Melting reconstruction features and solidification mechanism of heavy metal-containing slag

The relationships between microstructure and melting temperature of slag containing different heavy metals (Zn, Cu, Pb and Cr) were studied. Furthermore, the corresponding solidification mechanism and rule of heavy metals were analyzed by microscopic tests during melting and reconstructing process. Based on preliminary results, three conclusions were derived. Firstly, pure slag would begin to melt when the temperature reached 1 180 °C; however, Zn did not play any fluxing action. Secondly, upon adding Cu and Pb, the initial melting temperature of slag decreased by 5–8 °C and their fluxing effect was observed. Thirdly, the initial melting temperature and the reaction time for slag decreased by 22 °C and 6 s respectively after adding Cr; the fluxing action was significant under Cr. The results of X-ray diffraction (XRD) and Fourier transform infrared spectroscope (FTIR) analyses showed that the above heavy metals had little influence on the reconstruction of slag. Toxicity characteristic leaching procedure (TCLP) leaching tests showed a good solidification effect of the heavy metals with melting slag, fixation rate of Zn, Cu, Pb and Cr was 36.3%, 24.6%, 9.2% and 93.2%, respectively. The leaching toxicity of the heavy metals met the requirements for environmental emission after solidification treatment.