Entropy Of Adsorption Research Articles

Thermodynamic Parameters of Berberine with Kolliphor Mixtures Adsorption and Micellization.

The poor solubility of berberine (Ber) in water limits its practical use. Its solubility can be increased, among other ways, by the addition of surfactants. Of the surfactants, Kolliphor® ELP (ELP) and Kolliphor® RH 40 (RH40) can be very useful in this respect. The increase of Ber's solubility in water in the presence of ELP and RH40 should be reflected in the composition of the surface layers at the water-air interface and the micelles. The determined composition is reflected in the Gibbs energy of interactions of berberine with ELP and RH40 through the water phase and the standard Gibbs free energy, enthalpy, and entropy of adsorption and micellization. These energies were determined from the equations proposed by us, based on the Gibbs surface excess concentration of the Ber mixture with ELP and RH40, the activity of these compounds in the surface layer at the water-air interface and in the micelles obtained by the Hua and Rosen method, and the contributions of Ber, ELP, and RH40 to the reduction in the water surface tension. For this determination, the measurements of the surface tension of the aqueous solution of the Ber mixture with ELP or RH40 and that of the Ber mixture with these two surfactants, as well as the density and conductivity were performed. Moreover, the fluorescence emission spectra for the Ber + surfactant mixtures were recorded.

Characterization of polar surface groups on siliceous materials by inverse gas chromatography and the enthalpy-entropy compensation effect.

Surface-modified porous silica is a well-established composite material. To improve its embedding and application behavior, adsorption studies of various probe molecules have been performed using the technique of inverse gas chromatography (IGC). For this purpose, IGC experiments were carried out in the infinite dilution mode on macro-porous micro glass spheres before and after surface modification with (3-mercaptopropyl)trimethoxysilane. To provide information about the polar interactions between probe molecules and the silica surface, in particular, eleven polar molecules have been injected. In summary, the free surface energy for pristine silica ( = 229mJ/m2) and for (3-mercaptopropyl)trimethoxysilane-modified silica ( = 135mJ/m2) indicates a reduced wettability after surface modification. This is due to the reduction of the polar component of the free surface energy ( ) from 191mJ/m2 to 105mJ/m2. Simultaneously, with the reduction of surface silanol groups caused by surface modification of silica and, therefore, the decrease in polar interactions, a substantial loss of Lewis acidity was observed by various IGC approaches. Experiments with all silica materials have been conducted at temperatures in the range from 90°C to 120°C to determine the thermodynamic parameters, such as adsorption enthalpy ( ) and adsorption entropy ( ), using the Arrhenius regression procedure evaluating the IGC data. With the help of the enthalpy-entropy compensation, two types of adsorption complexes are assumed between polar probe molecules and the silica surface because of different isokinetic temperatures. Identical adsorption complexes with an isokinetic temperature of 370°C have been assigned to alkanes and weakly interacting polar probes such as benzene, toluene, dichloromethane, and chloroform. Polar probe molecules with typical functional groups such as OH, CO, and CN, having the ability to form hydrogen bonds to the silica surface, exhibit a lower isokinetic temperature of 60°C. Quantum chemical calculations of the probe molecules on a non-hydroxylated and hydroxylated silica cluster supported the formation of hydrogen bonds in the case of a strong polar adsorption complex with a bonding distance of 1.7nm-1.9nm to the silica surface.

Adsorption of textile dyes from aqueous solutions onto clay: Kinetic modelling and equilibrium isotherm analysis.

