Sorption Curves Research Articles

Separation of radiostrontium from seawater using various types of sorbents

The paper presents the results of separating radioactive strontium from seawater with commercially available local-produced sorbents (Modix, FD, MDM, DMM, Termoksid ZK, SRM-Sr) and the sorbent of our fabrication (MnO2–impregnated fiber) under static and dynamic conditions. Under the batch conditions, the distribution coefficients of strontium in seawater are determined. Under the flow conditions, output curves of strontium sorption at different seawater flow rates were obtained; the dynamic exchange capacity and total dynamic exchange capacity of the sorbents for strontium were calculated. The data obtained make it possible to calculate the amount of sorbent required to process a seawater sample of a given volume for determining the specific activity of strontium radionuclides in seawater.

Effects of Immersion Temperature on the Performance of a Marine Epoxy-Based Organic Coating for Ballast Tanks

The degradation behavior of an actual marine epoxy-based organic coating for ballast tanks immersed in 3.5% NaCl solution at different temperatures was investigated by employing electrochemical impedance spectroscopy and adhesion measurements. Elevated immersion temperature (e.g., 35, 45 and 55 °C) could greatly deteriorate coating protective performance, including barrier properties, wet adhesion strength, water uptake and diffusion, and this effect could become more pronounced with prolonged immersion time. The water diffusion based on water sorption curves was consistent with wet adhesion strength in temperature-dependent performance evaluation of the coating. The water uptake values at the quasi-saturation stage showed the expected temperature dependence when immersion temperature exceeded 35 °C. Breakpoint frequency could also be used for qualitatively evaluating the temperature-dependent and time-varying coating degradation behavior efficiently.

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.

Effects of considering moisture hysteresis on wood decay risk simulations of building envelopes

Wood decay risk assessment of building envelopes is commonly performed by engineers, architects and practitioners using results of Heat and Moisture Transfer (HMT) simulations and damage models. The commonly accepted HMT models use bijective sorption functions, accepting that materials reach hygrothermal equilibrium with the humidity contained in the air of the material’s pores and of the environment at a single MC. On the other hand, due to moisture hysteresis, equilibrium can be reached at different MCs for the same air condition, depending on previous equilibrium states. The aim of this work is to quantify the effect of considering hysteresis in HMT simulations and to evaluate its propagation in the risk assessment procedure for the case of wood decay. The software MATCH is used, implementation of an HMT model with hysteresis. Three timber walls are simulated in seven locations (Bolzano, Copenhagen, Hong Kong, Ottawa, Shanghai, Udine, and Vienna), first with hysteresis and then with simplified bijective sorption functions (adsorption, desorption, and mean sorption curve). MC and temperature time series are used to perform wood decay risk assessment with two damage models. The results show that the influence of hysteresis can be relevant, and that the choice of the sorption curve used in the simulations should be discussed. For the case of a CLT wall in Shanghai, simulated using the adsorption curve, a mean difference of 1.6% MC is found from the hysteresis case. This resulted in a difference of 0.7 decay rating in 10 years and 6% mass loss in 30 years.

Swelling and Drug Release in Polymers through the Theory of Poisson-Kac Stochastic Processes.

Experiments on swelling and solute transport in polymeric systems clearly indicate that the classical parabolic models fail to predict typical non-Fickian features of sorption kinetics. The formulation of moving-boundary transport models for solvent penetration and drug release in swelling polymeric systems is addressed hereby employing the theory of Poisson–Kac stochastic processes possessing finite propagation velocity. The hyperbolic continuous equations deriving from Poisson–Kac processes are extended to include the description of the temporal evolution of both the Glass–Gel and the Gel–Solvent interfaces. The influence of polymer relaxation time on sorption curves and drug release kinetics is addressed in detail.

