Abstract
•Indium (III) adsorption on raw, supercritical- and ultrasound-modified chitin was studied.•Monolayer and multilayer models were utilized to explain the indium (III) adsorption mechanism.•Indium (III) adsorption on all adsorbents involved multi-ionic and multi-anchorage processes.
The adsorption of indium (III) on raw, supercritical- and ultrasound-modified chitin was experimentally and theoretically studied. Experimental adsorption data demonstrated that the profile of all adsorption isotherms was different from a system to another. Indeed, the adsorption behavior of the systems indium (III) – chitin and indium (III) – supercritical-modified chitin tended to a saturation process at high concentration thus suggesting that the adsorption can be occurred by the formation of a fixed number of adsorbate layers. Contrary to this finding, the adsorption of indium (III) on an ultrasound-modified chitin can be associated to a variable number of layers involving two adsorption energies. Statistical physics models were selected to understand the adsorption data and they demonstrated that the adsorption of indium (III) – chitin and indium (III) – supercritical-modified chitin was achieved by the formation of one layer; while the adsorption of this adsorbate on an ultrasound-modified chitin was performed with a variable number of layers. Based on the modeling analysis, it was demonstrated that the ultrasonic treatment improved the properties of chitin to remove this pollutant: Qesat of ultrasound-modified chitin > Qesat of supercritical-modified chitin > Qesat of raw chitin. The interpretation of parameter n, which is defined as a number of bonded ions of indium (III) per responsible site of the adsorbent, was higher than 1 at high temperature. This result suggested that the indium adsorption was a multi-ionic mechanism. All adsorption systems were characterized by an estimation of the adsorption energy reflecting that the removal of this pollutant involved physical interactions. A general analysis of all model parameters indicated that the receptor site density and the adsorption energy controlled the indium adsorption.