Passive biochemical reactors amended with zero valent iron nanoparticles for acid mine drainage treatment

Abstract

The Acid mine drainage (AMD) are discharges characterized by low pH and high concentrations of sulfate and metals. The DAM can pollute soil and water ecosystems for long periods of time even if mining activities have stopped, therefore their treatment is a priority issue. In this study the size (~100 y ~25 nm) and concentration (5.0, 2.5 y 1.0?% p/p with respect to reactive mixture) of zero valent-iron nanoparticles (nZVI) were evaluated as amendment in the reactive mixture of biochemical passive reactors (BPR) to increase pH and alkalinity, promote sulfate reduction, and metal removal. Fourteen BPR was built in duplicate; six of them contained 125 g of reactive mixture, DAM and nZVI, the remaining six contained DAM and nZVI. Two were used as controls; one with only reactive mixture and another with only DAM. The reactors were remained in anaerobic conditions and were evaluated weekly for 5 weeks. The results show that in the reactors with reactive mixture the pH and alkalinity increased while decreasing the redox potential (ORP), achieving removal rates of metals >95?% (Fe2+, Zn2+ y Mn+2) and sulfate up to 83?%. In the reactor without reactive mixture, the pH was acid and ORP high while the removal of sulfate and metals was low, only is possible removal of Zn2+. The nZVI significantly improve the efficiency of the treatment with reactive mixture. However, it is essential to carryout studies on the toxicity of nanoparticles on the microbial community that participates in the bioremediation process.