LEACHING OF COBALT BEARING NICKEL SULFIDE AND FURNACE CONVERTER MATTES WITH ALKALINE GLYCINE, AND SUBSEQUENT SX AND IX

摘要

The paper presents the outcomes of exploratory research relating to the leaching of nickel and cobalt from Western Australian nickel-cobalt sulfide concentrates and smelter mattes, and the subsequent recovery and separation using solvent extraction (SX) and ion exchange (IX) using alkaline glycine solutions in mildly oxidizing environments. The results set an important foundation for direct leach approaches, particularly if upstream opportunities are considered (heap leach, in-situ leach, or vat leach, or bulk ore leach) from low grade Ni-Co resources. The results for cobalt are particularly exciting given the low recovery of cobalt in most smelting operations and the loss of cobalt to converter slags in conventional approaches. High extractions (90% for nickel and 83% for cobalt) from concentrates containing around 15% Ni and 0.3% Co were possible at room temperature using conventional bottle rolls over a 20 day period. Extractions of nickel and cobalt was around 60% and 55% after 48 hours. The concentrate contained cobalt-bearing pentlandite as the predominant Ni-Co mineralization, with pyrrhotite, pyrite, mica, garnet and talc as the predominant gangue minerals. It was found that running at milder alkaline pH (pH of 9) gave significant better leach extraction than operating at higher pH's (pH of 11) which is opposite to the behavior of copper sulfides (such as chalcopyrite, which tend to show improved leach kinetics at pH 10-11). This is convenient, given the difficulty of operating at high pH in Western Australia where high and hyper salinity leads to pH buffering around a pH of 8.9. It was also found that preoxidation of the concentrate proved to be detrimental (again opposite behavior to copper sulfide concentrates) and that the milder oxidizing conditions in a conventional bottle roll appeared to be optimal. The long leach times to achieve good recoveries implies that the leach approach is more suitable for an alkaline heap leach environment (assuming sufficient exposure of the cobalt bearing pentlandite) rather than a tank leach of the concentrate. Should concentrates be targeted, a concentrate coated gravel heal leach may be considered (compare with GEOCOAT? technology). Excellent extractions were also achieved of Ni and Co from furnace matte and converter matte. Direct leaching of granulated furnace matte has the potential of eliminating many of the logistical challenges around the converting aisle in the smelter and the batch nature of running converters with associated fugitive emissions and unsteady state SO2 gas evolution. In all cases (concentrates and mattes) the dissolution of iron, magnesium, silicon, manganese and other impurities were insignificant (low ppm range), significantly simplifying downstream recovery from solution and base metals refining. This is particularly important for iron removal which would normally have posed a significant solid-liquid separation and waste disposal cost. Excellent recovery from solution and separation of cobalt from nickel were achieved in both solvent extraction and ion exchange to produce the metals as concentrated nickel sulfate and cobalt sulfate solutions (using a conventional acidic strip). The bench scale results provides a basis to investigate nickel and cobalt recovery from various sulfide resources using a benign alkaline leach technology using non-toxic, non-volatile and cost effective reagents, where the reagents can be recycled to the leach after resetting the pH.