The commercial activated carbon commonly uses to reduce of dye amount in the textile industry effluents. In this study has focused on the use of a natural clay sample as low cost but potential adsorbent. For this purpose the adsorption of commercial textile dyes, Astrazon Red FBL and Astrazon Blue FGRL, onto clay was investigated. The physicochemical and topographic characteristics of natural clay sample were determined by scanning electron microscopy (SEM), X-Ray fluorescence spectrometry (XRF), X-Ray diffraction (XRD), thermogravimetric analysis (TGA), and cation exchange capacity measurements. It was determined that the major clay mineral was smectite with partial impurities. The effects of several operational parameters such as contact time, initial dye concentration, temperature, and adsorbent dosage on the adsorption process were evaluated. The adsorption kinetics was interpreted with pseudo-first order, pseudo-second order, and intra-particle diffusion models. The equilibrium adsorption data were analyzed using Langmuir, Freundlich, Redlich-Peterson, and Temkin isotherm models. It was determined that the adsorption equilibrium was reached in the first 60min for each dye. The amount of adsorbed dyes onto clay decreased with increasing temperature, similarly, it decreased with increasing sorbent dosage. The kinetic data were well described by pseudo-second order kinetic model, and adsorption equilibrium data was followed both Langmuir and Redlich-Peterson models for each dyes. The adsorption enthalpy and entropy values were calculated as -10.7kJ.mol-1 and -13.21J.mol-1.K-1 for astrazon red and those for astrazon blue -11.65kJ.mol-1 and 37.4J.mol-1.K-1, respectively. The experimental results support that the physical interactions between clay particles and dye molecules have an important role for the spontaneous adsorption of textile dyes onto the clay. This study revealed that clay could effectively be used as an alternative adsorbent with high removal percentages of astrazon red and astrazon blue.

Synergistic Effect of BaCl2 on Corrosion Inhibition of Copper by Mentha Spicata Oil in 1M Nitric Acid: Gravimetric and Raman Spectroscopy Studies

The effect of Mentha Spicata oil and the mixture of BaCl2 and Mentha Spicata oil on corrosion of copper in 1M HNO3 have been investigated using weight loss methods and Raman spectroscopy. The study revealed that copper is more efficiently inhibited by Mentha Spicata oil in the presence of BaCl2 than pure oil. The inhibition efficiencies increased with increased concentration of the additives. The highest inhibition efficiency of 56.12 % was observed with single Mentha Spicata oil. An improved inhibition efficiency of 75.13 % was observed with the mixture of Mentha Spicata oil and BaCl2 at 298 K in 1M HNO3, an effect attributed to synergism between Mentha Spicata oil and BaCl2. Inhibition efficiency decreased with increase in temperature from 298-328 K. The adsorption of inhibitor molecules on metal surface followed Frumkin and Langmuir isotherm. Thermodynamic parameters such as enthalpy ∆H, free energy of adsorption ∆G and entropy of adsorption are obtained from experimental temperatures ranging from 298-328 K. Raman Spectroscopy and mapping were used to characterize the surface layers.

New insights on the adsorption of floral odorants on Apis cerana cerana olfactory receptor AcerOr1: Theoretical modeling and thermodynamic study

Apis cerana cerana counted on its sensitive olfactory system to make survival activities in the surrounding environment and the olfactory receptors can be considered as a primary requirement of odorant detection, recognition and coding. Indeed, the exploitation of the olfactory system of insects in particular the Asian honeybee “Apis cerana cerana” can be the best experimental model to investigate the essentials of the chemosensitivity and may help to better understand the olfactory perception in insects. Hence, an advanced statistical physics modeling via the monolayer model with single energy (n ≠ 1) of the three dose-olfactory responses curves indicated that undecanoic acid, 1-octyl alcohol and 1-nonanol were docked with a mixed parallel and non-parallel orientation on AcerOr1. Furthermore, in the present work, the Apis cerana cerana olfactory receptor AcerOr1 showed high sensitivity and discrimination power to detect undecanoic acid, 1-octyl alcohol and 1-nonanol with concentrations at half saturations values of 10−7 mol/L and the molar adsorption energy values obtained from data fitting results, which were ranged from 17.91 to 24.00 kJ/mol, confirmed the exothermic and the physisorption nature of the adsorption of the studied floral odorants on AcerOr1. The studied experimental dose-response curves of undecanoic acid, 1-octyl alcohol and 1-nonanol provided access to quantitative (i.e., stereographic and energetic) characterizations of AcerOr1 via the determination of the olfactory receptor site size distributions (RSDs) and the adsorption energy distributions (AEDs). The stereographic characterization showed RSDs spread out from 0.20 to 8 nm presenting average values corresponding to the maximum of the peaks at 1.50 nm, at 1.10 nm and at 1.04 nm for undecanoic acid, 1-octyl alcohol and 1-nonanol, respectively. The energetic characterization presented AEDs ranged from 0 to 40 kJ/mol showing an approximate adsorption energy bands defined between 7.50 and 27.50 kJ/mol, between 15 and 33 kJ/mol and between 13.50 and 34.50 kJ/mol for undecanoic acid, 1-octyl alcohol and 1-nonanol, respectively. The utilization of the analytical expression of the olfactory threshold allowed giving important and helpful informations about the occupation rate of AcerOr1 binding sites that fired a minimal olfactory response at a honeybee olfactory receptor. Hence, the olfactory response can be detected only when 1.97 %, 1.13 % and 2.00 % of AcerOr1 binding sites were occupied by undecanoic acid, 1-octyl alcohol and 1-nonanol, respectively. Lastly, by means of the selected model, the thermodynamic potentials, such as the adsorption entropy, the Gibbs free enthalpy and the internal energy could be calculated and interpreted.

