Adsorption Rate Coefficient Research Articles

Dynamics of radionuclide electromigration in intact granite: An kinetic adsorption-advection-dispersion model and its application

Granite, as the natural barrier for the disposal of high-level radioactive waste, plays an important role in ensuring environmental and public safety. The safety assessment of the repository depends on the reliable migration parameters of radionuclides in granite. In this study, we developed a kinetic adsorption-advection-dispersion model based on first-order adsorption kinetics. It introduces a first-order adsorption rate coefficient to describe the kinetics of adsorption process and accounts for other crucial mechanisms affecting the migration of radionuclide ions, namely, the electromigration, electroosmosis, and dispersion. This model is then applied to interpret the experimental results of electromigration of tracer ions in intact granite. The results show that for the weakly adsorbed radionuclides studied, iodide and selenite, the effective diffusion coefficients and formation factors calculated by this model are in constant with those derived from the classical advection-dispersion model based on linear adsorption equilibrium. By contrast, for the moderately or strongly adsorbed tracer ions studied, including cobalt, cesium, and strontium, the migration parameters calculated by this model exhibit significantly less uncertainty than those obtained from the advection-dispersion model simulations. The advection-dispersion model based on the first order adsorption kinetics introduces the first order adsorption rate coefficient, and considers the influence of electromigration, electroosmosis and dispersion mechanism, which helps to explain the migration mechanism of nuclide ions in intact granite more accurately.

MICRO-SCALE CONTINUOUS CO2 ADSORPTION COLUMN DESIGN WITH ZEOLITE 5A ADSORBENT

CO2 is the primary greenhouse gas which mainly stems from human activities. Increased CO2 emission in the atmosphere promotes global warming, which adversely affects human health and the environment. Adsorption is proposed as one of the practical and economical methods for CO2 removal. Zeolite 5A is an adsorbent that can be employed in CO2 adsorption due to its high porosity and adsorption capacity. In this study, we investigate the CO2 adsorption behavior by zeolite 5A adsorbent in a continuous, micro-scale fixed-bed column at different bed heights. Gas chromatography was utilized to determine CO2 exit concentrations. The column pressure drop was calculated using Ergun's equation. The obtained data were analyzed in the form of breakthrough curves, then fitted to Thomas and Yoon-Nelson's mathematical model to obtain adsorption rate coefficient in the column. The experimental data of CO2 adsorption by zeolite 5A shows the good correspondence with both Thomas’s and Yoon-Nelson’s mathematical models. At a flow rate of 30 mL/min and bed height variations of 10 and 12 cm, the CO2 adsorption capacities (q0) were 0.0071 and 0.0099 mol/g, respectively. While the Thomas’s adsorption rate coefficient, kTH, for the same conditions were 0.4164 min-1 and 0.4342 min-1.

Experimental investigation and analysis of alumina/polymer/alginate composite desiccant materials

This study developed a novel lump activated alumina-based composite material (AACM), which composed of activated alumina, polyacrylic acid, sodium polyacrylate, and sodium alginate with a mass mixing ratio of 10:1.5:1.5:1.5. The 10:1.5:1.5:1.5 AACM had the rigid and compact structure without the problems of crack and disintegration. Moreover, due to great structure strength, air channels of 10:1.5:1.5:1.5 AACM can be made by the drilling machine, which was uncomplicated and fast, and can save the mold cost. Under the same adsorption conditions, equilibrium adsorption capacities of 10:1.5:1.5:1.5 AACM were 1.3–2.7 times higher than those of activated alumina in the range of 50–90% relative humidity, and 1.1−1.4 times better than those of a silica gel-based composite material (SGCM) in the high relative humidity (80−90% RH). The calculated results by a linear driving force model showed that 10:1.5:1.5:1.5 AACM possessed greater adsorption rate coefficients compared to activated alumina and SGCM. Moreover, the energy factor of 10:1.5:1.5:1.5 AACM was comparable to that of SGCM at the regenerative conditions of 50 °C and 15% RH, and it was 53% and 27% higher than activated alumina and SGCM, respectively, when using the return air for regeneration. Thus, the proposed AACM is competitive and flexible for extensive applications.

