Influence of Chlorine on the Fate of Pb and Cu during Clinkerization

The fate of heavy metals during clinkerization is of crucial significance to the utilization of solid waste as fuels and raw materials in cement kiln producing clinker. A ternary system of clinker-heavy metal-chlorine was developed that is more coincident with the condition of coprocessing of solid waste in cement kiln. The main goal of this study was to investigate the relationships among chlorine, volatilization and solidification of Cu/Pb, and the mineral phases of the clinker during clinkerization. The AlCl ₃ ·6H ₂ O (chlorine source) and PbO/CuO were mixed with cement raw meal in appropriate ratios to produce coprocessed clinkers. The volatilization and solidification of Pb and Cu were investigated experimentally using a combination of atomic absorption spectrometry, electron probe microanalysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy, optical microscope, and thermogravimetric and X-ray diffraction quantitative analyses. The volatilization ratios of Pb and Cu increased up to 46.18% and 34.04%, respectively, with increasing AlCl ₃ ·6H ₂ O content up to 1.6% compared to the cement mixtures without AlCl ₃ ·6H ₂ O addition (Pb and Cu volatilization ratios are 49.90% and 27.21%, respectively). Pb and Cu oxides can be transformed into Pb and Cu chlorides that are not stable and that have high vapor pressure. Pb and Cu are mainly concentrated in the interstitial phases of the clinker. The addition of AlCl ₃ ·6H ₂ O led to the increase of the crystal size of alite and belite. X-ray diffraction quantitative analyses proved that the content of silicate phase increased with the corresponding content of interstitial phases decreasing during clinkerization with the addition of AlCl ₃ ·6H ₂ O that decreased the ability of the clinker to solidify Pb and Cu in the produced clinkers. This research can help to promote understanding of the fate of heavy metals during the cement kiln coprocessing of solid wastes and can be meaningful for energy conservation and sustainable development.