Study of kinetics in the biosorption of lead onto native and chemically treated olive stone

In this research, olive stone was used as precursor for the development of new biosorbents for lead ions. Chemical treatments were analyzed in terms of their effects on physical–chemical properties and kinetics of lead removal. A kinetic study of the biosorption of lead ions by olive stone was analyzed according to six different kinetic models (pseudo first, pseudo second, pseudo n-order, Elovich, solid diffusion and double exponential models). The biosorption kinetic data were successfully described with pseudo-nth order and double exponential models for all biosorbents. The double exponential model allowed estimating the values of external and internal mass transfer coefficients. The values of external mass transfer coefficient (k_e) ranged from 42.62 × 10⁻⁶ to 508.3 × 10⁻⁶ m min⁻¹ and the internal mass transfer coefficient (k_i) from 3.76 × 10⁻⁶ to 73.4 × 10⁻⁶ m min⁻¹. On the other hand, the analysis of experimental data showed that chemical treatments of the biomass led to increase biosorption capacity of the native biomass.     

Packed bed column studies for the removal of synthetic dyes from textile wastewater using immobilised dead C. tropicalis

An efficient dye biosorbent was developed for the treatment of textile wastewater by entrapping dead cells of C. tropicalis, within sodium alginate matrix. The biosorbent performance was evaluated in packed bed column with different pH (3 to 6), wastewater strength (25%, 50% 75%), bed height (5 cm–15 cm) and flow rate (0.5 mL min^?1 to 1 mL min^?1). pH 5, undiluted wastewater, bed height 15 cm and flow rate 0.5 mL min^-1 were found to be optimum for dye biosorption. The linearized form of the modified Thomas model equation fitted well with the experimental data and described the dynamic adsorption of synthetic dyes from textile wastewater. The Bed depth service time model was used to express the effect of bed height on breakthrough curves. Dye laden immobilised dead C. tropicalis was regenerated using 0.01 mol L^?1 NaOH at an elutant flow rate of 1 mL min^?1. The reusability of the immobilised biomass was tested in consecutive adsorption–desorption cycles. The FT-IR spectral analysis showed the involvement of amine, hydroxyl, carbonyl, amide and phosphoryl groups in biosorption of dyes from wastewater. The analysis of treated samples showed almost zero colour and a significant decrease in Total Dissolved Solids (TDS).     

A novel cross-linked polyzwitterion/anion having pH-responsive carboxylate and sulfonate groups for the removal of Sr2+ from aqueous solution at low concentrations

A novel cross-linked polyzwitterion (CPZ) was synthesized via cycloterpolymerization of N,N-diallyl-N-sulfopropylammonioethanoic acid (92.5 mol%), a cross-linker 1,1,4,4-tetraallylpiperazinium dichloride (7.5 mol%), and sulfur dioxide (100 mol%) in the presence of azoisobutyronitrile in dimethylsulfoxide at 60 °C. CPZ, upon treatment with NaOH, was converted into a cross-linked polyzwitterion/anion (CPZA). The experimental data for the adsorption of Sr²⁺ on CPZA fitted the pseudo-second-order kinetic model and Freundlich as well as Temkin isotherm models. The adsorption process was spontaneous and exothermic in nature with negative values for both ΔG and ΔH. The low activation energy of 7.18 kJ/mol indicated the adsorption as a favorable process. The removal for the initial concentrations of 200 ppb and 1000 ppb (i.e., 1 ppm) of Sr²⁺ ions was observed to be 87% and 92%, respectively. An efficient synthetic access to the resin and excellent adsorption capacity and desorption would enable its use in the treatment of radioactive nuclear waste containing Sr²⁺ ions. The CPZA provided an opportunity to test the efficacy of a zwiiterionic/anionic group in the removal of Sr²⁺ ions in low concentrations.     

Kinetics,equilibrium and thermodynamic studies on biosorption of hexavalent chromium by dead fungal biomass of marine Aspergillus niger

Quite a number of reports are available on metal binding capacity of different groups of microorganisms. However, reports on the equilibrium studies on biosorption by marine fungi are quite inadequate. The present study was carried out in a batch system using dead biomass of marine Aspergillus niger for the sorption of Cr(VI). The removal rate of Cr(VI) was increased with a decrease in pH and an increase in Cr(VI) and biomass concentration. A. niger exhibited the highest Cr(VI) uptake of 117.33 mg g^?1 of biomass at pH 1.0 in the presence of 400 mg l^?1 Cr at 50 °C. Kinetics studies based on fractional power, zero order, first order, pseudo-first order, Elovich, second order and pseudo-second order rate expressions have also been carried out. The experimental data were analyzed using five, two-parameter isotherms (Langmuir, Freundlich, Dubinin–Radushkevich, Temkin and Halsey). It was observed that Langmuir model exhibited the best fit to experimental data. Thermodynamic parameters of the biosorption (ΔG°, ΔH° and ΔS°) were also determined.     