Insight into the interactions of albumin with TiO2 nanomaterials and calcium phosphate-based biomaterials by kinetic adsorption and spectroscopic studies

Among key factors determining the fate of biomaterials in vivo are their interactions with blood serum proteins, which can lead to either successful integration or rejection/encapsulation. Although there are a number of studies investigating the interactions between proteins and bioimplants, comparable data for different types of biomaterials are lacking. To fill this gap, the adsorption kinetics and binding interactions of bovine serum albumin (BSA) with calcium phosphates (CaPs), namely hydroxyapatite (HA) and calcium deficient apatite (CaDHA), different TiO2 nanomaterials (TiNMs) presenting various morphologies such as nanoparticles (TiNPs), nanoplatelets (TiNPls), nanotubes (TiNTs) and nanowires (TiNWs), as well as their composites with CaDHA (CaDHA/TiNMs) were investigated. The kinetics of BSA adsorption on all studied materials was best described by pseudo-second order kinetics. The rate coefficient values obtained for the composites were lower than those for CaDHA and the corresponding TiNMs, while the adsorption density was higher for the composites than for CaDHA, except for the composites with TiNTs. Adsorption on TiNWs, CaDHA and all composites involved intraparticle diffusion, which was the rate-limiting step only for CaDHA/TiNTs. Fluorimetric titration experiments revealed that the number of binding sites was in larger than 1, except for TiNTs and TiNWs, indicating positive binding cooperativity. Interestingly, the values of the binding constants were lower for the TiNMs with a higher adsorption rate coefficient. Overall, BSA adsorption on the studied materials proved to be a complex process, which depended on the different surface properties of the adsorbents. Which property had a dominant role depended on the chemical identity of the adsorbent. The obtained comparable data for different types of materials point to the way of modifying their protein adsorption and binding properties.

The kinetic adsorption of zinc metal ions in Bangka post tin mining water on chitosan from shrimp shells waste

The effect of deproteinization temperature on chitosan extraction process from shrimp shells waste used variation of temperature: 30, 60 and 90°C was studied. The results shown that the degree of deacetylation of chitosan (DD) decreased with increasing deproteinization temperature. This is probably due to excess polymerization reaction when the deproteinization temperature increases, thereby destroying the chitin structure. The highest chitosan DD achieved was up to 79.72% at temperature deproteinization of 30°C and the occurrence of deacetylation structurally demonstrated by the Fourier transform infrared characterization. The chitosan adsorption for zinc metal ions in Bangka post tin mining water shown that the systems of adsorption follow the pseudo second order kinetic model. Based on the equation of kinetics adsorption shown that the increase of chitosan DD causes the adsorption rate and maximum adsorption capacity increased. The increase of chitosan DD which is an indicator of the transformation of chitin into chitosan represents an increase in the number of amine groups which have a stronger metal ion adsorption. The highest of adsorption rate coefficient and maximum adsorption capacity was up to 1.215 g mg−1 min−1 and 0.15 mg g−1 respectively achieved at temperature deproteinization of 30°C.

Investigation on water vapor adsorption performance of carbon based composite adsorption material ACF-silica sol-LiCl

The composite adsorption material ACF-silica sol-LiCl (ASL) is prepared by impregnating activated carbon fiber (ACF) with silica sol and LiCl to improve the water vapor adsorption performance. The silica sol provides support to the soft ACF and solidifies it. The silica sol also increases the adhesion area in the ACF for the LiCl. The LiCl can effectively improve the water vapor adsorption performance of the ACF. The adsorption performance of the ASL is optimum when the LiCl impregnation concentration is 430 mg/L. Scanning electron microscope images show that the silica sol and LiCl fill the fibers pores and spaces between the fibers in the ACF after impregnation. And adsorption kinetics of the ASL is characterized using a linear driving force (LDF) model and experiments. Results show that ASL has a high dynamic water absorption rate and adsorption rate coefficient (k). The k of the ASL reaches 1.58 × 10−4−2.05 × 10−4, which is 0.27 × 10−4−0.59 × 10−4 higher than that of the ACF. Meanwhile, the results of water vapor isothermal adsorption tests show that the impregnation of silica sol and LiCl increases the hydrophilicity of the ACF, and thus greatly enhances its water vapor adsorption capacity. The adsorption capacity of the ACF is almost 0 at P/P0 < 0.2 and reaches a maximum of 0.5479 g/g at P/P0 = 0.65. The adsorption capacity of the ASL steadily increases with the relative pressure. When the relative pressure is close to 1, the adsorption capacity of the ASL reaches 2.2876 g/g, which is 2.67 times the maximum for the ACF.

