TOMRA says its patented multi-channel laser sorting technology is helping unlock the “full potential” of quartz deposits.

Quartz is one of the most common minerals found in all forms of rock, but it does not exist in high purity in nature, according to TOMRA. The challenge for mining operations serving the metallurgical and engineered stone industries is to reliably deliver quartz of consistently high chemical purity.

The scattering effect of the multiple laser beams from TOMRA’s ore sorting technology can be used to separate quartz-bearing rock from waste rock, with the sensors recognising the glowing crystals that are the tell-tale sign of quartz or quartz veins.

TOMRA says large and pure crystals can be clearly discriminated from other rocks or minerals with a smaller crystal structure, regardless of the colour or chemical composition.

“TOMRA’s laser sorter also stands out for being a gravity system rather than the conventional conveyor belt, so that both sides of the material are scanned and multiple characteristics such as surface structure, size, shape, brightness and colour distribution are processed simultaneously,” the company said. “Laboratory tests and field experience have shown that the recovery of valuable rocks can be increased by 20% while improving the quality of the product.”

Jens-Michael Bergmann, Industrial Mineral Segment Manager at TOMRA Sorting Mining, said the advantages for mine operations are multiple, “from a longer life of the mine to lower operating costs and a reduction of waste, with consequent lower haulage costs”.

He added: “It also enables them to guarantee consistent high-quality of product to their customers.”

TOMRA’s laser sorting technology also has environmental benefits due to the reduced waste and low water use, as only a small quantity of water is required for wet washing the rocks at the beginning of the process to avoid dust in the processing plant.

Laser sorting also eliminates the need for hand picking, which is required with colour sorting in order to achieve the high purity levels demanded by the metallurgy and engineered stone industries, according to TOMRA. This has a positive impact on the mining operation’s health and safety initiatives, as personnel are not exposed to silicon dust in the sorting process.

Spanish company Erimsa, part of Elkem ASA, one of the world’s leading suppliers of silicon-based advanced materials, has over 30 years’ experience in quartz extraction using an environmentally friendly method, according to TOMRA.

It specialises in the production of aggregates for the construction industry and metallurgical quartz, which means a consistently high chemical purity of the quartz is paramount. It originally achieved this level of quality through manual sorting, but, in 2000, the company introduced colour sorting technology.

TOMRA said: “However, in order to achieve the high level of purity they required, the sorters were calibrated in a way that resulted in high rejection rates of material containing quartz. This meant that hand picking was still required in order to improve the recovery and ensure the stability in the quality of the quartz that is key for Erimsa.”

Carlos Forján, Quality Manager at Erimsa, turned to TOMRA for its laser technology, which he thought would enable the company to sort good quality quartz regardless of the colour: “The main problem we have is in the complexity of sorting automatically when the quartz and the rejectable minerals have the same colour. I thought that laser technology would be the way to address this.”

In 2016, following tests conducted at TOMRA’s Centre in Wedel, Germany, a PRO Secondary LASER Dual sorting machine was installed at its processing plant in Salamanca.

At this operation, the quartz is extracted and washed to avoid dust in the plant, then it is screened by size. Materials over 70 mm are hand-picked by four operators; materials under 20 mm are shipped to aggregates and quartz sand customers; materials between 20 and 70 mm are fed to the TOMRA multi-channel laser machine, which sorts out the waste material. A final quality check is conducted by two operators to remove the rare pieces with quartz content that may have been ejected in the waste by the sorter, as it is calibrated to maximise recovery.

Forján said: “The TOMRA machine has enabled us to reduce costs while increasing our yield; our production has easily increased by 20% compared to when we used colour sorters combined with hand picking. Material that, in the past, was lost to the waste pile is now generating profit for us.

“The stability of the quality is an important goal, and we have achieved this with the laser sorter. It has been such a game-changer in our operation; we are planning the purchase of a second laser machine to replace an existing colour sorter.”

TOMRA’s laser sorters can also be combined with other sensors depending on the requirements.

This is the case for Mikroman Mining Company, which uses a combination of TOMRA laser and TOMRA colour sorters to differentiate products according to four qualities: white and light grey quartz with low iron oxide content for engineered stones; grey and yellow quartz for the glass industry; coloured quartz for ferrosilicon used in the metallurgical sector; and coloured gravel, also for ferrosilicon, which currently goes into the waste pile.

These precise distinctions, resulting in higher product quality, were not possible before the acquisition of the TOMRA machines, and today the company operates 13 colour sorters and three laser sorters in its various plants, according to TOMRA.