The traditional method for recovering platinum-group metals (Pt, Pa, Ir, Os, Rh, Ru and Au) is not economically viable in the case of low-grade deposits, but researchers from the Western Australian School of Mines, Curtin University (Perth; www.curtin.edu.au) and the Dept. of Processing Engineering, Stellenbosch University (Matieland, South Africa; www.sun.ac.za) may have found a cost-effective alternative.
One of the researchers, professor Jacques Eksteen of Curtin University, says the traditional smelting process can be replaced with low-cost leaching. He said: “We found that if we could recover economic levels of platinum metal using heap leaching, then we were able to recover it from solution.”
Platinum-group metals form a complex range of 30 to 40 minerals, each with a different resistance to leaching, making it difficult to find a unique solution for all deposits, explains Eksteen. Once leached, the metals are adsorbed from solution on to activated carbon, he says. The next step is to elute (wash with solvent) metals from the carbon in a concentrated form so they can be released one by one.
The researchers investigated the feasibility of eluting platinum- and palladium-cyanide complexes from activated carbon with the well-known ARRL (Anglo American Research Laboratory) process. The AARL process consists of three steps: a hot acid wash followed by a hot caustic cyanide pre-treatment and afterwards elution with hot deionized water at high pressures (up to 300 kPa). According to the researchers, test results show that effective elution of platinum- and palladium-cyanide with the AARL method is feasible.