A simplified equilibrium model for sorption of heavy metal ions from aqueous solutions on chitosan

The amounts of sorption of Cu2 , Ni2+, and Zn2+ from water on cross-linked chitosan were measured. Experiments were performed as a function of initial pH (2-5), total metal concentration (0.77-17 mol/m3), and metal concentration ratio (0.25-4) at 25 degrees C in single- and binary-metal systems. The sorption was so highly pH dependent that the isotherm could not be described by one specific equation. A simplified equilibrium model was thus proposed considering competitive sorption of proton and metal ions. The number of active sites on chitosan bound with one metal ion was adjustable and model parameters could be graphically determined. Given initial metal concentrations and solution pH, the proposed model could predict the amounts of sorption of proton and metals as well as the equilibrium pH. In general, application of the model parameters calculated in single-metal systems to the prediction of sorption in binary-metal systems was not satisfactory due to a remarkable effect of competitive sorption.     

Removal of copper ions from aqueous solution by tree fern

Tree fern, an agricultural by-product, was used for the sorptive removal of copper ions from aqueous solution. The experimental data was analysed by Langmuir, Freundlich and Redlich-Peterson isotherms. The equilibrium sorption capacity of copper ions was determined from the Langmuir equation and found to be 11.7 mg/g. A batch sorption model, based on the assumption of the pseudo-second-order mechanism, was developed to predict the rate constant of sorption, the equilibrium sorption capacity and the initial sorption rate with the effect of initial copper ion concentration and the tree fern dose. Various thermodynamic parameters, such as Delta G(0), Delta H(0) and Delta S(0), have been calculated. The thermodynamics of copper ion/tree fern system indicates spontaneous and endothermic nature of the process.     

Modeling Sorption Transport In Rooms And Sorption Filtration Systems For Building Air Quality Analysis

Adsorption, desorption and chemisorption are known to impact the dispersal of volatile organic and chemically reactive compounds in buildings. These same three processes may be used to advantage to control the levels of these compounds indoors using building sorption filtration devices. To add to the understanding of these processes, to provide the means to predict the impact of these processes on human exposure and to provide the tools needed to design gaseous filtration systems to mitigate the exposure to these compounds, a general approach to modeling the dynamics of these processes is presented. Equations are presented to account for the elemental advection, diffusion, sorption, and chemical transport steps affecting single component sorption dynamics in rooms and sorption filtration systems. These element equations are based on general principles and formulated in terms of fundamental physical parameters that may be determined using standard procedures. Models to predict room and sorption filtration system dynamics are formulated using assemblages of these element equations and a series of simplified models of these systems are derived. Initial applications to model single-component sorption transport in rooms and sorption filtration systems indicate that the approach has the potential to provide accurate predictions providing the sorption and chemical characteristics of the sorbate-sorbent system being considered are well-characterized. This potential is, however, compromised by the lack (or present uncertainty) of fundamental data relating to sorption equilibrium, porous diffusion, surface chemistry, and boundary layer mass transport     

Atrazine sorption on surface soils: time-dependent phase distribution and apparent desorption hysteresis

Non-equilibrium sorption-desorption behavior of atrazine was studied on two surface soils. Impact of sorption contact time was evaluated by interpreting temporal variations in Freundlich sorption isotherm parameters n(t) and K(F)(t) obtained from the phase distribution relationships. The extent of sorption linearity was very similar (n approximately 0.90) for the two soils at all sorption contact times. K(F)(t) increased with contact time and stabilized upon reaching apparent equilibrium. K(F) for woodland soil was significantly higher than that for agricultural soil. The Apparent Hysteresis Index (AHI) parameter was used to quantify sorption-desorption hysteresis arising from non-equilibrium sorption. AHI was a function of the sorption contact time and correlated well with K(F)(t). The woodland soil sorbed more herbicide due to its higher organic matter content. However, a larger fraction of the herbicide sorbed to this soil was released rapidly (within 24 h) following sorptive uptake. The differences in sorption-desorption behavior of atrazine in the two soils appear to be related to variations in the type and location of organic matter in the two soils. The parameters K(F)(t) and AHI(t) consistently demonstrated the effects that arise when batch systems are not brought to equilibrium during sorption studies.     