Molecular simulation of thermodynamic properties of CH4 and CO2 adsorption under different moisture content and pore size conditions

In order to further clarify the thermodynamic properties of CH4 and CO2 adsorption in coal, a Monte Carlo method with a giant regular system was used to simulate the adsorption behavior of CH4 and CO2 in coal at different moisture contents and pore sizes. The results show that the adsorption of CH4 and CO2 in coal molecules is negatively correlated with the moisture content. As the pore size increases, the wall superimposed effect decreases, the stability of adsorption becomes less stable, and the selectivity of CO2 adsorption decreases, but the space to accommodate gas molecules becomes larger, which makes the adsorption amount rise. The average heat of adsorption of CH4 and CO2 showed a decreasing and then increasing relationship with the moisture content, and a negative correlation with the pore size, and the effect of H2O on CO2 is stronger than that of CH4. With the increase of moisture content, the absolute value of adsorption energy increases overall, and the high potential of water clusters tends to attract CO2 molecules more. With the increase of pore size, the wall superimposed effect weakens and the adsorption stability becomes worse, which makes the absolute value of adsorption energy smaller. The overall adsorption entropy of CH4 and CO2 has a negative correlation with moisture content and a positive correlation with pore size. The comparison of the slope of the fitted curves of adsorption entropy at different moisture contents adds that CO2 mainly displaces CH4 molecules in the middle of the pores at 3% moisture content.

Advanced investigation of the olfactory perception of semiochemical TMT on OR5K1 and Olfr175 by statistical physics approach

The adsorption of the trimethylthiazoline (TMT) on the human olfactory receptor OR5K1 and the mouse olfactory receptor Olfr175 was the object of the present paper. The main contribution of this work was to characterize stereographically and energetically OR5K1 and Olfr175 activated by trimethylthiazoline molecules docked on the human and the mouse olfactory binding pockets using the grand canonical ensemble in statistical physics. The experimental data and the advanced statistical physics models revealed that the adsorption of the trimethylthiazoline on the human olfactory receptor OR5K1 can be interpreted using the monolayer model with single energy, while the monolayer model with two energies described the interaction between the trimethylthiazoline molecules and the mouse olfactory receptor Olfr175. In fact, the investigated odorant was shown to be docked by a multi-docking process and non parallel orientation on OR5K1 and Olfr175 since the values of the number of TMT molecules per binding site n were superior to 1. The proposed models were applied to calculate the human and the mouse olfactory receptor binding site size distributions relative to TMT, which were spread out from 0.30 to 20 nm with a maximum at about 1.75 nm for OR5K1 and from 1 to 25 nm with a peak at about 4.25 nm for Olfr175. Furthermore, it was found from the calculated molar adsorption energies, which were lower than 11 kJ/mol, that physical adsorption process was occurred in the two olfactory systems. The adsorption energy distributions relative to TMT can be also calculated in order to understand of olfaction process in general through the determination of olfactory bands (i. e., adsorption energy distribution bands), which were situated between 0 and 10.50 kJ/mol and between 3 and 12.50 kJ/mol for OR5K1 and Olfr175, respectively. Referring to the investigation of thermodynamic functions governing the adsorption process such as the adsorption entropy, the Gibbs free enthalpy and the internal energy, it may be noted that the disorder peak of the two olfactory systems was reached when the equilibrium concentration was equal to the concentration at half saturation. In addition, the Gibbs free enthalpy and the internal energy were calculated and their negative values indicated that the adsorption process involved in the olfactory mechanism was exothermic and spontaneous nature.

