Arsenate removal by layered double hydroxides embedded into spherical polymer beads: Batch and column studies

Copolymer-MnO2 nanocomposites for the adsorptive removal of organic pollutants from water

The copolymer beads prepared by suspension polymerisation were decorated with MnO₂ nanoparticles and successfully implemented for the efficient removal of toxic organic contaminants from water. Copolymer-MnO₂ nanocomposite was further analysed using XRD, SEM and optical microscope. The SEM images showed the surface characteristics of MnO₂ nanoparticles on copolymer beads. The efficiency of the copolymer-MnO₂ nanocomposite for the removal of model pollutant methylene blue and rhodamine B is then analysed by changing the concentration of pollutant. The results obtained exhibited 18.45 mg/g for methylene blue adsorption and 3.125 mg/g for rhodamine B. The adsorption equilibrium results were fitted to Langmuir adsorption isotherm for both methylene blue and rhodamine B adsorption. The desorption studies were performed for five consecutive cycles, and material was showing good regenerating capacity towards both organic pollutants. The obtained results show that copolymer-MnO₂ nanocomposite is an efficient material for the removal of organic contaminants from wastewater.

Development of novel Core-shell impregnated polyuronate composite beads for an eco-efficient removal of arsenic

Arsenic (As) can geogenically and anthropogenically contaminate the potable water resources and undoubtedly reduces its availability for human consumption. To circumvent this predicament, present study focuses on the development of a novel biosorbent by impregnating calcium cross-linked polyuronate (alginate) beads (CABs) with bilayer-oleic coated magnetite nanoparticles (CAB@BOFe) for As(V) removal. Initially, the system parameters (i.e., adsorbents dose (0.1- 3.0 g L-1), pH (4.0-13), reaction times (0-180 min) and sorbate concentrations (10-150 µg L-1)) were optimized to establish adsorbent at the lab-scale. CAB@BOFe had higher monolayer (ad)sorption capacity (∼62.5 µg g-1, 120 min) than CABs (∼17.9 µg g-1, 180 min). Electrostatic/Ion-dipole interactions and surface-complexation mechanisms mediated As(V) sorption onto CAB@BOFe mainly obeyed Langmuir isotherm (R2 ∼ 0.9) and well described by intraparticle diffusion process. Furthermore, it demonstrated an excellent arsenate removal performance from the single/multiple anionic contaminants simulated water samples which supported its prospective field applicability.

Optimization of Arsenic Removal from Aqueous Solutions Using Amidoxime Resin Hosted by Mesoporous Silica

The paper reports on the performances of cross-linked amidoxime hosted into mesoporous silica (AMOX) in the removal of As(III) and As(V). The optimum pH for sorption of As(III) and As(V) was pH 8 and pH 5, respectively. The PFO kinetic model and the Sips isotherm fitted the best the experimental data. The thermodynamic parameters were evaluated using the equilibrium constant values given by the Sips isotherm at different temperatures and found that the adsorption process of As(III) and As(V) was spontaneous and endothermic on all AMOX sorbents. The spent AMOX sorbents could be easily regenerated with 0.2 mol/L HCl solution and reused up to five sorption/desorption cycles with an average decrease of the adsorption capacity of 18%. The adverse effect of the co-existing inorganic anions on the adsorption of As(III) and As(V) onto the sorbent with the highest sorption capacity (AMOX3) was arranged in the following order: H2PO4 - > HCO3 - > NO3 - > SO4 2-.

Fe-based layered double hydroxides for removing arsenic from water: sorption-desorption-regeneration

Since the presence of arsenic in the waters of the world causes serious health effects on people, it is very important to remove it. Layered double hydroxides have a high surface area and high anion exchange capacity, and because of this feature, it is a potential adsorbent to remove arsenic. For regeneration and reuse of adsorbents, researchers in some limited studies have used agents such as acids and alkalis. Media replacement accounts for approximately 80% of the total operational and maintenance costs. In this paper, an adsorption/desorption/regeneration study was carried out with MgFeHT to determine the desorption properties of the adsorbent and to examine its reusability. The best alkaline desorption solution was determined from two different alkaline solutions: NaOH and KH₂PO₄. As(V) adsorption capacity of the MgFeHT at different pH (3-12) using the arsenic aqueous solution (with 2,000 μg As(V)/L) was evaluated. For the adsorption process, the experimental data are fitted well with the pseudo-second-order kinetic model and the Langmuir model. Moreover, the concentration of 2,000 μg/L arsenic was reduced to below the legal limit determined by the WHO (<10 μg/L). The regeneration studies were conducted on the adsorptive media used in the arsenic removal system. The regeneration efficiency of As(V) was maintained 98.5% for four regeneration cycles using 0.5 M NaOH. MgFeHT was successfully regenerated with an aqueous solution of NaOH and was reused with a small loss of sorption efficiency.

