Simultaneous removal of fluoride and nitrate from an aqueous mixture and semiconductor wastewater by sodium chloride mediated electro-generated aluminas (EGAs): Conversion of recovered fluoride into fluorapatite using plasterboard waste

International audienceElectro-generated aluminas (EGAs) were synthesized using sodium chloride electrolyte of 100 mM with Al/Al and Al/Fe electrodes operated at 800 mA for 1.5 h. The synthesized mesoporous EGAs, EGA (Al) and EGA (Fe) belonging to H2 type hysteresis contain the boehmite and bayerite phases as confirmed by XRD analysis and whose proportions are estimated to be 49.6 ± 0.3% and 50.4 ± 0.3% respectively by thermo-gravimetric study. The batch adsorption studies were conducted using the binary () mixture from which the adsorption efficiency was studied as a function of time (0–60 min), pH (3–10), initial concentration of fluoride or nitrate (100, 300, 500 and 1000 mgL−1) and temperature (15 °C, 25 °C, 35 °C and 45 °C) using EGA (Al) and EGA (Fe) adsorbents. The adsorptive removal of fluoride and nitrate from real effluent samples using EGAs was significant particularly in effluents E1 and E3 with residual concentrations within the safe limit of World Health Organization (WHO). Regeneration using 100 mM NaOH was quite consistent up to five consecutive cycles and the recovered fluoride was converted into fluorapatite. Taking into account the regeneration aspect, the cost analysis showed that 1 g EGA (Al) and EGA (Fe) was 0.464 USD and 0.508 USD respectively. The endothermic nature of adsorption through chemical forces was confirmed by the compliance of pseudo – second – order (kinetic), Langmuir and DKR (isotherm) models (R2 ≈ 0.99) along with thermodynamic parameters. Characterization of EGAs using FTIR, FESEM, XRD, XPS and BET was done to understand the adsorptive behavior between EGAs and the adsorbate () ions. The exhausted EGAs after fifth cycle of regeneration was mixed with ariake clay, plasterboard waste and cement in proper proportions and, made as specimens for the construction of bank bodies

Electrocoagulation in the dual application on the simultaneous removal of fluoride and nitrate anions through respective adsorption/reduction processes and modelling of continuous process

International audienceElectrocoagulation (EC) is known as an electrochemical process for the efficient removal of various pollutants including fluoride and nitrate anions. Continuous electrocoagulation (CEC) was applied to synthetic aqueous solutions containing mixtures of nitrate and fluoride anions both at initial concentrations of 0.1 g L−1 for simulation of effluents arising from the etching process in microelectronic industries. Several parameters such as electrode material, pH, current density, initial concentration as well as the presence of co-existing ions were studied. Without addition of an electrolyte, the optimizing conditions were found for aluminum electrodes at pH = 5.94, current density of 9.09 mA.cm−2 and distance between electrodes of 18 mm, leading to removal rates of 42.83% and 88.28% for nitrate and fluoride anions, respectively. The isolated electrogenerated solids were characterized by Energy Dispersion Spectroscopy (EDS) coupled to SEM, FT-IR, XRD, XPS, TGA and Raman spectroscopy. All the characterizations agree with the removals of nitrate and fluoride anions by reduction and adsorption, respectively. The anode and the cathode were involved, but the reduction and adsorption processes were independent of each other. The nitrate reduction was a cathodic reaction leading to hydroxide anions which were involved in the formation of electrogenerated adsorbents by reaction with the aluminum cations (or metal cations) arising from the anode oxidation. A modelling kinetic theory for a continuous electrocoagulation process was developed and applied to the treatment of artificial and real wastewaters. The treatment cost of the real wastewater was found at 2.3097 USD per m3. © 202