Zorba: Small Particles Big Opportunities

Zorba, a mix of shredded and pre-treated non-ferrous scrap metals, is often offloaded for low prices, but sensor based sorting can transform it into a valuable new revenue stream.

The global market for recovered mixed metals is continuing to expand. But when it comes to Zorba, a mix of shredded and pre-treated non-ferrous scrap metals, most metal reprocessors and MRF operators are missing a trick. There are commercial opportunities to exploit this often overlooked material.

By Jöerg Schunicht

Many reprocessors are being limited by using only traditional processing methods for zorba, while others are selling on the mixed material instead of directly recovering high quality fractions themselves.

Zorba is the collective term for shredded and pre-treated non-ferrous scrap metals, most usually originating from End-of-Life Vehicles (ELVs) or Waste Electrical and Electronic Equipment (WEEE). The specifications for Zorba were established by the Institute of Scrap Recycling Industries (ISRI) in the U.S., which defines Zorba as a 'shredded mixed non-ferrous metals consisting primarily of aluminium generated by eddy-current separator or other segregation techniques'.

Other non-ferrous metals found in Zorba include copper, lead, brass, magnesium, nickel, tin and zinc in elemental or alloyed (solid) form. Stainless steel is usually only present in small quantities as, depending on the grade of material, eddy current separators are normally not able to extract it from the product.

The current market

On a global scale, industrial production in all areas of modern life are creating an enormous demand for the non-ferrous metals that are commonly found in Zorba - in particular, copper, nickel and brass.

The potential market for these valuable fractions can be seen all around us in the products we use every day. The use of electronic products is now so widespread in all areas of life that there is vast demand for non-ferrous metals for use in production. As an example, the global requirement for copper to be used for on-board electrical systems in cars alone amounts to 1.5 million tonnes per year, equating to approximately 10% of global copper mine production.

An average ELV weighing a tonne contains not only steel, but approximately 79 kg of valuable non-ferrous metals such as copper, brass, aluminium and zinc. Nowadays, a large share of the overall resources used in production is obtained by using recycled metal components – a trend which is rising.

The recycling of aluminium scrap is also extremely lucrative – up to 95% of the energy costs can be saved when compared to the laborious extraction of the more costly primary resource. At the same time, worldwide demand for aluminium is steadily increasing in markets such as car manufacturing due to its lightweight properties.

As a result, it makes both commercial and economic sense to use high quality secondary raw material in place of a share of the virgin raw materials.

In response to this strong market demand, the recycling of non-ferrous metals from shredded end-of-life equipment, such as cars and domestic appliances, is steadily increasing in importance, with many raw materials such as copper or aluminium recovered in this manner.

However, market competition dictates that these fractions must be capable of being extracted to a higher degree of purity than ever before, with values of refined individual non-ferrous fractions being significantly higher than that of non-sorted ferrous mixtures. It is quickly becoming clear that the traditional methods of sorting Zorba often do not fulfill the quality requirements needed today.

Manually sorting the different, yet visually similar, metals found in Zorba is not easy and can hamper both quality and throughput Common technologies

The most commonly used methods for sorting mixed non-ferrous metals such as Zorba are manual sorting (handpicking) and sink-float treatments. These traditional methods can be limited in their success and/or especially their throughput, resulting in limited profits due to the high labour costs and low capacity speeds.

Manual sorting or handpicking of autoshredder fractions is a cost-intensive process in industrial countries, with a natural lower limit in terms of material recovery. Smaller metal parts under 20mm and wires cannot be easily sorted or, if they are, require a large amount of time and effort. Optically indistinguishable metals cannot be sorted and are therefore lost.

For example, it is not easy to manually identify and separate small pieces of various aluminium grades and metals, or to spot zinc or steel attachments encapsulated in aluminium. There is also the problem that colour sorting is nearly impossible for identical coloured materials, such as the all-grey metals of aluminium alloys, zinc and lead.

Sink-float processes, also known as dense media plants, are used to separate metals with different densities, such as separating aluminium from other non-ferrous metals. This process requires large amounts of water and other additives, the processing and disposal of which are an additional burden to the environment.

In terms of productivity, the sink-float method can only separate materials with different densities, while materials such as the valuable heavy metal mix of copper, brass, zinc and other heavy metals presenting an irresolvable problem for this method as they have similar densities. Furthermore, as sink-float processes normally use a water-based medium that moves with a current, there is the risk that light materials as well as materials with a large surface are captured by the current and misplaced into the wrong fractions.

Although there are dense media separation plants in Europe which successfully employ both of these methods, many plants still sell on their Zorba to processing contractors in low-wage countries which employ manual sorters and resell the fractions at a high profit.

