The toxic compounds and leaching characteristics of spent foundry sands

In foundry industry, the millions tones of spent sands were successfully us ed as landfill materials for many years. But this practise is becoming a pr oblem as the disposal costs increase rapidly and legislation gets tighter. However, there is not much experimental data to describe their chemical cha racteristics, especially for the leaching behaviour and toxic compounds of the different kinds of spent sands. This article aims to present the analys is of organic compounds and leaching characteristics of the spent foundry s ands. Based on the evaluation of the Chemistry of spent sands, the contents of the selected 32 polyaronmatic hydrocarbon (PAH) and other organic compo unds in 11 different spent foundry sands were analysed. The concentrations of As, Ba, Cd, Cr, Pb, Hg, Se, Ag, Cu and Zn in 11 different spent foundry sands were also measured with regard to leaching characteristics. The: pH-d ependent leaching characteristics of chromium were further investigated. It was found that all spent foundry sands contain PAHs in which naphthalene i s about 30%. The PAHs in green sands are much higher than those in chemical binder spent sands, even though phenolic/ester sands have higher PAHs than furan/acid and silicate sands. The leaching metals are very low in all spe nt foundry sands. The leached Cr increases with increasing pH of the eluted solution, which can be used in practise for shortening the leaching time o f the spent foundry sands.