Sorption Equilibrium Constants Research Articles

APPLICATION OF SUPER-CROSSLINKED POLYMERS AS CARRIERS OF HETEROGENEOUS BIOCATALYSTS FOR INULINHYDROLYSIS REACTION

n this work the study of adsorption immobilization of inulinase on super-crosslinked macroporous sorbents based on styrene and divinylbenzene: low-base anion exchanger A100, high-base anion exchanger A500R, strong acid cation exchanger C100H was carried out. The influence of the duration of the sorption process, the value of the concentration of hydrogen ions and the concentration of protein in solution on the amount of immobilized enzyme and the activity of the obtained heterogeneous biocatalysts is considered. It was revealed that adsorption reaches its max-imum value on average after 4 h at pH of 4.7-5.0 for the sorbents under consideration. The activity of the obtained heterogeneous biocatalysts is 64.8-83.5% of the activity of free inulinase. Although the activity of inulinase during adsorption on the polymer carriers used in the work decreases, the integral amount of the resulting product will be higher than for the native catalyst.The isotherms of inulinase adsorption on super-crosslinked polymers have been studied. The high stability of the obtained heterogeneous biocatalysts is explained by the high sorption capacity of super-crosslinkedsorbents. It was revealed that immobilized inulinase can be used during 8-11 consecutive cycles of the substrate hydrolysis reaction.Using the BET adsorption theory, the enzyme sorption isotherms were analyzed and the equilibrium sorption parameters werecalculated: the maximum amount of sorbed inulinase, the constants characterizing the sorbate-sorbent and sorbate-sorbate interaction. Among the considered carriers, the highest value of the sorption equilibrium constant (KL=4.25±0.04 l/mmol) corresponds to the inulinase-cation exchanger biocatalyst, the sorption ca-pacity of which is also the largest. The data obtained is of interest for evaluating the effectiveness of the use of sorbents as inulinase carriers in subsequent technological operations of processing of inulin-containing raw materials.

Adsorption properties of Kemerovo manganese ore toward zinc

Zinc is a toxic and a prevailing pollutant contained in wastewater in nonferrous metallurgy. With a view to ensuring the environmental safety, it is required to develop an integrated wastewater treatment technology to remove heavy metals from effluents. A promising approach to natural and waste water treatment is adsorption using various natural materials. The author analyzes the adsorption capacity of manganese ore from Durnovskoe and Usa deposits toward zinc in static conditions. The adsorption isotherms are described by the Langmuir equation at a high correlation factor. The maximal adsorption capacity, the sorption equilibrium constant and the change in the Gibbs energy are evaluated. Usa manganese ore reveals higher adsorption capacity toward zinc.

Sorption Recovery of Platinum Metals from Production Solutions of Sulfate-Chloride Leaching of Chromite Wastes

This paper discusses the scientific rationale for methods of platinum metals sorption centralization from saturated solutions with a high content of macrocomponents. Methods of sorption centralization of platinum and iridium using local anionites such as AH-31, AB-17-8, Purolite S985 are described. The sorbents used were conditioned to remove organic and mineral impurities. The sorption isotherms of platinum group metals 1/EC=f(1/Cp) at a temperature of 20 °C and a duration of 24 h were plotted. The data on the sorption recovery of platinum and iridium from individual and combined sulfate-chloride solutions were determined. Isotherms of iridium sorption from sulfate-chloride solution are formed. Results of the apparent sorption equilibrium constant and values of standard Gibbs energy (ΔG, kJ/mol) of ion exchange for sorption of platinum and iridium from individual and combined sulfate-chloride solutions are presented. Linearized isotherms and kinetic curves of joint sorption of platinum and iridium from sulfate-chloride solution are described. Comparative sorption of the platinum-group metals (PGM) by anionites AB-17-8 and Purolite S985 from sulfate-chloride solutions is shown. The sorption diagram of platinum and iridium from sulfate-chloride product solutions is presented. It has been revealed that complete recovery is achieved using chelation ion-exchange resin Purolite S985, with recovery of Pt up to 95% and Ir more than 73%. The sorption process is accompanied by intradiffusion constraints that are confirmed by the analysis of kinetic curves using Schmukler and Boyd–Adams models.

