Search Results (48)

This paper investigated the tunnel slags generated from a specific tunnel project to systematically assess their environmental risk through phase composition, chemical composition, acidification potential, and heavy metal speciation. Leaching experiments were conducted under various influencing factors, including particle size, time, liquid-to-solid ratio, pH, temperature. The release concentration of heavy metals from the tunnel slag particles follows the following order: Zn > Cu > Cr. This is primarily attributed to the preferential release of Zn under acidic conditions due to its high acid-soluble state, while Cr, which is predominantly present in the residual state, exhibits very low mobility. Furthermore, decreased particle sizes, increased liquid-to-solid ratios, elevated leaching temperatures, extended leaching times, and lower pH values can effectively promote the dissolution of heavy metals from the tunnel slag. The cumulative leaching curves of Cr, Cu, and Zn from the three types of tunnel slags conform to the Elovich equation (R² > 0.88), indicating that the release process of heavy metals is primarily controlled by diffusion mechanisms. The S- and Fe/Mg-rich characteristics of D3 confers a high acidification risk, accompanied by a rapid and persistent heavy metal release rate. In contrast, D2, which is influenced by the neutralizing effect of carbonate dissolution, releases heavy metals at a steady rate, while D1, which is dominated by inert minerals like quartz and muscovite, exhibits the slowest release rate. It is recommended that waste management engineering prioritize controlling S- and Fe/Mg-rich tunnel slags (D3) and mitigating risks of elements like Zn and Cu under acidic conditions. This study provides a scientific basis and technical support for the environmentally safe disposal and resource utilization of tunnel slag. Full article

Addressing the removal of hazardous phenolic pollutants from water, this study introduces an eco-friendly adsorbent composed of waste-derived hydrochar immobilized in alginate beads (Alg/HC). The physicochemical properties of the Alg/HC beads were characterized using SEM, XRD, and FTIR, confirming hydrochar encapsulation and partial structural preservation. Batch studies revealed a maximum 2-nitrophenol (2-NP) adsorption capacity of 15.80 ± 0.62 mg/g at 30 mg/L of 2-NP, with kinetics best described by the Elovich and pseudo-second-order models. Freundlich isotherm fitting indicated multilayer adsorption on heterogeneous surfaces, likely governed by hydrogen bonding and π–π interactions. In a fixed-bed column system, Alg/HC beads demonstrated a continuous adsorption capacity of 6.84 ± 0.45 mg/g at 10 mg/L of 2-NP, with breakthrough behavior modeled by the Yoon–Nelson and Thomas equations. The beads maintained stable performance across four regeneration cycles using a mild water/ethanol desorption method. This work represents the first study to explore Alg/HC composites for 2-NP removal in both batch and continuous modes, demonstrating their potential as low-cost, regenerable adsorbents for tertiary treatment of phenolic industrial wastewater. Full article

This study focused on optimizing key extraction parameters (ethanol concentration, temperature, and time) to enhance the extraction of hydroxycinnamic acids from A. graveolens leaves, applying a replicated 2³ full factorial design. The experimental results demonstrated that extraction conditions significantly influenced the yield of hydroxycinnamic acids. The optimum conditions were 50% ethanol for 80 min at 50 °C, yielding 103.75 µg/g of chlorogenic acid (ChA), 6.05 µg/g of ferulic acid (FA), and 2.19 µg/g of sinapic acid (SA). Therefore, the extract obtained with 50% ethanol showed the highest levels of polyphenols, flavonoids, and antioxidant potential, highlighting its suitability for use in both food-related products and pharmaceutical formulations. Additionally, the applicability of different mathematical models (unsteady-state diffusion, parabolic diffusion, and power law models, as well as Ponomaryov’s and Elovich’s equations) to describe and better understand the kinetics of hydroxycinnamic acid extraction from dill leaves was evaluated. The fit of each kinetic model to the experimental data was assessed using the root mean square error and the coefficient of determination. Among the five kinetic models, the unsteady-state diffusion model and Ponomaryov’s equation provided the best fit, exhibiting the highest accuracy. The activation energy for the extraction process was determined to be 5.85, 6.46, and 7.59 kJ/mol for ChA, FA, and SA, respectively. The extraction of hydroxycinnamic acids from dill leaves was found to be endothermic, irreversible, and spontaneous. Full article

