Sorption Kinetic Models Research Articles

Adsorption characteristics of Barmer bentonite for hazardous waste containment application

Low hydraulic conductivity and high chemical immobilization are the two characteristics that make bentonite a mandatory construction material for hazardous waste containment applications. We performed a comprehensive batch sorption study on Barmer bentonite (BB), an exclusive construction clay mined in India, using lead (Pb2+) as a model contaminant. The maximum adsorption capacity of BB was obtained as 55 mg g−1 at pH 5 and 27 ± 2℃. Adsorption was extremely rapid, with equilibrium attained <5 min for the BB. Increased adsorbent dosage resulted in higher Pb2+ percentage removal, while adsorption capacity decreased. Ionic strength, salt concentration, valency and ionic radius played a critical role in suppressing the adsorption of Pb2+. Clay fabric change was observed to be dispersed at low ionic strength and gradually attained aggregated face-to-face structures at high ionic strength. The simultaneous presence of other metals/salts strongly influenced Pb2+ removal by BB, while divalent salt exhibited high suppression of adsorptive reaction at low concentrations. Sorption isotherm and kinetic modeling results indicated the possibility of chemisorption of Pb2+ on BB. Based on the thermodynamic analysis, it was noted that Pb2+ adsorption on BB is exothermic, spontaneous and adsorption reaction is less favorable at a higher temperature.

Development and Validation of a Two-Stage Kinetic Sorption Model for Polymer and Surfactant Transport in Porous Media.

Understanding the sorption processes is critical to the successful design and implementation of a variety of technologies in subsurface application. Most transport models assume minimal interactions between adsorbed species and, thus, are unable to accurately describe the formation of adsorbed bilayers. To address this limitation, a two-stage kinetic sorption model is developed and incorporated into a one-dimensional advective-dispersive-reactive transport simulator. The model is evaluated using data obtained from column experiments conducted with a representative polymer [gum arabic (GA)] and a nonionic surfactant [Witconol 2722 (WT)] under a range of experimental conditions. Model simulations demonstrate that the first-stage polymer/surfactant-surface sorption rate is at least 1 order of magnitude greater than the second-stage rate, associated with bilayer formation, indicating that the first-stage reaction is more favorable. The reversibility of the second-stage sorption process is found to be compound-specific, with irreversible sorption observed for GA and prolonged tailing observed for WT. This study demonstrates that the developed two-stage kinetic model is superior to a two-stage equilibrium-based model in its replication of two-leg breakthrough curves observed in core flood experiments; the normalized root-mean-square error between measurement and regressed model simulations was reduced by an average of 41% with the kinetic approach.

Optimization of the sorption of selected polycyclic aromatic hydrocarbons by regenerable graphene wool.

A novel graphene wool (GW) material was used as adsorbent for the removal of phenanthrene (PHEN) and pyrene (PYR) from aqueous solution. Adsorption kinetics, adsorption isotherms, thermodynamics of adsorption and effect of pH, ionic strength, and temperature on the adsorption of PHEN and PYR onto GW were comprehensively investigated. Isothermal and kinetic experimental data were fitted to Langmuir, Freundlich, Temkin, Sips and Dubinin-Radushkevich models, as well as pseudo-first-order and pseudo-second-order kinetic models. The adsorption kinetic data best fit the pseudo-second-order kinetic model for PHEN and PYR sorption with R2 value >0.999, whilst the Sips model best fit isotherm data. Kinetic data revealed that 24 hr of contact between adsorbent and polycyclic aromatic hydrocarbons (PAHs) was sufficient for maximum adsorption, where the Langmuir maximum adsorption capacity of GW for PHEN and PYR was 5 and 20 mg g-1 and the optimum removal efficiency was 99.9% and 99.1%, respectively. Thermodynamic experiments revealed that adsorption processes were endothermic and spontaneous. Desorption experiments indicated that irreversible sorption occurred with a hysteresis index greater that zero for both PAHs. The high adsorption capacity and potential reusability of GW makes it a very attractive material for removal of hydrophobic organic micro-pollutants from water.

