Kinetics and mechanism of methylene blue sorption onto palm kernel fibre

The kinetics and mechanism of the sorptive removal of methylene blue dye from aqueous solution using palm kernel fibre as adsorbent have been investigated. Batch kinetic experiments were performed and system variables investigated includes pH and initial dye concentration. The kinetic data were fitted to the pseudo-first, pseudo-second, intraparticle diffusion and mass transfer models. The pseudo-first order reaction kinetics fitted to the experimental data only in the first 5 min of sorption and then deviated, while the pseudo-second order kinetic model was found to fit the experimental data for the entire sorption period with high coefficient of determination. Equations were developed using the pseudo-second order model, which predicts the amounts of methylene blue at any contact time and initial concentration within the given range. This suggests that the sorption of methylene blue onto palm kernel fibre follows a chemical activation mechanism. A mathematical relationship was also drawn between the equilibrium sorption capacity and the change in pH (ΔH⁺) at the end of the kinetic experiments with varying initial dye concentration, supporting the fact that chemical reaction (ion exchange) occurred and is important in the rate determining step. Mass transfer was found to be favoured at high concentrations while intraparticle diffusion was favoured at low concentrations.     

Biosorption of Cd(II) and Pb(II) onto brown seaweed, Lobophora variegata (Lamouroux): kinetic and equilibrium studies

The present work deals with the biosorption performance of raw and chemically modified biomass of the brown seaweed Lobophora variegata for removal of Cd(II) and Pb(II) from aqueous solution. The biosorption capacity was significantly altered by pH of the solution delineating that the higher the pH, the higher the Cd(II) and Pb(II) removal. Kinetic and isotherm experiments were carried out at the optimal pH 5.0. The metal removal rates were conspicuously rapid wherein 90% of the total sorption occurred within 90 min. Biomass treated with CaCl₂ demonstrated the highest potential for the sorption of the metal ions with the maximum uptake capacities i.e. 1.71 and 1.79 mmol g⁻¹ for Cd(II) and Pb(II), respectively. Kinetic data were satisfactorily manifested by a pseudo-second order chemical sorption process. The process mechanism consisting of both surface adsorption and pore diffusion was found to be complex. The sorption data have been analyzed and fitted to sorption isotherm of the Freundlich, Langmuir, and Redlich–Peterson models. The regression coefficient for both Langmuir and Redlich–Peterson isotherms were higher than those secured for Freundlich isotherm implying that the biosorption system is possibly monolayer coverage of the L. variegata surface by the cadmium and lead ions. FT-IR studies revealed that Cd(II) and Pb(II) binding to L. variegata occurred primarily through biomass carboxyl groups accompanied by momentous interactions of the biomass amino and amide groups. In this study, we have observed that L. variegata had maximum biosorption capacity for Cd(II) and Pb(II) reported so far for any marine algae. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Adsorption Optimization of Lead (II) Using Saccharum Bengalense as a Non-Conventional Low Cost Biosorbent: Isotherm and Thermodynamics Modeling

In the present study a novel biomass, derived from the pulp of Saccharum bengalense, was used as an adsorbent material for the removal of Pb (II) ions from aqueous solution. After 50 minutes contact time, almost 92% lead removal was possible at pH 6.0 under batch test conditions. The experimental data was analyzed using Langmuir, Freundlich, Timken and Dubinin-Radushkevich two parameters isotherm model, three parameters Redlich—Peterson, Sip and Toth models and four parameters Fritz Schlunder isotherm models. Langmuir, Redlich—Peterson and Fritz-Schlunder models were found to be the best fit models. Kinetic studies revealed that the sorption process was well explained with pseudo second-order kinetic model. Thermodynamic parameters including free energy change (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) have been calculated and reveal the spontaneous, endothermic and feasible nature of the adsorption process. The thermodynamic parameters of activation (ΔG ^#, ΔH ^#and ΔS ^#) were calculated from the pseudo-second order rate constant by using the Eyring equation. Results showed that Pb (II) adsorption onto SB is an associated mechanism and the reorientation step is entropy controlled.     

