Laboratory Investigation of the Control of Acid Mine Drainage Using Alkaline Paper Mill Waste

A great deal of research effort has been undertaken to find an effective solution to the problem of acid mine drainage. Indeed, Canadian legislation requires mining companies to respect environmental regulations by providing a rehabilitation plan with a financial guarantee. In order that the Canadian mining industry remains competitive, the proposed solutions have to be not only efficient but also economic, that is why the use of another waste material is attractive. The main objective of this study was to investigate the technical and environmental feasibility of stabilizing acid mine residues using alkaline paper mill waste produced by the pulp and paper industry as a basic source. The mineralogical characterization of the alkaline paper mill shows that calcite is the dominant mineral with hydrated lime (portlandite) present at a low content. The mineralogical characterization of the mining residues shows a polyphasic system where silica dominates the oxidized zone. On the other hand, a high pyrite content is present in the non-oxidized zone. The essential observations that emerge from the leaching tests undertaken in the laboratory can be summarized by the efficiency of the incorporation of the alkaline paper mill waste (1/3 waste and 2/3 mining residue) on the production of acid mine drainage. In fact, it can be observed that there is a reduction of the high toxicity elements like heavy metals. The increase in pH permits the reduction of catalytic bacterial activity and reduces the rate of oxidation in the mining residue.     

Field Investigation of Controlling Acid Mine Drainage Using Alkaline Paper Mill Waste

To verify in situ laboratory test results for the control of acid mine drainage using alkaline paper mill waste, five demonstration cells were built on the Ascot mine site in Sherbrooke (Québec, Canada). A monitoring program was set up to record temperature, leached water quality, oxygen concentration and electrical conductivity.Monitoring results showed that mixing mine residueswith alkaline paper mill waste and covering mine residues with paper mill waste allows an efficient control of acid mine drainage. The paper mill waste cover generates an alkaline front which results in metal precipitation as hydroxides. Also, an increase in pH results in an inhibitionof bacterial catalytic activity. Chemical analyses conducted on the collecting water shows a high reduction of leachingmetals to under ground water. Moreover, a significant reduction of diffusion of oxygen to the mine residue is observed.