Single and binary adsorption experiments and modeling of arsenic and fluoride using activated carbon as adsorbent

Abstract

Arsenic and fluoride are co-occurring contaminants in groundwater. This research investigated the competitive adsorption of arsenic and fluoride from aqueous solution on activated carbon. Batch experiments were used to study the behavior and efficiency of activated carbon to know the influence of adsorbent dosage, contact time, and solution pH of arsenic and fluoride in single and binary component systems. At optimum values, in single-component systems, activated carbon demonstrates efficient adsorption of arsenic and fluoride, achieving a percentage removal of 93.56% for arsenic and 72% for fluoride. Similarly, in binary-component systems, the percentage removal of As(V) is found to be 71.91%, while fluoride is removed at a rate of 90%. Kinetic studies showed that adsorption followed a pseudo-second-order kinetic mode, which suggests chemisorption. Langmuir, Freundlich, Toth, Redlich Petersons, and Modified Langmuir Freundlich (MLF) models were used to interpret the single adsorption isotherm data. The maximum uptake of arsenic and fluoride was 3.58 mg/g and 2.32 mg/g, respectively. It was noted that the Modified Langmuir Freundlich isotherm model gave a better fit with higher R2 and lower RMSE values. Extended Langmuir and Extended Freundlich isotherm models were used to interpret the competitive adsorption data. The competitive studies showed selectivity of adsorption for As(V) > F which suggested that the affinity of activated carbon was greater towards As(V) than fluoride. Also, As(V) showed antagonistic behavior with F.