Transformation of Mytella falcata residual shell into CaAl/LDH adsorbent: Removal of methyl orange and methylene blue dyes

This study analyzed the viability of using malacoculture residue (Mytella falcata) to produce layered double hydroxides (LDHs) and for its subsequent use as an adsorbent. The CaAl/LDH-RE material was produced with calcium oxide from the residue and the CaAl/LDH-AP was produced with a commercial reagent. Both were used to remove methyl orange (MO) and methylene blue (MB) dyes. The CaAl/LDH-RE presented a surface area of 28.54 m² g⁻¹, being 65.62% larger than the CaAl/LDH-AP material (17.23 m² g⁻¹). The adsorbents showed mesopores distributed on a surface formed by plates in the form of hexagonal sheets arranged in an overlapping manner. The dosage of 0.05 g L⁻¹ obtained the removal of 95% and 97% for MO, while for MB it was 94% and 93% using the adsorbents LDH/CaAl-AP and LDH/CaAl-RE, respectively. The system reached equilibrium at 90 min for MO and 120 min for MB. The pseudo-second order model well represented the kinetic data reaching 11.36 mg g⁻¹ (CaAl/LDH-RE) and 8.42 mg g⁻¹ (CaAl/LDH-AP) for MO, and 4.47 mg g⁻¹ (CaAl/LDH-RE) and 4.14 mg g⁻¹ (CaAl/LDH-AP) for MB. The Freundlich model better represented the isothermal data, where the temperature exerted little influence. Adsorbents showed similar removal percentages in real and synthetic matrices. The LDH/CaAl-RE can be applied in up to 3 cycles, maintaining its adsorption capacity. These results corroborate the use of MFW to produce CaAl/LDH-RE, which can be used for the efficient removal of organic pollutants in an aqueous solution.