External Mass Transfer Research Articles

Kinetics of hydrothermal reactions of n-butanol over Pt/Al2O3 catalyst for biopropane fuel gas production

Energy defossilisation using drop-in biofuels is an important step towards Net Zero. Producing low-carbon clean-burning propane fuel from biomass provides such additional sustainability benefits. In this work, kinetics of hydrothermal reactions of n-butanol, a biomass-derived feedstock, to produce propane over 5 wt% Pt/Al2O3 catalyst have been studied from 523- 573 K. Experimental data revealed negligible internal and external mass transfer effects and, when fitted to an integral power-rate law equation, gave activation energy of 70 kJ mol−1 (n-butanol reaction order = 1). Furthermore, an appropriate Langmuir-Hinshelwood model was developed, which predicted similar activation energy 62 kJ mol−1. Low adsorption enthalpies for n-butanol (–33.51 kJ mol−1) and water (−18.16 kJ mol−1) indicated weak interactions on the catalyst surface. These agreed with the fast reaction rate of ≈1.0 x 10-5 mol gcat-1 s−1 obtained at ≥ 548 K. As a new research area, generation of such accurate kinetics data will contribute to process development for large-scale biopropane production.

Removal of sulfamethoxazole using Fe-Mn biochar filtration columns: Influence of co-existing polystyrene microplastics

Emerging contaminants, particularly antibiotics and microplastics (MPs), present significant challenges in wastewater treatment and pose large ecological risks. This study investigates the removal efficiency of sulfamethoxazole (SMX) using Fe-Mn modified biochar (BFM) in fixed bed filtration columns, emphasizing the effect of the presence of polystyrene microplastics (PS-MPs) on SMX behavior in both water (pH ≈ 5.6) and selected wastewater (pH ≈ 8) systems. Batch sorption results show that 10 mg/L SMX in 50 mL water can be completely removed by 100 mg BFM sorbent. The Bed Depth Service Time model indicated the BFM column is feasible for SMX removal in scaled-up continuous wastewater flow operations, while the Yan model best elucidates SMX filtration behavior and suggests the dominant adsorption mechanisms include external mass transfer and intraparticle diffusion. The present of both 20 mg/L and 100 mg/L PS-MPs (pH ≈ 5.6) significantly reduced SMX retention due to competitive sorption. However, at pH 3.2, competitive sorption became negligible due to electrostatic interactions driving the PS-MPs sorption, while neutral charged SMX bound through hydrogen-bonds or π-π EDA interactions. Elevated pH shifted both PS-MPs and SMX sorption to non-electrostatic thus intensifying sorption competition, highlighting the influence of pH on their interaction dynamics. In wastewater, SMX filtration was slightly inhibited by 100 mg/L PS-MPs in BFM columns, whereas PS-MPs removal remained unaffected due to the high ionic strength and alkaline pH. These findings highlight the impact of MPs on pollution removal efficiency in filtration system, essential for enhancing biochar-based wastewater treatment strategies.

Photocatalytic antibiotic degradation in coated open microchannels by applying 2D and 3D flow modeling with kinetics

The accumulation of active pharmaceutical ingredients in the aqueous environment is a serious problem that will become even more concerning in the future. In this work, the photocatalytic degradation of ciprofloxacin (CIP) in aqueous solution was assessed over P25-TiO2 coated open microchannels with gravity-driven flow under UV-A irradiation. The deposition of different amounts of TiO2 in the microchannels was carried out via a facile, self-developed procedure. The degradation kinetics of ciprofloxacin was described via the Langmuir-Hinshelwood mechanism. Since the flow characteristics in the microchannel had influence on the concentration distribution of CIP in the microchannel, the coupled momentum and mass conservation law was solved numerically in MATLAB 2023a (2D case) as well as in ANYS Fluent 2023 R1 (2D and 3D cases). Although the implemented 2D model in MATLAB 2023a allowed the preliminary estimation of the selected kinetic parameters, namely adsorption equilibrium constant and specific Langmuir-Hinshelwood rate constant, the sensitivity of the model was not satisfactory which was attributed to the empirical correlations used for the estimation of the external mass transfer coefficient. The 2D and 3D models in ANSYS Fluent 2023 R1 predicted efficiently the outlet concentration of ciprofloxacin for different inlet CIP concentrations and liquid phase flow rates. Therefore, the as developed 2D and 3D models in ANSYS Fluent 2023 R1 can be used for the design of reactors containing coated microchannels with gravity-driven flow for photocatalytic degradation of active pharmaceutical ingredients.

