Modelization and implementation of free adsorption and electrosorption of Cr (VI) from wastewater using Al2O3 nanoparticles: assessment and comparison of the two processes.

The objective of this study was to apply the technique of electrosorption in order to assess the capacity of heterogeneous adsorption under an electric field. This was to enhance the adsorption capacity of the nanoparticles, to shorten the adsorption time, and to reduce the cost of the purification of contaminated waters. A final objective of this study was to compare the free adsorption (FA) and the electrosorption (ES) to understand the interface adsorbent/adsorbate at different contact conditions. For these purposes, a potentially efficient, environment-friendly absorbent was synthesized for dechromation purposes. The experimental design method generated optimum conditions as tc = 123 min, T = 318°K, and C0 = 100 mg/L. Freundlich's well-fitted modeling proved that the adsorption of chromate (VI) on nano-Al2O3 occurred on a homogenous surface. In addition, the adsorption coefficient intensity n did not only confirm monolayer adsorption but also indicated a favorable adsorption process. Thermodynamic studies confirmed the reaction spontaneity and the physisorption of the process. The electrosorption process was also tested using 20mA/cm2 as applied current density. Free-adsorption (FA) and electrosorption (ES) processes were compared. The maximum recorded yield was 99% for (EA) against 87% for (FA). EDS analysis recorded 11.3% of chromate adsorbate with free adsorption. The amount of Cr (VI) on nano-Al2O3 was 42.5 %. Nevertheless, the Al2O3 nanoparticles lost their crystallinity and exploded after the ES process. Mechanisms of both (FA) and (ES) were proposed.