An investigation on the effects of several anions on the dissolution of synthetic uraninite (UO 2 ) Rahul Ram, Fiona Charalambous, Scott McMaster, James Tardio, Suresh Bhargava ⁎ Centre for Advanced Materials and Industrial Chemistry Centre, School of Applied Sciences, RMIT University, GPO Box 2476, Melbourne VIC 3001, Australia abstract article info Article history: Received 24 August 2012 Received in revised form 27 February 2013 Accepted 18 March 2013 Available online 3 April 2013 Keywords: Uraninite dissolution Effect of anions Uranium ore gangue minerals With the increase in the demand for energy, there is an increased interest in nuclear power sourced from a number of uranium minerals, primarily tetravalent UO 2 . During the leaching of uranium from its ores, a number of gangue minerals are leached which lead to a number of different ions in the leach slurry. The current work undertaken focused on the effect of anions that typically leach from gangue minerals found in uranium bearing ore bodies on the dissolution of synthetic UO 2 . The anions studied were F - , Cl - , Br - , SO 4 2- , PO 4 3- and NO 3 - . Cl - and Br - were found to have no significant influence on UO 2 dissolution over the concentration range studied (0–1.8 g/L Cl - ;0–4 g/L Br - ), whilst F - was found to have a detrimental effect on UO 2 dissolution at low–medium concentration (0–0.3 g/L) and a positive effect on UO 2 dissolution when present in medium–high concentrations (0.5–1 g/L), when compared to the dissolution obtained in the presence of the other halides studied. Of the oxo-anions studied NO 3 - had a positive effect on UO 2 dissolution over the entire concentration range studied and PO 4 3- had a negative effect when present at medium–high concentrations. This was due to precipitation of FePO 4 at medium–high PO 4 3- concentra- tions. SO 4 2- had a negative effect when present at medium–high concentrations. This was most likely due to the formation of less effective Fe III based complexes, where the Fe III species present in solution play an important role in the UO 2 oxidation/dissolution mechanism. Results obtained on the influence of all anions investigated simultaneously are also presented and discussed. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The increasing amounts of electricity that will be required in fu- ture years have led to increased interest in generating some of this additional electricity using nuclear technology. The nuclear fuel re- quired for uranium based nuclear power generators is sourced from a number of uranium minerals. To date the majority of the uranium ores that have been processed have been high grade ores, however continued mining (and the most likely lack of discovery of new high grade ores) will undoubtedly lead to the need to process low grade ores in order to meet ongoing and/or increased future demands for uranium. In addition to the likely future need to process low grade ores, processing of uranium ores more efficiently/economically and with minimal environmental impact is a continuing interest. The primary uranium mineral found in most uranium bearing ore bodies around the world is tetravalent uraninite (UO 2 ). The majority of processes used worldwide to extract uranium from uranium min- erals such as UO 2 involve an acid dissolution step. The acid most com- monly used is sulphuric acid (H 2 SO 4 ) as it typically combines high leach performance and relatively low cost. Although sulphuric acid based leaching of uranium from UO 2 bearing ores has been conducted commercially for a number years there are still aspects of the dissolu- tion process that are poorly understood. One of these aspects is the role that gangue minerals (and species generated through the disso- lution of gangue minerals), which are present in uranium ore slurries, have on the dissolution of uranium minerals such as UO 2 . Based on previous studies that have been conducted on UO 2 dissolu- tion (in solutions containing ferric ion and sulphuric acid) it is widely accepted that the dissolution of UO 2 during uranium minerals process- ing involves the oxidation of UO 2 (by ferric ion) to produce soluble UO 2 2+ . UO 2 2+ subsequently reacts with sulphuric acid/sulphate to form sulphate complexes (Laxen, 1971; Nicol et al., 1975b) according to the following reactions (Eqs. (1) and (2)): UO 2 þ 2Fe 3þ →UO 2þ 2 þ 2Fe 2þ ð1Þ UO 2þ 2 þ 3SO 2- 4 →UO 2 ðSO 4 Þ 4- 3 : ð2Þ During uranium processing Fe containing minerals (typically hematite or magnetite) in the ore produce the ferric ion required, whilst in some cases a source of iron is added to the dissolution pro- cessing step. As mentioned earlier the slurries generated during tank based uranium minerals processing however also contain gangue min- erals which can be attacked by acid and hence release foreign species Hydrometallurgy 136 (2013) 93–104 ⁎ Corresponding author. Tel.: +61 3 9925 3365. E-mail address: suresh.bhargava@rmit.edu.au (S. Bhargava). 0304-386X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.hydromet.2013.03.003 Contents lists available at SciVerse ScienceDirect Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet