The use of pastefill as a solidification and stabilization process for the control of acid mine drainage

In this paper, the pollution potential of pyrite and arsenopyrite was examined through tailings from a European gold mine. The main objective of the project was to study the geochemical behaviour of the tailings both before and after their inclusion into a cementitious matrix. Such a study requires extensive characterization of the tailings. The performance of SSP was examined by studying the evolution of the leaching process in the tailings in alkaline media as well as the evolution of the microstructure and chemical composition of paste samples after enhanced leaching experiments done in a Soxhlet extractor. Both general and specific tendencies of weathering patterns were obtained from optical microscope observations coupled with a semi-quantitative EDS analysis in the weathering fronts. XRD SEM investigations and XPS were used to characterize the formation of secondary products. The main findings were that transfers inside paste samples are minimized due to the low permeability of the paste and the in situ precipitation of calcium sulphates and arsenates. These leaching tests show that lime enriched cement has high retention potential for arsenic, even though its porosity is increased by the dissolution of portlandite at the periphery of leached samples. In other samples, the carbonation of portlandite in the border front could be the factor which leads to arsenic release. As revealed by optical and SEM microscopies, the observed weathering fronts remain small, even in long duration experiments. These observations reinforce the interest in paste backfill using conventional hydraulic binders for the solidification and stabilization of sulphide tailings.