The Staged Photocatalytic Reactor in the Removal of Acetaminophen: Aspects of Adsorption and Photocatalysis.

The efficiency of a staged photocatalytic reactor prototype was evaluated on a semi-pilot scale with the removal of acetaminophen, for which anatase particles were synthesized by Sol-Gel and impregnated on rectangular plates of clay. X-ray diffraction and Energy Dispersive X-ray Fluorescence patterns show that the final composite is made up of Al2O3 (14 %), SiO2 (41 %), CaO (3 %) TiO2 (34 %), and Fe2O3 (7 %). The impregnation method favors the dispersion of Anatase on the surface of the adsorbent. TiO2-Anatase/Clay, classified as a macro-porous solid with H3-type hysteresis loops by N2 physisorption. Adsorption processes are improved when using TiO2-Anatase/Clay compared to using TiO2-Anatase. The external mass transfer has a greater influence on the removal rate. The dimensionless parameters of the Biot number indicate there are no limitations due to the diffusive effect on the interior of the particle. The evaluation of the kinetic data under the Langmuir-Hinshelwood equation shows a decrease in efficiency as the initial concentration increases. The acetaminophen molecule shows destabilization in the structure of the aromatic ring with a visible decrease in the signals of this functional group evaluated by High-Performance Liquid Chromatography and Raman Spectroscopy.

Effect of multi-component gas on removal of trace hydrogen sulfide activity from blast furnace gas using activated carbon adsorbent

Abstract In the steel industry, blast furnace gas (BFG) is huge with complex components. The existence of hydrogen sulfide (H2S) in the BFG can produce sulfur dioxide (SO2) after combustion, which will increase the source of SO2 pollution and make the desulphurization more difficult, to be threat to people health. At present, the removal of H2S by dry adsorption with modified activated carbon adsorbent is a high-precision and low-cost desulphurization method. However, the effect of complex gas components in BFG on the adsorption of H2S by activated carbon adsorbent is not sufficient. Based on the fixed bed adsorbent evaluation system, a new type of highly efficient copper-cerium oxide (Cu–Ce–O) modified activated carbon H2S adsorbent was developed. And the effects of carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), oxygen (O2), sulfur dioxide and hydrogen chloride (HCl) in BFG on the desulfurization activity of adsorbents were investigated. The results showed that the performance of H2S removal decreased in the presence of CO, CO2, HCl and SO2, and improved in the presence of H2 and O2. Other parameters were also studied which might influence the process. The application of modified activated carbon adsorbent in simulated BFG is basically stable. According to the fitting results of adsorption kinetics for the five adsorption models, as the atmosphere becomes BFG from N2, pore diffusion becomes the main adsorption form. However, the effects of internal diffusion, chemical adsorption and external mass transfer decreased. The Bangham model is the most suitable model to describe H2S adsorption process.

Mathematical modeling of bioactive extraction from cashew apple: Maxwell-Stefan approach to resolve effect of internal diffusivity and external mass transfer

Every year 2.2 giga-tons of cashew apples are produced and 80 % (unutilized fruit) of them are wasted and contain useful bioactives such as polyphenols and tannins (high molecular weight polyphenols). These bioactives can be separated using extraction: the nutraceutical value of which is of the order of 1 billion USD/year. However, extraction kinetics are normally fitted to simple phenomenological models. These models fail to establish the effect of shrinkage, temperature, thermodynamic parameters, and internal resistances on diffusion of solute. Hence, the objective of this study was to develop a Maxwell-Stefan model that can overcome the above shortcomings and optimize the extraction process of bioactives from cashew apples. The optimized parameters for the extraction process obtained were − solid:solvent ratio- 1:6, particle size (of solid) 125–250 μm, and the extraction temperature as 30 °C. The non-random two liquid (NRTL) activity coefficient model was first used to capture the thermodynamics of extraction effectively, followed by its utilization in the development of Maxwell-Stefan model to resolve the effect of internal diffusivity and external mass transfer coefficient. The model gave a good fit (R2 > 0.90) for all the parameters and could thus predict the extraction data greatly for all operating parameters including temperature, particle size, and solid:solvent ratio. This makes it eminently suitable for scale-up studies.

