Change Mechanism of Cd Form in Pyrolysis of Sewage Sludge

Pure compounds CdS and CdCO3 used as model compounds present in sewage sludge were pyrolyzed in the pyrolysis atmosphere of sewage sludge at different temperatures.The pyrolysis products of CdS and CdCO3 were analyzed by X-Ray diffraction(XRD) to investigate the change mechanism of Cd form in the pyrolysis of sewage sludge.The results showed that CdS in sewage sludge was stable at pyrolysis temperatures below 800 ℃,but decomposed above 800 ℃,and the reaction could be expressed as following:CdS→Cd(g)+S;CdCO3 in sewage sludge reacted as following:CdCO3→CdO+CO2,CdO+ sulfide(g)→CdS,in which the sulfide was generated in the process of sludge pyrolysis,but CdS generated during pyrolysis decomposes at higher temperatures above 800 ℃.