Highly efficient removal of glyphosate from water by hierarchical-pore UiO-66: Selectivity and effects of natural water particles

The selective removal of glyphosate (GP) from aqueous environments is crucial for ensuring human health and environmental sustainability. The preparation of hierarchical-pore MOFs and the reasonable regulation of the pore size are effective strategies for achieving selective removal. In this study, we applied hierarchical-pore UiO-66 analogues (HUiO-66s) synthesized by the template technique through a mild method for the removal of GP from water. The results showed that the maximum adsorption capacity of HUiO-66s was as high as 400 mg/g, which is higher than that of most reported adsorbents. Notably, HUiO-66s showed the highest adsorption rate and distribution coefficient for GP in a multivariate system containing different organophosphorus pesticides and antibiotics, exhibiting suitable selective adsorption performance for GP. Furthermore, GP adsorption onto HUiO-66-2 (prepared from 2 mL of MOF-5 template) did not affect the presence of competing anions and humic acids. Naturally occurring particles in the water body had an enhanced (i.e., Al2O3, sepiolite, and montmorillonite), reduced (i.e., illite and SiO2), or insignificant (i.e., kaolin) effect on the GP adsorption rate of HUiO-66-2. Further analysis based on the bulk adsorption results and microscopic characterisation indicated that the pore structure synergistically occurred with metal-ligand bonding, hydrogen bonding, and electrostatic interactions, which together determined the GP adsorption. Overall, the high adsorption and apparent adsorption selectivity of HUiO-66s facilitated the rapid separation and removal of GP in complex aqueous environments. Our findings provide insights into the transport and fate of MOFs and contaminants in natural aquatic systems.

Dynamic model for the simultaneous adsorption of water vapor and methane on shales

Water is almost ubiquitous in shale gas reservoirs. To analyze simultaneous water vapor and methane adsorption in shales, a dynamic model with a time-dependent boundary and diffusivity and a noninstantaneous adsorption mechanism was proposed. The analytical solution of the model was obtained via integral transformation method. The model was applied to match the dynamic data of simultaneous CH4–H2O adsorption. The results suggest that the strength for gas adsorption to shale is characterized by adsorption rate coefficient and desorption rate coefficient, where the adsorption strength of shale to water vapor is stronger than that to methane, and the conversion rate from water vapor to adsorbed water on adsorption sites is larger. The methane and water vapor diffusion coefficients first increase to a maximum and then decrease with time. The maximum methane diffusion coefficient ranges from 5.83 × 10−13–1.08 × 10−11 m2/s; the maximum water vapor diffusion coefficient ranges from 2.06 × 10−19–4.53 × 10−13 m2/s. The methane diffusivity and its variation rate are larger than those of water vapor. The methane and water vapor diffusion coefficients first increase with the density of free gases in pores and then decrease in the late period of the adsorption process. Water vapor reduces the adsorption strength of shale to methane and free methane-to-adsorbed methane conversion rate on adsorption sites. The methane diffusion coefficient in dry shale increases with time, and its growth rate reaches zero at adsorption equilibrium, which ranges from 6.60 × 10−14–4.82 × 10−11 m2/s; the methane diffusivity increases exponentially with the methane adsorption amount and free methane density in pores.

The Absorption Accelerating Behavior of Surface Modified Wool: Mechanism, Isotherm, Kinetic, and Thermodynamic Studies

ABSTRACT Even though wool has excellent fabric properties, its low absorption capacity hinders its efficient application in the textile industry and material field. Surface modification is one of the efficient ways of improving its inherent properties. However, the effect of surface modification on its absorption properties is not well understood. Herein, surface modification of wool was performed using deep eutectic solvent method. Several physical and chemical properties of the modified wool including chemical bonds, surface topography, and absorption capacity were analyzed. FTIR revealed that surface modification retained keratin molecular structure but only cleaved disulfide bonds. The second-derivatization of FTIR spectra further indicated that the secondary structure was also retained. SEM and EDS analyses revealed that scale modification etched the wool surface. Together, these changes improved the absorption capacity of wool. BET further revealed that surface modification increased the pole size of wool, a property that improves the adsorption capacity. Further analyses on diffusion coefficient, adsorption isotherm, adsorption kinetics, and thermodynamic parameters at a lower temperature revealed that surface modification followed Langmuir to Freundlich isotherm and pseudo-first-order model to pseudo-second-order model transformation. In particular, the adsorption content, rate and diffusion coefficient increased with decrease in the entropy and enthalpy of wool.

