酸热活化对海泡石吸附水溶液中Cd的影响机制

为增加SP（海泡石）的比表面积并提高其对水溶液中Cd的去除效率，采用HCl对SP进行酸热活化，探索制备HHSP（酸热活化海泡石）最佳的c（HCl）、酸改性时间和热活化温度，并比较SP和HHSP对Cd的吸附动力学和等温吸附特征，通过对吸附前后的SP和HHSP进行SEM-EDS（扫描电镜）、XRD（X射线衍射）和XPS（X射线光电子能谱）分析，以阐明HHSP吸附Cd的微观反应机理.结果表明:0.9 mol/L的HCl改性24 h后，500℃下热活化1 h制备的HHSP吸附性能最佳.准二级动力学模型和Langmuir等温吸附模型均能够很好地描述SP和HHSP对Cd的吸附特征.SP和HHSP对初始质量浓度为50 mg/L的溶液中Cd的去除率在2 h内分别达73.13%和85.96%，在24 h内达到吸附平衡.HHSP的最大饱和吸附量（q_max）为22.147 mg/g，比SP（4.200 mg/g）增加了4.23倍.酸热处理降低了SP的pH和pHpzc（零电荷点），表明在SP表面吸附活性中心增多.SEM-EDS显示，酸热活化未改变SP的纤维状结构，Cd吸附量由SP的1.57%增至HHSP的2.13%.XPS分析表明，SP和HHSP对Cd的吸附作用包括了表面羟基（-OH）络合作用以及产生CdCO₃、CdCl₂、CdO和Cd（OH）₂沉淀.XRD分析表明，酸改性通过清除SP的CaCO₃成分，比表面积增加，从而增加了HHSP对Cd的吸附量.研究显示，酸热活化可增加HHSP对Cd的吸附效能，为利用HHSP有效控制稻田土壤Cd生物有效性提供了有益途径. 

Efficiency and Mechanisms of Aqueous Cd Removal by Sepiolite Modified by Heat and Acidification

This study investigated the efficiency and mechanisms of Cd removal with sepiolite(SP) modified by heat and acidification(HHSP). The optimal acid concentration, reaction time and temperature was firstly explored. On this basis, the dynamics and isotherms of Cd adsorption by SP and HHSP were compared and the adsorption mechanisms were further investigated with SEM-EDS, XRD and XPS. The results show that the HHSP prepared with 0.9 mol/L HCl for 24 h and heating at 500℃ for 1h exhibited the highest Cd sorption capacity. The Cd sorption by both SP and HHSP followed the pseudo-second order kinetics, and 73.13% and 85.96% of adsorption occurred in the first 2 h, respectively. The adsorption reached equilibrium after 24 h when the initial Cd concentration was 50 mg/L. The maximum Cd adsorption capacity of HHSP was estimated to be 22.147 mg/g based on Langmuir model, which was 4.23 times as high as that of SP (4.200 mg/g). The pH and pHpzc of SP apparently decreased with acidification, indicating an increase in the adsorption sites for cations on the modified SP. SEM-EDS showed that the acidifying and heating treatment had little effect on the fibrous structure of SP, and the mass ratio of the adsorbed Cd increased from 1.57% for SP to 2.13% for HHSP. XPS analysis indicated that both Cd complexation by the surface hydroxyl (-OH) and precipitation of CdCO₃, CdCl₂, CdO and Cd (OH)₂ contributed to the Cd removal by SP and HHSP. XRD analysis demonstrated that the specific surface area of SP was increased by acid activation due to the removal of CaCO₃. The results of this study highlighted that the pre-treatment with acidification and heat can improve the effectiveness of HHSP for Cd immobilization, and provide a useful way to apply HHSP in mitigation of Cd bioavailability in paddy soil.