The Leaching of Palladium from Polymetallic Oxide Ores using Alkaline Ferricyanide Solutions

The present study investigated a novel method of alkaline ferricyanide leaching to extract palladium (Pd) from a Western Australian disseminated platinum-group metal (PGM) oxide ore that bears Ni and Cu. While cyanide has been used to leach Pd, it is well known for its toxicity and large consumption in the presence of base metals. A more benign alternative, in the form of alkaline ferricyanide, is evaluated in this research to serve the combined role of lixiviant and oxidant. Various leaching parameters, such as ferricyanide concentration (1-30 g/L), dissolved oxygen level (up to 25 ppm), pH (10-12), and temperature (20-80 & DEG;C), were investigated to evaluate Pd extraction. The Pd extraction was found to be the most sensitive to leach temperature with Pd extraction doubling when the temperature was raised from 20 & DEG;C to 80 & DEG;C. The highest Pd extraction of 76.1% was achieved at 10 g/L ferricyanide, pH 11, DO 15 ppm, 80 & DEG;C, and 10% solids. The alkaline ferricyanide leaching system showed high selectivity for Pd over other metals (Pt, Co, Ni, Cu). The co-extractions of base metals (Co, Cu, and Ni) were all below 2%, and that of Pt was below 10% over the range of temperatures investigated. Although conventional cyanidation at a low cyanide consumption (1 kg/t) showed slightly better performance in Pd extraction, the ferricyanide leaching significantly improved the settleability and filterability of the leaching slurry considering the finely ground nature and high-clay content of the lateritic oxide ores. In contrast, the cyanidation leaching slurry was found to filter or settle poorly.

Automated summary

The study explores a novel method of alkaline ferricyanide leaching to extract palladium (Pd) from a platinum-group metal (PGM) oxide ore containing Ni and Cu in Western Australia. The alkaline ferricyanide acts as both a leaching agent and an oxidant. Various parameters such as ferricyanide concentration, dissolved oxygen level, pH, and temperature were investigated, and the results show that Pd extraction is most sensitive to leach temperature. The alkaline ferricyanide leaching system exhibits high selectivity for Pd over other metals and significantly improves the settleability and filterability of the leaching slurry.