Covalent coating of coal refuse to inhibit leaching

Acid mine drainage (AMD) is a severe environmental problem that results from the oxidation of pyrite (FeS2) and various other metal sulfides. AMD is often associated with abandoned mines which produce acidic run-off waters that are rich in heavy metals. AMD also occurs in the areas surrounding coal refuse piles that have accumulated from coal cleaning processes. In the present work, the use of the disodium. salt of the ligand 1,3-benzenediamidoethanthiol (Na2BDET) is explored as a possible coating to prevent the dissolution of pyrite in coal. Unlike phosphate- and silica-based compounds, Na2BDET is believed to form covalent Fe-BDET linkages along the pyrite lattice. It was found that Fe leaching from BDET-coated coal is reduced by 99.3% when submerged in a pH 6.5 solution, by 97.5% when submerged in a pH 3.0 solution, and 66.4% when subjected to acidic and oxidative conditions. The ligand coating treatment also reduced the leaching of other heavy metals, such as Mn, Cu, Ni, Zn where a reduction of 88.3%, 64.7%, 70.5% and 89.5%, respectively, was observed in leaching after a 14-day simulated acid rain test. Additional leaching reductions were observed for metals such as Zn, Cu, Co, etc. at pH 6.5 and 3.0 when subjected to both oxidative and acidic conditions. (C) 2002 Elsevier Science Ltd. All rights reserved.