GB888188A - Improvements in the preparation of alkali metal dichromate - Google Patents

Abstract

<PICT:0888188/III/1> Alkali metal dichromate is prepared by passing carbon dioxide into an aqueous solution of alkali metal chromate and dichromate in which the concentration of CrO3 as dichromate is higher than the concentration of CrO3 as monochromate, and at a rate of at least twice the rate at which the carbon dioxide is absorbed. p A solution of chromate, e.g. sodium chromate, fed continuously through a line 2 mixes with a solution of dichromate flowing continuously through a line 4, and passes by line 6 to the top of a tower 8 where it is contacted countercurrently with carbon dioxide entering through a line 10. The carbon dioxide is fed at a rate more than twice, preferably four times, that at which it absorbed and unabsorbed gas, is recycled by a line 12, make-up gas entering at 14. Sodium dichromate solution passes to a filter 18, where precipitated sodium bicarbonate is removed, and then sodium dichromate is recovered from the solution. Some of the solution passes to an evaporator 38 where it is concentrated before being mixed with fresh sodium chromate solution. Potassium chromate also may be prepared. Specification 882,320 is referred to.