Adsorptive removal of Cd(II) and Pb(II) ions from aqueous solutions by using Turkish illitic clay

The ability of Turkish illitic clay (TIC) in removal of Cd(II) and Pb(II) ions from aqueous solutions has been examined in a batch adsorption process with respect to several experimental conditions including initial solution pH, contact time, initial metal ions concentration, temperature, ionic strength, and TIC concentration, etc. The characterization of TIC was performed by using FTIR, XRD and XRF techniques. The maximum uptake of Cd(II) (11.25 mg g⁻¹) and Pb(II) (238.98 mg g⁻¹) was observed when used 1.0 g L⁻¹ of TIC suspension, 50 mg L⁻¹ of initial Cd(II) and 250 mg L⁻¹ of initial Pb(II) concentration at initial pH 4.0 and contact time of 240 min at room temperature. The experimental data were analyzed by the Langmuir, Freundlich, Temkin and Dubinin Radushkevich (D-R) isotherm models. The monolayer adsorption capacity of TIC was found to be 13.09 mg g⁻¹ and 53.76 mg g⁻¹ for Cd(II) and Pb(II) ions, respectively. The kinetics of the adsorption was tested using pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models. The results showed that the adsorption of Cd(II) and Pb(II) ions onto TIC proceeds according to the pseudo-second-order model. Thermodynamic parameters including the Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) changes indicated that the present adsorption process was feasible, spontaneous and endothermic in the temperature range of 5–40 °C.     

Heavy-metal adsorption by non-living biomass

The adsorption of some heavy metals onto the walls of harvested, washed, and dried non-living biomass cells of different Pseudomonas strains was studied at optimum experimental conditions using a simplified single component system. The Langmuir adsorption model was found to be a suitable approach to describe the system via multi-step processes. Isotherms measured at 30.0°C and pH 5.5 with [M]_total?=?10–100 mM for tight, reversible Cr⁶⁺(aq), Ni²⁺(aq), Cu²⁺(aq) and Cd²⁺(aq) binding by the cell walls of the investigated biomass fit the Langmuir model and give the pH-independent stoichiometric site capacities ν _i and equilibrium constants K _i for metal binding at specific biomass sites i?=?A, B, C, and D. Tight binding sites A, B, and D of the non-living biomass are occupied by Cr^VI, sites A and C by Ni^II, sites A and D by Cd^II, and only site B by Cu^II. It is concluded that ν _i is a stoichiometric parameter that is independent of the magnitude of K _i for binding site i and that the studied heavy metals selectively and tightly bind at different biomass sites.     

Adsorption characteristics of siloxanes in landfill gas by the adsorption equilibrium test

Due to the increase in energy cost by constantly high oil prices and the obligation to reduce greenhouse effect gases, landfill gas is frequently used as an alternative energy source for producing heat and electricity. Most of landfill gas utility facilities, however, are experiencing problems controlling siloxanes from landfill gas as their catalytic oxidizers are becoming fouled by silicon dioxide dust. To evaluate adsorption characteristics of siloxanes, an adsorption equilibrium test was conducted and parameters in the Freundlich and Langmuir isotherms were analyzed. Coconut activated carbon (CA1), coal activated carbon (CA2), impregnated activated carbon (CA3), silicagel (NCA1), and activated alumina (NCA2) were used for the adsorption of the mixed siloxane which contained hexamethyldisiloxane (L2), octamethylcyclotetrasiloxane (D4), and decamethylcyclopentasiloxane (D5). L2 had higher removal efficiency in noncarbon adsorbents compared to carbon adsorbents. The application of Langmuir and Freundlich adsorption isotherm demonstrated that coconut based CA1 and CA3 provided higher adsorption capacity on L2. And CA2 and NCA1 provided higher adsorption capacity on D4 and D5. Based on the experimental results, L2, D4, and D5 were converted by adsorption and desorption in noncarbon adsorbents. Adsorption affinity of siloxane is considered to be affect by the pore size distribution of the adsorbents and by the molecular size of each siloxane.     

