Intraparticle Diffusion Rate Constant Research Articles

Low cost bio-sorbent 'maize bran' for the removal of cadmium from wastewater

A novel biosorbent maize bran has been successfully utilised for the removal of cadmium(II) from wastewater. The maximum removal of cadmium(n) has been found to be 94.5% at pH 8.6, initial Cd concentration 1.25 mg L - 1 and temperature 20°C. The effect of different parameters such as contact time, adsorbate concentration, pH of the medium and temperature have been investigated. Dynamics of the sorption process were studied and the values of rate constant of adsorption, rate constant of intraparticle diffusion and mass transfer coefficient were calculated. Various thermodynamic parameters such as ΔG o , ΔH o and ΔS o have also been evaluated and critically discussed. It has been concluded that the reaction was spontaneous and exothermic in nature. The applicability of Langmuir isotherm suggests the formation of monolayer coverage of the adsorbate on the surface of adsorbents.

Kinetic Study of Erbium Ion Adsorption on Activated Charcoal from Aqueous Solutions

The kinetics of the adsorption of erbium ions on activated charcoal from aqueous solutions has been studied in the temperature range of 10 to 40∘C. It was observed that the diffusion of erbium ions in to the pores of activated charcoal controls the kinetics of the adsorption process, and the values of intra-particle diffusion rate constant, kd (g/g ⋅ min1/2) were evaluated as 0.7 × 10−3 to 1.6 × 10−3 in the temperature range studied. Various thermodynamic parameters Δ H, Δ G and Δ S were also computed from values of the equilibrium constant KC. The results showed that the adsorption of erbium ions on activated charcoal is an endothermic process.

Kinetics and thermodynamics of Methylene Blue adsorption on Neem ( Azadirachta indica) leaf powder

The dye, Methylene Blue, was adsorbed on an adsorbent prepared from mature leaves of the Neem tree ( Azadirachta indica). A batch adsorption study was carried out with variable adsorbate concentration, adsorbent amount, pH, and temperature. Ninety-three percent of the dye could be removed by 2 g of the Neem leaf powder from 1 L of an aqueous solution containing 25 mg of the dye at 300 K. The adsorption followed pseudo first order kinetics with a mean rate constant of 3.73 × 10 −3 min −1 and an intra-particle diffusion rate constant of 6.36 × 10 −2 mg g −1 min −0.5. A possible mechanism of adsorption was suggested on the basis of concurrently operating surface adsorption and pore diffusion. The experimental data yielded excellent fits with Langmuir and Freundlich isotherm equations. The Langmuir monolayer capacity had a mean value of 8.76 mg g −1. The adsorption of the dye was endothermic in nature (Δ H: 4.62–16.74 kJ mol −1) and was accompanied by an increase in entropy (Δ S: 54.22–90.23 J mol −1 K −1) and a decrease in Gibbs energy (Δ G: −10.33 to −13.62 kJ mol −1 in the temperature range of 300–330 K). The results indicated that the dye, Methylene Blue, strongly interacts with a biomass-based adsorbent, the Neem leaf powder.

Adsorption dynamics and equilibrium studies of Zn (II) onto chitosan

Batch equilibration studies are conducted to determine the nature of adsorption of zinc (II) over chitosan. The factors affecting the adsorption process like particle size, contact time, dosage, pH, effects of chloride and nitrate are identified. The influence of temperature and co-ions on the adsorption process is verified. The fraction of adsorption,Y t and the intraparticle diffusion rate constant,k p are calculated at different environments and the results are discussed. The nature of adsorption of the zinc (II)-chitosan system is explained using Freundlich, Langmuir isotherms and thermodynamic parameters

Separation of vitamin E from palm fatty acid distillate using silica: II: Kinetics of batch adsorption

The kinetics of vitamin E batch adsorption onto silica was detailed in this study; as functions of initial vitamin E concentration, reaction temperature, agitation rate and silica mass. For all systems, the adsorption occurred rapidly initially and then proceeded gradually to equilibrium in about 5 min. It was found that the fraction of vitamin E adsorbed onto the silica at equilibrium was higher when the initial vitamin E concentration in the solution was lower. However, the reverse was true for the effects of agitation rate and silica mass. Increasing the reaction temperature would result in lower adsorption capacity, suggesting that adsorption of vitamin E onto silica was exothermic in nature. Two main adsorption mechanisms were involved during the vitamin E adsorption, namely external mass transfer and intraparticle diffusion. The external mass transfer coefficient, k f, and rate constant of intraparticle diffusion, k id, were determined for each system. It was noted that increasing the initial vitamin E concentration resulted in a decrease in k f values, but an increase in k id values. Increase in agitation rate facilitated the adsorption processes and therefore increased both k f and k id values. Meanwhile, a higher silica mass gave a lower k id value, indicating that the intraparticle diffusion rate was lower. The activation energies were considered high (−25.45 and −54.13 kJ mol −1 for external mass transfer and intrapartiele diffusion, respectively) suggesting that the adsorption appeared to be a chemosorption rather than low energy physiosorption process.