Synthesis and adsorption studies of novel hybrid mesoporous copolymer functionalized with protoporphyrin for batch and on-line solid-phase extraction of Cd2+ ions

A hybrid copolymer [poly(ethylene glycol dimethacrylate-co-protoporphyrin)-silica], synthesized by free radical copolymerization and sol–gel process was evaluated as novel adsorbent for solid-phase extraction of Cd²⁺ ions. Characterization of hybrid polymer was performed by FTIR, SEM and surface area analyzes. Adsorption isotherms built at pH 8.9 were very well adjusted (R² = 0.9982) to hybrid non-linear Langmuir–Freundlich model for two sites, indicating the existence of different affinity constants for binding sites, which was confirmed by Scatchard plot. The estimated maximum adsorption capacity was found to be 8.28 mg g^?1. The adsorption kinetics data also corroborated to the isotherm, where the Cd²⁺ ions adsorption followed the pseudo-second-order kinetic (R² = 0.998). The on-line preconcentration procedure, optimized by means of factorial designs, was based on sample preconcentration (16 mL) at pH 8.9 through 50.0 mg of hybrid copolymer packed in mini-column at 8.0 mL min^?1 flow rate. The on-line desorption of Cd²⁺ ions towards the FAAS detector was carried out in countercurrent at 5.0 mL min^?1 flow rate using 0.8 mol L^?1 HNO₃. Using the on-line preconcentration procedure, the maximum adsorption capacity determined from breakthrough curve was found to be 2.25 mg g^?1. Analytical curve ranged from 0.0 up to 50.0 μg L^?1 (r = 0.997), limit of detection of 0.27 μg L^?1, preconcentration factor of 38.4, sample throughput of 30 h^?1 and consumptive index of 0.41 mL, were achieved. The preconcentration method, very tolerable to several foreign ions, was successfully applied to the Cd²⁺ ions determination in water samples and cigarette sample. The accuracy was checked from analysis of certified reference materials.     

Adsorption of heavy metal ions from aqueous solution by fly ash

The removal characteristics of lead and copper ions from aqueous solution by fly ash were investigated under various conditions of contact time, pH and temperature. The influence of pH of the metal ion solutions on the uptake levels of the metal ions by fly ash were carried out between pH 4 and 12. The level of uptake of Pb²⁺ and Cu²⁺ ions by the fly ash generally increased, but not in a progressive manner, at higher pH values. The effect of temperature on the uptake of Pb²⁺ and Cu²⁺ ions was investigated between 30 °C and 60 °C, the adsorption of being enhanced at the lowest temperature. Rate constants were evaluated in terms of a first-order kinetics. The rate constant, k for uptake of Pb²⁺ and Cu²⁺ ions were 1.77 × 10⁻² s⁻¹ and 2.11 × 10⁻² s⁻¹, respectively. The experimental results underline the potential of coal fly ash for the recovery of metal ions from waste water. The main mechanisms involved in the removal of heavy metal ions from solution were adsorption at the surface of the fly ash and precipitation.     

The effects of the surface oxidation of activated carbon,the solution pH and the temperature on adsorption of ibuprofen

A commercial microporous–mesoporous granular activated carbon was modified by oxidation with either H₂O₂ in the presence or absence of ultrasonic irradiation, or NaOCl or by a thermal treatment under nitrogen flow. Raw and modified materials were characterized by N₂ adsorption–desorption measurements at 77 K, Boehm titrations, pH measurements and X-ray photoelectron spectroscopy. Ibuprofen adsorption kinetic and isotherm studies were carried out at pH 3 and 7 on raw and modified materials. The thermodynamic parameters of adsorption were calculated from the isotherms obtained at 298, 313 and 328 K. The pore size distribution of carbon loaded with ibuprofen brought out that adsorption occurred preferentially into the ultramicropores. The adsorption of ibuprofen on pristine activated carbon was found endothermic, spontaneous (ΔG° = −1.1 kJ mol⁻¹), and promoted at acidic pH through dispersive interactions. All explored oxidative treatments led mainly to the formation of carbonyl groups and in a less extent to lactonic and carboxylic groups. This then helped to enhance the adsorption uptake while decreasing adsorption Gibbs energy (notably −7.3 kJ mol⁻¹ after sonication in H₂O₂). The decrease of the adsorption capacity after bleaching was attributed to the presence of phenolic groups.     

