A Feasibility Study on Co-Processing of Soil Contaminated with Heavy Metals in Cement Kilns

Abstract

The national general survey manifests that the Chinese soil is suffering from serious contamination, mainly arising from heavy metals (HM). Due to the large amount of heavy metal waste, many researchers have performed the feasibility studies on co-processing this kind of waste in cement kilns. In this paper, we review these results from the perspectives of national standards, the crystal structure of clinker, and the volatility of metals in cement kiln system. The crystal structure of clinker mineral offers physical possibility for the solidification of HM atoms. The volatility studies also indicate that most of the metals will not emit from the kiln system. For the incorporated metals in clinker, their release ratio is very low, and the leaching HM atoms can be immediately enclosed by the cement hydration products. Based on these theoretical results, we measured the HM in the raw materials and in the cement product for 1 year in a cement plant. The bag filter dust contained high level of Tl with an average of 219.30 ppm. The other metals were almost solidified by the clinker. With the vaporization of Tl in the raw materials, the circulation pattern causes the accumulation and buildup of Tl in the system. The incorporation capacity of clinker on HM is predicted in this paper, but the incorporation ratio of HM from contaminated soil, the circulation pattern of HM in cement kiln system, and the emission of HM is currently not clear and further work is in progress.