Evaluation of the chemical stability of a landfilled primary lead smelting slag

A primary lead smelter operating in Santo Amaro, Bahia, Brazil, from 1960 to 1993 generated a large amount of slag that was landfilled close to the former smelter and used in roads and houses as a construction material. To evaluate the stability of the slag classical leaching procedures (TCLP, SWEP and SPLP) were applied. In addition, samples of the slag were placed in contact with HCl, HNO₃, HOAc and NaOH solutions for about 24 h at room temperature to simulate acidic and alkaline environments over a wide pH range. In the acidic environment Ca, Fe and Si are strongly solubilized, and Pb and Zn solubilization was significant only below pH 3. The lead slag was also in contact with purified water for a period of 30 days. The results show that Ca and Si were solubilized and Pb, Fe, and Zn were not detected in the solution. The solubilization kinetics are second order processes for both Ca and Si. The initial solubilization rate for Ca and Si are 4.6 and 0.6 mg/L/day, respectively. The main implication of these results is that the major potentially toxic elements of the lead slag landfilled at Santo Amaro were stabilized for a short contact time with pure water and for alkaline and acidic solutions to a pH of about 3 and the groundwater and the surface water contamination found at Santo Amaro smelter region cannot be directly attributed to the landfilled lead slag.