Modeling the sorption kinetics of divalent metal ions to hematite

The sorption kinetics of the divalent metals Zn, Co, Ni, and Cd to hematite were studied in single sorbate systems with high sorbate/sorbent ratios (from 1.67 to 3.33mol sorbate/mol sorption sites) in 10mM Na-piperazine N,N'-bis 2-ethane sulfonic acid (Na-PIPES) solution at pH 6.8. The experimental data showed a rapid initial sorption (half-time about 1min) followed by slower sorption that continued for 1-5 days. The sequence of fast to slow sorption kinetics was modeled by slow inner-sphere (IS) complexation in equilibrium with outer-sphere (OS) complexes. Although the OS reaction was fast and considered to be in equilibrium, the extent of OS complexation changed over time due to increased surface potential from the IS complexes. For example, the model showed that the dimensionless OS complexation function, K(os), decreased from 0.014 initially to 0.0016 at steady state due to sorption of 4x10(-5)M Zn(II) to 2gL(-1) hematite. Sorption rate constants, k(ads), for the various divalent metals ranged from 6.1 to 82.5M(-1)s(-1). Desorption rate constants, k(des), ranged from 5.2x10(-7) to 6.7x10(-5)s(-1). This study suggests that the conversion from OS to IS complex was the rate-determining step for the sorption of divalent metals on crystalline adsorbents.     

A new application of giant reed waste material for ammonium removal

Excess nitrogen is one of the main causes of eutrophication in water bodies. In this study, the undesirable agricultural lignocellulosic material giant reed was used to remove ammonium ions from aqueous solutions. Batch experiments were conducted to investigate the effect of various parameters such as contact time, initial ammonium concentration, adsorbent dosage, pH, particle size, agitation rate and phosphate coexisting during the ammonium adsorption process. The ammonium sorption capacity of fibrous giant reed (FGR) at equilibrium was 12.49?mg?N/g with a maximum removal efficiency of 76% observed within 30?min at pH range of 6.5–9.5. Results revealed that the Freundlich isotherm model fitted better with the sorption process than the Langmuir model, and the adsorption process was well described by pseudo-second-order kinetic model. FT-IR analyses indicated that complexation and ion exchange could be the main mechanisms for the ammonium removal by FGR. Results revealed that FGR has a sorption capacity comparable to that of other natural sorbents with the advantage of greater availability with no cost.     

Sorption of hydrophobic compounds by sediments, soils and suspended solids—II. Sorbent evaluation studies

Concepts underlying the sorption of hydrophobic compounds and models for representation of observed equilibrium relationships were presented in Part I of this series. The earlier paper also summarized and evaluated major factors which affect the sorption of pollutants in natural environmental systems. This second part of the series presents a detailed summary and evaluation of the sorption of a particular class of hydrophobic pollutants, polychlorinated biphenyls (PCB), on a variety of different types of sediments, soils, suspended solids, and microorganisms. Equilibrium models described in Part I are used here to describe and analyze the PCB sorption data.     

Sorbed atrazine shifts into non-desorbable sites of soil organic matter during aging

Soil-chemical contact time (aging) is an important determinant of the sorption and desorption characteristics of the organic contaminants and pesticides in the environment. The effects of aging on mechanism-specific sorption and desorption of atrazine were studied in soil and clay slurries. Sorption isotherm and desorption kinetic experiments were performed, and soil-water distribution coefficients and desorption rate parameters were evaluated using linear and non-linear sorption equations and a three-site desorption model, respectively. Aging time for sorption of atrazine in sterilized soil and clay slurries ranged from 2 days to 8 months. Atrazine sorption isotherms were nearly linear (r(2)>0.97) and sorption coefficients were strongly correlated to soil organic carbon content. Sorption distribution coefficients (K(d)) increased with increase in age in all five soils studied, but not for K-montmorillonite. Sorption non-linearity did not increase with increase in age except for the Houghton muck soil. Desorption profiles were well described by the three-site desorption model. The equilibrium site fraction (f(eq)) decreased and the non-desorbable site fraction (f(nd)) increased as a function of aging time in all soils. For K-montmorillonite, f(nd) approximately 0 regardless of aging, showing that aging phenomena are sorbent/mechanism specific. In all soils, it was found that when normalized to soil organic matter content, the concentration of atrazine in desorbable sites was relatively constant, whereas that in non-desorbable site increased. This, and the lack of aging effects on desorption from montmorillonite, suggests that sorption into non-desorbable sites of soil organic matter is primary source of increased atrazine sorption in soils during aging.     