Investigation on activated carbon-sodium polyacrylate coated aluminum sheets for desiccant coated heat exchanger

Adsorption and desorption properties of desiccants are of key significances to the dehumidification performance of a compact dehumidification component named desiccant coated heat exchanger. This work developed novel activated carbon (AC) - sodium polyacrylate (PAAS) composite coated aluminum sheets with high adsorption property and good desorption ability. Adsorption and desorption properties of AC-PAAS coated aluminum sheets were investigated under different air conditions. Cyclic adsorption-desorption features with internal-cooling/heating were conducted. Results showed that composite coated aluminum sheets had nearly 2∼3 times higher water uptake than an AC coated sample in the range of medium- to high-relative humidity (60%∼90% RH). More than 95% of adsorbed water in composite samples was released at 70 °C & 20% RH, and 86% was still desorbed when the air temperature was decreased to 40 °C. Adsorption capacities and rate coefficients of composite samples with internal-cooling could be 2.3 and 1.5 times higher than those without. This paper provides a way to develop composite desiccants with high cyclic water uptake performance in the fields of adsorption cooling, solid desiccant air-conditioning and atmospheric water harvesting.

Thermodynamic and kinetic coupling modeling for thallium(I) sorption at a heterogeneous titanium dioxide interface

The transformations of monovalent thallium (Tl) in an aqueous environment may be affected significantly by Tl(I) partitioning at the solid-water interface during sorption. Models used to quantify the kinetics of Tl(I) adsorption on heterogeneous adsorbents and formation of multiple complexes under a wide range of water chemistry conditions can accurately predict the environmental fate of thallium. In this study, Tl(I) sorption on representative titanium dioxide at different solution pH values and loading concentrations was investigated with two unified adsorption models, diffuse layer modeling and kinetics modeling. Three Tl(I) surface complexes, TiOTl, TiOHTl+, and TiOTlOH-, were used in the diffuse layer model and successfully described batch adsorption and the results of spectroscopic analyses. The contribution of TiOHTl+ to the adsorption capacity was much higher than those of TiOTl and TiOTlOH- under neutral and weakly alkaline conditions, while the species TiOTlOH- predominated among Tl(I) complexes in strongly alkaline environments. The adsorption and desorption rate coefficients derived from thermodynamics and kinetics coupling modeling suggested the influence of different complex characteristics on adsorption and desorption of Tl(I). Our results provide a comprehensive model for predicting the dynamic binding behavior of Tl at heterogeneous solid-water interfaces.

Comparative study on the water uptake kinetics and dehumidification performance of silica gel and aluminophosphate zeolites coatings

Desiccant coated heat exchanger (DCHE) systems have significant potential in improving dehumidification performance. The moisture transfer occurring in one single air channel of DCHE can dominate the overall system performance. In this study, the adsorber with an approximate air channel of DCHE was designed to experimentally investigate the kinetics of silica gel and two aluminophosphate zeolites (FAM Z01 and FAM Z05). Their dehumidification performances also were simulated at regeneration temperature range of 50–80 °C to reveal the applicability in air-cooled cross-flow DCHE. Results showed that linear driving force (LDF) model could well describe the dynamic water uptake behaviors. Adsorption rate coefficient kads increased with increasing inlet air humidity ratio and velocity, but decreased with increasing coating thickness. It is worth noting that increasing regeneration temperature had a little effect on kads, while desorption rate coefficient kdes increased significantly. Simulation results showed that moisture removal capacity (MRC) and dehumidification coefficient of performance (DCOP) of FAM Z05 coated DCHE could reach 0.495 g/kg and 0.57 at regeneration temperature of 50 °C, which were 2.3 and 15.4 times higher than these of silica gel and FAM Z01 coated DCHEs. It demonstrated that FAM Z05 was more promising to utilize lower-grade heat energy.