Chitosan modified with Reactive Blue 2 dye on adsorption equilibrium of Cu(II) and Ni(II) ions

This study aimed at immobilizing Reactive Blue 2 (RB 2) dye in chitosan microspheres through nucleophilic substitution reaction. The adsorbent chemical modification was confirmed by Raman spectroscopy and thermogravimetric analysis. This adsorption study was carried out with Cu(II) and Ni(II) ions and indicated a pH dependence, while the maximum adsorption occurred around pH 7.0 and 8.5, respectively. The pseudo second-order kinetic model resulted in the best fit with experimental data obtained from Cu(II) (R = 0.997) and Ni(II) (R = 0.995), also providing a rate constant, k₂, of 4.85 × 10⁻⁴ and 3.81 × 10⁻⁴ g (mg min)⁻¹, respectively, thus suggesting that adsorption rate of metal ions by chitosan-RB 2 depends on the concentration of ions on adsorbent surface, as well as on their concentration at equilibrium. The Langmuir and Freundlich isotherm models were employed in the analysis of the experimental data for the adsorption, in the form of linearized equations. Langmuir model resulted in the best fit for both metals and maximum adsorption was 57.0 mg g⁻¹ (0.90 mmol g⁻¹) for Cu(II) and 11.2 mg g⁻¹ (0.19 mmol g⁻¹) for Ni(II). The Cu(II) and Ni(II) ions were desorbed from chitosan-RB 2 with aqueous solutions of EDTA and H₂SO₄, respectively.     

Synthesis of NIPAAm-based polymer-grafted silica beads by surface-initiated ATRP using Me4Cyclam ligands and the thermo-responsive behaviors for lanthanide(III) ions

The applicability of atom transfer radical polymerization (ATRP) to the copolymerization of N-isopropylacrylamide (NIPAAm) with N-vinyl-2-pyrrolidone (NVP) was examined in CuCl/CuCl₂-catalyst system using tris[2-(dimethylamino)ethyl]amine (Me₆TREN) and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (Me₄Cyclam) as ligands. In the Me₆TREN system, less reactive NVP not only does not quantitatively copolymerize but also interferes with homopolymerization of NIPAAm units. In contrast, the Me₄Cyclam system under heating was more active, although the controllability for polymer homogeneity is lower than Me₆TREN system. The application of active Me₄Cyclam system to surface-initiated ATRP has successfully prepared silica beads surface-modified with NIPAAm copolymers of NVP and 4-vinylpyridine (VPy). The thermo-responsive behavior of surface-grafted NIPAAm-based polymers was investigated for lanthanide trivalent ions (Ln(III)) in different pH solutions. In the weak acidic solutions of pH = 5.4–5.6, all the surface-grafted polymers including poly(NIPAAm) exhibited only adsorption behavior with regular selectivity (Eu³⁺ > Sm³⁺ > Nd³⁺ > Ce³⁺ > La³⁺) below the phase-transition temperatures. In the more acidic solution of pH = 2.9, the surface-grafted poly(NIPAAm) and NVP copolymers exhibited adsorption and desorption behaviors below and above the phase-transition temperatures, while VPy copolymers exhibited only adsorption independent of temperature change. Furthermore, the adsorption capacity of all the surface-grafted polymers was deteriorated by the lowering of pH. The observed desorption and the deterioration of adsorption capacity suggest the weakening of adsorption strength for Ln(III) in low pH solutions. In this study, a possible adsorption/desorption mechanism of Ln(III) on surface-grafted NIPAAm-based polymers is discussed.     

Biomass grafted with polyamic acid for enhancement of cadmium(II) and lead(II) biosorption

In this study, a simple method was used to prepare modified biomass to improve its adsorption capacity for Cd²⁺ and Pb²⁺. The modified biomass of baker’s yeast was obtained by grafting polyamic acid, which was prepared via the reaction of pyromellitic dianhydride (PMDA) and lysine, onto the surface of glutaraldehyde-pretreated biomass at 50 °C for 3 h. The presence of polyamic acid on the biomass surface was verified by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), the morphologies of the biomass before and after modification were observed by microscope. Due to the high density of the carboxyl and amide groups on the biomass surface, the uptake for Cd²⁺ and Pb²⁺ showed a significant increase. According to Langmuir adsorption isotherm, the maximum uptake for Cd²⁺ and Pb²⁺ were 95.2 and 204.5 mg g⁻¹, which were 15- and 11-fold for that obtained on the uncontaminated biomass. The kinetics for Cd²⁺ and Pb²⁺ adsorption followed the pseudo-second-order model. The results of FTIR and XPS revealed that carboxyl, amide, and hydroxyl groups on the biomass surface were involved in the adsorption of Cd²⁺ and Pb²⁺.     

