Investigation on water defluoridation via batch and continuous mode using Ce-Al bimetallic oxide: Adsorption dynamics, electrochemical and LCA analysis

Abstract

With variable atomic ratios, Ce-Al bimetallic oxides were fabricated using the sol-gel combustion method and utilized for efficient fluoride removal. The synthesized bimetallic oxides were extensively studied using advanced characterization techniques, including TGA, XRD, FTIR, BET surface area analysis, EDX-assisted FESEM, XPS and impedance analysis. These techniques facilitate the interpretation of the chemical and physical properties of the synthesized material. The Ce-Al (1:1) bimetallic oxide was selected as an adsorbent for the defluoridation. The Ce-Al (1:1) oxide demonstrates a moderately high surface area of 108.67 m²/g. The sorption behaviour of fluoride on Ce-Al (1:1) was thoroughly investigated using batch and column modes. The maximum fluoride removal efficiency (99.4%) was achieved at a temperature of 45 °C and pH of 7.0 using an adsorbent dose of 0.18 g/L for 35 min. Pseudo-second-order kinetic model appropriately describes the sorption process. Freundlich's adsorption isotherm was more pertinent in representing fluoride adsorption behaviour. The maximum fluoride adsorption capacity is 146.73 mg/g at 45 °C. Thermodynamics study indicates fluoride adsorption on Ce-Al (1:1) bimetallic oxide is spontaneous and feasible. The adsorption mechanism was interpreted through XPS spectra, indicating that the physisorption process is mainly responsible for fluoride adsorption. An in-depth investigation of the adsorption dynamics was carried out using mass transfer models and found that the external diffusion process limits the overall adsorption rate. An electrochemical investigation was performed to understand the effect of fluoride adsorption on the electrochemical behaviour of bimetallic oxide. The fixed-bed column adsorption study suggested that the lower flow rate and increased bed height favourably impacted the overall defluoridation process, and column adsorption results were suitably interpreted through both the Adam-Bohart model and Yoon-Nelson dynamics model. The sustainable aspect of the defluoridation process was elucidated in terms of carbon footprint measurement using life cycle assessment analysis. The carbon footprint of the entire treatment process was calculated as 0.094 tons/year.

Keywords: Adsorption; Bimetallic-oxide; Column; Defluoridation; Electrochemistry.