Comparative Study on the Water Uptake Kinetics and Dehumidification Performance of Silica Gel and Fams Coatings

Desiccant coated heat exchanger (DCHE) systems handling sensible and latent heat simultaneously have significant potential in improving dehumidification performance. The DCHEs consist of a series of open air channels coated with porous desiccant, and the moisture transfer occurring in DCHEs usually can be represented by one single channel due to their structural symmetry. In this study, the adsorption kinetics of an adsorber with a parallel air channel coated with three low-temperature regenerative desiccants respectively, i.e. silica gel, FAM Z01 and FAM Z05 was experimentally investigated. Their dehumidification performances in DCHEs also were simulated at regeneration temperature range of 50-80°C. Results showed that the linear driving force (LDF) model can well describe the dynamic behavior of water uptake. Adsorption rate coefficient [[EQUATION]] increased with the increase in inlet air humidity ratio and air velocity, but decreased with increasing coating thickness. It is worth noting that the increasing regeneration temperature had a little effect on the [[EQUATION]] , while desorption rate coefficient [[EQUATION]] increased significantly. Simulation results indicated that the DCOP of Z05 DCHE can reach 0.66 at regeneration temperature of 50°C, which is 2.4 and 8.9 times higher than these of silica gel and Z01 DCHEs, respectively.

Non-equilibrium interplay between gas–particle partitioning and multiphase chemical reactions of semi-volatile compounds: mechanistic insights and practical implications for atmospheric modeling of polycyclic aromatic hydrocarbons

Abstract. Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic air pollutants. The dispersion of PAHs in the atmosphere is influenced by gas–particle partitioning and chemical loss. These processes are closely interlinked and may occur at vastly differing timescales, which complicates their mathematical description in chemical transport models. Here, we use a kinetic model that explicitly resolves mass transport and chemical reactions in the gas and particle phases to describe and explore the dynamic and non-equilibrium interplay of gas–particle partitioning and chemical losses of PAHs on soot particles. We define the equilibration timescale τeq of gas–particle partitioning as the e-folding time for relaxation of the system to the partitioning equilibrium. We find this metric to span from seconds to hours depending on temperature, particle surface area, and the type of PAH. The equilibration time can be approximated using a time-independent equation, τeq≈1kdes+kads, which depends on the desorption rate coefficient kdes and adsorption rate coefficient kads, both of which can be calculated from experimentally accessible parameters. The model reveals two regimes in which different physical processes control the equilibration timescale: a desorption-controlled and an adsorption-controlled regime. In a case study with the PAH pyrene, we illustrate how chemical loss can perturb the equilibrium particulate fraction at typical atmospheric concentrations of O3 and OH. For the surface reaction with O3, the perturbation is significant and increases with the gas-phase concentration of O3. Conversely, perturbations are smaller for reaction with the OH radical, which reacts with pyrene on both the surface of particles and in the gas phase. Global and regional chemical transport models typically approximate gas–particle partitioning with instantaneous-equilibration approaches. We highlight scenarios in which these approximations deviate from the explicitly coupled treatment of gas–particle partitioning and chemistry presented in this study. We find that the discrepancy between solutions depends on the operator-splitting time step and the choice of time step can help to minimize the discrepancy. The findings and techniques presented in this work not only are relevant for PAHs but can also be applied to other semi-volatile substances that undergo chemical reactions and mass transport between the gas and particle phase.

Surfactant-EOR in tight oil reservoirs: Current status and a systematic surfactant screening method with field experiments

