Mixed Surface Reaction Research Articles

Preparation of poly(divinylbenzene-co-methyl acrylate) adsorbent with tunable surface hydrophilicity for atrazine removal

To efficiently remove atrazine, it is crucial to facilitate synergistic adsorption effect between aromatic structure and hydrophilic adsorption sites through tuning surface hydrophilicity. Herein, we reported a polymer adsorbent which was synthesized by copolymerizing divinylbenzene (DVB) and methyl acrylate (MA) with different monomer ratio, and subsequently hydrolyzing the copolymer to obtain carboxyl group on its surface. The surface hydrophilicity could be easily adjusted by changing the ratio of monomer and the optimal feeding ratio was 4:1 (VDVB:VMA) in terms of porosity (specific surface area 712.92 m2/g) and hydrophilicity regarding atrazine adsorption. The adsorption process followed the Langmuir isotherm with a maximum adsorption capacity of 75.75 mg/g. The mixed surface reaction and film diffusion model revealed that the adsorption procedure is dramatically controlled by film diffusion. Atrazine molecules diffusive and bound with porous adsorbent via strong hydrogen bonding between N (triazine and amine) and carboxyl groups introduced by copolymerization. Furthermore, high porosity caused by aromatic crosslinked network provided sufficient adsorption sites through π-stacking interaction. This work not only supplies a highly efficient adsorbent for atrazine removal but also enables a platform for preparation of polymers with tunable porosity and surface hydrophilicity.

Influence of impeller clearance, impeller size and baffles on copper sorption on zeolite NaX: Do the size and position really matter?

Even though optimal mixing parameters may significantly influence the sorption process and its costs, the influence of hydrodynamics on sorption in a batch reactor hasn't yet been adequately studied. In this study, the hydrodynamic conditions produced by pitched blade turbine (PBT) impellers of various diameters and positions in baffled and unbaffled reactors were investigated. The objective was to investigate their influence on the just suspended impeller speed (NJS), power consumption per zeolite mass and the sorption process at the same temperature, initial copper solution concentration, and zeolite particle size in all the experiments conducted. The results show that NJS generally decreases as impeller diameter increases and is lower in the reactor without baffles. A transient multiphase computational fluid dynamics model was developed to provide valuable insight into the complex flow kinetics and it was found that the further the impeller is from the bottom of the baffled reactor the wider is the secondary suspension flow and the intensity of the flow below the impeller decreases. For this reason, complete suspension of the NaX zeolite particles in the solution was achieved at a higher PBT impeller speed. Due to the swirling motion of the suspension, this phenomenon is not observed in the unbaffled reactor for all the impellers used besides the smallest one. The power consumption per zeolite mass, at the state of complete zeolite suspension, increases in baffled reactor and decreases in unbaffled reactor with increasing impeller diameter having significantly lower values in the unbaffled reactor. The significantly lower power consumption per zeolite mass in an unbaffled system could be attributed to, not only the generally lower NJS values, but also to the resistance force which baffles make to the tangential fluid flow. The Ritchie model and Mixed surface reaction and diffusion controlled adsorption kinetic model were used for the kinetic analysis of the experimental kinetic data. The kinetic results indicate that the process is faster when the impeller is at the standard of bottom clearance, regardless of the presence of the baffles.

Impact of turbine impeller blade inclination on the batch sorption process

Batch sorption is a practical process used to remove various species from the wastewater. It is affected by different parameters such as initial concentrations, temperature, pH, surface area, coexisting ions, and mixing that need to be known for batch reactor design. Although reaction mixture in batch processes needs to be well-mixed, and there are many papers regarding sorption, mixing parameters are rather neglected. Therefore, the aim of this work was to analyse the impact of the turbine impeller blades inclination and baffle presence on sorption kinetics in the uncovered batch reactor. This impact was studied using copper (II) ions sorption on zeolite NaX particles. The experiments were conducted in the baffled and unbaffled reactor equipped with the four-blade turbine placed close to the vessel base. To determine the influence of impeller blades inclination on hydrodynamics and sorption kinetics, the blades inclination varied from 30° to 90°. A transient multiphase computational fluid dynamics model was developed to gain valuable insight into complex flow kinetics. The Ritchie model, Mixed surface reaction and diffusion-controlled sorption kinetic model, and Weber-Morris model were used for the kinetic analysis of the experimental kinetic data. According to Ψ and AARD values, the reaction is kinetic controlled regardless of the impeller blades inclination. The process is the fastest if the impeller with a blades inclination of 90° is used and in the baffled reactor. Concurrently, the energy consumption is the lowest for this impeller, regardless of the presence of the baffles.

