Adsorption of the Cationic Dye Ethyl Violet on Acid and Alkali-Treated Wild Carob Powder, A Low-Cost Adsorbent Derived from Forest Waste

The effect of acid-alkaline treatment of lignocellulosic material (wild carob forest wastes) on Ethyl violet adsorption was investigated. It was found that surface chemistry plays an important role in Ethyl Violet (EV) adsorption. HCl treatment produces more active acidic surface groups such as carboxylic and lactone, resulting in an increase in the adsorption of EV dye. The adsorption efficiency was higher for treated lignocellulosic material with HCl (WCHCl) compared to that treated with KOH (WCKOH); maximum biosorption capacities were 170 and 130 mg/g for WCHCl and WCKOH at pH 6, respectively. It was also found that for both treated materials less than 150 min was needed to reach equilibrium. The adsorption of a basic dye (i.e. ethyl violet or basic violet 4) was carried out by varying some process parameters, such as the initial concentration and pH. The adsorption process can be well described by means of a pseudo-second-order reaction model and experimental data were accurately expressed by the Sips and Langmuir models for both WCHCl and WCKOH.