Tight oil reservoirs typically have an estimated ultimate recovery of less than 10% after hydraulic fracturing, where enhanced oil recovery (EOR) technique is needed. Comparing to the gas-EOR, the surfactant-EOR neither alters the current fracturing procedure nor requires special injection facilities, and thus can be economically-viable under the current environment of low oil prices. However, tight rocks have small pores and large specific surface areas, which can make the adsorption rate of surfactants significant and thus limit the penetration depth of surfactants and its enhancement on oil recovery. In the published studies on the surfactant-EOR for shales and other tight reservoirs, this key parameter is only measured with the crushed rock samples, which can be underestimated comparing to that in the intact rock. Moreover, the dispersion coefficient that determines the penetration speed of a surfactant has never been directly measured in the tight rock, and the potential interaction between the surfactant and the friction reducer has neither been studied. In this study, a new form of surfactants is introduced, in which the wettability-alteration surfactants are firstly synthesized into oil-in-water microemulsions and then diluted to a designed concentration in the fracturing fluid. The thermodynamically-stable structure of microemulsion can minimize the adsorption rate of surfactants when transporting in the tight rock. Using coreflood experiments with UV–vis spectroscopy, the adsorption rate and dispersion coefficient of this form of surfactants are directly measured in tight rocks with a range of permeabilities, which are key parameters to modeling the EOR process and further scaling up laboratory findings for designing a field operation. To ensure the success of the surfactant-EOR technique in the field, the chosen surfactant needs to pass the preliminary screening including the aqueous stability test, the emulsion tendency test, the oil-water IFT measurement, and the shearing test; besides, it is also crucial to examine the compatibility between the slickwater and the wettability-alteration surfactant with different electric charges, which is seldom reported yet. In the end, the chosen surfactant is tested in two pairs of horizontal wells on one pad site, whose flowback water is collected and analyzed for better understanding the behavior of this surfactant.

Adsorption kinetic modeling of toxic vapors on activated carbon in the batch reactor

The compound ortho-chlorobenzylidene malononitrile (OCM) is the defining component of tear gas commonly referred to as CS gas. In present work, at first, OCM was changed from solid state to aerosol form (vapor) using thermal technique and then the kinetics of adsorption of OCM aerosol on a cylindrical activated carbon was experimentally investigated. For this purpose, an experimental setup was designed and manufactured for measurement of adsorbed-gas equilibrium pressure. The effects of the initial weight of OCM (3–15 mg) and time of adsorption were studied. The kinetic adsorption data were correlated with eight different models in order to select the best model for this system. The kinetic adsorption data were well described by fractal-like pseudo-first order (FL-PFO) with high correlation coefficient (average R2 > 0.9963) and the appropriate physical interpretation of model coefficients. In addition, the t test results confirm the high capability of FL-PFO model for the analysis of the kinetic data. The obtained results showed that the equilibrium adsorption time significantly increased and the adsorption rate coefficient decreased (to a minimum value) with increasing initial weight of OCM. Also, the analysis of adsorption data for this system confirms that there are heterogeneous sites in the adsorbent surface with different adsorption energies.

Low‐Spin‐State Hematite with Superior Adsorption of Anionic Contaminations for Water Purification

Hematite attracts intensive interest as an adsorbent for water purification, but the oversized dimension and inherent high-spin Fe(III) restrict its adsorption capability and kinetics. Herein a spatial-confinement strategy is reported that synthesizes ultrafine α-Fe2 O3 benefiting from nanogrids constructed by predeposition of TiO2 nanodots in the MCM-41 channel, and that tunes the spin-state of Fe(III) from high-spin to low-spin induced by the strong guest-host interaction between the ultrafine Fe2 O3 with SiO2 (MCM-41). The low-spin Fe(III) endorses strong bonding with anionic adsorbates, and significantly facilitates the electrons transfer from Fe2 O3 to SiO2 to form a highly positive charged surface, and thereby shows superior electrostatic multilayer adsorption performance to different kinds of anionic contaminations. Specifically, the maximum uptake, adsorption rate, and distribution coefficient (Kd ) for Rose Bengal dye reach as high as 1810 mg g-1 , 1644 g (g min)-1 , and 2.2 × 106 L kg-1 , which are more than 8, 230, and 3700 times higher than those of commercial activated carbon, respectively. It also shows outstanding purification performance for real field water. It is demonstrated that a strong guest-host interaction can alter the spin-state of transition metal oxides, which may pave a new way to improve their performance in adsorption and other applications like catalysis.

Determining rate coefficients for ion adsorption at the solid/water interface: better from desorption rate than from adsorption rate.