Correlating the Experimentally Determined CO Adsorption Enthalpy with the Electrochemical CO Reduction Performance on Cu Surfaces.

CO binding energy has been widely employed as a descriptor for effective catalysts in the electrochemical CO2 and CO reduction reactions (CO(2) RR), however, it has yet to be determined experimentally at electrochemical interfaces due to the lack of suitable techniques. In this work, we developed a method to determine the standard adsorption enthalpy of CO on Cu surfaces with quantitative surface enhanced infrared absorption spectroscopy. On dendritic Cu at -0.75 V vs. SHE, the standard adsorption enthalpy, entropy and Gibbs free energy were determined to 1.5±0.5 kJ mol-1 , ≈37.9±13.4 J/(mol K), and ≈-9.8±4.0 kJ mol-1 , respectively. Comparison of the standard adsorption enthalpy of oxide-derived Cu and dendritic Cu, as well as their CORR activities, suggests the presence of stronger binding sites on OD Cu, which could favor multicarbon products. The method developed in this work will help establish the correlation between the CO binding energy and the CO(2) RR activity.

Correlating the Experimentally Determined CO Adsorption Enthalpy with the Electrochemical CO Reduction Performance on Cu Surfaces

AbstractCO binding energy has been widely employed as a descriptor for effective catalysts in the electrochemical CO2 and CO reduction reactions (CO(2)RR), however, it has yet to be determined experimentally at electrochemical interfaces due to the lack of suitable techniques. In this work, we developed a method to determine the standard adsorption enthalpy of CO on Cu surfaces with quantitative surface enhanced infrared absorption spectroscopy. On dendritic Cu at −0.75 V vs. SHE, the standard adsorption enthalpy, entropy and Gibbs free energy were determined to 1.5±0.5 kJ mol−1, ≈37.9±13.4 J/(mol K), and ≈−9.8±4.0 kJ mol−1, respectively. Comparison of the standard adsorption enthalpy of oxide‐derived Cu and dendritic Cu, as well as their CORR activities, suggests the presence of stronger binding sites on OD Cu, which could favor multicarbon products. The method developed in this work will help establish the correlation between the CO binding energy and the CO(2)RR activity.

Water sorption properties of brewer's spent grain: A study aimed at its stabilization for further conversion into value-added products

Due to its high moisture content and perishability, the water adsorption isotherms, and thermodynamic properties of brewer's spent grain obtained from barley malt (BSGL) and wheat malt based (BSGW) were evaluated under storage and drying conditions. Chemically characterized BSGs were subjected to the static gravimetric method to experimentally obtain the water adsorption isotherms at ten temperatures (5–90 °C). As the best-fitted model (R2adj > 0.9928 e χ2 ≤ 0.0001), the GAB parameters were used to determine the adsorption surface area, spreading pressure, and thermodynamic properties. At temperatures from 5 to 50 °C, the adsorption isotherms of BSGL and BSGW showed convex curves, typical of type III isotherms. However, at temperatures above 60 °C, the curves started to present typical type II isotherms with sigmoid-shaped sorption behavior. The equilibrium moisture content of BSGs increased with increasing relative humidity and/or decreasing temperature. The spreading pressure increased as the water activity and temperature increased, contrary to that observed for the adsorption surface area. Thermodynamic analysis showed that the net isosteric heat of adsorption, enthalpy, and differential entropy decreased as the equilibrium moisture increased. The compensation theory was confirmed, and its results indicated that the adsorption processes were enthalpy-driven. The positive values for Gibbs free energy indicated that the adsorption processes were not spontaneous, which may be related to the composition of BSGs in terms of lipids and proteins. From an energy and stability point of view, a water activity of 0.4 is the ideal condition for the storage of BSGs.

Separation, purification, and crystallization of 1,5-pentanediamine hydrochloride from fermentation broth by cation resin.

