The solvent extraction and stripping of chromium with Cyanex~R 272

摘要

Solvent extraction following pressure acid leaching (PAL) is becoming the technology of choice for treating nickel laterite ores as it allows high recoveries of both the nickel and cobalt from these ores. Early plant experience, however, indicate that impurity control particularly in the solvent extraction stage still hinders full optimisation of this technology. Dissolved chromium, both as chromium(III) and chromium(VI), is one of the major impurities of PAL-generated pregnant leach stream (PLS) and little is known about its solvent extraction behaviour with Cyanex~R 272, the predominant extractant for the separation of nickel and cobalt. Only a few studies have been reported and with apparently conflicting results. This study investigated the solvent extraction behaviour of chromium with Cyanex~R 272. The effects of various experimental variables such as the metal oxidation state; pH; presence of anions such as nitrate, chloride, sulphate and acetate including the conditions of extraction relevant to the separation of nickel and cobalt directly from the partially neutralised PLS as well as the effect of the extracted species on stripping are discussed. The nature and forms of the extracted species are inferred from slope analysis and UV-VIS spectroscopy data.