Equilibrium and Kinetic Studies on the Removal of Reactive Red 2 Dye from an Aqueous Solution Using a Positively Charged Functional Group of the Nymphaea rubra Biosorbent

Nymphaea rubra stem was used as a low cost and easily available biosorbent for the removal of Reactive Red 2 dye from an aqueous solution. Initially, the effects of biosorbent dosage (0.2–1.0 g L^–1), pH (1–6), and dye concentration (30–110 mg L^–1) on dye removal were studied. Batch experiments were carried out for biosorption kinetics and isotherm studies. The results showed that dye uptake capacity was found to increase with a decrease in biosorbent dosage. Equilibrium uptake capacity was found to be greatest at a pH value of 2.0, when compared to all other pH values studied. The equilibrium biosorption isotherms were analyzed by the Freundlich and Langmuir models. The equilibrium data was found to fit very well with the Freundlich isotherm model when compared to the Langmuir isotherm model. The kinetic data was analyzed using pseudo-first order and pseudo-second order kinetic models. From the results, it was observed that the kinetic data was found to fit the pseudo-second order kinetic model very well. The surface morphology of the stem of the N. rubra biosorbent was exemplified by scanning electron microscopy. Fourier transform infrared analysis was employed to confirm the existence of an amine group in the stem of N. rubra.     

Biosorption Kinetics and Isotherm Studies of Cd(II) by Dried Enteromorpha compressa Macroalgae Cells from Aqueous Solutions

For the first time ever, Enteromorpha compressa macroalgae (ECM), which is commonly found in Turkey, has been used as biosorbent by us. This study aims to investigate the biosorption of Cd²⁺ from aqueous solutions in a batch system by using an alga of ECM in different concentrations, pH levels, agitation rates (90–150 rpm), and contact periods. The maximum biosorption capacity of the ECM was found to be 9.50 mg/g at pH 6, Cd²⁺ initial concentration of 10 mg/L and agitation rate 150 rpm. Cadmium removal efficiency was about 95%. The experimental isotherm data were analyzed using the Langmuir and Freundlich equations. Isotherm parameters for both equations were determined and discussed. The stated biosorption mechanism is explained by the Freundlich isotherm (r² = 0.998) theory. Two simplified kinetic models including a pseudo‐first‐ and second‐order equation were selected to follow the biosorption process. Kinetic parameters; rate constants, equilibrium adsorption capacities and related correlation coefficients, for each kinetic model were calculated and discussed. It was shown that the biosorption of cadmium onto ECM could be described by the pseudo‐second‐order equation (r² > 0.99).     

Cercis siliquastrum Tree Leaves as an Efficient Adsorbent for Removal of Ag(I): Response Surface Optimization and Characterization of Biosorption

The Cercis siliquastrum tree leaves are introduced as a low cost biosorbent for removal of Ag(I) from aqueous solution in a batch system. FT‐IR, XRD analysis, and potentiometric titration illustrate that the adsorption took place and the acidic functional group (carboxyl) of the sorbent was involved in the biosorption process. In addition, it was observed that the pH beyond pH_pzc 4.4 is favorable for the removal procedure. The effect of operating variables such as initial pH, temperature, initial metal ion concentration, and sorbent mass on the Ag(I) biosorption was analyzed using response surface methodology (RSM). The proposed quadratic model resulting from the central composite design approach (CCD) fitted very well to the experimental data. The optimum condition obtained with RSM was an initial concentration of Ag(I) of 85 mg L^?1, pH = 6.3 and sorbent mass 0.19 g. The applicability of different kinetic and isotherm models for current biosorption process was evaluated. The isotherm, kinetic, and thermodynamic studies showed the details of sorbate‐sorbent behavior. The competitive effect of alkaline and alkaline earth metal ions during the loading of Ag(I) was also considered.     

