Evaluation of the adsorption performance and thermal treatment-associated regeneration of adsorbents for formaldehyde removal.

Indoor air pollution remains a major concern, with formaldehyde (HCHO) a primary contributor due to its long emission period and associated health risks, including skin allergies, coughing, and bronchitis. This study evaluated the adsorption performance and economic efficiency of various adsorbents (biochar, activated carbon, zeolites A, X, and Y) selected for HCHO removal. The impact of thermal treatment on adsorbent regeneration was also assessed. The experimental apparatus featured an adsorption column and HCHO concentration meter with an electrochemical sensor designed for adsorption analysis. Zeolite X exhibited the highest adsorption performance, followed by zeolite A, zeolite Y, activated carbon, and biochar. All adsorbents displayed increased HCHO removal rates with an extended length/diameter (L/D) ratio of the adsorption column. Zeolite A demonstrated the highest economic efficiency, followed by zeolite X, activated carbon, zeolite Y, and biochar. Higher L/D ratios improved economic efficiency and prolonged the replacement cycle (the optimal timing for adsorbent replacement to maintain high adsorption performance). Sensitivity analysis of adsorbent regeneration under varying thermal treatment conditions (150, 120, and 80°C) and durations (60, 45, and 30 min) revealed minimal changes in adsorption efficiency (±3%). The results indicated the potential of adsorbent regeneration under energy-efficient thermal treatment conditions (80°C, 30 min). In conclusion, this study underscores the importance of a comprehensive assessment, considering factors such as adsorption performance, replacement cycle, economic efficiency, and regeneration performance for the selection of optimal adsorbents for HCHO adsorption and removal.Implications: This study underscores the importance of adsorption technology for the removal of formaldehyde and similar volatile organic compounds (VOCs), highlighting the potential of alternative adsorbents, such as environmentally friendly biochar, in addition to traditional strategies, such as activated carbon and zeolites. Our findings demonstrate the feasibility of adsorbent regeneration under energy-efficient thermal treatment conditions. These results hold promise for improving indoor air quality, reducing environmental pollutants, and enhancing responses to air contaminants like fine dust and VOCs.

Applicability of ferric(III) hydroxide as a phosphate-selective adsorbent for sewage treatment.

This research was undertaken to evaluate the usability of ferric(III) hydroxide for phosphate removal from sewage. Batch adsorption experiments, partly fixed bed column experiments, were conducted to study the influence of various factors, competing anions and contact time on the adsorption of phosphate on ferric(III) hydroxide. Processing ferric iron in the form of akaganeite (ß-FeOOH) greatly increased the adsorption capacity for phosphate. The optimum phosphate removal was observed in the pHeq ≤ 6.0. All results from this study demonstrate the potential usability of ß-FeOOH as a good phosphate-selective adsorbent for the phosphate removal system for a sewage treatment plant.

Utilization of waste bittern from saltern as a source for magnesium and an absorbent for carbon dioxide capture.

During solar salt production, large quantities of bittern, a liquid by-product containing high inorganic substance concentrations, are produced. The purpose of this research was to examine the utilization of waste bittern generated from salterns as a source for Mg production and as an absorbent for carbon dioxide (CO2) capture. The study was conducted in a sequential two-step process. At NaOH/Mg molar ratios of 2.70-2.75 and pH 9.5-10.0, > 99% Mg precipitation from the bittern was achieved. After washing with water, 100-120 g/L of precipitate containing 94% Mg(OH)2 was recovered from the bittern. At the optimum NH4OH concentration of 5%, 120 g of sodium bicarbonate precipitate per liter of bittern were recovered, which was equivalent to 63 g CO2 captured per liter of bittern. These results can be used to support the use of bittern as a resource and reduce economic losses during solar salt production.

Applications and limits of theoretical adsorption models for predicting the adsorption properties of adsorbents.

