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In this study the moisture sorption isotherm of grape seed was determined by using a static gravimetric method at 35-65°C and 0.108-0.821 water activity range. The sorption isotherms were found to be typical sigmoid shape of most food materials. Five models including the Brunauer-Emmett-Teller (2-parameter), Guggenheim, Anderson and De Boer (3-parameter), Oswin (2-parameter), Ferro-Fontan (3-parameter) and Peleg (4-parameter) models were considered to fit the experimental data. The Ferro- Fontan and Peleg equations (at three temperatures 35, 45, 65°C) having R2 greater than 0.97 and lower values of standard error of estimate and deviation modulus gave the best fit of the experimental data throughout the entire range of water activity. The net isosteric heat of sorption, calculated by Calusius-Clapeyron equation on experimental data, was found to be a polynomial and exponential function of equilibrium moisture content within the temperature range investigated.
The present study looks at the adsorption of polyethylene glycol onto activated carbon with the different molecular weight. The amount of PEG adsorbed on activated carbon depends on temperatures and pH. The adsorption capacities were determined through the adsorption isotherms. The results of the adsorption isotherm and kinetic studies show that the adsorption process can be well described with the Langmuir model. After linearization of the Arrhenius equation the activated energy had been estimated.
This article studies the adsorption behaviours of Cu, Ni, and Zn in various natural soils. The effects of contact time, adsorption isotherm, and temperature were investigated using the batch method. The column method was also adopted, to simulate the conditions found in the field. The results indicate that the adsorption isotherm can be satisfactorily described using the Freundlich and Langmuir models. Almost all soils showed adsorption capacities, in the order of Ni>Cu>Zn. The adsorption capacity of the metals increased when temperatures increased. From the column test, we find that heavy metals can be leached from the soil using distilled water. After leaching, the adsorption capacity of the soils slightly increased.
Agricultural ecosystems are differently sensitive to heavy metal inputs, which at present are directly related to human activities. Lead is of particular concern due to its ability to threaten soil quality and human health. The investigated soil samples were collected from different agricultural soils (under cereal croppings) moderately subjected to activity of the Głogów Copper Smelter (Poland). They consisted of an acidic soil (Dystri-Gleyic Fluvisols - S₁) and three near neutral to slightly alkaline soils (Haplic Luvisols - S₂, Gleyic Fluvisols - S₃ and Molli-Gleyic Fluvisols - S₄). These soils were tested in order to determine the impact of additional Pb inputs on its dynamics and mobility. Of all the soils studied, S₂, S₃ and S4 have exhibited higher acid buffer capacities than S₁. Lead sorption parameters, such as Langmuir adsorption maximum (amax) and parameters related to interaction energies (b) as well as the Freundlich partition parameter (KF), were used for comparing the reactivity and dynamics of added Pb into these soils. The data showed that S₂, S₃ and S₄ retained more Pb than did S₁, characterized by low specific surface area (SSA) and cation exchange capacity (CEC). Charge-based (SDCEC) and specific surface-based (SDSSA) sorption densities were also used for evaluating the direct impact of additional Pb inputs. These parameters revealed that S₂, S₃ and S₄ may support greater inputs of Pb with less threat to its mobility, in contrast to S₁. Therefore, any practices leading to additional Pb inputs into the latter soil may result in serious Pb mobility. The negative values of the Gibbs free energy changes (ΔGo) for Pb dynamics in the studied soils confirm that the ion exchange process proceeded naturally and spontaneously with a markedly high affinity for Pb ions developed by S₂, S₃ and S₄, and low affinity by S₁.
A comparison of the linear least-squares method and a trial-and-error non-linear method of three widely used isotherms (the Langmuir, Freundlich, and Redlich-Peterson) were examined in an experiment using lead ion sorption onto peat at different temperatures. The four Langmuir linear equations are discussed. Langmuir isotherm parameters obtained from the four Langmuir linear equations using the linear method differed but they were the same when using the non-linear method. Langmuir-1 is the most popular linear form, and it had the highest coefficient of determination compared with the other Langmuir linear equations. The Redlich-Peterson and Langmuir isotherms produced higher coefficients of determination. There are two separate regions depicting the Freundlich isotherm. The results show that that non-linear method may be a better way to obtain the parameters.
The study was aimed at investigating the hygroscopicity of food concentrates. The sorption phenomenon measurement was made with a static method on the basis of steam adsorption isotherms analysis and with a dynamic method by determination of steam adsorption kinetics and process rate. Sorption isotherms were determined at water activity range of aw=0.07-0.98. The monomolecular layer capacity Vm and corresponding water activity and the adsorption specific surface were determined after rearrangement of the sorption isotherms BET. Steam adsorption isotherms of the researched croutons are corresponding to the type II in the Brunauer’s classification. While for the researched powders constituting the pea soup concentrate, sorption isotherms were the indirect type between II and III according to the Brunauer’s classification. Higher monolayer capacity and the adsorption specific surface characterised croutons and powders of the producer A, which achieved results indicating a better flexibility to the re-hydration process.
Experiments were conducted to study the sorption behaviour of dimethoate in three Indian soils at different temperatures. A kinetic study showed that adsorption equilibrium was reached within 15 h at different initial levels of pesticide concentration. Applicability of the pseudo second order kinetic model suggested that the adsorption process was complex and several mechanisms were involved. The Freundlich model explained the adsorption behaviour adequately and the isotherms were of S-type. The adsorption process was found to be strongly affected by temperature. The Gibbs free energy change, ΔGº values (from -15.81 to -16.60 kJ mol-1) indicated that the process was spontaneous and exothermic in nature. The change in enthalpy of adsorption, ΔH° values (from -17.729 to -21.539 kJ mol-1) suggested that relatively weak H-bond forces were the main driving forces for adsorption. Desorption was found to be concentration- and temperature-depen- dent with higher desorption occurring at higher temperature and concentration levels. The results signify the importance of temperature in controlling the mobility of dimethoate in water bodies.
W warunkach laboratoryjnych przebadano kształtowanie się izotermy powietrza i liścia fasoli w zależności od wilgotności i potencjału wodnego gleby piaskowej i pyłowej. Do wyznaczenia izotermy zastosowano termowizor AGA-750, wykonujący pomiary w podczerwieni. Na podstawie badań stwierdzono prostoliniowi} korelację między wilgotnością gleby piaskowej i pyłowej a różnicą izotermy powietrza i liścia fasoli Ai = 0.15582 + 0.0098 Wm, gdy Wm > 4.3%. Ponadto uzyskano dwie krzywe charakterystyczne dla gleby piaskowej i pyłowej, przedstawiające zależność między potencjałem wodnym gleby i różnicą izotermy powietrza i liścia. Wspomniane krzywe pozwoliły wnioskować, że dla fasoli rosnącej na glebie piaskowej ograniczenia w transpiracji wystąpiły, zanim potencjał wodny gleby osiągnął wartość odpowiadającą punktowi trwałego więdnięcia, natomiast dla roślin rosnących na pyle zjawisko to zaznaczyło się po przekroczeniu wspomnianego punktu.
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