2) Net Acid Generation (NAG) Test
NAG pH values in the range of 5.02–6.10 and NAG in the range of 0.08–0.31 kg H2SO4 t-1 were observed in all samples. The NAG pH was less than the pH value because of the sulphur content from pyrite or sulphide ores in the tailings. After adding H2O2 to oxi-dize organic matter and sulphur in the sample, the pH decreases (NAG pH). From the expe-rimental results, this NAG pH can represent a cut-off according to Table 2 and a graph bet-ween NAG pH and calculated NAG is shown in Figure 5. The graph indicates that all samples have low to non-acid forming potentials which suggests that strong metal cyanide complexes presented in the tailings and these strong metal cyanide complexes cannot dissociate to a significant extent because there is potential to generate H2SO4 from sulphide ores to reduce pH to a level favorable to dissociation of strong complexes.