Mobility of platinum-group elements during weathering processes

Begin of project: March 1, 2012

End of project: February 28, 2015

Status of project: September 1, 2014

Platinum-group elements (PGE) form a group of rare and precious metals. These metals are ruthenium, rhodium, palladium, osmium, iridium and platinum and are mostly associated with deposits of chromite and Fe-Ni-Cu sulfides. Platinum-group elements have similar chemical and physical properties and are important resources for industry and technology. The main application areas for PGE are catalysts in the automobile industry as well as jewelry and electronic industry. Therefore, PGE are of enormous significance for the German economy. More than 70 percent of the world’s resources of PGE occur in the Bushveld Complex in South Africa. In this gigantic rock body PGE are mined from three ore bodies: the UG-2 chromitite, the Merensky Reef and the Platreef. PGE grades in weathered rocks overlying these primary PGE ores are of economic interest. However, recovery of the PGE from oxidized ores is poor, because the mineralogical siting of the PGE in weathered rocks is poorly known and conventional methods of recovery often fail. Therefore, oxidized PGE ores are stockpiled and not further processed at the moment.

In the project “mobility of platinum-group elements during weathering processes”, field and laboratory work are complemented by experimental studies on the solubility of PGE, and the precipitation of PGE at conditions close to the Earth surface, including the influence of organic materials. The principal objective is to understand the mechanisms responsible for PGE remobilization during weathering processes. The final goal is to model PGE mobilization in different mineralogical associations (chromite-, sulfide-hosted) during tropical/subtropical weathering. This knowledge will allow predicting mineralogical associations in oxidized ores and that in turn will help optimizing mining strategies and recovery plants. In order to obtain this goal, rock samples from fresh and weathered PGE ores from the Platreef in the northern Bushveld Complex are studied in detail. The Platreef is an up to 400 meter thick ore body mined by open-pit mining operations. Additional to the work at the BGR, German universities are involved with the investigations of PGE ores from the Bushveld Complex. At the Martin-Luther-University Halle-Wittenberg fresh and weathered ores from the Merensky Reef are studied in detail. Further, at the Jacobs University in Bremen, selective leaching experiments are applied on PGE ores in order to significantly increase the recovery rates of PGE from weathered PGE ores.

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