SORPTION OF HEAVY METAL CATIONS FROM A WATER-SALT SYSTEMBY NATURAL MONTMORILLONITE

The sorption properties of natural montmorillonite from the Tagan deposit with respect to heavy metal cations were researched on the model system "Mn2+–Co2+– Ni2+–V4+–H2O–montmorillonite". The influence of temperature, duration of the process and concentration of solutions, as well as the norm of the sorbent on the degree of sorption of cations is considered. The optimal conditions for the sorption process (25о С, 30 min, Т:Ж = 1,5:100) have been determined, at which the degree of solution purification is up to 86.36% cations of Co2+, 85.59% of Ni2+, 82.64% of Mn2+ and 52.29% of V4+. The nature of the sorption curves is determined by the nature of the sorbed cation. According to the absorption efficiency of natural montmorillonite, ions are arranged in the following order: Ni2+≥ Co2+> Mn2+> V4+. The results of the conducted studies indicate the possibility of effective use of bentonite clays of the Tagan field in the purification of wastewater from heavy metal cations

The waste-to-energy technology of the energy sector

Nowadays a problem of reducing anthropogenic impact on the environment is important. In the present article a perspective method of waste-to-energy technology of the energy sector is reviewed. This article focuses on the carbonate sludge (large-tonnage industrial waste) produced by power stations that is used as a sorption material, and adsorption properties of carbonate sludge, its influence on activated sludge is considered. Sludge is a microporous sorbent which is confirmed by the sorption curves for oil products and ammonia nitrogen. The carbonate sludge increases the activated sludge volume index by improving its sedimentation properties and the efficiency of centrifugation during activated sludge dewatering due to the rupture of hydrate shells of activated sludge. Granules that can be used as a fuel are obtained at the following mass ratios: excess activated sludge - 70%, carbonate sludge - 8%, binder - 22% by weight (starch and technical lignosulfonate). The production technology of fuel granules for incineration has been developed based on the research results.

Searching for optimum adsorption curve for metal sorption on soils: comparison of various isotherm models fitted by different error functions

Studies comparing numerous sorption curve models and different error functions are lacking completely for soil-metal adsorption systems. We aimed to fill this gap by studying several isotherm models and error functions on soil-metal systems with different sorption curve types. The combination of fifteen sorption curve models and seven error functions were studied for Cd, Cu, Pb, and Zn in competitive systems in four soils with different geochemical properties. Statistical calculations were carried out to compare the results of the minimizing procedures and the fit of the sorption curve models. Although different sorption models and error functions may provide some variation in fitting the models to the experimental data, these differences are mostly not significant statistically. Several sorption models showed very good performances (Brouers-Sotolongo, Sips, Hill, Langmuir-Freundlich) for varying sorption curve types in the studied soil-metal systems, and further models can be suggested for certain sorption curve types. The ERRSQ error function exhibited the lowest error distribution between the experimental data and predicted sorption curves for almost each studied cases. Consequently, their combined use could be suggested for the study of metal sorption in the studied soils. Besides testing more than one sorption isotherm model and error function combination, evaluating the shape of the sorption curve and excluding non-adsorption processes could be advised for reliable data evaluation in soil-metal sorption system.

Investigation of the Pressure Dependent Hydrogen Solubility in a Martensitic Stainless Steel Using a Thermal Agile Tubular Autoclave and Thermal Desorption Spectroscopy

Hydrogen is nowadays in focus as an energy carrier that is locally emission free. Especially in combination with fuel-cells, hydrogen offers the possibility of a CO2 neutral mobility, provided that the hydrogen is produced with renewable energy. Structural parts of automotive components are often made of steel, but unfortunately they may show degradation of the mechanical properties when in contact with hydrogen. Under certain service conditions, hydrogen uptake into the applied material can occur. To ensure a safe operation of automotive components, it is therefore necessary to investigate the time, temperature and pressure dependent hydrogen uptake of certain steels, e.g., to deduct suitable testing concepts that also consider a long term service application. To investigate the material dependent hydrogen uptake, a tubular autoclave was set-up. The underlying paper describes the set-up of this autoclave that can be pressurised up to 20 MPa at room temperature and can be heated up to a temperature of 250 °C, due to an externally applied heating sleeve. The second focus of the paper is the investigation of the pressure dependent hydrogen solubility of the martensitic stainless steel 1.4418. The autoclave offers a very fast insertion and exertion of samples and therefore has significant advantages compared to commonly larger autoclaves. Results of hydrogen charging experiments are presented, that were conducted on the Nickel-martensitic stainless steel 1.4418. Cylindrical samples 3 mm in diameter and 10 mm in length were hydrogen charged within the autoclave and subsequently measured using thermal desorption spectroscopy (TDS). The results show how hydrogen sorption curves can be effectively collected to investigate its dependence on time, temperature and hydrogen pressure, thus enabling, e.g., the deduction of hydrogen diffusion coefficients and hydrogen pre-charging concepts for material testing.

