Effectiveness of 3, 4 and 5- Parameters Adsorption Equilibrium Isotherm Models in Describing Arsenic Removal

Abstract

The presence and removal of arsenic ions and salts from the environment have become worldwide environmental issues and problems because of the harmful and toxic nature of the substance. The paper presents the effectiveness of higher adsorption parameters (3, 4 and 5) in describing arsenic removal from aqueous solutions. Raw eggshells from chickens were collected from an institutional farm in Nigeria. These collected raw eggshells were washed with distilled water to remove impurities, air dried to reduce the moisture content and powdered eggshells using a silver crest blender. Energy Dispersive Spectroscopy and scanning electron microscope images of the powdered eggshell were evaluated at selected magnifications. The powdered eggshell's adsorption rates were examined in synthetic and typical arsenic-contaminated water. Parameters of adsorption equilibrium models were determined using Microsoft Excel Solver. The performances of these adsorption equilibrium models in describing arsenic removal from these arsenic-contaminated waters were evaluated statistically using the Model of Selection Criterion (MSC) and Akaike Information Criterion (AIC). The study revealed that the elemental compositions of powdered eggshells are carbon, aluminium, iron, silicon, calcium and oxygen with traces of sodium, magnesium and manganese. The mechanism of arsenic removal by adsorption using powdered eggshell includes redox and replacement reactions. Adsorption equilibrium analysis established that adsorption models' 5 and 4 parameters described the relationship between arsenic removal and the mass of the adsorbent better than the 3 and 2 parameters of adsorption models based on the values of MSC and AIC. All the 5 and 4 parameters of the adsorption models had MSC values greater than 3.0 (equivalent to greater than 0.95 correlation coefficient, 68.75 % and 17.65 % for 3 and 2 parameters of adsorption models. It was concluded that powdered eggshells removed arsenic from aqueous solutions, the removal rate was affected by the nature of the water and 5 and 4 parameters of adsorption models were effective in the description of arsenic removal by powdered eggshell.