1,5-Pentanediamine hydrochloride (PDAH) was an important raw material for the preparation of bio-based pentamethylene diisocyanate (PDI). PDI has shown excellent properties in the application of adhesives and thermosetting polyurethane. In this study, PDAH was recovered from 1,5-pentanediamine (PDA) fermentation broth using a cation exchange resin and purified by crystallization. D152 was selected as the most suitable resin for purifying PDAH. The effects of solution pH, initial temperature, concentration of PDA, and adsorption time were studied by the static adsorption method. The equilibrium adsorption data were well fitted to Langmiur, Freundlich, and Temkin-Pyzhev adsorption isotherms. The adsorption free energy, enthalpy, and entropy were calculated. The experimental data were well described by the pseudo first-order kinetics model. The dynamic experiment in the fixed bed column showed that under optimal conditions, the adsorption capacity reached 96.45mgg-1, and the recovery proportion of the effective section reached 80.16%. In addition, the crystallization of the PDAH solution obtained by elution proved that the crystal product quality of resin eluting solution was highest. Thus, our research will contribute to the industrial scale-up of the separation of PDAH.

Pb(II) Removal from Aqueous Solutions by Adsorption on Stabilized Zero-Valent Iron Nanoparticles—A Green Approach

Nano zero-valent iron particles (nZVFe) are known as one of the most effective materials for the treatment of contaminated water. However, a strong tendency to agglomerate has been reported as one of their major drawbacks. The present study describes a green approach to synthesizing stabilized nZVFe, using biomass as a porous support material. Therefore, in the first step, biomass-derived activated carbon was prepared by thermochemical procedure from rice straw (RSAC), and then the RSAC-supported nZVFe composite (nZVFe–RSAC) was employed to extract Pb(II) from aqueous solution and was successfully synthesized by the sodium borohydride reduction method. It was confirmed through scanning electron microscopy (SEM) and X-ray diffraction (XRD) characteristics that the nZVFe particles are uniformly dispersed. Results of the batch experiments showed that 6 (g L−1) of this nanocomposite could effectively remove about 97% of Pb(II) ions at pH = 6 from aqueous solution. The maximum adsorption capacities of the RS, RSAC, and nZVFe–RSAC were 23.3, 67.8, and 140.8 (mg g−1), respectively. Based on the results of the adsorption isotherm studies, the adsorption of Pb(II) on nZVFe–RSAC is consistent with the Langmuir–Freundlich isotherm model R2=0.996). The thermodynamic outcomes exhibited the endothermic, possible, and spontaneous nature of adsorption. Adsorption enthalpy and entropy values were determined as 32.2 kJ mol−1 and 216.9 J mol−1 K−1, respectively. Adsorption kinetics data showed that Pb(II) adsorption onto nZVFe–RSAC was fitted well according to a pseudo-second-order model. Most importantly, the investigation of the adsorption mechanism showed that nZVFe particles are involved in the removal of Pb(II) ions through two main processes, namely Pb adsorption on the surface of nZVFe particles and direct role in the redox reaction. Subsequently, all intermediates produced through the redox reaction between nZVFe and Pb(II) were adsorbed on the nZVFe–RSAC surface. According to the results of the NZVFe–RSAC recyclability experiments, even after five cycles of recovery, this nanocomposite can retain more than 60% of its initial removal efficiency. So, the nZVFe–RSAC nanocomposite could be a promising material for permeable reactive barriers given its potential for removing Pb(II) ions. Due to low-cost and wide availability of iron salts as well as rice biowaste, combined with the high adsorption capacity, make nZVFe–RSAC an appropriate choice for use in the field of Pb(II) removal from contaminated water.

Enhancing Corrosion Resistance of Carbon Steel in Sulfuric Acid Using β-cyclodextrin as an Inhibitor

The corrosion process leads to substantial economic losses, particularly in the industrial sector, emphasizing the importance of preventive measures. This study aimed to investigate the impact of inhibitor concentration, immersion duration, and temperature on the corrosion of carbon steel in a sulfuric acid environment, assessed through mass loss measurements. Inhibition efficiency displayed a positive correlation with increasing inhibitor concentration, while it declined as temperatures rose. In a 0.5 M sulfuric acid solution, β-cyclodextrin (β-CD) exhibited an inhibition efficiency of 62.26% at a concentration of 1 mM. The addition of potassium iodide (KI) significantly enhanced the inhibition efficiency to 97.98%, indicating a synergistic effect. The study encompassed various calculations, including the determination of activation energy (Ea), activation enthalpy (ΔHa), activation entropy (ΔSa), adsorption-free energy (ΔGads), adsorption enthalpy (ΔHads), and adsorption entropy (ΔSads). The adsorption of the inhibitor onto the carbon steel surface conformed to the Langmuir adsorption isotherm. Additionally, Scanning Electron Microscopy (SEM) investigations provided further verification of β-cyclodextrin's adsorption on the carbon steel surface.

