http://repository.ust.hk/ir/bitstream/1783.1-645/1/323k.pdf

A comparison of chemisorption kinetic models applied to pollutant removal on various sorbents

A review of the mechanisms of solute sorption onto various biosorbents has been performed. The mechanisms have been subdivided into reaction based systems and diffusion based systems and the literature has been reviewed in accordance with these two groups. The range of solute-sorbent systems reviewed include metal ions, dyestuffs and several organic substances in aqueous systems onto a wide range of biosorbents and mineral earths. Extensive tables are presented summarising isotherm types, sorption capacities, kinetic models which have been applied particularly to biosorbent systems but also to many other adsorbent materials.

http://dns2.asia.edu.tw/~ysho/YSHO-English/Publications/PDF/Sep%20Pur%20Met29,%20189.pdf

Kinetics of pollutant sorption by biosorbents: review

Chitin is the world's second most abundant naturally occurring polysaccharide. Much of this is disposed of as waste from seafood crustacean, mainly in shrimps, prawns, crabs, and lobsters, where it occurs as a significant component in the shells/exoskeletons of crustacea. Due to its widespread abundance, its chemical and physical versatility, and the problems of its disposal as a waste material, a wide range of value-added applications of chitin and chitosan is being initiated, investigated, and developed. The widely ranging value-added applications of chitin and chitosan are presented in this review. Chitin and its derivative, chitosan, both highly stable and difficult to degrade materials, can be obtained as 10–20% w/w from the waste seafood shells by suitable chemical processing. One of the significant developments in the new range of applications is the study of the ability of chitosan, as a potentially major environmental treatment material, to remove metal ions from wastewaters. Chitosan is the deac...

Application of Chitosan for the Removal of Metals From Wastewaters by Adsorption—Mechanisms and Models Review

In modeling subsurface contaminant transport, sorption is often simplified by assuming instantaneous equilibrium, isotherm linearity, and sorption‐desorption singularity. Data exhibiting behavior that deviates from that predicted by this simple model have been reported, challenging the validity of these assumptions. This nonideal sorptive behavior has been attributed to several different factors, including kinetic sorption reactions, diffusive mass transfer resistances, isotherm nonlinearity, and sorption‐desorption nonsingularity. These factors are examined and their relative impact on contaminant transport is evaluated. For hydrophobic organic compounds, physical nonequilibrium (i.e., rate‐limited mass‐transfer in aggregated or layered systems) and intraorganic matter diffusion (rate‐limited diffusion within the sorbent organic matter matrix) are probably the predominant factors causing nonideality. The relative importance of these factors is scale‐dependent. For smaller scale systems, mass‐transfer lim...

Sorption nonideality during organic contaminant transport in porous media

Industries generating wastewater with elevated concentrations of pollutants (e.g. metals, dyes, phenolic compounds, anions, etc.) need specialized atreatment systems. Adsorption is one of the most extensively applied techniques for the removal of pollutants from the industrial effluents. The prominent and emerging trend of subjecting biosorbent in the adsorption technology is mainly because of their natural existence, abundance, renewable, biodegradable and economic features. The adsorption isotherm equations used to describe the experimental data and the thermodynamic assumptions of the models often provide some insight into the sorption mechanism, the surface properties and affinity of the biosorbent. This paper presents a state of the art on the review of adsorption isotherm models in an exhaustive manner on the basis of two, three, four and five parameters respectively. Focuses on the various sources of agricultural byproducts as biosorbents and describes on the potential applications of different adsorption isotherm models for the evaluation of the wastewater pollutants biosorption. It is evident from the literature survey that various adsorption isotherm models have been considered under study by the researchers but mostly two and three parameter isotherm model were best fitted the equilibrium data. This paper reviews the adsorption isotherm models on the basis of parameters that can be applied for exploring a novel biosorbents.

Relevance of isotherm models in biosorption of pollutants by agricultural byproducts

A branched pore kinetic model for aqueous phase activated carbon adsorption is presented in which the carbon particle is separated into rapidly and slowly diffusing regions. The model was developed to overcome problems arising from a single rate parameter analysis and is shown to describe experimental data well. In addition to very different rates of transport in the two regions, parameters estimated by regression analysis indicated differences in the adsorptive charac- teristics. As an approximation to the microscopic description of the diffusional process, a model has been developed in this work which divides the carbon particle into two regions of different diffusion rates. The regions are loosely termed macropores and micropores. (These terms should not be confused with their conventional uses to define certain pore size ranges.) Relatively rapid diffusion and adsorption occur in the macropores, and the remaining slow approach to equilibrium occurs in the mi- cropores. The micropores are assumed to be homogeneously distrib- uted throughout the particle and to branch off the larger mac- ropore network which is responsible for radial transport. A schematic diagram of the proposed model is shown in Figure 2. In many respects, the model is similar in form to the dual rate models developed for catalysts of pelletized microporous parti- cles or for molecular sieves (Furusawa and Smith, 1973b; Ruckenstein et al., 1971; Shah and Ruthven, 1977). However, it is not possible to define the dimensions of the microporous sub-units when dealing with activated carbons. Thus, a lumped parameter approach was used to describe diffusion in the micropores. A surface diffusion mechanism was assumed to be responsible for transport in the macropores. Batch kinetic experiments were conducted over extended periods using a closed system, liquid-phase Carberry reactor to obtain accurate data for evaluation of the model parameters. CONCLUSIONS AND SIGNIFICANCE Experimental data collected for the adsorption of phenolics onto activated carbon are accurately described by the pro- posed model. The data show that the observed behavior during a batch kinetic experiment, if followed for a sufficiently long period, is not consistent with a single intraparticle diffusion rate model. Furthermore, by viewing activated carbon adsorp- tion as a dual mechanism rather than as a single mechanism process, equilibrium isotherms and relatively short-term batch kinetic data can be shown to be compatible. From the model parameters which were obtained by regression analysis of the data, several conclusions can be drawn. Measured surface diffusion coeffwients within the macro- pore network are comparable to previously reported

A branched pore kinetic model for activated carbon adsorption

Attainment of equilibrium in activated carbon isotherm studies involving the adsorption of phenol and o-chlorophenol from 10 g/l. aqueous solutions onto Filtrasorb F400 activated carbon at 20C showed that extended contacting periods should be allowed during isotherm evaluations to ensure that equilibrium is obtained. Granular activated carbon (12 x 40 mesh) took up to three weeks to reach equilibrium with phenol and up to five weeks with o-chlorophenol; powdered carbon (passed through a No. 200 US Standard Sieve) isotherms took 3-5 days to reach equilibrium. Up to 80% of the adsorptive equilibrium was reached in the first few hours but the remaining capacity was utilized very slowly, which explains variations in isotherm behavior previously reported in the literature. The results were satisfactorily correlated by a dual-rate model involving macro- and micropores with differing diffusion rates and mechanisms.

Attainment of equilibrium in activated carbon isotherm studies

An activated carbon adsorption model is presented which predicts performance of adsorption beds using parameters evaluated from batch tests. The proposed dual rate model assumes that a fraction of ...

Russell G. Peel

Papers

A branched pore kinetic model for activated carbon adsorption

Attainment of equilibrium in activated carbon isotherm studies

Dual Rate Kinetic Model of Fixed Bed Adsorber