Study On Preparation Of Clay-based Composite Materials And The Adsorption Properties For Heavy Metal Ions

It is a hot research topic in the adsorption field that the cheap materials with excellent adsorption performance and environmental protection are selected as adsorbents to effectively remove the heavy metal ions in the wastewater. As the palygorskite have many advantages, such as cheap, big surface area and the surface with negative charge. It has better adsorption performance. In order to increase adsorption capacity of palygorskite, it was modified using different methods in this thesis. When the palygorskite composite materials were used as adsorbents to remove metal ions, they had high adsorption capacity, fast adsorption rate, high selective adsorption of metal ions and good reusability. The adsorption equilibrium was analyzed using the isotherm model and the kinetic model. The main research works are as follows:1. The CMC/PGS composites were prepared by combining sodium carboxymethyl cellulose and palygorskite using g-?2,3-epoxypropoxy? propytrimethoxysilane?KH-560? as the crosslinking agent in alkaline solution. The composites were characterized by FTIR, TG, XRD and SEM/EDS analysis techniques. The effects of pH value, adsorption time, adsorption temperature and Pb²⁺ concentration on the adsorption capacity of Pb²⁺ were investigated. The results showed that the maximum adsorption capacity for Pb²⁺ was 97.8 mg/g?in comparison with 48.6 mg/g for PGS?at 291 K, the amount of the adsorbent was 10 mg and the initial concentration of Pb²⁺was 100 mg/L at pH 5.0. The adsorption process of Pb²⁺ was in accordance with the pseudo-second-order kinetic model and the adsorption isotherms of Pb²⁺ could be well described with the Langmuir equation.2. PGS/CMC-g-HEMA composites were prepared by free radical copolymerization, the graft copolymerization of 2-hydroxyethyl methacrylate?HEMA?with sodium carboxymethyl cellulose?CMC? was carried out using N,N-methylene bisacrylamide?MBA? as crosslinking agent and the palygorskite as the carrier. The adsorption of Pb²⁺ from in single aqueous solution and the adsorption of Pb²⁺ andCu²⁺ in complex solution with PGS/CMC-g-HEMA were studied. The effects of pH,contact time and temperature were investigated. The results indicated that the maximum adsorption capacity for Pb²⁺ was 33.8 mg/g at 293 K. Kinetic and isotherm studies of Pb²⁺ revealed that adsorption data followed the Langmuir isotherm and the pseudo-second-order kinetic model. The concentration of the complex solution was more than 40 mg/L, the selective adsorption of Pb²⁺ on PGS/CMC-g-HEMA. In addition,adsorption desorption cycle of the PGS/CMC-g-HEMA for Pb²⁺ showed good repetition.3. Palygorskite/Mg-Al layered double hydroxides?PGS/MgAl-LDH? and its calcined form?PGS/CLDH? was synthesized by coprecipitation method using urea as a precipitator in the aqueous solution of the palygorskite. The obtained materials were characterized by FTIR, TG, XRD and SEM/EDS and the adsorption performances were evaluated for the removal of Pb²⁺, Cu²⁺ and Ni²⁺ in the aqueous solution. In view of these results, the composites showed a highly effective Pb²⁺ removal property. The adsorption capacity of the three kinds of heavy metal ions was increased after the calcination of the composites. The equilibrium data of Pb²⁺, Cu²⁺ and Ni²⁺ ions was fitted the Langmuir isotherm, the adsorption capacity of Pb²⁺ was higher than those of Cu²⁺ and Ni²⁺ ions. From kinetic studies, it was found that the pseudo-second-order kinetic model provided the best correlation of the experimental data. In addition, the adsorption mechanism of three kinds of heavy metal ions was discussed.