The precipitation of mixed hydroxide is increasingly being considered as an intermediate step in the hydrometallurgical processing of nickel and cobalt. Producers currently receive roughly 75% of the value of the contained nickel and zero value for contained cobalt. In this paper, a new selective leach process for refining the mixed hydroxide is described that allows for recovery of the majority of the nickel as final metal product and realizes value for the cobalt. The features of the new process are compared with two other alternative routes (1) acid leaching followed by solvent extraction of the cobalt and (2) ammonia leaching followed by solvent extraction of the nickel. The outcomes of a process simulation for the selective acid leaching process are presented along with capital and operating cost estimates. The operating and capital costs of the process are estimated to ±50%. For the processing of 50,000 t-Ni/y in the form of MHP, the operating cost is estimated to be $93 million AUD ($0.87 per lb of Ni contained in MHP) and the capital cost as defined for this study is estimated to be $287 million AUD. A new 20 year plant processing MHP would have a payback period of less than 2 years, an IRR of over 60% and an NPV of greater than $1.5 billion AUD. Over 94% of the total value (nickel and cobalt) contained in the MHP is extracted by the new process.
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