The physicochemical properties of natural bentonite and its sorbents were studied. It has been established the modification of natural bentonites using polyhydroxoxides of iron (III) (mod.1_Fe_5-c) and aluminum (III) (mod.1_Al_5-c) by the “co-precipitation” method led to changes in their chemical composition, structure, and sorption properties. It was shown that modified sorbents based on natural bentonite are finely porous (nanostructured) objects with a predominance of pores of 1.5–8.0 nm in size. The modification of bentonite with iron (III) and aluminum compounds by the “co-precipitation” method also leads to an increase in the sorption capacity of the obtained sorbents with respect to bichromate and arsenate anions. A kinetic analysis showed that, at the initial stage, the sorption process was controlled by an external diffusion factor, that is, the diffusion of the sorbent from the solution to the liquid film on the surface of the sorbent. The sorption process then began to proceed in a mixed diffusion mode when it limited both the external diffusion factor and the intra-diffusion factor (diffusion of the sorbent to the active centers through the system of pores and capillaries). To clarify the contribution of the chemical stage to the rate of adsorption of bichromate and arsenate anions by the sorbents under study, kinetic curves were processed using equations of chemical kinetics (pseudo-first-order, pseudo-second-order, and Elovich models). It was found that the adsorption of the studied anions by the modified sorbents based on natural bentonite was best described by a pseudo-second-order kinetic model. The high value of the correlation coefficient for the Elovich model (R² > 0.9) allows us to conclude that there are structural disorders in the porous system of the studied sorbents, and their surfaces can be considered heterogeneous. Considering that heterogeneous processes occur on the surface of the sorbent, it is natural that all surface properties (structure, chemical composition of the surface layer, etc.) play an important role in anion adsorption. Full article

Ecosystems are negatively impacted by pharmaceutical-contaminated water in different ways. In this work, a new biosorbent obtained by immobilizing Lactococcus lactis in a calcium alginate matrix was developed for the removal of pharmaceuticals from aqueous solutions. Ethacridine lactate (EL) was selected as the target drug. Lactococcus Lactis biomass was chosen for the biosorbent synthesis for two reasons: (i) the microbial biomass used in the food industry allows the development of a low-cost biosorbent from available and renewable materials, and (ii) there is no literature mentioning the use of Lactococcus Lactis biomass immobilized in natural polymers as a biosorbent for the removal of pharmaceuticals. The characterization of the synthesized biosorbent named 5% LLA was performed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysis. Additionally, particle size and the point of zero charge were established. Batch biosorption investigations showed that using 5% LLA at an initial pH of 3.0 and a biosorbent dose of 2 g/L resulted in up to 80% EL removal efficiency for all EL initial concentrations (20–60 mg/L). Four equilibrium isotherms, given in the order of Redlich–Peterson > Freundlich > Hill > Temkin, are particularly relevant for describing the experimental data for EL biosorption on the 5% LLA biosorbent using correlation coefficient values. Kinetic parameters were determined using kinetic models such as pseudo-first-order, pseudo-second-order, Elovich, Avrami and Weber–Morris. The pseudo-second-order kinetics model provides the greatest fit among the evaluated equations, with correlation coefficients greater than 0.99. According to the study’s findings, the developed biocomposite is a potentially useful material for the removal of pharmaceuticals from aqueous matrices. Full article

