Analysis and evaluation of heavy metal uptake and release by insoluble starch xanthate in aqueous environment

Abstract

This paper presents the finding of the investigation on the behaviour of metal removal and recovery using insoluble starch xanthate. It is hypothesized that metal-xanthate interaction is a net result of the two simultaneous reactions - (i) reversible complexation of metal with xanthate groups, and (ii) decomposition of the xanthates. The affinity, and also the selectivity sequence of metals for xanthate groups is postulated to follow the reverse order of metal-ethyl xanthate solubilities. Further decomposition of xanthates is viewed advantageous for metal recovery. Metal recovery is predicted to follow reverse order of metal-selectivity for xanthates. Results of the laboratory experiments carried out on insoluble starch (corn) xanthate are used to test the hypothesis. The selectivity of metals for ISX follows the sequence Hg(II)>Cu(II)>Cd(II)>Ni(II) which correlates with metal-ethyl xanthate Ksp values. The recovery of metals from metal-ISX sludge is attempted by using mineral acids (hydrochloric, sulfuric and nitric), oxidizing agents (chlorine solution and hydrogen peroxide) and eluting agent (EDTA). The results of metal removal and recovery are in accordance with the proposed hypothesis.