Removal and Recovery of Chromium from Aqueous Solutions by Reduction-Absorption Microreactor

A rutin-Cr(III) loaded alginate microspheres, which can act as reduction-adsorption microreactor, was designed to reduce Cr(VI) to Cr(III) and recover it. Different from the rutin-Cr(III) complex in alginate-chitosan microcapsule we previously reported, which can sustained release rutin-Cr(III) and reduce Cr(VI) to Cr(III), this microreactor can not only reduce Cr(VI) but also adsorb/recover Cr(III) in aqueous solution. This microreactor was prepared by loading metal complex of rutin into alginate microsphere. It was found that Cr(VI) was initially reduced to Cr(III) by rutin-Cr(III), and then the product Cr(III) was absorbed in the microspheres. Both Cr(VI) reduction rate and Cr(III) adsorption rate were pH-dependent. Cr(VI) can be completely reduced to Cr(III) at pH 1–4 with a reduction capability of 1.27 (±0.078) mmol/g (pH 1, 4 h). The highest blank alginate microsphere adsorption capacity was 1.82 (±0.042) mmol/g at pH 4. It was assumed that reduction-adsorption was the mechanism of total Cr removal by the reduction-absorption microreactor. Recovery experiment showed that 93% and 98% of Cr(III) can be recovered by EDTA and sodium citrate, respectively.