Nonideal Transport and Extended Elution Tailing of PFOS in Soil

The objective of this research was to examine the influence of nonideal sorption/desorption on the transport of polyfluorinated alkyl substances (PFASs) in soil, with a specific focus on characterizing and quantifying potential extended, mass-transfer-limited elution behavior. Perfluorooctane sulfonic acid (PFOS) was used as a representative PFAS, and miscible-displacement experiments were conducted with two soils comprising contrasting geochemical properties. The influence of nonlinear, rate-limited, hysteretic, and irreversible sorption/desorption on transport was investigated through experiments and model simulations. The breakthrough curves measured for PFOS transport in the two soils were asymmetrical and exhibited extensive elution tailing, indicating that sorption/desorption was significantly nonideal. The widely used two-domain sorption kinetics model could not fully simulate the observed transport behavior, whereas a multirate model employing a continuous distribution of sorption domains was successful. The overall results indicated that sorption/desorption was significantly rate-limited and that nonlinear, hysteretic, and irreversible sorption/desorption had minimal impact on PFOS transport. Comparison of PFOS transport data to data reported for two hydrophobic organic contaminants (HOCs) showed that the HOCs exhibited much more extensive elution tailing, likely reflecting differences in sorption/desorption mechanisms. The projected influence of rate-limited sorption/desorption on PFOS transport at the field scale was investigated through simulation. The results of the study suggest that rate-limited sorption/desorption may affect the field-scale transport of PFOS and other PFAS for systems influenced by transient or short-residence-time conditions and in some cases could possibly increase the amount of flushing required to reduce PFOS concentrations to levels below those associated with human-health concerns.

Grafting of quaternary ammonium groups for uranium(VI) recovery: application on natural acidic leaching liquor

Grafting of quaternary ammonium group is the main goal of this research for uranium recovery. The sorbent was investigated by FTIR, SEM–EDX, elemental analysis, thermogravemetric and XPS analyses, it shows high and fast loading performance (176.49 mg U g−1), the total equilibrium reached within 25 min, fitted by first order rate equation and Sips model for sorption kinetics and isotherms respectively. Complete desorption achieved after 30 min by 1.0 M NaCl in 0.1 M H2SO4. Sorption/desorption was measured after 10 cycles without significant loss in the capacity. Finally, the sorbent applied for uranium recovery of leaching solution from sulfuric acid on gibbsite bearing shale ore materials.

CO2 sorption kinetic study and modeling on doped-Li4SiO4 under different temperatures and CO2 partial pressures

The present study investigated the CO2 sorption mechanism on lithium orthosilicate (Li4SiO4) doped with potassium carbonate (K2CO3) in form of powders and macroporous pellets. The CO2 sorption performance was studied under different temperatures (540–580 °C) and CO2 partial pressures (0.04–0.50 atm). The results showed that the addition of K2CO3 improved the CO2 uptake rate and capacity, mainly at low-moderate CO2 partial pressures, owing to an increase of diffusion rate through the product layer. Moreover, a modified shrinking core model was developed to explain the mechanisms that occur during the sorption introducing a CO2 diffusion coefficient through the product layer depending on the Li4SiO4 conversion. The results showed an excellent fitting of the modified shrinking core model to the experimental data obtained in the tested sorption temperature and CO2 partial pressure range, both for the sorbent in powder and pellet form. Thus, the proposed model could be employed to well simulate the CO2 sorption kinetic behavior on K2CO3 doped Li4SiO4-based sorbents.

Sorption of polyhalogenated carbazoles (PHCs) to microplastics

The sorption of 5 Polyhalogenated carbazoles (PHCs) [3,6-dibromocarbazole (3,6-BCZ), 3,6-dichlorocarbazole (3,6-CCZ), 3,6-diiodocarbazole (3,6-ICZ), 2,7-dibromocarbazole (2,7-BCZ) and 3-bromocarbazole (3-BCZ)] on to three microplastics [polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC)] in a simulated seawater system are studied. Sorption isotherms demonstrated that PVC had the maximum sorption capacity, which can be attributed to polar-polar interaction. The sorption kinetics model showed that the sorption process was controlled by both intraparticle and film diffusion. The sorption of PHCs to microplastics was significantly influenced by temperature, the sorption capacity first increased gradually and then decreased with the increasing temperature. Increasing the salinity decreased the sorption of PHCs onto PP, PE, PVC microplastics. Our results indicated that all three kinds of microplastics can serve as carriers for PHCs in the aquatic environment, which put marine ecosystems at higher risks.

