Liquid limit and hydraulic conductivity of brown coal composites

Adequate waste disposal is currently under high demand in Australia, due to a rapid growth in population. Australia’s scarcity and cost for the use of clays (most commonly used landfill liner material) have resulted in a search for alternative materials to achieve satisfactory performance in landfill design. This study explored liquid limit and hydraulic conductivity (HC) of coal composites for potential landfill liner use. Brown coal (lignite) was mixed with polyacrylamide (PAM) or sodium bentonite (Bt) to investigate liquid limits (LL), HC, and swelling behaviour. Each additive was subject to distilled water and sodium chloride solution (50 g/l) to investigate the effects of pore fluid chemistry. The addition of 2 wt% PAM resulted in approximately 82 percentage point (pp) increase in the LL of lignite with distilled water and 76 pp increase with 50 g/l sodium chloride (NaCl) solution. The HC of lignite also decreased by more than two orders of magnitude as the PAM content increased. The swell index of lignite composites increased with the addition of PAM. This exploratory study has found the unique property of brown coal and its composites that the LL, HC and swell index do not deteriorate significantly in the presence of highly concentrated electrolyte solution (50 g/l NaCl). Such distinct properties will be beneficial over currently used landfill liner materials.