GB1047174A - Process and apparatus for continuous separation of solid substances contained in a liquid - Google Patents

Abstract

A mixture of liquid and solids is forced upwardly along a column, at least a part of which is of upwardly-increasing cross-section; liquid is withdrawn through a filter surrounding the column below the top, and solids are withdrawn from the top of the column. Optionally, washing liquid is introduced at the top of the column for downward flow through the solids and withdrawal with the filtrate. The process may be used to wash uranium ore in acid, the acid reacting with the uranium in the ore to give a uranate which is then separated from the acid solution. In application to the purification of crystals, according to one embodiment, warm solution to be crystallized is injected centrally at the foot of the column into a short open-topped chamber; a cooling liquid in which the above solution is insoluble is introduced to the region around the chamber, circulates through the chamber and column foot, and is heated in the chamber (to a temperature lower than that of the solution, however), so that a rising current is established, in which crystals form and constitute the solids at the appropriate part of the column. The washing liquid in this case is melted crystals. In a modification of the above arrangement the chamber has a series of transverse perforated plates for dispersing the solution in the cooling liquid, and a device for generating pulses of liquid is located at the foot of the column below the solution injector. In another embodiment a U-shaped tubular structure is provided of which the above-mentioned column constitutes one limb; the other limb is a "feed" limb. In one form of this, the solution to be crystallized is introduced downwardly at the top of the feed limb while cooling liquid is introduced radially into the solution stream and, optionally, tangentially below the resulting liquid level. In another form, the cooling fluid (either a compressed gas or a liquid in which the above solution is insoluble) is injected centrally downwardly to the throat of a Venturi-like device at the top of the feed limb, the solution to be crystallized being sucked in at the side. For ordinary filtration, where the solids are of low concentration, it may be necessary to add other solid granular materials to form the bed. The washing flow of melted crystals, moving downwards, carries with it the impurities as it proceeds through the body of crystals, and is then removed through the filter: thus the further the crystals rise to the upper end of the column, the better are they purified.