Leaching performance of Al-bearing spent LiFePO4 cathode powder in H2SO4 aqueous solution

The leaching performance and leaching kinetics of LiFePO4 (LFP) and Al in Al-bearing spent LFP cathode powder were systematically studied. The effects of temperature (273−368 K), stirring speed (200−950 r/min), reaction time (0−240 min), acid-to-material ratio (0.1:1−1:1 mL/g) and liquid-to-solid ratio (3:1−9:1 mL/g) on the leaching process were investigated. The results show that the concentration of reactants and the temperature have a greater impact on the leaching of Al. Under the optimal conditions, leaching efficiencies of LFP and Al are 91.53% and 15.98%, respectively. The kinetic study shows that the leaching of LFP is kinetically controlled by mixed surface reaction and diffusion, with an activation energy of 22.990 kJ/mol; whereas the leaching of Al is only controlled by surface chemical reaction, with an activation energy of 46.581 kJ/mol. A low leaching temperature can effectively suppress the dissolving of Al during the acid leaching of the spent LFP cathode material.

Synthesis, characterization and application of cross-linked chitosan/oxalic acid hydrogels to improve azo dye (Reactive Red 195) adsorption

Cross-linked oxalic acid/chitosan hydrogels (ChOxb) were synthesized, characterized and tested for the adsorption of azo-dyes (Reactive Red 195 RR195) in contaminated wastewater; this novel biodegradable material was highly efficient. SEM-EDS and N2 adsorption/desorption were used to analyze specific area; FTIR-ATR spectra evidenced electrostatic interactions between protonated amino groups of chitosan and oxalate ions (intensity decrease and shift of amide-II band). Adsorption performance in batch assays showed a maximum percentage of removal of 90.6%, at pH = 4 (initial dye concentration of 300 mg.L−1). The maximum adsorption capacity (Qm) at pH = 4 was 110.7 mg.g−1, positioning ChOxb as one of the most efficient adsorption materials. Oxalic acid (natural organic acid) is an eco-friendly cross-linking agent that reduced swelling and improved chemical stability of ChOxb at low pH = 2.5. Redlich-Peterson adsorption isotherm presented the best fit; adsorption thermodynamic parameters were evaluated. Mixed surface reaction and diffusion-controlled kinetic model was the equation that best fitted kinetic data. FTIR-ATR, SEM-EDS and Z-potential showed electrostatic interactions between dye and amino groups of ChOxb; ChOxd can be reused without losing adsorption capacity and competitive electrostatic interactions between ChOxb-nitrate were observed. This new bio-material is an excellent alternative for the removal of RR195, improving Qm with better structural and functional properties.

Nano-titania/light expanded clay aggregate fixed bed as an effective adsorbent for removal of organic pollutant from water: Equilibrium and kinetic studies

A constructed fixed bed of light expanded clay aggregate coated with nano-titania particles has been applied as an effective adsorbent fixed bed to remove an anionic azo dye, direct red 16, from aqueous solution. This process was carried out using a recycled batch system under environmental temperature. Initial pH of the adsorbate solution imposed a severe effect on the adsorption process so that the best and worst performances of the prepared beds belonged to the acidic and basic pHs of 3 and 10, respectively. Various equilibrium and kinetic models were applied for analyzing experimental data related to several initial concentrations of DR16. Langmuir-Freundlich isotherm and mixed surface reaction and diffusion-controlled kinetic model satisfactorily described equilibrium and kinetic adsorption data, respectively. The models suggested that there is heterogeneity in this system and diffusion step at the same time with surface reaction determines the overall rate of the adsorption process. Appropriate and considerably stable performance of the used nano-titania/light expanded clay aggregate fixed beds after regeneration is one of the outstanding characters of the prepared beds. It is noteworthy that based on tests, the removal efficiency of the pollutant with the initial concentration of 25 mg/L was about 95% after 25 min (under pH 3 and T = 25 °C). It is while the adsorbent beds still worked steadily after about 65 times of reuses which can keep approximately all the adsorption capacity remaining. Therefore, features such as the high and relatively fast removal of the adsorbate, the facility and high rate in the regeneration can candidate the prepared fixed beds as an effective adsorbent for wastewater treatment.