Methanogenesis kinetics of organic matter of the leachate in an up-flow anaerobic sludge blanket reactor

Understanding the treatment of leachate mediated by the development of anaerobic sludge makes it possible to create an effective design process of biodegradation technology. This study used an up-flow anaerobic sludge blanket (UASB) reactor equipped with a gas–liquid-solid separator to capture CH4 for treating landfill leachate to improve understanding of methanogenesis kinetics of organic matter. The performance of UASB was able to remove 154.75 g/L of chemical oxygen demand (COD) content of the leachate originally anticipated to emit 2.99 L of CH4 production into the atmosphere. The trend in the variation of internal mass transfer (IMT) factor was close to the global mass transfer factor; however, it was far higher than that of external mass transfer (EMT) factor. After 30 days of the experiment, methanogenesis kinetics of organic matter of the leachate were supported mainly by the breakdown of complex molecules. The rate-limiting step of CH4 desorption was controlled by IMT at the beginning and then by EMT after 30 days of the experiment. The strongly decreased EMT factor was counterbalanced by an increased value of the IMT factor at before 5 days of the experiment. It would be of interest to predict the methanogenesis kinetics of CH4 desorption using the Generalized Fulazzaky equations, which cannot be evaluated using other models. Analysis of the methanogenesis kinetics of organic matter of the leachate provides a new insight into the performance of UASB reactor, which may contribute to advanced treatment of landfill leachate in the future.

Mercury Capture Performance and Kinetics of CCl4-Adsorbed Activated Carbon Pretreated by the Mechanochemical Method.

In the present work, CCl4-adsorbed activated carbon pretreated by the mechanochemical method (CCl4-AC) was produced for gas-phase mercury capture. The physicochemical properties of the CCl4-AC sorbent were analyzed via N2 adsorption, scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The mercury capture performance of the CCl4-AC sorbent under different flue gas components was investigated in a fixed-bed experimental device. The programmed temperature desorption of mercury was used to determine the mercury capture product of the spent CCl4-AC. Finally, the mass transfer factor model proposed by Fulazzaky was used to analyze mercury capture on the CCl4-AC for clarifying its characteristics. The results showed that the prepared CCl4-AC can be used as a mercury sorbent because of its high mercury capture performance. Mercury capture by the CCl4-AC was interfered by SO2 and promoted by O2 and H2O. Hg-temperature programmed desorption (Hg-TPD) analysis indicated that the main mercury capture products of the CCl4-AC were HgCl2 and HgO. Because of the presence of SO2 in flue gas, there was a little Hg2SO4 formation on the sorbent. XPS analysis showed that the functional group of C-Cl played the dominant role in Hg0 capture, and part of the C-Cl groups were converted into Cl- after mercury capture. The mercury desorption energy of the spent CCl4-AC was 50.49 kJ/mol and stronger compared with that of raw activated carbon. Mass transfer analysis displayed that surface adsorption was the main form at the beginning of mercury adsorption, and the external mass transfer was the mercury adsorption rate-controlling step. Then, mercury adsorption entered the second stage; internal diffusion adsorption stage with internal mass transfer became the adsorption rate control step.

Mixed-Mode Adsorption of l-Tryptophan on D301 Resin through Hydrophobic Interaction/Ion Exchange/Ion Exclusion: Equilibrium and Kinetics Study.

The adsorption of l-tryptophan (l-Trp) was studied based on the hydrophobic interaction/ion exchange/ion exclusion mixed-mode adsorption resin D301. Firstly, the interaction mode between l-Trp and resin was analyzed by studying the influence of pH variation on the adsorption capability and the dissociation state of l-Trp. Secondly, the adsorption mechanism was illuminated by studying the adsorption equilibrium and kinetic behaviors. The adsorption equilibrium and a kinetics model were constructed. The augmentation of pH gradually elicited an enhancement in the adsorption capacity of l-Trp. l-Trp existing in varied dissociation states could be adsorbed by the resin, and the interaction mode relied upon the pH of the solution. An integrated adsorption equilibrium model with the coadsorption of different dissociation states of l-Trp was developed and could predict the adsorption isotherms at various pH levels satisfactorily. Both external mass transfer and intra-particle diffusion collectively imposed constraints on the mass transfer process of l-Trp onto the resin. An improved liquid film linear driving force model (ILM) was constructed, and the model provided a satisfactory fit for the adsorption kinetics curves of l-Trp at various pH levels. l-Trp molecules had a high mass transfer rate at a relatively low solution pH.

