Physical-chemical characterization of metal hydroxides sludge waste obtained from electrocoagulation processes and its application as adsorbent for organic pollutants removal in aqueous solution

The present work aims at the reuse of metal hydroxide sludge generated by an electrocoagulation process. Its application in the adsorption of pollutants present in aqueous medium is also studied using Congo red as a molecule model and batch reactors. The characterization results demonstrate the presence of the boehmite phase with acceptable textural properties as adsorbent and high stability under different pH conditions. During the adsorption tests, it was shown that both, the pH and the initial concentration, produces a negative influence in the percentage of Congo red retention attributed to the electrostatic repulsion between OH- and Congo red at high pH values on one hand and the absence of active sites at high concentration levels on the other hand. On the contrary, the increase in Congo red adsorption was proportional to the temperature associated with the thermodynamic characteristics of the adsorption process that are also presented in this work. The performance of the adsorption followed a second-order kinetics that indicates that adsorption followed a cation exchange process between the adsorbent and adsorbate; besides that different models were applied (Freundlich, Langmuir and Temkin), the Freundlich model described the better adsorption process of Congo red indicating adsorption on a heterogeneous surface and multilayer formation.