J.L. Broadhurst

A life-cycle-based review of sulfur dioxide abatement installations in the South African platinum group metal sector

In the late 2000s, several South African platinum producers retrofitted sulfur dioxide abatement technologies to smelters in the Rustenburg area. While such end-of-pipe technologies can reduce local environmental impacts, they may also increase impacts associated material and energy use. Two methodologies were fused to study how these retrofits have shifted environmental burdens, and whether such knowledge would have been useful to design decision-makers. A life cycle assessment was carried out to determine the environmental impacts associated with the key design choices of these smelter and furnace flue gas SO2 abatement technologies, viz. technology choice and the fractional recovery of SO2. The two technology options used by industries and investigated were i) concentrated dual-alkali srubbing and ii) a srubber feeding an acid plant. The results show that the concentrated dual-alkali process has, overall, higher environmental impacts than the scrubber with acid plant. Notably, for the former, all environmental impacts (except acidification) increase with increasing SO2 recovery, whereas for the latter some impacts reduce with increasing recovery due to the by-product sulfuric acid that replaces acid otherwise produced. Subsequently, the results of the LCA were combined with insights from expert interviews to explore design decision-making in the minerals industry, and whether incorporating LCA in formal environmental assessment processes would be of any value to the minerals industry. Expert interviews revealed that incorporating LCA could enable the quantification of impacts for the different technology options, and help justify the chosen options. We argue that normalised results would enable more meaningful interpretation of LCA to further assist such decision-making processes.

Process Decisions Focused on the Prevention of AMD Formation on Beneficiating Sulfide Minerals

Acid Mine Drainage (AMD) from voluminous sulfide-bearing wastes contributes to the environmental burden of mineral processing. To diminish burden and its time frame of risk, the disposal of sulfidic waste materials is re-examined through the valuable distinction between reactive or active gangue materials contributing to AMD generation and largely unreactive passive gangue. In an example process for disposal of tails from mineral sulfide beneficiation, a proof of concept is provided for inclusion of a non-selective sulfide float preceding or following selective separation of the desired mineral sulfide. The environmental benefit of subsequent reduction of sulfide in the tailings from 3.7 to 0.2% on AMD generation potential is quantified through a combination of methodologies including MPA, ANC, NAPP, NAG and microbial testing. Sulfide reduction from 4 to 1% reduces AMD generation. Further reduction below 1% S yields diminishing returns. The environmental benefit of separating ‘active’ and ‘passive’ gangue material prior to disposal is shown, and the reduced active gangue fraction determined through material balance.