The selective leaching of uranium, vanadium and phosphorus from phosphate ore with hydrochloric acid
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states-Idaho, Montana, Utah, and Wyomingcompose the western phosphate field. 80 pct of this field lies in southeastern Idaho, which accounts for almost 35 pct of the U.S. phosphate reserves. In 1975 about four to five million m e t r i c tons of phosphate ore were produced in southeastern Idaho, accounting for 11 pet of the U.S. production.~ T h e r e are five processing plants in southeastern Idaho manufacturing most of this ore into elemental phosphorus, phosphate fertilizers, and animal feed supplements. Two methods are used to process phosphate ores in Idaho, each accounting for about 50 pct of the production. The thermal process involves the reduction of phosphate to elemental phosphorus by coke and quartzite at high temperature in an electric furnace. Another method, the wet acid process, involves the reaction of sulfuric acid with phosphate rock to produce phosphoric acid. Phosphate ore must be upgraded by countercurrent cyclone washing p r i o r to wet acid processing. Frequently, the ()re is also calcined p r i o r to acid treatment. The phosphate ores mined from southeastern Idaho contain high concentrations of t r a c e elements, containing an a v e r a g e of 90 ppm uranium and 0.3 pct vanadium. Vanadium is selectively concentrated by a factor of 1000 in the ferrophosphorus button produced in the thermal process. Uranium concentrates to 120 ppm in the calcium silicate s l a g .2 In o r d e r to understand the problem of by-product recovery from southern Idaho phosphate deposits, it is important to understand the variable nature of the deposits. The phosphate has deposited in layers of different composition and texture, s High P2Os content layers are separated by layers of cherty s h a l e with J. L. CLEMENTS, K. A. PRISBREY, and P. R. TAYLOR are Graduate Student, Assistant Professor of Metallurgy and Assistant Professor of Metallurgical Engineering, respectively, Department of Mining Engineeringand Metallurgy, College of Mines, University of Idaho, Moscow, 1D 83843. Manuscript submitted Jtdy 6, 1979. METALLURGICAL TRANSACTIONS B
low P2Os. Alternate layers, notably those near the surface, have l a r g e amounts of black carbonaceous materials that have seeped homogeneously throughout the matrix. Individual phosphate pellets are surrounded by cherty s h a l e m a t r i x with a variation of shapes.4 Much of the phosphate is coal black due to the presence of organics. The s t r a t a has been heavily faulted, folded, and convoluted so that following one particular l a y e r would often lead a mining venture deep underground. P h o s phate recovery is additionally complicated by failure of most conventional m i n e r a l processing techniques to upgrade the ore. The washing technique used for producing wet acid feed is successful on "weathered" strata only. "Unweathered" s t r a t a are not upgraded sufficiently for wet acid processing despite high P20~ content. This is apparently due to the preferential grinding of softer phosphate pellets into s l i m e size fractions too fine for recovery in the washi
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