The release of heavy metals in stabilised MSW by oxidation

Leaching experiments on partly stabilised MSW under oxic conditions have be en carried out. The objective of the study was to investigate the effects o n heavy metals in anaerobically stabilised MSW during the exposure to air. It was suspected that the oxidation could increase the mobility of heavy me tals, and, thus, trigger a chemical time bomb (CTB). The experiments and si milar investigations indicate that the initial oxidation of the most reacti ve compounds, such as some organic substances and acid volatile sulphides ( AVS), will not mobilise large amounts of the total amount of heavy metals. However, the concentration in the leachate might increase up to one order o f magnitude due to complexation with dissolved organic matter. The mobilisa tion is restricted by the presence of buffering substances in the waste, wh ich are able to buffer neutral to weak alkaline leachates. The high buffer capacity of partly stabilised MSW indicates that acid leachates and CTBs wi ll be avoided for a long period of time. However, acid leachates may appear earlier than expected in heterogeneously structured media where oxidation processes are enhanced along channels, which constitute favourable pathways for water and intruding air. (C) 1999 Elsevier Science B.V. All rights res erved.