Fibres, plastics and minerals – these are the most challenging materials at a vehicle’s end-of-life stage. Negative economic values, strict regulations on landfilling and increasing incineration gate fees are forcing the recycling sector to take action. But what about the mineral fractions?
This article was previously published in Recycling Technology >>
The mineral fraction from end-of-life vehicles (ELVs) – also termed the ‘sand fraction’ or ‘glass fraction’ – is typically
composed of glass particles, sand, stones and other dirt. Given that ELVs are not spotlessly clean when delivered to dismantling and recycling facilities, generation of these materials is substantial in weight terms. While fibres are more voluminous than weighty, minerals represent a dense by-product which should either be consigned to proper disposal or recycled under current European laws.
Unlike with metals and plastics, there is no real market driver for ELV mineral separation and application; in fact, this is conducted only in countries or regions where landfill tariffs are high. And unlike with ELV fibres, minerals have a high density and lower transportation costs per tonne, thus allowing application in regions further afield.
Around 2-3 million metric tonnes of shredder light fraction (SLF) is generated every year at shredder sites around Europe and the mineral fractions are sieved into different sizes. Depending on the design of the post-shredder process, the mineral content accounts for up to 30% of SLF by weight.
Current outlets, such as for salt mine backfilling, are classified under many national regulations in Europe as ‘useful applications’ (the same category as energy recovery) rather than as material recycling. Recycling of the minerals would add between three and five percentage points to the overall ELV recycling rate. Post-shredder arrangements vary between shredders but, in all instances, it is not economically attractive to upgrade minerals for a clean recycling purpose under regulation-free market conditions.
Minerals represent the real ‘dead end’ for ELVs and possess all those characteristics that are unwanted along the entire recycling chain: a strong negative value owing to hazardous characteristics; and more rapid machinery wear owing to the hardness and brittleness of the material.
As with other light fractions of shredder residue, proper ELV depollution results in lower concentrations of hazardous substances, such as the heavy metals lead, mercury, cadmium and chromium VI as well mineral oil. Furthermore, segregated treatment of ELVs and other scrap is useful.
An essential problem is that mineral fractions, owing to their hazardous characteristics, are low on the list of materials that final processing companies are prepared to accept. These fractions are also subject to many regulatory changes and interpretations which often make outlets temporary in nature.
Removal of window glass prior to shredding the ELV hulk results in a less voluminous sand fraction. Car dismantlers may receive better prices from shredders for ‘glass-free’ hulks and could sell this material back into the glass market.
However, the day-to-day reality in Europe is that dismantling stations cannot justify the operational cost entailed by removing the window glass. The following are outlets for this glass: mineral wool; bottle glass; grinding products;
glass beads; side rails; and foam glass. Despite these high-quality applications, values of recycled glass are low and volumes are small when generated at a car dismantling site.
In addition, potential energy savings from glass are small when compared to other materials: for example, recycling 1 kg of glass will result in the same amount of energy saved as recycling 180 g of newspapers, 150 g of steel or 12 g
Post-shredding technology factories have been making steady progress towards reducing the impact of glass contamination by updating their processes and improving individual items of machinery. Separating minerals
out of the SLF stream typically involves various sieving steps, magnetic separation, zigzag classifiers and air tables. Special arrangements should be made to prevent wear on machinery and pipelines resulting from the material’s
Innovation can be applied to various areas, such as improving mechanical processes and developing cost-effective outlets which are classified as material recycling. Both are imperatives if the costs of a post-shredder recycling operation are to be balanced. In practice, innovation is only an option where landfill taxes and tariffs start at Euro 150 per tonne or in cases of strict recycling targets.
- A mineral fraction processed in a cement kiln ends up in the cement product while off gas treatment takes care of the hazardous substances. The result is an inert material which can be used directly in, for example, construction applications. However, this is a rather expensive process and the material is not always popular with treatment companies.
- In a high-temperature melting process, all organic content is burned off while the minerals are melted into a basalt stream, thereby providing energy. All hazardous elements become part of the crystalline structure, thus preventing leaching. It offers a durable solution which is the subject of further studies at ARN in the Netherlands.
- Biological treatment coupled with immobilisation may have a substantial future impact. Bacteria ‘eat’ the oil and, via the immobilisation route, heavy metals are neutralised.
The final product can be used as a sub-layer in road construction.
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