Minerals processing techniques may help save scrap metals.

Tens of thousands of old car bodies, washing machines and refrigerators disappear into huge shredding machines at metal-recycling plants in Australia’s capital cities every year.

Electromagnets pull out the large steel fragments for melting down in electric arc furnaces, and further separation steps remove larger fragments of non-magnetic metals like brass and aluminium.

The separation process leaves large volumes of a watery sludge containing small particles of steel, copper wire, brass, lead and aluminium, mixed with vinyl and other plastics, synthetic fibres, fabric, rubber, glass, quartz, and wood. Recyclers typically send the sludge for disposal in landfill or toxicwaste dumps.

With landfill costs rising, and community opposition to toxic waste dumps growing, Mr Warren Bruckard of CSIRO Minerals has been investigating whether metals recyclers could apply mineral processing techniques – used to concentrate ores in the minerals industry – to recover potentially valuable products from the sludge, while at the same time reducing its volume and toxicity.

Mr Bruckard’s team conducted a detailed analysis of sludge from a recycling plant operated by Smorgon Steel subsidiary Metalcorp Recyclers at Laverton, in Victoria, and determined that it contained about 3.1kg of recoverable copper per tonne of dry feed, and about 33kg/tonne of clean steel.

The proposed process involves hydraulic classifying to remove material such as plastic, foam and rubber; magnetic separation to concentrate clean steel; and gravity concentration in a jig to separate low-density materials like calcite and glass from the high-density metals like copper, lead and brass.

Mr Bruckard said that, at some metal recycling plants, the value of the recovered products could more than offset the cost of installing and operating the add-on process in the future.

He believes metals recyclers will take up this or similar technologies in the future as landfill costs continue to rise, and legislation to regulate toxic wastes becomes more stringent.

For further information contact:
CSIRO Enquiries
Email: solve@csiro.au      Web: www.csiro.au
Tel: 1300 363 400       International: +61 3 9545 2176

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Last Updated: November 11, 2004
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