The results as presented in Fig. 4 indicated that an increase in the initial acid concentration resulted in an increase in Fe and Cr concentration, passing through a maximum at 1.1 s and decreasing as acid concentration was further increased. Considerable reduction in both Fe and Cr concentrations were achieved with pH management. In the case of Fe the concentration was decreased from a value of 70.2 to about 1.0 mg/L for sample S18, and from 120.8 to 0.4 mg/L for sample S26. Cr level in the leach solution decreased 36.0 to 0.4 mg/L for sample S18, and from 46 mg/L to 0.1 mg/L for sample S26.