Preparation Of A Novel RE Ions-Crosslinked Alginate/Modified Diatomite Macroparticle Composite And Their Adsorption On Anionic Dyes

The rapid development of industrialization has led to an increase in the use of synthetic dyes and the discharge of wastewater,making research on dye wastewater treatment technology particularly important and urgent.Therefore,the development of eco-friendly and efficient dye wastewater treatment technology has always been a focus of attention in the environmental protection industry.Adsorption method has been widely used due to its simple operation and the abundance of materials available.However,conventional adsorbents are costly,difficult to separate and difficult to reuse.In order to improve the comprehensive performance of the adsorbents,two rare earth ion cross-linked alginate/modified diatomite macroparticle composites（CPAM-Dia/SA-La and CPAM-Dia/SA-Ce）were successfully prepared in this study by using Diatomite（Dia）as the raw material,modified by polyacrylamide（CPAM）and then cross-linked by La（III）ions and Ce（III）ions respectively to polymerize sodium alginate（SA）as the skeleton,and characterized by SEM-EDS,FT-IR,UV-vis,XRD,BET and XPS analytical methods.Using two composite gels as biosorbents,the preparation and adsorption conditions of the composites were obtained through the adsorption of Acid blue（AB 113）and Congo red（CR）dyes by CPAM-Dia/SA-La,as well as the adsorption of Acid blue（AB 80）and Direct green（DG 6）dyes by CPAM-Dia/SA-Ce.The adsorption efficiency of two biosorbents on dyes was evaluated.The specific research results are as follows:（1）The optimized preparation conditions of CPAM-Dia/SA-La and CPAM-Dia/SA-Ce composite gels were as follows:The CPAM-Dia solution of 8 g/L mass concentration was added to SA solutions of 16 g/L and 20 g/L with stirred evenly at 298 K,and the mixed solutions were dropped into La（NO₃）₃ and Ce（NO₃）₃ crosslinking agent solutions with mass concentration of 40 g/L,respectively.After the crosslinking polymerisation reactions were completed,the products were aged for 90min and washed with deionised water to neutral,then dried CPAM-Dia/SA-La and CPAM-Dia/SA-Ce gel spheres were obtained,respectively.（2）The samples were characterized by SEM-EDS,XRD,FT-IR and UV-vis analysis techniques.The results showed that the surfaces of the successfully synthesized macroparticle gel composites composite gels had rich layered structures and uneven depth and irregular fold groove.The diameter of the particles is greater than 1.3 mm,which can be easily separated from the water body after adsorbing pollutants and can effectively prevent secondary pollution to the environment.The specific surface area and pore size of CPAM-Dia/SA-Ce gel spheres measured by N₂ adsorption/desorption technology are 3.10 m²/g and 0.0024 cm³/g,respectively,CPAM-Dia/SA-Ce belong to mesoporous adsorption material.（3）The optimal conditions for adsorption of AB 113 and CR anionic dyes by CPAM-Dia/SA-La composite were as follows:The initial concentrations of AB 113 and CR dye solutions were 3500 mg/L and1900 mg/L,and their natural p H values were 7.08 and 9.94,respectively.When the adsorption time was 60 min,the adsorption capacities and corresponding removal rates of AB 113 and CR by the CPAM-Dia/SA-La composite at 298 K could reach 2696 mg/g and 92.4%,1477 mg/g and93.3%,respectively.At p H=2.0,the adsorption capacities and removal rate reached the highest,reaching 2907 mg/g and 99.7%,1578 mg/g and99.5%,respectively,and then slightly decreased with the increase of p H to 10.Therefore,the composite gels can be effectively used for the treatment of natural acidity dye wastewater.The adsorption capacity of CPAM-Dia/SA-La for AB 113 is 48 times that of Dia for AB 113.The optimal conditions for adsorption of AB 80 and DG 6 anionic dyes by CPAM-Dia/SA-Ce composite were as follows:The initial concentrations of AB 80 and DG 6 dye solutions were both 1500 mg/L,and their natural p H values were 6.83 and 8.20,respectively.When the adsorption time was 60 min,the adsorption capacities and corresponding removal rates of AB 80 and DG 6 by the CPAM-Dia/SA-Ce composite at298 K could reach 1188 mg/g and 95.5%,1171 mg/g and 93.7%,respectively.At p H=2.0,the adsorption capacities and removal rate reached the highest,reaching 1208 mg/g and 96.6%,1232 mg/g and98.5%,respectively,reached,respectively,and then slightly decreased with the increase of p H to 8.Therefore,CPAM-Dia/SA-Ce composite gels can be effectively used for the treatment of natural acidity dye wastewater.The adsorption capacity of CPAM-Dia/SA-Ce for AB 80 and DG 6 is 3.4 and 7.5 times that of Dia for AB 80 and DG 6.（4）The two composite gels had fast adsorption speed and short equilibrium time for four dyes,and the adsorption processes could be described by the Pseudo-second-order rate model,and the isothermal adsorption was in line with the Langmuir model.The adsorption reactions were all spontaneous reactions with exothermic and increased confusion.（5）The analytical results of FT-IR,UV-vis and XPS before and after the adsorption of anionic dyes showed that the dye adsorption mechanism by the composites was mainly electrostatic adsorption,multiple hydrogen bonding and complexation reaction.（6）CPAM-Dia/SA-La and CPAM-Dia/SA-Ce composites saturated with adsorbed dyes can be desorbed and regenerated with 0.03 mol/L EDTA solution,5%La（Ⅲ）ions and Ce（Ⅲ）ions solutions respectively,and recycled at least three times.In this study,as eco-friendly and easily separable macroparticle biosorbents,the prepared CPAM-Dia/SA-La and CPAM-Dia/SA-Ce composite gels have great advantages such as the green availability of raw materials,the simplicity of the synthesis method,superlarge adsorption capacities,wide range of acidity used for dye wastewater,complete recovery and recyclability,and are very attractive materials having broad application prospect in the treatment of high concentration anionic dye wastewater.