Environmental characterization of Sarcheshmeh Cu-smelting slag, Kerman, Iran: Application of geochemistry, mineralogy and single extraction methods

Abstract

Annually, more than 370,000tons of slag waste is produced in Sarcheshmeh Copper Complex, the biggest Cu-producer in Iran. Geochemical, mineralogical and single extraction methods were used in order to evaluate the contamination potential of metal(loid)s associated with Sarcheshmeh smelting slags. Results showed that, like the other non-ferrous or base metal slags, Sarcheshmeh slags are considered as one of the metalliferous smelting wastes with the multi-elemental contamination potential of most of the potentially toxic elements. Mineralogical studies revealed that the mineral assemblage of the investigated samples is controlled by at least three main factors, including: (1) primary mineralogy of the ore concentrate (chalcocite, chalcopyrite, covellite±pyrite); (2) smelting process (magnetite, fayalite, pyroxene); and (3) weathering reactions in arid to semiarid climate conditions [thenardite (Na2SO4), bonattite (CuSO4·3H2O) and gypsum (CaSO4·2H2O)]. Results obtained from the U.S. EPA toxicity characteristic leaching procedure (TCLP) and water soluble tests revealed that the order of leachability of target elements from the most to the least in the slag samples is as S≫Cu>>Zn>Fe>Mo>Pb>Ni>Mn>Co>As>Se>Sb>Cd>Cr=Sn=Ag=Bi. The maximum contamination potential, higher than the considered toxicity regulatory levels (one-hundred times the U.S. EPA maximum contamination level in drinking water), of As (9.35mg/L), Mo (186.7mg/L), Sb (3.50mg/L) and Se (6.12mg/L) was observed in the alkaline leached solutions (pH9.67) of the sediments associated with the slag dump drainages, while the maximum concentrations of the other investigated elements such as Cu, Co, Cd, Fe, and Zn were measured in the acidic (pH<5) leached solutions. Annually, about 18.7% of Sarcheshmeh reverberatory slags are used for other purposes such as sandblasting. Wind blowing slag particles, produced from the grinding and sieving facilities, are responsible for the enrichment of elements such as As, Cu, Mo, Pb, Sb, Sn, Zn, Cr, S and Fe in the topsoils around the slag preparation site. Based on the acid acetic (0.43mol/L) and EDTA (0.05mol/L) leaching tests, the solubility and thus the bioavailability of these potentially toxic elements also were increased in the surface contaminated soils, a subject that is very important from environmental point of view. Obtained results also emphasize on the need for the greater caution in the slag waste management.