Claims
- 1. A method fpr continuously insolubilizing essentially all water-solubilized hexavalent chromium compounds leached from a chrome ore residue obtained by production of chromium chemicals for chromite ore by roasting the ore under alkaline oxidizing conditions to form water-soluble hexavalent chromium compounds, which comprises adding to said residue a sulfur-containing reductant, thereby continuously effecting reduction of said water-solubilized hexavalent chromium compounds in the presence of an aqueous medium under conditions sufficient to reduce said water-solubilized hexavalent chromium compounds to their insoluble form.
- 2. The method of claim 1 wherein at least part of the aqueous medium is separated from the residue and recycled for use in the reduction of water-solubilized hexavalent chromium compounds in said chrome ore residue.
- 3. The method of claim 1 wherein the reduction is an organic sulfur-containing compound, selected from the group consisting of thiourea, thioglycolic acid, sodium xanthate, thioacetamide and bis(dimethylthiocarbamoyl)disulfide.
- 4. The method of claim 1 wherein the reductant is calcium sulfide.
- 5. The method of claim 1 wherein the reductant is sodium hydrosulfide.
- 6. The method of claim 1 in which the reductant is produced by reaction of a calcium compound contained in said or residue with an added sulfide.
- 7. The method of claim 1 wherein the reductant is selected from the group consisting of alkali metal and alkaline earth metal sulfides, and the sulfide ions are present in an amount of at least equivalent to about one-third of the amount of sulfide ions stoichiometrically required to reduce the total water-soluble hexavalent chromium compounds in the chrome ore residue to the trivalent state.
- 8. The method of claim 1 wherein the reductant is selected from the group consisting of alkali metal and alkaline earth metal hydrosulfides and wherein polysulfide formation is suppressed by the addition of a minor amount of sodium sulfite to the chrome ore residue.
- 9. The process of claim 4 wherein the amount of calcium sulfide added is equivalent to from about 1 to 3 moles of calcium sulfide per 2 moles of hexavalent chromium, calculated as CrO.sub.4, in said chrome ore residue.
- 10. The process of claim 5 wherein the amount of sodium hydrosulfide added is equivalent to from about 1 to 3 moles of sodium hydrosulfide per 2 moles of hexavalent chromium, calculated as CrO.sub.4, in said chrome ore residue.
- 11. The method of claim 1 wherein the sulfur-containing reductant is selected from the group consisting of alkali metal and alkaline earth metal hydrosulfides and mixtures thereof.
- 12. The method of claim 1 wherein the sulfur-containing reductant is selected from the group consisting of alkali metal and alkaline earth metal sulfides.
- 13. The method of claim 1 wherein the sulfur-containing reductant is selected from the group consisting of alkali metal and alkaline earth metal dithionites.
- 14. The method of claim 1 wherein the chrome ore residue contains water-soluble hexavalent chromium compounds in an amount of from about 0.5 to 5 percent chromium, based on the weight of the chrome ore residue.
Parent Case Info
This is a continuation of application Ser. No. 281,588 filed Aug. 17, 1972, now abandoned.
US Referenced Citations (5)
Continuations (1)
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Number |
Date |
Country |
Parent |
281588 |
Aug 1972 |
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