Among the many proposals in the EU Circular Economy Package is that of counting metals recycled from Incinerator Bottom Ash (IBA) against the recycling targets in the Waste Framework Directive and the Packaging and Packaging Waste Directive. It’s a prospect which has been warmly welcomed by both the metal packaging and waste management industries.
However, metals are not the only recyclable material to be found in IBA. It is also possible to recover aggregates for use in construction. One company that’s heavily involved in advancing the recovery of both fractions is Dutch firm Inascho, which has developed a technology to increase both the quantity and quality of metals recovered from IBA, as well as to produce a high grade aggregate material.
“When it comes to metal processing you can do a lot with ordinary magnets,” says Rogier van de Weijer, business development director at Inashco. “However, to recover very fine metal particles, down to half a millimeter is much more difficult. The difficulty is mainly because when the ash is discharged from the incinerators goes to a water bath to cool and it becomes a very muddy, slurry-like material.”
Speaking with WMW van de Weijer explains that because of the weight of the minerals which are stuck to them, conventional magnetic sorting can’t accurately sort these very fine particles.
“What we do with our Advanced Dry Recovery (ADR) machine is to accelerate the material,” he explains. “The metal component is relatively heavy compared to the adhering minerals, so it accelerates faster and the sticky minerals drop off within the first five metres – a small copper fragment will fly eight metres so you can separate them.”
With this type of ballistic separation the materials are sorted according to their characteristics. For example, a copper particle of 0.5mm will behave in a similar fashion to a small stone of 2-3mm. This means that this initial ballistic separation stage produces a fraction containing small sub 1mm metal fragments mixed with a larger stone fraction. Crucially, however, the light and sticky mineral fraction will have been removed.
“This sticky fraction is usually 35-40% of the mass,” says van de Weijer. “By removing it you have liberated the metals from the stickiness and they can roll freely on a conveyer belt. If you then run the material past a magnet the full magnetic force is acting on the particles and they can be propelled into the correct box.”
Non-Ferrous Fraction
Once the ADR process has been completed the product is run over eddy currents to produce a non-ferrous concentrate which contains copper, zinc, aluminium, palladium, etc.
van de Weijer explains that when processing this material, if you produce a very high grade of recovered metals you have a lower recovery rate, while a very high recovery rate will lead to a lower grade of material. This is known as the grade recovery curve.
“We usually end up with a recovery rate of 85-90%, and a grade of around 40-45%,” he says. “The material has a very high concentration compared to the bottom ash that it came from, but it still have a low grade. So we take that material through to the next process to recover the heavy and light metals, and to separate rest of the minerals – and we do that by density separation.”
In this process the materials are processed based on the speed at which they sink in water. This allows the heavy non-ferrous fraction to reach a purity of around 90% and enables the “copper/zinc scrap mix” to be sold on to a smelter.
Because it melts in the incineration process the aluminum tends to be mixed with a high percentage of mineral fragments. However, because the heavier metals have already been removed the eddy current separator can be adjusted much more accurately to recover aluminum at a grade of around 85%. This fraction too can then be sold to a smelter.
Mineral recovery
In addition to recovering metals Inashco has also developed uses for the minerals present in the ash as an aggregate construction material which can be used even in groundwater areas. To do this the sulphates and chlorides must first be washed from the product.
“We remove the pollutants that could potentially leach out to make a clean product that can safely be used in the environment,” explains van de Weijer. “As of the 1 January 2017, in the Netherlands the Green Deal will be in place. It will mean that the industry has to clean minerals so that they can be freely used as an aggregate – it will have an ‘end-of-waste’ status in as much as it will be freely applicable as if it were a primary material.”
The material is also suitable for use in unreinforced concrete products such as building blocks, bricks, tiles and pipes.
The Future
van de Weijer is upbeat about the future for Inashco’s technology. Since being founded in 2008 the company has not only developed the technology, but has already got an installation base of 27 facilities globally.
In Europe he see the Circular Economy Package as a big potential driver for further adoption of the technology, an argues that in addition to counting the metals recycled from bottom ash against national recycling targets, it would “make complete sense” to also count the minerals recovered too.
In the US, where it is common to have ‘monofills’ which contain nothing but IBA, there is also the potential to mine historical deposits.
With energy recovery expected to play an increasing role in waste management globally, it seems a fair assumption that the recovery of both metals and minerals from the ash will be a growing trend.
