CaAl类水滑石的磷酸根吸附性能及其影响因素研究

Exploring and Evaluation of CaAl Hydrotalcite-like Adsorbents on Phosphate Recycling

本研究采用共沉淀法成功制备了CaAl类水滑石(CaAl-LDH),并运用扫描电子显微镜(SEM)和热重/差示扫描量热分析(TG-DSC)技术对CaAl-LDH的形貌及热稳定性进行了表征.利用合成含磷溶液及真实含磷污水,探究了CaAl-LDH对磷酸根的吸附性能及其主要影响因素.结果表明:制备的CaAl-LDH具备类水滑石的典型六边形层片状结构以及较好的热稳定性.CaAl-LDH吸附磷酸根的规律符合Langmuir吸附等温方程,理论最大吸附容量为162.3mg/g.吸附动力学过程符合假二级动力学方程.几种竞争阴离子对吸附的干扰作用由强到弱为23CO->24SO->3NO-.吸附真实含磷污水中磷酸根时,10h左右达最大去除率,可将污水中磷浓度降低到极低水平.因此,制备的CaAl-LDH具有很好的磷酸根吸附性能,是一种应用前景广阔的污水磷酸根吸附回收利用材料.

We synthesized Ca Al-Cl layered double hydroxide（Ca Al-LDH） by co-precipitation and evaluated its performance in phosphate adsorption. Calcium fluoride（0.25 mol） and sodium meta-aluminate（0.1 mol） were poured into a beaker that contained 0.2 mol sodium hydroxide. The suspension was aged at 25 ℃ for 4 h under vigorous stirring. The acquired sludge was filtered and washed using distilled water, dried at 60 ℃, and then ground to powder for further study. Phosphate stock solution was prepared using sodium di-hydrogen phosphate, and used for adsorption kinetic and isotherm research. The impact factors（e.g., competitive anions, adsorbent dosage, and adsorption time） of phosphate removal by Ca Al-LDH were researched using industrial effluents. Adsorption processes were studied in 50 m L centrifuge tubes, with shaking by a thermostatic oscillator for planned time intervals. Mixtures were filtered through a 0.22 μm membrane before analysis. Samples before and after phosphate adsorption were characterized by scanning electron microscopy to observe morphological characteristics. Thermo-gravimetry/differential scanning calorimetry was used to study the sample thermo-stability. Metal ions（e.g. calcium, aluminum） and phosphate concentration were determined by inductively coupled plasma atomic emission spectrometry. We observed a typical hydrotalcite structure in the Ca Al-LDH by scanning electron microscopy, which indicates that the obtained materials are well-defined hexagonal platelet-like particles. The synthesized Ca Al-LDH had good thermo-stability based on thermo-gravimetry/differential scanning calorimetry, and pyrolysis showed four mass loss stages. From batch adsorption experiments, we found that the adsorption fitted a Langmuir model（R2=0.997） very well; the maximum adsorption capacity（qmax） of 162.3 mg/g corresponded to the experimental data（166.9 mg/g）, and is significantly higher than previous reports. The adsorption kinetics followed a pseudo-second-order model（R^2=0.998）. Additionally, co-existing competitive anions influenced phosphate adsorption in the order of CO3^2-〉SO4^2-〉NO3^-. Adsorbent dosage and contact time could also impact Ca Al-LDH phosphate adsorption capacity. Ca Al-LDH in this study could be applied in the recovery and reuse of phosphate from industrial wastewater because of its outstanding performance and stability.