Batch Kinetic Studies Research Articles

Analytical capabilities of total reflection X-ray fluorescence spectrometry for silver nanoparticles determination in soil adsorption studies

In recent years, the production of silver nanoparticles (AgNPs) has grown due to their antibacterial properties. This fact enhances the release of these particles into the environment, especially in soils that are the major sink. To better understand adsorption processes in soils, usually batch kinetic studies are carried out. In this context, we tested the possibilities of using total reflection X-ray fluorescence spectrometry (TXRF) to monitor the silver content in soil adsorption kinetic studies. It was found that the lower limit of detection for Ag (through Ag-Kα detection) in aqueous solutions was around 37μg·L−1, which was suitable to carry out this kind of studies. Moreover, the direct analysis of Ag adsorbed onto soil after the kinetic studies was investigated. In this case, the limit of detection for Ag was around 1.7mg·kg−1. All TXRF results were compared with those obtained by inductively coupled plasma optic emission spectrometry and good agreement was found. The batch adsorption tests performed showed that 98% of polyvinylpyrrolidone coated AgNPs were retained on the tested soils in <6h.

Thermodynamics and kinetics study of defluoridation using Ca-SiO2-TiO2 as adsorbent: Column studies and statistical approach

Fluoride contamination of water is a potential health and environmental hazard worldwide. This study focuses on defluoridation efficiency in aqueous system by novel adsorbents, i.e., calcium impregnated silica (Ca-SiO2) and calcium impregnated silica combined with titanium dioxide (Ca-SiO2-TiO2). Comparative batch study was carried out using both adsorbents Ca-SiO2 and Ca-SiO2-TiO2 for fluoride removal efficiency in different experimental conditions where it was observed that chemically modified Ca-SiO2-TiO2 acted as a better adsorbent for defluoridation than Ca-SiO2. Thus, further batch isotherm and kinetics studies were performed using Ca-SiO2-TiO2. The phenomenon of fluoride ion uptake is realized by Langmuir and Freundlich isotherm model. Langmuir isotherm shows satisfactory fit to the experimental data. The rate of adsorption shows that the pseudo-second-order rate fitted the adsorption kinetics better than the pseudo-first-order rate equation. The mechanism of adsorption process was illustrated by calculating Gibbs free energy, enthalpy and entropy from thermodynamic studies. To further confirm the applicability of the adsorbent, a fixed bed study was carried out in column mode. Thomas and bed-depth-service-time (BDST) model were well-fitted to the experimental results. The optimal operating conditions of defluoridation were found by using response surface methodology (RSM) with the help of Design Expert Software. The maximum percentage of fluoride removal was 92.41% in case of calcium impregnated silica combined with titanium dioxide (Ca-SiO2-TiO2). Thus, it may be concluded that chemically synthesized Ca-SiO2-TiO2 could be used as an environmentally and economically safe adsorbent for defluoridation of waste water.

Removal of methylene blue by seed-watermelon pulp-based low-cost adsorbent: Study of adsorption isotherms and kinetic models

ABSTRACTBased on the abundance of seed-watermelon pulp (SWP) in Xinjiang, China, SWP was employed to prepare low-cost adsorbent toward the removal of methylene blue (MB). The effects of contact time at different initial concentration were studied. The widely used adsorption isotherm models including Langmuir, Freundlich, and Temkin isotherms were employed to depict the adsorption process. The Langmuir isotherm was best fitted to the experimental data. Batch kinetic studies showed that an equilibrium time of 300 minutes was needed for the adsorption. The adsorption properties can be well described by pseudo-second-order kinetic model and the MB uptake was not controlled by intraparticle diffusion mechanism.

