Equilibrium and kinetic studies for the sorption of 3-methoxybenzaldehyde on activated kaolinites

The sorption of 3-methoxybenzaldehyde on activated kaolinites has been investigated at different temperatures. Two types of activation tests were performed. The sorption equilibrium was studied by sorption isotherms in the temperature range 303-333K for natural (untreated), thermally and acid activated kaolinites. It was shown that the isotherm shapes were not affected by temperature and activation types of kaolinite. The absorbance data at 312nm were fitted reasonably well with the Langmuir and Freundlich isotherm models and the model parameters were determined for different temperatures. Thermodynamic quantities such as Gibbs free energy (DeltaG), the enthalpy (DeltaH) and the entropy change of sorption (DeltaS) were determined for natural, thermally and acid activated kaolinites. It was shown that the sorption processes were an endothermic reactions, controlled by physical mechanisms and spontaneously. Adsorption capacity of acid activated kaolinite for 3-methoxybenzaldehyde was higher compared to that of natural and thermally activated kaolinites at various temperatures. The adsorption and desorption rate constants (k(a) and k(d)) were obtained separately by applying a geometric approach to the first order Langmuir model. This method provided good conformity between the K from Langmuir parameters and K(geo) (k(a)/k(d)) from geometric approach.     

Equilibrium and kinetic studies of copper adsorption by activated carbon

Copper adsorption by granular activated carbon is reported in this paper. The experimental section includes titrations of activated carbon, as well as equilibrium and kinetic studies of copper adsorption. The potentiometric titration results show that the point of zero charge is 9.5, and that the surface charge increases with decreasing pH. The adsorption of copper strongly depends on solution pH and increases from 10 to 95% at pH ranging from 2.3 to 8. A dramatic increase in pH and emission of small gas bubbles are observed during the experiments, which may result from adsorption of hydrogen ion and/or reduction-oxidation reactions. The two-pK triple-layer model is employed to describe copper adsorption. KINEQL, an adsorption kinetics algorithm, is used to represent the experimental data, and it is found that the model can describe reasonably well the experimental measurements of surface charge, adsorption equilibrium, and adsorption kinetics. Calculations show that formation of the surface-metal complexes SO⁻Cu²⁺ and SO⁻CuOH⁺ (a hydrolysis product of SO⁻Cu ²⁺) in the outer layer around the surface of carbon results in removal of copper ion. It is also found that mass transfer controls the adsorption rate, and that adsorption occurs in the micropore region where both external mass transfer and diffusion are important.     

Comparative sorption kinetic studies of ammonium onto zeolite

The sorption kinetics of ammonium onto three types of zeolite, natural zeolite, natural zeolite covered by biofilm and ammonium-bearing zeolite covered by biofilm, at two particle sizes were studied. The pseudo-first order and pseudo-second order models were fitted to the results by a non-linear method. The batch sorption model, based on a pseudo-second order mechanism, was applied to predict the rate constant of sorption, the equilibrium capacity and the initial sorption rate. Ion exchange between NH(4)(+) and cations in the zeolite increased with decreasing particle size of the zeolite. Biofilm covered on the zeolite did not affect the ion exchange for the smaller particle size but decreased the ion exchange capacity by 22% for the larger particle size. In addition, bioregeneration should be considered for the recovery of ion exchange capacity of the bio-zeolite made from ammonium-bearing zeolite by the microorganisms in the biofilm, 78.0 and 63.9% regeneration for the smaller and larger particle size of zeolite, respectively.     

Equilibrium studies of sorption of lead(II) ions by different pectin compounds

The adsorption of Pb(II) ions from aqueous solution by different pectin compounds was studied in a batch sorption system. Water-soluble low- and high-esterified pectins and insoluble calcium pectate beads were investigated. The lead-binding capacity of all pectin compounds was highest within the pH range from 7 to 8. The binding capacities and rates of Pb(II) ions by pectin compounds were evaluated. The Langmuir, Freundlich and BET sorption models were applied to describe the isotherms and isotherm constants. Sorption isothermal data could be well interpreted by the Langmuir model. These results obtained through the study suggest that pectin compounds are favorable sorbers. The largest amount of Pb(II) ions were bound by pectin with the low degree of esterfication. Therefore, pectin substances may be considered as perspective for sorption and removal of Pb(II) ions from wastewaters.     

