Method of preparing chromium

Claim 2

A process for the electrolytic production of chromium metal comprising the steps of: a. electrolyzing an electrolyte comprising an alkali metal chromate, chromic acid, and from 0.4 to 1.5 weight percent sulfate ion, basis total chromic acid in the feed in a first electrolytic cell; b. forming chromium metal at a cathode of said first electrolytic cell; c. removing an effluent stream depleted in chromic acid content from said first electrolytic cell and introducing a portion of said effluent stream into an anolyte chamber of a second electrolytic cell; d. introducing an aqueous liquid composition containing an alkali metal chromate and an alkali metal dichromate into the anolyte chamber of said second electrolytic cell; and e. passing an electrolyzing current through said second electrolytic cell, removing an effluent comprising an alkali metal chromate and chromic acid from the anolyte chamber of said second electrolytic cell, and introducing the effluent from the anolyte chamber of the second electrolytic cell into the first electrolytic cell.

Claim 3

The process of claim 1 wherein a membrane divides the first cell into an anolyte chamber and a catholyte chamber, comprising: a. providing a catholyte liquor containing the chromic acid, sodium dichromate, and sulfate ion in the catholyte chamber of said first cell and an anolyte liquor containing sulfuric acid in the anolyte chamber of said first cell; b. removing a catholyte liquor effluent stream from the catholyte chamber of said first cell and introducing a portion of the catholyte liquor effluent stream from the first cell to the anolyte chamber of the second cell; and c. withdrawing an anolyte liquor effluent from the anolyte chamber of said second cell and introducing a portion of the anolyte liquor effluent stream from the second cell to the catholyte chamber of the first cell.

Claim 4

The process of claim 2 wherein the catholyte liquor of said first cell contains alkali metal chloride.

Claim 5

The process of claim 3 wherein the alkali metal chloride content in the catholyte liquor of said first electrolytic cell is from about 0.05 molar to about 0.20 molar.

Claim 6

The process of claim 1 wherein the mole ratio of chromic acid to alkali metal chromate in the electrolyte of said first electrolytic cell is greater than about 0.5:1.

Claim 7

The process of claim 5 wherein the mole ratio of chromic acid to alkali metal chromate in the electrolyte of said first electrolytic cell is from about 0.5:1 to about 2.0:1.

Claim 8

The process of claim 1 wherein the effluent from said second electrolytic cell is above about 20° C.

Claim 9

The process of claim 7 wherein the effluent from said second electrolytic cell is between about 60 and about 80° C.

Claim 10

The process of claim 1 wherein the electrolyte in said first electrolytic cell comprises from about 10 to about 30 weight percent total alkali metal dichromate and chromic acid.

Claim 11

The process of claim 1 wherein the electrolyte in said first electrolytic cell contains from about 0.4 to about 1.5 weight percent sulfuric acid, basis total chromic acid in the feed.

Claim 12

The process of claim 1 wherein the electrolyte in said first electrolytic cell contains from about 0.75 weight percent to 1.5 weight percent alkali metal sulfate, basis chromic acid in the feed.

Claim 13

The process of claim 1 wherein the feed temperature to the first electrolytic cell is below about 20° C.

Claim 14

The process of claim 1 wherein the effluent from the first electrolytic cell contains less than about 15 weight percent total alkali metal dichromate and chromic acid.

Claim 15

The process of claim 1 wherein the effluent temperature from the first electrolytic cell is above about 20° C.

Claim 16

The process of claim 1 wherein the feed to the second electrolytic cell contains from about 3 to about 4 weight percent alkali metal chromate and from about 40 to about 60 weight percent alkali metal dichromate.

Claim 17

The process of claim 1 wherein the feed to the second electrolytic cell contains from about 700 to about 900 grams per liter of alkali metal chromate and alkali metal dichromate.

Claim 18

The process of claim 1 wherein electrolysis is conducted in said second electrolytic cell at a current density of from 100 to 600 amperes per square foot.

Claim 19

A process for the electrolytic production of chromium metal comprising the steps of: a. electrolyzing a catholyte liquor comprising an alkali metal chromate, chromic acid, and fluoride ion at a chromic acid to fluoride ion ratio of about 200:1 to about 300:1 in a catholyte chamber of a first electrolytic cell; b. providing an anolyte liquor containing sulfuric acid in an anolyte chamber of said first electrolytic cell; c. forming chromium metal at a cathode of said first electrolytic cell; d. removing a catholyte liquor effluent stream depleted in chromic acid content from the catholyte chamber of said first electrolytic cell and introducing a portion of said first electrolytic cell catholyte effluent stream into an anolyte chamber of a second electrolytic cell; e. introducing an aqueous liquid composition containing an alkali metal chromate and an alkali metal dichromate into the anolyte chamber of said second electrolytic cell; and f. passing an electrolyzing current through said second electrolytic cell, removing an anolyte liquor effluent comprising an alkali metal chromate and chromic acid from the anolyte chamber of said second electrolytic cell, and introducing the second electrolytic cell anolyte liquor effluent into the catholyte chamber of first electrolytic cell.

Claim 20

A process for the electrolytic production of chromium metal comprising the steps of: a. electrolyzing a catholyte liquor comprising an alkali metal chromate, chromic acid, and fluoride ion at a chromic acid to fluoride ion ratio of about 200:1 to about 300:1 in a catholyte chamber of a first electrolytic cell; b. providing an anolyte liquor containing sulfuric acid in an anolyte chamber of said first electrolytic cell; c. forming chromium metal at a cathode of said first electrolytic cell; d. removing a catholyte liquor effluent stream depleted in chromic acid content from the catholyte chamber of said first electrolytic cell and introducing a portion of said first electrolytic cell catholyte effluent stream into an anolyte chamber of a second electrolytic cell; e. introducing an aqueous liquid composition containing an alkali metal chromate and an alkali metal dichromate into the anolyte chamber of said second electrolytic cell; and f. passing an electrolyzing current through said second electrolytic cell, removing an anolyte liquor effluent comprising an alkali metal chromate and chromic acid from the anolyte chamber of said second electrolytic cell, and introducing the second electrolytic cell anolyte liquor effluent into the catholyte chamber of first electrolytic cell.

Claim 21

The process of claim 18 wherein the catholyte liquor of said first cell contains alkali metal chloride.

Claim 22

The process of claim 19 wherein the alkali metal chloride content in the catholyte liquor of said first electrolytic cell is from about 0.05 molar to about 0.20 molar.