Improving Till by Adding Green Liquor Dregs in Sealing Layers to Control AMD - A Pilot Study

摘要

A common solution to minimize the formation of acid mine drainage (AMD) in sulphide-bearing mine waste is to use a conventional cover. The cover is usually constructed by using natural soils, in the boreal zone often till. Shortage of fine-grained till close to mines suitable as sealant material is often an issue. In the last years, considerable research has been carried out to use residual products from other industries in the control of AMD. Green liquor dregs (GLD), an alkaline and inorganic residual product generated by the sulphate pulp and paper mills, has shown desirable properties such as low hydraulic conductivity, high water retention capacity as well as long term sustainability, to be a candidate for constructing sealing layers in cover system designs. However, the geotechnical strength of the material is insufficient for engineering applications. If this issue can be overcome, developing a cover system with GLD would be possible. The challenge remains of finding a solution that is viable in regards to logistics and transport economics. To reduce transportation costs but take advantage of the physical properties of the residual product, GLD was blended with two types of till in a pilot scale study with the aim to optimize the use of GLD in a sealing layer application. 5-15% (wet weight) GLD was found sufficient to take full advantage of the physical properties of the residual product and to minimize transportation costs. Different mixing techniques were also evaluated. The results show that the quality of the till in regards to hydraulic conductivity and water holding capacity could be improved with the addition of only 5% GLD. A short and efficient mixing was preferred since mixing the material too vigorously released the bounded water resulting in increased water content and a reduction of the compaction efficiency. It results in a material that is difficult to apply and use in sealing layer constructions. Transportation, mixing and application costs are comparable or lower than of fine-grained till.