镁铝双金属氢氧化物及氧化物去除硫离子(S^(2-))性能及其机理研究

Performance and Mechanism of Mg, Al Layered Double Hydroxides and Layered Duble Oxides for Sulfide Anion (S2-) Removal

利用层状双金属氢氧化物(LDHs)层间阴离子的可交换性及其结构记忆效应,研究了氯离子插层镁铝双金属氢氧化物(MgAl-Cl-LDHs)及镁铝双金属氧化物(MgAl-LDO)去除S2-的性能及机理。采用X射线粉末衍射(XRD)、红外光谱(FTIR)、紫外-可见光谱(UV-Vis)和电感耦合等离子体原子发射光谱(ICP)等表征技术,详细探讨了焙烧复原法及离子交换法得到的不同产物的结构和去除S2-性能,提出了MgAl-Cl-LDHs和MgAl-LDO对S2-的不同去除机理。结果表明,MgAl-LDO具有较MgAl-Cl-LDHs更为优良的去除S2-性能。文中所有去除实验的pH值均为9,此时S2-发生水解且主要以HS-存在于溶液中。采用MgAl-Cl-LDHs为前体时,HS-的离子交换能力比Cl-弱,不能通过与Cl-交换进入层间,S2-的去除机理主要是表面吸附HS-及将其氧化成S2O32-。以MgAl-LDO为前体时,HS-通过LDO结构恢复能迅速进入层间,且受MgAl-LDO的催化氧化性能的影响,在结构恢复的同时HS-被氧化成S2O32-、S2-和S3-,可以高效去除溶液中的S2-。nMg/nAl比为2的LDHs在500℃下焙烧的产物MgAl-LDO对S2-的去除率能够达到98%以上,以MgAl-LDO去除S2-的方法可作为一种高效除S2-的方法。

Based on the exchangeable property of the interlayer anions and the so-called ＂memory effect＂ of the layered double hydroxides （LDHs）, the capacities and mechanisms for sulfide anion （S^2-） removal were studied using chloride-containing MgAl-LDHs （MgAl-Cl-LDHs） and the layered double oxides （MgAl-LDO）. Structures of the products obtained by anion exchange and reconstruction, and the removal capacities were characterized by XRD, FTIR, UV-Vis and ICP, and the different mechanisms for MgAl-Cl-LDHs and MgAl-LDO were proposed. The results indicate that the removal capacity for MgAl-LDO is much greater than that for MgAl-Cl-LDHs. In this work S^2- removal test was proceed at pH of 9, and then S^2- was hydrolyzed, and mainly existed as HS^- in the solution. When MgAl-Cl-LDHs was used as the precursor to remove S^2-, due to the weaker exchange capacity for HS^- compared to Cl^-, HS^- could not enter the interlayer through anion exchange with Cl^-. Adsorption of HS^- to the sample＇s surface and oxidation to S2O3^2- are the removal mechanism for MgAl-Cl-LDHs. While when MgAl-LDO was used as the precursor, during the structure recovering, HS^- entered the interlayer qickly, and was oxidized to thiosulfate anion （S2O3^2-） and polysulfide anions （S2^- and S3^-） simultaneously. Therefore, MgAl-LDO can remove S^2- efficiently. The products of LDHs with Mg/Al molar ratio of 2 calcined at 500℃ were shown to have a high degree of removal capacity at above 98%.