Homogeneous Surface Diffusion Research Articles

Batch and continuous adsorption of Cu(II) and Zn(II) ions from aqueous solution on bi-functionalized sugarcane-based biosorbent.

A new one-pot synthesis method optimized by a 23 experimental design was developed to prepare a biosorbent, sugarcane bagasse cellulose succinate pyromellitate (SBSPy), for the removal of Cu(II) and Zn(II) from single-component aqueous solutions, in batch and continuous modes. The bi-functionalization of the biosorbent with ligands of different chemical structures increased its selectivity, improving its performance for removing pollutants from contaminated water. The succinate moiety favored Cu(II) adsorption, while the pyromellitate moiety favored Zn(II) adsorption. Sugarcane bagasse (SB) and SBSPy were characterized using several techniques. Analysis by 13C Multi-CP SS NMR and FTIR revealed the best order of addition of each anhydride that maximized the chemical modification of SB. The maximum adsorption capacities of SBSPy for Cu(II) and Zn(II), in batch mode, were 1.19 and 0.95mmolg-1, respectively. Homogeneous surface diffusion, intraparticle diffusion, and Boyd models were used to determine the steps involved in the adsorption process. Isothermal titration calorimetry was used to assess changes in enthalpy of adsorption as a function of SBSPy surface coverage. Fixed-bed column adsorption of Cu(II) and Zn(II) was performed in three cycles, showing that SBSPy has potential to be used in water treatment. Breakthrough curves were well fitted by the Thomas and Bohart-Adams models.

Utilization of Modified Attapulgite for the Removal of Sr(II), Co(II), and Ni(II) Ions from Multicomponent System, Part I: Kinetic Studies.

Radionuclide sorption by natural and modified clays is extensively accepted to be an important process from the radioactive waste point of view. This work focused on modification of natural attapulgite with a layered double hydroxide to produce a novel chemisorbent for Sr2+, Ni2+, and Co2+ removal from multicomponent solution. The structural and surface characteristics of both attapulgite (ATP) and modified attapulgite (LDH-ATP) were investigated using XRD, FTIR, SEM, and thermal analysis. Comparison of sorption features of Sr2+, Ni2+, and Co2+ onto ATP and LDH-ATP was achieved; the results indicated that LDH-ATP was the most efficient sorbent for Sr2+, Ni2+, and Co2+. Kinetic studies established that the sorption is fast and reaching >90% within 30 min. The sorption of Sr2+, Ni2+, and Co2+ are well defined by non-linear pseudo-second-order model and controlled by an intra-particle diffusion mechanism. The diffusivity was determined using homogeneous surface diffusion (HSDM) model and found in the order 10-13 m2/min; this confirmed that the sorption of the three ions is chemisorption process. LDH-ATP can be employed as a candidate chemisorbent for the removal of some metal ions from waste solution.

Modeling of adsorption kinetics and equilibria of acid dyes onto activated carbon in single- and binary-component systems

Adsorptive removal of Acid Blue 127 and Acid Yellow 17 from their single and binary solutions has been studied using powdered activated carbon (PAC). The dyes used extensively for dying of nylon fiber in textile industry are known as Nylomine Blue P-B (NB) and Nylomine Yellow P-4G (NY), respectively. Time-dependent results obtained from single-component system have been better predicted by two resistance diffusion model rather than homogeneous surface diffusion. The magnitudes of film- and intraparticle diffusion coefficients calculated from McKay equation are ∼10−9 and ∼10−15 m2 s−1, whereas surface diffusion coefficients have been estimated as ∼10−13 m2 s−1 using Vermeulen approximation. Experimental equilibrium isotherms have been evaluated by changing initial dye concentrations in the range of 0.02–1.00 of mmol L−1. Freundlich isotherm parameters for individual solutions of the dyes have been used to predict their equilibrium behaviors in binary solutions by applying extended Freundlich model. Langmuir isotherm model and its extended form have also been fitted to the data for single- and binary-dye solutions, respectively. Thermodynamic functions derived from the temperature dependence of adsorption equilibrium constants in 298–318 K range show that adsorption processes are endothermic but spontaneous.