Carbon sources influence on heterotrophic ammonia assimilation: Performance and mechanism

Different carbon contents of organic carbon sources can be used as the reaction substrates of heterotrophic ammonia assimilation (HAA), which effectively dominates the recovery of available nutrients in wastewater. However, the influences of organic carbon sources on nutrient metabolism, degradation kinetics, and functional microbes of HAA were largely unknown. Here, HAA bioreactors fed with acetate, glucose, sucrose, starch, methanol, and sludge alkaline fermentation liquid (SAFL) were constructed to compare the nitrogen recovery performance, kinetic analysis, sludge characteristics, and microbial community structure. Higher COD and NH4+-N removal efficiencies were found in bioreactors supplied with acetate, glucose, and SAFL. Kinetic analysis showed that the acetate-fed bioreactor had more efficient organic utilization for assimilation. Corynebacterium, Pseudohoeflea, and Methylophaga emerged as the primary assimilation bacteria for typical carbon sources of organic acids, sugars, and alcohols, whereas Halomonas, Corynebacterium, and Marinobacter dominated in SAFL. Acetate- and SAFL-supported sludge particles displayed enhanced internal and external oxygen mass transfer, along with heightened sedimentation performance and deconsolidation ability. High-quality assimilative gene expression, assimilative enzyme activity, and assimilated organic nitrogen product synthesis with direct effects were observed in a reactor supplied with acetate and SAFL. The cost-effectiveness of SAFL preparation positions it as a promising candidate for practical engineering applications. This research underscored the pivotal role of different carbon contents in the nutrient recovery process of the HAA reaction, providing essential insights for optimizing wastewater treatment strategies and enhancing environmental sustainability.

Selective recovery of esterase from Trichoderma harzianum through adsorption: Insights on enzymatic catalysis, adsorption isotherms and kinetics

In recent years, numerous attempts have been made to develop a low-cost adsorbent for selectively recovering industrially important products from fermentation broth or complex mixtures. The current study is a novel attempt to selectively adsorb esterase from Trichoderma harzianum using cheap adsorbents like bentonite (BT), activated charcoal (AC), silicon dioxide (SiO2), and titanium dioxide (TiO2). AC had the highest esterase adsorption of 97.58% due to its larger surface area of 594.45 m3/g. SiO2 was found to have the highest selectivity over esterase, with an estimated purification fold of 7.2. Interestingly, the purification fold of 5.5 was found in the BT-extracted fermentation broth. The functional (FT-IR) and morphological analysis (SEM-EDX) were used to characterize the adsorption of esterase. Esterase adsorption on AC, SiO2, and TiO2 was well fitted by Freundlich isotherm, demonstrating multilayer adsorption of esterase. A pseudo-second-order kinetic model was developed for esterase adsorption in various adsorbents. Thermodynamic analysis revealed that adsorption is an endothermic process. AC has the lowest Gibbs free energy of −10.96 kJ/mol, which supports the spontaneous maximum adsorption of both esterase and protein. In the desorption study, the maximum recovery of esterase from TiO2 using sodium chloride was 41.34 %. Unlike other adsorbents, the AC-adsorbed esterase maintained its catalytic activity and stability, implying that it could be used as an immobilization system for commercial applications. According to the kinetic analysis, the overall rate of the reaction was controlled by reaction kinetics rather than external mass transfer resistance, as indicated by the Damkohler number.