Equilibrium modeling and kinetic studies on the adsorption of basic dye by a low-cost adsorbent: coconut (Cocos nucifera) bunch waste

In this paper, the ability of coconut bunch waste (CBW), an agricultural waste available in large quantity in Malaysia, to remove basic dye (methylene blue) from aqueous solution by adsorption was studied. Batch mode experiments were conducted at 30 degrees C to study the effects of pH and initial concentration of methylene blue (MB). Equilibrium adsorption isotherms and kinetics were investigated. The experimental data were analyzed by the Langmuir, Freundlich and Temkin models of adsorption. The adsorption isotherm data were fitted well to Langmuir isotherm and the monolayer adsorption capacity was found to be 70.92 mg/g at 30 degrees C. The kinetic data obtained at different concentrations have been analyzed using a pseudo-first-order, pseudo-second-order equation and intraparticle diffusion equation. The experimental data fitted very well the pseudo-second-order kinetic model.     

Equilibrium and kinetic studies on free cyanide adsorption from aqueous solution by activated carbon

Adsorption equilibrium and kinetics of free cyanide onto activated carbon were investigated in the batch tests, and the effects of contact time (1–72 h) and initial cyanide concentrations in the range of 102–532 mg/L were studied. Linear regression was used to determine the best fit of equilibrium and kinetics expressions. The two-parameter models including Freundlich, Dubinin–Radushkevich, Temkin and four different linearized forms of Langmuir and three-parameter models including Redlich–Peterson and Koble–Corrigan were employed for fitting the equilibrium data and it was found that, three-parameter models fitted the data better than the two-parameter models and among the three-parameter models the equilibrium data are best represented by Koble–Corrigan model. A number of kinetic models including fractional power, zero order, first order, pseudo-first order, Elovich, second order, intraparticle diffusion and four different linearized forms of pseudo-second order models were tested to fit the kinetic data. The latter was found to be consistent with the data. Intraparticle diffusion plots show that the adsorption process of free cyanide is a two steps process. In the first step, the adsorption of cyanide is fast while in the second step, cyanide adsorption slows down.     

Equilibrium and kinetic mechanism for Reactive Black 5 sorption onto high lime Soma fly ash

Batch adsorption studies were carried out for the sorption of C.I. Reactive Black 5, a reactive dye, onto high lime fly ash, obtained from Soma Thermal Power Plant (Turkey), to be low cost adsorbent. The effect of various experimental parameters such as contact time, adsorbent dose and initial dye concentration were investigated. Determination of the adsorption equilibrium concentrations was determined by UV-vis spectrophotometry analytical method. Equilibrium data were fitted to the Freundlich and Langmuir isotherm equations and the equilibrium data were found to be well represented by the Freundlich isotherm equation. The adsorption kinetics of C.I. Reactive Black 5 onto high lime fly ash were also studied to characterize of the surface complexation reaction. A pseudo-second-order mechanism has been developed to predict the rate constant of the adsorption, the equilibrium capacity and initial adsorption rate with the effect of initial concentration. A single-stage batch adsorber design of the adsorption of C.I. Reactive Black 5 onto high lime fly ash has been studied based on the Freundlich isotherm equation.     