Water adsorption on acetylene black carbon

Differential heat, isotherm, thermokinetics, and entropy of water adsorption on the black carbon were studied by the adsorption-calorimetric method at 303 K. The adsorption mechanism, type, and number of formed ion-molecular complexes were determined. Thermokinetics of adsorption on the black carbon and the law of migration of exchange cations were determined, and the adsorption energy of gases and vapors was calculated. The adsorption isotherm is described by the two-and three-dimensional mathematical equations of the volume-saturation theory of micro-pores (TVSM).

Basic thermodynamic characteristics of toluene adsorption in Cu2+ZSM-5 Zeolite

This paper presents the results of isotherms and basic (ΔH, ΔF and ΔS) thermodynamic characteristics of toluene adsorption in CuZSM-5 zeolite. For measurements of isotherms and differential heat of adsorption, a system consisting of a universal high-vacuum adsorption unit and an attached differential modified Tian-Calve microcalorimeter DAC-1-1A was used to provide direct quantitative and qualitative characteristics of the nature and forces of adsorption interaction. The correlation between the adsorption-energy characteristics wasfound and the molecular mechanismof toluene adsorption in CuZSM-5 zeolite in the whole filling region was revealed. Toluene adsorbed in CuZSM-5 zeolite is located in the first coordination sphere with Cu2+ cation, forming two-dimensional complexes. It was found that the charge density significantly affects the mechanism, the energy of adsorption and the number of adsorbed molecules. It was determined that the average molar entropy of toluene adsorption in CuZSM5 zeolite indicates that the mobility of toluene molecules in zeolite is below the liquid phase and close to that of the solid phase, indicating that the mobility of toluene molecules on cations is strongly inhibited. This work shows how calorimetric data can be used to complement crystal structure results and detect subtle adsorbent/adsorbate interactions at the molecular level.

Calorimetric study of methanol adsorption in LiZSM-5 and CsZSM-5 zeolites

This paper presents isotherms and basic (ΔH, ΔF, and ΔS) thermodynamic characteristics of methanol adsorption in Li3,37ZSM-5 and Cs3,17ZSM-5 zeolites obtained by the calorimetric method. For measurements of isotherms and differential heat of adsorption, a system consisting of a universal high-vacuum adsorption unit and an attached differential modified Tian-Calvet type microcalorimeter, DAC-1-1A, which directly quantifies and qualifies the nature and forces of adsorption interaction, was used. The adsorption isotherm is described by the equations of the volumetric micropore filling theory (VMOT). The correlation between the adsorption-energy characteristics is found, and the molecular mechanism of methanol adsorption in Li3,37ZSM-5 and Cs3,17ZSM-5 zeolites throughout the filling region is revealed. Methanol adsorbed in Li3,37ZSM-5 and Cs3,17ZSM-5 zeolites is located in the first coordination sphere with cations Li+ and Cs+, forming tetra- and trimeric complexes. It is found that the charge density significantly affects the adsorption mechanism, the adsorption energy, and the number of adsorbed molecules. It was determined that the average molar entropy of ammonia adsorption on LiZSM-5 and CsZSM-5 zeolites indicates that the mobility of methanol molecules in the zeolite is below the liquid phase and close to the mobility of the solid phase, indicating a strong inhibition of mobility of methanol adsorbed on cations. This work shows how calorimetric data can complement crystal structure results and detect subtle adsorbent/adsorbate interactions at the molecular level.

