水化普通硅酸盐水泥吸附水中氟化物的动力学与热力学解析

以水化普通硅酸盐水泥颗粒为除氟吸附剂,对其吸附水中氟化物的动力学和热力学过程进行了解析.结果表明:水化普通硅酸盐水泥对氟化物的吸附平衡时间为192 h,20℃时其吸附容量为14.63 mg/g,4℃时为13.14 mg/g.吸附速率特性与准二级动力学模型拟合性较好且吸附速率由颗粒内部扩散速率控制,吸附行为均满足Langmuir吸附等温式.吸附焓变为16.56 kJ/mol,表明该吸附过程是以化学吸附为主的吸热反应；吸附熵变为正值,说明该吸附过程是熵推动为主的过程；吉布斯自由能在4和20℃时均为负值,说明该吸附反应是一个自发过程.脱附研究与XRD分析结果也证实,该吸附反应以化学吸附过程为主.

Kinetic and Thermodynamic Analysis of Fluoride Adsorption to Hydrated Portland Cement

The kinetic and thermodynamic processes of fluoride adsorption to hydrated Portland cement(HPC) were studied.The results indicated that the adsorption equilibrium was reached in 192 h,and the adsorption capacities were 14.63 mg/g at 20 ℃ and 13.14 mg/g at 4 ℃.Kinetic data were well described by the pseudo-second-order model,and the adsorption rate was controlled by the intra-particle diffusion.The fluoride adsorption behavior of the particles of HPC was appropriately fitted to the Langmuir isotherm.The adsorption enthalpy change of 16.56 kJ/mol indicated that the adsorption process was mainly a chemical adsorption,and the adsorption was an endothermic reaction.The positive entropy change meant that the randomness was increased at the solidsolution interface during the adsorption of fluoride onto HPC.The adsorption of fluoride to HPC was a spontaneous process,since the changes of adsorption Gibbs free energy were negative at both 4 and 20 ℃.The results of the desorption study and XRD analysis also suggested that the process of fluoride adsorption by HPC was mainly a chemical adsorption.