Recycling valuable metals from wastes by means of mechanochemical processing

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A new process composed of co-grinding and subsequent water leaching to recover rare metals from various types of waste has been developed by means of mechanochemical treatment. A solid state reaction is stimulated by co-grinding the rare-metal-containing waste with additives to transform the state of target metals into a feasible state for easy recovery, water leaching for example. Additive for co-grinding is chosen based on the existing state of target element.In 2003, a research target was put at the recovery of cobalt from cathode material of secondary battery by grinding with PVC to form chlorides through the mechanically stimulated solid state reaction. The metal is recovered by leaching the ground sample with water due to the easy dissolution of chlorides in water.In 2004, an effort is put on the treatment of waste catalysts from oil refinery industry where sulfides of molybdenum, vanadium, cobalt and nickel are used. Oxidization of these sulfides was tested by co-grinding them with CaO without heating. It has been found that it is possible to oxidize these sulfides. The formation of calcium molybdate or vanadate leads to the low yields when water leaching these ground sample.In 2005, manganese dioxide (MnO_2) was used as additive. Co-grinding sulfides with MnO_2 and sodium carbonate results in the formation of sodium molybdate and vanadate, which are easily dissolved in water. Several experimental parameters such as grinding time, adding molar ratio have been tested and the optimum experimental conditions have been determined to obtain recovering yield as high as 90% for molybdenum. After water leaching, leaching with acid solution can be applied to leach cobalt and nickel. Further leaching with alkali solution is applied to recover vanadium. The potential for practical application is under discussion with related company and contribution of the mechanochemical processing is expected to sustainable supply of rare metals.