CO2 emissions in the recovery and recycling of aluminium from MSWI bottom ash

Abstract

In the Netherlands, aluminium and other metals are recovered from Municipal Solid Waste Incinerator bottom ash. Over the last years additional attention has been given to the recovery of non-ferrous metals especially, with the signing of a green deal between the Dutch Government and the Dutch Waste Management Association for instance. For 2012, it is estimated that 41.2 ktonne metallic aluminium, in various alloy compositions, was incinerated as part of the waste. It is assessed that 14.2 ktonne clean aluminium was recovered and 19.2 ktonne metallic aluminium can additionally be recovered from the bottom ash. This can be done with recent developed and deployed technologies, such as Advanced Dry Recovery which is added to the existing systems, or other techniques in the future. Due to the incineration process 7.2 ktonne metallic aluminium is mainly lost to oxidation. The oxidation of aluminium to corundum (Al2O3) generates however an additional amount of energy on top of the combustion energy from the waste in the furnace. Based on the oxidation to corundum it is estimated that 0.19 PJ of energy is additionally generated on a total of almost 72 PJ. In the supply chain that follows, 1.3 ktonne of additional losses will occur, after which 13.5 ktonne of aluminium ends up in semi-finished products, mainly as aluminium ingots. This gives an overall recycling factor of 33 %. The recovered aluminium will mainly be used to cast DIN 226 alloys, which are applied in for example engine parts. In the recovery and recycling of aluminium from MSWI bottom ash 210.3 ktonne of CO2 are emitted. Therewith it saves, compared with the production of primary aluminium produced in Europe, 7 940 kg CO2 per tonne aluminium recycled and saves 34 % CO2 emission, which would have be emitted with the production of the total amount of 41.2 ktonne primary aluminium produced in Europe. This in contrast, to the used comparison with regular aluminium scrap, where 97 % less CO2 is emitted than primary aluminium. The main challenge for the coming years is to reduce the amount of aluminium unrecovered in bottom ash, therewith increasing the emission savings.