Acid-base accounting was applied to evaluate the acid generating potential of waste rock dumps of different ages at a nickel mine
in Zimbabwe. Metal concentrations in soils surrounding the dumps were also assessed. The net neutralising potential (NNP) of
waste rock samples was derived from the maximum potential acidity (MPA) and the neutralising potential (NP). MPA and NP
were determined based on total sulphur and acid consumption respectively. Waste rock dumps (WRDs) had more (p<0.05)
sulphur (2.7-3.3%) than the control (0.8±0.03%). MPA values were 103.1±9.27, 103.1±6.33, 84.4±4.19 and 24.7±0.10
kgCaCO3tonne-1 for WRD-0 (fresh), WRD-8 (8years), WRD-16 (16years) and control waste rock samples respectively. NNP
values for the WRDs (5.0-7.9 kgCaCO3tonne-1) were lower (p<0.05) than those for the control (101.16±0.10 kgCaCO3tonne-1).
Neutralising potential ratios (NPRs) were 1.1±0.10, 1.1±0.06, 1.1 ±0.03 and 5.1±0.01 for WRD-0, WRD-8, WRD-16 and control
samples respectively. Mean metal concentrations in the surrounding soils were higher (p<0.05) at all soil depths than the control.
Concentrations were 195.1±4.60(Ni), 131.7±4.90(Cu), 60.0±1.77(Zn), 1220.5±9.44(Fe) and 7.0 ±0.210.14 mg/kg(Pb) in the 0-30
cm soil depth. Values generally decreased with soil depth, suggesting a surface source for the metals. The NNP and NPR criteria
indicated uncertainty in ARD potential from the WRD samples. The study showed that ABA results were inconclusive but the
technique remains important as an alternative for rapid preliminary tests. For inconclusive ABA results, a precautionary measure
would be to consider the material as potentially acid generating. To prevent the acidic drainage, neutralization with alkaline
material and use of engineered containment systems are advisable.