Probing Substrate/Catalyst Effects Using QSPR Analysis on Friedel-Crafts Acylation Reactions over Hierarchical BEA Zeolites.

Attempts to optimize heterogeneous catalysis often lack quantitative comparative analysis. The use of kinetic modelling leads to rate (k) and relative sorption equilibrium constants (K), which can be further rationalized using Quantitative Structure-Property Relationships (QSPR) based on Multiple Linear Regressions (MLR). Friedel-Crafts acylation using commercial and hierarchical BEA zeolites as heterogeneous catalysts, acetic anhydride as the acylating agent, and a set of seven substrates with different sizes and chemical functionalities were herein studied. Catalytic results were correlated with the physicochemical properties of substrates and catalysts. From this analysis, a robust set of equations was obtained allowing inferences about the dominant factors governing the processes. Not entirely surprising, the rate and sorption equilibrium constants were found to be explained in part by common factors but of opposite signs: higher and stronger adsorption forces increase reaction rates, but they also make the zeolite active sites less accessible to new reactant molecules. The most relevant parameters are related to the substrates’ molecular size, which can be associated with different reaction steps, namely accessibility to micropores, diffusion capacity, and polarizability of molecules. The relatively large set of substrates used here reinforces previous findings and brings further insights into the factors that hamper/speed up Friedel-Crafts reactions in heterogeneous media.

Characteristics of Natural Mineral Sorbent for Water Treatment of Drinking Water from Underground Sources

The results of research of sorption characteristics of natural mineral material – marsh ferromanganese ore are presented. Indicators of physical properties and mechanical strength, specific surface area of grains of ore samples were determined. The high efficiency of extraction of manganese and iron ions from underground waters by this natural material without the use of additional reagents is revealed. The kinetics of the sorption process was studied. It is shown that the extraction of manganese and iron ions from water solutions by marsh ferromanganese ore proceeds by a sorption-catalytic mechanism. For each ion, the values of the sorption capacity of the sorbent, the sorption equilibrium constants, and the kinetic parameters of the sorption process are calculated.

Influence of Acid Sites on Xylene Transport in MFI Type Zeolites

The influence of Brønsted acidic sites at the pore entrance of MFI type zeolites on the transport of p-xylene was investigated by comparing the diffusion rates on samples with and without Al. The pore entrance rate is directly proportional to the concentration of molecules on the external surface. Brønsted acid sites lead to a higher sorption equilibrium constant of xylene because of stronger binding by about 3 kJ·mol–1, compared to a neutral surface. The stronger binding energy reduces the apparent but not the true energy of activation for the pore entrance step of p-xylene, leading to an enhanced pore entrance rate.

PURIFICATION OF FE3+ CONTAINING WASTEWATER USING NATURAL SORBENTS

Abstract. Bentonites in natural or activated forms, i.e. after chemical treatment with acids, have high adsorption properties and are widely used as a natural adsorbent. The increase in the adsorption capacity of bentonite sorbents during heat treatment at 100–200 ° C is caused by the removal of adsorbed and chemical water that leads to an increase in the overall porosity. By thermal and hydrothermal treatments, the properties of natural sorbents can be varied within wide limits, giving them selectivity with respect to certain dissolved substances. It is known that the irradiation of water systems by microwaves leads to their heating, that is, this method of pre-treatment of sorbents combines their hydro-thermal treatment with high-frequency irradiation. The aim of the work is to investigate the process of absorption of iron (III) by bentonite clay under the influence of microwave radiation. The sorption properties of bentonites were studied under static conditions. For comparison purposes, adsorption was performed on natural bentonite under normal conditions without any pre-treatment and under the action of ultra-high-frequency electromagnetic radiation. The Langmuir equation was used to describe the experimental adsorption isotherms. The maximum sorption capacity of the treated sample was found to be 1.66 times higher than that of the untreated one and was 63.7 and 38.3 mg / g, respectively. The sorption equilibrium constant of the irradiated sample is 42% lower than that of the native one. This indicates that the sorption equilibrium under the action of ultra-high frequency radiation comes in 1.7 times faster than under normal conditions. Therefore, compared to the untreated sample, microwave irradiated bentonite has better sorption characteristics for iron (III), so it can be a promising sorbent for the purification of natural and wastewater.