Sol–gel-derived thiocyanato-functionalized silica gel sorbents for adsorption of Fe(III) ions from aqueous solution: kinetics, isotherms and thermodynamics

Adsorption characteristics of Fe(III) ions onto thiocyanato-functionalized silica gel sorbent were investigated under various conditions of contact time, initial metal concentration and temperature. The equilibrium isotherms, kinetics and thermodynamics of Fe(III) ions adsorption onto the surface of thiocyanato-functionalized silica gel from aqueous solution were investigated. Batch kinetic studies showed that an equilibrium time of 30 min was required for the adsorption of Fe(III) ions onto thiocyanato-functionalized silica gel. The estimated maximum capacities of Fe(III) ions adsorbed by thiocyanato-functionalized silica gel were 112.2 mg g−1. The equilibrium adsorption data of thiocyanato-functionalized silica gel for Fe(III) ions best fitted to the Langmuir isotherm since the correlation coefficients for the Langmuir isotherm were higher than that for the Freundlich and Dubinin–Radushkevich isotherms. The kinetic data were well described by the pseudo-second-order model. Spontaneous, endothermic and random characteristics of the process were confirmed by thermodynamic analysis.

Adsorption kinetic studies for removal of methylene blue using activated carbon prepared from sugar beet pulp

Sugar beet pulp is an abundant, renewable and low-cost precursor for production of activated carbon. In the present study, sugar beet pulp based activated carbon was prepared by using phosphoric acid as activating agent for adsorption of methylene blue. The conditions of preparation process had a significant influence on the adsorption of methylene blue, and the optimal preparation conditions were obtained as follows: liquid-to-solid ratio of 5, temperature of 450 °C and phosphoric acid concentration of 3 mol/L. The properties of sugar beet pulp based activated carbon were characterized by nitrogen adsorption isotherm. The adsorption increases as the increase of contact time, adsorption temperature and pH, and initial concentration of methylene blue. Batch kinetic studies showed that an equilibrium time of 100 min was needed for the adsorption, and the adsorbance of methylene blue is 244.76 mg/g at equilibration. Kinetic models, Weber’s pore diffusion model and Boyd’s equation were applied to the experimental data to study the mechanism of adsorption and the controlled step. The results showed that the adsorption kinetics followed the pseudo-second-order type kinetic model, intraparticle diffusion was not the rate-limiting mechanism and adsorption process was controlled by film diffusion.

Exploring Arsenic Adsorption at low Concentration onto Modified Leonardite

The removal of As(V) from aqueous solutions by leonardite loaded with ferric ions (Fe-leonardite) has been investigated. The influence of pH, contact time, and arsenate concentration on the adsorption process were evaluated. Batch kinetic studies showed that equilibrium time was reached at 24 h of contact time. Equilibrium data obtained with low initial arsenate concentrations (10–400 ppb) were fitted to both Langmuir and Freundlich models, and the maximum adsorption capacity was estimated to be 322 μg g−1. Arsenic sorption was evaluated in continuous mode to reproduce industrial applications and to determine the conditions where the process was controlled by either mass transfer or reaction rate. A maximum sorption capacity of 905 μg g−1 was obtained in continuous experiments. These results indicate that Fe-leonardite is a great potential material for removing arsenate at low initial concentrations from contaminated water.

Studies on removal of Pb(II) and Cr(III) using graphene oxide based inverse spinel nickel ferrite nano-composite as sorbent

Synthesis of a hybrid graphene oxide based inverse spinel nickel ferrite (GONF) nano-composite material and subsequent utilization in heavy metal removal from aqueous solution is described in the present study. The synthesized GONF was characterized using X-ray diffraction (XRD), Fourier transform-infrared resonance (FT-IR), and X-ray photoelectron (XPS) spectroscopies. The morphology, the surface area and pore volume of GONF were evaluated by scanning electron microscopy (SEM) and BET analysis, respectively. GONF was successfully used for the removal of Pb(II) and Cr(III) by batch adsorption techniques. Batch kinetics studies revealed that the sorption of Pb(II) and Cr(III) onto GONF was well described by a pseudo-second-order equation. The sorption equilibrium data of Pb(II) and Cr(III) was well tuned to the Langmuir isotherm model than the Freundlich and Temkin isotherm models. Hence, the sorption of Pb(II) and Cr(III) onto GONF occurred through monolayer chemisorptions on the homogeneous surface of GONF. The pH sorption results suggest that the sorption occurs through a complexed mechanism. The sorption of metal ions increased with increasing temperature, which is evident for an endothermic chemisorption by inner-sphere surface complexation. The overall obtained results demonstrated the GONF as an effective sorbent for Pb(II) and Cr(III) removal from wastewater.