Adsorption thermodynamics and kinetics of Cr(VI) on KIP210 resin

Series of resin selection experiments were carried out and the KIP210 strong base anion exchange resin was confirmed to have the maximum equilibrium adsorption capacity to remove Cr(VI) from wastewater. The adsorption thermodynamics and kinetics of Cr(VI) on KIP210 resin were investigated completely and systematically. The static experiments were performed to study the effects of various parameters, such as shaking speed, resin dosage and pH during the adsorption process. The results indicate that the effect of external diffusion is eliminated at 160 rpm, the best pH value is 3.0 and the removal percentage of Cr(VI) increases with the increase of the resin dosage. The adsorption of Cr(VI) on KIP210 agrees well with the Langmuir isotherm and the adsorption parameters of thermodynamics are ΔH = 26.5 kJ mol⁻¹, ΔS = 126.7 J mol⁻¹ K⁻¹ and ΔG < 0. It demonstrates that the adsorption of Cr(VI) on KIP210 is a spontaneously endothermic physisorption process. Moreover, the adsorption process can be described well by a pseudo-second-order kinetic model and the activation energy is 30.9 kJ mol⁻¹. The kinetic analysis showed that the adsorption rate is controlled by intraparticle diffusion. The resin is successfully regenerated using the NaOH solutions.     

Chitin as biosorbent for phenol removal from aqueous solution: Equilibrium,kinetic and thermodynamic studies

Phenol removal from aqueous solution was studied employing chitin as low cost biosorbent. Initial biosorption tests carried out in the pH range 2–10 pointed out an optimum pH of 2. Temperature and initial phenol concentration were then varied in the ranges 15 ≤ T ≤ 50 °C and 10.4 ≤ C₀ ≤ 90.8 mg L⁻¹, respectively. The good applicability of Langmuir, Freundlich and Temkin models (R² = 0.990–0.993) to describe equilibrium isotherms suggested an intermediate mono-/multilayer biosorption mechanism along with a semi-homogeneous architecture of biosorbent surface. Biosorption capacity progressively increased from 3.56 to 12.7 mg g⁻¹ when starting phenol concentration was raised from 10.4 to 90.8 mg L⁻¹, and the related sorption kinetics was investigated by pseudo first-order, pseudo second-order and intraparticle diffusion models. The pseudo second-order model, which showed the best fit of experimental data (R² = 0.999), allowed estimating a second-order rate constant of 0.151 g mg⁻¹ h⁻¹ and a theoretical sorption capacity of 7.63 mg g⁻¹. Phenol biosorption capacity increased with temperature up to a maximum value, beyond which it decreased, suggesting the occurrence of a thermoinactivation equilibrium. Finally, to identify the main functional groups involved in phenol biosorption, both raw and phenol-bound materials were explored by FT-IR spectroscopy.     

Synthesis,structure and oxygen thermally programmed desorption spectra of La1−xCaxAlyFe1−yO3−δ perovskites

Perovskites La_1−xCa_xAl_yFe_1−yO_3−δ (x, y = 0 to 1) were prepared by high-temperature solid-state synthesis based on mixtures of oxides produced by colloidal milling. The XRD analysis showed that perovskites La_0.5Ca_0.5Al_yFe_1−yO_3−δ with a high Fe content (1 − y = 0.8–1.0) were of orthorhombic structure, perovskites with a medium Fe content (1 − y = 0.8–0.5) were of rhombohedral structure, and perovskite with the lowest Fe content (1 − y = 0.2) were of cubic structure. Thermally programmed desorption (TPD) of oxygen revealed that chemical desorption of oxygen in the temperature range from 200 to 1000 °C had proceeded in the two desorption peaks. The low-temperature α-peak (in the 200–550 °C temperature range) was brought about by oxygen liberated from oxygen vacancies; the high-temperature β-peak (in the 550–1000 °C temperature range) corresponded to the reduction of Fe⁴⁺ to Fe³⁺. The chemidesorption oxygen capacity increased with increasing Ca content and decreased with increasing Al content in the perovskites. The Al³⁺ ions restricted, probably for kinetic reasons, the reduction of Fe⁴⁺ and the high-temperature oxygen desorption associated with it.     

