Laboratory evaluation of Fe0 barriers to treat acidic leachates

In the present study, flow-through column experiments using a series of continuous-flow columns were conducted to investigate the performance of Fe⁰ permeable reactive barriers (PRB) for the treatment of acidic leachates generated in active or abandoned mining and waste disposal sites. Simulated AMD solutions of low and high metal ion concentration were pumped at different flow rates into the laboratory system. Concentration profiles under steady-state transport conditions were developed by measuring metal ion concentration at various sampling ports. Results show that metal ion removal is mainly accomplished via redox reactions that initiate precipitation of mineral phases. Sulfate green rust was identified from the analysis of precipitates formed on the iron surface; sulfate and heavy metals uptake by green rust is a secondary clean up mechanism. Experimental results as well as geochemical modeling by PHREEQC-2 indicate that cadmium and copper are removed by redox reactions while aluminum, manganese, nickel, cobalt and zinc are mainly removed as metal hydroxides. It is therefore seen than zero-valent iron barriers can be used as an environmentally and economically viable remediation technology for the clean up of acidic leachates loaded with several inorganic contaminants and sulfates and the subsequent prevention of groundwater contamination.