城市污泥热解重金属Cd的形态变化机理

Change Mechanism of Cd Form in Pyrolysis of Sewage Sludge

利用纯化合物CdS、CdCO3模拟污泥中重金属Cd的主要存在形式,在污泥的热解气氛下,对CdS、CdCO3进行加热处理,并对热解产物进行X-射线衍射分析,确定产物的组成,从而探究出污泥的热解时重金属Cd的形态变化机理。结果表明,Cd的硫化物在低于800℃热解时以稳定的形态存在于污泥中,而在高于900℃会分解形成Cd单质,其反应可以用以下式子表示CdS→Cd(g)+S;镉的碳酸盐热解时发生了以下变化:CdCO3→CdO+CO2,CdO+硫化物(g)→CdS,其中硫化物是污泥热解过程中产生的,高温(>800℃)热解时生成的CdS发生再分解。

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 ℃.