Biosorption of Cd(II), Ni(II) and Pb(II) from Aqueous Solution by Dried Biomass of Aspergillus niger: Application of Response Surface Methodology to the Optimization of Process Parameters

In this study, the biosorption of Cd(II), Ni(II) and Pb(II) on Aspergillus niger in a batch system was investigated, and optimal condition determined by means of central composite design (CCD) under response surface methodology (RSM). Biomass inactivated by heat and pretreated by alkali solution was used in the determination of optimal conditions. The effect of initial solution pH, biomass dose and initial ion concentration on the removal efficiency of metal ions by A. niger was optimized using a design of experiment (DOE) method. Experimental results indicated that the optimal conditions for biosorption were 5.22 g/L, 89.93 mg/L and 6.01 for biomass dose, initial ion concentration and solution pH, respectively. Enhancement of metal biosorption capacity of the dried biomass by pretreatment with sodium hydroxide was observed. Maximal removal efficiencies for Cd(II), Ni(III) and Pb(II) ions of 98, 80 and 99% were achieved, respectively. The biosorption capacity of A. niger biomass obtained for Cd(II), Ni(II) and Pb(II) ions was 2.2, 1.6 and 4.7 mg/g, respectively. According to these observations the fungal biomass of A. niger is a suitable biosorbent for the removal of heavy metals from aqueous solutions. Multiple response optimization was applied to the experimental data to discover the optimal conditions for a set of responses, simultaneously, by using a desirability function.     

Removal of Chromium from Synthetic Effluent using Nymphaea rubra

In the present work, biosorption of Cr(VI) by Nymphaea rubra was investigated in batch studies. Batch experiments were conducted to study the effect of initial sorbent dosage, solution pH and initial Cr(VI) concentration. The results showed that the equilibrium uptake capacity was increased with decrease in biomass dosage. The Cr(VI) removal was influenced by the initial chromium compound concentration. Langmuir and Freundlich adsorption isotherm models were used to represent the equilibrium data. The Freundlich isotherm model was fitted very well with the equilibrium data when compared to Langmuir isotherm model. The sorption results were analyzed for pseudo‐first order and pseudo‐second order kinetic model. It was observed that the kinetic data fitted very well with the pseudo‐second order rate equation when compared to the pseudo‐first order rate equation. Fourier transform infrared spectrum showed the presence of different functional groups in the biomass. The surface morphology of the sorbent was exemplified by SEM analysis. Aquatic weeds seem to be a promising biosorbent for the removal of chromium ions from water environment. This paper reports the research findings of a laboratory‐based study on the removal of Cr(VI) from the synthetic solution using the dried stem of N. rubra as a biosorbent.     

Study of the Interaction Mechanism in the Biosorption of Copper(II) Ions onto Posidonia oceanica and Peat

A systematic approach was used to characterize the biosorption of copper(II) onto two biosorbents, Posidonia oceanica and peat, focusing on the interaction mechanisms, the copper(II) sorption–desorption process and the thermal behavior of the biosorbents. Sorption isotherms at pH 4–6 were obtained and the experimental data were fitted to the Langmuir model with a maximum uptake (q_max) at pH 6 of 85.78 and 49.69 mg g^?1, for P. oceanica and peat, respectively. A sequential desorption (SD) with water, Ca(NO₃)₂, and EDTA was applied to copper‐saturated biosorbents. Around 65–70% copper(II) were desorbed with EDTA, indicating that this heavy metal was strongly bound. The reversibility of copper(II) sorption was obtained by desorption with HCl and SD. Fourier transform IR spectroscopy (FTIR) analysis detected the presence of peaks associated with OH groups in aromatic and aliphatic structures, CH, CH₂, and CH₃ in aliphatic structures, COO^? and COOH groups and unsaturated aromatic structures on the surface of both biosorbents, as well as peaks corresponding to Si? O groups on the surface of peat. The results of SEM‐EDX and FTIR analysis of copper‐saturated samples demonstrated that ion exchange was one of the mechanisms involved in copper(II) retention. Thermal analysis of biosorbent samples showed that copper(II) sorption–desorption processes affected the thermal stability of the biosorbents.     