Adsorptive removal of Cr(VI) from aqueous solution: kinetic, isotherm, thermodynamics, toxicity, scale-up design, and GA modeling

Chromium (VI) is a well-known toxic, industrial, water pollutant which has various, adverse effects on environmental health. Utilization of agricultural waste in effluent water treatment would minimize the problem of water pollution. The present study deals with the use of three types of nut shells for Cr(VI) removal. Adsorbents are characterized, using point of zero charges (pHpzc), FTIR, BET surface area analysis, and SEM. The variation of different operating parameters on metal removal was conducted. The best sorption kinetic model was pseudo-second order. The adsorption process is both physical and chemical, and this depends on temperature. The Cr(VI) adsorption is spontaneous and endothermic. According to isotherm studies, Langmuir isotherm model fits fairly well for all adsorbents. Regeneration studies suggest that the adsorbents have proper regeneration criteria and can be used for multiple times. Study on RBC count of Gallus gallus domesticus gives concrete evidence of deadly effects of Cr(VI). It also figures out that the effluent solution treated with bio-adsorbents is less harmful. The scale-up design procedure is reported here. This study proved that groundnut shell, walnut shell, and almond shell have immense potential and can be utilized even after regeneration as replacement of commercial adsorbents for industrial wastewater. GA–ANN modeling has been developed for the best possible wastewater treatment management.

Gamma radiation induced preparation of polyampholyte nanocomposite polymers for removal of Co(II)

A series of polyampholyte nanocomposite biopolymers, poly(N,N-diallyldimethylammonium chloride-co-acrylamide) grafted on carboxymethylcellulose/iron(III) oxide [P(DADMAC-AAm)CMC/Fe2O3] and poly(N,N-diallyldimethylammonium chloride-co‐sodium acrylate) grafted on carboxymethylcellulose/iron(III) oxide [P(DADMAC-SA)CMC/Fe2O3], was prepared with different molar ratios of anionic groups to cationic groups using gamma irradiation. The grafting properties and swelling behavior were investigated as a function of grafting conditions such as DADMAC, AAm, SA, and CMC concentrations and absorbed dose. Fourier transform infrared spectroscopic analysis (FTIR) confirmed the graft copolymerization. Scanning electron microscope (SEM) was employed to check the morphological structure of CMC, P(DADMAC-AAm)CMC/Fe2O3, and P(DADMAC-SA)CMC/Fe2O3. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) further characterized the grafted copolymers and showed their high thermal stability. Using batch sorption experiments and 60Co as a radiotracer, P(DADMAC-AAm)CMC/Fe2O3 and P(DADMAC-SA)CMC/Fe2O3 were evaluated for Co(II) removal from aqueous solutions. Experimentally, P(DADMAC-AAm)CMC/Fe2O3 and P(DADMAC-SA)CMC/Fe2O3 show high sorption capacity of Co(II), i.e. 69.67 mg g−1 and 75.17 mg g−1, respectively, which makes them potential sorbents for Co(II) removal from water/wastewater. Finally, the Co(II) sorption was examined using sorption isotherm and kinetic models. Cobalt sorption was best fitted to Langmuir model which suggests the sorption is of chemisorption type. On the other hand, the sorption kinetics was best represented by the pseudo-first-order kinetic model.

Sorption Properties of Sodium and Potassium Aluminosilicates from Alkaline Hydrolyzates of Rice Straw

Sodium and potassium aluminosilicates samples are synthesized from solutions formed via the alkaline hydrolysis of rice straw. The fabricated samples are characterized by means of X-ray diffraction analysis and IR-spectroscopy, and their elemental composition, particle morphology, specific surface area, and thermal properties are determined. The sorption properties of the synthesized aluminosilicates with respect to Cs+ ions are investigated under static conditions. Kinetic curves and sorption isotherms are provided and a sorption kinetic model is described.

Preparation of various thiol-functionalized carbon-based materials for enhanced removal of mercury from aqueous solution.

In this work, biochar (BC), activated carbon (AC), and graphene oxide (GO) were thiol-functionalized using 3-mercaptopropyltrimethoxysilane (3-MPTS) (named as BCS, ACS, and GOS, respectively). BCS, ACS, and GOS were synthesized mainly via the interaction between hydrolyzed 3-MPTS and surface oxygen-containing functional groups (e.g., -OH, O-C=O, and C=O) and π-π interaction. The materials before and after modification were characterized and tested for mercury removal, including sorption kinetics and isotherms, the effects of adsorbent dosage, initial pH, and ionic strength. Pseudo-second-order sorption kinetic model (R2= 0.992~1.000) and Langmuir sorption isotherm model (R2 = 0.964~0.998) fitted well with the sorption data of mercury. GOS had the most -SH groups with the largest adsorption capacity for Hg2+ and CH3Hg+ (449.6 and 127.5mg/g), followed by ACS (235.7 and 86.7mg/g) and BCS (175.6 and 30.3mg/g), which were much larger than GO (96.7 and 4.9mg/g), AC (81.1 and 24.6mg/g), and BC (95.6 and 9.4mg/g). GOS and ACS showed stable mercury adsorption properties at a wide pH range (2~9) and ionic strength (0.01~0.1mol/L). Mercury maybe removed by ligand exchange, surface complexation, and electrostatic attraction.

