Control of acid mine drainage from an abandoned mine in Morocco by using cement kiln dust and fly ash as amendments

Abstract

Acid Mine Drainage (AMD) is one of the major problems of the mining industry that is causing prominent environmental damages. It occurs naturally when sulfide tailings oxidize and generate an acidic leachate containing acid leachate loaded with heavy metals (Pb, Fe, Zn, Cu, Cd, As ...) and other toxic compounds. During mining activities and after mine closure, storage of discharges places (waste rock piles and tailings parks) might be responsible for the production of acid leachate which will have adverse consequences on the environment. The Kettara abandoned mine (Morocco) has produced from 1965 to 1982 more than 3 Mt of mine wastes that are rich in sulfides (pyrrhotite and pyrite). The physicochemical characterization of these mine wastes confirmed their strong potential to produce Acid Mine drainage (AMD) with a pH varying between 2.9 and 1.5. In order to control AMD in Kettara mine site, AMD neutralization tests were undertaken in the laboratory using two types of alkaline industrial by-products as amendments. The latter consisted of alkaline fly ash (Fly Ash: FA) from the thermal power plant of Jorf Lasfar in El Jadida and cement kiln dust (Cement Kiln Dust: CKD), from Lafarge cement of Bouskoura near the city of Casablanca, Morocco. The tests in leaching columns objectives are to determine the ratios of CKD, FA and residues who may neutralize the phenomenon of DMA in Kettara site. The leaching columns tests show that the use the industrial by-products allows increase the leachate pH to values of about 6.5 and 7.13 and the substantial reduction of metals concentrations such as Fe (from 0,01 to <0,12 mg/L) and Cu (<0,02mg/L). The AMD from Kettara mine tailings could be reduced by adding amendments composed of 80% of CKD and 20% of FA. This method of treatment with CKD and FA allow recycling and valorization of industrial waste cement plants and thermal power plants.