Zn(II) Ion Biosorption onto Surface of Eucalyptus Leaf Biomass: Isotherm,Kinetic, and Mechanistic Modeling

Bioremediation of Zn(II) by biosorption across aqueous phase on to surface of eucalyptus leaf powder has been investigated in present research work. The adsorptive potential of eucalyptus leaf powder was evaluated as function of pH, temperature, contact time, agitation rate and particle size. Maximum metal ion uptake and percentage removal capacity of eucalyptus leaf powder were 23.5 mg g⁻¹ and 94%, respectively, at optimized pH 5, 20 ± 1°C, contact time 6 h, particle size 0.5 mm and agitation rate 200 rpm. The biomass surface analysis revealed the fact that the biomass surface was heterogeneous and porous in nature. The functional groups like amine, amide, carboxyl, hydroxyl, and methyl groups, significantly important for metal ion binding were present on biomass surface in tremendous amount. Additionally, the Fourier transformation IR spectrum analysis of acid and base activated eucalyptus leaf biomass ruled out all the possibilities of the presence of surface functional groups mentioned above. The reaction rate was studied by applying two rate limiting models pseudo first and pseudo second order. Pseudo second order model was found to be more suitable (R² = 0.998) in comparison to pseudo first order (R² = 0.724). Adsorption equilibrium of batch stirred reaction data fitting shows the dominance of Langmuir isotherm (R² = 0.99) against Freundlich isotherm (R² = 0.887) model with equipartitional involvement of both film and intra particle diffusion as rate limiting steps at differential status of contact time.     

Adsorption of Pb(II) Ions from Aqueous Solutions by Date Bead Carbon Activated with ZnCl2

This study reports on the adsorption characteristics of Pb(II) ions from aqueous solutions using ZnCl₂‐activated date (Phoenix dactylifera) bead (ADB) carbon with respect to change in adsorbent dosage, initial pH, contact time, initial concentration, and temperature of the solution. Kinetic studies of the data showed that the adsorption follows the pseudo‐second‐order kinetic model. Thermodynamic parameters, enthalpy change (ΔH° = 55.11 kJ/mol), entropy change (ΔS° = ? 0.193 kJ/mol/K), and Gibbs free energy change (ΔG°) were also calculated for the uptake of Pb(II) ions. These parameters show that adsorption on the surface of ADB was feasible, spontaneous in nature, and endothermic between temperatures of 298.2 and 318.2 K. The equilibrium data better fitted the Langmuir and Freundlich isotherm models than the D–R adsorption isotherm model for studying the adsorption behavior of Pb(II) onto the ADB carbon. It could be observed that the maximum adsorption capacity of ADB was 76.92 mg/g at 318.2 K and pH 6.5.     

Adsorption Kinetic and Equilibrium Studies on Removal of Lead(II) onto Glutamic Acid/Sepiolite

In this study, a modified method was used to increase the adsorption of lead ions from aqueous solutions by using modified clay mineral on the laboratory scale. Adsorption experiments have been carried out on the use of both thermal activated sepiolite (TAS) and their glutamate/sepiolite modification (GS) as adsorbents. The experimental data was analyzed using adsorption kinetic models (pseudo first‐ and second‐order equations). The pseudo second‐order kinetic model fitted well to the kinetic data (R² ≥ 0.99). Then, the Freundlich and Langmuir models were applied to describe the uptake of Pb(II) on GS and the Langmuir isotherm model agrees well with the equilibrium experimental data (R² ≥ 0.97). The maximum adsorption capacity was observed to be 128.205 mg/g by GS according to the Langmuir equation. Desorption efficiency of the GS was studied by the batch method using EDTA, HCl, and HNO₃ solutions. Desorption of 69.18, 74.55, and 80% of Pb(II) from GS was achieved with 0.1 M EDTA, 0.1 M HCl, and 0.1 M HNO₃ solutions, respectively. FTIR analysis suggests the importance of functional groups such as amino, hydroxyl, and carboxyl during Pb(II) removal. SEM observations demonstrated that an important interaction at the lead‐modified sepiolite interface occurred during the adsorption process. In addition, the thermodynamic constants was calculated that the values of the Gibbs free energy (ΔG*), enthalpy (ΔH*), and entropy (ΔS*) of modification were 86.79 kJ/mol, ?18.91 kJ/mol, and ?354.70 J/mol/K, respectively. The negative value of ΔH* shows exothermic nature of adsorption.     

