The leaching of uranium from betafite

Betafite is a uranium-titanium-tantalum-niobium complex oxide mineral generally described as (Ca,U)(2) (Ti,Nb,Ta)(2) O-6 (OH). Significantly lower uranium extractions have been observed when betafite containing ores has been treated via conventional process flow sheets. Therefore it is necessary to understand the leaching behaviour of this mineral in order to open the potential for it to become an economic source of uranium in the future. The leaching kinetics and reaction mechanism of uranium from a natural, metamict betafite sample have been investigated using varied temperature under oxidative acidic conditions. The practically complete extraction of uranium was observed by leaching the natural betafite in a solution containing 214.5 g/L H2SO4 and 2.0 g/L Fe3+ at 89 degrees C for a period of 48 h. Alternative leaching conditions using 57.1 g/L H2SO4 and 36.7 g/L Fe3+ at the same temperature also resulted in practically complete extraction of uranium but improved the selectivity for uranium over titanium, tantalum and niobium. Kinetic modelling has indicated that the rate of the leaching process is controlled by the rate of diffusion of products or reactants involved in the dissolution reaction to the reacting surface through a solid product layer containing niobium. A portion of the betafite mineral sample used in the leaching testwork was rectystallised by heating in air at 1100 degrees C. The crystalline form of betafite was then leached under conditions similar to those applied to the metamict mineral to determine how crystal structure may affect the extraction of uranium. Less than 12% uranium was extracted from the recrystallised betafite under the conditions that gave practically complete extraction of uranium from the natural betafite sample which gives strong evidence that heat treatment prior to leaching should be avoided. The thermal recrystallisation of betafite in the present study appears to have resulted in tantalum enrichment on the surface of the betafite particles, which may be related to the lower extraction of uranium observed. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.