UTILIZATION OF HYDROXYAPATITE/CRAB SHELL CHITOSAN COMPOSITES IN REMOVAL OF AQUEOUS CONGO RED: INFLUENCE FACTORS, ADSORPTION KINETICS AND ISOTHERM

By Nguyen Trung Hieu, Ha Tuan Anh
DOI: 10.37550/tdmu.EJS/2025.02.627

Due to the limitations of traditional adsorbents for dyeing wastewater, this study combined natural adsorbent (CS, chitosan) and hydroxyapatite (HAp) to form a composite for enhancing the adsorption of aqueous Congo red (CR). The chitosan was prepared from crab shells (Somanniathelphusa sinensis) with a deacetylation degree of about 89%. The HAp and HAp-CS composites were prepared by precipitation in high pH (~10) with the help of concentrated ammonia water (25%). The crab shell chitosan and chitin were characterized by the FTIR method, and the HAp and HAp-CS composites were analyzed using the SEM method. The CR adsorption experiments were carried out in batch form and sampled once for each condition. The results showed that the characteristic peaks in the FTIR spectrum confirmed the success of the crab shell chitosan preparation. The HAp and HAp-CS composites possess porous structures and seem to have a high surface area. The CR adsorptions reached optimal after 5-15 min. contacting, the adsorption efficiency tended to decrease with the initial concentration of CR and increase with the adsorbent dosage. The initial pH of the solution affected the adsorption efficiency for the 70%HAp-CS and 30%HAp-CS composites but had almost no effect on the adsorption capacity of 0%HAp-CS and 50%HAp-CS. The 50%HAp-CS composite had the best adsorption capacity among the synthesized composites (qmax = 769.2mg/g). The adsorption isotherm and kinetics best fit the Langmuir isotherm and pseudo-second-order kinetics model.