Preparation and characterizations of thermally regenerable electro-generated adsorbents (EGAs) for a competitor electrocoagulation process

Abstract

Abstract The electrochemical preparation of Electro-Generated Adsorbents (EGAs) coupled with regeneration of spent adsorbents was recently shown as an alternative to prepare adsorbents for a competitor electrocoagulation process. In this paper, two EGAs were investigated as thermally regenerable adsorbents. These adsorbents called EGANaCl and EGA NaNO 3 were prepared by electrolysis in NaCl and NaNO3 electrolytes, respectively, with aluminum electrodes. The physical analyses showed that they were mixtures of nano-crystallized AlOOH and three Al(OH)3. The sedimentation behavior of these adsorbents showed that they were not homogenous materials. Raman spectra revealed that bayerite was the main aluminum hydroxide. Despite analogous XRD patterns of the two investigated EGAs, notable differences could be found during their preparation. The removals of doxycycline (DC) and oxytetracycline (OTC) were performed in six successive regenerations by heating adsorbents at 500 °C. OTC removals were constant at 98% and 70%, while DC removals decreased from 98% to 78% and from 96% to 92%, for EGANaCl and EGA NaNO 3 respectively. XRD analysis of the heated adsorbents showed the disappearance of the initial crystalline compounds and the formation of a low amount of crystallized gamma alumina Al2.67O4 which was found to be stable during the following thermal treatments at 500 °C.