Effect of different soil layers on porewater to remediate acidic surface environment at a close mine site

Abstract

This paper describes the chemistry of porewater when constructing different soil layers on acidic weathered rock of a closed mine to remediate the surface environment. Three cases were set on a flat surface of the site, all under different layer systems. Case 1 was only composed of weathered rocks. A top neutralization layer was constructed on the weathered rocks in case 2, whereas both an upper low permeable and middle neutralization layers were constructed on the weathered rocks in case 3. The low permeable layer of 30 cm thick consists of clay, and the neutralization layer of 30 cm thick consists of the mixture of the weathered rock and calcium carbonate as a neutralizer. Porewater sampling systems and soil sensors to measure temperature, water content, and electrical conductivity were set at different depths.In case 1, steadily high concentrations of heavy metals were observed regardless of the depth, and the pH ranged from 2 to 4. In cases 2 and 3, a dramatic decrease in concentrations of heavy metals was observed, even below the neutralization layer. For both cases pH values were circumneutral. There were no significant seasonable changes in heavy metals concentrations and pH of porewater by considering the temperature and precipitation. In addition, the water content of the layers in case 3 fluctuated more mildly than that in cases 1 and 2, indicating that the low permeable layer reduced the rate of infiltration.Therefore, a significant reduction in the load of heavy metals released from the site can be achieved by both implementing neutralization and low permeable layers.

Comparison of potentially toxic metals leaching from weathered rocks at a closed mine site between laboratory columns and field observation

“…The pH, ORP, temperature, and EC were measured immediately after collection, and the leachates were filtered before chemical analysis. The room temperature during the experimental period (November 2009to April 2011 was 15±2 o C. The variation in temperature does not have a significant effect in the leaching of potentially toxic metals as reported in a previous study (Salinas Villafane et al, 2012). Throughout the remainder of the paper, column 1 is referred to as case 1, column 2 as case 2, and column 3 as case 3.…”