A Comparative Study of the Adsorption of Industrial Anionic Dyes with Bone Char and Activated Carbon Cloth

This study presents a comparative analysis of the adsorption behavior of three industrial ionic dyes—Indigo Carmine (IC), Congo Red (CR), and Evans Blue (EB)—using two adsorbent materials with distinct physicochemical and textural properties: bone char (BC) and activated carbon cloth (ACC). The main objective was to evaluate and compare the adsorption equilibrium and kinetics of these dyes on both materials. Equilibrium behavior was analyzed using the Prausnitz–Radke isotherm model, while adsorption kinetics were evaluated using PVSDM. The results showed that adsorption onto BC was primarily driven by electrostatic interactions, enhanced by the presence of hydroxyapatite. The maximum adsorbed amounts were determined to be 0.296, 0.107, and 0.0614 mmol g−1 for CR, IC, and EB, respectively. In contrast, adsorption on ACC was influenced by both electrostatic and hydrophobic forces due to its carbonaceous composition. IC exhibited significantly higher adsorption on ACC (1.087 mmol g−1), whereas CR and EB only 0.269 mmol g−1 and 0.028 mmol g−1, respectively. Kinetic studies revealed that intraparticle transport was the rate-limiting step across all systems. Specifically, pore volume diffusion controlled the adsorption rate on ACC, with mean diffusion coefficients of 9.72 × 10−8, 1.83 × 10−9, and 1.48 × 10−10 cm2 s−1 for IC, CR and EB, respectively. Conversely, for BC, adsorption surface diffusion played a dominant role in the adsorption of IC and CR, with mean diffusion coefficients of 1.62 × 10−9 and 7.28 × 10−10 for IC and CR, respectively. These findings underscore the importance of considering both equilibrium and kinetic parameters in the design of efficient wastewater treatment systems.