While the composition of solutions encountered by the mining and concentrate processing industries is more complicated than that of a chemical process stream, global supplier of advanced technologies for purification Dow Water & Process Solutions believes that schemes should be developed that will allow recovery of some of the high-value platinum-group metals (PGMs) for greater profits and lower levels of metals in wash streams.
The company emphasises that, as the price of PGMs continues to soar as a result of new applications emerging and growing, uncertainty in financial institutions is driving demand for tangible assets. Some of the metals comprising PGMs, that were previously not of commercial interest, represent significant value.
Dow Water & Process Solutions researchers Robert Goltz and Matt Rodgers have found that PGMs have a unique chemistry that can be harnessed for selective separation from other metals using anion exchange resins that pull these halo anions out of solution for further refinement and separation by using a very concentrated acid or other complexing agent like thiourea.
Goltz and Rodgers note that the chemical processing industry has, for a number of decades, been using PGMs as catalysts for different processes and reactions. However, these catalysts often leach the PGMs off the support and into the product stream, out of the downstream pipes and equipment or in wash streams. They stress that the development of recovery schemes for these PGMs is important to the viability of these chemical processes.
Goltz and Rodgers have found that some plating operations produce sludge and waste that contain low levels of PGMs and, when dissolved under acid conditions, valuable metals such as platinum, palladium and rhodium can be recovered from these strongly acidic solutions. They add that the data indicates an almost complete removal of these metals in the presence of significant concentrations of copper and zinc, with negligible loading of other metals.
Further, they say, the data indicates that the very high selectivity that the resin has for PGMs, over the copper, nickel, zinc and iron present, makes recovery of the metals by ashing practical and cost effective, ensuring that less of it ends up in wash streams.