Mechanism of heavy metal uptake by electron paramagnetic resonance and FTIR: Enhanced manganese(II) removal onto waste acorn of Quercus ithaburensis

This study aimed to use waste acorn of Quercus ithaburensis (WAQI) for biosorption Mn(II) from synthetic wastewater. Parameters such as metal concentration, pH, biosorbent concentration, stirring speed, particle size, and temperature were investigated by using batch kinetic studies. The percent removal of Mn(II) with native WAQI was 66.67%, this rose to 99.97% with activation processing. The mathematical description of the biosorption equilibrium and the adsorption mechanism were examined.Thermodynamic investigations indicate that adsorption reactions are spontaneous and slightly endothermic. ΔH° and ΔS° were found as 2.33 kJ mol−1 and 0.013 kJ mol−1 K−1, respectively. The activation energy of biosorption was calculated as 6.29 kJ mol−1.

Kinetic Uptake Studies of Powdered Materials in Solution.

Challenges exist for the study of time dependent sorption processes for heterogeneous systems, especially in the case of dispersed nanomaterials in solvents or solutions because they are not well suited to conventional batch kinetic experiments. In this study, a comparison of batch versus a one-pot setup in two variable configurations was evaluated for the study of uptake kinetics in heterogeneous (solid/solution) systems: (i) conventional batch method; (ii) one-pot system with dispersed adsorbent in solution with a semi-permeable barrier (filter paper or dialysis tubing) for in situ sampling; and (iii) one-pot system with an adsorbent confined in a semi-permeable barrier (dialysis tubing or filter paper barrier) with ex situ sampling. The sorbent systems evaluated herein include several cyclodextrin-based polyurethane materials with two types of phenolic dyes: p-nitrophenol and phenolphthalein. The one-pot kinetics method with in situ (Method ii) or ex situ (Method iii) sampling described herein offers significant advantages for the study of heterogeneous sorption kinetics of highly dispersed sorbent materials with particles sizes across a range of dimensions from the micron to nanometer scale. The method described herein will contribute positively to the development of advanced studies for heterogeneous sorption processes where an assessment of the relative uptake properties is required at different experimental conditions. The results of this study will be advantageous for the study of nanomaterials with significant benefits over batch kinetic studies for a wide range of heterogeneous sorption processes.

Biosorptive Removal of Cadmium (II) Ions from Aqueous Solution by Chemically Modified Onion Skin: Batch Equilibrium, Kinetic and Thermodynamic Studies

The biosorption potential of chemically modified onion skin (CMOS) for cadmium (II) ions (Cd2+) from its aqueous solutions at different conditions of initial Cd2+ concentration, contact time, pH, and temperature was investigated under batch mode. The results showed that biosorption of Cd2+ is influenced by these different conditions. The equilibrium biosorption data were analyzed by two-parameter (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R)), three-parameter (Redlich-Peterson, Sips, Toth, and Khan), and four-parameter (Baudu and Fritz-Schluender) isotherm models using linear and nonlinear regression methods. The best-fitting isotherms to describe the biosorption data of the Cd2+ CMOS system were found to be those of Freundlich, Sips, and Fritz-Schluender for the two-, three-, and four-parameter models, respectively. A maximum biosorption capacity (Qmax) of 18.34 mg/g was obtained for CMOS as compared with 11.90 mg/g for raw onion skin. The biosorption kinetics followed a pseudo second-order kinetic model and the biosorption mechanisms were controlled by boundary layer surface diffusion. The thermodynamic parameters of Gibbs free energy (ΔGo), enthalpy (ΔHo), entropy change of biosorption (ΔSo), and activation energy (Ea) were evaluated and it was found that the biosorption process was spontaneous, feasible, endothermic, and predominantly a physisorption process, however, with some element of chemisorption. A single-stage batch adsorber was designed for different biosorbent dose-to-effluent volume ratios using the Fritz–Schluender equation. The CMOS could be regenerated and reused for up to five cycles with no significant loss of efficiency. Therefore, CMOS has potential for application as an effective biosorbent for the removal of Cd2+ from aqueous solutions.

