Use of non-treated shrimp-shells for textile dye removal from wastewater

This paper investigates the removal of direct dyes through adsorption on chitin-containing residues. As representative waste, the shells of two shrimp species are tested. Removal percentage up to 90% for the tested dyes are obtained in about 2 h, using 2.1 mg mL−1 of shells, simply dried and grinded. Comparative analyses are also conducted on commercial chitin and chitosan flakes. Kinetic tests are carried out in batch and at lab scale. Data are modeled through the pseudo second-order kinetic law, and a value of modeling efficiency close to 1 is obtained. Adsorption isotherms are traced with the temperature varying between 10 °C and 50 °C. The results are first analyzed using the Langmuir expression, and then interpreted following a statistical physics approach to obtain a deeper understanding of the phenomenon at the molecular level. The anchorage number, the steric hinderance coefficient, and the half saturation coefficient are derived. All experimental data indicate a monolayer adsorption process that is limited to the existing micro-porosity, favored by concentration gradient diffusion, and characterized by several anchorage points for each single molecule.