INFLUENCE OF CHEMICAL PRE-TREATMENT ON THE LEACHING BEHAVIOUR OF BOTTOM ASH

Abstract

International audienceThe valorisation of municipal solid waste incineration bottom ash is conditioned by its intrinsic content in pollutant elements such as BTEX, PCBs, hydrocarbons… and by potential release of mineral trace elements. An important percentage of bottom ash is currently not valorised because of regulation constraints. In this context, the objective of our study is to evaluate the influence of chemical pre-treatment on the leaching behaviour of bottom ash.Firstly, the influence of different parameters on the efficiency of the chemical treatment has been investigated. Based on these results an optimised protocol has been developed, consisting of several steps of washing and rinsing. Secondly, for a better understanding of the leaching mechanisms involved, the leaching behaviour of this material has been modelled, using the geochemical modelling tool PhreeqC ®. The results show that the pre-treatment protocol defined is effective for most elements. There is a good coherence between experimental and simulated data for elements such as calcium and sulphur-these elements have been well described in the mineralogical assemblage. Results are less convincing for other elements (e.g. antimony) for which not enough data exists yet, in order to correctly define their geochemical speciation in the MSWI-BA. To conclude, a short washing step with a hydrochloric acid solution 0.2M and a low liquid-to-solid ratio, followed by two rinsing steps, shows an important decrease in the leachability of MTE and anions from bottom ash