Reagent selection for recovery of nickel and cobalt from nitric acid nickel laterite leach solutions by solvent extraction

© 2015 Elsevier Ltd. All rights reserved.There is currently no commercial process for recovery of nickel and cobalt from a nitrate-based laterite leach liquor via solvent extraction. Such a process is becoming of interest as nitric acid leaching of nickel laterite ores is progressed by Direct Nickel. Although commercially proven solvent extraction processes do exist for nickel and cobalt extraction from sulphate-based laterite leach liquors, little is known regarding their application to nitrate-based liquors. In the present paper three different solvent extraction systems are compared from a commercialisation standpoint in order to inform future process development. These systems were: neodecanoic acid (Versatic™10)/tributylphosphate (TBP), Versatic 10/pyridine carboxylate (PC), and an aliphatic hydroxyoxime based extractant (LIX®63)/Versatic 10/PC. On the basis of acceptable separation of nickel and cobalt from manganese and magnesium, and ease of metal stripping, the synergistic combination of Versatic 10 and a pyridine carboxylate (in this case nonyl-4-PC) was identified as the most promising system for application to a nitrate-based laterite leach liquor

The use of pyridine derivatives as accelerators in the solvent extraction of nickel from a nitrate matrix by LIX®63/Versatic™10

Direct solvent extraction (DSX) for the purification of nickel and cobalt from laterite leach liquors is an attractive alternative to precipitation of an intermediate product. With commercialisation of the Direct Nickel nitric acid leaching process, application of this technology to high magnesium bearing nitrate liquors has become of interest. The combination of the hydroxyoxime LIX®63 and the carboxylic acid Versatic™10 results in synergistic extraction of nickel and cobalt and can selectively remove these metals from calcium and magnesium. Nickel stripping, however, is particularly slow. Previously, the accelerator tributylphosphate has been used to increase the rate of nickel stripping. Unfortunately, a high concentration is required which detrimentally increases the required pH for nickel extraction. Pyridine derivatives combined with Versatic 10 also result in synergistic extraction of nickel and cobalt with reasonable stripping rates, although at higher extraction pH and with poorer separation from calcium. The combination of the three reagents (LIX 63, Versatic 10, and a pyridine derivative) was therefore investigated to determine if high metal separation and reasonable nickel stripping rates could be achieved in the same system. Nonyl-4-pyridine carboxylate at lower concentrations than required with tributylphosphate resulted in faster nickel stripping and extraction when using LIX 63/Versatic 10 without impacting nickel extraction pH. A statistical experimental design was subsequently used to model the effects of the reagent concentrations in the tertiary system on nickel and cobalt extraction and to determine optimum reagent concentrations

Reagent Degradation in the Synergistic Solvent Extraction System LIX®63/Versatic™10/Nonyl-4PC

Direct solvent extraction of nickel and cobalt from nitrate-based leach liquors has become of interest due to the successful piloting of nitric acid processes for treating nickel laterite ores. The current study investigated the stability of both hydroxyoxime and nonyl-4PC (nonyl-4-pyridine carboxylate) in LIX 63/Versatic 10/nonyl-4PC under conditions relevant to the recovery of nickel and cobalt from a nitrate-based leach liquor with stripping into sulfuric acid. Nonyl-4PC increased both the rate of hydroxyoxime degradation under the pH 1.5 extract conditions required for a potential nickel–cobalt separation process and the rate of cobalt poisoning of LIX 63. Under strip conditions and the pH 4 extract conditions required for co-extraction of nickel and cobalt, nonyl-4PC did not otherwise affect the rate of hydroxyoxime loss. Additionally, the presence of nitrate anions did not increase the loss of either hydroxyoxime or nonyl-4PC. The combination LIX 63/Versatic 10/nonyl-4PC therefore appears prospective for the co-extraction of nickel and cobalt at pH 4 from nitrate-based leach liquors

Geometallurgy of uranium deposits

Mineralogical controls exert significant control over the extraction of uranium from its ores. Uranium speciation, associated mineralogy, deportment and uranium mineral availability are all factors for consideration when assessing leachability. This study presents data from laboratory uranium extractions undertaken on several contrasting uranium ores from a wide range of orebodies. The results provide insight into the mineralogical factors of importance when considering uranium extraction. These results are presented within the wider context of geometallurgy and demonstrate how geometallurgical assessment, even at an early stage of mine development, can greatly assist in the design of a suitable extraction scheme