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How to get 99% metal purity

metal processors

Some UK scrap metal processors are resigned to the fact that they will not be able to meet China’s new contamination limits. They will have to find alternative end markets for the material, which will inevitably mean reduced rev­enue.

But for those that are heavily dependent on China as an export market, their only option is to invest in a way that ensures their material is accepted.

Recycling companies have traditionally used manual or sink-float treatments to sort mixed non-ferrous metals, but these methods are limited in success and gener­ally have higher operational costs.

Manual sorting has lower limits in terms of material recovery because parts of less than 20mm and wires cannot be sorted by hand easily or, if they are, require a large amount of time and effort. Nor can optically indistinguishable metals be sorted manually and are therefore lost.

Sorting by colour is also impos­sible for identical materials such as the all-grey aluminium alloys, stainless steel, zinc and lead.

Other metal recyclers use sink-float processes, also known as dense media plants, to separate metals with different densities, for example aluminium from other non-ferrous metals.

This process requires large amounts of water and other expensive additives, the process­ing and disposal of which represent an additional burden. The sink-float method can only separate materials with different den­sities: the valuable heavy metal mix of copper, brass, stainless steel and zinc presents an unsolvable problem for this method.

As well as being inefficient and uneconomical, such methods are incapable of achieving the required 99% metals purity levels set by the Chinese government.

But there is a tried and tested, financially viable solution that enables metal processors to achieve 99% purity of non-ferrous fractions. That solution is sen­sor-based sorting, an automated, low-maintenance technology that uses colour, x-ray and near-infra­red sensors to achieve precision, with high throughputs and con­sistently top-quality end fractions.

For non-ferrous scrap products such as zurik and zorba, operators can attain National Sword purity levels with the com­bined technologies of Tomra’s X-Tract and Combisense machines.

By passing zorba through an x-ray transmission unit to separate aluminium from heavy metals, X-Tract can achieve alu­minium purities of 98-99%. From the remaining heavy metals, Combisense then takes out valuable fragments of copper, brass and grey metals.

Complementing these machines, Tomra’s laser-induced breakdown spectroscopy sorting technology employs a laser which can monitor the entire width of the belt, eliminating the complex and costly need to separate materials into single lanes.

zorba and zurik

zorba and zurik

The specifications for zorba and zurik were established by the Institute of Scrap Recycling Industries in the US.

It defines zorba as shredded mixed non-ferrous metals consisting primarily of aluminium generated by eddy-current separator or other segregation techniques.

Zurik is a combination of shredded non-ferrous metals mainly comprising stainless steel, plus insulated copper wire, aluminum, copper, lead, magnesium and other metals, accumulated from auto and appliance shredders and generated by downstream computer sensing equipment.

In the separation of aluminium wrought alloys, this enables sort­ing accuracies of 99% purity or greater, with high throughputs of three to seven tonnes an hour.

The beauty of sensor-based sorting is that the equipment can be up and running within a matter of weeks. This is essential when China’s lower contamination lim­its are already being enforced. Running costs are around 80% less than that of dense media plants, and typical payback period is between six and 36 months.

The flexible nature of the tech­nology allows it to be operated in conjunction with existing process­ing methods. Because the equip­ment can be purchased as modules over time, this helps to keep costs down and represents a major advantage over traditional plant methods, where the entire system must be bought upfront.

There is, understandably, a lot of fear and uncertainty about what the future holds for metal processors in terms of China’s ever-tightening final product purity requirements. But, in reality, UK metal processors really have only three options: invest in their facil­ities, find alternative markets or accept reduced revenue for their material.

Gavin Russell is sales engineer at Tomra Sorting Solutions

Tomra has published a free guide to help recyclers meet China’s National Sword standards

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