Solubilization of phosphate, uranium, and iron from apatite- and uranium-containing rock samples in synthetic and microbiologically produced acid leach solutions

Abstract

The solubilization of phosphate was investigated using apatite and P-containing uranium rock samples in acid solutions. The concentration of soluble phosphate usually increased upon 24-h extraction followed by subsequent precipitation. Uranium solubilization was investigated using leach solutions that contained about 3 g/l ferric iron produced by bacterial oxidation of iron pyrite. 1–94% extraction of uranium was attained within 24h, with the poor recovery associated with a rock sample containing an excessive amount of alkaline material. Reducing equivalents (permanganate-consuming substances) in the acid leach solutions could be oxidized by inoculation with iron-oxidizing thiobacilli (Thiobacillus ferrooxidans). Chemical analysis of iron indicated that most of the iron was in the oxidized form. Stable iron colloids were not present in significant amounts in the leach solutions. Acidic ferric sulfate containing about 6 g/l Fe3+ was also used as a leach solution. Repeated use of the leach solution with rock samples did not decrease the efficiency of the leaching but soluble uranium reached a toxic concentration and thus prevented the bacterial re-oxidation of ferrous iron in the leach solution.