Solvent Extraction of Selenate and Chromate Using a Diaminocalix[4]arene

The extraction of Se(VI) and Cr(VI) using a diammoniumcalix[4]arene was investigated. A study of parameters such as ligand concentration, pH or diluent was carried out and allowed to specify the stoichiometry of the extracted species. It was shown that Se(VI) is extracted into CHCl₃ as (LH₂²⁺, Cl^-, HSeO₄^-) and ((LH₂²⁺)₂, 2Cl^-, SeO₄^2-)species at pH 2.6. An increase of pH or an addition of 5% or 10% decanol in CHCl₃ favors the extraction of SeO₄^2- over HSeO₄^- but leads to a drastic decrease of seleniumextraction. Cr(VI) was shown to be extracted as(LH₂²⁺, Cl^-, HCrO₄^-) at pH 2.6 and probably as (LH⁺, HCrO₄^-) for higher pH.