NEUTRALIZATION OF ACID-MINE TAILINGS BY A DDITION OF ALKALINE SLUDGESFROM PULP AND PAPER-INDUSTRY

Mine tailings generating addic effluents were neutralized by alkaline sludges produced in pulp and paper mill operations. Depending on the p roportion of sludge added, the resulting pH values increased from 3.96 to between 10.9 and 12.4. The sludge incorporation also increased the buffer capacity of the mining residues. Leaching studies conducted in laboratory columns for a period of about 25 weeks showed the efficacy of sludge incorporation with acid mine tailings. The basic sludges we re well mixed with the mining wastes in varying proportions (33, 50, 6 7, and 75% v/v). It was observed that this incorporation improved the leachate quality considerably. Therefore the leachate pH of the mixtur es remained stable between 11.5 and 12.5 compared to a pH of 3.7 for t he leachate coming out of the blank column. The metal concentration of Cu, Zn and Mn in the leachate was reduced by 80 to 100 %. In the case of Pb, however, the reduction was not as significant. On the other ha nd, microbiological tests revealed that addition of alkaline sludges s lowed down the acidification process although not completely. Selectiv e sequential extractions performed on the mine tailings showed dearly that some metals like Cu, Pb and Zn were more easily leachable than ot hers like Al, Fe and Mn.