This paper (re Panton Sill) provides some insight on the met challenges that POD faces. Guess this is why the team continues to look for a scaleable hydromet leach process.
Flotation recovery from PGM bearing ores depends on the mineralogy of the ore and the way the deposit is formed. From the beneficiation point of view, PGM-bearing ores can be classified into the following categories: (1) Deposits of magmatic origin, where the PGMs are associated with base metal sulphides, typical deposit: Merensky Reef in South Africa; (2) Chromium deposits containing PGM minerals, where the relationship between chromium, the PGMs and the type of PGM minerals in these deposits depends largely on the geological environment. Therefore, the processing characteristics of these ore types are quite variable; (3) High chromium oxidized PGM ores, these ores are found in Brazil and Australia. These ores belong to a group of highly refractory ores and usually give poor concentrate grade and PGM recovery. The PGMs are either associated with oxidized sulphides (pyrite, nickel), or partly present as PGM alloys (Bulatovic, 2003; Chapman et al., 2011).
***** The remoteness of the site, the size of the deposit, and the challenges to produce high-grade, low-chromite flotation concentrates suitable for smelting, has initiated research into hydrometallurgical extraction options as processing alternatives.
From an economic perspective, it is important to find a suitable method to extract all the PGMs and precious metals (gold). Whilst palladium and gold were found to be less problematic for most lixiviants, platinum minerals are often much more refractory. In particular, sperrylite (PtAs2) has been found to be refractory to direct leach approaches. Sperrylite is the dominant Pt-bearing mineral in the PGM-enriched chromitites and accounts for about 55.31% of the Pt in Panton Sill Deposit. Therefore, it is crucial from a financial feasibility perspective that a suitable lixiviant be found that can leach sperrylite.
During the course of 2019, a new method was developed to process the flotation concentrate with conventional roasting followed by HCl/NaCl/H2O2 leaching, and the results showed almost all the PGMs were leached. In this leaching system, hydrogen peroxide (H2O2) was used as the oxidizing agent, hydrochloric acid (HCl) was used as the leaching agent and sodium chloride (NaCl) was employed to provide chloride ions (Cl−) for PGM complexing. The results show that increasing the percent solids of the leach slurry up to 25% didn’t affect the extraction and most of the PGMs were extracted (97% Pt, 90% Pd and 97% Au). Furthermore, the precipitation process demonstrated a good separation of PGMs and base metals from other gangue metals like iron/aluminium.
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