Remediation of Soils Contaminated with Mercury During Artisanal and Small-Scale Gold Mining Operations in Colombia Using Silver-Coated Plates

Abstract

As early as the 1500s, the practice of mercury amalgamation was applied in America for gold mining. Its steady and widespread use lead to detrimental implications for the environment and public health. The most vulnerable are local communities relying on small-scale and artisanal gold mining (ASGM) as their main economic activity. Initiatives to protect human health and the environment from mercury pollution have developed from The Minamata Convention. This research evaluated the viability of using Silver-Coated Plates (SCP) as a remediation technology for mining-related, mercury-contaminated soils. Experiments were carried out at a laboratory scale to (Phase I) model soils spiked with Hg2+ to low, intermediate, and high initial concentrations, and (Phase II) ASGM-contaminated soils from Colombia. The experiments conducted during phase I defined that SCP could be used as electrodes within electrokinetic cells to achieve soil remediation. The phase II experiments demonstrated higher efficiencies for mercury removal using the SCP for the ASGM soils (≥90%) than for the model soils (59% - 86%). This was explained by the different prevalent mercury species of the two kinds of soil evaluated. Mobile mercury species were abundant in the ASGM-soil while adsorbed mercuric compounds prevailed in the model soil. Supplementary tests conducted on the aqueous phase gave insights into the mechanisms of mercury removal by the SCP (eg. chemical affinities, pH, mineralisation). The SCP technology was found to be an optimal alternative tool for remediating soils, though its potential for water treatment requires further study. This thesis opens the path for future endeavours of research in the field of mercury decontamination for contaminated soils, but also for mercury-contaminated water.