Phenol removal from effluent by rice husk carbon: batch and column studies

Environmental pollution has become a cause of great concern as it continues to increase day by day. One of the major toxic pollutants nowadays is phenol. In the present investigation, experiments were conducted to study the potential of rice husk carbon to adsorb phenol in batch and column operations. Batch studies were carried out to find the optimum values of parameters like initial concentration, adsorbent dose and pH. Column studies were carried out to estimate the time required for the phenol concentration to reach the saturation value and effect of initial concentration on phenol removal. Batch isotherm and kinetic studies were also carried out. The values of contact time, pH and adsorbent dose for initial concentration of 1,000 mg/l and 100 ml of effluent volume were observed to be 100 minutes 5 and 2.5 grams respectively. The time required for saturation decreased with increasing concentration. The saturation time for initial concentration of 1,000 mg/l was 60 minutes against 90 minutes for 250 mg/l. The equilibrium data for phenol uptake followed Freundlich isotherm more closely than Langmuir isotherm. The kinetics of phenol removal best fitted second order model, thought it agreed reasonably well with first order model.

The Investigation of Phenol Removal from Aqueous Solutions by Water Hyacinth

The potential of water hyacinth ash for phenol adsorption from aqueous solution was studied. Batch kinetic and isotherm studies were carried out under varying experimental conditions of contact time, pH, phenol concentration, and solution temperature. The adsorption of phenol was studied at pH 7. Batch adsorption models, based on the assumption of the pseudo-first-order, pseudo-second-order, and Elovich models, were applied to examine the kinetics of the adsorption. The results showed that kinetic data followed closely to the Elovich kinetic model. The experimental data were further analyzed by the expression of Boyd and the intraparticle diffusion model to determine the actual rate controlling steps. The overall rate of phenol uptake was found to be controlled by external mass transfer at the beginning of adsorption; then it gradually changed to intraparticle diffusion control at a later stage. Various adsorption models were used for the mathematical description of adsorption equilibrium and it was found that the experimental data fitted very well to the Langmuir model. Different thermodynamic parameters such as free energy, enthalpy, and entropy have been calculated and it was concluded that with the increase in temperature adsorption decreases, indicating the exothermic nature of the process.

Removal of cadmium, chromium, copper, lead and zinc ions by alisma plantago aquatica

Heavy metals are major toxic pollutants with severe health effects on humans. They are released into the environment from a variety of industrial activities. Alisma plantago aquatica (APA) was used as adsorbent to remove Cd(II), Pb (II), Zn(II) Cr(III) and Cu(II) from aqueous solution. The batch kinetic studies revealed that the adsorption was influenced by initial pH, concentration and temperature. Adsorption isotherm models like Langmuir and Freundlich were used to analyse the equilibrium data. Temperature change in the range 20–50°C affected the adsorption capacity. Enthalpy data revealed that the adsorption is endothermic in nature. Equilibrium is described by Langmuir isotherm. Isotherm studies have been used to determine the thermodynamic parameters of the process. The adsorption kinetic data was fitted with second order kinetic model than first order model. FTIR analysis of alisma plantago aquatica revealed the presence of hydroxyl, carboxyl and carbonyl groups which are participating in the adsorption of metal ions.

Redox stability of As(III) on schwertmannite surfaces

As(III)-enriched mine discharge often drains through Fe(III)-mineral abundant land covers which makes the understanding of its fate and redox behaviour extremely important. We therefore conducted batch kinetic and equilibrium studies at pH 3.0±0.05 in anoxic media coupled with spectroscopic and microscopic examinations at variable conditions to understand possible As(III) binding mechanisms and the redox stability of As(III) on schwertmannite, a prominent ferric mineral in acid mine drainage environments. Schwertmannite acted as an efficient scavenger for As(III) compared to goethite at identical sorbent:solute ratios. As K-edge X-ray absorption near-edge structure (XANES) demonstrated partial oxidation of sorbed As(III) to As(V) on both the minerals depending on the Fe(III)/As(III) ratios (goethite acted as a better oxidant than schwertmannite). Sorbed As(III) and As(V) coordinated in a bidentate binuclear binding mechanism with As(III)/As(V)–O and As(III)/As(V)–Fe interatomic distances as 1.78/1.69 and 3.37/3.31Å, respectively. Scanning (SEM-EDX) and transmission (TEM) electron microscopic, and IR spectroscopic measurements revealed the formation of As-containing surface coatings by sorbed As on schwertmannite.