Designing chitosan based magnetic beads with conocarpus waste-derived biochar for efficient sulfathiazole removal from contaminated water

The development of a simple method to synthesize highly efficient and stable magnetic microsphere beads for sulfathiazole (STZ) removal from contaminated aqueous media was demonstrated in this study. Conocarpus (Conocarpus erectus L.) tree waste (CW) derived biochar (BC) was modified to fabricate chitosan-BC (CBC) and magnetic CBC (CBC-Fe) microsphere beads. Proximate, chemical, and structural properties of the produced adsorbents were investigated. Kinetics, equilibrium, and pH adsorption batch trials were conducted to evaluate the effectiveness of the synthesized adsorbents for STZ removal. All adsorbents exhibited the highest STZ adsorption at pH 5.0. STZ adsorption kinetics data was best emulated using pseudo-second order and Elovich models. The equilibrium adsorption data was best emulated using Langmuir, Freundlich, Redlich–Peterson, and Temkin models. CBC-Fe demonstrated the highest Elovich, pseudo-second order, and power function rate constants, as well as the highest apparent diffusion rate constant. Additionally, Langmuir isotherm predicted maximum adsorption capacity was the highest for CBC-Fe (98.67 mg g⁻¹), followed by CBC (56.54 mg g⁻¹) and BC (48.63 mg g⁻¹). CBC-Fe and CBC removed 74.5%–108.8% and 16.2%–25.6% more STZ, respectively, than that of pristine BC. π-π electron-donor–acceptor interactions and Lewis acid-base reactions were the main mechanisms for STZ removal; however, intraparticle diffusion and H-bonding further contributed in the adsorption process. The higher efficiency of CBC-Fe for STZ adsorption could be due to its magnetic properties as well as stronger and conducting microsphere beads, which degraded the STZ molecules through generation of HO^• radicals.     

The efficiency of the red alga Mastocarpus stellatus for remediation of cadmium pollution

This work reports the results of the study for cadmium binding by the dead red macroalga Mastocarpus stellatus. Kinetics sorption experiments demonstrated the high rate of metal biosorption: the system attained over 50% of the total biomass cadmium uptake within 2 min of contact and over 90% in the first 9 min. The kinetic data were successfully described by a pseudo-second order model with rate constants ranging from 1.06 to 10 gmmol(-1)min(-1), as a function of initial metal concentration and temperature. The equilibrium binding was accurately represented in terms of Langmuir and Langmuir-Freundlich models. The sorption isotherms at constant pH showed uptake values as 0.49 mmol g(-1) (at pH 2.4), 0.56 mmol g(-1) (at pH 4) and 0.59 mmol g(-1) (at pH 6), while the affinity constant values were between 0.6 and 5 mmol(-1) L (Langmuir fit). The acid-base properties of the alga were also studied, obtaining the total number of acid groups, 2.5 mmol g(-1), and their apparent pK value, 1.56, using the Katchalsky model. Desorption studies were conducted employing different HNO(3) concentrations and desorption times.     

Effect of temperature on phosphorus sorption to sediments from shallow eutrophic lakes

The availability of phosphorus (P) in lakes is dependent on the sorption characteristics of the underlying sediments. Temperature is a crucial factor affecting the P sorption in sediments. The objective of this study was to evaluate the effect of temperature on sorption of P by sediments from two eutrophic lakes. The study was carried out using short-term batch experiments at 4, 20 and 30 °C. Phosphorus sorption kinetics, isotherms, fractionation and desorption were investigated. The P sorption was dependent on sediment type and temperature (p < 0.001). The Mei sediments showed a higher sorption rate and sorption capacity than Hua sediments. The P sorption kinetics were best described by a pseudo second order model (R² > 0.97). Activation energies derived from the kinetics rate constant indicated that P sorption onto the two sediments was controlled by a diffusion process. For both sediments, Freundlich model fit the P sorption isotherms well and the calculated apparent sorption heat was 6.37 kJ mol⁻¹ for Mei sediments and 8.67 kJ mol⁻¹ for Hua sediments. This indicated that P sorption onto both sediments was endothermic. Adding P significantly increased the soluble and loosely bound P (S/L-P), aluminum-bound P (Al-P) and iron-bound P (Fe-P) (p < 0.05). The amount of Al-P and Fe-P was markedly higher at 30 °C than at 4 °C (p < 0.05). Subsequent P desorption indicated that adsorbed P was highly labile, in particular for Hua sediment. The degree of P mobility that occurred during sediment sorption was inversely related to the temperature at the time of sorption. A significant relationship (R² = 0.978) between phosphorus sorption maximum and oxalate-extractable Fe and Al at different temperatures reflects that the amorphous contents of Fe and Al are responsible for the temperature effect on P sorption.     