Study of Removal of Nickel(II) from Aqueous Solutions by Sorption

The results of study of the sorption of nickel(II) ions from aqueous solutions by a finely porous carbon adsorbent (CA) and its modified analogs are presented. Organic reagents selective towards nickel(II) are applied as modifying agents. The isotherms of adsorption are obtained in various temperature modes. The thermodynamic parameters of adsorption are calculated. The increase in the limiting sorption capacity values and the sorption equilibrium constants is established for the modified samples in comparison with the initial ones.

TOXICOLOGICAL PROPERTIES OF HEAVY METALS ADSORBED ON THE SURFACE OF ACTIVATED CARBON

The article studies the effect of activated carbon with sorption capacity saturated by manganese (II) and chromium (III) ions on the vital activity of organisms and systems. Desorption of the toxic component from the surface of the sorbent occurs in accordance with the sorption equilibrium constant. This can produce a polluting effect on the water passing through carbon, on the activity of the soil microorganisms, and on the areas allocated for storage of used sorbents. The article presents new data on the effect of extracts of activated carbon saturated with manganese (II) and chromium (III) salts on the parameters of the blood of laboratory mice and the vital activity of soil microorganisms. The authors synthesized activated carbons with manganese (II) and chromium (III) ions adsorbed on the surface. The activity of alanine aminotransferase and aspartate aminotransferase and the content of total protein, albumin, urea, medium molecular weight molecules, malonic dialdehyde, and products of protein oxidation were identified in the blood of mice after oral administration of extracts of sorbents. After contact with the soil, the effect of adsorbed metals on its catalase and phosphatase activity was detected, as well as changes in the number and composition of soil microorganisms. The study demonstrated that carbons, with a sorption capacity filled by metal ions, affected some of the studied parameters. The authors recorded an increase in the number of products of lipid peroxidation and in urea content after the administration of sorbent suspensions; at the same time, a decrease in the total protein content in the blood of mice was noted. Manganese-adsorbed by carbon also causes a decrease in the number of oligonitrophilic, oligotrophic, and amylolytic groups of soil microorganisms, as well as a simplification of the generic structure of soil micromycetes due to the disappearance of rare genera of Miceliasterilia, Myrothecium.

Sorption of Cu2+ and Zn2+ Ions by Humic Acids of Tundra Peat Gley Soils (Histic Reductaquic Cryosols)

Sorption properties of humic acid (HA) preparations extracted from the peaty horizon of peat gley tundra soil (Histic Reductaquic Cryosols) are characterized. The kinetic and thermodynamic sorption parameters of Cu2+ and Zn2+ ions by HAs are calculated. The sorption of the study heavy metal ions by HA preparations is estimated to be truly approximated by the pseudo-first-order response equation. The negative values of the Gibbs energy change at temperatures of 298.0 К and 314.3 К for Сu2+ (–26.2 and –24.5 kJ/mol, respectively) and Zn2+ ions (–22.2 and –22.0 kJ/mol, respectively) attest to the possibility of self-sorption of the study ions within the considered temperature range. Changes in the sorption enthalpy values (–33.1 kJ/mol for Cu2+ ions and –4.5 kJ/mol for Zn2+ ions) characterize both reactions as exothermal reactions. As the temperature rises, the sorption equilibrium constant for Сu2+ ions considerably decreases, whereas it does not change significantly for Zn2+ ions. The decreasing sorption equilibrium constants with the rise in temperature point to the equilibrium shift towards desorption. This is a characteristic feature of physical sorption that indicates possible existence of two fixation mechanisms of ions on the surface of HA preparations, namely, physical sorption and сhemisorption.

Dispersion of charged solute in charged micro- and nanochannel with reversible sorption.

We study dispersion of a charged solute in a charged micro- and nanochannel with reversible sorption and derive an analytical solution for mass fraction in the fluid, transport velocity and dispersion coefficient. Electrical double layer formed on the charged surface gives rise to a charge-dependent solute transport by modifying the transverse distribution of the solute. We discuss the effect of sorption and electrical double layer on solute transport and show that the coupling between sorption and electrical double layer gives rise to charge-dependent transport even for a thin double layer. However, in this case, it can be reduced to a simple non-charge-dependent case by introducing the intrinsic sorption equilibrium constant.

