Chromium extraction with organic solvents Part 2. Extraction with TBP and with Primene 81R

The use of a neutral reactive (TBP) and an alkalyne one (Primene 81R) in order to carry out the extraction of chromium from aqueous solutions was studied. The following systems were tested: Cr(VI)/TBP, Cr(III)/Primene 81R, Cr(VI)/Primene 81R. In the same way the stripping of both systems were studied. TBP can easily extract Cr(VI) using pure TBP as organic phase and an aqueous phase with a concentration of sulphuric acid between 0.5 and 2 N. The kinetics of the process is very fast. NaOH solutions were used for stripping, reaching maximum yields with IN NaOH solutions. Primene 81R can extract not only Cr(III) but also Cr(VI). Extraction of Cr(III) must be made at values of pH around 6; this value has to be reached by addition of extraction agent. Extraction of Cr(VI) must be made at values of pH between 3 and 5. Extraction kinetics of Cr(III) and Cr(VI) are both fast. In order to carry out the reextraction, NaOH solutions can be used. Cr(III) is recovered as a chromium hydroxide precipitate if final pH is alkalyne; solutions of NaOH with a concentration equal or higher than 4N must be used for the stripping of Cr(VI), and the solution obtained contains chromium as Cr(III) and Cr(VI).