Green liquor dregs-amended till to cover sulfidic mine waste.
The mining industry produces massive amounts of waste that without treatment and in contact with oxygen can result in acid rock drainage (ARD) and increased leaching of metals. In Sweden, the common way to manage the mine waste after closure is to apply a soil coverage on top of the waste deposition. The purpose of the soil cover is to hinder the oxygen transport to the waste rock underneath. This is achieved by minimizing the water transport to the waster rock and by creating a water saturated layer on top of the waste rock to deter the oxygen diffusion through the air in the pores. The access to a suitable cover-material is however limited and can lead to extensive costs for the mining company. This creates a great driving force for alternative solutions, e.g. bentonite amendment to till. However, bentonite production is costly both economically and environmentally due to time- and resource- consuming production. Recycling of industrial residues as a cover material is another option. The recycling is beneficial for many parts, i.e. the industry producing the residue, the mining industry that will use the residue and the society in its strive for zero waste. An industrial residue that has potential to improve the sealing layer qualities of a local till is Green Liquor Dregs (GLD), a residue from pulp production in a paper mill.
The study can be devided into a laboratory part and a field part. In the laboratory part 5 to 20 wt. % of GLD from different paper mills, were mixed with three tills with varying particle size distributions (PSD) and total solid content (TSC). The objectives of the study were to investigate if GLD addition can improve a till so it can be used in a sealing layer, how the fines- and clay content in the tills affects the hydraulic conductivity (HC) and the water retention capacity (WRC) of the till-GLD mixtures, and how the initial water content will affect the HC in the different mixtures.
In the field part a pilot cell and an experimental surface consiting of till and 10 wt. % GLD has been constructed. the soil cover has been instrumented with oxygen provbes, temperature probes, soil moisture probes and pore pressure probes to evaluate the effectivness of the cover to prohibit oxygen diffusion to the waste rock underneath.