Study of extraction of iron (III) from chromium sulphate solution

Abstract

ABSTRACT This work reports a study of the extraction of iron (III) deeply from the chromium sulphate solution in which most of the iron was precipitated with oxalic acid. Di(2-ethylhexyl)phosphoric acid (P204) was employed, and the conditions of the extraction process were optimised according to a sequential experiment design. The concentration of iron (III) in the solution could be reduced to less than 2 mg L−1 and the iron (III) extraction efficiency can reach up to 99.7% when the solution feed pH value, the phase ratio, P204 concentration, saponification rate, and extraction stages were 2.0, 1:1, 15% (v/v), 60%, and 2, respectively. During this process, other impurities in the solution such as Ni and Mn can also be reduced simultaneously. Further, post-extraction, highly pure chromium sulphate can be obtained. The experimental results show that when the organic was stripped with 4 mol L−1 HCl, 95% Fe in the organic phase can be stripped after three stripped series with O/A being 1:1, and then P204 can be re-utilised. The extraction process can also address the difficulty in separating iron (III) thoroughly from the chromium sulphate solution in the new chromic salt process with ferrochrome as raw material.