Reactive RED 195 dye removal using chitosan coacervated particles as bio-sorbent: Analysis of kinetics, equilibrium and adsorption mechanisms

Chitosan particles (CP) prepared by coacervation technique were used as bio-sorbent material to remove the azo RR-195 dye; removal percentage (%RM) and adsorption capacity (Q) in batch adsorption experiments under different conditions of bio-sorbent doses, agitation speed and pH medium were determined; the maximum pH of dye removal was 4. Different adsorption equilibrium isotherms were tested and Redlich-Peterson was the model that best fitted experimental results. From the adsorption thermodynamic parameters, it was concluded that the adsorption process of RR-195 onto CP is spontaneous, favorable (ΔG<0), endothermic (ΔH>0) and the dye molecules show affinity for the bio-sorbent (ΔS>0). The maximum monolayer adsorption capacity (Qm) of CP was 82.1 mg.g−1 at pH = 4 and 318 K; therefore coacervated chitosan particles are among the top three adsorbent agents for this dye. The %RM was 84.2% in 10 h when the initial concentration of the dye was 300 mg.L−1. The mixed surface reaction and diffusion-controlled kinetic model (MSR-DCK), fitted satisfactorily experimental results, by considering simultaneous mechanisms of diffusion and adsorption process in the active sites. Fourier transform infrared spectroscopy (FTIR) with attenuated total reflection (ATR), scanning electron microscope-energy dispersion spectrometry X-ray (SEM-EDS) and Zeta potential analysis revealed that the interaction between dye molecules and the bio-sorbent are of an electrostatic nature. Desorption/regeneration experiments indicated that CP can be used in adsorptions/desorption cycles for the removal of wastewater containing RR-195. The information presented in this work demonstrates that CP can be a potent eco-friendly bio-adsorbent for the remediation of industrial wastewater.

Adsorption of Vanadium (V) from SCR Catalyst Leaching Solution and Application in Methyl Orange.

In this study, we explored an effective and low-cost catalyst and its adsorption capacity and catalytic capacity for Methyl Orange Fenton oxidation degradation were investigated. The catalyst was directly prepared by reuse of magnetic iron oxide (Fe3O4) after saturated adsorption of vanadium (V) from waste SCR (Selective Catalytic Reduction) catalyst. The obtained catalyst was characterized by FTIR, XPS and the results showed that vanadium (V) adsorption process of Fe3O4 nanoparticles was non-redox reaction. The effects of pH, adsorption kinetics and equilibrium isotherms of adsorption were assessed. Adsorption of vanadium (V) ions by Fe3O4 nanoparticles could be well described by the Sips isotherm model which controlled by the mixed surface reaction and diffusion (MSRDC) adsorption kinetic model. The results show that vanadium (V) was mainly adsorbed on external surface of the Fe3O4 nanoparticles. The separation-recovering tungsten (VI) and vanadium (V) from waste SCR catalyst alkaline solution through pH adjustment was also investigated in this study. The results obtained from the experiments indicated that tungsten (VI) was selectively adsorbed from vanadium (V)/tungsten (VI) mixed solution in certain acidic condition by Fe3O4 nanoparticle to realize their recovery. Tungsten (V) with some impurity can be obtained by releasing from adsorbent, which can be confirmed by ICP-AES. The Methyl Orange degradation catalytic performance illustrated that the catalyst could improve Fenton reaction effectively at pH = 3.0 compare to Fe3O4 nanoparticles alone. Therefore, Fe3O4 nanoparticle adsorbed vanadium (V) has a potential to be employed as a heterogeneous Fenton-like catalyst in the present contribution, and its catalytic activity was mainly evaluated in terms of the decoloration efficiency of Methyl Orange.

Preparation of modified Mg/Al layered double hydroxide in saccharide system and its application to remove As(V) from glucose solution

A starch modified Mg/Al layered double hydroxide (LDH) adsorbent was firstly synthesized by co-precipitation method. The adsorbent was characterized by Fourier transform infrared spectrometry (FT-IR), X-ray fluorescence spectrum (XFS), X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM), N2 adsorption–desorption analysis and thermogravimetric analysis (TGA). The experimental results indicated that high surface areas had been achieved after the removal of starch molecules through calcination (denoted as C-S-LDH). The maxium adsorption capacity of C-S-LDH for As(V) was increased by 36.0% compared with calcined LDH (C-LDH) at pH 7.04 in glucose solution (C-S-LDH: 8.141 mg/g, C-LDH: 5.987 mg/g). The kinetic study showed that the adsorption of As(V) by C-S-LDH was well represented by mixed surface reaction and diffusion-controlled (MSRDC) kinetics. These results have important implication for the design of absorbents in complex system.

