Biosulfides Precipitation in Weathered Tailings Amended with Food Waste-based Compost and Zeolite

Tailings are mine wastes in the form of slurries stacked in mine sites abandoned after the exhaustion of ores. There are approximately 5000 abandoned mine sites in Korea, and tailings have become a serious environmental problem. Long-term environmental exposure of tailings can cause release of acidic and high concentrations of sulfate- and metal-contaminated water (acid mine drainage, AMD). Organic and/or inorganic amendments have been studied for AMD prevention and passive in situ treatment of pore water. This study tests locally available food waste-based compost as a viable amendment, in addition to the need for sustainable ways to dispose of compost, in response to a new environmental law. To examine the feasibility, three bioreactors were constructed, filled with mixtures of tailings, food waste-based compost, and zeolite. During the 4-wk experimental period, feeding water ormedium were poured in one reactor. The leachates were investigated in terms of chemistry and microbiology. Compared with the unamended reactor, the leachate from two mixture-filled reactors showed increased pH, formation of sulfate reduction conditions, and highly efficient metal removal. Black-colored precipitates observed at the end of the experiment suggested the formation of metal biosulfides, following the activity of sulfate reduction mediated by sulfate-reducing bacteria (SRB). Mineralogical analysis of these precipitates confirmed the presence of biosulfides, mainly of Fe and Pb. Moreover, microbial and molecular biological analyses revealed that several species of heterotrophic bacteria (SRB and iron-reducing bacteria) were present in the solids recovered from the bioreactors. Microbial consortium, such as SRB species (Desulfotomaculum putei), and cellulosic-degrader (Ruminococcus sp.) were identified. This study provides promising results on the application potential of food waste-based compost for prevention of AMD generation and passive in situ treatment of pore water in weathered tailings in Korea and elsewhere.