Effect of coexisting ions on adsorptive removal of arsenate by Mg-Fe-(CO3) LDH: multi-component adsorption and ANN-based multivariate modeling

The adsorptive removal of a pollutant from water is significantly affected by the presence of coexisting ions with various concentrations. Here, we have studied adsorption of arsenate [As(V)] by calcined Mg-Fe-(CO₃)-LDH in the presence of different cations (Mg²⁺, Na⁺, K⁺, Ca²⁺, and Fe³⁺) and anions (CO₃^2‒, Cl^‒, PO₄^3‒, SO₄^2‒, and NO₃^‒) with their different concentrations to simulate the field condition. The experimental results indicated that Ca²⁺, Mg²⁺_, and Fe³⁺ have a synergistic effect on removal efficiency of As(V), whereas PO₄^3‒ and CO₃^2‒ ions have a significant antagonistic impact. Overall, the order of inhibiting effect of coexisting anions on adsorption of As(V) was arrived as NO₃^-˂Cl^-<SO₄^2-<CO₃^2-<PO₄^3-. Among them, competitive adsorption of phosphate with arsenic at different initial phosphate concentrations was found to be responsive to formulate a binary adsorption system. We have also developed a modified non-competitive Langmuir and Langmuir-Freundlich models; however, the modified competitive Langmuir model was arrived to be the most adequate model for this binary system. An Artificial Neural Network based multivariate prediction model was developed, delineating the impact of coexisting ions on the adsorption system. The proposed method may appropriately demonstrate the overall system and exhibited a significantly adequate prediction model with high R², high F-value, and low error values.

Current Trends of Arsenic Adsorption in Continuous Mode: Literature Review and Future Perspectives

Arsenic is a toxic element for humans and a major pollutant in drinking water. Natural and anthropogenic sources can release As into water bodies. The countries with the greatest arsenic contamination issues lack the affordable technology to attain the maximum permitted concentrations. Adsorption can be a highly efficient and low-cost option for advanced water treatment, and the development of new cheap adsorbents is essential to expand access to water with a safe concentration of arsenic. This paper aims to review the state of the art of arsenic adsorption from water in continuous mode and the latest progress in the regeneration and recovery of arsenic. The disposal of the exhausted bed is also discussed. Fixed-bed column tests conducted with novel adsorbents like binary metal oxides and biosorbents achieved the highest adsorption capacities of 28.95 mg/g and 74.8 mg/g, respectively. Iron-coated materials presented the best results compared to adsorbents under other treatments. High recovery rates of 99% and several cycles of bed regeneration were achieved, which can aggregate economic value for the process. Overall, further pilot-scale research is recommended to evaluate the feasibility of novel adsorbents for industrial purposes.

Batch and packed bed techniques for adsorptive aqueous phase removal of selected phenoxyacetic acid herbicide using sugar industry waste ash

Batch and packed bed adsorption of 4-chloro-2-methylphenoxyacetic acid (MCPA) herbicide was performed using bagasse fly ash (BFA) as an adsorbent. In batch process, characteristics of adsorbent, and the influence of adsorbent dosage, initial herbicide concentration, time, pH, particle size of adsorbent and temperature on adsorption were studied. Results disclose higher removal of MCPA on bigger particles of BFA owing to higher specific surface area because of greater carbon and lesser silica percentage in bigger particles. Application of isotherm models in present study indicates the best fitting of Langmuir and Temkin isotherms whereas the kinetic models suggest the suitability of pseudo second order and Elovich models. Thermodynamic study specifies the temperature preferred adsorption process. In packed bed technique, the effect of influent concentration, flow rate and bed height were investigated. The deactivation kinetic model which was previously considered only for studies in gas-solid adsorption is applied in this study to solid-liquid adsorption along with conventional packed bed models. In packed bed study, Bohart-Adams and Wolborska models are appropriate to explain the experimental data upto 60% saturation of the column. The deactivation kinetic model is found the best to elucidate the nature of breakthrough curves till the complete saturation of column. Batch capacity and packed bed capacity per m2 specific surface area of BFA is found about two and three times greater than the previously used adsorbents for MCPA respectively.