Montmorillonite/graphene oxide nanocomposite as superior adsorbent for the adsorption of Rhodamine B and Nickel ion in binary system

A series of montmorillonite reduced graphene oxide (MrGO) composites were synthesized using different ratios (5, 10, 15 and 20) of montmorillonite (MMt) to GO. The synthesized composites were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, surface area analyzer (BET), and Fourier transform- infrared spectroscopy. The adsorption capacity and efficiency of the synthesised composites were examined towards removal of Rhodamine B (RhB) and Nickel ion (Ni2+). The results were compared with that of GO and commercial MMt clay. The kinetic sorption models were evaluated, and it was observed that sorption follows the pseudo-second-order kinetics. Adsorption isotherm was best fit into the Langmuir model (R2 = 0.996 for RhB & 0.957 for Ni2+). Among all the synthesized composites, MrGO-2, a composite of GO and montmorillonite with (1:10) ratio, showed maximum activity towards the adsorption of Rhodamine B and Ni2+ calculated to be 625 mg/g and 178 mg/g respectively at neutral pH condition. From the calculated ΔG0 (−3.99 & −0.71 kJ mol−1), ΔH (28.6 & 4.61 kJ mol−1) and ΔS (−107.5 & −17.8 J mol−1 K) values for RhB & Ni2+ respectively, it can be unambiguously inferred that the adsorption process was feasible, endothermic and exhibiting least randomness, respectively. The prepared MrGO composites showed good adsorption capacity towards efficient removal of RhB and Ni2+ in single as well as binary system.

Rice and wheat straw ashes: Characterization and modeling of pretilachlor sorption kinetics and adsorption isotherm

The rice straw ash (RSA) and wheat straw ash (WSA) were explored as low cost adsorbent for pretilachlor removal from water. The ashes were characterized and sorption behavior of pretilachlor was evaluated. Kinetics study suggested that the modified Elovich model best explained the pretilachlor sorption on both the ashes. The adsorption data were analyzed using 2-, 3- and 4-parameter models and nine error functions were used to compute the best fit isotherm by nonlinear regression analysis. The pretilachlor was more sorbed onto the RSA (22.0–92.2%) than the WSA (11.4–61.4%) and percent adsorption decreased with increase in the herbicide concentration in solution. Isotherm model optimization analysis suggested that the Freundlich and the Temkin isotherms were the best models to predict the pretilachlor adsorption onto the RSA and the WSA. The error analysis suggested that the reciprocal of the observed squared (ROS) and the reciprocal of the predicted squared (RPS) error functions provided the best determination of the adsorption constants for the Freundlich and the Temkin isotherms, respectively. The RSA, which exhibited higher pretilachlor sorption potential, can be utilized as low cost adsorbent for pesticide removal from contaminated water.

Immobilization of layered double hydroxide in poly(vinylidene fluoride)/poly(vinyl alcohol) polymer matrices to synthesize bead-type adsorbents for phosphate removal from natural water

Layered double hydroxide (LDH) has been widely used as an adsorbent to remove contaminants from aqueous solutions. However, LDH in powder form might not be suitable in water and wastewater treatment systems due to low hydraulic conductivity and sludge production. Therefore, it is necessary to synthesize bead-type adsorbents for application in treatment systems. In this study, LDH beads were prepared through immobilization of powdered MgFe LDH in polymer matrices, composed of poly(vinylidene fluoride) and poly(vinyl alcohol). The LDH beads had an average size of 2.4 ± 0.6 mm with a Brunauer-Emmett-Teller (BET) specific surface area of 30.41 m2/g and total pore volume of 0.12 cm3/g. Batch experiments were conducted on the use of the LDH beads for phosphate sorption in stream water (pH = 6.9, ionic strength = 613 μS/cm) collected from the Seoho stream located in Suwon, Korea. Fourier-transform infrared (FTIR) spectrometer and X-ray photoelectron spectroscopy (XPS) were used to analyze the chemical characteristics of the LDH beads before and after phosphate sorption. Phosphate sorption to the LDH beads remained relatively constant at initial pH values of 5–9. The LDH beads could be used repeatedly for phosphate sorption through desorption with a NaOH solution. The equilibrium time for the phosphate sorption was 3 h, whereas the maximum sorption capacity was 2.050 mgP/g. In addition, the phosphate sorption increased with a rise in temperature from 15 to 45 °C. Under dynamic flow conditions (flow rate = 4.9 and 9.8 mL/min; bed depth = 10, 20, and 30 cm; inner diameter of column = 2.5 cm), fixed-bed column experiments were performed to test the applicability of the LDH beads in the phosphate removal from the stream water. The phosphate sorption capacity of the column was quantified to be 1.175 mgP/g at given experimental conditions (bed depth = 30 cm; flow rate = 4.9 mL/min). The performance of fixed-bed columns was quantified by analyzing phosphate breakthrough curves with fixed-bed kinetic sorption models (Bohart-Adams and modified dose-response models). This study demonstrated that the LDH beads could be successfully applied as adsorbents for phosphate removal from natural water.

