Abstract
The discharge of contaminated industrial and mining wastes may contain heavy metals. Water contamination by these heavy metals can cause significant environmental and medical issues. Over the years researchers have tried to develop synthetic adsorbents for the remediation of heavy metals from drinking water but their usage is very limited due to the extensive costs. Thus, to develop low cost methods which can be used on a larger scale for the removal of heavy metals from drinking water has become a challenge for us in this era. In this work we have investigated the efficiency of weathered mine tailings containing mineral dypingite and pyroaurite for the removal of heavy metals from contaminated water. This was done by reacting the samples with heavy metals and performing column experiments using the samples from mine tailings. The samples from the mine tailings were cut to 1cm3 chip and subsequently reacted with different heavy metals including Cu, Pb, Cd and Cr. The areas in chips with mineral pyroaurite and dypingite were first characterized to see the changes after the experiments using SEM-BSE imaging and XRD characterization. The column was filled with selected material from mine tailings and CdCl2+NaCl solution was passed through it. The fluid samples from the column experiments were characterized by using ICPMS and IC and the reacted column material was characterized using SEM and XRD. The SEM-BSE images from the chip experiments showed that Cd, Pb and Cr were preferentially sorbed/precipitated on dypingite whereas Cu was sorbed on pyroaurite. Pb and Cd precipitated in the form of cerrusite (PbCO3) and Otavite (CdCO3) on the surface of dypingite respectively. However, the SEM-BSE along with EDS images from reacted column material revealed different results. Cd in this case was precipitated on both pyroaurite and dypingite and formed otavite. XRD results suggest constant mineralogy before and after the experiment. The results from column experiments showed that Cl- is not working as an ideal conservative tracer. The concentration of Cd in the column was accommodated up till after 1.2 pore volume when the concentration of Cd reached a peak with more than ten times of the inlet concentration. This sudden increase in the concentration of Cd was most likely due to the fine grained otavite precipitates that got through the column.