An accelerated kinetic leach test for geochemical and environmental characterisation of acid and metalliferous drainage

Abstract

A new bench scale accelerated kinetic leach column (KLC) test was developed to assess the acid and metalliferous drainage (AMD) potential of six historic mine wastes from Tasmania, Australia. Preliminary geochemical static tests evaluated three of the samples as potentially acid-forming (PAF) and two as uncertain because they contain considerable amounts of both acid-neutralising and acid-generating minerals. Mineralogy-based AMD potential evaluated the < 1 mm size fractions of the two samples as PAF. The follow-up accelerated KLC test conducted over 100 days showed that five samples had a 10-day lag phase followed by the onset of acid generation. The 10-day drying cycles from day 30 increased the leachate pH by ≤ 1.5 units possibly from the rapid precipitation of secondary minerals and encapsulation of sulfide minerals. The samples released metal(loid)s including Al, As, Cd, Cr, Cu, Pb, and Zn in concentrations posing moderate to extreme risk to freshwater throughout the test period. The leaching kinetics indicated that the mine waste samples can generate AMD for centuries, thus AMD management strategies at the mine sites may be necessary for environmental protection. A comparison of pH and water hazard indices showed that the accelerated KLC is a rapid geochemical and environmental screening tool between static tests and long-term KLC tests that can validate and complement conventional methods.