Cd(II), Pb(II) and Zn(II) Removal from Contaminated Water by Biosorption Using Activated Sludge Biomass

Biosorption using activated sludge biomass (ASB) as a potentially sustainable technology for the treatment of wastewater containing different metal ions (Cd(II), Pb(II) and Zn(II)) was investigated. ASB metal uptake clearly competed with protons consumed by microbial biomass compared with control tests with non‐activated sludge biomass. Biosorption tests confirmed maximum exchange between metal ions and protons at pH 2.0–4.5. It was revealed by the study that the amount of metal ions released from the biomass increased with biomass sludge concentration. The result showed that maximum absorption of metal ions was observed for Cd(II) at pH 3.5, Pb(II) at pH 4.0, and pH 4.5 for Zn(II) ions. The maximum absorption capacities of ASB for Cd(II), Pb(II) and Zn(II) were determined to be 59.3, 68.5 and 86.5%, respectively. The biosorption of heavy metals was directly proportional to ASB stabilization corresponding to a reduction in heavy metals in the order of Cd < Pb < Zn. The order of increase of biosorption of metal ions in ASB was Zn(II) < Pb(II) < Cd(II), and this was opposite to that of non active sludge. The results indicate that ASB is a sustainable tools for the bioremediation of Cd(II), Pb(II) and Zn(II) ions from industrial sludge and wastewater treatment plants.     

Assessment of the Biosorption Characteristics of a Spent Cottonseed Husk Substrate for the Decolorization of Methylene Blue

This study concentrates on the possible application of the spent cottonseed husk substrate (SCHS), an agricultural waste used after the cultivation of white rot fungus Flammulina velutipes, to adsorb methylene blue (MB) from aqueous solutions. Batch studies were carried out with variable initial solution pH, adsorbent amount, reaction time, temperature, and initial MB concentration. MB uptake was favorable at pH ranging from 4.0 to 12.0, and the equilibrium adsorption capacity of 143.5 mg g^?1 can be reached promptly within about 240 min. The combination analysis of FTIR and BET techniques revealed that the massive functional groups on the biosorbent surface, such as hydroxyl and carboxyl, were responsible for the biosorption of MB. It was found that adsorption data matched the pseudo‐second order kinetic and Langmuir isotherm models. Thermodynamic parameters of free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°), obtained from biosorption MB ranging from 293 to 313 K, showed that the sorption experiment was a spontaneous and endothermic process. The study highlighted a new pathway to develop a new potential utilization of SCHS as a low‐cost sorbent for the removal of MB pollutants from wastewater.     

Adsorption of Metal Ions onto the Chemically Modified Agricultural Waste

This paper discusses about the adsorption of metal ions such as Cu(II), Cd(II), Zn(II), and Ni(II) from aqueous solution by sulfuric acid treated cashew nut shell (STCNS). The adsorption process depends on the solution pH, adsorbent dose, contact time, initial metal ions concentration, and temperature. The adsorption kinetics was relatively fast and equilibrium was reached at 30 min. The adsorption equilibrium follows Langmuir adsorption isotherm model. The maximum adsorption capacity values of the modified cashew nut shell (CNS) for metal ions were 406.6 mg/g for Cu(II), 436.7 mg/g for Cd(II), 455.7 mg/g for Zn(II), and 456.3 mg/g for Ni(II). The thermodynamic study shows the adsorption of metal ions onto the STCNS was spontaneous and exothermic in nature. The kinetics of metal ions adsorption onto the STCNS followed a pseudo‐second‐order kinetic model. The external mass transfer controlled metal ions removal at the earlier stages and intraparticle diffusion at the later stages of adsorption. A Boyd kinetic plot confirms that the external mass transfer was the slowest step involved in the adsorption of metal ions onto the STCNS. A single‐stage batch adsorber was designed using the Langmuir adsorption isotherm equation.     

