Reuse of heavy metal-containing sludges in cement production

The feasibility of the replacement of raw material for cement production by heavy metal-containing sludge from surface finishing and electroplating industries was investigated. The effect of heavy metal content in the cement raw mix on the crystalline formation in cement production was also examined by XRD analyses. It was found that both sludges were applicable for the replacement of raw mix for cement production by moderate conditioning of the sludge compositions with several compositional parameters. As the replacement of raw mix by sludge was within 15%, the formation of tricalcium silicate (C ₃S) phase in cement would be enhanced by the introduced heavy metals. While owing to a high level of heavy metals concentration (> 1.5%) in cement raw mix, C₃S crystalline in cement would be inhibited by a large sludge replacement (> 15%). During the sintering process, over 90% of the high volatile elements such as Pb would evaporate in high temperature, yet 90% of the less volatile elements such as Cu, Cr and Ni would be trapped in clinkers. Most of all, the results of leaching test shows that the trapped elements in hydrated samples would not leach out under acidic conditions. The reuse of heavy metal-containing sludges as cement raw material would not cause leaching hazard from sintered clinkers. Heavy metal-containing sludges thus should have the potential to be utilized as alternative raw materials in cement production.