CONTROLLING THE RHEOLOGY OF A METAL ORE RESIDUE

Abstract

The invention concerns a method for preparing an aqueous mineral suspension from an aqueous metal ore residue into which a polymer (P) is introduced having a molecular mass Mw measured by GPC ranging from 2,000 to 20,000 g/mol and prepared by radical polymerisation of at least one anionic monomer (M). The invention also concerns the suspension produced, the Brookfield viscosity of which is lower than 1,800 mPa.Math.s or the yield point of which is lower than 80 Pa.

Claims

1. A method for preparing an aqueous mineral suspension, the method comprising: adding, in an aqueous metal ore residue, at least one polymer (P), wherein the aqueous mineral suspension has a dry solid content greater than 40% by weight of the aqueous mineral suspension and the aqueous mineral suspension has at least one property selected from the group consisting of: a Brookfield viscosity, measured at 100 rpm and at 25° C., of less than 1,800 mPa.Math.s, 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 and 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, and wherein the at least one polymer (P) has a molecular mass Mw, measured by GPC, ranging from 2,000 to 20,000 g/mol and the at least one polymer (P) is 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 at least one ion selected from the group consisting of Fe.sup.II, Fe.sup.III, Cu.sup.I, and Cu.sup.II.

2. The method according to claim 1, wherein the aqueous mineral suspension has a viscosity of less than 1,500 mPa.Math.s.

3. The method according to claim 1, in which the aqueous mineral suspension has: a flow threshold of less than 70 Pa; a flow threshold greater than 10 Pa and less than 80 Pa; a flow threshold greater than 10 Pa and less than 70 Pa.

4. The method according to claim 1, wherein the aqueous mineral suspension has a dry solids content greater than 50% by weight.

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

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

7. The method according to claim 1, wherein: a metal ore of the aqueous metal ore residue 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, or the aqueous metal ore residue comprises a residual amount of a metal of less than 2,000 g per tonne (dry/dry) relative to an amount of the aqueous metal ore residue.

8. The method according to claim 1, wherein the at least one polymer (P) is added: before pumping the aqueous metal ore residue; during pumping the aqueous metal ore residue; after pumping the aqueous metal ore residue; before flocculation of the aqueous metal ore residue; during flocculation of the aqueous metal ore residue; after flocculation of the aqueous metal ore residue; before concentration of the aqueous metal ore residue; during concentration of the aqueous metal ore residue; after concentration of the aqueous metal ore residue; before conveying the aqueous metal ore residue; before storing the aqueous metal ore residue, or during storing the aqueous metal ore residue.

9. The method according to claim 1, wherein: the polymerisation reaction is also carried out in the presence of at least one compound comprising phosphorus in the oxidation 1 state; 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 at least one compound comprising a bisulphite ion; the polymerisation reaction is also carried out in the presence of from 0.05 to 5% by weight, relative to a 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; 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; or the polymer (P) is completely or partially neutralised or the polymerisation reaction uses: 100% by weight of the at least one anionic monomer (M) or from 70% to 99.5% by weight of the at least one anionic monomer (M) and from 0.5% to 30% by weight of at least one other monomer.

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

11. 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), (CH.sub.2CH(CH.sub.3)O).sub.y, (CH(CH.sub.3)CH.sub.2O), 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 a sum of x+y+z is comprised in a range from 10 to 150.

12. An aqueous mineral suspension with a dry solids content that is greater than 50% by weight of the aqueous mineral suspension and having at least one property chosen among: a Brookfield viscosity, measured at 100 rpm and at 25° C., of less than 1,800 mPa.Math.s, 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 and 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, wherein the aqueous mineral suspension comprises an aqueous metal ore residue and a polymer (P) with a molecular mass Mw, measured by GPC, ranging from 2,000 to 20,000 g/mol and prepared by 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 chosen among Fe.sup.II, Fe.sup.III, Cu.sup.I, Cu.sup.II and mixtures thereof.