The current study comprehensively investigates the adsorption behavior of chromium (Cr(III)) in wastewater using Algerian kaolinite clay. The structural and textural properties of the kaolinite clay are extensively characterized through a range of analytical methods, including XRD, FTIR, SEM-EDS, XPS, laser granulometry, N₂ adsorption isotherm, and TGA–DTA. The point of zero charge and zeta potential are also assessed. Chromium adsorption reached equilibrium within five minutes, achieving a maximum removal rate of 99% at pH 5. Adsorption equilibrium is modeled using the Langmuir, Freundlich, Temkin, Elovich, and Dubinin–Radushkevitch equations, with the Langmuir isotherm accurately describing the adsorption process and yielding a maximum adsorption capacity of 8.422 mg/g for Cr(III). Thermodynamic parameters suggest the spontaneous and endothermic nature of Cr(III) sorption, with an activation energy of 26.665 kJ/mol, indicating the importance of diffusion in the sorption process. Furthermore, advanced DFT computations, including COSMO-RS, molecular orbitals, IGM, RDG, and QTAIM analyses, are conducted to elucidate the nature of adsorption, revealing strong binding interactions between Cr(III) ions and the kaolinite surface. The integration of theoretical and experimental data not only enhances the understanding of Cr(III) removal using kaolinite but also demonstrates the effectiveness of this clay adsorbent for wastewater treatment. Furthermore, this study highlights the synergistic application of empirical research and computational modeling in elucidating complex adsorption processes. Full article

Currently, adsorption is considered a promising technology for CO₂ separation with a wide range of adsorbents. A detailed study of equilibrium and kinetics plays a crucial role in the design and operation of industrial adsorption units. In this study, isotherm and kinetics of CO₂ adsorption on two RSS-derived AC samples previously prepared in our laboratory were evaluated using equilibrium experiments for pure CO₂ at 25 °C and 40 °C and 1 bar. Blank and IL-functionalized AC showed CO₂ adsorption capacity of 2.16 mmol/g, 1.96 mmol/g, 1.12 mmol/g and 1.71 mmol/g at 25 °C and 40 °C, respectively. Langmuir, Freundlich, and Temkin equations were used to model adsorption isotherm in low-pressure regions. The obtained results revealed that the Freundlich model provides an accurate fitting to the experimental findings, which indicate that the adsorption process occurs in a heterogeneous phase. Additionally, kinetic analysis was performed by using four empirical models, namely pseudo-first order, pseudo-second order, Elovich, and Avrami’s fractional models. Among the considered kinetic models, the pseudo-second order model fits best for both blank and IL-functionalized AC. Intra-particle and Boyd’s film diffusion models were evaluated for the adsorption mechanism. Full article

Magnesium deficiency is a pervasive and recurrent factor that significantly restricts crop production, primarily attributable to the low levels of exchangeable magnesium (ex-Mg) present in acidic soil conditions. This deficiency exerts a pronounced negative influence on the sustainability and progress of agricultural development. Hence the current study aspired at modeling the kinetics of Exchangeable Magnesium release from 3 fertilizer sources i.e., Epsom salt (MgSO₄·7H₂O), Magnesite (MgCO₃) and Dolomite [CaMg(CO₃)₂] in the acidic soil of the Nilgiris district in Tamil Nadu, India. Four mathematical models were verified—Power function, parabolic diffusion, Simple-Elovich, and first-order to explain cumulative Mg²⁺ release. Power function was noticed to be an outstanding empirical equation finely fitted to the experimental data. The intensity, as well as the modality of the release pattern, was predicted by the numerical parameters. The power function as well as Parabolic Diffusion portrayed the Mg²⁺ release kinetics best as verified by the maximum correlation coefficients (r²). The parabolic diffusion model also designated the data as suitable, signifying diffusion-controlled exchange. From the derived dissolution rates, it was conceivable to agree Epsom salt (MgSO₄·7H₂O) from which the release was faster than the other two magnesium sources. In conclusion, these outcomes provided an insight into the temporal dynamics of magnesium availability in acidic soil, highlighting the importance of understanding its release kinetics for sustainable agriculture development. The findings contribute to the broader knowledge of magnesium management strategies, aiding in the development of targeted interventions to alleviate magnesium deficiency and optimize crop productivity in acidic soil environments. Full article