Kinetic and equilibrium models for biosorption of Cr(VI) on chemically modified seaweed,Cystoseira indica

The biosorption data of hexavalent chromium by marine brown algae Cystoseira indica, which was chemically modified by crosslinking with epichlorohydrin (CB1, CB2), or oxidized by potassium permanganate (CB3), or only washed with distilled water (RB), has been used for kinetic studies based on fractional power, Elovich, pseudo-first order and pseudo-second order rate expressions. Five three parameter biosorption isotherm models, viz. Redlich–Peterson, Sips, Khan, Radke–Prausnitz and Toth are tested for their applicability apart from 6 two-parameter models. Non-linear curve fitting procedure was adopted for fitting the kinetic as well as equilibrium data in the kinetic and isotherm models and for the determination of parameters. The time-dependent Cr(VI) biosorption data were well-described by pseudo-second-order kinetic model. The intraparticle diffusion study revealed that film diffusion might be involved in Cr(VI) biosorption in the present case. Among the two-parameter models, the Langmuir model produces the best fit, while, among the three-parameter models, the best fit is produced by the Khan model, for the biosorption of Cr(VI) on all the four biosorbents studied.     

Influence of organic matter and solute concentration on nitrate sorption in batch and diffusion-cell experiments

Nitrate sorption potentials of three surface soils (soils-1-3) were evaluated under different solute concentrations, i.e. 1-100 mg L⁻¹. Batch and diffusion-cell adsorption experiments were conducted to delineate the diffusion property and maximum specific nitrate adsorption capacity (MSNAC) of the soils. Ho’s pseudo-second order model well fitted the batch adsorption kinetics data (R² > 0.99). Subsequently, the MSNAC was estimated using Langmuir and Freundlich isotherms; however, the best-fit was obtained with Langmuir isotherm. Interestingly, the batch adsorption experiments over-estimated the MSNAC of the soils compared with the diffusion-cell tests. On the other hand, a proportionate increase in the MSNAC was observed with the increase in soil organic matter content (OM) under the batch and diffusion-cell tests. Therefore, increasing the soil OM by the application of natural compost could stop nitrate leaching from agricultural fields and also increase the fertility of soil.     

Equilibrium and Kinetic Studies of Cd2+ Biosorption by the Brown Algae Sargassum fusiforme

A fundamental investigation of the biosorption of Cd²⁺ from aqueous solution by the edible seaweed Sargassum fusiforme was performed under batch conditions. The influences of experimental parameters, such as the initial pH, sorption time, temperature, and initial Cd²⁺ concentration, on Cd²⁺ uptake by S. fusiforme were evaluated. The results indicated that the biosorption of Cd²⁺ depended on the initial Cd²⁺ concentration, as well as the pH. The uptake of Cd²⁺ could be described by the Langmuir isotherm model, and both the Langmuir biosorption equilibrium constant and the maximum biosorption capacity of the monolayer decreased with increasing temperature, thereby confirming the exothermic character of the sorption process. The biosorption kinetics follows the pseudo-second-order kinetic model, and intraparticle diffusion is the sole rate-limiting step for the entire biosorption period. These fundamental equilibrium and kinetic results can support further studies to the removal of cadmium from S. fusiforme harvested from cadmium-polluted waters.     

