PARTICLE SIZE CONTROL METHOD

Abstract

The invention relates to a method for grinding phosphate rock in the presence of a particular anionic polymer having a molecular weight of between 1000 and 90000 g/mol, which makes it possible to control the extent (S) of the volume distribution of the particle size of obtained phosphate mineral particles. The invention also relates to a method for improving the production yield of a phosphate rock grinding method.

Claims

1. A method for preparing an aqueous suspension of phosphate mineral particles, comprising: grinding a of at least one phosphate material in the presence of water and an anionic polymer (P) with a molecular mass by weight (M.sub.W) between 1,000 and 90,000 g/mol, wherein the anionic polymer (P) is obtained by polymerisation reaction of at least one acid selected from the group consisting of acrylic acid, methacrylic acid and salts thereof, wherein a span (S) of a volume distribution of particle sizes [(d.sub.0.9−d.sub.0.1)/d.sub.0.5] measured by laser diffraction is less than 4.1.

2. The method according to claim 1, wherein the span (S) is less than 4.0.

3. The method according to claim 1 further comprising separating a fraction of particles of the phosphate material whose size d.sub.0.1 is less than 4 μm.

4. The method according to claim 3, wherein the separation is carried out in a liquid-cyclone, centrifuge or a combination thereof.

5. The method according to claim 3, wherein a concentration by weight of the phosphate mineral particles of the aqueous suspension during the grinding is greater than 10%.

6. The method according to claim 5, wherein the particles of the phosphate material have a size d.sub.0.9 before the grinding that is greater than 800 μm.

7. The method according to claim 6, wherein the particles of the phosphate material have a size d.sub.0.5 after the grinding that is less than 300 μm.

8. The method according to claim 1, wherein a grinding time is less than 5 hrs and 30 min.

9. The method according to claim 1, wherein a grinding time is reduced by at least 10% relative to a grinding time in an absence of the anionic polymer (P).

10. The method according to claim 1, wherein the anionic polymer (P) is partially or completely neutralised.

11. The method according to claim 1, wherein the anionic polymer (P) is obtained by a polymerisation reaction with at least one acid selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, itaconic acid and salts thereof or at least one ester of an acid chosen among acrylic acid and methacrylic acid.

12. The method according to claim 1, wherein the anionic polymer (P) has a molecular mass by weight (M.sub.W) between 2,000 and 90,000 g/mol.

13. The method according to claim 1, wherein an amount by weight (dry/dry) of the anionic polymer (P) is between 0.07 and 2% relative to an amount of the phosphate material.

14. An aqueous suspension of mineral particles of a phosphate material, comprising: at least one anionic polymer (P) with a molecular mass by weight (M.sub.W) between 1,000 and 90,000 g/mol, wherein the anionic polymer (P) is obtained by polymerisation reaction of at least one acid selected from the group consisting of acrylic acid, methacrylic acid and salts thereof, wherein a span (S) of a volume distribution of particle sizes [(d.sub.0.9−d.sub.0.1)/d.sub.0.5] measured by laser diffraction is less than 4.1.

15. A suspension obtained by the method of claim 1.

16.-19. (canceled)

20. The method according to claim 11, wherein the anionic polymer (P) is partially or completely neutralised by at least one derivative selected from the group consisting of lithium, sodium, calcium, magnesium and mixtures thereof.

Description

[0052] The following examples illustrate the various aspects of the invention.

[0053] An aqueous suspension of phosphate material is prepared by grinding a phosphate rock in the presence of a polymer (P1) or a polymer (P2) defined according to the invention.

[0054] Different polymers were prepared and then used in the preparation of phosphate rock slurries by grinding.

[0055] Preparation of the polymer (P1):

[0056] The following are introduced into a synthesis reactor equipped with a mechanical stirring system and an oil bath heating system:

[0057] water: 241.069 g,

[0058] copper sulphate pentahydrate: 0.323 g,

[0059] ferrous sulphate heptahydrate: 0.276 g.

[0060] The medium is heated to 95° C., then the following are added simultaneously and continuously, over 2 hours:

[0061] an aqueous solution of 3.5 g of DPTTC sodium salt (CAS # 86470-33-2) at 20.9% by weight, diluted in 31 g of water,

[0062] 35.3 g of hydrogen peroxide 130 V diluted in 9.4 g of water and

[0063] 279.9 g of acrylic acid diluted in 31 g of water.