The present study aimed to investigate the potential of a new lignocellulosic biosorbent material derived from mature leaves of sour cherry (Prunus cerasus L.) for removing methylene blue and crystal violet dyes from aqueous solutions. The material was first characterized using several specific techniques (SEM, FTIR, color analysis). Then, the adsorption process mechanism was investigated through studies related to adsorption equilibrium, kinetics, and thermodynamics. A desorption study was also performed. Results showed that the Sips isotherm provided the best fit for the adsorption process of both dyes, with a maximum adsorption capacity of 168.6 (mg g⁻¹) for methylene blue and 524.1 (mg g⁻¹) for crystal violet, outperforming the capacity of other similar adsorbents. The contact time needed to reach equilibrium was 40 min for both studied dyes. The Elovich equation is the most suitable model for describing the adsorption of methylene blue, while the general order model is better suited for the adsorption of crystal violet dye. Thermodynamic analyses revealed the adsorption process to be spontaneous, favorable, and exothermic, with physical adsorption involved as the primary mechanism. The obtained results suggest that sour cherry leaves powder can be a highly efficient, eco-friendly, and cost-effective adsorbent for removing methylene blue and crystal violet dyes from aqueous solutions. Full article

To solve radioecological and oceanological problems (estimate the vertical transport, flows of particulate organic carbon, phosphorus biodynamics, submarine groundwater discharge, etc.), it is necessary to determine the natural values of the radionuclides’ activity in seawater and particulate matter. For the first time, the radionuclides’ sorption from seawater was studied using sorbents based on activated carbon modified with iron(III) ferrocyanide (FIC) and based on activated carbon modified with iron(III) hydroxide (FIC A—activated FIC) obtained by FIC sorbent treatment with sodium hydroxide solution. The possibility of trace amounts of phosphorus, beryllium, and cesium recovery in laboratory conditions has been investigated. Distribution coefficients, dynamic, and total dynamic exchange capacities were determined. The physicochemical regularities (isotherm and kinetics) of sorption have been studied. The results obtained are characterized via Langmuir, Freindlich, and Dubinin–Radushkevich isotherm equations, as well as pseudo-first and pseudo-second-order kinetic models, intraparticle diffusion, and the Elovich model. Under expeditionary conditions, the sorption efficiency of ¹³⁷Cs using FIC sorbent, ⁷Be, ³²P, and ³³P—using FIC A sorbent with a single-column method by adding a stable tracer, as well as the sorption efficiency of radionuclides ²¹⁰Pb and ²³⁴Th with their natural content by FIC A sorbent in a two-column mode from large volumes of seawater was assessed. High values of efficiency of their recovery by the studied sorbents were achieved. Full article

For the first time, a comprehensive study of sorbents based on manganese dioxide was carried out for beryllium sorption from seawater in laboratory and expeditionary conditions. The possibility of using several commercially available sorbents based on manganese dioxide (Modix, MDM, DMM, PAN-MnO₂) and phosphorus(V) oxide (PD) for ⁷Be recovery from seawater for solving oceanological problems was evaluated. Beryllium sorption under static and dynamic conditions was studied. The distribution coefficients and dynamic and total dynamic exchange capacities were determined. Sorbents Modix (K_d = (2.2 ± 0.1) × 10³ mL/g) and MDM (K_d = (2.4 ± 0.2) × 10³ mL/g) showed high efficiency. The dependences of the degree of recovery on time (kinetics) and the capacity of the sorbent on the beryllium equilibrium concentration in solution (isotherm) were established. The data obtained were processed using kinetic models (intraparticle diffusion, pseudo-first and pseudo-second orders, Elovich model) and sorption isotherm equations (Langmuir, Freindlich, Dubinin–Radushkevich). The paper contains results of expeditionary studies to evaluate the sorption efficiency of ⁷Be from large volumes of the Black Sea water by various sorbents. We also compared the sorption efficiency of ⁷Be for the considered sorbents with aluminum oxide and previously obtained sorbents based on iron(III) hydroxide. Full article

Magnetic carbon xerogels were synthesized via direct sonication to load magnetite nanoparticles in sol–gel polycondensation onto resorcinol-formaldehyde gels. The resulting organic gels were carbonized and subjected to surface modification using H₂O₂ and characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The desorption capacity was optimized using response surface methodology, with the adsorbent dose identified as the most significant quantitative factor. The kinetic adsorption was well described using the Elovich and Power equations. The regeneration capacity was evaluated over four sequential adsorption–desorption cycles, demonstrating the possibility of reusing the adsorbent and reducing the environmental impact. Full article

