Structural modification of nano bentonite by aluminum, iron pillarization and 3D growth of silica mesoporous framework for arsenic removal from gold mine wastewater.

Abstract

The elevated contamination of arsenic species emitted from gold mine activities causes serious environmental problems. The modification of natural bentonite clay to obtain the adsorbent with high porosity, large surface area, and high adsorption capacity creates a new group of porous and heterostructure materials for immobilization of arsenic species from gold mine wastewater under alkaline condition, owing to the gold cyanidation process. There is a limited approach in alkaline mine wastewater, because of the negative surface charge of most adsorbents. In this research, the adsorbability of arsenic under synthetic and real alkaline wastewater was investigated for the first time. The Visual MINTEQ geochemical modeling software was applied to simulate the arsenic species under different pH, temperature and co-existing ions in mine wastewater obtained from dewatering unit in Zarshuran gold mine. Optimized parameters and better adsorbent were initially determined from synthetic alkaline wastewater, then the efficiency of the adsorption process in real alkaline mine wastewater was measured. In real wastewater treatment, the obtained adsorption efficiency higher than 70% with high reusability in the alkaline condition is an appropriated for only one step process. The major mechanism for adsorption was chemical with complexation in rapid and slow diffusion into the active sites.