Enhanced adsorption of ciprofloxacin from an aqueous solution using a novel CaMgAl-layered double hydroxide/red mud composite

This work reports on CaMgAl-layered double hydroxide (LDH) based red mud (RM) composite prepared via a co-precipitation method, characterized by transmission electron microscopy (TEM), powder X-ray diffraction patterns (XRD), field-emission scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Brunauer-Emmett-Teller analysis (BET), and Fourier transform infrared spectra (FTIR) and subsequently used for elimination of ciprofloxacin (CIP) from an aqueous solution in batch mode experiments. Langmuir isotherm model provided a better fit of CIP adsorption onto CaMgAl/RM composites than a Freundlich isotherm model; indicating a monolayer adsorption phenomena. Pseudo-second-order kinetic models describe the kinetics of adsorption while the adsorption mechanisms were controlled by external mass transfer and intra-particle diffusion. Thermodynamic analysis indicated that the CIP adsorption onto CaMgAl-LDH/RM was exothermic and spontaneous in nature. The prepared adsorbent exhibited superior affinity towards CIP adsorption which yielded a maximum CIP adsorption capacity of up to 138 mg/g. The higher removal efficiency (89.45 %) was reached under the best conditions (pH 7, agitation speed 150 rpm, adsorbent dosage 0.5 g/100 ml, concentration of contaminant 70 ppm, and 90 min contact time). Moreover, the synthesized adsorbent can be recovered after six consecutive regeneration cycles with a minimal reduction in the adsorption ability of 31 %. In conclusion, this study demonstrated that the CaMgAl-LDH/RM composite could be a promising adsorbent for removing antibiotics from wastewater.

The efficient elimination of lead ions from aqueous solution using MgCuAl-Layered double hydroxides@montmorillonite composite: A kinetic, isotherm and statistical analysis

In this study, a MgCuAl-layered double hydroxide (MCA-LDH)-based montmorillonite cationic clay (MMT) composite was synthesized via a co-precipitation method and then characterized using various analytical techniques, including BET surface area, TEM, XRD, FT-IR, and SEM/EDS analysis, to confirm the successful loading of LDH onto MMT. The material was subsequently used as a novel adsorbent for Pb2+ ion removal from aqueous solution in batch mode experiments. The effects of important variables on Pb2+ adsorption were investigated, and the values of these variables were optimized using the central composite design (CCD) of the response surface methodology (RSM). The results showed that the favorable conditions for the adsorption of Pb2+ onto the MCA-LDH@MMt composite were pH 5, an initial Pb2+ concentration of 85 mg/l, and an adsorbent dose of 0.225 g/100 ml. Under these conditions, the maximum adsorption efficiency was 89.1%. Using the RSM methodology, a quadratic polynomial equation was obtained that expresses the relationship between the adsorption efficiency and the effective parameters. The results show that pH and temperature had a greater effect on the adsorption efficiency. The pseudo-second-order model kinetically well fitted the adsorption process, while external mass transfer and intra-particle diffusion controlled the adsorption mechanics. The Langmuir isotherm model fitted the isotherm to the adsorption process, yielding a capacity of 132.83 mg/g. The thermodynamic study showed that the spontaneous adsorption of Pb2+ onto MCA-LDH@MMt composites is exothermic in nature. Moreover, there was a mere 30% reduction in the removal efficiency after five consecutive regeneration cycles. In conclusion, this work demonstrated that the MCA-LDH@MMt composite could be a promising adsorbent for the treatment of aqueous solutions contaminated with heavy metals.

Kinetics of cashew apple drying through mechanistic models and analysis of the effects of drying conditions on the retention of bioactive compounds

AbstractGlobal cashew nut production is nearly 4 million tons per year, valued at 7 billion US dollars. Remarkably, almost the entire cashew apple crop, amounting to 20 million tons annually, goes to waste. However, the cashew apple contains valuable nutraceutical compounds, including tannins, polyphenols, and carotenoids, estimated to be worth 150 million US dollars annually. Due to the highly perishable nature of cashew apples, degradation is a significant issue. In response, the current work has established drying as an effective preservation technique for these bioactive components. The effect of drying temperature on bioactive compounds has been thoroughly investigated. The non‐random two liquid (NRTL) activity coefficient model effectively captures the thermodynamics of the drying process. To facilitate the selection and design of drying equipment, two mechanistic mass transfer models were developed. The first model employs the Maxwell‐Stefan framework to account for internal diffusion, with external mass transfer resistance appearing as a boundary condition. While this model works well for products like grapes, it proved inadequate for explaining the drying behaviour of cashew apples. Consequently, a second model was developed, postulating rapid moisture transport by capillary action within the cashew apple. This model effectively captures the effects of a wide range of operating conditions, using only external mass transfer resistance as the tuneable kinetic parameter. This mechanistic model is more suitable for dryer design compared to conventional phenomenological models like the logarithmic model and the two‐term exponential model.