This study evaluated nanocellulose derived from discarded palm leaves for its ability to remove cobalt ions from industrial wastewater. The process involved extracting cellulose nanocrystals (CNCs) from date palm leaves through a series of repeated chemical treatments. The study examined the adsorption rates of cobalt ions under various conditions using different techniques. Two equilibrium models, the Langmuir and Freundlich models, were employed, and the Langmuir model was found to be consistent with the experimental data. The maximum amount of cobalt ions adsorbed at room temperature was 5.98 mg/g. Furthermore, several kinetic models were used to gain insight into the adsorption mechanism, including the pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models. The pseudo-second-order model provided an accurate description of the adsorption process, while the Elovich equation suggested a chemical reaction between cobalt ions and nanocellulose, involving multiple chemical reactions and mass-transfer processes. Kinetic parameters were critical in interpreting the results, and the study’s findings were in agreement with the pseudo-second-order and intraparticle models, indicating general chemical reactions and diffusion resistance. Full article

This study includes the characterization and exploitation of an abundant agricultural waste in Algeria, Alfa (Stipa tenacissima L.) leaf powder (ALP) as a biosorbent for the removal of hazardous triphenylmethane dyes, malachite green (basic green 4) and crystal violet (basic violet 3), from aqueous media under various operating conditions in batch mode. The effect of experimental parameters such as initial dye concentration (10–40 mg/L), contact time (0–300 min), biosorbent dose (2.5–5.5 g/L), initial pH (2–8), temperature (298–328 K), and ionic strength on dye sorption was investigated. The results of both dyes show that the increase in initial concentration, contact time, temperature, and initial pH of solution leads to an increase in biosorbed quantity, unlike the effect of ionic strength. The biosorption kinetics for triphenylmethane dyes on ALP was analyzed by pseudo-first-order, pseudo-second-order, Elovich, and intraparticle diffusion models proposed by the Weber–Morris equation. Equilibrium sorption data were analyzed by six isotherms, namely the Langmuir, Freundlich, Harkins–Jura, Flory–Huggins, Elovich, and Kiselev isotherms. The thermodynamic parameters were evaluated for both dyes. The thermodynamic results suggest that both dyes’ biosorption is a typical physical process, spontaneous and endothermic in nature. Full article

Initial periods of adsorption kinetics play an important role in estimating the initial adsorption rate and rate constant of an adsorption process. Several adsorption processes rapidly occur, and the experimental data of adsorption kinetics under the initial periods can contain potential errors. The pseudo-second-order (PSO) kinetic model has been popularly applied in the field of adsorption. The use of the nonlinear optimization method to obtain the parameters of the PSO model can minimize error functions during modelling compared to the linear method. However, the nonlinear method has limitations in that it cannot directly recognize potential errors in the experimental points of time-dependent adsorption, especially under the initial periods. In this study, for the first time, the different linear types (Types 1–6) of the PSO model are applied to discover the error points under the initial periods. Results indicated that the fitting method using its linear equations (Types 2–5) is really helpful for identifying the error (doubtful) experimental points from the initial periods of adsorption kinetics. The imprecise points lead to low adjusted R² (adj-R²), high reduced χ² (red-χ²), and high Bayesian information criterion (BIC) values. After removing these points, the experimental data were adequately fitted with the PSO model. Statistical analyses demonstrated that the nonlinear method must be used for modelling the PSO model because its red-χ² and BIC were lower than the linear method. Type 1 has been extensively applied in the literature because of its very high adj-R² value (0.9999) and its excellent fitting to experimental points. However, its application should be limited because the potential errors from experimental points are not identified by this type. For comparison, the other kinetic models (i.e., pseudo-first-order, pseudo-nth-order, Avrami, and Elovich) are applied. The modelling result using the nonlinear forms of these models indicated that the fault experimental points from the initial periods were not detected in this study. Full article