Development of redox-recyclable ion exchange materials for the removal and recovery of heavy metal contaminants from aqueous media.

摘要

Alkali metal or proton intercalated molybdenum disulfides, A_xMoS₂ (where A = H+, Na+, or K+ and x 1.3) were investigated as redox-recyclable ion exchange extractants for the soft, aqueous metal ions Hg2+, Pb2+ and Ag+. The charge on the MoS₂x− layers was successfully decreased from its initial value of 1.3− to 0.80− by contacting Li _1.3MoS₂ with an aqueous solution of ANO₃ and was determined by hydrogen (H₂) gas evolution and mass balance studies. The charge compensating cations were a combination of Li+ (from the original solid) and A+ from the reaction solution.; The thiospinels Cu₂MSn₃S₈ (M = Fe, Mn) were also investigated as ion exchange extractants for heavy metal cations. Mass balance experiments indicated exchange of both copper and transition metal ions out of the solid for soft heavy metal cations in solution. This ion exchange reaction was slow as well as incomplete with low ion removal over time periods up to 6 days, even in the presence of excess extractant. In addition, these extractants performed poorly in aqueous acid.; Direct synthetic methods were used to prepare the following new thiospinels: CuMnSn₃S₈; Cu₂Sn₃S₈; CuFeSn₃S₈; Li₂FeSn₃S₈; and LiCuFeSn₃S₈. The compounds Na₂FeSn ₃S₈ and NaCuFeSn₃S₈ were also synthesized, however these two solids did not crystallize with a spinel structure.; Proton-activated thiospinels were synthesized with stoichiometries ranging from H_0.10Cu_1.96Fe_0.97Sn₃S ₈ to H_0.18Cu_1.90Fe_0.96Sn₃S ₈ through a reaction between the parent spinel and aqueous acid. The degree of protonation depended on the contact time between the parent solid and an acidic solution.; In all cases, the alkali metal and proton intercalated thiospinels out-performed the parent spinel compounds in terms of total metal ion extracted as well as extraction time. Using mass balance experiments, the mechanism of metal ion removal with the proton activated thiospinels was shown to be ion exchange. Metal ion recovery from various spinels investigated showed that heating to 500°C resulted in the release and recovery of reduced metal.