Adsorption of picloram herbicide on montmorillonite: Kinetic and equilibrium studies

The kinetics of the adsorption of picloram (PCM) onto montmorillonite (Mt) was studied in situ by attenuated total reflectance Fourier-transform infrared spectra (ATR-FTIR). Pseudo-first-order, pseudo-second-order, intra-particle diffusion and mixed surface reaction intra-particle diffusion-controlled kinetic models were applied to the experimental results. The latter was the model that best represented the experimental results. The adsorption equilibrium isotherms revealed the presence of two independent adsorption processes on different surface sites. The adsorption isotherms normalized by the surface area were fitted with the Langmuir and Freundlich models to obtain the respective parameters.Due to the anionic form of PCM, the adsorption onto the external clay mineral surface sites followed by the entrance of the PCM molecule into the Mt basal space in a less energetically favorable pathway was proposed. The interaction of PCM with montmorillonite surface sites through nitrogen of the pyridine ring and carboxylic group by forming an inner sphere complex was confirmed by ATR-FTIR.

Characteristics of selective fluoride adsorption by biocarbon-Mg/Al layered double hydroxides composites from protein solutions: Kinetics and equilibrium isotherms study

In the study, two novel applied biocarbon-Mg/Al layered double hydroxides composites (CPLDH and CPLDH-Ca) were successfully prepared and characterized by TEM, ICP-AES, XFS, EDS, FTIR, XRD, BET and pHpzc. The fluoride removal efficiency (RF) and protein recovery ratio (RP) of the adsorbents were studied in protein systems of lysozyme (LSZ) and bovine serum albumin (BSA). The results showed that the CPLDH-Ca presented remarkable performance for selective fluoride removal from protein solution. It reached the maximum RF of 92.1% and 94.8% at the CPLDH-Ca dose of 2.0g/L in LSZ and BSA system, respectively. The RP in both systems of LSZ and BSA were more than 90%. Additionally, the RP of CPLDH-Ca increased with the increase of ionic strengths, and it almost can be 100% with more than 93% RF. Fluoride adsorption by the CPLDH-Ca with different initial fluoride concentrations was found to obey the mixed surface reaction and diffusion controlled adsorption kinetic model, and the overall reaction rate is probably controlled by intra-particle diffusion, boundary layer diffusion and reaction process. The adsorption isotherms of fluoride in BSA system fit the Langmuir–Freundlich model well. The BSA has synergistic effect on fluoride adsorption and the degree increased with the increase of the initial BSA concentration.

Mixed Surface Reaction and Diffusion-Controlled Kinetic Model for Adsorption at the Solid/Solution Interface

The effects of diffusion and surface reaction mechanisms have been considered conjointly to investigate the kinetics of adsorption. A new model has been proposed for the modeling of adsorption kinetics at the solid/solution interface in batch systems. Based on generated data points (t, q) by using of the new model, it was found that there is a deviation from linearity as a downward curvature at initial times of adsorption in usual t/q vs time plot, when diffusion contributes to the rate-controlling step of adsorption. Moreover, results of nonlinear fitting to the different experimental data show that the mixed surface reaction and diffusion-controlled model can be useful for kinetics modeling of adsorption in which pure surface reaction or mixed surface reaction and diffusion contribute to the rate-controlling step of adsorption.

A mixed surface reaction kinetic model for the reductive leaching of manganese dioxide with acidic sulfur dioxide