One of the most common approaches in the adsorption kinetics literature is to compare the fitting performance of several empirical or non-empirical equations (pseudo-first order, pseudo-second order, Elovich, parabolic diffusion, etc.) with the aim of selecting the equation that best describes the experimental data. This is normally a futile fitting exercise that leads to the determination of ambiguous rate parameters, without providing insights into the behaviour of the studied system. A more realistic approach is to treat it as a combination of mass transport and chemical reaction under controlled conditions, and thus actual adsorption-desorption rate parameters are readily estimated. This article applies a simple and realistic physicochemical model to describe and understand the adsorption-desorption kinetics of ions at the solid/water interface. The model is applied to an ATR-FTIR study of phosphate adsorption-desorption on goethite, which is a very well-known and reference system, ideal for testing the performance of a physicochemical treatment that combines transport and reaction. Always the same phosphate species (monodentate mononuclear protonated) was present at the goethite surface during adsorption-desorption. There was an excellent agreement between theory and experiments at a variety of phosphate concentrations and surface coverages for adsorption kinetics, desorption kinetics and equilibrium situations, employing just one set of rate coefficients. The use of rate vs. adsorption curves permitted easy detection of conditions of transport- and reaction-controlled kinetics. The phosphate-goethite system is a fast-adsorbing/slow-desorbing system, with an adsorption rate constant k = 1.26 × 103 s-1 and a desorption rate constant kd = 1.66 × 10-5 s-1. Therefore, adsorption was transport-controlled and desorption was reaction-controlled. The half-life of the desorption reaction is 41 700 s (11.6 h) but for adsorption it would take only a few seconds in the absence of transport control. For this kind of system, which is ubiquitous in nature and technological processes, it is easier to determine rate constants from desorption than from adsorption experiments.

Thermal conductivity and sorption performance of nano-silver powder/FAPO-34 composite fin

Desiccant coated aluminum fins are an important part of desiccant coated heat exchangers (DCHEs). The overall performance of DCHE-based systems benefits from improved heat and mass transfer characteristics of desiccant coated aluminum fins. In this paper, a new type of nano-silver powder supported FAPO-34 composite fin is proposed. Samples with different mass percentages of nano-silver powder were fabricated and related characteristics including thermal conductivity, cycle water uptake and adsorption/desorption performance were investigated. Our experimental results show greatly improved thermal conductivity of nano-silver powder supported composite sheets. Analysis of the adsorption testing confirmed that the nano-silver powder improved dynamic adsorption performance, and adsorption rate coefficients of composite sheets increasing by 6–103% compared with that of a pure FAPO-34 coated sheet. The composite samples also exhibited better dynamic desorption performance, in that their desorption rate coefficients increased to be 1.3–2.3 times as great as those of the pure FAPO-34 sample.

Effect of Hydraulic Liquid and Sea Water on the Mechanical Characteristics of Polymeric Fibrous Structures

The degradation of the mechanical characteristics of typical composite materials under the action of the working liquid is studied. Polypropylene and epoxy specimens reinforced with a glass fabric with the warp fiber orientation 0, ± 45, and 90° have been investigated according to the ISO 527-4 standard. The materials were a polypropylene composite based on stitched glass fabric and an epoxy-bonded glass fabric and carbon fabric reinforced composite. The basic mechanical characteristics of the materials under investigation have been determined. The specimens were kept in an AMg10 hydraulic liquid and in sea water for 910 hours with periodic weighing. The characteristics of the process of adsorption of working liquids by the materials under investigation: adsorption rate coefficient and the maximum amount of the adsorbed liquid have been determined. An investigation to detect damages caused by the liquids adsorbed by materials has been carried out. The specimens with adsorbed liquids were held at 255–373 K with subsequent tensile test. It has been found that the liquid in the material causes its swelling owing to liquid pressure. It is assumed that the characteristics degrade in proportion to swelling pressure. The effect of the above liquids on the strength characteristics of the materials under investigation has been studied by keeping them in these liquids for different time intervals (0–840 h), followed by a tensile test. The effect of through-thickness stitching along the test direction 90° on the mechanical characteristics of a material with a liquid in comparison with other test directions has been studied. The laws governing the effect of the above liquids on the mechanical characteristics of materials in time have been established. Based on experimental data, a model of the behavior of the composite under investigation under the above conditions has been developed, and numerical calculations have been performed. The calculated curves give a fairly good fit to experimental data, which confirms the described approach to be correct.