Description

EXAMPLES

[0127] The following examples illustrate the various aspects of the invention.

[0128] The polymers used in the method according to the invention are prepared.

[0129] Polymer (P1) is prepared by placing 156 g of water and 0.013 g of iron sulphate heptahydrate into a one-litre glass reactor with mechanical stirring and oil bath heating.

[0130] Using a dosing pump, 271 g of acrylic acid at 100% by weight are weighed into a 500 mL beaker.

[0131] Using a dosing pump, 3.3 g of persulphate diluted with 15 g of water are weighed into a 20 mL test tube.

[0132] Using a dosing pump, 115 g of sodium bisulphite at 40% by weight are weighed into a 200 mL test tube.

[0133] The reactor is heated to 80° C.

[0134] 30% of the persulphate solution is injected rapidly and then the remainder of this solution, the acrylic acid and the bisulphite solution are injected in parallel in: [0135] 3 h for the acrylic acid and [0136] 3.5 h for the persulphate and the bisulphite.

[0137] The reaction medium is kept at 80° C.

[0138] The medium is then heat-treated for 30 minutes with a solution of 0.3 g of persulphate in 4 g of water and then 4.5 g of hydrogen peroxide at 130 V.

[0139] Lastly, the pumps are rinsed with water.

[0140] The medium is heated again for 60 min at 80° C.

[0141] 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 2,500 g/mol.

[0142] Polymer (P2) is prepared by placing 212 g of water and 0.08 g of iron sulphate heptahydrate into a one-litre glass reactor with mechanical stirring and oil bath heating.

[0143] Using a dosing pump, 303 g of acrylic acid at 100% by weight and 15 g of water are weighed into a 500 mL beaker.

[0144] Using a dosing pump, 25.6 g of sodium hypophosphite monohydrate diluted with 30 g of water are weighed into a 100 mL test tube.

[0145] Using a dosing pump, 21 g of hydrogen peroxide at 130 V and 35 g of water are weighed into a 100 mL test tube.

[0146] 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.

[0147] Lastly, the pumps are rinsed with water.

[0148] The medium is heated again for 60 min at 95° C.

[0149] 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 (P2) is obtained, with a molecular mass, measured by GPC, of 4,500 g/mol.

[0150] 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. This aqueous copper ore residue is in the form of a water-based suspension.

[0151] Various measures were taken beforehand on the aqueous residue in the absence of the polymer according to the invention: [0152] particle size distribution using a Mastersizer 2000 laser granulometer (Malvern), [0153] solid content using a Mettler-Toledo dry balance, [0154] Brookfield viscosity at 100 rpm using a Brookfield DV3T viscometer with a suitable spindle, [0155] flow limit value using a Brookfield DV3T viscometer using a winged module and [0156] flow speed using a No. 4 Ford Cup viscometer.

[0157] The particle size distribution by volume shows the presence of multiple particle populations with different sizes: D(0.1)=1.6 μm, D(0.5)=25 μm, D(0.84)=195 μm, D(0.9)=252 μm, and D(0.99)=501 μm.

[0158] The other characteristics are shown in Table 1.

TABLE-US-00001 TABLE 1 % Solids content 55.8 Brookfield viscosity at 100 rpm, in mPa .Math. s 1,220 pH 10.0 Conductivity in μS/cm 2,700 Viscosity, No. 4 Ford cup, in s 25

[0159] A concentration of the aqueous residue is then prepared by decanting and separating a portion of the supernatant water to form an aqueous residue whose characteristics are shown in Table 2.

TABLE-US-00002 TABLE 2 % Solids content 60.5 Brookfield viscosity at 100 rpm, in mPa .Math. s 3,016 pH 10.1 Conductivity in μS/cm 2,320 Viscosity, No. 4 Ford cup, in s /

[0160] A sample of suspension of aqueous residue of reconcentrated copper ore is transferred into a 500 mL beaker and then mechanically stirred with a Raynerie mixer. Stirring varies from 800 to 1,000 rpm.