Preparation and characterization of magnetic chelating resin based on chitosan for adsorption of Cu(II), Co(II), and Ni(II) ions

Cross-linked magnetic chitosan–diacetylmonoxime Schiff’s base resin (CSMO) was prepared for adsorption of metal ions. CSMO obtained was investigated by means of scanning electron microscope (SEM), FTIR, ¹H NMR, wide-angle X-ray diffraction (WAXRD), magnetic properties and thermogravimetric analysis (TGA). The adsorption properties of cross-linked magnetic CSMO resin toward Cu²⁺, Co²⁺ and Ni²⁺ ions were evaluated. Various factors affecting the uptake behavior such as contact time, temperature, pH and initial concentration of the metal ions were investigated. The kinetics was evaluated utilizing the pseudo-first-order and pseudo-second-order. The equilibrium data were analyzed using the Langmuir, Freundlich, and Tempkin isotherm models. The adsorption kinetics followed the mechanism of the pseudo-second-order equation for all systems studied, evidencing chemical sorption as the rate-limiting step of adsorption mechanism and not involving a mass transfer in solution. The best interpretation for the equilibrium data was given by Langmuir isotherm, and the maximum adsorption capacities were 95 ± 4, 60 ± 1.5, and 47 ± 1.5 mg/g for Cu²⁺, Co²⁺ and Ni²⁺ ions, respectively. Cross-linked magnetic CSMO displayed higher adsorption capacity for Cu²⁺ in all pH ranges studied. The adsorption capacity of the metal ions decreased with increasing temperature. The metal ion-loaded cross-linked magnetic CSMO were regenerated with an efficiency of greater than 84% using 0.01–0.1 M ethylendiamine tetraacetic acid (EDTA).     

Adsorption Behavior of Rhodamine B on UiO-66

The adsorption characteristics of UiO-66 (a Zr-containing metal–organic framework formed by terephthalate) for Rhodamine B (RhB), such as isotherms, kinetics and thermodynamics, were investigated systematically. The batch adsorption data conform well to the Langmuir and Freundlich isotherms. The adsorption kinetics of UiO-66 for RhB can be well described by the pseudo first-order model, and the adsorption thermodynamic parameters ΔG₀, ΔH₀ and ΔS₀ at 273 K are − 6.282 kJ·mol^− 1, 15.096 kJ·mol^− 1 and 78.052 J·mol^− 1·K^− 1, respectively. The thermodynamic analyses show that the adsorption process of RhB on UiO-66 is more favorable at higher temperatures. UiO-66 can be regenerated by desorbing in DMF solution with ultrasonic for 1 h. UiO-66 can keep good performance for at least six cycles of sorption/desorption.     

Influence of regeneration conditions on the cyclic performance of amine-grafted mesoporous silica for CO2 capture: An experimental and statistical study

This work deals with the behavior of amine-grafted mesoporous silica (referred to as TRI-PE-MCM-41) throughout adsorption–desorption cycles in the presence of 5% CO₂/N₂ using various regeneration conditions in batch experiments. The criteria proposed to determine the optimum regeneration conditions are the working adsorption capacity, the rate of desorption and the change of adsorption capacity between consecutive cycles. Using a 2³ factorial design of experiments, the impact on the performance of the adsorbent of different levels of temperature, pressure, and flow rate of purge gas during desorption was determined. It was found that all the parameters under study have a statistically significant influence on the working adsorption capacity, but only temperature is influential with respect to desorption rate. Regeneration using temperature swing was found to be attractive, as the highest CO₂ adsorption capacity (1.95 mmol g^?1) and the fastest desorption rate (9.82×10^?4 mmol g^?1 s^?1) occurred when desorption was carried out at 150 °C. However, if vacuum is applied, regeneration can be achieved at a temperature as low as 70 °C with only a 13% penalty in terms of working adsorption capacity. It was also demonstrated that under the proper regeneration conditions, TRI-PE-MCM-41 is stable over 100 adsorption–desorption cycles.     

