水泥窑共处置过程中水泥生料对Pb与Cd的吸附/冷凝特性

Research on Condensation and Absorption Characteristics of Cement Raw Meal for Pb and Cd during Co-Processing in Cement Kilns

为了研究水泥窑共处置过程中水泥生料对Pb、Cd的吸附/冷凝特性,采用氮吸附仪和SEM（场发射扫描电镜）对水泥生料的基本物理性质（比表面积、孔径和微观表面积）进行研究;同时,利用小型试验装置对重金属Pb、Cd的氧化物（Pb O、Cd O）展开了吸附/冷凝研究.结果表明：水泥生料的比表面积（2.49 m2/g）较小,微观表面结构致密无孔,因此,在水泥窑共处置过程中水泥生料对重金属的吸附/冷凝作用以冷凝为主.进入控温立式炉的重金属可分为三部分：1冷凝在管壁上,其中Pb、Cd分别占各自入炉总量的67%~72%、58%~65%;2吸附/冷凝在水泥生料上,其中Pb、Cd分别占各自入炉总量的13%~17%、16%~21%;3随烟气释放到空气中,其中Pb、Cd分别占各自入炉总量的10%~18%、14%~26%.水泥生料对Pb、Cd的吸附/冷凝特性均可用双常数方程拟合,线性拟合的相关系数均在0.95以上.动力学方程拟合得到水泥生料对Pb、Cd的吸附/冷凝活化能,二者分别为5.827、6.050 k J/mol,由此可预测水泥生料对Pb和Cd的吸附/冷凝量.

The basic physical characteristics of cement raw meal, such as surface area, pore volume and micro-structure, were investigated by SEM, BET and particle size analysis. Additionally, the condensation and absorption characteristics of the cement raw meal for Pb and Cd were studied in an experimental furnace. The results showed that the cement raw meal has quite small surface area （2.49 mZ/g） and compact structure. The results of the experiment indicated that the behavior of heavy metals （e. g. Pb, Cd） in the vertical furnace could be divided into three parts： 1 ）condensing on the wall of the vertical furnace, which occupied approximately 67%-72% of Pb and 58%- 65% for Cd; 2） condensation and absorption on the cement raw meal, which occupied 13%-17% of Pb and 16%-21% of Cd; 3）release into the atmosphere, which occupied 10%-18% of Pb and 14%-26% of Cd. The condensation and absorption of the cement raw meal for Pb and Cd both increased with time, but decreased as the temperature increased, The condensation and absorption kinetics could be well described by the double constant rate equation; a high correlation coefficient exceeding 0.95 was obtained. According to the data from double constant rate equation combined with the dynamic equation, the apparent activation energy could be calculated. The apparent activation energy of condensation and absorption for Pb was 5. 827 kJ/mol, and for Cd was 6. 050 kJ/mol. These could be used to predict the condensation and absorption quantity of the cement raw meal for Pb and Cd during co-processing in cement kilns.