Removal of Cadmium (II) from Aqueous Solutions onto Dodonaeae Viscose Leg Powder Using a Green Process: Isotherms, Kinetics and Thermodynamics

In the present study, batch adsorption experiments of hazardous cadmium ions, Cd(II), onto low-cost Dodonaeae Viscose Legs (DVLs) surface were conducted with respect to contact time, solution pH, adsorbent dosage, initial Cd concentration and temperature. Sorption isotherm, kinetic and thermodynamic models were used to describe the equilibrium stage and their constants were determined. The DVLs were used without chemical or physical activation processes. The results showed that the optimum adsorption capacity of DVLs for Cd(II) ions was found to be 25.29 mg/g at solution pH 5.26, 50 min and 303K. DVL adsorption data was fitted well with Langmuir isotherm. The mean free energy was found to be 1.82E-02 using Dubinin-Radushkevich (DRK) isotherm, which indicates that the adsorption of Cd(II) ions onto DVL surface is physical adsorption. The activation energy (Ea) was 3.06 kJ/mol, which confirms that Cd(II)-DVL adsorption process is physical sorption. Pseudo-first-order, pseudo-second-order, Elovich, intra-particle and extra-particle diffusion models were used to describe the adsorption kinetics. The results show strong correspondence to a pseudo-second-order kinetics. Thermodynamic parameters suggested that the adsorption of Cd(II) ions onto DVL surface is an exothermic process.

A novel, effective, and feasible method for deacidifying kiwifruit wine by weakly basic ion exchange resins

AbstractIn this study, an effective deacidification process for kiwifruit wine using ion exchange resins was investigated. Static adsorption experiments were conducted to screen an appropriate resin and optimize the volume ratio of resin to wine. Dynamic adsorption experiments were conducted to optimize the flow rate. Sensory and chemical analysis of the deacidified kiwifruit wine were also performed. The results demonstrated that 330 resin with a maximum adsorption capacity decreased total acid and citric acid to 4.32 and 1.39 g/L in kiwifruit wine. The acid adsorption process fitted Ho's sorption kinetic model well. The volume ratio of the 330 resin to wine and the feed flow rate were further optimized to be 1:30 and 4 mL/min. Kiwifruit wine with total acid and citric acid contents of 7.98 and 4.74 g/L was obtained, under optimum conditions, while preserving alcohol, vitamin C (Vc), flavonoids and phenol content, and improving the flavor.Practical applicationsThe high acidity in kiwifruit wine depress the sensory quality and attraction to consumers. Resins are applied for liquid treatment because of high efficiency, insolubility and low cost. This work showed that 330 resin treatment is a promising method to deacidify kiwifruit wine and provided an economical and effective processing method for kiwifruit processing enterprises. Monitoring acidity change and kiwifruit wine quality help enterprises better control the process. Furthermore, the easy removal of resins will greatly reduce energy consumption, resulting in lower processing cost.

Sorption of benzene and naphthalene on (semi)-arid coastal soil as a function of salinity and temperature