Modelling diffusion and adsorption of As species in Fe/GAC adsorbent beds

AbstractBACKGROUND: Arsenic decontamination of drinking water by adsorption is a simple and robust operation. When designing packed bed adsorbers for arsenic, the main problems are the slow diffusion kinetics of As in microporous media and the lack of simple equations for predicting the performance of the equipment. Commercial iron‐doped granular activated carbon adsorbents (Fe/GAC) for groundwater arsenic abatement were studied in this work. Basic parameters for arsenate (AsV) adsorption were measured and their performance at larger scale was simulated with an approximate analytical model.RESULTS: In the 0–300 µgAs L−1 range, the AsV adsorption isotherm on Fe/GAC was found to be approximately linear. Assuming Henry's law for adsorption and homogeneous surface diffusion with constant diffusivity for intrapellet mass transfer, an approximate model for flow and adsorption of arsenate inside packed bed adsorbers was developed, and reduced to an analytic compact solution using the quasi‐lognormal distribution (Q‐LND) approximation. The use of this model with fitted and reported parameters enabled the approximate simulation of industrial adsorbers and home point‐of‐use filters. Results show that industrial adsorbers meet the breakthrough condition with incomplete utilization of the adsorbent unless convenient process configurations are used. In point‐of‐use systems with short residence times intraparticle diffusion would drastically reduce the adsorbent performance.CONCLUSION: Assuming linear adsorption of AsV over Fe/GAC, an analytical approximate solution for flow and adsorption in packed beds can be obtained. The model seems to represent correctly the main features of industrial and home filters, however, more experimental data is necessary for scale‐up purposes. Copyright © 2011 Society of Chemical Industry

Equilibrium and kinetics of vancomycin adsorption on polymeric adsorbent

AbstractIsolation step of vancomycin, a glycopeptide antibiotic, is usually done from fermentation broth filtrate, while its adsorption directly from the whole broth could rationalize the process. The equilibrium and kinetics of vancomycin adsorption from broth supernatant, diluted and whole broth on polymeric adsorbent was studied in this work. Experimental equilibrium data was correlated with Sips, Langmuir, Freundlich, and linear adsorption isotherms. Agreement between measured and regressed data for the first three mentioned models did not vary much and was relatively high. The maximum adsorbed amount for supernatant was higher than for fermentation broths because mycelium particles blocked adsorbent surface. Liquid film mass transfer studies showed that external mass transfer resistance could have been neglected. Diffusion of vancomycin inside adsorbent particles was acknowledged using a nonstructural, homogenous surface diffusion and bidisperse pore models. Model simulations indicated that kinetics of the process could be improved by using smaller adsorbent particles. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Three-Component Competitive Adsorption Model for Fixed-Bed and Moving-Bed Granular Activated Carbon Adsorbers. Part I. Model Development

Heterogeneous natural organic matter (NOM) present in all natural waters impedes trace organic contaminant adsorption, and predictive modeling of granular activated carbon (GAC) adsorber performance is often compromised by inadequate accounting forthese competitive effects. Thus, a 3-component adsorption model, COMPSORB-GAC, is developed that separately tracks NOM adsorption and its competitive effects as a function of NOM surface loading. In this model, NOM is simplified into two fictive fractions with distinct competitive effects on trace compound adsorption: a smaller, strongly competing fraction that reduces equilibrium capacity and a larger pore-blocking fraction that reduces adsorption kinetics (both external film mass transfer and surface diffusion). COMPSORB-GAC tracks these two NOM fractions, along with the trace compound, and changes adsorption parameters according to the local surface loading of the two NOM fractions. Model parameters are allowed to vary both temporally and spatially to reflect differences in the NOM preloading conditions that occur in GAC columns. This dual-resistance model is based on homogeneous surface diffusion with external film mass-transfer limitations. The governing equations are expressed in a moving-grid finite-difference formulation to accommodate the modeling of spatially varying parameters and moving-bed reactors with counter-current adsorbent flow. A series of short-term adsorption tests with fresh and preloaded GAC is proposed to determine the necessary model input parameters. The accompanying manuscript demonstrates the parameterization procedure and verifies the model with experimental data.

Adsorption of Pesticides on Carbonaceous and Polymeric Materials from Aqueous Solutions: A Review

Carbonaceous and polymeric materials have been extensively used in adsorption processes for the removal of pesticides from aqueous solutions. The aim of this review is the systematic and comparative presentation of the possibilities of the above adsorbents, arising from the data reported in the literature for the period 1990–2004. A brief description of each article is given in tables. The data is divided into two groups, based on the chemical structure of adsorbent (carbonaceous or polymeric material) and is given in tables. In each table information on the type of adsorbent (powder, granular, fibers, cloths, resins, cartridges etc), pesticide structure, experimental conditions, aim and results of each work, is reported. In addition, data is included concerning single pesticides adsorption, competitive adsorption, parameters of adsorption isotherms (Langmuir, Freundlich, Dubinin–Radushkevich) and kinetic model's parameters (homogeneous surface diffusion model‐HSDM, equivalent background compound‐EBC, Peel model), such as surface diffusion coefficients and mass transfer coefficients. Information on adsorption yields, effect of various factors on adsorption effectiveness, static or continuous operation, laboratory, pilot or industrial scale process and combination of adsorption with other methods, is also included.

