Enhanced adsorption of fluoride from aqueous solution using an iron-modified attapulgite adsorbent

Application of artificial neural network for prediction of fluoride removal efficiency using neutralized activated red mud from aqueous medium in a continuous fixed bed column

The present research work approaches the removal of fluoride from aqueous medium using neutralized activated red mud (NARM) in a continuous fixed bed column. Artificial neural network (ANN) technique was applied effectively for optimization of the model for the practicability of the removal process. The consequences of various experimental variables, like bed length, adsorbate concentration, experimental time, and adsorbate solution flow rate are studied to know the breakthrough point and saturation times. The highest removal potentiality of NARM was considered to be 3.815 mg g^-1 of F^- in the bed height of 15 cm, starting concentration 1 ppm, susceptible time 120 min, adsorbate solution flow rate 0.5 mL min^-1, and constant room temperature, respectively. Bohart-Adams and Thomas models were considered to describe the fixed bed column effect to the bed height and adsorbate concentrations. The experimental data were applied to a back propagation (BP) learning algorithm programme with a four-seven-one architecture model. The artificial neural network model was considered to be functioning correctly as absolute relative percentage error throughout the learning period. Differentiation between the predicted outcomes from ANN model and actual results from experimental analysis affords a high degree of correlation (R² = 0.998) stipulating that the model was able to predict the adsorption efficiency. Experimented adsorbent materials were characterized using different instrumental analysis that is scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD).

Strategic optimization of phase-selective thermochemically amended terra-firma originating from excavation-squander for geogenic fluoride adsorption: a combined experimental and in silico approach

An inimitable adsorbent "FI-TM-BWCC," emanated from meta-phase-selective thermochemical modulation of excavation-squander (mine waste)-derived terra-firma (blackish white china clay, i.e., BWCC), is explored in the present work for fluoride (F^-) adsorption purpose. FI-TM-BWCC portrayed an excellent adsorption efficiency (95% removal capacity and Q_e: 99 mg/g, at initial adsorbate dose: 10 mg/L, pH: 7±0.5, adsorbent dosage: ~600 mg, exposure time: 60 min). At identical experimental conditions, the F^- scavenging phenomenon was superior than two analogous adsorbents: (i) biopolymer chitosan and glutaraldehyde cross-linked BWCC (CG@BWCC, wherein F^- removal efficiency: 74%) and (ii) meta-phase-selective thermally moduled BWCC (TM-BWCC, removal efficiency: 75%). BWCC predominantly comprises kaolinite and a trace amount of anatase along with prime elemental compositions: 41.71% Al₂O₃, 49.80 % SiO₂, 4.25% Fe₂O₃, and 3.93% TiO₂, as revealed by PXRD and XRF analyses. The thermochemical modulation pathway significantly escalated the BET surface area of BWCC (~11.92 m²/g, avg. pore radius: 23.64 Å, i.e., mesoporous in nature) to FI-TM-BWCC (216.95 m²/g, avg. pore radius: 31.41 Å). The fluoride-adsorbed F^-•••FI-TM-BWCC species revealed a reduced surface area of 21.5 m²/g, which was explained in the light of ion exchange pathway on FI-TM-BWCC's non-uniform surface (surface roughness/S_A of 1597 nm, reduced to 1179 nm after F^- uptake). The spontaneous F^-•••FI-TM-BWCC interaction (ΔG⁰ = -6.25 kJ) occurred following chemisorption-controlled ion exchange (CCIE) pathway as appearance of a F1s band at 685.5 eV was rationalized for Si-F bond formation; corroborating pseudo second-order (PSO) kinetics and resembling Freundlich isotherm. The usefulness of FI-TM-BWCC was diversified through field validation with natural groundwater specimens and proposition of a gravity-fed defluoridation unit. The flow rate was documented to be ~11 liters per hour (LPH) by implementing viscous turbulence fluent model. The experimental findings certainly followed the premise conventions of sustainability metrics upholding socio-economic equipoise.

Evaluation of fluoride adsorption in solution by synthetic Al2 O3 /CeO2 : A fixed-bed column study

A highly efficient fluoride adsorbent Al₂ O₃ /CeO₂ was synthesized in this work and used it to fluoride removal in the fixed-bed adsorption through changing the different experimental conditions (influent F^- concentration, flow velocity, and bed heights). The adsorption capacity was 9.72 mg/g. In addition, the Adams-Bohart and Thomas models were used to fit and evaluate the column breakthrough curve of fluoride removal process by Al₂ O₃ /CeO₂ , and the correlation coefficients (R² ) of the Thomas model were close to 1 under all experimental conditions. The structure of Al₂ O₃ /CeO₂ and the adsorption mechanism were confirmed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), N₂ adsorption and desorption isotherm, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Moreover, the adsorption of fluoride (F^- ) was mainly through metal binding (MF) and hydroxyl binding (AlOH⋯F) on the surface of the Al₂ O₃ /CeO₂ . Furthermore, the regeneration and coexisting anions studies of Al₂ O₃ /CeO₂ were carried out, and the efficiency of adsorption was still above 70% after five cycles. PRACTITIONER POINTS: Removal of fluoride was studied by fixed-bed experiment, and the adsorption capacity of composite Al₂ O₃ /CeO₂ was 9.72 mg/g. The metal complex played important role in fluoride removal and reusability makes a long-term application for fluoride adsorption. Fluoride wastewater is pumped to the fixed-bed column, and fluoride ions are absorbed by Al₂ O₃ /CeO₂ through fluoride metal complex and aluminum hydrofluoride.

Defluoridation using biomimetically synthesized nano zirconium chitosan composite: kinetic and equilibrium studies

The present study reports a novel approach for synthesis of Zr nanoparticles using aqueous extract of Aloe vera. Resulting nanoparticles were embedded into chitosan biopolymer and termed as CNZr composite. The composite was subjected to detailed adsorption studies for removal of fluoride from aqueous solution. The synthesized Zr nanoparticles showed UV-vis absorption peak at 420nm. TEM result showed the formation of polydispersed, nanoparticles ranging from 18nm to 42nm. SAED and XRD analysis suggested an fcc (face centered cubic) Zr crystallites. EDAX analysis suggested that Zr was an integral component of synthesized nanoparticles. FT-IR study indicated that functional group like NH, CO, CN and CC were involved in particle formation. The adsorption of fluoride on to CNZr composite worked well at pH 7.0, where ∼99% of fluoride was found to be adsorbed on adsorbent. Langmuir isotherm model best fitted the equilibrium data since it presented higher R(2) value than Freundlich model. In comparison to pseudo-first order kinetic model, the pseudo-second order model could explain adsorption kinetic behavior of F(-) onto CNZr composite satisfactorily with a good correlation coefficient. The present study revealed that CNZr composite may work as an effective tool for removal of fluoride from contaminated water.