Environmental behaviour of stabilised foundry sludge.

Environmental characterisation of foundry sludge (FS) and the stabilised/solidified (S/S) derived products has been performed according to the leaching behaviour. Portland cement and lime have been used as binders and foundry sand fines, activated carbon and black carbon have been used as additives in the S/S processes. The results of the characterisation show that the behaviour of the waste in acid media is mainly influenced by the inorganic components of the waste, while the organic matter only has an influence in the redox potential of the leachates. Due to the complexity of the waste, a computer modelling of equilibrium (MINTEQ) has been used in order to compare the experimental extractability with the simulated curves of the metallic species. The zinc content in the leachate is close related to the theoretical curves in the waste and all S/S products, while the rest of the metals do not show a coherent behaviour with the hydroxides evolution. The results of compliance testing allow to obtain the best S/S formulations using activated and black carbon as sorbents. The comparison between different leaching procedures leads to equivalent results depending only on the pH.