Waste slag from the phosphoria phosphate formation in Utah, Idaho, and Montana contains one of the nation's largest reserves of uranium. Large quantities of phosphate slag was premised in pretreatments and fluorite from before solidifying. By appropriate pretreatment, it was anticipated to stimulate selective leaching of valuable constituents at low acid consumption. In this project, the mechanisms of leaching were identified by analysis of leaching kinetics. The change in mechanisms associated with slag pretreatments were identified and quantified in terms of mass transfer, solid-state diffusion, and chemical reaction rates. A kinetic leaching model was used to predict treatments that were potentially economical. Although this research did not show that the economics of dilute acid leaching are favorable, it does point toward some innovations.