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Municipal solid waste incineration (MSWI) bottom ash contains economically significant levels of silver and gold. Bottom ashes from incinerators at Amsterdam and Ludwigshafen were sampled, processed, and analyzed to determine the composition, size, and mass distribution of the precious metals. In order to establish accurate statistics of the gold particles, a sample of heavy non-ferrous metals produced from 15 tons of wet processed Amsterdam ash was analyzed by a new technology called magnetic density separation (MDS). Amsterdam's bottom ash contains approximately 10 ppm of silver and 0.4 ppm of gold, which was found in particulate form in all size fractions below 20 mm. The sample from Ludwigshafen was too small to give accurate values on the gold content, but the silver content was found to be identical to the value measured for the Amsterdam ash. Precious metal value in particles smaller than 2 mm seems to derive mainly from waste of electrical and electronic equipment (WEEE), whereas larger precious metal particles are from jewelry and constitute the major part of the economic value. Economical analysis shows that separation of precious metals from the ash may be viable with the presently high prices of non-ferrous metals. In order to recover the precious metals, bottom ash must first be classified into different size fractions. Then, the heavy non-ferrous (HNF) metals should be concentrated by physical separation (eddy current separation, density separation, etc.). Finally, MDS can separate gold from the other HNF metals (copper, zinc). Goldenriched concentrates can be sold to the precious metal smelter and the copper-zinc fraction to a brass or copper smelter.

Abstract:The industrial implementation of Magnetic Density Separation (MDS) in the recycling of raw materials requires more than just the science of understanding why it works ('know-why') and the technology of how that can be accomplished ('know-how'). In addition, detailed knowledge of the market for streams of end-of-life products (supply side) and the market for recycled raw materials (demand side) are paramount to optimize the practical implementation and the design of an industrial plant. Indeed, in such a plant MDS is used to separate mixed streams of recycled materials into product streams which comply with market demands on grade and purity of the product compared with virgin streams. A recently developed non-linear innovation model is used to connect four fundamental cycles which continuously interact in the process of turning MDS technology into green business. The strength of this Cyclic Innovation Model lies in connecting technical capabilities with societal market needs. Only when a good match between the two is found a new technology such as, MDS develop into an innovation. The separation of polyolefins from end-of-life product is selected as one of the first industrial-sized applications of MDS in recycling. CIM is used to identify opportunities and challenges which need to be addressed to turn the MDS technology into an innovation that builds an economically attractive business in the context of a green society.

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In view of the predicted diamond shortage in 2010, a number of innovative processes have been proposed recovering <2 mm diamonds which are currently lost in tailings. One of these innovations is based on the ferrohydrostatic separation (FHS) as developed by De Beers. This new method, known as magnetic density separation, creates an apparent density range inside a ferromagnetic fluid in order to create multiple density fractions in a single process. Results of lab-scale experiments separating a mixture of orthoclase, calcite, olivine and ilmenite are presented. In this mixture olivine represents the diamond fraction. Orthoclase and calcite simulate the lighter density minerals while ilmenite represents the heavy density fraction.