Equilibrium and kinetic adsorption study of Basic Yellow 28 and Basic Red 46 by a boron industry waste

In this study, the adsorption characteristics of Basic Yellow 28 (BY 28) and Basic Red 46 (BR 46) onto boron waste (BW), a waste produced from boron processing plant were investigated. The equilibrium adsorption isotherms and kinetics were investigated. The adsorption equilibrium data were analyzed by using various adsorption isotherm models and the results have shown that adsorption behavior of two dyes could be described reasonably well by a generalized isotherm. Kinetic studies indicated that the kinetics of the adsorption of BY 28 and BR 46 onto BW follows a pseudo-second-order model. The result showed that the BW exhibited high-adsorption capacity for basic dyes and the capacity slightly decreased with increasing temperature. The maximum adsorption capacities of BY 28 and BR 46 are reported at 75.00 and 74.73mgg(-1), respectively. The dye adsorption depended on the initial pH of the solution with maximum uptake occurring at about pH 9 and electrokinetic behavior of BW. Activation energy of 15.23kJ/mol for BY 28 and 18.15kJ/mol for BR 46 were determined confirming the nature of the physisorption onto BW. These results indicate that BW could be employed as low-cost material for the removal of the textile dyes from effluents.     

甲基紫光度法测定红霉素肠溶片中的红霉素

在pH 6.8条件下,用二次石英蒸馏水为溶剂,甲基紫和红霉素在常温下可以反应形成稳定的离子缔合物,导致吸收光谱发生变化,且在一定范围内吸光度变化值与红霉素的浓度成正比,从而建立一种测定红霉素的分光光度法.实验表明:该方法灵敏度较高(ε=1.63×104 L/(mol/cm)),精密度好(对15.00 mL 5.0×10-3 mg/mL红霉素测定6次,RSD=0.9％).红霉素的浓度在0.000 8～0.050 mg/mL范围内服从Beer定律,方法的检出限为0.18 μg/mL.该方法简便可靠,重现性和选择性好,可用于红霉素肠溶片中红霉素含量的测定.     

Equilibrium, kinetic and thermodynamic studies on the adsorption of phenol onto chitin

The adsorption of phenol onto chitin, a naturally occurring material was studied as a function of initial pH, temperature and initial phenol concentration. The highest phenol adsorption capacity was determined as 21.5 mgg(-1) for 300 mgdm(-3) initial phenol concentration at pH 1.0 and 40 degrees C. Adsorption data were well described by the Freundlich Model, although they could be modeled by the Langmuir equation. The pseudo-first-order and pseudo-second-order kinetic models were applied to test the experimental data. The pseudo-second-order kinetic model provided the best correlation of the experimental data compared to the pseudo-first-order model. The thermodynamic constants of the adsorption process; DeltaG degrees , DeltaH degrees and DeltaS degrees were evaluated as -19.4 kJmol(-1) (at 40 degrees C), 10.2 kJmol(-1) and 0.093 kJmol(-1)K(-1), respectively. These showed that adsorption of phenol on chitin was endothermic and spontaneous.     

Equilibrium,kinetic and thermodynamic studies on the adsorption of phenol onto graphene

Graphene, a new member of carbon family, has been prepared, characterized and used as adsorbent to remove phenol from aqueous solution. The effect parameters including pH, dosage, contact time, and temperature on the adsorption properties of phenol onto graphene were investigated. The results showed that the maximum adsorption capacity can reach 28.26 mg/g at the conditions of initial phenol concentration of 50 mg/L, pH 6.3 and 285 K. Adsorption data were well described by both Freundlich and Langmuir models. The kinetic study illustrated that the adsorption of phenol onto graphene fit the pseudo second-order model. The thermodynamic parameters indicated that the adsorption of phenol onto graphene was endothermic and spontaneous.     

Equilibrium and kinetic studies in adsorption of heavy metals using biosorbent: a summary of recent studies

Distinctive adsorption equilibria and kinetic models are of extensive use in explaining the biosorption of heavy metals, denoting the need to highlight and summarize their essential issues, which is the main purpose of this paper. As a general trend, up until now, most studies on the biosorption of heavy metal ions by miscellaneous biosorbent types have been directed toward the uptake of single metal in preference to multicomponent systems. In particular, Langmuir and Freundlich models are the most common isotherms for correlating biosorption experimental data though other isotherms, which were initially established for gas phase applications, can also be extended onto biosorption system. In kinetic modeling, the pseudo-first and -second order equations are considered as the most celebrated models.     