Sorption kinetic analysis for the removal of cadmium ions from effluents using bone char

The adsorption of cadmium ions onto bone char has been studied using a batch adsorber. The experimental data was analyzed using four sorption kinetic models--the pseudo-first order, the Ritchie second order, the modified second order and the Elovich equations--to determine the best-fit equation for the sorption of metal ions onto bone char. The best-fit equation was identified using the sum of the errors squared (SSE). Finally, equilibrium studies were used to evaluate the sorption capacity of bone char for cadmium ions and experimental results showed this to be 0.57 mmol g-1 at an equilibrium solution concentration of 3.0 mmol dm-3. Since the sorption capacity is relatively high, bone char can be considered as a suitable sorbent for the adsorption of cadmium in wastewater treatment systems.     

Implications of short and long term (30 days) sorption on the desorption kinetic of trace metals (Cd, Zn, Co, Mn, Fe, Ag, Cs) associated with river suspended matter

The desorption kinetic of trace elements (Cd, Zn, Co, Mn, Fe, Ag, and Cs) associated with Loire river natural suspended particulate matter (SPM; 0.4-63 microm) was followed up on times varying from 0.5 h to 30 days, from SPM previously contaminated during 1 h, 24 h and 30 days. Long term sorption kinetics indicated that the difference between sorption occurring during the period 0-30 days (time investigated in this study) and the period 0-48 h (time often used for sorption experiments) ranges from few to 25% according to the element. Desorption kinetics show that, whatever the age of the complex formed during the sorption step, the release tends to equilibrium between complexed and dissolved elements equivalent to the equilibrium obtained for sorption after a given time. However, the time to get this equilibrium depends on the aging of the complex and on the element. All the above features indicate different types of complexes formation and strength of the binding according to the age of the complex and according to the element. Using a multi-compartmental model, simulating the transfer of metals between water and different types of particulate sites, the relationships between the parameters describing slow and rapid processes helped in explaining the "aging" effect observed.     

非饱和土层中污染物运移过程的数值分析

针对填埋场下部为压实粘土衬里、非饱和土层和含水层的三层结构体系,建立了描述填埋场污染物运移的一维控制方程,在控制方程中考虑了压实粘土衬里的平衡非线性吸附方程与非饱和土层的线性吸附方程。采用数值法求解控制方程,通过变动参数探讨了污染物在三层结构体系中运移过程的各种影响因素。     

Wasserdampfsorptionsverhalten ausgewählter heimischer und überseeischer Holzarten

Water vapour sorption behaviour of selected domestic and overseas wood species. At 21 domestic and 11 overseas wood species the equilibrium moisture content at 20 °C and 35, 50, 65, 80 and 95% relative humidity was experimentally determined in the adsorption phase. The experimentally determined average values were computed with help of the Hailwood Horrobin model to get selected parameters such as fiber saturation point, mono‐ and polymolecular sorption, specific surface, hypothetical molecular weight as well as inaccessibility of the sorbent to the sorbate. Tables for the equilibrium moisture contents at 20 °C computed in 2% steps of relative humidity are presented. The fiber saturation point computed with the Hailwood‐Horrobin model lies for all examined wood in the range from 22% to 36%, on the average with approx. 30%. There are substantial deviations in the fiber saturation point between the individual wood species. The tendencies for the characteristics of the sorption analysis were pointed out.     

Heavy metal removal by clinoptilolite. An equilibrium study in multi-component systems

Ternary and quaternary ion-exchange equilibria have been studied between heavy metal solution (Pb(2+), Cd(2+), Cu(2+)) and Na-form of clinoptilolite. The value of the ion-exchange equilibrium constant was estimated using the Langmuir, Competitive Langmuir, and thermodynamic sorption models. For each isotherm, calculations were done taking into account the concentration of ions in both phases. Additionally, for the thermodynamic isotherm, two other cases were considered: activity of ions in the liquid phase and concentration in the solid phase; activity of ions in both phases. The activity coefficients of ions in the liquid phase were determined using Pitzer's model; activity coefficients in the solid phase were estimated by Wilson's model. It was found that the exchange capacity for a given M(2+) is not constant and differs in one- or multi-component systems. The results show that the equilibrium model based on the law of mass action, which considers nonideal behavior of both phases, allows one to achieve the best approach to the real multi-component equilibrium data in all studied systems.     

Development of a kinetic basis for bioavailability of sorbed naphthalene in soil slurries

The degradation of naphthalene in soil-slurry systems was studied using four different organisms and two soils. Organisms with zero-order, first-order, and Michaelis-Menten rates were selected. The soils had substantially different sorption distribution coefficients. Sorption and desorption was evaluated in abiotic soil-slurry systems. The desorption process was described by a model that accounts for equilibrium, rate-limited and non-desorbing sites. Biodegradation parameters were measured in soil-extract solutions. Bioavailability assays, inoculated soil slurries, were conducted and both liquid- and sorbed-phase naphthalene concentrations were measured over time. For the less sorptive soil, the results could be explained by sequential desorption and degradation processes. For the other soil, enhanced degradation was clearly observed for the organisms with first-order and Michaelis-Menten rates. Several explanations are explored for these observations including direct sorbed-phase degradation and the development of elevated substrate concentrations at the organism/sorbent interface. No enhancement was found for the organism with zero-order kinetics.     