Investigation of isotherms of differential heat-entropy adsorption of carbonyl sulfide in CaA zeolite during gas purification

The task of this research cycle was to measure adsorption isotherms (а) in the temperature range from 273 to 373 K, based on isotherms measured at different temperatures, to calculate isosteric heats (Qd) and entropies (∆Sd) of adsorption in order to select an effective adsorbent for purifying natural gas and oil products from sulfur-containing compounds. This article presents the results of studies of the isotherms of COS adsorption on CaA, carried out at four temperatures: 273, 298, 303, and 373 K, and the corresponding thermodynamic functions of adsorption in CaA zeolite.

Adsorption of sulfur on Lanxess Lewatit® AF 5 resin during the acidic albion leaching process for chalcopyrite

Elemental sulfur is one of the major byproducts of the acidic Albion leaching process for chalcopyrite. It is a challenging component in the leach solution as it impedes gold recovery from the residue. Lanxess Lewatit® AF 5 (AF 5) is a microporous carbon-based resin, which is being investigated for the removal of elemental sulfur during this leaching process. In the current research, a series of leaching experiments were performed as a function of temperature, agitation speed and concentrate to AF 5 ratio. Using these results, the adsorption isotherms, the kinetics and the thermodynamics of sulfur removal were studied. One hundred percent of the elemental sulfur could be adsorbed by the AF 5 resin from the acidic Albion leaching process for chalcopyrite. Adsorption isotherms at various temperatures were determined using the Langmuir and Freundlich models. The maximum sorption capacity of AF 5 at 95 °C was 488 mg/g. The kinetic data were fitted to pseudo-first order (PFO) and pseudo-second order (PSO) models and it was shown that the PFO model was best suited to describe the results. The rapid kinetics of sulfur adsorption were attributed to the open pore structure of the AF 5. The Gibbs free energy, enthalpy and entropy of sulfur adsorption by AF 5 were determined as follows: ΔGadso = −1.9 kJ/mol, ΔHadso = −9.1 kJ/mol, and ΔSadso = −0.1 kJ/(mol K). The negative free energy and enthalpy changes demonstrated that the adsorption of elemental sulfur was both spontaneous and exothermic over the temperature range studied.

Isotherms of differential heat and entropy adsorption of carbonyl sulfide in zeolite NaX when cleaning gases

The task of this research cycle was to measure adsorption isotherms (а) in the temperature range from 273 to 373 K, based on isotherms measured at different temperatures, to calculate isosteric heats (Qd) and entropies (∆Sd) of adsorption in order to select an effective adsorbent for purifying natural gas and oil products from sulfur-containing compounds. This article presents the results of studies of the isotherms of COS adsorption on NaX, carried out at four temperatures: 273, 298, 303, and 373 K, and the corresponding thermodynamic functions of adsorption in NaX zeolite.

Mechanism of H2O Vapor Adsorption in A Type Zeolites: A Model Based on Adsorption Calorimetry

In this study, the energy characteristics of water vapor adsorption in NaA and NaA(NaBO2) zeolites were measured by adsorption calorimetry. Information of differential heats, isotherms, entropy and kinetic of adsorption in the matrix of NaA and NaA(NaBO2) zeolites were obtained. Adsorption isotherms (a) and differential heats of adsorption (Qd) of water vapor by NaA and NaA(NaBO2) zeolites were measured at 303 K. The heats of adsorption are stepwise and each step corresponds to the stoichiometric formation of adsorption complexes of H2O molecules with Na+ or H+ ions, (H2O)n/Na+ or H+, (n = 1-4), which are located on the SIII, SII and SI crystallographic positions of NaA and NaA(NaBO2). Hydration mechanism of NaA and NaA(NaBO2) are complex and at saturation, the zeolites are occupied by the next water zeolitic host/guest systems: NaA – 2.2[(H2O)4/Na+III+H+], 3[(H2O)2/Na+II] and 6.6[(H2O)2/Na+I]; NaA(NaBO2) - 2[(H2O)4/Na+III], 3[(H2O)4/Na+II] and 6.86[(H2O)/Na+I]. The complete hydration of the α- and β cages of NaA amounts thus to 21,8 and 6,2 respectively H2O/u.c. and α-cage of NaA(NaBO2) – 26,3 H2O/u.c. The mean molar integral adsorption entropy of water is ~-30,5 J/mol K less than the entropy of the bulk liquid. This value nearly the same as entropy of crystalline water so the mobility of water in the zeolitic matrix is solidlike.