Treatment of complex heavy-metal mining waste using zero-valent iron powder, iron (III) hydroxide pellets and transformed red-muds power and pellets

The paper presents the results of a laboratory investigation conducted to assess the suitability of zero-valent iron, iron(III) hydroxide and transformed red mud (TRM) for remediation of mine sites contaminated by metal sulphide mine tailings. The study has been conducted with tailing waste from an abandoned arsenic mine characterized by the high-level presence of As together with heavy metals such as Cd, Cu, Ni, Pb, and Zn in acid percolate. On the bases of the results of bottle leaching tests carried out on mining waste treated with different proportions of zero-valent iron and TRM powder; subsequent column tests were performed on: untreated tailing waste, waste mixed with zero-valent iron upon a permeable reactive barrier (PRB) of transformed red mud pellets, or waste upon a double permeable reactive barrier constituted of iron hydroxide pellets and TRM pellets. The results evidenced the ability of zero-valent iron and TRM to drastically decrease As and heavy metal contents of the waste leachate, with immobilisation efficiencies of up to 99% for Cu, Cd and Zn , of up to 97% for As and of up to 92% for Pb, even after14 BV had passed.