore residue when concentrating this residue by settling.

[0139] This settling test is carried out using a suspension with a solids content of 30% by weight. This suspension with a solids content of 30% by weight is prepared by diluting the aqueous suspension of residue with a solids content of 63.5% by weight.

[0140] A sample of suspension of aqueous copper ore residue at 30% by weight is transferred into a 500 mL beaker and then mechanically stirred with a Raynerie mixer. Stirring is carried out at 500 rpm.

[0141] Then, a polymer (P1) according to the invention is added at a dose of 0.05% by weight dry/dry relative to the dry residue and the mixture is left under stirring for 15 min.

[0142] The dispersed suspension is then incorporated into a 2-litre graduated test tube with a mechanical stirrer at 0.8 rpm.

[0143] A fixed dose of an acrylamide flocculating agent is incorporated at a dose equivalent to 12 g/T dry/dry of residue.

[0144] A test is carried out using the polymer (P1) and a comparative test is carried out without any polymer in the suspension.

[0145] After preparing a sample of the suspension, settling takes place gradually over time due to the phenomenon of flocculation of the solid particles comprised in the aqueous copper ore residue. These particles agglomerate to form heavier particle clusters. These clusters then settle faster. The aqueous supernatant phase is on the surface and the settled phase is at the bottom of the test tube.

[0146] At 25° C. and using a Brookfield DV3T viscometer with a suitable bladed module, the flow thresholds are measured on samples of the aqueous suspension of copper ore residue at 30% by weight of solids content.

[0147] The flow threshold (Pa) of the suspension is measured after it has been subjected to a very low shear rate (approximately 1 to 10 s.sup.−1) (UN-YS). This corresponds to the flow threshold of the aqueous suspension of copper ore residue at the bottom of a thickener.

[0148] The flow threshold (Pa) of the suspension is also measured after it has been subjected to a very high shear rate (approximately 100 to 1,000 s.sup.−1) (FS-YS).

[0149] This corresponds to the flow threshold of the aqueous suspension of copper ore residue at the outlet of a thickener.

[0150] The settling speed is also measured using the scale on the test tube and a stopwatch. This measure is performed by observing the separation of the supernatant water phase and settling phase. It is measured in cm/minute and then converted to meter/hour (m/h).

[0151] The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Suspension UN-YS FS-YS Settling speed % Solids content Without additive 400 41 7.6 64.6 With polymer (P1) 218 15 7.1 63.7

[0152] Moreover, a test is carried out using semi-industrial equipment. The settler is cylindrical with a clear wall.

[0153] It has a capacity of 30 L and is stirred by means of a low-power motor supplying a stirring speed of 1 rpm. The suspension of aqueous copper ore residue used has a solids content of 69% by weight dry/dry.

[0154] A fixed dose of an acrylamide flocculating agent is incorporated at a dose equivalent to 12 g/T dry/dry of residue.

[0155] The suspension is prepared in a similar manner to the previous preparation, at a solids content of 30% by weight dry/dry. The polymer dose remains the same. It is 0.05% by weight dry/dry. The polymer (P1) is introduced into the top of the thickener parallel to the feed shaft. The feed shaft is the area through which the aqueous ore residue is fed and the flocculant introduced.

[0156] The instrument used for the concentration of aqueous residue in the presence of a polymer according to the invention is a Plexiglass pilot thickener with a low-intensity stirrer that generates a stirring speed of 1 rpm. The flow threshold (Pa) of the suspension is measured after it has been subjected to a mean shear rate (approximately 10 to 100 s.sup.−1) (MS-YS). This corresponds to the flow threshold at the conveying pump that sends the aqueous copper ore residue to the storage units.

[0157] The flow threshold (Pa) of the suspension is also measured after it has been subjected to a very high shear rate (approximately 1,000 to 10,000 s.sup.−1) (HFS-YS). This corresponds to the flow threshold in the pipe located after the conveying pump at the outlet of a thickener and that conveys the aqueous copper ore residue to the storage units. The results are shown in Table 2.

[0158] The settling speed is also measured using the scale on the test tube and a stopwatch. This measure is performed by observing the separation of the supernatant water phase and settling phase. It is measured in cm/minute and then converted to meter/hour (m/h). It is comprised between 7 and 8 m/h.

TABLE-US-00002 TABLE 2 Suspension MS-YS HFS-YS % Solids content Without additive 175 50 69 With polymer (P1 )  60 20 69

[0159] It can be seen that with the use of a polymer according to the invention, increasing the solids content of the aqueous suspension of copper ore residue at a thickener output does not result in a viscosity drift in the suspension.

[0160] This more consistent suspension can still be stirred using conventional equipment and is easier to handle, thus helping to prevent the risk of clogging the stirrers.

[0161] In addition, its improved solids content makes it possible to reduce water consumption relative to the amount of copper ore residue processed.

[0162] These tests also show that the presence of the polymer (P1) according to the invention significantly improves the flow threshold values of the aqueous suspensions of copper ore residue without disrupting the settling speed inside the concentration device.

[0163] Controlling the rheology at the outlet of a thickener makes it easier to discharge and convey this aqueous suspension to storage pools.