Brussels — Aluminium is, after iron , the most abundant metallic component of the incinerator bottom ashes (IBA) and originates largely from used aluminium packaging not (yet) collected separately for recycling. This fraction usually ends up in the residual household waste which, in most Western-European countries, is then sent for incineration. But today, many WtE plants extract a non-ferrous metals fraction from the incinerator bottom ashes in quantities ranging from 0.5 to 3.0 per cent, with aluminium constituting 55-70 per cent of it.
Over the past 20 years several studies have been carried out regarding the behaviour of metals during and after incineration in Waste-to-Energy (WtE) plants but little is known about one of the most well-known non-ferrous metals, aluminium (Al). But during 2011-2012, the European Aluminium Association (EAA) was actively involved in a significant study at two different Italian incinerators to better understand the behaviour of several aluminum packaging items as they move through the incinerator.
These tests were initiated by the Italian aluminium packaging recovery scheme Consorzio Imballaggi Alluminio (CiAl) and the Polytechnic University of Milan. The results from this Italian project, combined with those of prior experiments in three other West-European countries, have shed some new light on the basic understanding behind the transfer ratios of aluminium from metal packaging to the IBA.
Unexpectedly high transfer ratios
Whilst the scope and scale of the five tests were limited, the results are converging and this allows us to draw the following conclusions:
- Minimum metal transfer ratios for thin Al foils are at least 40 per cent and for Al cans well above 80 per cent;
- Minimum metal transfer ratios for mixed Al packs (from flexible to semi-rigid and rigid) in a typical situation are between 50-75 per cent, depending on the foil share in the mixed aluminium packaging fraction;
- The grain (particle) sizes of metallic Al in the IBA varies significantly. This appears to depend on the operational parameters of each plant. Metallic Al was found in all grain sizes, also in the fractions below 5mm and even below 1mm.
An average of 2.3 per cent metallic Al
As not all European WtE incinerators currently recover the metal from the IBA, it has been estimated that, taking 2006 as the reference year, there should still be an average of 2.3 per cent metallic Al in the European bottom ashes. This represents an impressive tonnage of ‘hidden’ aluminium waiting for recovery; equivalent in tonnage to the annual production of a modern smelter!
It is expected that the pressure from new EU waste legislation targeting the phasing out of landfilling, increased recycling and more efficient energy recovery of waste will result in an increase in the volume of waste being processed by WtE incinerators in the next decade. This should result into two to three times more aluminium recovered from bottom ashes by 2020, offering some important economic and environmental benefits to Europe in terms of raw materials saving – provided all WtE facilities make the relatively small investment to recover it.
Source: European Aluminium Association (EAA) / European Aluminium Foil Association (Alufoil)