Kinetics,Isotherms, and Thermodynamics of Hg(II) Biosorption onto Carica papaya

Carica papaya, a novel sorbent, was evaluated for sorption of Hg(II) from synthetic aqueous solutions using various pseudo-second order kinetic models as well as equilibrium sorption models. Batch kinetic and equilibrium experiments were carried out for the sorption of Hg(II) onto C. papaya at pH 6.5 and solid to liquid ratio (s/l) 1.0 g L^?1. The kinetic data were fitted to second order models of Sobkowsk and Czerwinski, Ritchie, Blanchard, Ho and McKay, whereas Langmuir, Freundlich, and Redlich-Peterson models were used for the equilibrium data. A comparative study on both linear and nonlinear regression showed that the Sobkowsk and Czerwinski and Ritchie's second order model were the same. Ho and McKay's pseudo-second order model fitted well to the experimental data when compared with the other second order kinetic expressions. Langmuir isotherm parameters obtained from the four Langmuir linear equations by using linear method were dissimilar, but were the same when nonlinear method was used. Additionally, various thermodynamic parameters, such as ΔG ⁰, ΔH ⁰, and ΔS ⁰, were calculated. The negative values of Gibbs free energy (ΔG ⁰) and ΔH ⁰ confirmed the intrinsic nature of biosorption process and exothermic, respectively. The negative value of ΔS ⁰ showed the decreased randomness at the solid-solution interface during biosorption.     

Study of multicompound sorption of Lead and Pyrene on a reconstituted soil: batch and fixed bed column tests

Many polluted sites are simultaneously contaminated with polycyclic aromatic hydrocarbons and heavy metals. In the present study, batch and continuous column experiments were performed utilizing self-composition soil to describe the sorption behavior of two contaminants: lead (Pb²⁺) and pyrene (PYR). Operational conditions such as contact time, bed depth, and flow rate were optimized. The effect of soil organic matter content on the process of adsorption of both contaminants was investigated. The presence of PYR in solution at neutral pH (6.0–7.5) decreased Pb²⁺ sorption. Similar behavior was observed for PYR in the presence of Pb²⁺ in solution. At room temperature, batch experimental data conducted as a function of contact time were analyzed using the Langmuir and Freundlich isotherms. Results revealed that Pb²⁺ sorption isotherms were fitted better by the Langmuir model and PYR sorption isotherms were fitted better by the Freundlich model. Column adsorption experiments were carried out at room temperature and under operating parameters (bed depth, flow rate, and initial contaminant concentration). Breakthrough curves were well fitted to the two-site first-order kinetic model with a sum of square errors less than 0.14. The Pb²⁺ adsorption kinetic data were processed also for the Thomas model with a good accuracy.     

Adsorption of Victoria blue by carbon/Ba/alginate beads: Kinetics,thermodynamics and isotherm studies

The kinetic, thermodynamic and isotherm modeling studies were carried out on adsorptive removal of Victoria blue (VB) dye using activated carbon, Ba/alginate and modified carbon/Ba/alginate polymer beads. The feasibility of sorption process was determined by varying the experimental parameters viz., dye concentration (4–20 mg L⁻¹), contact time (10–90 min), pH (3–10), adsorbent dose (0.5–2.5 g) and temperature (303–343 K). Freundlich and Langmuir isotherms were determined and ascertained with the dimensionless separation factor (R_L). Lagergren's pseudo-first order, pseudo-second order and intraparticle diffusion model equations were used to analyze the kinetics of the adsorption process. The thermodynamic consistency of adsorption was found with Gibbs free energy (ΔG°), changes in enthalpy (ΔH°) and entropy (ΔS°) were calculated using the Van’t Hoff plot. The polymer beads were characterized using Fourier Transform Infrared Spectroscopy (FTIR) and their morphology was determined by scanning electron microscopy (SEM).     

Synthesis and characterization of novel guar gum hydrogels and their use as Cu sorbents

To prepare novel hydrogels for use in water technologies, guar gum was subjected to acid hydrolysis. The depolymerized guar gum obtained there from and the native guar gum were oxidized to their respective polycarboxylic forms using NO_x as oxidant. All these polymers were crosslinked with N,N-methylenebisacrylamide, and were used as Cu²⁺ sorbents. The candidate hydrogel exhibiting the highest uptake was used further to investigate the effect of external stimuli on sorption. The sorption on hydrogels was fast as the highest sorption was observed after 2 h at 40 °C and 20 ppm of Cu²⁺ ions. The hydrogel prepared from the oxidized guar gum afforded the maximum sorption capacity of 125.893 mg g⁻¹. Langmuir and Freundlich isotherms, and pseudo second order kinetics matches the experimental data. The evidence of sorption was obtained by characterizing Cu²⁺-loaded hydrogels by FTIR spectroscopy.     