Synthesis of novel adsorbent by intercalation of biopolymer in LDH for the removal of arsenic from synthetic and natural water

This study focuses on the synthesis of nanocomposites named CCA and CZA that were prepared by the incorporation of cellulose (CL) in the Ca/Al and Zn/Al layered double hydroxide (LDH), respectively. These materials were then used for the uptake of As(III) and As(V) from aqueous medium. Characterization of both nanocomposites (CCA and CZA) was done using FTIR and Raman analysis to identify the functional groups, N₂ adsorption-desorption isotherms to determine the specific surface area and pore geometry and XPS analysis to obtain the surface atomic composition. Some other characters were investigated using simultaneous TGA and DTA and elemental chemical analysis (CHNS/O). The crystallinity of the prepared nanocomposites was displayed by XRD patterns. Furthermore, the sheet-like structure of the LDHs and the irregularity of surface morphology with porous structure were observed by TEM and SEM microphotographs. Optimization of maximum adsorption capacity was adjusted using different parameters including pH, contact time and adsorbent dosage. The pseudo-second-order model was in good fitting with kinetics results. The adsorption isotherm results showed that CZA exhibits better adsorption capacity for As(III) than CCA and the Langmuir isotherm model described the data well for both nanocomposites. Thermodynamic studies illustrated the endothermic nature of CCA and exothermic nature on CZA, as well as the fact that the adsorption process is spontaneous. A real water sample collected from well located in Gabes (Tunisia), has also been treated. The obtained experimental results were confirmed that these sorbents are efficient for the treatment of hazardous toxic species such as.

Modeling and analysis of adsorptive removal of arsenite by Mg-Fe-(CO3) layer double hydroxide with its application in real-life groundwater

The kinetic, isotherm and thermodynamic modeling of the adsorption of arsenite by layered double hydroxide have been performed to analyze the feasibility, efficacy and mechanism of the system. The fast uptake was observed during the initial phase of the process, which reached equilibrium at 240 min following Elovich model. The diffusion kinetic model exhibited that the rate-limiting step of adsorption was controlled by film diffusion as well as intraparticle diffusion. The isotherm modeling revealed the applicability of the Freundlich equation with the K_f values as 8.19-13.99 (mg g^-1)(L mg^-1)^1/n at 283-323 K showing the increasing trend of adsorption capacity, which was further confirmed by the positive value of ΔH⁰ (9.49 kJ mol^-1) demonstrating the endothermic nature of the adsorption process. The spontaneous nature of the adsorption reaction was established by the negative values of ΔG⁰. Application of the calcined Mg-Fe-LDH adsorbent for the removal of arsenic from real arsenic contaminated groundwater was also successfully performed. The effect of process parameters of the adsorption system was modeled by an artificial neural network (ANN) for adsorption capacity and removal efficiency. The optimized model exhibited high R², F-value and low values of error functions, establishing the significant applicability of the ANN model.

Arsenic removal from water/wastewater using layered double hydroxide derived adsorbents, a critical review

Arsenic pollution has become a worldwide environmental concern. Dangerous arsenic concentrations in natural waters threaten the health of millions of people, and this has received significant attention. Among the various technologies that have been developed for arsenic removal from water, the use of adsorption technology is considered to be a prevailing method, because the adsorption approach usually has high removal efficiency and the advantage of convenience of handling. In recent years, layered double hydroxides (LDHs) have become prime candidates for arsenic removal, due to their hydrophilic nature and cationic layered structures. Research on arsenic removal using LDHs is mainly focused on (1) the influence of the synthesis method and composition of the LDH, (2) the influence of the particle size of the LDH, (3) the influence of the Mg/Al ratio in LDHs, (4) LDH-based hybrids and (5) the competition with other anions. This paper provides a review of the currently available literature focusing on arsenic removal using LDHs for the five parts mentioned above. In addition, based on this overview, a closing section will suggest research efforts for future work. It is expected that this review will provide a summary of the main research in this area, and will also shed light on the direction of future development.