Stabilization of heavy metals from lead-zinc ore tailings with sodium diethyl dithiocarbamate functionalized montmorillonite (DDTC-Mt): Leaching characteristics and remediating mechanism

The mining and processing of lead-zinc ores produce many lead-zinc ore tailings, which can cause harm by releasing toxic metal ions to the environment. Therefore, the leaching characteristics, acid generation capacity, and fractions of released heavy metals from two Pb-Zn tailings, one from Guangxi designated as F and another from Inner Mongolia designated as YD, have been investigated in this work. Here, sodium diethyl dithiocarbamate functionalized montmorillonite (DDTC-Mt) was synthesized to remediate both F and YD tailings. It was found that YD tailings have a stronger acid generation potential than F tailings, and both of them could be further oxidized and release acid. Moreover, YD showed a certain buffering capacity to acid rain due to its higher calcite content, while the leaching amounts of heavy metals from F was larger than YD resulting from the former's higher weathering degree. DDTC-Mt resulted in a superior stabilization performance to Zn, Mn and Pb from both tailings with optimal stabilization ratios, which are all above 94%. The remediating effect of DDTC-Mt on F was better than that of YD, which could be ascribed to the fact that F contained lower amount of carbonate minerals because of a higher degree of weathering in the latter. The leaching amounts and stabilization ratios of the four elements increased with increasing time and dose of DDTC-Mt, however, temperature and pH showed little or no effect. Mineralogical analysis showed minerals in F and YD before and after leaching were mainly quartz, while the contents of sphalerite and pyrite in F-DDTC-Mt and YD-DDTC-Mt decreased although they were more than those in F and YD without DDTC-Mt after leaching for 72 h. DDTC-Mt could inhibit the release of heavy metals to a certain extent by covering the surface of tailings via complexation and precipitation. Furthermore, DDTC-Mt coating can prevent the oxidation of tailings.