Mg-Al-Cl^(-)LDH对磷的吸附性能及其机理

Adsorption performance and mechanism of Mg-Al-Cl^(-)LDH on phosphate

通过成核/晶化隔离法制备了氯离子型镁铝层状双金属氢氧化物(Mg-Al-Cl^(-)LDH),并用于磷酸盐的吸附;借助扫描电镜(SEM)、X射线衍射仪(XRD)、傅里叶红外光谱仪(FT-IR)、X射线光电子能谱(XPS)进行了表征,并探究其吸附磷酸盐的机理。结果表明:当pH为4~7时,Mg-Al-Cl^(-)LDH对磷的吸附效果较好,而在碱性条件下吸附量会下降;磷质量浓度为50 mg·L^(−1),当pH为5时,Mg-Al-Cl^(-)LDH投加量为2 g·L^(−1)时,磷去除率可达到100%;共存离子CO_(3)^(2−)会对吸附产生一定影响,当CO_(3)^(2−)质量浓度为50 mg·L^(−1)时,磷去除率由87%降低到63%。Mg-Al-Cl^(-)LDH对磷的吸附过程在前15 min迅速,90 min时达到平衡,符合准二级动力学和Sips吸附等温模型,说明主要吸附过程以化学吸附为主,理论最大吸附量为62.46 mg·g^(−1)。表征结果表明,Mg-Al-Cl^(-)LDH为典型的六边形层片结构,吸附后依旧保持该结构。Mg-Al-Cl^(-)LDH对磷的吸附机理主要为静电吸引、层间阴离子交换、配体交换过程。

The chloride ion type magnesium aluminum layered double hydroxide(Mg-Al-Cl^(-)LDH)was prepared by nucleation and crystallization isolation method,and used to absorb phosphate.Scanning electron microscope(SEM),X-ray diffractometer(XRD),Fourier Infrared Spectroscopy(FT-IR)and X-ray Photoelectron Spectroscopy(XPS)were employed to characterize the fresh and P absorbedMg-Al-Cl^(-)LDH and identify the corresponding adsorption mechanism.The results show that Mg-Al-Cl^(-)LDH had a good adsorption performance towards phosphate at pH 4~7,whereas the adsorption capacity decreased under alkaline conditions.At the initial phosphate concentration of 50 mg·L^(−1),pH 5 and Mg-Al-Cl^(-)LDH dosage of 2 g·L^(−1),the phosphate removal rate could reach 100%.The coexisting anion of CO_(3)^(2−)had a certain influence on the adsorption,at its concentration of 50 mg·L^(−1),the phosphate removal rate decreased from 87%to 63%.The phosphate adsorption process on Mg-Al-Cl^(-)LDH was rapid in the first 15 min,then reached equilibrium in 90 min,which conformed to the pesudo-second-order kinetics and the Sips adsorption isotherm model.This indicated that the adsorption process was dominated by chemical adsorption with the maximum theoretical adsorption capacity of 62.46 mg·g^(−1).The characterization results showed that Mg-Al-Cl^(-)LDH was a typical hexagonal layered structure and still maintained it after adsorption.The phosphate adsorption mechanism on Mg-Al-Cl^(-)LDH was mainly electrostatic attraction,interlayer anion exchange and ligand exchange.