Adsorption Characteristics of Congo Red Dye onto Calcinated Mytilus edulis Shell Powders

Dye wastewater poses a significant threat to aquatic organisms due to its high toxicity. Reducing or eliminating the dye waste from the water is necessary for a healthy and sustainable aquaculture. This study investigated the adsorption properties of Congo red dye on Mytilus edulis shell powders prepared by calcination at 500°C, 700°C, and 900°C The modified shell powder products were analyzed by SEM (scanning eletron microscopy) and FTIR (fourier transform infrared spectroscopy) for the morphology and structural characterization. The effects of different calcination temperatures, reaction times, reaction temperatures, and initial concentration of Congo red on the adsorption properties were investigated. The adsorption kinetics and isothermal adsorption models were also established. The results revealed that the shell powder calcinated at 900° showed the best adsorption capacity on Congo red from aqueous solution. The adsorption reaction reached equilibrium after 150 min and followed by the pseudo-second-order kinetic model. At 25°C, 96.2% of the Congo red in the solution could be removed, and the adsorption capacity could reach at least 1015 mg g⁻¹. The adsorption isotherm is fit with the Freundlich model, indicating a multiphase adsorption process. These results are helpful for cleaning and treating printing and dyeing effluents as well as high-value utilization of shell waste resources.