[0064] Cooking continues for 1.5 hours at 95° C.

[0065] A polyacrylic acid solution with an Mw of 5,700 g/mol and an Ip of 2.5 is obtained (measured by SEC).

[0066] The polyacrylic acid solution is treated with:

[0067] sodium hydroxide 50% by weight in water: 145 g,

[0068] water: 66.660 g,

[0069] hydrated lime 97% by weight in water: 42.5 g.

[0070] Lastly, the pH of the resulting polymer (P1) is adjusted to 8.7 with sodium hydroxide and to a final concentration of 35% of dry solids content in water.

[0071] Preparation of the polymer (P2):

[0072] The following are introduced into a synthesis reactor equipped with a mechanical stirring system and an oil bath heating system:

[0073] water: 241.069 g,

[0074] copper sulphate pentahydrate: 0.323 g,

[0075] ferrous sulphate heptahydrate: 0.276 g.

[0076] The medium is heated to 95° C., then the following are added simultaneously and continuously, over 2 hours:

[0077] an aqueous solution of 3.5 g of DPTTC sodium salt (CAS # 86470-33-2) at 20.9% by weight, diluted in 31 g of water,

[0078] 35.3 g of hydrogen peroxide 130 V diluted in 9.4 g of water and

[0079] 279.9 g of acrylic acid diluted in 31 g of water.

[0080] Cooking continues for 1.5 hours at 95° C.

[0081] A polyacrylic acid solution with an Mw of 5,700 g/mol and an Ip of 2.5 is obtained (measured by SEC).

[0082] The polyacrylic acid solution is treated with an aqueous solution of sodium hydroxide at 50% by weight in water to achieve a pH value of 8.5.

[0083] Lastly, the pH of the resulting polymer (P2) is adjusted to 8.5 with sodium hydroxide and to a final concentration of 42% of dry solids content in water.

[0084] Preparation of the polymer (P3):

[0085] The following are introduced into a synthesis reactor equipped with a mechanical stirring system and an oil bath heating system:

[0086] water: 190 g,

[0087] maleic anhydride: 107.1 g,

[0088] ferrous sulphate heptahydrate: 0.0065 g,

[0089] sodium hydroxide 50% by weight in water: 169 g.

[0090] The medium is heated to 95° C., then the following are added simultaneously and continuously, over 2 hours:

[0091] 16 g of hydrogen peroxide 130 V,

[0092] 2.93 g of sodium persulphate diluted in 33 g of water and

[0093] 131 g of acrylic acid diluted in 37 g of water.

[0094] Cooking continues for 1.5 hours at 95° C.

[0095] A copolymer solution of acrylic acid and of partially-neutralised maleic acid is obtained.

[0096] The polymeric acid solution is treated with an aqueous solution of sodium hydroxide at 50% by weight in water to achieve a pH value of 8.2.

[0097] The solution is then brought to a final concentration of 35% of dry solids content in water.

[0098] The molecular mass by weight of the polymer thus obtained is about 18,000 g/mol with a polymolecularity index of 3.2.

[0099] Preparation of suspensions according to the invention:

[0100] Phosphate rock from a mine in China (Guizhou Province) was sieved to separate particles larger than 2.5 mm in size and to separate particles smaller than 40 μm in size.

[0101] The sieved rock was then quartered to prepare representative samples with an average mass equal to 320 g±4% that are identical in terms of particle size distribution.

[0102] A representative sample is a sample taken in a probabilistic manner such that all of the elements of the batch have an equal probability of being selected for the sample.

[0103] The sample collection does not alter the property to be estimated. The conditions are listed in Table 1.

TABLE-US-00001 TABLE 1 Test A Test B Solids content (% by weight) 20 40 Number of beads and cylinders (g) 2,823 2,823 Amount of water (g) 1,280 960 Amount of dry phosphate rock (g) 320 640 Amount of polymer (P) (% by dry/ 0.1 0.2 dry weight)

[0104] The samples are ground separately using a ball mill at a solids content of 20% or 40% by weight in a 4 L jar containing ceramic beads 19 mm in diameter (0.850 L, 1,858 g) and 15×15 mm ceramic cylinders (0.450 L, 965 g) according to the data shown in Table 1.

