Process for manufacturing high solids suspensions of mineral materials
The present invention relates to a process for manufacturing high solids aqueous suspensions of mineral materials comprising the steps of providing at least one mineral material, preparing an aqueous suspension comprising the at least one mineral material, grinding the resulting aqueous suspension, centrifuging the ground aqueous suspension, and concentrating the centrifuged product of step d) by flash cooling; the high solids aqueous suspension of mineral materials obtained by this process, as well as the use thereof.
1. A process for manufacturing a high solids aqueous suspension of mineral material, the process comprising the steps of:
a) providing at least one mineral material,
b) preparing an aqueous suspension comprising the at least one mineral material of step a),
c) grinding the aqueous suspension of the mineral material of step b),
d) concentrating the aqueous suspension of ground mineral material of step c) by flash cooling in a flash cooler comprising an inlet and an outlet, wherein the temperature of the aqueous suspension at the inlet of the flash cooler is from 70 to 105° C., and the temperature of the aqueous suspension at the outlet of the flash cooler is less than 60 to 30° C., to obtain an aqueous suspension having a final solids content of 80 to 85 wt %,
wherein at least one dispersing agent is added to the aqueous suspension of step b), wherein the at least one dispersing agent is added completely before grinding step c), or stepwise before and during grinding step c), or before and during and/or after grinding step c), and
wherein the at least one dispersing agent is a homopolymer or copolymer of a polycarboxylic acid, acrylic acid, methacrylic acid or maleic acid, a partially or completely neutralized acid salt thereof that is neutralized with sodium, lithium, potassium, ammonium, calcium, magnesium, strontium, aluminium or any mixture thereof, a derivative of a polycarboxylic acid, an ester based on acrylic acid, methacrylic acid, maleic acid, fumaric acid, or itaconic, an acryl amide or acrylic ester, a methylmethacrylate, or any mixture thereof, an alkali polyphosphate, or any mixture thereof.
2. The process according to claim 1 , wherein the at least one mineral material is natural calcium carbonate (GCC), marble, chalk, limestone, precipitated calcium carbonate (PCC), aragonitic PCC, vateritic PCC and/or calcitic PCC, prismatic PCC, rhombohedral PCC, scalenohedral PCC, surface modified calcium carbonate; dolomite, talc, bentonite, clay, magnesite, satin white, sepiolite, huntite, diatomite, a silicate, or any mixture thereof.
3. The process according claim 1 , wherein from 40 to 85 wt % of the at least one mineral material in step a) has particles having an equivalent spherical diameter of <10 μm.
4. The process according to claim 1 , wherein the aqueous suspension, before step d), has a solids content of from above 70 to 80 wt %, based on the total weight of the suspension.
5. The process according to claim 1 , wherein the total amount of the at least one dispersing agent added before grinding step c), or before and during step c), or before and during and/or after grinding step c), is from about 0.01 to 1.25 wt %, based on the dry weight of the mineral material.
6. The process according to claim 1 , wherein the molecular weight Mw of the at least one dispersing agent is in the range of from 1000 to 15000 g/mol.
7. The process according to claim 1 , wherein before, during, or after step c), but before step d), at least one earth alkali oxide and/or hydroxide is added to the aqueous suspension of step b).
8. The process according to claim 7 , wherein the earth alkali oxide and/or hydroxide is added in an amount of from about 0.001 to 0.1 wt %, based on the dry weight of the mineral material.
9. The process according to claim 1 , wherein before, during, or after step c), but before step d), lime and/or burnt dolomite is added to the aqueous suspension of step b).
10. The process according to claim 1 , wherein step c) is carried out several times.
11. The process according to claim 1 , wherein from 20 to 70 wt % of the at least one mineral material has particles having a particle size of <2 μm after step c).
12. The process according to claim 1 , wherein from 10 to 90 wt % of the at least one mineral material has particles having a particle size of <1 μm after step c).
13. The process according to claim 1 , wherein after grinding step c), the aqueous suspension of ground mineral material is subjected to a separation step.
14. The process according to claim 1 , wherein after grinding step c), the aqueous suspension of ground mineral material is subjected to screening, filtration, or centrifugation.
15. The process according to claim 1 , wherein in step d), the aqueous suspension is exposed to reduced pressure.
16. The process according to claim 1 , wherein in step d), the aqueous suspension is exposed to a pressure of from 200 to 500 mbar.
17. The process according to claim 1 , wherein the final solids content of the aqueous suspension obtained in step d) is from 80 to 84 wt %.
18. The process according to claim 1 , wherein the final solids content of the aqueous suspension obtained in step d) is at least 1 wt % higher than the initial solids content of the aqueous suspension obtained in step b).
19. The process according to claim 1 , wherein the final aqueous suspension after step d) has a Brookfield viscosity of from 50 to 1000 mPa·s.