Abstract: A slurry of solid particles suspended in water or some other liquid is elevated in a riser tube, extending upward from a closed vessel, under hydraulic pressure from the same liquid descending into the vessel from a hydrostatic column whose height is less than that of the riser tube; liquid exiting at the top of that tube is recirculated to the vessel through the column after being freed from the accompanying solids. The excess height of the riser tube is made possible by the admission of bubbles of air or some other gas into the tube at its lower end. Fresh particles to be entrained by the rising liquid are fed into the closed vessel via a gated conduit maintaining the hydrostatic pressure therein.