Pore-scale modelling of dynamic interaction between SVOCs and airborne particles with lattice Boltzmann method

Semivolatile organic compounds (SVOCs) can be easily adsorbed on the suspended particulate matter (PM), and the exchange of SVOCs across the air-particle interface is crucial for the determination of their exposure on human. In the present study, an airborne particle with a diameter of 2.5 μm is fully reconstructed and applied to investigate the SVOCs transport mechanism and the adsorption/desorption process. The pore size distribution of the particle is statistically estimated, based on which Knudsen and Fick diffusion mechanisms are considered. The sorption process between the adsorbed SVOCs on the element carbon (EC) and SVOCs in organic matter (OM) is performed with Langmuir-isotherm model. The effective diffusivity in particle is numerically predicted and compared with the existing empirical study. The influences of the equilibrium sorption constant and the volume fraction of organic matter and carbon on the dynamic interaction process are also explored. Results show that the effective diffusivity of the PM particle with low porosity predicted with the present model is much lower than that adopted by the Bruggeman equation. The amount of adsorbed di-2-ethyhexyl phthalate (DEHP) on EC is predominant compared with the gas phase in pores and dissolved phase in PM. The total amount of DEHP transporting from air to the PM particle is highly influenced by the equilibrium sorption constant and the volume fraction of EC. The influence of volume fraction of OM on the total amount of adsorbed DEHP is slight.

Sorption of aniline derivatives on carbon fabric

The statistical adsorption of the chloro- and nitroderivatives of aniline on carbon fabric UVIS-AK was studied. The sorption isotherms of anilines on carbon fabric and coals were constructed at room temperature and a comparative analysis of their sorption activity was performed. The sorption isotherms were linearized in the coordinates of the Langmuir and Dubinin-Radushkevich equations. The main sorption parameters were calculated: the characteristic adsorption energies of anilines, changes in the Gibbs energies, monolayer capacities, and sorption equilibrium constants.

Kinetics and equilibrium modeling of uranium(VI) sorption by bituminous shale from aqueous solution

Sorption of U(VI) onto a bituminous shale (BS) from a nuclear power plant project site in Black Sea region was investigated for potential risk assessment when it releases into the environment with contaminated ground and surface water. The sorption characteristics of the BS for U(VI) recovery were evaluated as a function of contact time, adsorbent dosage, initial concentration, pH and temperature. Kinetic results fit better with pseudo-second-order model rather than pseudo-first-order. The possibility of diffusion process was analyzed based on Weber–Morris intra-particle diffusion model. The McKay equation assuming film- and intraparticle diffusion better predicted the data than the Vermeulen approximation presuming surface diffusion. Equilibrium sorption data were modeled according to the Langmuir, Dubinin–Radushkevich (D–R) and Freundlich isotherm equations. Sorption capacity increased from 0.10 to 0.15mmolg−1 in 298–318K temperature range. FT-IR analysis and pH dependent sorption studies conducted in hydroxide and carbonate media revealed that U(VI) species were sorbed in uranyl and its hydroxo forms on the BS. Desorption studies showed that U(VI) leaching with Black Sea water was negligible from the loaded BS. The activation parameters (Ea, ΔH∗ and ΔG∗) estimated from diffusion coefficients indicated the presence of an energy barrier in the sorption system. However, thermodynamic functions derived from sorption equilibrium constants showed that overall sorption process was spontaneous in nature and entropy controlled.

CO2 Sorption on Coals: Contribution of Minerals and Influence of Supercritical CO2 Pre-exposure

