The impact of additives on the retention of heavy metals in the bottom ash during RDF incineration

Up to now, a few studies on the efficiency of heavy metal(-oid)s capture by a sorbent directly mixed with fuel, have been performed. For this reason, the main objective of the study is to determine whether or not such a solution is effective when RDF is incinerated. The paper presents a two-step analysis of the impact of three sorbents (ammonium sulphate, kaolinite and halloysite) in three dosages (2, 4 and 8 wt%) on heavy metal(-oid)s retention in the bottom ash. 12 heavy metal(-oid)s were taken into consideration - As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, V and Zn. Samples were incinerated in a lab-scale tubular reactor at two temperatures - 900 °C and 1100 °C. The first step of investigation constitutes ICP analysis of heavy metal(-oid)s content in the bottom ash, coupled with SEM/EDS analysis. Afterwards, the second step was to determine the stability of formed additive-heavy metal(-oid)s complexes via leachability tests in neutral and acid environments. The performed research has shown that ammonium sulphate is effective in Cr, Cu and Hg capture, halloysite – in Cd, Co, V and Mn capture, whereas kaolinite – in Pb capture. •None of the additives show the tendency to As, Ni, Sb and Zn capture in the ash.•Ammonium sulphate captures and immobilises Cr and Cu in the bottom ash.•Halloysite is effective in Cd, Co, V and Mn capture in the bottom ash.•Kaolinite is the most effective in Pb capture.