Use of activated carbons prepared from sawdust and rice-husk for adsorption of acid dyes: a case study of Acid Yellow 36

Activated carbons, prepared from low-cost mahogany sawdust and rice husk have been utilized as the adsorbents for the removal of acid dyes from aqueous solution. An acid dye, Acid Yellow 36 has been used as the adsorbate. Results show that a pH value of 3 is favourable for the adsorption of acid dye. The isothermal data could be well described by the Langmuir and Freundlich equations. Kinetic parameters of adsorption such as the Langergren pseudo-first-order constant and the intraparticle diffusion rate constant were determined. For the present adsorption process, intraparticle diffusion of dye molecule within the particle has been identified to be rate limiting. The adsorption capacities of sawdust carbon (SDC) and rice husk carbon (RHC) were found to be 183.8 mg and 86.9 mg per g of the adsorbent respectively. The results indicate that SDC and RHC could be employed as low-cost alternatives to commercial activated carbon in wastewater treatment for the removal of acid dyes.

Use of cellulose-based wastes for adsorption of dyes from aqueous solutions

Low-cost banana and orange peels were prepared as adsorbents for the adsorption of dyes from aqueous solutions. Dye concentration and pH were varied. The adsorption capacities for both peels decreased in the order methyl orange (MO) > methylene blue (MB) > Rhodamine B (RB) > Congo red (CR) > methyl violet (MV) > amido black 10B (AB). The isotherm data could be well described by the Freundlich and Langmuir equations in the concentration range of 10–120 mg/l. An alkaline pH was favorable for the adsorption of dyes. Based on the adsorption capacity, it was shown that banana peel was more effective than orange peel. Kinetic parameters of adsorption such as the Langergren rate constant and the intraparticle diffusion rate constant were determined. For the present adsorption process intraparticle diffusion of dyes within the particle was identified to be rate limiting. Both peel wastes were shown to be promising materials for adsorption removal of dyes from aqueous solutions.

REMOVAL OF HEXAVALENT CHROMIUM BY ADSORPTION ONTO FIRECLAY AND IMPREGNATED FIRECLAY

The removal of hexavalent chromium from its aqueous solutions by adsorption onto fireclay (FC) and impregnated fireclay (IFC) has been studied at 30°C. The adsorption process follows the Langmuir-type adsorption behavior, and the extent of adsorption is more for impregnated fireclay. It is found that electrostatic and H-bonding interactions play a key role in binding the adsorbate molecules to the adsorbent surface. The adsorption process is affected greatly by variation in pH and temperature of the system. Low pH and high temperature favor the adsorption process. Various kinetic and adsorption parameters such as rate constant for adsorption, intraparticle diffusion rate constant, diffusion coefficient, and adsorption capacity have been evaluated to reflect the experimental findings.

Reactivity of Coal Char with Steam and Carbon Dioxide

To develop a simulation-model of the Hokkaishi-coal gasification pilot plant, a kinetic analysis of coal-char gasification was investigated. Experiments were conducted on the elementary reaction of C-CO2 and C-H2O.Taiheiyo char pre-treated at 600°C same as fed-char into the pilot plant was used as the test samples. Samples were gasified in a 28 mmφ small batch type fluidized bed reactor made of quartz.Reaction rate of the carbon was determined from the observed data of the produced gas.Both reaction processes of C-H2O and C-CO2 were predicted considerably well by a modified mathematical model of unreacted core, namely the rate constant of intraparticle diffusion was corrected dividing by square of unreacted carbon conversion.The activation energy of the C-H2O reaction was 31.2 kcal/mole and 38.5 kcal/mole for the intraparticle diffusion and interfacial reaction respectively. And also, the activa-tion energy of the C-CO2 reaction were 94.5 kcal/mole, and 44.1 kcal/mole respectively.From the results of measured values dx/dt, it was confirmed that the C-H2O reaction processed superiorly as compared with the C-CO2 reaction.