Will TOMRA’s laser-based sorting technology shake up HPQ processing?

By Cameron Perks
Published: Friday, 09 June 2017

Despite HPQ having no standard processing route, there are new technologies which seek to increase sorting capabilities, making it easier for producers to separate their HPQ by impurities, Cameron Perks, IM Correspondent, finds.

High-purity quartz (HPQ) is known for its high-tech applications: from semiconductors to solar silicon applications, HPQ has found its way into various everyday items. 

There is no standard processing route to making HPQ. Depending on end-application and starting-purity, raw quartz is processed into its high-purity form by both off-the-shelf technologies, as well as via tailor-made specialty solutions. 

In the book titled 'Quartz: Deposits, Mineralogy and Analytics’, Dorfner ANZAPLAN’s Reiner Haus, Sebastian Prinz and Christopher Priess, explain how based on the specific characteristics of the quartz deposit, a processing route may be achieved.

In general, a processing route consists of the following main stages: pre-processing (mechanical), physical processing, chemical leaching and thermal treatment. For many, selective mining is where processing begins, and is a common method of sorting out which quartz will qualify for subsequent processing steps. This, as well as costly hand-sorting practices is what optical sorting has set out to replace in recent years. 

According to Haus et al. optical sorting can be applied with high efficiency down to the 3-5mm range. As the name suggests, the method is used to separate quartz fragments containing different optical properties, namely colour. 

Colour is useful, as rose quartz may indicate elevated levels of phosphorous, a deleterious element for solar application. In smoky quartz, elevated radiation levels may indicate the presence of alpha radiation sources uranium and thorium, known to cause soft error in memory devices.

Too many impurities, commonly in the form of aluminium, iron, lithium and phosphorous will lower the end-product melting point risking premature mechanical failure when working at high temperatures, and may contaminate ultra-pure silicon
metal through processes of diffusion and devitrification.

Several other sensor-based sorting systems exist, finding applications in a wide variety of commodities. X-ray and near-infrared technologies are two that can be used in sorting HPQ. X-ray technology enables materials to be recognised and separated based on their specific atomic density regardless of dust coating or surface moisture, while NIR technology scans the reflection characteristics of minerals in the invisible 700-2500 nm wavelengths of light. The nature of this technology means that it require a clean rock surface, achieved by washing, de-dusting or drying or by a combination of these.

TOMRA, a Norweigian based company specialising in sorting solutions for food, recycling and mining industries, looks to have added a new device to the market dubbed as a Multi-Channel Laser sorting technology.

The new system utilises the monochromatic nature of laser light, which ranges in spectrum from invisible ultraviolet and infrared, to the complete spectrum of visible light. Taking advantage of its existing patented food-sorting technology, TOMRA has devised a way to sort rocks and minerals independent of their colour or chemical composition, stating: "The high quality, pure quartz rocks and pebbles can be identified unambiguously and differentiated from the unwanted pieces, even if the impurities are invisible to all the other sensor technologies or even the human eye."  

The method has been tested, with results indicating that "the recovery of valuable rocks could be increased by more than 20%" compared to colour sorting, "while at the same time, the quality of the product is increased" TOMRA told IM.

TOMRA is confident that their technology will benefit mines through a greater recovery rate, resulting in a longer life of mine, allowing less waste and therefor lowering overall costs of production.

Just like in all sorting methods, the economic justification will depend on the operator’s optimum product size, their required throughput volumes, as well as their tolerances for acceptable variation in quality. When IM spoke with TOMRA, their answer to this, presumably like many others, was to tell those considering a sensor-based technology to "try it out" for themselves.

 High-purity silicon metal from low-purity quartz?

In announcement made on 16th  May, Canada-based and TSX listed company HPQ Silicon Resources Inc. said that it has achieved a new scaling up milestone in their attempt to produce a high-purity silicon metal from low-purity quartz feedstock.

The low-purity quartz, which has 98.14% SiO2, has been upgraded to 99.97% SiO2 in tests to date, but the company says it hopes to purify the quartz to the "5N [99.999% purity] threshold at the bench scale", where their product will qualify as solar grade silicon metal. 

The testwork has been conducted with Pyrogenesis’ PUREVAP™ system, a world leader in design, development, manufacture and commercialisation of advanced plasma processes who counts the US Airforce as one of their clients. Pyrogenesis signed contracts late last year worth Canadian dollar (C$) $8.3m ($6.08m*) for the sale of a 200 tpa pilot system, as well as the IP for PUREVAP™ "as it relates exclusively to the production of silicon metal from quartz" to HPQ Silicon Resources Inc.

*Conversion made May 2017