Treatment of arsenic (III) contaminated water by dynamically modified iron-coated sand (DMICS)

In this paper, dynamically modified iron-coated sand (DMICS) was synthesized by dynamic soaking of iron onto the sand. The DMICS was tested for As(III) removal from the aqueous solution by adsorption studies. The effects of particle size, initial arsenic concentration and adsorbent dose on arsenic removal efficiencies were evaluated by batch kinetic studies. Two batch kinetic models i.e. chemical reaction rate and pseudo-second order have been applied to see the behaviour of As(III) adsorption over DMICS. Langmuir, Freundlich and Temkin isotherms were used to describe the equilibrium studies data. Langmuir isotherm was found better fit when compared with other isotherms based on coefficient of correlation (R2) values. The maximum adsorption capacity of DMICS was calculated as 0.29 mg/g as per Langmuir isotherm. The adsorption process was pH-dependent and maximum arsenic removal occurred in the pH range of 6–8. Scanning electron microscope was conducted on arsenic-loaded sand whereas, X-ray diffractogram (XRD) analysis was conducted on plain sand, DMICS and arsenic-loaded DMICS. XRD spectra supported the presence of arsenic on the surfaces of DMICS. The breakthrough and exhaustion times for 60 cm media column were 114 h and 200 h, respectively, based on column studies data. The DMICS has shown a good potential for arsenic remediation from aqueous medium.

Mechanism of arsenic removal using chitosan and nanochitosan

Chitosan, a natural polysaccharide copolymer of glucosamine and N-acetyl-glucosamine, possesses one free primary amine and two free hydroxyl groups on each glucosamine unit. It has a polycationic nature and an abundance of amine functional groups. The sorption equilibrium and kinetics of arsenate onto chitosan flakes have been studied. The effect of pH on the adsorption capacity and the uptake kinetics is an important parameter to investigate the adsorption mechanism of anionic species such as arsenate ions on the protonated amine groups of chitosan. The equilibrium sorption and batch kinetic studies of arsenate ions on chitosan were performed at initial As concentration of 250–11,000μgL−1 and initial pH ranging from pH=3.50–5.50. The experimental results showed that initially for approximately the first 30min there is a rapid and high adsorption of arsenate ions onto the chitosan leading to a maximum uptake capacity after this short time. However, this stage is followed by a slow desorption of arsenate from the chitosan with a steady increase in solution pH. A novel reversible pseudo-first order kinetic model was developed and applied to correlate this newly reported adsorption–desorption phenomenon. The physical and chemical properties of chitosan were studied and presented in terms of its surface and structural properties such as the degree of deacetylation, crystallinity, surface charge and its swelling properties.

Preparation of hydrophobic granular silica aerogels and adsorption of phenol from water

Granular silica aerogels with different degrees of hydrophobicity were prepared via sol–gel synthesis followed by drying at ambient pressure. The effects of preparation conditions, including pH and modification time, on aerogel characterization were investigated. The aerogels were characterized using nitrogen adsorption at 77K. We found that the aerogel was a nano-structured material with high specific surface area and high porosity. The aerogels were used for phenol adsorption from water. The effects of hydrophobicity degree, phenol concentration, and contact time were studied. Batch kinetic and isotherm studies were carried out to evaluate the effects of contact time and phenol concentration. The Freundlich model and the pseudo-second-order fitted the experimental data. The results also indicated that the phenol adsorption process involved both boundary layer diffusion and intraparticle diffusion. When the equilibrium concentration of phenol was 290mgL−1, the adsorption of phenol on the aerogel was 142mgg−1.

