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:: Old Gold Tailings Power Solar Energy's Future
Tailings from Australia's gold-rush could help a Victorian company strike it rich in a modern-day venture to produce speciality, high-value feedstocks that could be used in solar-grade silicon production. If successful, the work has the potential to increase solar energy use.
Creswick Quartz already recovers quartz (SiO2) from the waste tailings of late 19th century alluvial gold mines and supplies it as architectural-quality quartz to landscape and construction industries and to niche markets.
These quartz deposits - at Creswick, west of Melbourne - are of a high quality with low impurity levels, giving the company the option to produce higher quality quartz for use as feedstock in pure silica and silicon production. It is a possibility Creswick Quartz has been exploring with the Minerals Down Under Flagship.
Leading the project is CSIRO scientist Dr Hal Aral. He says the goal is to develop a commercially viable and environmentally sustainable quartz-purification process that produces metallurgical and solar grade silicon feedstock, all from the waste tailings of Victoria's early gold industry.
The purification process has the potential to lead to cheaper silicon solar cells - something that depends critically on the availability of inexpensive solar grade silicon feedstock - and, with that, increase solar energy use.
Already, physical and chemical treatment is showing that the research team can produce various particle sizes that are 99.995 per cent pure silica, a step towards the goal of 99.999 per cent pure silica that is needed for solar-grade silicon production.
Silicon (Si) occurs naturally in many silicate minerals, but the most important source for silicon production is quartz. With the right processes, Creswick Quartz could supply high-quality, fine-particle sized (down to 10 to 20 microns) and lump (20 to 80 millimetre) quartz suitable for both metallurgical and solar-grade silicon production.
Metallurgical-grade silicon usually has a purity of 98 to 99.5 per cent, mostly because the purity of the quartz feedstock is low.
However, Creswick's inherently high purity lump quartz has an advantage over many. It is low in boron, phosphorus and lithium and is suited to ultra-high metallurgical-grade silicon production.
Solar-grade silicon - at 99.999 to 99.9999 per cent pure silicon - is manufactured from scraps of semiconductor-grade silicon which, in turn, is produced from metallurgical grade silicon. Semiconductor-grade silicon processing includes chlorination and complex downstream work, which Dr Aral says is tedious and expensive, eventually making the final cost of silicon products very high.
Additionally, the demand for solar grade silicon is now greater than the amount of scrap the electronics industry can supply. It means the industry is looking for high-purity, fine-particle-sized feedstocks for solar-grade silicon production.
Creswick Quartz CEO Chris Karamountzos says the company has been busy extensively drilling to expand its existing reserves in order to meet increasingly global demand for feedstock. For the research team, the next stage is to demonstrate the CSIRO-developed physical and chemical treatment processes at a large scale.
Dr Aral says his team wants to create a process that produces high-purity feedstocks and which also uses less energy and produces less greenhouse gases than existing processes.
The work is an example of how researchers and industry are working towards a new level of sustainability, he says. "The aim is to convert old mining tailings into new, high-value feedstocks."
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