Chemical reaction- and particle diffusion-based kinetic modeling of metal biosorption by a Phormidium sp.-dominated cyanobacterial mat

The present study explores the suitability of chemical reaction-based and diffusion-based kinetic models for defining the biosorption of Cu(II), Cd(II) and Pb(II) by Phormidium sp.-dominated mat. The time-course data of metal sorption by the test mat significantly (r² = 0.932-0.999) fitted to the chemical reaction-based models namely pseudo-first-order, -second-order, and the general rate law. However, these models fail to accurately describe the kinetics of metal biosorption due either to prefixed order or unjustifiable change in rate constant and reaction order with varying concentrations of metal and biomass in the solution. The diffusion-based models, namely, the intra-particle diffusion model and the external mass transfer model fitted well to the time-course metal sorption data, thus suggesting involvement of both external and intra-particle diffusion processes in sorption of test metals by mat biomass. However, the Boyd kinetic expression clearly showed that the external mass transfer is the dominant process.     

Comparative evaluation for the sorption capacity of four carbonaceous sorbents to phenol

Sorption kinetics and isotherms of phenol by four carbonaceous sorbents (activated carbon (AC), mesoporous carbon (MPC), bamboo biochar (BBC) and oak wood biochar (OBC)) were compared in this study. MPC has the fastest sorption rate and initial sorption potential, which were indicated by sorption rate constants and initial sorption rate “h” in a pseudo-second-order kinetic model. The ordered and straight pore structure of MPC facilitated the accessibility of phenol. The AC showed the greatest sorption capacity towards phenol with maximum sorption of 123 mg/g as calculated by the Langmuir model. High surface area, complexity of pore structure, and the strong binding force of the π–π electron-donor-acceptor interaction between phenol molecules and AC were the main mechanisms. The BBC and OBC had much slower sorption and lower sorption capacity (33.04 and 29.86 mg/g, respectively), compared to MPC (73.00 mg/g) and AC, indicating an ineffective potential for phenol removal from water.     

Influence of Bentonite Proportion in Natural Clay on Pb2+ ions Sorption: Response Surface Methodology,Kinetics and Equilibrium Studies

The influence of natural clay's bentonite proportion on Pb²⁺ sorption capacity was investigated using response surface methodology (RSM), kinetics and equilibrium studies. Experiments were conducted at different initial pH (3–7), bentonite to clay ratio (0–100%), initial Pb²⁺ ions concentration (20–120 mg/L) and sorbent dosage (0.2–1 g). Under the RSM study, data obtained from 27 experiments undertaken were found to fitted second-order polynomial model (R² = 0.998 and R²-predicted = 0.994). Analysis of variance showed that the Pb²⁺ sorption capacity was influenced according to the order; initial concentration> mass of adsorbent > initial pH > bentonite proportion. Optimal operating conditions were obtained at initial pH 5, 0.2 g sorbent dosage, 30% bentonite to clay ratio and 100 mg/L Pb²⁺ ion concentration. Regardless of the bentonite proportion, Pb²⁺ sorption kinetics followed pseudo-second-order associated with intra-particle diffusion. The sorption isotherm for the clay which was described by Freundlich yielded higher adsorption capacity (25 mg/g) while that of the bentonite was described by Langmuir model with lower maximum sorption capacity of 15 mg/g. These results suggest that sorption of the Pb²⁺ ions was not likely to significantly impact on the removal of Pb²⁺ ions during electrokinetic remediation process of clay having different proportion of bentonite.     

黏土矿物中重金属离子的吸附规律及竞争吸附

采用等温吸附法,研究了重金属铜、铅、镉、镍在膨润土中的吸附特征,发现膨润土对铜、铅的吸附明显强于镉、镍,吸附强度大小顺序为Pb2 >Cu2 >Ni2 >Cd2 。Langmuir和Freundlich方程对这4种金属离子等温吸附的拟合均呈极显著关系。Pb2 、Cd2 、Ni2 分别与Cu2 的双组分竞争吸附表明,黏土矿物对4种离子具有"选择性吸附"。在Pb2 、Ni2 、Cd2 的存在条件下,黏土矿物对Cu2 的吸附产生不同程度的下降;100mg/LCu2 对Pb2 的影响不大,但可完全抑制Ni2 、Cd2 的吸附。建立了IAS和LCA模型来预测Pb2 与Cu2 的双组分竞争吸附,并对LCA模型进行修正,提出了更符合实际情况的竞争吸附模型。文章最后用LCA修正模型对Pb2 与Cu2 的双组分竞争吸附进行了模拟。     

Norfloxacin Sorption to Different Fractions in Sediments from Typical Water Systems in China

Sorption isotherms of Norfloxacin (NOF) to different fractions from six typical sediments in China were determined to compare the NOF sorption behavior and contribution of different fractions to total sorption. All sorption isotherms were nonlinear and fitted well with the Freundlich model. Sorption coefficients (K _f) by original sediments changed in larger magnitude, from 114 (mg/g)/(mg/L)ⁿ to 5271 (mg/g)/(mg/L)ⁿ, and black carbon with more aromatic carbon has more sorption capacity and nonlinearity. The sorption capacity K _f values were found to significantly correlate with SSA (specific surface area), OC (organic carbon), BC (black carbon), and TON (total organic nitrogen) (p < 0.05), but had no obvious relation with pH, CEC (cation exchange capacity), TOC/TON, and BC/TOC. The DOC removed, NaOH extracted, and 375°C heated fractions showed more nonlinear sorption than the original sediments, suggesting more heterogeneous sorption sites in these fractions. Among different sediment fractions, the 375°C heating fractions were responsible for >50% of the total NOF sorption over the whole concentration range. The contribution of DOC removed fractions to the total sorption was the highest at higher NOF concentration.     

Potentiality of lignin from the Kraft pulping process for removal of trace nickel from wastewater: effect of demineralisation

An industrial raw Kraft lignin was investigated to ascertain its potential use for removal of trace Ni(II) ion from wastewater by using dilute solutions (0.34-1.7 mM) as models. The effect of demineralisation on its metal sorption ability was examined by employing acid pre-treated samples. Under fixed pre-established equilibrium conditions, the raw lignin exhibited a lower effectiveness than the demineralised one, with the latter attaining an almost complete removal of Ni(II) ions. For both lignins, sorption kinetics was properly described by a pseudo-second order rate model. Equilibrium isotherms were also determined and adequately represented by conventional two-parameter models. The higher nickel sorption capacity for the demineralised lignin compared to the raw sample was consistent with enhancements in the negative magnitude of zeta potential, sodium sorption capacity, and content of phenolic hydroxyl groups occasioned by the acid pre-treatment. Accordingly, demineralisation appears as a readily convenient strategy to improve the behaviour of industrial Kraft lignin for potential use as a biosorbent of trace nickel from polluted water.     

Study of water sorption on modified Agave fibres

Polymer composite materials are usually reinforced by synthetic matter such as carbon or glass fibres. However, owing to their good mechanical properties and low density, natural fibres are now increasingly being considered as reinforcement. With the aim of a new natural fibre based composite, various chemical treatments have been performed on Agave (Americana L.) fibres in order to improve their compatibility with the polymer matrix and to reduce their affinity for water. The effect of these treatments on the fibre water sorption power has been investigated by means of a micro-balance. Equilibrium water sorption isotherms have been deduced from weight variations of the fibres under water vapor pressure increments. Several specific physico-chemical models have been tested to describe the water sorption isotherms. The Park’s model was found to describe the experimental results accurately and over a wide activity range. The sorption kinetics was also exploited in order to evaluate the diffusivity of water in the fibres. The variation of the water diffusion coefficient with water concentration is in agreement with the triple sorption mode described by the Park’s model. These results show a global increase of moisture resistance of the fibres after chemical treatment. This effect is interpreted in terms of chemical and structural modifications of the cell-wall structure.