Dynamic,Mechanistic, and Thermodynamic Modeling of Zn(II) Ion Biosorption onto Zinc Sequestering Bacterium VMSDCM

The surface of the bacterial cells before the biosorption of Zn(II) ion has been found rough, heterogeneous, and non‐crystalline together with tremendous protrusions and negatively charged functional groups. The bacterium was characterized as rod shaped with Gram‐negative type of cell wall structure. In reaction dynamics, pseudo‐second‐order kinetics with higher linear correlation coefficient (R²) ranging between 0.97 and 0.99, lower sum of square errors (SSE) (0.035–0.081) and chi (χ²) (0.0013–0.009) provided a better explanation of sorption of Zn(II) ion on bacterium surface as compared to pseudo‐first‐order model. The removal of Zn(II) was governed by both film and intra‐particle diffusion at onset and later stage of sorption of metal ion on the surface of bacterial cells. The R² (0.92–0.94) for intra‐particle diffusion model was quite higher with lower values of SSE (9.56–16.33) and chi (χ²) (11.26–19.65) against the Bangham's model. The positive value of ΔH (16.628 × 10^?6 kJ/mol) and ΔS (5320.90 kJ/mol/K) showed that the biosorption of Zn(II) ion across liquid phase on bacterial surface was endothermic with increased randomness at solid–liquid interface. The negative values of ΔG demarcated the whole process as spontaneous in nature. In the present work, the distribution coefficient was found to be > 0.5 at various temperature ranges. At the attainment of equilibrium, the residual concentration of Zn(II) ion in liquid phase was around 0.6 mg/L, which was much below the limit described by United States Environmental Protection Agency (USEPA), i.e. 5 mg/L.     

Chromium Removal through Biosorption and Bioaccumulation by Bacteria from Tannery Effluents Contaminated Soil

Four bacterial isolates (two resistant and two sensitive to chromium) were isolated from soil contaminated with tannery effluents at Jajmau (Kanpur), India, and were identified by 16S rDNA gene sequencing as Stenotrophomonas maltophilia, Exiguobacterium sp., Pantoea sp., and Aeromonas sp. Biosorption of chromium by dried and living biomasses was determined in the resistant and sensitive isolates. The effect of pH, initial metal concentration, and contact time on biosorption was studied. At pH 2.5 the living biomass of chromium resistant isolate Exiguobacterium sp. ZM‐2 biosorbed maximum amount of Cr⁶⁺ (29.8 mg/g) whereas the dried biomass of this isolate biosorbed 20.1 mg/g at an initial concentration of 100 mg/L. In case of chromate sensitive isolates, much difference was not observed in biosorption capacities between their dried and living biomasses. The maximum biosorption of Cr³⁺ was observed at pH 4.5. However, biosorption was identical in resistant and sensitive isolates. The data on chromium biosorption were analyzed using Langmuir and Freundlich isotherm model. The biosorption data of Cr⁶⁺ and Cr³⁺ from aqueous solution were better fitted in Langmuir isotherm model compared to Freundlich isotherm model. Metal recovery through desorption was observed better with dried biomasses compared to the living biomasses for both types of chromium ions. Bioaccumulation of chromate was found higher in chromate resistant isolates compared to the chromate sensitive isolates. Transmission electron microscopy confirmed the accumulation of chromium in cytoplasm in the resistant isolates.     