Sorptionsverhalten organischer Schadstoffe in heterogenem Aquifermaterial am Beispiel des Phenanthrens

In laboratory batch experiments equilibrium sorption and sorption kinetics of phenanthrene in the different petrographic components of a gravel aquifer material (river Neckar valley) and the source rocks of the valley sediments were investigated. The sorption coefficients depend on organic carbon content and the composition of the organic matter. The sorption kinetics follow the intraparticle pore diffusion modell. Diffusivities can be predicted from the intraparticle porosity analogous to Archie's Law. No significant influence of weathering processes and transport of the aquifer sediments was found for the sorption parameters.     

Estimation of saponite sorptive properties with regard to fluoride ions

Equilibrium sorption of fluoride ions by saponite has been investigated at pH of the equilibrium solution characteristic of natural waters. A theoretical model of the equilibrium sorption of fluoride ions by saponite exchange groups selective with regard to such ions was proposed. The total exchange capacity of the specified exchange groups and their equilibrium constant were also found.     

The sorption dynamics of sulfuric acid by weakly-basic polyacryl anion exchangers synthesized based on polyamines

The article has investigated the sorption dynamics of sulfuric acid by weakly basic polyacryl anion exchangers Relite MG 1 and Relite MG 1/P in the form of a free base within a broad range of filtration rate. It has been proved that a limiting stage for sorption kinetics in the hydrodynamic filtration modes characteristic of the operation of OH filters of the first stage of water desalination plants is internal diffusion. The process is satisfactorily described by an asymptomatic solution of the system of equations of the theoretical model of sorption internal-diffusion dynamics. It has been established that a type of the matrix of ion exchangers does not affect sulfuric acid sorption parameters. We have found a single value of the coefficient of mass transfer in sorption of sulfuric acid by any weakly basic polyacryl anion exchangers synthesized based on polyamines.     

Manganese-oxide-coated alumina: a promising sorbent for defluoridation of water

In this study, adsorption potential of a new sorbent manganese-oxide-coated alumina (MOCA) was investigated for defluoridation of drinking water using batch and continuous mode experiments. The effects of different parameters such as pH, initial fluoride concentration and co-existing ions (usually present in groundwater sample) were studied to understand the adsorption behavior of the sorbent under various conditions. Optimum removal of fluoride ions occurred in a pH range of 4-7. Results of the present study indicate that fluoride adsorption rate and adsorption capacity of MOCA are far superior to that of activated alumina (AA), which was used as the base material for MOCA preparation. The MOCA can be effectively regenerated using 2.5% NaOH as eluent. The Langmuir equilibrium model was found to be suitable for describing the fluoride sorption on AA and MOCA. The maximum fluoride uptake capacity for MOCA and AA was found to be 2.85 and 1.08 mg g(-1), respectively. The kinetic results showed that the fluoride sorption to MOCA followed pseudo--second-order kinetics with a correlation coefficient greater than 0.98. The fluoride sorption capacity at breakthrough point for both the adsorbents was greatly influenced by bed depth. A bed depth service time (BDST) approach was adopted to describe the continuous flow system. The batch and column studies demonstrated the superiority of MOCA over AA in removing fluoride from the drinking water system.     

Development of multimetal binding model and application to binary metal biosorption onto peat biomass

Biosorption of Cr(3+), Cu(2+) and Cd(2+) from binary metal solutions onto peat in the batch systems was investigated at pH 4. The order of maximum uptake was Cr>or=Cu>Cd and maximum uptake levels of ca. 0.4 mmol/g were observed for chromium and copper while cadmium was taken up to a maximum of ca. 0.2 mmol/g. Co-ion competition resulted in up to 70 percent decrease of primary metal uptake. A novel approach to multicomponent sorption modelling involving regression to the total metal taken up was adopted. Two extended Langmuir-type models were found to exhibit good fit to the experimental data. Using the simpler model of these, three-dimensional sorption surfaces were generated which describe the metal uptake as a function of equilibrium concentrations of both metals. These methods allow prediction of metal uptakes over a continuum of concentrations of both metals in binary systems.