Equilibrium, kinetic and thermodynamic studies of adsorption of fluoride onto plaster of Paris

Batch sorption system using plaster of Paris as an adsorbent was investigated to remove fluoride ions from aqueous solutions. The system variables studied include initial concentration of the sorbate, agitation time, adsorbent dose, pH, co-ions and temperature. The experimental data fitted well to the Freundlich and Langmuir isotherms. Thermodynamic parameters such as DeltaH degrees , DeltaS degrees and DeltaG degrees were calculated indicating that the adsorption was a spontaneous and exothermic. Kinetic studies reveal that the adsorption is first order. A mechanism involving three stages (external surface adsorption, intraparticle diffusion and final equilibrium) has been proposed for the adsorption of F(-) onto plaster of Paris. XRD patterns of the adsorbent were recorded to get a better in sight into the mechanism of adsorption process.     

Evaluating in-vessel composting in treating sewage sludge and agricultural waste by examining and determining the kinetic reactions of the process

This paper presents the evaluation of the performance of an in-vessel composting system by examining the kinetic reactions of the processes developed for the treatment of sewage sludge and agricultural waste. The aim of this work is (a) to describe the composting process using a kinetic model that is based on the biodegradable organic matter losses during decomposition of the substrate, (b) to evaluate the efficiency of the bioxidation process that takes place in the system and (c) to determine the factors and the rate at which they limit the composting process. The simulation of the composting process considers a first-order kinetic model including the environmental parameters (environmental correction factors) that influence bioxidation of the biodegradable organic matter (BOM) of the substrate namely temperature, moisture content and oxygen concentration. The experimental results, recorded and monitored throughout the composting processes, were fitted using the proposed model. The results obtained suggest that the system operates efficiently by recording increased levels of BOM losses, high decomposition rates while composting limitations, due to the environmental conditions, is not significant during the main stages of the processes.     

Equilibrium,kinetics and thermodynamic studies for sorption of chlorobenzenes on CTMAB modified bentonite and kaolinite

The sorption of chlorobenzenes (CBs) by cetyltrimethylammonium bromide (CTMAB) modified bentonite and kaolinite was investigated. The sorption isotherms for CBs were nearly linear, suggesting that sorption could be described by a distribution process. The distribution coefficient (K_d) was primarily affected by the amount of sorbed surfactant. The organic carbon normalized sorption coefficient (K_oc), however, was particularly dependent on arrangement of the surfactant cations. The K_d of CBs was larger for CTMAB-bentonites than that for CTMAB-kaolinites, while the case for K_oc was opposite. Thus, the clay mineral structure and morphology had a considerable influence on the surfactant arrangement, which was responsible for the partitioning of CBs. The sorption of CBs onto both CTMAB-bentonites and CTMAB-kaolinites followed pseudo-second-order kinetics. The intra-particle diffusion model for sorption was also investigated and compared to identify sorption mechanism. The sorption of CBs both on CTMAB-bentonites and CTMAB-kaolinites was exothermic in nature and accompanied by an increase in entropy and a decrease in Gibbs energy in the temperature range of 15–35 °C. The results indicated that CBs strongly interacted with CTMAB modified bentonite and kaolinite.     

Sorption of SPADNS azo dye on polystyrene anion exchangers: Equilibrium and kinetic studies

The sorption of SPANDS from aqueous solution onto the macroporous polystyrene anion exchangers of weakly basic Amberlyst A-21 and strongly basic Amberlyst A-29 in a batch method was studied. The effect of initial dye concentration and phase contact time was considered to evaluate the sorption capacity of anion exchangers. Equilibrium data were attempted by various adsorption isotherms including the Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models. A comparison of kinetic models applied to the adsorption rate constants and equilibrium sorption capacities was made for the Lagergren first-order, pseudo second-order and Morris–Weber intraparticle diffusion kinetic models. The results showed that the adsorption isotherm is in the good agreement with the Langmuir equation and that the adsorption kinetics of SPADNS on both anion exchangers can be best described by the pseudo second-order model.     

