Lime treatment
Methods of obtaining a solution of calcium ions from lime (e.g. carbide lime) are disclosed. In one aspect the method comprises (i) treating the lime with an aqueous solution of a polyhydroxy compound (preferably sorbitol) having three or more hydroxy groups and a straight chain of 3 to 8 carbon atoms; and (ii) optionally separating insoluble impurities from the solution resulting from (i). In another aspect the method comprises (iii) treating carbide lime with an aqueous solution of a polyhydroxy compound (e.g. sorbitol or sucrose) to extract calcium from the carbide lime; and (iv) separating insoluble impurities from the solution resulting from (i). The solutions obtained may be treated with precipitating agent to obtain a solid calcium containing product. The product may be calcium carbonate obtained by treating the solution with carbon dioxide as the precipitating agent.
1. A method of obtaining precipitated calcium carbonate from carbide lime, comprising the steps of:
(a) dissolving carbide lime in an aqueous solution comprising 10% to 80% of a polyhydroxy compound of the formula: HOCH 2 (CHOH) n CH2OH; where n is 2 to 6;
(b) removing insoluble impurities from the solution resulting from (a); and
(c) contacting the purified solution resulting from (b) with CO 2 to precipitate calcium carbonate from the purified solution while allowing the solution to achieve a temperature in excess of 25° C.
2. A method according to claim 1 wherein said polyhydroxy compound comprises one or more members selected from the group consisting of sorbitol, xylitol, threitol, and mannitol.
3. A method according to claim 1 wherein said polyhydroxy compound comprises sorbitol.
4. A method according to claim 1 wherein the polyhydroxy compound is employed as a 10% to 60% by weight solution.
5. A method according to claim 1 wherein the amount of carbide lime is such as to provide 3-12 parts by weight per 10 to 80% by weight of the polyhydroxy compound.
6. The method of claim 1 wherein said polyhydroxy compound is a polyhydroxy sugar alcohol.
7. The method of claim 1 wherein said polyhydroxy compound is a polyhydroxy compound of the formula: HOCH 2 (CHOH) n CH2OH; where n is 4.
8. A method of obtaining precipitated calcium carbonate from lime, comprising the steps of:
(a) dissolving a lime-containing material in an aqueous solution comprising 10% to 80% of one or more polyhydroxy compounds of the formula: HOCH 2 (CHOH) n CH2OH; where n is 2 to 6;
(b) removing insoluble impurities from the solution resulting from (a); and
(c) contacting the purified solution resulting from (b) with CO 2 to precipitate calcium carbonate from the purified solution while allowing the solution to achieve a temperature in excess of 25° C.
9. The method according to claim 8 wherein the lime is a product of the calcining of limestone or dolomite.
10. A method according to claim 8 wherein said polyhydroxy compound comprises one or more members selected from the group consisting of sorbitol, xylitol, threitol, and mannitol.
11. A method according to claim 8 wherein said polyhydroxy compound comprises sorbitol.
12. A method according to claim 8 wherein said polyhydroxy compound comprises about 80% sorbitol.
13. A method according to claim 8 wherein said polyhydroxy compound is sorbitol.
14. A method according to claim 8 wherein the polyhydroxy compound is employed as a 10% to 60% by weight solution.
15. A method according to claim 14 wherein the polyhydroxy compound is employed as a 15% to 40% by weight solution.
16. A method according to claim 8 wherein the amount of carbide lime is such as to provide 3-12 parts by weight per 10 to 80% by weight of the polyhydroxy compound.