The objective of this study is to evaluate the applicability of adsorption models for predicting the properties of adsorbents. The kinetics of the adsorption of NO3- ions on a PP-g-AA-Am non-woven fabric have been investigated under equilibrium conditions in both batch and fixed bed column processes. The adsorption equilibrium experiments in the batch process were carried out under different adsorbate concentration and adsorbent dosage conditions and the results were analyzed using adsorption isotherm models, energy models, and kinetic models. The results of the analysis indicate that the adsorption occurring at a fixed adsorbate concentration with a varying adsorbent dosage occur more easily compared to those under a fixed adsorbent dosage with a varying adsorbate concentration. In the second part of the study, the experimental data obtained using fixed bed columns were fit to Bed Depth Service Time, Bohart-Adams, Clark, and Wolborska models, to predict the breakthrough curves and determine the column kinetic parameters. The adsorption properties of the NO3- ions on the PP-g-AA-Am non-woven fabric were differently described by different models for both the batch and fixed bed column process. Therefore, it appears reasonable to assume that the adsorption properties were dominated by multiple mechanisms, depending on the experimental conditions.

Defluoridation from aqueous solution by lanthanum hydroxide.

This research was undertaken to evaluate the feasibility of lanthanum hydroxide for fluoride removal from aqueous solutions. A batch sorption experiments were conducted to study the influence of various factors such as pH, presence of competing anions, contact time, initial fluoride concentration and temperature on the sorption of fluoride on lanthanum hydroxide. The optimum fluoride removal was observed in the pH(eq)≤7.5. The presence of competing anions showed no adverse effect on fluoride removal. The equilibrium data reasonably fitted the Langmuir isotherm model, and the maximum monolayer sorption capacity was found to be 242.2 mg/g at pH(eq)≤7.5 and 24.8 mg/g at pH(eq)>10.0. The pseudo-second-order kinetic model described well the kinetic data, and resulted in the activation energy of 53.4-68.8 kJ/mol. It was suggested that the overall rate of fluoride sorption is likely to be controlled by the chemical process. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° indicated that the nature of fluoride sorption is spontaneous and endothermic. The used lanthanum hydroxide could be regenerated by washing with NaOH solution. Results from this study demonstrate the potential usability of lanthanum hydroxide as a good fluoride selective sorbent.

Adsorption characteristics of anionic nutrients onto the PP-g-AA-Am non-woven fabric prepared by photoinduced graft and subsequent chemical modification.

PP-g-AA-Am non-woven fabric, which possesses anionic exchangeable function, was prepared by chemical modification of carboxyl group in PP-g-AA non-woven fabric to amine group using diethylene triamine. Its sorption characteristics for anionic nutrients including isotherm, kinetics, effects of pH and co-anions, and regeneration efficiency were studied by batch sorption experiments. Sorption equilibriums of PO(4)-P on PP-g-AA-Am fabric were well described by the Langmuir isotherm model, and their sorption energies were ranged between 9.94 and 15.96 kJ/mol indicating an ion exchange process as primary sorption mechanism. Sorption kinetic data fitted with pseudo-second-order kinetic model and indicated that both external and intraparticle diffusion took part in sorption processes. The uptake of PO(4)-P by PP-g-AA-Am fabric increased with increasing pH of solution and its optimum pH region was in pH >or=4, whereas the uptake of NO(3)-N and NO(2)-N was higher in weak and strong acidic pH region, respectively. The sorption selectivity for anions by PP-g-AA-Am fabric was increased in the order: SO(4)>or=PO(4)>NO(3)>Cl. The PP-g-AA-Am fabric could be regenerated by a simple acid washing process without lowering the sorption capacity or physical durability.

Preparation of anion exchanger by amination of acrylic acid grafted polypropylene nonwoven fiber and its ion-exchange property.

To develop the polymeric adsorbent that possess anionic exchangeable function, PP-g-AA-Am fibers were prepared by photoinduced grafting of acrylic acid (AA) onto polypropylene (PP) nonwoven fibers and subsequent conversion of carboxyl group in grafted AA to an amine (Am) group by reaction with diethylene triamine (DETA). The amination of grafted AA increased with increase in the degree of grafting, the reaction time and temperature of the chemical modification process. Catalytic effect of metal chlorides such as AlCl(3) and FeCl(3) on the amination of grafted AA was significant but not essential to lead the amination. FT-IR and solid (13)C NMR data indicate that amine group was introduced into PP-g-AA fiber through amide linkage between grafted AA and DETA. The anion exchange capacity of PP-g-AA-Am fiber increased with increase in the degree of amination, but reached maximum value at about 60% amination of 150% grafted AA. PP-g-AA-Am fiber showed much higher maximum capacity for PO(4)-P and a similar capacity for NO(3)-N compared to commercial anion resins. Furthermore, the PP-g-AA-Am fiber also has adsorption ability for cations because of unaminated residual carboxyl group.