Review A review of acid leaching of uraninite Suresh K. Bhargava a, ⁎, Rahul Ram a , Mark Pownceby b , Stephen Grocott c , Bob Ring d , James Tardio a , Lathe Jones a a Centre for Advanced Materials and Industrial Chemistry (CAMIC), School of Applied Sciences, RMIT University, GPO Box 2476, Melbourne, VIC 3001, Australia b CSIRO Process Science and Engineering, Bayview Avenue, Clayton, Victoria 3168, Australia c Rio Tinto Technology and Innovation, Research Avenue, Bundoora, VIC 3083, Australia d ANSTO Minerals, Lucas Heights, Sydney, NSW 2032, Australia abstract article info Article history: Received 6 June 2014 Received in revised form 27 October 2014 Accepted 29 October 2014 Available online 4 November 2014 Keywords: Review Acid leaching Uraninite Uraninite is mined/processed more than any other uranium mineral for the production of uranium based com- pounds that are subsequently used to produce nuclear fuel. This review article provides a concise account of the available literature on one of the major processes involved in processing uraninite bearing ores, acid leaching. Improvements in the processes used to leach uraninite are required in order to ensure efficiency in the processing of lower grade uraninite bearing ores with minimal environmental impacts. This in turn requires improvements in our understanding of uraninite leaching. The main topics covered in this review include: uraninite structure, composition and low temperature geochemistry; the chemistry of uraninite leaching; key factors that influence uraninite leaching; and leach process technologies. The research that has been reviewed clearly establishes the influence of parameters such as temperature, acid concentration and particle size. The influence of other param- eters however, such as solution Fe 3+ to Fe 2+ ratio (solution E h ), total Fe concentration, foreign ions present in the leach slurry and uraninite composition is yet to be established. Based on the literature available on the aforemen- tioned factors the chemistry/processes involved in uraninite leaching are quite complex and require significant further studies. From the literature reviewed it is clear that variations in mineral chemistry in individual ore types across multiple deposits also make it essential that before any extraction process is considered, detailed ore characterisation studies of pre- and post-leach residues are of vital importance in order to fully understand the interrelationship between chemistry, mineralogy (ore and gangue), mineral liberation and potential leaching behaviour of uranium. © 2014 Published by Elsevier B.V. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2. Uraninite: occurrence, structure, composition and low temperature geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.1. Occurrence (genesis) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2. Structure and composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.3. Uraninite low temperature geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3. Acid sulfate leaching of uraninite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.1. Uraninite redox chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.1.1. Effect of E h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.1.2. Effect of Fe 3+ , Fe 2+ , Fe 3+ /Fe 2+ and Fe TOT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.2. Leaching of natural uraninite and synthetic uraninite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.1. Effect of foreign ions released from gangue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.2. Effect of substitutional impurities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.2.3. Effect of acid concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.2.4. Effect of temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3.2.5. Effect of grain size, liberation, metamictisation and pulp density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 3.2.6. Effect of other uranium bearing minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Hydrometallurgy 151 (2015) 10–24 ⁎ Corresponding author. Tel.: +61 3 9925 3365. E-mail address: suresh.bhargava@rmit.edu.au (S.K. Bhargava). http://dx.doi.org/10.1016/j.hydromet.2014.10.015 0304-386X/© 2014 Published by Elsevier B.V. Contents lists available at ScienceDirect Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet