Lagergren Model Research Articles

Impacts of calcium-alginate density on equilibrium and kinetics of lead(II) sorption onto hydrogel beads

Chronic exposure to Pb2+ above the 15-μg/L US Environmental Protection Agency action level for drinking water has been shown to cause a host of health problems in humans. Thus, it is important to study new methods available for the treatment and removal of Pb2+ from drinking water and wastewater, where elevated levels of heavy metals are found. Alginate-based beads represent one such possible method for heavy metal removal. The impact of alginate density on the equilibrium and kinetics of Pb2+ sorption onto hydrogel beads was investigated using Ca-alginate beads ranging from 1% to 8% (w/v) and exposed to Pb2+ concentrations ranging from 100 to 1,000 mg/L. When Ca-alginate beads were characterized using Fourier transform infrared analysis, the carboxylic acid groups of the mannuronate and guluronate residues in alginate were the primary functional groups that interacted with Pb2+. Hydration of Ca-alginate beads was also examined and found to decrease as Ca-alginate density increased. A positive correlation was observed between Ca-alginate hydration and Pb2+ sorption. Sorption of Pb2+ was fast, reaching equilibrium after approximately 4 h, and is well described by the Langmuir adsorption isotherm. Maximum sorption capacities for 1%, 4%, and 8% beads were 500 ± 100, 360 ± 30, and 240 ± 20 mg/g (dry weight), respectively. The kinetics of sorption were best described by the pseudo-second-order Lagergren model, with rate constants determined as 3.2 ± 0.1 × 10−4, 1.0 ± 0.1 × 10−4, and 1.6 ± 0.1 × 10−4 g mg−1 min−1 for 1%, 4%, and 8% beads, respectively.

Decolourization of pulp and paper mill effluents using heat-treated coal: a comparison with activated charcoal

A comparison between activated charcoal and heat-treated coal for decolourization of pulp and paper mill waste water was studied. The heat-treated coal was prepared in an inert atmosphere at 800°C. The adsorption dynamics that include batch contact–time study, kinetics along with adsorption isotherms were carried out. The study shows that heat-treated coal is a suitable adsorbent and can be used for the decolourization of pulp and paper mill effluent streams. The maximum removal was achieved at the initial stages of contact, and the overall adsorption was a slow process. However, the equilibrium concentration in the case of both the adsorbents reaches at almost same time. The linear plot of the Lagergren model shows its applicability and first-order kinetics.

THE SORPTION OF LEAD(II) IONS FROM AQUEOUS SOLUTIONS ON PEAT: KINETICS STUDY

The lead(II) ions sorption from aqueous solutions on three types of peat from Poiana Stampei (Romania) was studied. The peat was drawing from different deeps, such as 5-10 cm deep (peat 1), 0.5-1.0 m deep (peat 2) and from > 1.5 m deep (peat 3). The influence of several experimental parameters (initial lead concentration, contact time) was studied in batch experiments. The kinetics of sorption was followed based on the amount of lead(II) ions retained at various time intervals. The results show that sorption (chemical bonding) might be rate-limiting elementary process in the sorption of lead(II) ions on peat. The experimental data were analyzed using two kinetics models: pseudo-first order Lagergren model and pseudo-second order Ho model. On the basis of these models, the kinetics parameters (the rate constant, the equilibrium sorption capacity and the initial sorption rate) for lead(II) ions sorption onto all three types of peat were calculated and discussed.

Removal of phosphate anions from aqueous solutions using polypyrrole‐coated sawdust as a novel sorbent

AbstractThis work was focused on the removal of phosphate ions using polypyrrole‐coated sawdust as a novel cost‐effective sorbent. The phosphate uptake followed the Langmuir sorption isotherm, and the sorption capacity at 20, 35, and 50°C was found to be 17.33, 23.41, and 30.39 mg/g, respectively; this indicated favorable sorption at higher temperatures. The kinetic uptake data were modeled with the Lagergren equation, first‐order and second‐order kinetic models, and the simple Elovich model. The results indicated that the Lagergren model best described the uptake data. The intraparticle diffusion coefficient, as determined for 250–211‐ and 630–600‐μm sorbent particles at 20°C, was found to be 287.3 × 10−2 and 228.3 × 10−2 mg g−1 min−1, respectively. The intraparticle diffusion was also confirmed with the Bangham equation. The sorption mean free energy, calculated with the Dubinin–Radushkevich equation, was found to be 10.98 kJ/mol, thus confirming an ion‐exchange regulated sorption process. The positive value of the enthalpy change (i.e., 4.23 kJ/mol) confirmed the endothermic nature of the sorption process. The negative values of the change in the standard free energy were indicative of the spontaneous nature of the sorption process. Finally, the activation energy of the sorption process for 250–212‐μm particles, determined with the Arrhenius equation, was found to be 41.68 J/mol. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Avaliação da eficiência de caulinita intercalada com dimetilsulfóxido em adsorção com o Zn(II) em meio aquoso: cinética do processo de adsorção

Amostras de caulinita oriundas da região do Rio Capim, estado do Pará, Brasil, foram intercaladas com dimetilsulfóxido - DMSO. As amostras de caulinita naturais e intercaladas foram utilizadas em processo de adsorção com Zn(II) em meio aquoso em pH 5,0 e temperatura controlada de 298 ± 1K. As propriedades físico-químicas das amostras de caulinita foram otimizadas pelo processo de intercalação, como: área superficial de 14,74 para 91,72 m²g-1 (A1) e diâmetro de poros de 2,79 para 10,72 nm (A1). A análise dos resultados experimentais de adsorção foi feita pelos modelos de Langmuir, Temkin e Freundlich. O modelo de Langmuir apresentou melhor aproximação com os dados experimentais de adsorção. Estes resultados foram bem representados pelo modelo cinético de segunda ordem de Lagergren, com a taxa constante K2 no intervalo de 4,76x10-3 a 11,81x10-3 g(mmol.min)-1 (A2). O processo de adsorção foi considerado rápido alcançando o equilíbrio em 180 min.

Kinetic and equilibrium studies on the removal of Cd2+ ions from water using polyacrylamide grafted rice (Oryza sativa) husk and (Tectona grandis) saw dust

The increase in the use of heavy metals has resulted in an increased flux of metallic substances into the aquatic environment which poses a danger to human health. The present work relates to the removal of cadmium ions by treatment with polyacrylamide grafted rice (Oryza sativa) husk/saguan (Tectona grandis) saw dust. The drinking water guideline value recommended by WHO for cadmium is 0.005 ppm.The adsorbent has been prepared by treatment of rice husk/saw dust with acrylamide. Removal has been studied at various pH values for different times of contact and adsorbate concentrations and is found to be pH-dependent, maximum removal occurs at pH 9 and at a contact time of 180 min for both the adsorbents. The results were found to be consistent with both the Langmuir and Freundlich isotherm models. The value of n (rate constant) determined at pH 9 has been found to be 1 (within experimental limits). This is further substantiated by applying the Lagergren model. The intra-particle diffusion constants were determined by the Morris-Weber model. Continuous flow column studies have also been undertaken and the breakthrough characteristics were determined. Desorption has been affected with 0.5M HCl. The results suggest that both polyacrylamide grafted rice husk/saw dust can be used as efficient and cost effective adsorbents for cadmium ion removal.

Adsorption of Congo red from aqueous solutions onto Ca-bentonite

The ability of Ca-bentonite to remove Congo red dye from aqueous solutions has been carried out as a function of contact time, temperature (20–50 °C), pH (5–10) and concentration (50–200 mg L −1). An amount of 0.2 g of Ca-bentonite could remove more than 90.0% of the dye from 100 mg L −1 Congo red dye solution for the temperature range studied here. The amount of dye adsorbed per unit weight of Ca-bentonite increased from 23.25 to 85.29 mg g −1 with increasing concentration from 50 to 200 mg L −1, but it had a little change with temperature and decreased slightly with increasing pH. The kinetics of adsorption in view of three kinetic models, i.e., the pseudo-first-order Lagergren model, the pseudo-second-order model and the intraparticle diffusion model, was discussed. The pseudo-second-order kinetic model described the adsorption of Congo red on Ca-bentonite very well. Analysis of adsorption results obtained at 20 °C showed that the adsorption pattern on Ca-bentonite followed the Freundlich isotherms. It was indicative of the heterogeneity of the adsorption sites on the clay particles. From thermodynamic studies, it was seen that the adsorption was spontaneous and endothermic.

DEACIDIFICATION OF ADLAY SEED (COIX LACHRYMA‐JOBI VAR. MAYUEN) MISCELLA WITH ANION‐EXCHANGE RESIN

ABSTRACT This study examined the potential of ion‐exchange adsorption technique for the deacidification of adlay seed miscella. The adsorption properties, including the adsorption isotherms, thermodynamics and kinetics, of free fatty acids (FFAs) onto anion‐exchange resin LSD‐263 were investigated. Regression results showed that the Freundlich model can describe the adsorption isotherm better than the Langmuir model can. The positive values of enthalpy indicated that an endothermic process in our study range – the negative value of free energy indicated the spontaneous nature of the adsorption process – and the positive values of entropy showed the increased randomness at the solid/liquid interface during the adsorption process. The Lagergren first‐order model and the Ho pseudo second‐order model were used to investigate the adsorption data and Ho's model could present the experimental data better than Lagergren's model could. The adsorption constant increase with temperature indicated that higher temperature would benefit the adsorption process. Analysis of adlay seed oils revealed that the application of LSD‐263 could get a high % removal of FFAs (about 90%) and partly remove phospholipids (68.58%) and pigments (64.41%) without significant change of oil content and fatty acid composition. PRACTICAL APPLICATIONSConventional neutralization of vegetable oils by alkali or physical refining is considered very energy consuming. In addition, all the refining operations subject oils to high temperatures. High temperatures seem to be the most harmful parameter, which is responsible for hydrolytic, oxidative and polymerization alterations.Improving the quality of processed oils by reducing side effects and energy consumption has been among the most attractive research areas throughout the past half‐century. Due to its characteristic as a highly effective and energy‐saving technology, ion‐exchange processing has the potential of being an alternative vegetable‐refining technique. However, there has not been much fundamental research concerning the adsorption of free fatty acids from vegetable oils by anion‐exchange resins.Deacidification of vegetable oil with ion‐exchange resins can be operated at low temperature (<50C). These mild conditions, which contrast with the condition in industry practices, are expected to preserve the sensitive and bioactive components in vegetable oils. Moreover, due to high separation effectiveness, ion‐exchange processing can be done with vegetable miscella itself without any further solvent removal by evaporation.

Batch removal of malachite green from aqueous solutions by adsorption on oil palm trunk fibre: Equilibrium isotherms and kinetic studies

Oil palm trunk fibre (OPTF) – an agricultural solid waste – was used as low-cost adsorbent to remove malachite green (MG) from aqueous solutions. The operating variables studied were contact time, initial dye concentration, and solution pH. Equilibrium adsorption data were analyzed by three isotherms, namely the Freundlich isotherm, the Langmuir isotherm, and the multilayer adsorption isotherm. The best fit to the data was obtained with the multilayer adsorption. The monolayer adsorption capacity of OPTF was found to be 149.35 mg/g at 30 °C. Adsorption kinetic data were modeled using the Lagergren pseudo-first-order, Ho's pseudo-second-order and Elovich models. It was found that the Lagergren's model could be used for the prediction of the system's kinetics. The overall rate of dye uptake was found to be controlled by external mass transfer at the beginning of adsorption, then for initial MG concentrations of 25, 50, 100, 150, and 300 mg/L the rate-control changed to intraparticle diffusion at a later stage, but for initial MG concentrations 200 and 250 mg/L no evidence was found of intraparticle diffusion at any period of adsorption. It was found that with increasing the initial concentration of MG, the pore-diffusion coefficient increased while the film-diffusion coefficient decreased.

Effect of alkyl tail and oxyethylation degree on the cosorption of nonionic surfactant and nickel (II) by polyacrylic acid-functionalized cation exchanger

Mutual effect of nickel (II) and oxyethylated higher fatty alcohols C n H 2 n+1 O(C 2H 4O) m H (nonionic surfactants ALM-10 at n of 12–14, m ∼ 10 and OS-20 at n ∼ 18, m ∼ 20) on kinetics and equilibrium of their cosorption, needed for designing the industrial adsorption columns, has been investigated to establish the adequacy of polyacrylic acid-functionalized cation exchanger Duolite ES-468 for the treatment of nickel plating rinse water in closed loop systems. Mutual effect depends on the length of hydrophobic chain (number of carbon atoms in alkyl tail n) and the length of hydrophilic chain (oxyethylation degree, number of –C 2H 4O– head groups m in the molecule of nonionic surfactant), and is affected by the solution acidity. External mass transfer of ALM-10 through the liquid film, surrounding the bead of cation exchanger, proceeds faster than that of OS-20, although is slower than that of nickel (II). Mutual interference with the external mass transfer, arising from the simultaneous film diffusion of not only nickel (II) free cations and ALM-10 free molecules but also their associates, has been observed. Although the action of nickel (II) onto the external mass transfer of OS-20, having the oxyethylation degree and mean molecular mass twice as high as those of ALM-10, was insignificant. Effective intraparticle diffusivity ( D ef), determined using Vermeulen model, valid for the whole range of the fractional attainment of equilibrium, is considerably higher for OS-20 than that for ALM-10. The action of nickel (II) promotes the intraparticle diffusion of ALM-10 but hinders that of OS-20. Intraparticle diffusion of nickel (II) is enhanced greatly by the action of ALM-10 and OS-20. Kinetic curves refer to the monolayer sorption, corresponding to Lagergren pseudo-first-order kinetic equation; equilibrium specific sorption ( a eq) of nickel (II) and nonionic surfactants, predicted using Lagergren model, corresponds to that, determined experimentally. On increasing the solution pH from 3 to 5 the sorption of nonionic surfactant, proceeding by hydrogen bonding of oxygen in –C 2H 4O– head groups with hydrogen in protonated carboxyl groups decreases, whereas the sorption of nickel (II), proceeding mostly by ion exchange, increases. a eq of ALM-10, having length of alkyl tail and degree of oxyethylation twice as low as those of OS-20, is higher, and at low concentration ( C < 0.5 C 0) breakthrough the break point occurs later than that of OS-20. The action of nickel (II) results in an increase in a eq for both ALM-10 and OS-20. Duolite ES 468 cation exchanger is applicable for recycling wastewater, containing nonionic surfactant and nickel (II), including nickel plating rinse water, preventing pollution of environment with heavy metal (II) and nonionic surfactant, and reducing water consumption.

Adsorption characteristics of Congo Red on coal-based mesoporous activated carbon

Adsorption of Congo Red dye (CR) on bituminous coal-based mesoporous activated carbon (AC) from aqueous solutions was studied. The ACs used differed significantly in terms of total surface area, pore volume distribution and surface charge properties. The mesopore contribution to the total pore volume ranged from 52 to 83%. The adsorption tests were performed under static conditions at solution pH 7.8–8.3. The pH at the point of zero charge (pH PZC) for ACs used was over 10. It was found that the higher the fraction of mesopores with a size between 10 and 50 nm, the shorter the time to achieve the equilibrium stage for CR adsorption. The kinetics of adsorption in view of three kinetic models, i.e. the first-order Lagergren model, the pseudo-second-order model and the intraparticle diffusion model, was discussed. The pseudo-second-order kinetic model describes the adsorption of CR on mesoporous activated carbon very well. The correlation coefficients ranged from 0.980 to 0.991. The intraparticle diffusion into small mesopores was found to be the rate-limiting step in the adsorption process. The equilibrium adsorption data were interpreted using Langmuir and Freundlich models. The adsorption of CR was better represented by the Langmuir equation. The monolayer adsorption capacity of ACs was found to increase with increasing both the mesopore volume and the mesopore contribution to their porous texture. The effect of solution ionic strength on the uptake of CR by two different mesoporous carbons was also investigated.

Kinetics and mechanism of adsorption of methylene blue from aqueous solution by nitric-acid treated water-hyacinth

Kinetics adsorption experiments were conducted to evaluate the adsorption characteristics of a cationic dye (methylene blue, MB) onto nitric-acid treated water-hyacinth (N-WH). Results showed that N-WH can remove MB effectively from aqueous solution. The loading of MB onto N-WH was found to increase significantly with increasing the initial MB concentration, but the residual concentration of MB in solution also increased. A complete removal of MB from solution was only achieved at the lower range of initial MB concentration (less than 286 mg/L). Temperature had a slight effect on the amount adsorbed at equilibrium. The adsorption rate was fast and more than half of the adsorbed-MB was removed in the first 15 min at room temperature, which makes the process practical for industrial application. The adsorption kinetics at room temperature could be expressed by the pseudo second order model, while at higher temperatures (45–80 °C) and low MB concentration (97 mg/L) both Lagergren's model and the pseudo second order model can be used to predict the kinetics of adsorption. The overall rate of dye uptake was found to be controlled by external mass transfer at the beginning of adsorption, then gradually changed to intraparticle diffusion control at a later stage. The initial period where external mass transfer is the rate controlling step was found to increase with increasing initial MB concentration and decrease with increasing temperature. The increase in temperature was also found to increase the rate of adsorption and reduce the time required to reach equilibrium. The initial rate of adsorption, h o, was calculated, it was found to increase with increasing temperature, while the increase in MB concentration decreased h o at the lower concentration range then increased h o again at high concentration. The value of the activation coefficient, E, was found to be 8.207 kJ/mol, which indicates a diffusion controlled process.

Kinetic modeling of adsorption of di-2-pyridylketone salicyloylhydrazone on silica gel

The kinetics of DPKSH (di-2-pyridylketone salicyloylhydrazone) adsorption onto silica gel has been investigated at ( 25 ± 1 ) ° C and pH 1 and 4.7. The kinetics of adsorption of DPKSH is discussed using three kinetic models, the first-order Lagergren model, the pseudo-second-order model, and the intraparticle diffusion model. The adsorption of DPKSH, at pH 1 and 4.7, onto silica gel proceeds according to the pseudo-second-order model and the correlation coefficients were very close to 1. The intraparticle diffusion of DPKSH molecules within the silica gel particles was identified as the rate-limiting step. The parameters of the pseudo-second-order model are q max , calc = 1.02 × 10 −4 and 1.5 × 10 −4 g DPKSH/g silica; k 2 = 3.01 × 10 4 and 9.67 × 10 4 h −1 g silica/g DPKSH, respectively, for pH 1 and 4.7.

Dye removal by low cost adsorbents: Hazelnut shells in comparison with wood sawdust

Batch adsorption of Methylene Blue, up to 1000 mg L −1, and Acid Blue 25, up to 500 mg L −1, onto ground hazelnut shells was studied in comparison with sawdust of various species of wood, in order to explore the potential use of this material as low cost adsorbent for dye removal in dyehouse effluents. The adsorption kinetics was investigated according to Lagergren's model, but the best fit was achieved by a second order equation. The equilibrium data were processed according to Langmuir's model and higher adsorption capacity values towards both dyes were shown by hazelnut shells than wood sawdust. Moreover, fixed bed adsorption of Methylene Blue was performed on hazelnut shell columns and the breakthrough curves were determined by varying bed depth, flow rate and influent concentration. The data were processed according to Bohart–Adams model and the column performances could be predicted by the bed depth service time (BDST) approach.

Removal of cyanocobalamine from aqueous solution using mesoporous activated carbon

The adsorption of cyanocobalamine was studied using coal-based mesoporous activated carbon (AC). The ACs tested showed a comparable pore volume, around 0.5 cm 3 g −1, but different contribution of mesopores ranging from 0.53 to 0.82 cm 3 g −1. The adsorption of cyanocobalamine was carried out in slightly alkaline solution in static conditions. Three kinetic models including a first-order Lagergren model, a pseudo-second-order model, and an intraparticle diffusion model were applied to describe the kinetics and mechanism of adsorption. The adsorption of cyanocobalamine on mesoporous carbons followed the pseudo-second-order model. The diffusion of cyanocobalamine molecule within smaller mesopores was identified to be the rate-limiting step. The analysis of adsorption equilibrium data indicates that the adsorption of cyanocobalamine better fits the Langmuir equation than the Freundlich equation. The Langmuir adsorption capacity of the carbon is strongly related to the degree of mesoporosity development. Among ACs tested, the carbon with the highest mesopore volume and mesopore width of 10–50 nm shows the greater ability to remove cyanocobalamine from aqueous solution. The effect of pore-size distribution on the kinetics and mechanism of adsorption has been discussed.

Preparation and characterization of activated carbons from Sterculia alata nutshell by chemical activation with zinc chloride to remove phenol from wastewater

Nutshells of Sterculia alata, a forest waste, were used to prepare activated carbons by zinc chloride activation under four different activation atmospheres, to develop carbons with substantial capability, and to adsorb phenol from wastewater. Experiments were carried out at different chemical ratios (activating agent/precursor). Effect of carbonization temperature and time are the important variables, which had significant effect on the pore structure of carbon. Developed activated carbon was characterized by SEM analysis. Pore volume and surface area were estimated by Hg porosimetry and BET surface area analyses. The carbons showed surface area and micropore volumes of around 712 m2/g and 0.542 cm3/g, respectively. The activated carbon developed shows substantial capability to adsorb phenol from wastewater. The kinetic data were fitted to the models of intraparticle diffusion, pseudo-second order, and Lagergren model and followed more closely the pseudo-second-order chemisorption model. The isotherm equilibrium data were well-fitted by the Langmuir and Freundlich models. The maximum uptake of phenol was found at pH 3.5.

Biosorption of phenolic compounds by the brown alga Sargassum muticum

AbstractPhenol, 2‐chlorophenol (2‐CP), and 4‐chlorophenol (4‐CP) biosorption on Sargassum muticum, an invasive macroalga in Europe, has been investigated. The efficiency of this biosorbent was studied measuring the equilibrium uptake using the batch technique. A chemical pre‐treatment with CaCl2 has been employed in this study in order to improve the stability as well as the sorption capacity of the algal biomass. The influence of pH on the equilibrium binding and the effect of the algal dose were evaluated. The experimental data at pH = 1 have been analysed using Langmuir and Freundlich isotherms. It was found that the maximum sorption capacity of chlorophenols, qmax = 251 mg g−1 for 4‐CP and qmax = 79 mg g−1 for 2‐CP, as well as that of a binary mixture of both chlorophenols, qmax = 108 mg g−1, is much higher than that of phenol, qmax = 4.6 mg g−1. Moreover, sorption kinetics have been performed and it was observed that the equilibrium was reached in less than 10 h. Kinetic data have been fitted to the first order Lagergren model, from which the rate constant and the sorption capacity were determined. Finally, biosorption of the phenolic compounds examined in the present study on Sargassum muticum biomass was observed to be correlated with the octanol‐water partitioning coefficients of the phenols. This result allows us to postulate that hydrophobic interactions are the main responsible for the sorption equilibrium binding. Copyright © 2006 Society of Chemical Industry

