In the age of environmental responsibility, old cars no longer rust away disgracefully, overgrown by weeds in remote country paddocks. Today they disappear into the jaws of huge shredding machines in metal recycling plants, along with broken washing machines, refrigerators and other metal wastes.
The recycling plants recover the bigger bits of metal, but produce large amounts of difficult sludge that is usually sent to landfill. Along with lots of water the sludge contains a mess of small bits of steel, copper, brass, solder and aluminium, mixed with vinyl and other plastics, synthetic fibres, fabric, rubber, glass, quartz and wood.
CSIRO Minerals' Warren Bruckard turned to minerals processing techniques for ideas to tackle the sludge. His team carefully analysed the sludge physically and chemically.
"We found every tonne of dry sludge contained about 3.1kg of recoverable copper and about 33kg of clean steel," says Mr Bruckard.
"While it's good to recycle as much as we can, the recovered materials are fairly low in value and so any process we develop needs to be simple and cheap."
The method developed involves using a sorting process to remove plastic, rubber and other low-density, non-metallic stuff, then magnetic separation to recover clean steel, and finally a gravity technique to separate low-density materials like glass from high-density metals like copper, lead and brass.
The full story can be found in the February issue of Process, available at http://www.minerals.csiro.au/processfeb05.
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For more information on Process please contact:
Meg Rive, Editor
+61 03 9545 8614
+61 0438 007 301
meg.rive@csiro.au