Environmental properties of vitrified fly ash from hazardous and municipal waste incineration

A process for vitrification of fly ash has been developed by the Swedish company ScanArc Plasma Technologies AB, and the Norwegian company Kvaerner Oil & Gas a.s. The process is named VITROARC®. During 1996 the process was tested on different types of fly-ash under different process conditions, and the slag produced was tested for leaching behaviour in an extensive program at Netherlands Energy Reseaserch Foundation (ECN) in Holland. The project was supported by N.V. Afvalsverwerking Rijnmond (AVR) which also delivered most of the fly ash. Fly ash was also delivered from AVR Chemi and Roteb in Holland, Tiru in France and Borlãnge Energiverk in Sweden. The main target of the program was to verify that the produced slag fulfilled the requirements to category I material according to the Dutch regulation for building materials. During this particular program about 50 tonnes of fly ash have been vitrified individually and mixed in series of tests under different conditions. The tests have been performed in a pilot plant with capacity of processing one ton of flyash per hour. The main conclusions from this study are as follows: the VITROARC process does produce a slag material that qualifies directly for category 1 material for almost all elements. In most cases well below the crucial limit value. In the evaluation of the leaching behaviour of vitrified slag from fly ash antimony leaching proves to be the only crucial aspect in view of the Dutch regulatory requirements for building materials. The leachability of Sb varies around the limit value. It should be noted that compared with other materials, the leachability of the slag is largely surface related and almost surface limited. This implies that the leaching from VITROARC® slag in the long term will be far less than in most systems, meeting the criteria also for Sb, but showing a steady release of material due to solubility control. This benefit of the treatment cannot be evaluated in the current regulatory rules in Holland. It should also be noted that the Sb limit value for N1 quality in the Dutch regulation for construction materials (0.054 mg/kg) is extremely low compared for instance to As (0.91 mg/kg), bearing in mind that As is regarded as being 10 times more poisonous than Sb is that leaching limits for Sb are not given in several other regulations. An overall conclusion from this is that the process represents a reliable, environment friendly and safe solution for stabilising and converting incinerator fly ash into useful products. The slag is also tested according to German, Austrian and Swiss regulations and fulfils their requirements for disposal of inert material. Also according to French and US regulations the leaching from the VITROARC® slag is below the regulatory limits.