The carbon dioxide (CO2) sorption isotherms of coals from different ranks and coals treated by HCl, HCl and HF sequentially by supercritical carbon dioxide (SCCO2) alone and with H2O (SCCO2/H2O), and by N2 with H2O (N2/H2O) are compared to study the influence of minerals in coals and the influence of SCCO2. The sorption isotherms and the maximum adsorbed amounts from Langmuir plots for different samples reveal that the contribution from the sorption of minerals is relatively small but that the minerals can act as an obstacle, preventing CO2 from adsorbing on the carbonaceous matrix. Generally, HCl-soluble minerals account for about 5–24% of the mineral content of test coals, while HCl-insoluble/HF-soluble minerals account for about 74–94%. Although the content of HCl-insoluble/HF-soluble minerals is much higher than that of HCl-soluble minerals, HCl leaching causes more change than HF leaching. It may be related to the distribution of the minerals in coal. The small variation of the Langmuir constant between parent and treated samples indicates only a small contribution from the minerals or the acid-leaching process. Similar sorption behaviors are observed for the SCCO2/H2O-treated and SCCO2-treated coal samples, as well as the untreated and N2/H2O-treated coal samples for QS and DT coals. A higher sorption capacity of the former pair indicates that the pre-exposure of coal in SCCO2 alone or with H2O leads to a similar increase in CO2 sorption capacity. H2O in pretreating does not make a significant difference in CO2 sorption capacity. No clear change on the magnitude of the Langmuir constant can be observed among the untreated and treated coal samples. It seems that the pre-exposure of coal to SCCO2 or SCCO2 with H2O induces a change on the sorption capacity but no change on the sorption equilibrium constant. The pretreating may cause a change on the sorption sites but not on the basic properties of the carbonaceous moiety.

Vertical transport of anthropogenic mercury in the ocean

We investigate the vertical transport of mercury (Hg) within the ocean using a simple box diffusion model to represent vertical water transport coupled with a particulate Hg flux. The particulate flux assumes that the Hg content of marine particles is proportional to the Hg concentration of surface waters via a sorption equilibrium constant, Kd. The model is forced with the observed factor of 3 increase in atmospheric Hg deposition over the industrial era. The modeled vertical profile of oceanic Hg shows a subsurface maximum at ∼500 m depth due to remineralization of Hg bound to sinking organic particles, consistent with observations. Model results indicate that surface (top 100 m) concentrations of Hg have increased by 150% since preindustrial times. Over the past 150 years, 280 Mmol of anthropogenic Hg have accumulated in the ocean, representing a 18% increase in the total oceanic Hg content. We find that 36% of the anthropogenic Hg occurs in the top 400 m and only 7% occurs below 1500 m. Over the industrial era, we find that 14% of cumulative anthropogenic emissions have accumulated in the ocean. Our model results show that half of the accumulation of anthropogenic Hg in the ocean is due to sinking on particulates. A sensitivity analysis indicates that the model results are most dependent on the value of Kd.

Equilibrium studies of copper ion adsorption onto palm kernel fibre

The equilibrium sorption of copper ions from aqueous solution using a new adsorbent, palm kernel fibre, has been studied. Palm kernel fibre is obtained in large amounts as a waste product of palm oil production. Batch equilibrium studies were carried out and system variables such as solution pH, sorbent dose, and sorption temperature were varied. The equilibrium sorption data was then analyzed using the Langmuir, Freundlich, Dubinin–Radushkevich (D–R) and Temkin isotherms. The fit of these isotherm models to the equilibrium sorption data was determined, using the linear coefficient of determination, r 2, and the non-linear Chi-square, χ 2 error analysis. The results revealed that sorption was pH dependent and increased with increasing solution pH above the pH PZC of the palm kernel fibre with an optimum dose of 10 g/dm 3. The equilibrium data were found to fit the Langmuir isotherm model best, with a monolayer capacity of 3.17 × 10 −4 mol/g at 339 K. The sorption equilibrium constant, K a, increased with increasing temperature, indicating that bond strength between sorbate and sorbent increased with temperature and sorption was endothermic. This was confirmed by the increase in the values of the Temkin isotherm constant, B 1, with increasing temperature. The Dubinin–Radushkevich (D–R) isotherm parameter, free energy, E, was in the range of 15.7–16.7 kJ/mol suggesting that the sorption mechanism was ion exchange. Desorption studies showed that a high percentage of the copper was desorbed from the adsorbent using acid solutions (HCl, HNO 3 and CH 3COOH) and the desorption percentage increased with acid concentration. The thermodynamics of the copper ions/palm kernel fibre system indicate that the process is spontaneous and endothermic.

