The toxic compounds and leaching characteristics of spent foundry sands

In foundry industry, the millions tones of spent sands were successfully used as landfill materials for many years. But this practise is becoming a problem as the disposal costs increase rapidly and legislation gets tighter. However, there is not much experimental data to describe their chemical characteristics, especially for the leaching behaviour and toxic compounds of the different kinds of spent sands. This article aims to present the analysis of organic compounds and leaching characteristics of the spent foundry sands. Based on the evaluation of the Chemistry of spent sands, the contents of the selected 32 polyaronmatic hydrocarbon (PAH) and other organic compounds 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-dependent leaching characteristics of chromium were further investigated. It was found that all spent foundry sands contain PAHs in which naphthalene is 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 spent foundry sands. The leached Cr increases with increasing pH of the eluted solution, which can be used in practise for shortening the leaching time of the spent foundry sands.