Razor Clam (Ensis directus) Shell as a Low-Cost Adsorbent for Anionic and Cationic Dyes in Aqueous Solutions

Abstract

The ultimate objective of this study was to investigate the potential application of razor clam (Ensis directus) shell (RCS) for the removal of synthetic dyes from aqueous solutions. Adsorption of anionic dye (congo red, CR) and cationic dye (methylene blue, MB) was studied under different experimental conditions such as initial pH solution, adsorbent dosage and initial dyes concentration. High affinity of CR towards RCS was obtained at an acidic medium (pH 2.0), while alkaline medium (pH 8.0) was favourable for MB adsorption. The removal for both dyes exhibited a reverse trend with increasing the initial dyes concentration. Adsorption equilibrium data were fitted to Freundlich and Langmuir isotherm models. A better correlation (R 2 > 0.95) was obtained with Freundlich isotherm model. The adsorption capacity (K F) of RCS for CR and MB was estimated as 6.52 and 0.66 mg/g, respectively. The regeneration of RCS was evaluated in a desorption study, of which hydrochloric acid (HCl) and acetic acid (CH 3 COOH) was used as desorption agents. HCl (0.5 mol/L) was the best desorption agent, due to its ability to desorb 81% of CR and 67% of MB. The feasibility of RCS was compared with olive tree derived activated carbon, a commercial adsorbent for water treatment in Libya. Based on results obtained from competitive and comparative studies, it can be concluded that RCS, a fishery waste-based material, is a promising low-cost adsorbent for the remediation of water contaminated with toxic dyes.