Study of sorbents for analysis of radiocesium in seawater samples by one-column method

The paper presents the results of the cesium sorption from seawater with commercially available sorbents (Anfezh, Niket, Uniket, FSS, FD-M, Axionit RCs, Termoxid 35, Termoxid 3A, NKF-C) under the batch and flow conditions, including the distribution coefficients of 137Cs, the dynamic exchange capacity and the total dynamic exchange capacity of the sorbents for cesium as well as the output curves of cesium sorption at different flow rates of the seawater. The data obtained makes it possible to select the most effective sorbents for concentrating and analyzing radiocesium in seawater. Some of the sorbents are effective for 137Cs sorption from seawater. The maximum distribution coefficients of 137Cs under the batch conditions are more than 6 × 104 mL g−1 for the sorbents Anfezh and FD-M. The maximum values of the total dynamic exchange capacity in the process of the non-radioactive cesium sorption for the Uniket and Niket sorbents are 77.7 and 88.8 mg g−1, respectively.

Pertechnetate/Perrhenate Surface Complexation on Bamboo Engineered Biochar.

The work deals with the evaluation of biochar samples prepared from Phyllostachys Viridiglaucescens bamboo. This evaluation consists of the characterization of prepared materials’ structural properties, batch and dynamic sorption experiments, and potentiometric titrations. The batch technique was focused on obtaining basic sorption data of 99mTcO4− on biochar samples including influence of pH, contact time, and Freundlich isotherm. ReO4−, which has very similar chemical properties to 99mTcO4−, was used as a carrier in the experiments. Theoretical modeling of titration curves of biochar samples was based on the application of surface complexation models, namely, so called Chemical Equilibrium Model (CEM) and Ion Exchange Model (IExM). In this case it is assumed that there are two types of surface groups, namely, the so-called layer and edge sites. The dynamic experimental data of sorption curves were fitted by a model based on complementary error function erfc(x).

К ОЦЕНКЕ ПРИМЕНИМОСТИ АНАЛИТИЧЕСКИХ СООТНОШЕНИЙ МАССОПЕРЕНОСА ДЛЯ ОПРЕДЕЛЕНИЯ КОНСТАНТ СОРБЦИИ В ПОЛИМЕРНЫХ МАТЕРИАЛАХ РДТТ

The use of analytical solutions for Frick`s diffusion equation to define the main sorption constants leading to the necessity to solve the united problem is shown. To be more exact this is the application assessment of analytical solutions for more often used experimental results and the determination of the representative sample dimensions in the experiments which are need to construct the sorption/desorption curves. By numerical experiments it is established that the most exact values of masstransfer constants are determined for small and middle values of diffuser absorption temporary process with the help of analytical solutions. Because of the difference in real sample dimensions and structural models used for analytical solutions which as a rule are presented in the form of semi-infinite plates it is necessary to minimize the influence of side surfaces in real samples on the accuracy of masstransfer parameters determination. The numerical-analytic study according to the geometry of polymeric samples from the point of view their representation to define diffusion, solubility and swelling coefficients is conducted. Herewith it is brought out that to obtain the values of masstransfer constants to an accuracy of not more 3 %, the sample geometric features must be chosen with relative dimensions L/h >10 (L – width, h – height of sample, accordingly) – the conditions of plane omnidirectional absorption of the diffuser into the right-angle-formed plates. To obtain the diffusion, solubility and swelling coefficients to an accuracy of not more 3 % the cylinder samples with relative dimensions D/h >15 (D – diameter, h – height, accordingly) should be preferably used. The algorithm of masstransfer constants determination when jointly use the sorption curves and the numerical method of diffusion analysis – finite element method is proposed. Herewith the advantages of such approach removing the sample size and shape limits are shown in comparison with the analytical methods of diffusion analysis.