An alternative to this third party involvement is for recyclers to upgrade their own mixed metals material on site and sell individual fractions of materials such as copper, brass and zinc onto the market for higher profits than ever before. This is where sensor-based sorting technology plays a vital role.

Why sensor-based sorting makes sense

Globally, there is an increase in demand for sensor-based sorting technology for the treatment of Zorba. Different sensors can be used to perform different sorting tasks, combining superior precision with high throughputs and consistently high quality end fractions with very high purity rates.

Sensor-based sorting for metals works by combining different technologies to enable the recovery of high purity metal fractions from even the most difficult fractions in terms of composition, grain size and mix from mixed waste and metal streams.

By using X-ray transmission (XRT) technology to identify and separate material based on its atomic density and also targeting fractions by colour, it is possible to remove any heavy metals from aluminium scrap to produce a melt-ready aluminium fraction, and then to sort the remaining heavy metals to recover clean fractions of copper, brass and mixed heavy grey metals.

Sensor-based sorting also presents opportunities for processing fractions that were previously unattainable using traditional methods, such as fine materials or Printed Circuit Boards (PCBs). Due to the growing demand for commodities in general, and the increasingly smaller sizes of electronic components, it is now worthwhile to focus more on the treatment of small grain sizes below 10mm.

An example of this can be seen in copper fines. Copper granulate, recovered by the recycling of copper containing wires, is already a high-value resource. However, not all impurities can currently be removed by common technologies, such as screening or densimetric tables, with non-copper materials like brass, lead or stainless steel remaining in the product. With sensor-based sorting technology, it is now possible to detect and efficiently sort material below 1mm and automatically remove these finest particles, upgrading copper granulate to a purity of up to 99.9%, and consequently substantially increasing its value.

With the high global demand for non-ferrous metals it is increasingly important to maximise the recovery of these materials from the waste stream. And doing so offers some significant economic opportunities for the recycling industry. Zorba's future

There's no denying that the sorting process for Zorba is more complex than processing other fractions, but the commercial advantages are clear to see. The sorting of Zorba leads to high quality end fractions of a range of metals including aluminium, copper and brass, which can then be sold on to re-melters – both within domestic regions and overseas – at a much higher market values.

Employing sensor-based sorting methods adds value to each of the target metals and guarantees high quality end fractions. The systems do not represent a massive investment, and their flexibility allows them to work effectively in conjunction with existing processing methods where needed, helping to keep start-up and operational costs down.

The technology is also suitable for smaller processors or those wanting to explore more 'niche' markets. Whereas methods such as dense media separation only work with high throughput, sensor-based sorting can also be used by operators that have lower amounts of material available and are more flexible in their approach to processing different materials.

The markets for Zorba – both for the initial untreated material and for the final treated fractions – are thriving. Consumer demand for consumables such as cars and electronic devices shows no sign of slowing down, providing a steady stream of both input material and valuable opportunities for quality end fractions.

With the predicted continued growth in worldwide demand for high quality non-ferrous metal fractions, it is time for a new approach to processing this valuable and in-demand Zorba waste stream. The traditional manual and dense media methods historically used represent a tried and tested way of extracting value but, with sensor-based sorting, reprocessors now have a genuine opportunity to achieve top market prices for high quality recovered fractions.

The metal recycling industry has a lot of potential due to the considerable global demand for secondary raw materials. However, without using the latest sorting equipment, valuable materials can be lost in the residual waste stream and the quality of the recovered fractions can fail to generate real value.

Jörg Schunicht is business development manager at TITECH.

Sensor-based sorting: high grade aluminium from Zorba

Alumetal is one of the largest aluminium casting alloy producers in Europe. The Alumetal Group, which dates back to 1953, includes three manufacturing facilities located in Kty, Gorzyce and Nowa Sól in Poland. These plants produce aluminium alloys manufactured from recycled aluminium scrap.

The Nowa Sól facility is the latest addition for the Group, and was opened in 2011. The facility is set up and designed to produce high grade aluminium scrap for re-melting and supply to the automotive industry, which then reprocesses the recovered material into eco-efficient, high-end products.

Installed within the plant are three high speed sensor-based sorting systems, capable of processing up to 30 tonnes of Zorba material per hour.

After the material has been processed by shredding and screening, the X-ray based machines remove the heavy metals and high alloy aluminum, resulting in a high quality product ready for re-melting.

"The use of sensor-based sorting technology was new to us," explains Andrzej Slupski, Alumetal's business development manager.

"It gives additional benefits when compared to conventional sorting methods, and the installation of these devices has allowed the purchasing and processing of a higher amount of a specific grade of scrap. We're delighted with the results achieved to date at our Nowa Sól plant," he adds.