Environmental Leaching – Predicting Real Long-Term Site-Specifi c Leaching Performance

Environmental leaching methods such as the TCLP and ASLP are widely used to assess wastes including mining and mineral processing by-products, but they were originally designed for regulatory pass/fail testing under co-disposal municipal landfill conditions and are not suitable for predicting site-specific leaching performance. Their underlying assumptions often create worst-case acidic leaching scenarios that may overestimate contaminant mobility for mineral wastes typically stored in neutral to alkaline mono-fills. Recently issued ISO/TS leaching standards (ISO/TS 21268-3:2007 and ISO/TS 21268-4:2007) aim instead to characterise leaching behaviour of soil-type wastes and predict long-term performance by examining release over time and as a function of key controlling parameters such as pH. This preliminary study applies these ISO methods to representative mineral industry by-products (including red mud, sulphide tailings and incinerator ash) and compares the results with those from TCLP/ASLP tests. Where direct comparisons were possible, TCLP/ASLP generally extracted similar or higher amounts of components than tests at equivalent pH without acetate buffer or tests simulating long-term leaching in eluates defined by waste type. The findings suggest that the ISO methods can provide more realistic long-term leaching estimates across a range of soil pH conditions and could offer a better basis for planning waste handling, treatment and potential reuse.