Sorption of Cd(II) and Pb(II) from aqueous solutions onto Agave americana fibers

The potential of Agave americana fibers as biosorbent was investigated in batch Pb(II) and Cd(II) removal as a function of pH, initial metal concentration and temperature. Metal sorption followed pseudo-second-order kinetics with excellent correlation. The Langmuir model was successfully applied to describe the sorption isotherms. Under optimum conditions (20 °C, pH 5.0, contact time of 30–60 min and 5 g L −1 biomass concentration), the maximum sorption capacity of A. americana fibers was 40.0 mg g −1 for Pb and 12.5 mg g −1 for Cd, respectively. The results obtained at different temperatures allowed estimating the thermodynamic parameters (Δ G°, Δ H° and Δ S°) from the sorption equilibrium constants. The positive Δ H° value obtained for sorption of both metals indicates the endothermic nature of the process. A. americana fibers were also analyzed by IR-FT spectroscopy and scanning electron and metallographic microscopy, with the aim of investigating the interactions of biomass functional groups with cations and evaluating the mechanisms involved in metal sorption.

Preparation and properties of modified spherically granulated chitosan for sorption of 137Cs from solutions

A composite sorbent based on spherically granulated chitosan modified with a mixed ferrocyanide K2Cu3[Fe(CN6)]2 (SGC-FC) was prepared. The sorbent is highly effective toward 137Cs. The physicochemical parameters of 137Cs+ sorption by this sorbent were determined: total and equilibrium static exchange capacity, dynamic exchange capacity, sorption equilibrium constants, etc. The influence of the chemical composition of the solution on the 137Cs+ sorption by SGC-FC was examined in detail. Based on the calculated value of the dimensionless Biot number Bi, a conclusion was made that the kinetics of 137Cs+ sorption on SGC-FC is mainly determined by external diffusion of 137Cs+ ions to reaction centers of the sorbent. The possibility of using the sorbent in monitoring of sea areas was considered.

Interaction between U(VI) and SrTiO 3 surfaces versus temperature

The purpose of this work is the study of the interaction mechanisms between U(VI) ions and SrTiO 3 surfaces as a function of pH and temperature (25, 50, 75 and 90 °C) by coupling thermodynamic and spectroscopic approaches. First, the reactivity towards U(VI) for both surface sites of the strontium titanate ( Ti O and Sr O) has been investigated as a function of the temperature. The N 2-BET specific area was measured: 2.4 ± 0.2 m 2 g − 1 . The surface site density has been determined from potentiometric titrations (6 sites/nm 2 for each site Ti O and Sr O). The potentiometric titration data have been simulated, for each temperature, using the FITEQL 4.0 software and the constant capacitance model, taking into account both protonation of the Sr OH surface sites and deprotonation of the Ti OH ones (one p K model). The intrinsic strontium protonation constant increases with an increasing temperature, while the titanate deprotonation one decreases. Moreover, both enthalpy and entropy changes corresponding to the surface acid–base reactions have been evaluated using the van't Hoff relation. The uranium(VI) ions are sorbed onto SrTiO 3 surfaces in the 0.5–5.0 pH range with an initial cation concentration equal to 10 − 4 M . The U(VI) surface complexes were identified by using time-resolved laser-induced fluorescence spectroscopy (TRLFS). For all the studied samples, the fluorescence spectra and the corresponding lifetime values do not change with the pH and the temperature. Two U(VI) complexes sorbed onto SrTiO 3 were detected and the corresponding lifetimes are 60 ± 5 and 12 ± 2 μs whatever the temperature (25, 50, 75 and 90 °C). The sorption edges were simulated with the FITEQL 4.0 code. The sorption equilibrium constants of the U(VI)/SrTiO 3 system between 25 and 90 °C were obtained with the constant capacitance model (CCM), considering two reactive surface sites. According to the spectroscopic characterization, two types of surface complexes, namely [( SrOH)( TiOH)UO 2] 2+ and [( TiOH)( TiO)UO 2] 2+, were considered. Finally, enthalpy ( Δ r H ° ) and entropy ( Δ r S ° ) changes were calculated from the temperature-dependent sorption constants, by the application of the van't Hoff formalism. The formation of the [( SrOH)( TiOH)UO 2] 2+ surface complex was found to present an endothermic character associated to an increase in the disorder of the system. On the contrary, the formation of the [( TiOH)( TiO)UO 2] 2+ surface complex led to an exothermic process with only a slight increase in the disorder of the system.