Considerable activities from the oil and natural gas sector have risen some concerns about the pollution of soil and groundwater by petroleum hydrocarbons (PHCs) in (semi)-arid coastal regions. The understanding of the fate and transport of PHCs in these regions is therefore necessary to develop strategies for remediation. To quantify the sorption rates of PHCs in (semi)-arid coastal soil environments, we conducted a series of controlled-laboratory batch experiments under variable temperature and salinity conditions. The soil samples were collected from the eastern coast of Qatar which is near the two largest off-shore oil and natural gas fields of the country (North Gas and Al-Shaheen Oil Fields), and the volatile benzene and naphthalene were used as PHCs. The characterization of soil samples showed sand classification with the texture class of sabkha and saline beach sandy soils with calcite as potential dominant mineral. The concentrations of dissolved chloride and sodium were found to be high (> 400 mg L−1) with a chloride-to‑sodium ratio of about 1.7. The results of sorption experiments showed that the rates of naphthalene sorption were more than for benzene, where the initial aqueous concentrations of benzene and naphthalene were reduced at equilibrium due to sorption by about 14–25% and 65–79%, respectively. This difference was attributed mainly to the organic carbon-water partitioning coefficient which is higher for naphthalene. The sorption rate experiments showed that sorption was stronger for benzene under higher salinity and lower temperature conditions. The sorption of naphthalene was not affected by the change in salinity but increased by 18% when the temperature decreased from 35 to 5 °C. A sorption kinetic model was also applied to define the sorption behavior of benzene and naphthalene for the coastal soil collected in Qatar and the best fits were achieved with the Langmuir sorption isotherm.

Assessment of kinetic and isotherm models for competitive sorption of Cs+ and Sr2+ from binary metal solution onto nanosized zeolite

ABSTRACTThis study examined the sorption performance of synthesized nanosized zeolite for the elimination of Cs+ and Sr2+ cations in a binary metal system. The influence of pH, sorbent amount, temperature, and contact time was studied. The relationship between each of these parameters and the removal efficiency was investigated. An analysis of the rate data was performed using both pseudo-first- and second-order reaction models. The ranking of three equilibrium sorption isotherm models used (Redlich–Peterson, Langmuir, and Freundlich) with a variety of numbers of parameters was determined using the corrected Akaike’s information criterion. The results demonstrate that a pseudo-second-order model fits the sorption kinetic data better than a pseudo-first-order model. The isotherm model rank order that best described the data statistically was Redlich–Peterson > Langmuir > Freundlich for the cesium ions and Langmuir > Redlich–Peterson > Freundlich for the strontium ions. Our results revealed that the existence of Sr2+ caused a significant reduction of Cs+ sorption in the binary metal mixture according to a lumped parameter model and vice versa. The results show that the synthesized material’s surface had a relatively stronger affinity for Cs+ than for Sr2+.

Kinetic and equilibrium studies for cadmium biosorption from contaminated water using Cassia fistula biomass

Cadmium (Cd) contamination of the water resources is one of the serious environmental issues. The present study aims to (1) evaluate the biosorption potential of Cassia fistula biomass for the removal of Cd from contaminated water and validate the experimental results with kinetic and equilibrium sorption models, (2) assess the removal of Cd from groundwater samples in the presence of other competing ions in the solution. The C. fistula biomass was characterized using Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller technique and scanning electron microscopy to understand the role of its physical properties in Cd biosorption and removal. The effects of biosorbent dose, initial Cd concentrations, contact time and presence of competing cations in groundwater samples at constant pH and temperature (27 ± 1.5 °C) were studied. At equilibrium (90 min), Cd removal (98–16%) and biosorption (6.26–0.34 mg/g) were recorded depending on the experimental conditions. The Langmuir model yielded a better approximation of the experimental data at equilibrium $$\left( {Q_{\hbox{max} } = 7.24{\text{ mg/g, }}R^{2} = 0.99} \right)$$ rather than Freundlich model. The pseudo-second-order kinetic model explained well the kinetic behavior of Cd biosorption. Results revealed a decline in the Cd removal (12.7 and 6% at 0.25 and 1.0 g/100 mL, respectively) in the presence of cations in the water samples. The results proved that C. fistula is a very effective and environment friendly alternative adsorbent for the removal (98%) of Cd from the aqueous system.

Kinetics of Competitive Sorption in Decontamination of Materials from Radionuclides

kinetic model of the mass transfer of a microcomponent in the simplest competitive system from the sorbed state (A) into a solution (B) and then into a sorbent (C) in accordance with the scheme A ⇄ B ⇄ C was formulated within the framework of competitive sorption statics. The kinetic equations were solved numerically. The influence exerted by the weight of competing sorbents А and С and by the degree of reversibility of linear reactions on the nonequilibrium decontamination factor Kdec(t) was determined. The time in which the equilibrium decontamination factor is attained for the model of chemical sorption kinetics was estimated from the experimental data on the rate constants of direct and reverse heterogeneous reactions and on the distribution coefficients of Cs(I) in the SiO2 (A)–CsCl solution (B)–Prussian Blue (C) system.