Process for disposal of insoluble tailings that remain when solubilizing uncalcined or calcined trona in the process of producing soda ash, in which tailings are slurried with a saturated or substantially saturated solution of sodium carbonate, sodium bicarbonate and mixtures thereof, pumping said slurry into a well connected to an underground mined-out cavity with sufficient pressure to prevent the build-up of tailings from plugging the bottom of the well opening, dispersing and settling said tailings and a retained portion of the solution in the cavity, removing solution from said cavity and conveying it to the surface, recovering the removed solution for recycle and slurrying of additional tailings, and adding as make-up liquor to replace the solution retained in the cavity, a saturated or substantially saturated solution of sodium carbonate, sodium bicarbonate and mixtures thereof. The preferred solution employed in this process is purge solution which is discarded from a crystallizer circuit.