Cooperative adsorption of bisphenol-A and chromium(III) ions from water on activated carbons prepared from olive-mill waste

The aim of this study was to investigate the simultaneous adsorption of bisphenol A (BPA) and chromium ions from aqueous solution on activated carbons (both commercial and prepared from olive-mill waste), analyzing both kinetic and equilibrium adsorption data. The effects of solution pH and ionic strength on the adsorption processes were also studied, as well as the chemical interactions between the carbon surface and the pollutants. The activated carbon prepared from olive-mill waste showed: a large surface area (up to 1641 m² g⁻¹), a highly heterogeneous micropore distribution, and a basic chemical nature. The pore volume diffusion model was used to predict the adsorption kinetics of both pollutants. The effective diffusion coefficients ranged between 1.15 × 10⁻⁶ and 9.18 × 10⁻⁷ cm² s⁻¹ for the BPA–Cr(III) system and between 1.65 × 10⁻⁶ and 2.8 × 10⁻⁶ cm² s⁻¹ for the Cr(III)–BPA system. The presence of both Cr(III) and BPA in the binary systems increases the adsorption effective diffusion coefficients and therefore the overall adsorption rate of each pollutant. The increased adsorption of each adsorbate when both pollutants are present is due to the in situ formation of complex compounds between Cr(III), acting as central metallic cation, and BPA, acting as ligand, during adsorption of both adsorbates on activated carbon.     

Adsorptive removal of tetrahydrothiophene (THT) and tert-butylmercaptan (TBM) using Na-Y and AgNa-Y zeolites for fuel cell applications

Adsorptive removal of tetrahydrothiophene (THT) and tert-butylmercaptan (TBM) that are widely used sulfur odorants in pipeline natural gas was studied using AgNa-Y zeolites at ambient temperature and atmospheric pressure. The AgNa-Y were obtained via Ag⁺-exchange with Na⁺ of Na-Y at various exchange levels, and the contributions of formed adsorption sites (Ag⁺, Na⁺, Ag⁰, H⁺, and Ag₂O) in the THT and TBM adsorption uptake and selectivity were characterized. THT adsorption strength on these sites followed an order of Ag⁺ > Na⁺ ∼ Ag⁰ > H⁺ > Ag₂O. The adsorption strength of THT on Na⁺ sites was sufficiently high, thus an increase in the Ag⁺-exchange level did not lead to a notable increase in the breakthrough THT uptake. Differently, adsorption of TBM on Na⁺ sites was weak, whereas that on Ag⁺ sites was strong. This resulted in a marked increase in the breakthrough TBM uptake with an increase in the Ag⁺-exchange level, showing an order of magnitude higher uptake on AgNa-Y compared with that on Na-Y. Noticeably, the adsorption strength of THT on these adsorption sites was higher than that of TBM. This resulted in an almost 100% adsorption selectivity for THT over TBM, when these two sulfur species coexisted in the feed stream.     

Adsorption of chromate and para-nitrochlorobenzene on inorganic–organic montmorillonite

Batch studies of chromate and para-nitrochlorobenzene (p-NCB) on montmorillonite modified by poly(hydroxo aluminium) ions (Al) and cetyl trimethylammonium bromide (CTMAB) are reported. The amounts adsorbed decreased in the order Al-CTMA-mont > CTMA-mont > Al-mont > montmorillonite. Adsorption of chromate on Al-CTMA-mont reached a maximum at pH = 4 while p-NCB was pH independent. The adsorption kinetics could be described by the pseudo-second-order model. The adsorption rates for chromate and p-NCB were 9.73 and 5.78 mg g^? 1 min^? 1, respectively. The adsorption capacity of chromate and p-NCB on Al-CTMA-mont calculated by the Langmuir model was 2.3 × 10^? 4 and 2.2 × 10^? 4 mol/g, the values of the adsorption energy of the Dubinin-Radushkevitch (D-R) model were 13.9 and 7.8 kJ/mol. These results implied that the chromate adsorption proceeded as chemisorption, mainly by ion exchange whereas p-NCB was bound by van der Waals forces.     

Removal of Cu(II) by biosorption onto coconut shell in fixed-bed column systems

Biosorption of Cu(II) onto coconut shell, an agricultural biomaterial, was studied in a fixed-bed column. The Cu(II) biosorption column had the best performance at 10 mg L^?1 inlet Cu(II) concentration, 10 mL min^?1 flow rate and 20 cm bed depth. The equilibrium uptake of Cu(II) amounted to 7.25 mg g^?1. The simulation of the breakthrough curve was successful with the BDST and Yoon–Nelson models, but the entire breakthrough curve was best predicted by the Clark model. The design of a fixed bed column for Cu(II) removal from wastewater by biosorption onto coconut shell can be done based on these models.