Experimental study on one-dimensional settlement of alkali wastes backfilled to abandoned salt caverns

The method of solution mining to explore halite will generate large quantities of abandoned caverns, while soda ash production whose raw materials are the brine produced by solution mining will generate abundant alkali wastes. The process that alkali wastes are mixed with the brines into slurry and pumped back into the abandoned caverns is defined as in-situ backfill. The settling behavior of the slurry is very important to the backfill effect. As a preliminary study to investigate the behavior of waste particles in brine-filled caverns, laboratory one-dimensional settlement experiments on two types of alkali wastes collected from different soda ash production techniques are conducted. The main results are: (1) the settlement of alkali wastes with a small amount of clay particles, whose flocs are small and independent, can be classified as uniform settling of flocculation, and that with a large amount of clay particles, whose flocs are large and connected, is net settling of flocculation; (2) the settling process of waste particles can be divided into four phases: flocculation phase, settling phase, primary consolidation phase and secondary consolidation phase; (3) by comparing the settling processes, durations of the first three phases are longer for the slurry with net settling of flocculation; (4) the void ratios of the two sediments are both very large when the primary consolidation is completed, indicating that there is a large amount of free water in the sediments. The settling behavior of the two types of alkali wastes is revealed, and the relevant factors are analyzed. This research may provide certain reference value for the study of the settling mechanism and site backfill.