Method for producing aqueous suspensions of mineral fillers, the thus obtained aqueous suspensions of mineral fillers and the use thereof
The invention concerns a process for the preparation of aqueous suspensions of fluid mineral matter, which are able to be pumped and conveyed by the end user immediately after the filtration stage, possibly followed by a compression, which process comprises filtration in two separate stages. The invention also concerns aqueous suspensions of mineral matter obtained and their uses.
1. A process for the preparation of a concentrated cake comprising performing two separate stages of filtration, wherein in the first filtration stage, a pre-layer of mineral matter is formed on a filtration membrane in the absence of a dispersant agent, and in the second filtration stage, which is operated continuous to the first filtration stage, the pre-layer of mineral matter from the first filtration stage is treated on the filtration membrane with a second aqueous suspension containing a dispersant agent to obtain a filtrate and a concentrated cake, wherein the quantity of the dispersant agent in the filtrate is controlled and limited by a continuous measurement of the electrical conductivity of the filtrate, and wherein the second filtration stage is stopped as soon as the electrical conductivity of the filtrate increases.
2. The process of claim 1 , wherein the second aqueous suspension contains mineral matter and the dispersant agent.
3. The process of claim 1 , wherein the second aqueous suspension contains the dispersant agent but not mineral matter.
4. The process of claim 1 , wherein the dispersant agent used in the second filtration stage is present between 0.01% and 10% by dry weight of dispersant relative to the dry weight of mineral matter filtered.
5. The process of claim 1 , wherein the dispersant agent used in the second filtration stage is present between 0.1% and 2% by dry weight of dispersant relative to the dry weight of mineral matter filtered.
6. The process of claim 1 , wherein the electrical conductivity is measured using an HI 8820N conductivity meter from Hanna Instruments (Portugal).
7. The process of claim 1 , wherein the dispersant agent is sodium polyacrylate.
8. The process of claim 1 , wherein the concentrated cake is subjected to compression.
9. The process of claim 1 , wherein the concentrated cake is subjected to shearing.
10. The process of claim 1 , wherein the mineral matter is natural calcium carbonate, chalk, calcite, marble, synthetic calcium carbonate, precipitated calcium carbonate, mixed carbonates of magnesium and calcium, dolomite, magnesium carbonate, zinc carbonate, lime, magnesia, barium sulphate, barita, calcium sulphate, silica, magnesio-silicate, talc, wollastonite, clay, alumino-silicate, kaolin, mica, metal or alkaline-earth oxides or hydroxides, magnesium hydroxide, iron oxide, zinc oxide, titanium oxide, titanium dioxide, or any mixtures thereof.
11. The process of claim 1 , wherein the mineral matter is natural calcium carbonate, precipitated calcium carbonate, titanium dioxide, kaolin, aluminium hydroxide, clay or any mixtures thereof.
12. The process of claim 1 , wherein the mineral matter is natural calcium carbonate.
13. The process of claim 1 , wherein the mineral matter is precipitated calcium carbonate.
14. The process of claim 1 , wherein the mineral matter is titanium dioxide.
15. The process of claim 14 , wherein the titanium dioxide is in its anatase or rutile form.
16. The process of claim 1 , wherein the mineral matter is kaolin.
17. The process of claim 1 , wherein the mineral matter is aluminium hydroxide.
18. The process of claim 1 , wherein the mineral matter is clay.
19. The process of claim 1 , wherein an aqueous suspension of mineral matter is obtained from the concentrated cake.
20. The process of claim 19 , wherein the aqueous suspension of mineral matter is obtained from shearing the concentrated cake.
21. The process of claim 1 , wherein the filtrate obtained from the second filtration stage contains a near-zero quantity of dispersant.