Assessment of technological and nutritional qualities of the powder of prickly pear cladodes at four ages of growth

Rich in bioactive and nutritional phytochemicals, the cladode is an important part of prickly pear plant (cactus). Its processing into powder is a way of adding value allowing its use as a food, dietary supplement and cosmetic ingredient. This work aims to assess the suitability for processing into powder of prickly pear cladodes at four ages of growth and to assess technological and nutritional qualities of the obtained powders. The cladodes belonging to the Opuntia ficus-indica species, aged less than one year, one year, from 1.5 to 2 years and from 3 to 3.5 years, were harvested in Skhour Rhamna (Centre of Morocco). The quality of the fresh cladodes and the cladodes powder was evaluated by studying powder yield, humidity, water absorption index (WAI), water activity (aw), sorption curves, colour, total titratable acidity, pH, soluble solids, cellulose and ash contents. This work has highlighted the suitability of the cladodes of different ages for processing into powder. The resulted powders were characterized by different and interesting characteristics in terms of technological and nutritional qualities allowing their orientation towards different uses. WAI values, which increased with age, provided information on different rheological properties of powders when using as an ingredient in liquid or semi-solid formulations and on different saturation effects when using in food preparations. Moreover, aw values, lower than 0.29, can ensure a good biochemical and microbial stability. The sorption behaviors of cladodes powder, almost similar for the four studied ages, are moderately hygroscopic. The appreciation of the colour using the Hunter Lab scale, showed an opposite trend of a* and L* parameters, with age, between fresh cladodes and their powders indicating that the smaller the cladodes age, the greenest the resulting powder. Having an acidic pH, powders recorded also increases of cellulose and ash contents with the cladodes age.

Динамика сорбции борной кислоты борселективным анионитом типа СБ

Investigation and choice of an effective sorbent are significant for protection of water bodies against boron The boron high concentration in natural waters produces toxic impact on aquatic biota due to its high biological activity. This paper studied the dynamics of boric acid sorption from aqueous solutions by polycondensation anionite SB-1 synthesized on the base of monoethanolamine and epichlorohydrin. The anion exchanger contained aminooxyethyl and alcohol functional groups in its structure. Methods. It has been established the influences of the ion form of the anionite on the dynamic characteristics of boron sorption from both a model boric acid aqueous solution (0.43 mol/dm3) and an industrial wastewater effluent after boric acid production (0.47 mol/dm3), other things being equal (pH = 5.0; the volume rate of the solution passing through the anionite layer = 1.5 ml/min∙cm2; t = 20 0C). Structural studies to determine the form of boron in the anionite phase were performed using the IR spectroscopic method. Dynamic characteristics of boron sorption (the cation and overall ion-exchange capacity values, period of the protecting effect of the filter) were determined graphically from the sorption curves. Results. It has been found that the hydroxyl form of the anion exchanger SB-1, in comparison with the chlorine form, performs superequivalent boron sorption while boron sorption from both a model and real production solutions. For the first time we have demonstrated that at the initial stage, boric acid sorption is carried out owing to the chemisorption, resulting to the formation of stable hydroxoborate forms [B(OH)4]– in the ionite phase. As the anionite is being saturated and the concentration of free functional hydroxyl groups is decreasing, the formation of polynuclear forms of boric acid [B4O5(OH)4]2– occurs in the anionite phase by sorption of boric acid molecules on free tetrahydroxoborate anions and, further, the complex formation of polynuclear forms of boron by the nitrogen atom of aminooxyethyl functional groups. It has been stated that desorption of boron from anionite is considered to be effective when carried out with a 2 n. NaOH solution with a regeneration degree of 0.995.

