Claims
- 1. A process for the preparation of sodium dichromate and sodium dichromate solutions comprising:
- (1) alkaline oxidizing roasting chromium ores to yield a roast;
- (2) leaching the roast with water to yield a mash;
- (3) adjusting the pH of the mash to 7 to 9.5;
- (4) filtering the mash to remove insoluble constituents to yield a sodium monochromate solution;
- (5) converting the monochromate ions in the sodium monochromate solution into dichromate ions to yield a sodium dichromate solution by a process consisting of the following steps (5a)-(5e):
- (5a) concentrating the sodium monochromate solution from an initial concentration of 300 to 500 g/l of Na.sub.2 CrO.sub.4 to a final concentration of 700 to 1000 g/l of Na.sub.2 CrO.sub.4 ;
- (5b) converting 75 to 95% of the monochromate ions in the solution resulting from step (5a) into dichromate ions by the addition of an acid or by electrolysis or by reaction with carbon dioxide under pressure to yield a solution containing both monochromate ions and dichromate ions;
- (5c) cooling the solution resulting from step (5b) to a temperature of -5.degree. C. to -25.degree. C.; then
- (5d) filtering the solution resulting from step (5c) to remove those sulfates precipitating as a result of steps (5a)-(5c); and
- (5e) converting residual monochromate ions in the solution resulting from step (5d) into dichromate ions by the addition of chromic acid or by electrolysis or by reaction with carbon dioxide to yield the sodium dichromate solution, said conversion of residual monochromate ions into dichromate ions being carried out optionally after concentration of the solution resulting from step (5d); and then
- (6) either recovering a sodium dichromate solution or crystallizing sodium dichromate by concentration of the sodium dichromate solution to produce sodium dichromate.
- 2. Process according to claim 1, which comprises in step (5d) converting 80 to 95% of monochromate ions in the solution resulting from step (5a) into dichromate ions.
- 3. Process according to claim 2, which comprises in step (5b) converting 80 to 95% of monochromate ions in the solution resulting from step (5a) into dichromate ions by reaction with carbon dioxide under pressure.
- 4. Process according to claim 3, which comprises in step (5e) converting residual monochromate ions in the solution resulting from step (5d) into dichromate ions by electrolysis.
- 5. Process according to claim 1, which comprises removing polyvalent cations and vanadium after step (4).
- 6. Process according to claim 1, wherein step (5e) is carried out after concentration of the solution resulting from step (5d).
- 7. Process according to claim 1, which further comprises converting the sodium dichromate solution recovered in step (6) into chromic acid by electrolysis.
Priority Claims (1)
Number |
Date |
Country |
Kind |
3837266 |
Nov 1988 |
DEX |
|
Parent Case Info
This application is a continuation, of application Ser. No. 422,842, filed Oct. 17, 1989, abandonded.
US Referenced Citations (4)
Foreign Referenced Citations (8)
Number |
Date |
Country |
739447 |
Jul 1966 |
CAX |
0047799 |
Mar 1982 |
EPX |
113086 |
Feb 1898 |
DE2 |
1173884 |
Apr 1960 |
DEX |
1093338 |
Nov 1960 |
DEX |
1205508 |
May 1962 |
DEX |
11900 |
Feb 1978 |
JPX |
989314 |
Apr 1965 |
GBX |
Non-Patent Literature Citations (1)
Entry |
Winnacker-Kuchler, Chemische Technologie (Chemical Technology), vol. 2, 4th edition, 1982, p. 657 to p. 664. |
Continuations (1)
|
Number |
Date |
Country |
Parent |
422842 |
Oct 1989 |
|