Research On Adsorption Properties Of Pb²⁺ And Cd²⁺ On Lignocellulose Based Hydrogels

The lignocellulose, acrylic acid and the montmorillonite as main raw materials to prepare lignocellulose-g-acrylic acid/montmorillonite nanocomposite hydrogels (LNC-g-AA/MMT) by a in situ intercalative polymerization technology. LNC-g-AA/MMT were used as adsorbent to adsorb Pb2+、Cd2+from aqueous. In the adsorption examination, the effects of initial metal ions concentration, initial solution pH, contact time and contact temperature on adsorption capacity of LNC-g-AA/MMT for Pb2+、Cd2+were investigated, determining the optimum conditions of adsorption. In order to explore the adsorption mechanism of the nanocomposite hydrogels, the adsorption isotherm and adsorption kinetics models were researched. In the desorption examination, the effects of HNO3concentration, desorption time and desorption temperature were studied, determining the optimum desorption condition, at the same time, the nanocomposite hydrogels of regeneration were explored. In order to analyze the change of structure and surface properties of the nanocomposite, the structure of hydrogels were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), infrared spectroscope (FT-IR) and the specific surface area analyzer.The research results were summarized as follows:1. The characterization results indicated that the copolymer of the Lignocellulose-g-acrylic acid (LNC-g-AA) into the interlayer of the montmorillonite by destroying the crystal structure of the montmorillonite, forming a new nanocomposite material which intercalated-exfoliated type. At the same time, many porous were been seen in the surface of the nanocomposite hydrogels. The Fourier transforms infrared spectra of LNC-g-AA/MMT nanocomposite and adsorption of metal ions on LNC-g-AA/MMT nanocomposite showed that the hydroxyl and carboxyl were involved in the reaction in the adsorption process. Complexing adsorption and ion exchange adsorption play a main role in the adsorption process, physical adsorption share is very small.2. In single adsorption examination, the effects of initial metal ions concentration, initial solution pH, contact time and contact temperature on adsorption capacity of LNC-g-AA/MMT for Pb2+、Cd2+from aqueous were investigated, the results show that the adsorption capacity of LNC-g-AA/MMT for Pb2+was achieved918.2mg/g when the initial concentration of Pb2+solution0.04mol/L, solution pH5.7, contact time120min and contact temperature30℃. The adsorption capacity of LNC-g-AA/MMT for Cd2+was achieved482.5mg/g when the initial concentration of Cd2+solution0.05mol/L, solution pH5.5, contact time60min and contact temperature30℃. The adsorption isotherms and kinetics have been studied, which implied that the all adsorption processes were in good agreement with the Langmuir isotherm model and Pseudo-second-order model, respectively.3. In the desorption examination, we researched the effects of the concentration of HNO3, the desorption time and desorption temperature on desorption capacity of LNC-g-AA/MMT for metal ions from aqueous. The research results determined that the maximum desorption capacity and efficiency of LNC-g-AA/MMT for Pb2+are821.9mg/g and90%respectively after using desorption agent0.06mol/L HNO3at30℃and contact time of60min. The maximum desorption capacity and efficiency of LNC-g-AA/MMT for Cd2+are448.2mg/g and92.9%respectively after using desorption agent0.04mol/L HNO3at30℃and contact time of60min. The cycle adsorption-desorption results showed that the rate of desorption of LNC-g-AA/MMT nanocomposite hydrogels for metal ions were more than75.9%after three times of cycle adsorption-desorption.4. The competitive adsorption of Pb2+、Cd2+metal ions from aqueous by LNC-g-AA/MMT nanocomposite hydrogels were investigation in the adsorption examination of mixed metal ions. The results as follow:(1) In the initial concentration of Pb2+、Cd2+solutions under the same condition, the adsorption capacity of LNC-g-AA/MMT for Pb2+was764.1mg/g, dropping16.8%than single metal ions when the concentration of Pb2+solution was0.04mol/L, the contact time was120min and the adsorption capacity of LNC-g-AA/MMT for Cd2+was207.0mg/g, dropping57.1%than single metal ions when the concentration of Cd2+solution was0.05mol/L, the contact time was120min.(2) In the initial concentration of Pb2+、Cd2+solutions under not the same condition, when the initial concentration of Cd2+was more than0.01mol/L, the adsorption capacity of LNC-g-AA/MMT for Pb2+was less than single metal ions and the adsorption capacity of LNC-g-AA/MMT for Cd2+decreased rapidly in the presence of Pb+.(3) The initial concentration of Pb2+、Cd2+solutions were0.04and0.05mol/L respectively in the mixed metal ions solutions, the time of equilibrium adsorption of LNC-g-AA/MMT for Pb2+、 Cd2+was120min. Compared with the single metal ions adsorption, mixed ions had a little effects on the time of equilibrium adsorption for Pb2+, however there was a60min delay for Cd2+.