Experimental and Isothermal Studies on Sorption of Congo Red by Modified Mycelial Biomass of Wood‐rotting Fungus

Batch biosorption experiments were carried out for the removal of Congo red from aqueous solution using native and pretreated mycelial pellets/biomass of Trametes versicolor. The effect of process parameters such as contact time, dye concentration, and pH on the extent of Congo red biosorption has been investigated. Higher dye concentrations resulted in lower biosorption. Increases in biomass dosage led to increases in the levels of biosorption. Biosorption kinetics and equilibrium data are essential basic requirements to develop an effective and accurate design model for the removal of the dye. A kinetic study showed that the biosorption of the dye on fungal biomass was a gradual process. Pseudo‐first‐order, pseudo‐second‐order, and Bangham's model were used to fit the experimental data. The results of the kinetic studies showed that the second‐order kinetic model fitted well for the present experimental data. Equilibrium isotherms were analyzed by Langmuir, Freundlich, Dubnin‐Radushkevich, and Temkin isotherms. The biosorption equilibrium data obeyed the Langmuir and Temkin isotherms well. Acidic pH was favorable for the biosorption of the dye. Studies on the pH effect and desorption show that chemisorption seems to play a major role in the biosorption process. Among the native and pretreated biomass studied, autoclaved biomass showed a better biosorption capacity.     

Removal of Copper,Nickel, and Zinc Ions from Electroplating Rinse Water

Removal of copper, nickel, and zinc ions from synthetic electroplating rinse water was investigated using cationic exchange resin (Ceralite IR 120). Batch ion exchange studies were carried out to optimize the various experimental parameters (such as contact time, pH, and dosage). Influence of co‐existing cations, chelating agent EDTA on the removal of metal ion of interest was also studied. Sorption isotherm data obtained at different experimental conditions were fitted with Langmuir, Freundlich, Redlich–Peterson, and Toth models. A maximum adsorption capacity of 164 mg g^?1 for Cu(II), 109 mg g^?1 for Ni(II), and 105 mg g^?1 for Zn(II) was observed at optimum experimental conditions according to Langmuir model. The kinetic data for metal ions adsorption process follows pseudo second‐order. Presence of EDTA and co‐ions markedly alters the metal ion removal. Continuous column ion exchange experiments were also conducted. The breakeven point of the column was obtained after recovering effectively several liters of rinse water. The treated rinse water could be recycled in rinsing operations. The Thomas and Adams–Bohart models were applied to column studies and the constants were evaluated. Desorption of the adsorbed metal ions from the resin column was studied by conducting a model experiments with Cu(II) ions loaded ion exchange resin column using sulfuric acid as eluant. A novel lead oxide coated Ti substrate dimensionally stable (DSA) anode was prepared for recovery of copper ions as metal foil from regenerated liquor by electro winning at different current densities (50–300 A cm^?2).     

Oreganum Stalks as a New Biosorbent to Remove Textile Dyes from Aqueous Solutions

In the present study, Oreganum onites L. stalks in natural and chemically modified with HNO³ and H³PO⁴ used as adsorbent for removal of both acidic and basic dyes from waters. The adsorption was studied as a function of pH and contact time by batch method. All tested biosorbents were characterized by FT‐IR, scanning electron microscopy, and measuring the pH dependence of the zeta potential. The adsorption isotherms were fitted to Langmuir isotherm. The maximum adsorption capacity of dyes was 280.73 mg g^?1 for Basic Red 18, 147.06 mg g^?1 for methylene blue and 112.36 for Acid Red 111, which is comparable to that of other lignocellulosic materials. The modification process was considerably increased the biosorption capacity of lignocellulosic material, resulting in a 56–63% increase in the biosorption capacity of basic dyes and a 125% increase in the biosorption capacity of acidic dye. The present study illustrated that the most effective factors in the adsorption of basic dye were surface charge and acidic groups on lignocellulosic biosorbents, while non‐electrostatic forces as well as electrostatic forces were also effective in the adsorption of acidic dye. In conclusion, Oreganum stalks can be considered as a very prospective adsorbent for the removal of tested basic and acidic dyes.     

