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::Nano Approach adds Value to Waste Materials
Urban mining: it’s an idea whose time has not yet come, in Australia at least. But Dr Seng Lim from CSIRO’s Future Manufacturing Flagship says there are higher concentrations of some precious metals in urban landfills than there are in raw ore deposits.
While the science, infrastructure and processes involved in mining new orebodies are all reasonably well established, the same is not so for the recycling or mining of new-age electronic wastes for their valuable metals. Yet this is where significant quantities of gold, platinum, palladium, silver and indium can be found, often buried amid other more hazardous materials including lead, chromium and mercury.
Dr Lim is involved in the development of a new class of mineral-based nanoparticle products, which he believes may provide the potential financial incentive needed to encourage the recovery of these valuable metals from waste.
He says by attaching rare minerals (in the form of metal oxides) as nanoparticles to a larger micron-sized substrate it is possible to improve the functional performance of powdered substrate products such as alumina, silica or iron. The process also adds significant value to a comparatively cheap substrate.
The powdered substrate might be worth anything from $10 per tonne to several hundred dollars per tonne, but could be transformed into a product worth hundreds of dollars per kilogram with a rare metal nanocoating.
Adding a number of different nano-layers could further enhance the functionality of particles and new products. CSIRO’s research has developed techniques to both create and apply the nanoparticles to substrates in a single pass, greatly improving the manageability and handling of typically nano-based materials.
Dr Lim says manufacturing and consumer markets are driving much of the research to improve the functionality of products. One example is silver oxide nanoparticles incorporated into clothing and medical bandages as an antibacterial agent and to reduce odour.
Another is extending the life of catalysts for industrial applications. “By attaching the valuable active metal as nanoparticles we effectively provide a greater surface area and functionality, and this is where the chemical reactions occur, so it significantly increases the performance of the chemical processes," Dr Lim says.
He says many products being developed from “new materials” could just as easily be made from recycled metals. This would transform mining or industrial residues and salvaged electronic waste into new highly-valued, highly functional materials.
Dr Lim believes these value-adding opportunities could help to underpin formal product stewardship processes incorporating recycling in the electronics industry, as well as extending limited resources of rare metals. China has already restricted the mining of a number of rare minerals including indium, which is widely used in display electronics such as televisions. “If we can create value in waste materials, through a value-added application, then economic forces will make people look for them," Dr Lim says.
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