Pilot Plant for Metal Recovery from Flotation Tailings

Processing residues and waste rock are prominent features of mining activities. Especially flota-tion tailings lead to huge land consumption and are a potential source of environmental hazards. In addition, their geotechnical handling is very challenging. On the other hand, the tailings often comprise remains of valuable metals, which more and more came into the focus of scientific investigations and technology developments due to decreasing metal concentrations in the raw ores. G.E.O.S. engaged in the metal recovery from tailings in the frame of several projects with different partners. The scientific approach in these projects concentrated on combination of metal recovery with the removal of contaminants. In the ideal scenario the residues from these approaches can be utilized for underground backfilling or dump construction. So these projects can be regarded as a holistic approach for remediation. Based on laboratory scale results a pilot plant for metal recovery from flotation tailings was developed which comprises several mod-ules.
The first project concentrated on bioleaching of flotation tailings material from an old Freiberg Pb-Zn-ore processing facility (closed in 1968) by an airlift reactor (100 L). As a result, up to 90 % In and almost 100 % Zn were leached from the material which showed initial concentra-tions of 14 ppm In and 10,000 ppm Zn. In another project together with Polish partners an am-moniac leaching process for processing of carbonatic tailings material from Cu concentrate flota-tion was developed. By leaching untreated homogenized tailings material a Cu recovery of 45 % was achieved. After pre-concentration of the material through re-grinding and flotation the re-covery could even be increased to 85 – 90 %.
Motivated by these results a pilot plant was designed consisting of three modules: a) leaching module, b) metal recovery module and c) environmental module. The leaching module compris-es a 1.5 m³ airlift reactor, one decanter centrifuge for effective solid/liquid separation and sever-al stirring and storage tanks needed for continuous process operation and for washing the leach-ing residue. In the metal recovery module (feed 5-10 L/h) are integrated as main processing stages: solvent extraction, absorber columns (activated carbon, IX resin) and one electrolysis cell. Iron can be precipitated as schwertmannite or ferrihydrite (biological/chemical oxidation). The environmental module is designed as classical precipitation, flocculation and sedimentation unit for treatment of remaining liquids from the metal recovery module to meet the discharge parameters. The pilot plant is currently under construction. The commissioning is planned for May 2019.