Regeneration of heavy metal contaminated soils for cement production by cement kiln co-processing

Abstract

Co-processing is considered as an effective way to reduce the cost and environmental footprints for cement production by replacing fuel or raw materials with wastes. In this study, we investigated the influences of co-processing of heavy metal-contaminated soil in cement kiln on the engineering integrity and heavy metal leachability of cement powders and cement mortars. The replacements of the contaminated soil were set at 0, 3.0, 7.6, and 10.0 wt.%. Engineering integrity of the cement products was verified first using typical performance tests, followed by three heavy metal leaching tests, namely Toxicity Characteristic Leaching Procedure (TCLP), EDTA-mediated TCLP and Synthetic Precipitation Leaching Procedure (SPLP). The results showed that in TCLP, only Cr was the concern, in which leachates of cement powders produced by co-processing with > 7.6% soils exceeded the TCLP Cr limit (5.0 mg/L), whereas all leachates of cement mortars met the regulations. EDTA-mediated TCLP could potentially release higher Cr concentrations, indicating that cautions were still needed when applying the cement products in harsh environments. Preliminary economic assessment indicated that using co-processing to treat heavy metal-contaminated soils can bring benefits for both cement industry and soil polluter. Overall, cement kiln co-processing could be an attractive alternative for the remediation of heavy metal-contaminated soil to revive the contaminated site and reduce the environmental impacts of cement production.