Arsenic(III) Adsorption by Mixed-Oxide-Coated Sand: Kinetic Modeling and Desorption Studies

Abstract

A media developed in the laboratory by applying a coating of iron and manganese to a quartz sand surface, known as mixed-oxide-coated sand (MOCS) is tested in this paper for arsenic(III) adsorption from water. The media has shown alkali resistance. Scanning electron microscope (SEM) images of MOCS have shown uneven and chapped morphology throughout the coated sand surfaces, whereas images of plane quartz sand are flat. The pattern of X-ray diffractograms of plane sand, MOCS, and arsenic-loaded MOCS are similar. The MOCS has an XRD pattern like typical crystalline material. The Langmuir and Freundlich isotherm equations could be used to describe the partitioning behavior of systems at different pH and media doses. Studies on pH effect have shown maximum As(III) removal near neutral pH. The batch kinetic studies data were tested using active available site (AAS) and chemical reaction rate models. The rate constants, equilibrium sorption capacity, and normalized standard deviations were calculated for all models. The tested models almost accurately predict the sorption capacity with respect to time for the whole range of data points. However, sorption kinetic data were better correlated using an AAS equation model based on normalized standard deviation. The results of desorption studies using different regenerants show that 0.2 M NaOH has high desorption efficiency compared with other regenerants for desorption of As(III) from MOCS. The impact of pH on desorption of arsenic(III) was also studied, and results have shown that high pH values show a significant reduction in quantity of arsenic(III) as compared with lower pH values. At pH 11.1, the percentage of arsenic extraction was highest from MOCS media.