Equilibrium and kinetic modelling of Cd(II) biosorption by algae Gelidium and agar extraction algal waste

In this study an industrial algal waste from agar extraction has been used as an inexpensive and effective biosorbent for cadmium (II) removal from aqueous solutions. This biosorbent was compared with the algae Gelidium itself, which is the raw material for agar extraction. Equilibrium data follow both Langmuir and Redlich–Peterson models. The parameters of Langmuir equilibrium model are q max = 1 8.0 mg g - 1 , b = 0.1 9 mg l - 1 and q max = 9.7 mg g - 1 , b = 0.1 6 mg l - 1 , respectively for Gelidium and the algal waste. Kinetic experiments were conducted at initial Cd(II) concentrations in the range 6–91 mg l −1. Data were fitted to pseudo-first- and second-order Lagergren models. For an initial Cd(II) concentration of 91 mg l −1 the parameters of the pseudo-first-order Lagergren model are k 1 , ads = 0.1 7 and 0.87 min −1; q eq = 1 6.3 and 8.7 mg g −1, respectively, for Gelidium and algal waste. Kinetic constants vary with the initial metal concentration. The adsorptive behaviour of biosorbent particles was modelled using a batch reactor mass transfer kinetic model. The model successfully predicts Cd(II) concentration profiles and provides significant insights on the biosorbents performance. The homogeneous diffusivity, D h, is in the range 0.5–2.2×10 −8 and 2.1–10.4×10 −8 cm 2 s −1, respectively, for Gelidium and algal waste.

Influence of pH, ionic strength and temperature on lead biosorption by Gelidium and agar extraction algal waste

An algal industrial waste from an agar extraction process was used as an inexpensive and efficient biosorbent for Pb 2+ removal from aqueous solutions. This biosorbent was compared with the alga Gelidium, the raw material for agar extraction. The effects of various physico-chemical parameters on Pb 2+ biosorption were investigated in a batch contactor in order to explain the adsorption mechanism. Kinetic and equilibrium experiments were conducted at different values of pH (3.0, 4.0 and 5.3), ionic strength (0.001 and 0.1 M) and temperature (10–45 °C). Uptake kinetics follows the pseudo-second-order Lagergren model and equilibrium is well described by Langmuir isotherm. Maximum biosorption capacities for Gelidium algae and algal waste were found to be 64 ± 2 and 44 ± 3 mg Pb 2+/g biosorbent, respectively. Biosorption of Pb 2+ was highly pH dependent, decreasing with pH. Good performances were obtained even under high ionic strength values. Changes in standard enthalpy and activation energy during biosorption were determined.

Equilibrium and kinetic modelling of Pb 2+ biosorption by granulated agar extraction algal waste

An algal industrial waste from the agar extraction process was immobilized with an organic polymer (polyacrylonitrile, PAN) and used as a biosorbent for Pb 2+ removal from aqueous solutions. The effects of the initial concentration, stirring velocity and particles diameter on Pb 2+ biosorption were investigated in a batch system in order to explain the adsorption mechanism. Uptake kinetics follows the second-order Lagergren model and equilibrium is well described by the Langmuir isotherm. Maximum biosorption capacity of the composite material was found to be 20.5 ± 0.8 mg Pb 2+/g. Kinetic constants vary with the initial metal concentration. The adsorptive behaviour of biosorbent particles was modelled using a batch reactor mass transfer kinetic model. The model successfully predicts Pb 2+ concentration profiles and provides significant insights on the biosorbent performance. The homogeneous diffusion coefficient ( D h) for particles with diameter between 0.5 < d p < 1 mm and for an initial concentration of 94 mg Pb 2+/l solution was found to be 3.2 × 10 −8 cm 2 s −1.