Biochar-based Ion-imprinted Polymers For Arsenic Immobilization In Soils

In this paper,using surface ion imprinting technology,arsenic ion imprinted polymer was prepared by adding template ion arsenite with functional monomer 4-vinylpyridine and cross-linking agent ethylene glycol dimethacrylate to biochar prepared from kitchen waste as a carrier,and the ion imprinted polymer was initiated by azo diisobutyronitrile to optimize the material preparation conditions and design experiments to determine the effect of ion imprinted polymer on arsenic treatment in water and soil,respectively.After single-factor as well as orthogonal tests,the optimal formulation for the preparation of the imprinted polymer was determined as pre-polymerization pH=7,functional monomer to cross-linker ratio c（4-VP）:c（EGDMA）=1:10,and eluent concentration c（HCl）=0.8 mol/L.Afterwards,the material was characterized using scanning electron microscopy（SEM）,energy spectrum testing（EDS）,infrared testing（FT-IR）,X-ray diffraction（XRD）,thermogravimetry（TG）,and specific surface area（BET）,which resulted in a homogeneous particle size and good distribution of the polymer on the surface of the carrier with good morphological characteristics.The main elemental composition of the material is C and O in the ratio of 74.50:25.50,and the material has infrared characteristic peaks of biochar,4-vinylpyridine and ethylene glycol dimethacrylate,so the composition of the material includes vinylpyridine and ethylene glycol dimethacrylate as well as biochar.The process of imprinting was also confirmed in the IR spectra:the addition of As to the imprinted polymer led to a significant decrease in the intensity of the characteristic peaks of the imprinted polymer.X-ray diffraction did not show a sharp peak packet,did not show obvious crystalline features,and the material was typical of macromolecular organics.The material starts to decompose only at 290°C and has good thermal stability.The specific surface area is 3.78 m²/g for imprinted polymers and 4.38 m²/g for non-imprinted polymers,which can be used for adsorption.A single-factor test was conducted to determine the subsequent adsorption conditions of the materials.The test factors included solution pH,adsorption temperature,and initial arsenite concentration of the solution,and the results were:solution pH=5.0,adsorption temperature 25°C,and initial arsenite concentration 100 mg/L.The thermodynamic and adsorption selectivity of the materials were studied under the previously determined adsorption conditions,and the results were:the adsorption of arsenite ions by the materials conforms to the Langmuir adsorption isotherm equation,and the adsorption belongs to the monomolecular layer adsorption;the thermodynamic parametersΔG<0 andΔH>0,and the reaction belongs to the spontaneous heat absorption reaction.The adsorption selectivity of the materials was investigated,and the results were:the ion-imprinted polymers showed significant selectivity between NO₃^-,SO₄^2-,Cl^-and As O₃^3-,and the selectivity coefficient could reach more than 1.50.The selectivity for PO₄^3-adsorption was not very obvious,and the selectivity coefficient was 1.32,which was less than 1.50.The material was used for the immobilization of arsenic in soil,and the results showed that the material was used for the immobilization of free arsenic in laboratory trivalent arsenic blended soil with the amount of free arsenic of 115 mg/kg,and the immobilization effect could reach 45%,and the immobilization reached stability in the 5th week.The experiments were designed to investigate the effects of acidity,organic matter and phosphate fertilizer on the immobilization effect,and the results showed that acidity would have a serious effect on the adsorption effect,and the immobilization efficiency decreased from 45.70%to 27.81%after 8 weeks of simulated acid rain flushing at pH=3.0;phosphate would also have a significant interference with the adsorption stability,and the immobilization efficiency decreased from45.70%to 31.94%;organic matter had little effect on the immobilization effect,and the efficiency of immobilization remained in the range of 43.25%to 48.21%.The mechanism of arsenic immobilization by the material was initially investigated using infrared spectroscopy,and the results showed that the adsorption of the material to arsenic in soil was physical.The materials were used for the immobilization of free arsenic from the tailings of an arsenic smelter with a free arsenic content of 106 mg/kg.The results were:the efficiency of immobilization of the materials was around 38.40%,the immobilization reached stability at the 5th week,and the materials did not promote the conversion between tri-and pentavalent arsenic.