Carbonate effects and pH-dependence of uranium sorption onto bacteriogenic iron oxides: kinetic and equilibrium studies

The removal of U(VI) from groundwaters by adsorption onto bacteriogenic iron oxides (BIOS) has been investigated under batch mode. The adsorbent dosage, the uranium concentration, the concentration of carbonate and the use of a real groundwater spiked with uranium comprised the examined parameters. In addition, the effect of pH was examined in two different water matrixes, i.e., in distilled water and in real groundwater. Equilibrium studies were carried out to determine the maximum adsorption capacity of BIOS and the data correlated well with the Langmuir and Freundlich models. The presence of carbonate affected adversely the adsorption of U(VI) onto BIOS. The maximum adsorption capacity of BIOS was 9.25 mg g(-1) at 0.1mM carbonate concentration and decreased to 6.93 mg g(-1) at 0.5mM carbonate concentration, whereas at carbonate concentration of 2mM practically no adsorption occurred. The data were further analyzed using the pseudo-second order kinetic equation, which fitted best the experimental results. The initial adsorption rate (h) was found to increase with decreasing the concentration of carbonate in all cases. When experiments were accomplished in the absence of carbonate, the pH values did not have an effect on the adsorption of U(VI). However, the extent of U(VI) adsorption was strongly pH-dependent when the experiments were carried out in the real groundwater. The maximum adsorption capacity increased sharply as the pH decreased and optimum removal was obtained in the pH range 3.2-4.0, thus bacteriogenic iron oxides can found application in the removal of U(VI) by adsorption from low pH or low carbonate waters.     

Equilibrium sorption of paraffins in HZSM-5

The sorption of linear, branched and cyclic hydrocarbons into the zeolite HZSM-5, over a wide temperature range is described. Over the reduced temperature range (T_r) of 0.7–1.0, linear paraffins behave as condensed liquids and the entire pore structure is available to them. Simply branched paraffins behave similarly but, as is also true for cyclic paraffins, less of the zeolite structure is accessible to them.     

Equilibrium and kinetic aspects of brittle fracture

The lattice statics method for simulating a brittle crack will be employed to answer the following questions: (1) What is the energy-based criterion for crack stability, (2) At a given stress intensity in the stable region, what is the kinetic barrier for crack motion, and (3) What assumptions break down in the Griffith theory when generalized to a lattice model. A simple model is used in the analysis, but this model is general enough to provide a conceptual framework for more realistic models.     

Equilibrium, kinetic and thermodynamic studies on the adsorption of m-cresol onto micro- and mesoporous carbon

Investigations were conducted in batch mode to study the adsorption behaviour of m-cresol on a porous carbon prepared from rice husk (RHAC) by varying the parameters such as agitation time, m-cresol concentration (50-300 mg/l), pH (2.5-10) and temperature (293-323 K). Studies showed that the adsorption decreased with increase in pH and temperature. The isotherm data were fitted to Langmuir, Freundlich, and Dubinin-Radushkevic (D-R) models. The kinetic models such as pseudo-first-order, pseudo-second-order and intraparticle diffusion models were selected to understand the reaction pathways and mechanism of adsorption process. The thermodynamic equilibrium coefficients obtained at different temperatures were used to evaluate the thermodynamic constants DeltaG degrees, DeltaH degrees and DeltaS degrees. The sorption process was found to be exothermic in nature (DeltaH degrees : -23.46 to -25.40 kJ/mol) with a decrease in entropy (DeltaS degrees: -19.44 to -35.87 J/(mol K)). The negative value of Gibbs free energy, DeltaG degrees indicates that the adsorption occurs via a spontaneous process. The decrease in the value of -DeltaG degrees from 17.70 to 13.54 kJ/mol with increase in pH and temperature indicates that the adsorption of m-cresol onto activated carbon is less favourable at higher temperature and pH range. The influence of mesopore and a possible mechanism of adsorption is also suggested.