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

International audienceThe 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 EGA NaCl and EGANaNO 3 were prepared by electrolysis in NaCl and NaNO 3 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 EGA NaCl and EGANaNO 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 Al 2.67 O 4 which was found to be stable during the following thermal treatments at 500 °C. © 2019 Taiwan Institute of Chemical Engineer

Treatment of artificial pharmaceutical wastewater containing amoxicillin by a sequential electrocoagulation with calcium salt followed by nanofiltration

International audienceThe present study deals with the treatment of an artificial pharmaceutical waste which contained amoxicillin (AMX) by using successively an electrocoagulation (EC) with Ca(NO3)2 as an electrolyte and a nanofiltration (NF) with a Nanomax-50 membrane. The effect of the current intensity and of the operating pressure was investigated for separately EC and NF, respectively. The AMX removal as a function of pH and initial AMX concentration was also investigated for the separately conducted EC and NF processes. The best percentage removal of AMX by EC and NF was recorded to be 52.7 % and 99.0 %, respectively. In the case of the sequential processes EC followed by NF, the removal of AMX was 98.2 % and 97.5 % at pH 2.5 and 10, respectively. The contribution of both EC and NF towards the AMX removal efficiency in the case of the sequential process was very much significant. It is remarkable that the EC pre-treated feed into NF was explored with several benefits such as high removal efficiency, calcium involved in EC process, prolonged membrane life and reduced power consumption. The electrogenerated solids (the sediment and the cathode deposit) were characterized using Fourier Transform Infra-red spectroscopy (FTIR), Energy Dispersive Spectroscopy (EDS) coupled to Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Thermo Gravimetry Analysis (TGA). It appeared that calcium was involved in the electrogenerated solids. It gave a cathode deposit of Ca(OH)2 in which some AMX was embedded

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

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

Preparation of mesoporous alumina electro-generated by electrocoagulation in NaCl electrolyte and application in fluoride removal with consistent regenerations

International audienceThe fluoride adsorption by Electro-Generated Adsorbents (EGA) was briefly and recently shown. In this paper, the preparation of a particular EGA and its characteristics are presented. For the first time, the fluoride adsorption of one EGA was deeply investigated showing that the regeneration of this material leads to an efficient process which was better than an electrocoagulation one. The investigated adsorbent called EGANaCl was prepared by electrolysis in NaCl electrolyte with aluminum electrodes and was characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), FTIR and BET studies. The physical analyses showed that EGANaCl was a mesoporous mixture of AlOOH and three Al(OH)3 which contain the chlorine element and registered the surface area of 114.31 m2 g−1. The presence of chlorine explains the pH increase observed during the electrolysis. The fluoride adsorption as a function of pH, initial fluoride concentration, EGANaCl dose, temperature, co-ions and cycles of regeneration was studied using batch methods. Among the kinetic models, the pseudo – second – order model was superior to others and among the adsorption isotherms, Langmuir model fits well as compared to that of Freundlich model based on the regression coefficient values. Determination of thermodynamic parameters such as ΔH and ΔG respectively revealed the nature of endothermic and temperature – driven nature of the fluoride sorption process. The maximum adsorption capacity of EGANaCl was found to be 16.33 mg g−1 at 27 °C and a maximum fluoride removal occurred at pH 6.55. The spent adsorbent showed the defluoridation efficiency of 95.53% up to fifth regeneration with diluted NaOH. Factorial design matrix and analysis of variance using JMP model have also been extensively discussed in this paper. © 2017 The Author