Previous researchers have rationalised the kinetics of dissolution of manganese dioxide in acidic sulfur dioxide solutions on the basis of either the adsorption of reactants followed by reactions with HSO 3 − and SO 2 or a two-electron surface electrochemical reaction with H + and HSO 3 −, the species involved in the equilibrium: SO 2(aq)+H 2O=H ++HSO 3 −. This paper revisits the reported rate data for the dissolution of MnO 2 in the form of plates [Herring and Ravitz, Trans. SME/AIME 231 (1965) 191] or particles [Miller and Wan, Hydrometallurgy 10 (1983) 219] to show that the rate of dissolution can be rationalised on the basis of a fast redox reaction : (i) MnO 2(s)+SO 2(aq)+H 2O=MnOOH(s)+HSO 3(aq) followed by one of the two rate determining redox reactions: (ii) MnOOH(s)+HSO 3(aq)=MnSO 4 0(aq)+H 2O or Mn(OH)HSO 4(s), (iii) MnOOH(s)+SO 2(aq)=MnO(s)+HSO 3(aq) depending on the pH of the medium. Whilst the rate equation for (iii) agrees with the electrochemical kinetic model reported previously, the dissolution of the solid Mn(OH)HSO 4 or the direct reaction: (iv) MnO 2(s)+SO 2(aq)=MnSO 4 0(aq) also appear to be rate controlling. The two rate constants k 1 and k 2 based on a shrinking sphere kinetic model: 1−(1− X) 1/3= k 1 K 0.5[SO 2] 0.5( t/ rρ)+ k 2[SO 2]( t/ rρ), for the leaching of monosized pyrolusite and electrolytically prepared MnO 2 particles, are in reasonable agreement with k 1 and k 2 based on the dissolution kinetics of MnO 2 plates.

Mixed transport/reaction control of gypsum dissolution kinetics in aqueous solutions and initiation of gypsum karst

Experiments with gypsum in aqueous solutions at 25°C, low ionic strengths, and a range of saturation states indicate a mixed surface reaction and diffusional transport control of gypsum dissolution kinetics. Dissolution rates were determined in a mixed flow/rotating disc reactor operating under steady-state conditions, in which polished gypsum discs were rotated at constant speed and reactant solutions were continuously fed into the reactor. Rates increase with velocity of spin under laminar conditions (low rates of spin), but increase asymptotically to a constant rate as turbulent conditions develop with increasing spin velocity, experiencing a small jump in magnitude across the laminar–turbulent transition. A linear dependence of rates on the square root of spin velocity in the laminar regime is consistent with rates being limited by transport through a hydrodynamic boundary layer. The increase in rate with onset of turbulence accompanies a near discontinuous drop in hydrodynamic boundary layer thickness across the transition. A relative independence of rates on spinning velocity in the turbulent regime plus a nonlinear dependence of rates on saturation state are factors consistent with surface reaction control. Together these behaviors implicate a `mixed' transport and reaction control of gypsum dissolution kinetics. A rate law which combines both kinetic mechanisms and can reproduce experimental results under laminar flow conditions is proposed as follows: R=k t 1−Ω ± b +ζ 1− 1+ 2(1−Ω ± b ζ 1/2 where k t is the rate coefficient for transport control, and Ω ± b is the mean ionic saturation state of the bulk fluid. The dimensionless parameter ζ(=D m ± eq /2δk + where m ± eq=mean ionic molal equilibrium concentration, D is the diffusion coefficient through the hydrodynamic boundary layer, δ equals the boundary layer thickness and k + is the rate constant for surface reaction control) indicates which process, transport or surface reaction, dominates, and is sensitive to the hydrodynamic conditions in the reactor. For the range of conditions used in our experiments, ζ varies from about 1.4 to 4.5. Rates of gypsum dissolution were also determined in situ in a cavern system in the Permian Blaine Formation, southwestern Oklahoma. Although the flow conditions in the caverns were not determinable, there is good agreement between lab- and field-determined rates in that field rate magnitudes lie within a range of rates determined experimentally under zero to low spin velocities A numerical model coupling fluid flow and gypsum reaction in an idealized circular conduit is used to estimate the distance which undersaturated solutions will travel into small incipient conduits before saturation is achieved. Simulations of conduit wall dissolution show end-member behaviors of conduit formation and surface denudation that depend on flow boundary conditions (constant discharge or constant hydraulic gradient) and initial conduit radius. Surface-control of dissolution rates, which becomes more influential with higher fluid flow velocity, has the effect that rates decrease more slowly as saturation is approached than otherwise would occur if rates were controlled by transport alone. This has the effect that reactive solutions can penetrate much farther into gypsum-bearing karst conduits than heretofore thought possible, influencing timing and mechanism of karst development as well as stability of engineered structures above karst terrain.

The Kinetics of Crystal Growth in Barium Sulfate Precipitation. III. Mixed Surface Reaction and Diffusion Controlled Rate of Growth.

The Kinetics of Crystal Growth in Barium Sulfate Precipitation. III. Mixed Surface Reaction and Diffusion Controlled Rate of Growth.