Optimization and Characterization of Tl(I) Adsorption onto Modified Ulmus carpinifolia Tree Leaves

Ulmus carpinifolia tree leaves were successfully used to remove Tl(I) from aqueous solution in a batch system. In order to improve the uptake capacity of sorbent, it was modified by various chemical agents such as NaOH, HNO₃, NH₃, NaCl, NaHCO₃, and CaCl₂. Among the modifiers, NaCl was the best. Equilibrium behavior of sorbent with Tl(I) was examined by the several isotherms. Considering modified U. carpinifolia equilibrium data fitted well to the Langmuir model with maximum capacity of 54.6 mg/g. The other isotherms such as: Freundlich and Dubinin‐Redushkevich (D‐R) models were also examined. The central composite design (CCD) was successfully employed for optimization of biosorption process. An empirical model was given through using response surface methodology. Also its validation was recognized by using relevant statistical tests such as ANOVA. The optimum conditions of biosorption: pH, m (amount of sorbent) and C (initial concentration) were found to be 7.9, 11.4 g/L, and 8.8 mg/L, respectively. On the other hand thermodynamic parameters: ΔG, ΔH, and ΔS were evaluated: the obtained results show that biosorption process was spontaneous and exothermic. Eventually, FT‐IR analysis confirmed that the main functional groups of sorbent have been involved through the biosorption process.     

Equilibrium,Thermodynamic, and Kinetic Studies on Lead (II) Biosorption from Aqueous Solution by Saccharomyces cerevisiae Biomass

This paper presents a biosorption procedure for the preconcentration of Pb²⁺ ions using Saccharomyces cerevisiae biomass. The influence of several factors including pH, biomass dosage, contact time, and temperature on biosorption efficiency were optimized. At optimum value of all the equilibrium, thermodynamic, and kinetic parameters of Pb²⁺ ion biosorption was investigated by testing the Langmuir and Freundlich models and first and second order kinetic models were applied. The biosorption capacity of S. cerevisiae biomass was determined 89.6 mg/g, while the retained Pb²⁺ ions by S. cerevisiae were reversibly eluted using 5 mol/L HNO₃. Due to the high stability of S. cerevisiae the applied biomass can be used successively ten times with a slightly decrease (about 20%) in the recovery of Pb²⁺ ions. The calculated thermodynamic parameters, ΔG°, ΔH°, and ΔS° showed that the biosorption of Pb²⁺ ion onto S. cerevisiae biomass was feasible, spontaneous, and endothermic under examined conditions. The results of kinetic analysis showed that the biosorption processes of Pb²⁺ ions onto S. cerevisiae biomass followed pseudo second order kinetics.     

Biosorption of Methylene Blue from Aqueous Solution Using a Bioenergy Forest Waste: Xanthoceras sorbifolia Seed Coat

Xanthoceras sorbifolia seed coat (XSSC), a bioenergy forest waste, was used for the adsorption of methylene blue (MB) from aqueous solutions. The effects of adsorbent dosage, pH, adsorbate concentration and contact time on MB biosorption were studied. The equilibrium adsorption data was analyzed by Langmuir and Freundlich isotherm models. The results indicated that the Langmuir model provided the best correlation with the experimental data. The adsorption capacity of XSSC for MB was determined with the Langmuir model and was found to be 178.6 mg/g at 298 K. The adsorption kinetic data was modeled using the pseudo‐first order, pseudo‐second order, and intraparticle diffusion kinetic equations. It was seen that the pseudo‐second order equation could describe the adsorption kinetics, and intraparticle diffusion was not the sole rate controlling factor. Thermodynamic parameters were also evaluated. Standard Gibbs free energy was spontaneous for all interactions, and the biosorption process exhibited exothermic standard enthalpy values. The results indicated that XSSC is an attractive alternative for removing cationic dyes from wastewater.