[0105] Aqueous suspensions of phosphate rock are prepared by grinding under test conditions A and in the presence of polymers (P1), (P2) and (P3) respectively, in an amount of 0.1% by dry/dry weight, relative to the amount of rock. The grinding time is set at 2 hours and 20 minutes.

[0106] The particle size of the samples is measured with a laser granulometer (Malvern Mastersizer 2000) and processed with Mastersizer 2000 software version 5.61 (refractive index 1.51, pump speed: 1,250 rpm, mixer speed: 750 rpm, ultrasound stirring at 50% of the power throughout the measurement). Seven measurements, spaced 10 s apart, are taken per aliquot. Three wash cycles are run between each series of three measurements.

[0107] For each suspension, seven repeat measurements are taken, the particle size is measured, and the results of the average particle size measurements are shown in Table 2.

TABLE-US-00002 TABLE 2 Particle size (μm) Polymer d.sub.0.1 d.sub.0.5 d.sub.0.9 Span (S) P1 4.085 198.371 388.446 1.938 P2 6.073 233.306 876.110 3.732 P3 4.934 278.785 1,026.326 3.664

[0108] The use of polymers (P1), (P2) and (P3) enables excellent control of the particle size of the prepared suspensions as well as achieving a span (S) of much less than 4.1.

[0109] Other aqueous suspensions of phosphate rock are prepared by grinding under test conditions A in the absence of polymer and in the presence of polymer (P1) in an amount of 0.1% by dry/dry weight relative to the amount of rock. The target particle size day is less than 200 μm (198 μm±1.5%).

[0110] For each suspension, seven repeat measurements are taken, the particle size is measured, and the results of the average particle size measurements are shown in Table 3.

[0111] The time required to achieve the target particle size is assessed. The results are shown in Table 3.

TABLE-US-00003 TABLE 3 Grinding Particle size (μm) Polymer time d.sub.0.1 d.sub.0.5 d.sub.0.9 Span (S) None 4 hrs 4.368 200.588 836.604 4.149 P1 2 hrs 20 min 4.085 198.371 388.446 1.938

[0112] The use of polymer (P1) makes it possible to achieve a much smaller span (S) relative to the preparation of a suspension in the absence of polymer. Moreover, the time required to achieve this result is reduced by more than 40%. Other aqueous suspensions of phosphate rock are prepared by grinding under test conditions B in the absence of polymer and in the presence of polymer (P1) in an amount of 0.2% by dry/dry weight relative to the amount of rock. The target particle size d.sub.0.5 is less than 200 μm (198 μm ±1.5%).

[0113] For each suspension, seven repeat measurements are taken, the particle size is measured, and the results of the average particle size measurements are shown in Table 4.

[0114] The time required to achieve the target particle size is assessed. The results are shown in Table 4.

TABLE-US-00004 TABLE 4 Grinding Particle size (μm) Polymer time d.sub.0.1 d.sub.0.5 d.sub.0.9 Span (S) None 6 hrs 3.419 199.069 895.315 4.480 P1 4 hrs 3.759 195.711 762.673 3.877

[0115] For highly concentrated suspensions, the use of polymer (P1) makes it possible to achieve a much smaller span (S) relative to the preparation of a suspension in the absence of polymer. Moreover, the time required to achieve this result is reduced by more than 30%.

[0116] Table 5 presents the comparison of these different results.

TABLE-US-00005 TABLE 5 Grinding % Solids Particle size (μm) Polymer time content d.sub.0.1 d.sub.0.5 d.sub.0.9 Span (S) None 4 hrs 20 4.368 200.588 836.604 4.149 P1 (0.1%) 2 hrs 20 min 20 4.085 198.371 388.446 1.938 None 6 hrs 40 3.419 199.069 895.315 4.480 P1 (0.2%) 4 hrs 40 3.759 195.711 762.673 3.877

[0117] The method according to the invention makes it possible to prepare an aqueous suspension of phosphate material according to the invention that is particularly effective in achieving the target particle size distribution values and controlling the span (S) for different solids contents during grinding. The span (S) and the grinding times are particularly reduced through the use of polymers (P).