Cyclic freeze–thaw to enhance the stability of coal tailings

Laboratory freezing experiments were conducted to evaluate the feasibility of using cyclic freeze–thaw to enhance the surface stability of coal mine fine tailings. Undrained shear strength increased from non-measurable to 10 kPa after five cycles of freeze–thaw in tailings samples with initial moisture contents of 84% and 102%. Cyclic freeze–thaw also significantly dewatered the tailings samples. Decanting the melt water after each thaw reduced the water content of each sample by approximately 50%. A large scale one dimensional freezing test was also conducted to determine the advance of frost within the fine tailings and to understand how moisture migrates as the tailings freeze. Water was attracted to the freezing front from tailings ahead of the advancing front, decreasing the moisture content within the still unfrozen tailings. As the freezing front passed, the tailings were dewatered further at temperatures below 0 °C. Unfrozen microscale water from within the frozen tailings was attracted to a three dimensional network of ice lenses surrounding the frozen soil peds. The laboratory experiments suggest freeze–thaw may be a technically feasible method to increase the strength and surface stability of fine tailings.