Preparation and Adsorption Characteristics of Novel Molecular Sieve for High Efficiency Arsenic Removal

Abstract

In order to enhance the adsorption performance of 4A molecular sieve for arsenic in aqueous solution,using MS as a carrier,iron-loaded molecular sieves(FMS)and iron-manganese molecular sieves(FMMS)were prepared as adsorbents for arsenic removal by impregnation method.The MS and FMS were characterized by SEM,FT-IR and BET,and carried out batch experiments to investigate the adsorption and removal effects of FMS and FMMS for pentavalent arsenic(As^5+)and trivalent arsenic(As^3+).The adsorption kinetics,isothermal adsorption test and adsorption thermodynamics of the FMS adsorption process were performed.The results show that the specific surface area of FMS is significantly increased and the surface structure of the material is improved.The specific surface area and pore volume of the FMS increased from^27.38 m^2 g and 0.068 cm^3 g to 281.25 m^2 g and 0.16 cm^3 g,respectively.Meanwhile,the average pore size decreased from 9.93 nm to 2.21 nm.This could cause the dense coarse particles to become an adsorbent with loose porous microstructure.FT-IR analysis shows that iron oxide formed in the iron salt impregnation process is mainly combined with O-H,Al-O and Si-O in the molecular sieve structure.The results of batch experiments with 4 mg L As^5+indicate that the removal rate increases by about 70%after the material modification.Moreover,the adsorption process is in accordance with the quasi second-order adsorption kinetics,and the correlation coefficient(R 2)is 0.99,indicating that the chemical adsorption plays an important role in the adsorption process.The Freundlich isotherm adsorption model fits the adsorption data well with a correlation coefficient(R 2)is 0.98,and the maximum adsorption capacity is calculated to be 9.9 mg g.Furthermore,the calculation of thermodynamic parametersΔG,ΔH andΔS find that temperature increase is favorable for adsorption,and the disorder degree between solid and liquid on the surface of the material increases during the reaction.Compared with FMS,FMMS can effectively improve the removal performance of As^3+.The initial concentrationof coexistence conditions wereρ(As^3+As^5+)=2.0,4.0,6.0 mg L,the removal rate of FMMS is increased by about 26.34%,28.06%and 28.09%,respectively.The research shows that the use of iron salt impregnation method to modify MS can effectively increase the adsorption capacity of As^5+and As^3+,and can give full play to the practical application value of the material.