Adsorption Behavior and Removal Mechanism of Arsenic from Water by Fe(III)-Modified 13X Molecular Sieves

Abstract

Presented are the synthesis and characterization of Fe(III)-modified 13X molecular sieves and their application as a novel adsorbent for removing arsenic from aqueous solutions. Batch experimental results showed that Fe(III) adsorption by 13X molecular sieves matched well with the Langmuir adsorption isotherm. The adsorption kinetics of arsenic on the Fe(III)-modified molecular sieves fit well with a pseudo-second-order model. The Langmuir adsorption isotherms of arsenic adsorption indicated the highest adsorption capacities of 1167.79 for As(V) at pH 4 and 731.56 mg/kg for As(III) at pH 9. The Fe(III)-modified 13X molecular sieves removed much more As(V) than As(III) at equivalent arsenic concentrations, regardless of the pH conditions. After As(V) removal, the Fe(III)-modified 13X molecular sieves were characterized by PXRD, SEM-EDX, and ATR-FTIR to analyze the morphology and arsenic speciation. The results of PXRD and SEM-EDX spectroscopy indicated that the material was physically stable after As(V) adsorption. ATR-FTIR spectroscopy showed that the formation of inner-sphere surface complexations between Fe hydroxide on the surface of the molecular sieves and As(V) could be a plausible mechanism for the uptake of arsenic by the Fe(III)-modified 13X molecular sieves. Therefore, the relatively low cost and remarkable arsenic-adsorption performance make the title material a promising absorbent for the treatment of arsenic in wastewater.