External Mass Transfer Performance Studies in a Micropacked Bed Reactor with Pd/PDA/Nickel Foam

External Mass Transfer Performance Studies in a Micropacked Bed Reactor with Pd/PDA/Nickel Foam

Concentration of heavy metal ions from aqueous media under dynamic conditions using a composite sorbent based on chitosan and silica

Objectives. The study set out to investigate the sorption, toxicological, and regeneration properties of a composite sorbent based on chitosan hydrogel and unsuspended silicon dioxide (chitosan–colloidal silica), which manifest themselves under dynamic conditions of purification of aqueous solutions, as a means of removing heavy metal ions.Methods. The total dynamic exchange capacity of a chitosan–colloidal silica composite sorbent was evaluated under dynamic sorption conditions by passing solutions containing Zn(II), Cd(II), Cu(II), and Cr(III) ions having a concentration of 240–251 mg/L through a fixed sorption bed. The method for determining acute toxicity using daphnia (Daphnia magna Straus) is based on the direct calculation of the mortality of daphnia exposed to toxic substances contained in the test aqueous extract in comparison with a reference culture in samples that do not contain toxic substances. The regeneration ability of the sorbent was assessed by counting the number of sorption–desorption cycles using 0.1 M NaOH and 0.1 M NaHCO3 eluents, as well as aqueous solutions of H2O2 (1 and 3%).Results. The effectiveness of the chitosan–colloidal silica composite sorbent in the process of dynamic purification of aqueous media to remove Cu(II), Zn(II), Cd(II), and Cr(III) ions was established. After determining the times of ion breakthrough and saturation of the developed sorbent, its dynamic exchange capacity was calculated by processing the kinetic curves of sorption of heavy metal ions under dynamic conditions. The results of regeneration of the sorbent were presented in the context of the possibility of its reuse. It is shown that the sorbent can withstand up to five sorption–desorption cycles while maintaining a level copper cation extraction above 90%.Conclusions. Analysis of the kinetic curves demonstrated that the driving force behind the removal of heavy metals from aqueous media by means of the obtained sorbent is the external diffusion mass transfer of ions from the mobile phase of the solution. Biotesting of samples showed that the developed chitosan-based sorbent does not have acute toxicity.

Выбор сорбента для элиминации ионов железа из сточных и природных вод

Natural waters and wastewaters often contain heavy metals, e.g., iron. Iron ore mining contaminates groundwater with iron up to 30 maximal permissible concentrations (MPC) as this element gets washed out from rock and soil. Adsorption is the most effective and economically feasible method of additional purification of natural and wastewater from iron. Its efficiency depends on the type of adsorbent. The research objective was to select the most efficient sorption material to eliminate water from iron, as well as to establish the adsorption patterns for different sorbents, thus creating sustainable and effective purification. The study featured carbonaceous sorbent of the SKD-515 grade, mineral sorption materials with aluminosilicate of the AC grade, and silicate-based sorbent of the ODM-2F grade. The porous structure was studied by porometry methods while the surface image was obtained using scanning electron microscopy. Other indicators included equilibrium, kinetics, and dynamics of iron adsorption by various sorbents. The Freundlich and Langmuir equations made it possible to calculate the key adsorption parameters. The Gibbs energy values were obtained from the Langmuir equation and equaled 11.93–20.66 kJ/mol, which indicated the physical nature of the adsorption process. Under static conditions, the sorbents demonstrated a high adsorption capacity with respect to iron, depending on the structure, and could be arranged as AC > SKD-515 > ODM-2F. In SKD-515, iron adsorption occurred in micropores; in AC and ODM-2F, it took place in mesopores. The kinetics of iron extraction showed that the adsorption process was limited by external mass transfer. The research provided a new understanding of iron adsorption by materials of various structures. The conclusions were supported by scanning electron microscopy images. Initial concentration, flow velocity, and loading layer height were studied in dynamics, i.e., during continuous operation of the adsorption column. The system proved extremely effective and reached 99.0% Fe3+ extraction under the following conditions: flow rate = 1 L/min, loading column height = 0.15 m, column diameter = 0.05 m, initial concentration = 0.5 mg/L (5 MPC). The column performance was tested at an initial concentration of iron ions of 50 MPC, which simulated the wastewater treatment at industrial enterprises. This comprehensive study of iron adsorption from wastewater proved the efficiency of the mineral sorption materials with aluminosilicate of AC grade.

