Metals recovery from acid mine drainage and possibilities for their utilization

Extraction of coal, gold, and polymetallic ore, as well as their modifications, has left a lot of dumps of waste material, tailings, and abandoned mines in the world. Sulphide minerals in these deposits under aerobic conditions (air and water) are liable to microbio-chemical biodegradation by litotrophic bacteria and archaea, resulting in acid mine drainage (AMD) production. Processes caused by litotrophic microorganisms, namely Acidithiobacillus sp. and Leptospirillum sp, have occurred in the soil dump of pyritized hydroquartzite in the area of Banská Štiavnica – Šobov. They bring about AMD production, with dominant components of Fe, Al, and sulphates. This article deals with active modification/treatment (gaining of Fe-sorbents, Fe-pigments) and remediation (decreasing concentration of contaminants – heavy metal, sulphate) of AMD from this area. The products of various purities, phase compositions, and properties, including surface properties, can be synthesized from AMD depending on the reaction conditions. Obtained Fe-oxyhydroxides can be transformed thermally to hematite structure (basic ferric pigment). The other method of utilizing of Fe-sludge is the creation of ferrites (general structure MFe2O4 (M – Me+2), e. g. zinc ferrite. In an application of alkaline industrial effluents, especially red mud bauxite and blast furnace slag, in batch experiment and neutralization of AMD, it has been shown that it is possible to reduce contents of Fe, Al, Cu, Zn, Mn, and sulphates with these agents.