Pore Blockage Effects on Atrazine Adsorption in a Powdered Activated Carbon/Membrane System. I: Model Development

The mechanism of pore blockage plays an important role in competitive adsorption of trace organic compounds by microporous materials, such as activated carbon. An accurate description of the pore blockage effect of natural organic matter (NOM) on adsorption kinetics is a necessary part in the development of kinetic models for process design and performance prediction. In this study, a bisolute kinetic model based on homogeneous surface diffusion was developed to predict atrazine adsorption in a continuous flow powdered activated carbon (PAC)/membrane filtration system, incorporating the pore blockage effect. In order to elucidate the pore blockage effect, the system used in this study was simplified by representing the pore-blocking fraction of NOM with a single compound, poly(styrene sulfonate) with a nominal molecular weight of 1,800 Dalton. The surface diffusion coefficient of atrazine was modeled as a function of the surface concentration of the pore-blocking compound, which was also calculated by the model. The adsorption process was modeled for PAC application as either a pulse input or a step input; the quality of membrane backwash water was also used as a variable. Part II of this study, which appears in the companion paper, presents the model verification with a bench-scale PAC/microfiltration system, as well as model simulations that show optimal operating conditions for this system.

Adsorption and desorption studies in the aqueous phase for the toluene/activated carbon system

AbstractThe activated carbon adsorption and desorption of toluene in single‐component aqueous solutions were investigated. Adsorption equilibrium and batch rate studies were conducted to measure the capacity of Filtasorb‐300 (F‐300) for toluene and to determine the effects of the initial toluene concentration, the F‐300 particle size, and the hydrodynamic conditions in the liquid phase on the rate of toluene adsorption on F‐300. The results of the adsorption rate experiments were successfully fitted with the homogeneous surface diffusion (HSD) model and a surface diffusion coefficient which varies exponentially with surface coverage. The model also accounted for the dependence of the external toluene mass transfer coefficient on the hydrodynamic conditions in the liquid phase. The reversibility of toluene adsorption on F‐300 was addressed in desorption equilibrium experiments which indicated that only about five percent of the toluene molecules adsorb irreversibly on the surface of F‐300. Batch desorption rate studies were conducted for different initial toluene surface concentrations, F‐300 particle sizes, and liquid/solid ratios. Use of the previously determined toluene transport parameters in the HSD model allowed for successful prediction of the experimental desorption rates.

GAC Adsorber Design for Removal of Chlorinated Pesticides

The cost-effective removal of alachlor and heptachlor from drinking water by GAC adsorption was investigated. Alachlor and heptachlor represent two classes of chlorinated pesticides, the acetanilides and the cyclodienes, respectively. Transformation of these pesticides prior to and upon adsorption is an important aspect concerning their fate. In aqueous solution, heptachlor undergoes complete hydrolysis to 1-hydroxychlordene (1-HC) with a half-life of three days decreeing the use of 1-HC in GAC investigation. The dispersed-flow homogeneous-surface diffusion model (DFHSDM) was used for predicting the dynamic behavior of the fixed-bed adsorber for the target pollutants. Model parameters were obtained from bench-scale equilibrium, rate, and mini-column experiments. The model was able to successfully predict/simulate mini-column data in both organic free water and humic acid background solution. Significant reduction in adsorber performance was experienced in the presence of humic acid dur to competitive interaction. Full-scale adsorbers were designed through up-scaling procedures to estimate carbon utilization rates. Cost for removal of alachlor was $0.113/1,000 gal ($0.03/m³) treated in a 10-mgd (38 × 10³ m³/day) plant with 5-min EBCT, and 4 gpm/sq ft (235 m³/m²/d) surface loading for an influent concentration of 100 μ\Ng/L and treatment objective of 2 μ\Ng/L. The cost was increased to $0.135/1,000 gal in the presence of humic acid. The cost for removal of 1-HC was, in general, 30% higher than that for alachlor.