Enhanced fluoride removal from water using acid-modified red clay soil from the Loess Plateau of China

ABSTRACT The discharge of fluoride-containing wastewater poses a severe threat to global water resources, ecosystems, and human health. Urgently needed are economically feasible and environmentally sustainable solutions for worldwide fluoride contamination. This study explores utilizing unmodified and modified red clay soils from China's Loess Plateau as adsorbents for fluoride mitigation. Sulfuric acid-modified red clay soil showed higher fluoride removal than unmodified, NaOH-modified, and thermally modified soils. Fluoride adsorption decreased with rising pH from 2.0 to 10.0 for unmodified (67.67–3.91%) and acid-modified red clay soil (90.44–32.06%). The Langmuir model better described the data (R2 = 0.9821, 0.9901 for unmodified, acid-modified soil), improving maximum adsorption capacity by 252%. Pseudo-second-order kinetics (R2 = 0.9925, 0.9954 for unmodified, acid-modified soil) accurately described the kinetic data. Acid modification improved reaction rates, shortening the breakpoint from 6.694 to 2.318 min1/2. Over time, the process transitioned from intraparticle diffusion to external mass transfer and intraparticle diffusion. FTIR analysis showed that acid modification strengthened ligand exchange and provided ion exchange opportunities. This study advances fluoride adsorption through innovative clay soil utilization, offering economical, viable, and environmentally friendly solutions.

Kinetics studies on the ascorbic acid extraction from roselle (Hibiscus sabdariffa) calyces

The effect of processing conditions of roselle (Hibiscus sabdariffa) calyces on the vitamin C content of the extracts was studied to develop models that best describe the process. The extraction parameters are the processing time (5, 10, 15 mins), process temperature (30oC, 50℃, 75℃ and 100℃), and calyx-water mass ratio (1:50, 1:20 and 1:10). These samples were tested for ascorbic acid using the spectrophotometric method. Statistical analysis was conducted on the experimental results and regression models were developed. A total of six mathematical models were selected for the description of vitamin C extraction from the calyces. The results showed that time, temperature and calyx-water mass ratio have a linear significant effect (p ≤ 0.01); while time-temperature and temperature-ratio had a significant (p ≤ 0.05) interaction effect; time and temperature had a significant (p ≤ 0.05) quadratic effect on the vitamin C content of the extract. Pseudo-first-order gave the highest overall coefficient of determination R2 and lowest overall root mean square error (RMSE). The activation energy of vitamin C ranged from 3 to 8.4 kJ; the effective diffusion coefficient ranged from 1.5×10-9 to 5.0×10-7 m 2 s -1 ; while mass diffusivity ranged from 3.11×10-5 to 8.6×10-4 ms-1 . The Biot number calculated ranged between 33.93 and 541.94 which showed that there is an insignificant external mass transfer resistance.

Mercury removal mechanism of mechanochemical sulfur modified straw coke: Density functional theory calculation and kinetic fitting

Mechanochemical sulfur modified straw coke (S-SC) has broad application prospects for flue gas mercury removal due to its high mercury removal efficiency, low cost, and stable mercury removal products. The density functional theory calculation and kinetic fitting were combined to explore the mercury removal mechanism about the influence of the oxygen-containing functional groups and variable sulfur forms on Hg0 removal by S-SC in the atmosphere with or without SO2 based on the previous experimental study. The results show that oxygen-containing functional groups promote Hg0 adsorption by the naked raw straw coke (NSC), which follows C = O > COOH > C-O. Elemental sulfur (S4) benefits Hg0 adsorption on NSC significantly with Hg0 adsorption energy of −237.5 kJ/mol in the stable form of HgS. C = O will weaken the promoting effect of S4 on Hg0 adsorption but can effectively reduce SO2 and Hg0 adsorption competition. For 21 %-ES-SC, Hg0 adsorption on active sites (mainly chemical adsorption) is the primary control step, and external mass transfer plays an important role. This work deeply elucidates the mercury removal mechanism by S-SC and gives a studying strategy of a combination of micro and macro analysis. It can provide guidance for the development of high-performance flue-gas mercury removal adsorbents.