Abstract: The present invention relates to the processing of phosphoric acid by crystallization. Wet-process phosphoric acid is purified by cooling it to supersaturated conditions and adding relatively large amounts of fine, relatively pure seed crystal. Crystallization thereafter proceeds under conditions which substantially favor crystal growth on the seeds which are added and disfavor secondary nucleation. To prevent the crystallizing magma from reaching a viscosity which would render further processing difficult, the present invention provides for recycling raffinate in an amount sufficient to maintain the solids content of the crystallizing magma below about 40%.

Abstract: A method for the recovery of precious metals such as gold and silver from various ore types is disclosed which involves subjecting a slurry of the ore to a simultaneous leaching and cementation process with a reagent such as an alkaline cyanide solution providing for the leaching requirement and a reducing metal affording cementation. The reducing metal is selected from the group consisting of cadmium, copper, iron, lead, molybdenum, tin, zinc and alloys and mixtures comprising at least two of these metals. The simultaneous leaching and cementation occur under conditions controlled to afford at least partial dissolution of the precious metal values from the ore, whereby continuous transfer of these values from the ore onto the surface of the reducing metal is promoted. The resultant cementation product, i.e., the reducing metal with precious metal values cemented thereon, is separated from the ore slurry and subjected to a subsequent precious metal recovery step by conventional methods.