[0161] Then, a polymer (P1) according to the invention is added (0.1% by weight dry/dry) and the mixture is left under stirring for 5 to 10 min.

[0162] Stirring is then stopped to allow the Brookfield viscosities, pH and conductivity measures to be taken. The test is repeated, adding different amounts of polymer. The results are shown in Table 3.

TABLE-US-00003 TABLE 3 Polymer (P1) % by weight dry/dry of Brookfield viscosity at Conductivity polymer 100 rpm (mPa .Math. s) pH (μS/cm) 0 3,032 9.9 2,410 0.07 1,374 9.9 2,580 0.09 1,186 9.9 2,560 0.1 1,070 9.9 2,590

[0163] A dose of 0.1% by weight dry/dry of polymer (P1) makes it possible to significantly reduce the viscosity of the aqueous residue. The aqueous suspension of copper ore residue can then be handled easily.

[0164] Another test is conducted without any polymer and with two polymers (P1) and (P2) according to the invention at this dose of 0.1% by weight dry/dry. The results are shown in Table 4.

TABLE-US-00004 TABLE 4 Residue without with polymer with polymer additive (P1) (P2) % by weight dry/dry 0 0.1 0.1 pH 10.1 9.9 9.3 Conductivity in 2,320 2,590 2,940 % Solids content 60.5 60.9 60.5 Brookfield viscosity at 3,016 1,070 1,188 100 rpm (mPa .Math. s)

[0165] A dose of 0.1% by weight dry/dry of polymer (P1) or of polymer (P2) thus also makes it possible to significantly reduce the viscosity of the aqueous residue.

[0166] The flow threshold of this aqueous copper ore residue with a solids content of 61% was then measured at a temperature of 25° C. using a Brookfield DV3T rheometer with imposed shearing, equipped with a spindle with suitable blades. Without destroying the underlying structure, the bladed spindle is immersed into the material up to the first immersion mark.

[0167] After a five-minute wait time, the measure is taken without pre-shearing at a speed of 0.5 rpm. This relatively low speed is preferred so as to minimise the inertia effect of the bladed spindle. The variation in torsional loading measured by the instrument in order to maintain a spin speed of 0.5 rpm is tracked over time.

[0168] The value of the flow limit or flow threshold of the aqueous residue is indicated by the instrument when this variation is zero. The results obtained are shown in Table 5.

TABLE-US-00005 TABLE 5 Residue Flow Threshold (Pa) Time without with polymer with polymer (min) additive (P1) (P2) 0 55 32 26 2 60 48 37 4 58 46 36 6 55 42 33 8 / 38 31 10 / 33 30 12 54 31 27 14 / 29 28 16 / / / 18 / / / 20 50 28 28

[0169] Aqueous suspensions of aqueous copper ore residue with a solids content of 58%, with or without polymers (P1) and (P2), are then prepared according to the invention. The characteristics of these suspensions are measured. The results obtained are shown in Table 6.

TABLE-US-00006 TABLE 6 Residue without with polymer with polymer additive (P1) (P2) % by weight dry/dry 0 0.1 0.1 pH 9.8 10.0 10.0 Conductivity in 2,160 2,770 2,820 Brookfield viscosity at 2,196 838 824 100 rpm (mPa .Math. s)

[0170] It can thus be seen that aqueous suspensions of reference copper residue with a solids content of 55%, 61% or 58% have high viscosities.

[0171] The addition of polymer (P1) or of polymer (P2) according to the invention makes it possible to significantly lower these viscosities as well as to control the flow threshold of these suspensions.

[0172] With the polymers according to the invention, it is therefore possible to disperse aqueous copper ore residues, in particular at the output of a thickener, which have high solids contents while controlling their rheology.