Commercial steel wool for reduction of hexavalent chromium in wastewater: batch kinetic studies and rate model

The present study aims at searching the potential of commercial grade steel wool in reducing hexavalent chromium in aqueous phase under batch mode. About 30 % of the initial hexavalent chromium was found to reduce within 2 h at a pH of 3. However, on testing the combined effects of different process parameters, namely the solution pH, wool loading, etc., the optimum batch parametric condition has been fixed. A moving boundary type kinetic model, which takes into account the effect of passivation along with the direct reduction mechanism to simulate the gross uptake profile of Cr(VI) from the bulk solution is proposed. The effective pore diffusivity of Cr(VI) in commercial steel wool was determined by a suitable global optimization technique. Additionally, the model is also capable to simulate the decline of active external surface area of the wool caused by passivation with time. A good match of the experimental data and model-simulated transient bulk concentration of Cr(VI) (under optimum parametric condition only) establishes the general validity of the proposed model.

Removal Efficiency, Adsorption Kinetics and Isotherms of Phenolic Compounds from Aqueous Solution Using Rice Bran Ash

In the present study, a porous rice bran ash powder was synthesized and tested for the removal of phenolic compounds from aqueous solution. The size of the rice bran ash particles was 14.49 nm, with a BET surface area of 50.14 m2g-1. Adsorption of phenol, 2-chlorophenol and 4-chlorophenol was conducted at various contact times, solution pHs, adsorbate concentrations and rice bran ash dosages in a batch reactor. Batch kinetic studies showed that an equilibration within 240 min could be achieved at pH as low as 5.0 ± 0.2 for the adsorption of 50 mg L-1 phenolic compounds concentration. Removal efficiency of 2-chlorophenol was lower than phenol and 4-chlorophenol. The phenol, 2-chlorophenol and 4-chlorophenol maximum removal efficiency was observed at an initial pH of 5 ± 0.2. Also the maximum predicted adsorption capacities were 4.6332, 3.6749 and 4.3060 mg g-1 for phenol, 2-chlorophenol and 4-chlorophenol, respectively. The capacity of phenol, 2-chlorophenol and 4-chlorophenol adsorption at equilibrium increased with the increase of initial concentration (50- 400 mg L-1) and decreased with the increase of adsorbent dosage (2.5-10 g L-1). The isotherm evaluations revealed that the equilibrium data for 2-chlorophenol and 4-chlorophenol could be fitted with the Freundlich model, whereas the equilibrium data for phenol fitted with Langmuir model best. In addition, the adsorption kinetic data were found fit the test results well based on a pseudo-second-order rate for selected phenolic compounds.

Thermodynamic and Kinetic Controls on Cotransport of Pantoea agglomerans Cells and Zn through Clean and Iron Oxide Coated Sand Columns

Recent observations that subsurface bacteria quickly adsorb metal contaminants raise concerns that they may enhance metal transport, given the high mobility of bacteria themselves. However, metal adsorption to bacteria is also reversible, suggesting that mobility within porous medium will depend on the interplay between adsorption-desorption kinetics and thermodynamic driving forces for adsorption. Till now there has been no systematic investigation of these important interactions. This study investigates the thermodynamic and kinetic controls of cotransport of Pantoea agglomerans cells and Zn in quartz and iron-oxide coated sand (IOCS) packed columns. Batch kinetic studies show that significant Zn sorption on IOCS takes place within two hours. Adsorption onto P. agglomerans surfaces reaches equilibrium within 30 min. Experiments in flow through quartz sand systems demonstrate that bacteria have negligible effect on zinc mobility, regardless of ionic strength and pH conditions. Zinc transport exhibits significant retardation in IOCS columns at high pH in the absence of cells. Yet, when mobile bacteria (non attached) are passed through simultaneously with zinc, no facilitated transport is observed. Adsorption onto cells becomes significant and plays a role in mobile metal speciation only once the IOCS is saturated with zinc. This suggests that IOCS exhibits stronger affinity for Zn than cell surfaces. However, when bacteria and Zn are preassociated on entering the column, zinc transport is initially facilitated. Subsequently, zinc partly desorbs from the cells and redistributes onto the IOCS as a result of the higher thermodynamic affinity for IOCS.