污泥焚烧中铅的形态转化及脱除的热力学平衡研究

Thermodynamic Equilibrium Analysis of Transformation and Removal of Lead During Sludge Incineration

利用热力学平衡模型预测了污泥焚烧过程中铅的形态转化和迁移规律,并采用系统吉布斯自由能最小的原理对Al2O3,SiO2,TiO2和CaO4种吸附剂吸附污泥燃烧中铅的效果进行了模拟计算.探讨了痕量元素Pb与S,Cl的相互作用及S和Cl的存在对吸附剂与Pb反应的影响.研究结果表明,污泥焚烧中Pb的形态转化受到S,Cl及矿物质的影响较大.有S存在情况下,Pb在低温条件下主要以固态PbSO4存在,温度较高时以气态PbO存在;Cl较易和Pb结合形成低沸点的金属氯化物而导致Pb的挥发,并且Cl含量的增加会加速Pb的挥发.4种吸附剂对污泥焚烧中Pb都有一定的脱除能力,其中Al2O3可以在较宽温度范围对Pb进行捕集,而CaO对Pb的化学吸附能力较差.由于S,Cl与Pb有更强的反应性,因此S,Cl的存在对吸附剂与铅的反应有抑制作用,使有效吸附的温度范围变窄,吸附效率降低,甚至失去脱除Pb的能力,并且Cl的影响大于S.

The thermodynamic equilibrium model were applied to predict the transformation of lead during the sludge incineration and the adsorption effects of Pb by four sorbents（Al2O3,SiO2,TiO2 and CaO） were simulated with the minimized Gibbs free energy approach.The interaction between Pb and sulfur,chlorine,together with the reaction between sorbents and Pb caused by sulfur and chlorine were considered in this procedure.The result showed that the transformation of Pb was affected greatly by sulfur,chlorine and minerals.At low temperature the lead existed in the form of PbSO4（solid） under the presence of sulfur,while it changed into PbO（gas） at high temperature.The Pb was volatized because chlorine was easy to combine with Pb forming the metal chloride with low boiling point,and the increase of chlorine could speed up the volatilization of Pb.The four sorbents mentioned above were able to remove Pb in some degree.Al2O3 could capture Pb in a wide range of temperature,while CaO was not so good.Because sulfur and chlorine had stronger reaction with Pb,they restrained the reaction between sorbents and Pb,during which effective temperature area was narrowed,adsorption rate was reduced,and even Pb removal ability was lost.The effect of chlorine appeared much more than that of sulfur.