Сорбционное извлечение радионуклидов стронция из поверхностных вод природным алюмосиликатом

The contamination of large volumes of surface waters with radionuclides is caused by the appearance of a significant number of objects that pose a potential radiation hazard. The search and development of affordable, environmentally friendly sorbents for the purification of such waters is an urgent task, the solution of which will make it possible to propose effective measures for the purification of natural water bodies from pollution. The article presents the result of research of sorption reduction of 90Sr radionuclide from aqueous solutions with experimental samples under static and dynamic conditions. Methods. We have defined the strontium concentration range within which the reduced component distribution between solid and liquid phases obeys Henry law. The granulated sorbent distribution index in the Henry area was Kd=(3.46±0.2)•102 ml/g in terms of strontium and this is comparable with the Kd=200 ml/g value of the initial natural glauconite. The obtained value of the sorbent static exchange capacity in terms of strontium in the (10-5 – 1) g/l concentration range is ≥ 4.2 mg/g. We investigated the sorption kinetics in the recirculation mode. We have presented the output curves of the strontium sorption with the developed sorbent in the dynamic mode. The strontium distribution index was at least 2.42 ∙ 103 ml/g and this approximately 10 times exceeded the value obtained under the static conditions. After passing of 900 column volumes of the model solution through the column, no compacting of the sorbent was observed and this confirmed preserving of its hydro/dynamic characteristics and the possibility to use it as a filter loads in ant water treatment systems. Results. The sorbent produced from local mineral raw material is applicable and feasible for use in treatment of the Ural region water bodies contaminated with 90Sr. We have demonstrated good perspective of the natural aluminum silicate glauconite of the Karinsk deposit (Chelyabinsk Oblast, Russia) granulated with bonding tap water use as a sorbent for extraction of strontium radionuclide from natural waters in the process of radioactive-contaminated territories.

Microporosity of Polynorbornenes by Positron Annihilation and Sorption Data

Based on positron annihilation and low-temperature gas (CO2) sorption data, we discuss the nature of size distribution of micropores in a number of polynorbornenes with various substituent groups in the side chain. The local stiffness of highly permeable glassy polymers suggests that they are microheterogeneous. In this case, distributions that are bimodal in nature seem quite possible, although unimodal cases cannot be excluded either. The positron annihilation data are consistent with these concepts and correlate with permeability. At the same time, the positron and sorption data on porosity are found to have discrepancies, which are explained either by limited mobility of the positronium atom or by inaccuracy of description of the sorption curve according to the density functional theory (NLDFT) and the Monte Carlo method (GCMC).

Study of isothermic absorption model of moisture content of fibrous instant corn rice

In general, storage of food products made from grains is carried out in an environment with uncontrolled air temperature and humidity. In this situation, changes in temperature and humidity will continue according to daily weather patterns. Food products stored in this environment will experience adsorption and desorption processes alternately and continuously throughout the day. Dried food that has not reached its equilibrium moisture content tends to absorb moisture during storage so that it will trigger a decrease in quality through a series of physical, chemical, and microbiological processes. The relationship between water activity and equilibrium moisture content during storage can be approached with an isothermic sorption model. The purpose of this research is to determine the equilibrium moisture content of fibrous instant corn rice in various relative humidity (RH) values and to find a mathematical model from isothermic sorption curve of fibrous instant corn rice. The research methodologies include the production of fibrous instant corn rice, the determination of equilibrium moisture content at various RH (40%-90%), and mathematical modeling of isothermic sorption curves with standard model approaches (Caurie, Hasley, and Oswin). The results showed that the water vapor adsorption process occurred in the isothermic sorption experiments of fibrous instant corn rice at a temperature of 30°C which was marked by an increase in the moisture content of the instant fibrous instant corn rice at 40-90% RH. Hasley equation model: (log [ln (1/aw)] = -3.2810 - 3.0945 log Me), Caurrie: (ln Me = -3.3084 + 1.8163 aw) and Oswin: (ln Me = -2.3301 + 0.2805 ln [aw/(1-aw)]) can accurately describe the isothermic adsorption of fibrous instant corn rice at 30°C because it has an Mean Relative Determination (MRD) value of less than 5.

