SOME ASPECTS OF THE MECHANISMS OF SOLUBILIZATION AND INSOLUBILIZATION OF URANIUM FROM GRANITES BY HETEROTROPHIC MICROORGANISMS

Abstract

In batch cultures, complex microflora from granitic mountain mass, promoted solubilization of U in presence of amino-acids as sole source of carbon and energy. Solubilized U amounted up to 100 mg U/1 in presence of microorganisms but was less than 35 mg U/1 in absence of microorganisms (sterile controls). Microflora involved contained different strains of bacteria, Pseudomonas fluorescens, P. putida, Achromobacter, Bacterium, Gaffkya or Peptococcus. In experimental design of factorial type with semi-continuous flow devices, the activity of different microflora from known forest soil was compared. Microflora specifically withstanding partial sterilization and comprising different Pseudomonas Bacillus licheniformis, B. cereus, B. lentus, B. polymyxa, B. megaterium, plus one or two unidentified yeasts promoted significantly microbial solubilization of U by synthesis of complexing agents with high complexing capacity for Al and Fe, but lower complexing capacity for U. But anaerobic microflora induced by waterlogging was much less active as compared by solubilization with control microflora. From the comparison of the different strains involved, Pseudomonas appeared to be the most active. In presence of an "organo-urany1" solution, obtained by adding glutamic or aspartic acids to uranium ore in sterile conditions, different bacteria originating from samples of granitic mountains mass could grow : Achromobacter, Brevibacterium, Acinetobacter, Gaffkya or Peptococcus, Pseudomonas, showing that such microorganisms could contribute to U deposition by metabolising organo-uranium compounds. Leaching and ecological implications of such processes are discussed.