Experimental Investigation of Moisture Sorption Isotherms for Mefenamic Acid Tablets

The moisture sorption isotherms of Mefenamic acid tablets were investigated by measuring the experimental equilibrium moisture content (EMC) using the static method of saturated salt solutions at three temperatures (25, 35, and 45°C) and water activity range from 0.056 to 0.8434. The results showed that EMC increased when relative humidity increased and the sorption capacity decreased, the tablets became less hygroscopic and more stable when the temperature increased at constant water activity. The sorption curves had a sigmoid shape, type II according to Brunauer’s classification. The hysteresis effect was significant along with the whole sorption process. The results were fitted to three models: Oswin, Smith, and Guggenhein - Anderson and de Boer. According to the fitting results, the GAB model was the most appropriate model to describe the sorption behavior of Mefenamic acid; it had a regression coefficient range (0.9803-0.994), %E (0.69-4.06), and low values of SEE (0.85-2.2). The monolayer moisture content was calculated using the GAB model and it was concluded that the tablets should be stored at moisture content equal or slightly higher than (0.2046, 0.1843, and 0.1437 %) for desorption and (0.2073, 0.1269, and 0.1452 %) for adsorption for the three temperatures.

Moisture sorption characteristics of chhana murki

Moisture sorption characteristics of Chhana murki were investigated at a temperature of 20oC, 30oC, and 40oC using the static gravimetric method. Sorption curves obtained were sigmoid in shape and classified as type II. Equilibrium moisture content increased with an increase in water activity and decreases with an increase in temperature. Among the BET ,GAB, and Caurie models tested, the BET and GAB models were found better to predict EMC data. BET monolayer decreased from 5.77 g H2O /100 g of solids at 20oC to 4.83 g H2O /100 g of solids at 40oC. The GAB monolayer value decreased from 5.90 g H2O /100 g of solids at 20oC to 5.14 g H2O /100 g of solids at 40oC. The properties of sorbed water viz., number of adsorbed monolayer, percent bound and non-freezable water and surface area of sorption were determined using Caurie equation. Net isosteric heat of sorption decreased with a corresponding increase in moisture content, initially rapidly up to 15.89 g of water/100 g of solids and then approaching a constant value.

In situ study of the temperature activated kinetics of water sorption in an epoxy varnish

The dielectric permittivity of a polyepoxy varnish with a glass transition temperature (Tg) of 61 °C is monitored during immersion in a 0.5 M NaCl aqueous solution, by electrochemical impedance spectroscopy, at various temperatures in the range [21; 78] °C. The sorption curves are first analysed with a Fickian approach. An Arrhenius-type dependence of the apparent coefficient of diffusion is observed, with no visible influence of Tg. Below 46 °C, the sorption curves clearly do not obey Fick′s second law of diffusion. On another hand, the Kohlrausch-Williams-Watts function (KWW) satisfactorily fits all the isothermal sorption curves. The KWW time constant has the same temperature activation as the apparent coefficient of diffusion, and likewise is unaffected by Tg. The KWW stretching exponent displays a strong dependence on Tg, correlates with the Fickian behaviour observed in the rubbery state, and is thought to be governed by molecular heterogeneities in the polyepoxy network. A linear rule of mixture is used to estimate the water uptake in the polyepoxy varnish as a function of temperature. The originality of this work lies in the in situ analysis of water uptake kinetics (constant immersion), which is performed above (rubbery state) and below (glassy state) the Tg of the polyepoxy coating.