Removal of Cr(VI) from aqueous solution using waste weed, Salvinia cucullata

Biosorption studies of Cr(VI) were carried out using waste weed, Salvinia cucullata. Various adsorption parameters were studied, such as agitation speed, contact time, pH, particle size, and concentrations of adsorbent and adsorbate. The equilibrium was achieved in 12 h. A lower pH favoured adsorption of Cr(VI). The kinetics followed pseudo-second-order rate equations. The adsorption isotherm obeyed both the Langmuir and Freundlich models. The calculated activation energy (1.1 kJ mol^-1) suggested that the adsorption followed a diffusion-controlled mechanism. Various thermodynamic parameters such as Δ G^°, Δ H^°, and Δ S^° were also calculated. The positive values of enthalpy indicated the endothermic nature of the reaction, and Δ S^° showed the increasing randomness at the solid liquid interface of Cr(VI) on the adsorbent, which revealed the ease of adsorption reaction. These thermo-dynamic parameters showed the spontaneity of the reaction. The maximum adsorption of uptake (232 mg g^-1) compared well with reported values of similar adsorbents. The rate-determining step was observed to follow an intra-particle diffusion model.     

Evaluation of Abelmoschus esculentus (lady's finger) seed as a novel biosorbent for the removal of Acid Blue 113 dye from aqueous solutions

The use of a new biosorbent derived from Abelmoschus esculentus (A. esculentus) seed for the removal of Acid Blue 113 (AB113) in aqueous solutions was investigated in batch mode. Biosorption studies were carried out under varying operational parameters including initial pH, biosorbent dosage, contact time, initial dye concentration and temperature. The results indicated that the biosorption properties were strongly dependent on initial pH. Fourier transform infrared spectroscopy analysis revealed that hydroxyl, carboxylic and amide functional groups present on the biosorbent surface were involved in the dye removal process. Equilibrium data were best fitted by the Langmuir model. The maximum biosorption capacity was 169.9 ± 3.1 mg g⁻¹ at 25 °C and initial pH 5.5. The kinetic data were in good agreement with the pseudo-second-order kinetic model. The process was controlled by diffusion through boundary layer at the initial stage followed by intra-particle diffusion at the later stage. Thermodynamic evaluation showed that the process was endothermic and spontaneous. The present study suggests that A. esculentus seed with maximum biosorption capacity which compared well with values reported in the literature can be a potential biosorbent for AB113 dye removal.     

无机柱撑膨润土对有机锡废水中锡的吸附研究

利用天然膨润土、羟基铁和羟基铁铝柱撑膨润土进行了吸附有机锡废水中总锡的实验.研究了膨润土投加量、pH、吸附时间和吸附等温线的变化规律.结果表明,达到吸附平衡的时间为1 h;总锡的吸附去除率最佳吸附pH在6.0～9.0;膨润土的投加量大于10 g/L时,总锡吸附去除率可达到最大值;总锡在天然膨润土上的吸附符合Freundlich吸附等温方程,而总锡在柱撑膨润土上的吸附同时符合Freundlich和Langmuir吸附等温方程;柱撑膨润土吸附活性位的数量是决定吸附性能的关键因素.在对总锡的吸附过程中,膨润土吸附容量的大小和吸附作用强弱的顺序为:羟基铁铝柱撑膨润土＞羟基铁柱撑膨润土＞天然膨润土.     

Contributions of adsorption,bioreduction and desorption to uranium immobilization by extracellular polymeric substances

● EPS immobilizes U(VI) via adsorption, bioreduction and desorption. ● This work provides a framework to quantify the three immobilization processes. ● The non-equilibrium adsorption of U follows pseudo-second-order kinetics. ● The equilibrium adsorption of U followed Langmuir and Freundlich isotherms. Hexavalent uranium (U(VI)) can be immobilized by various microbes. The role of extracellular polymeric substances (EPS) in U(VI) immobilization has not been quantified. This work provides a model framework to quantify the contributions of three processes involved in EPS-mediated U(VI) immobilization: adsorption, bioreduction and desorption. Loosely associated EPS was extracted from a pure bacterial strain, Klebsiella sp. J1, and then exposed to H₂ and O₂ (no bioreduction control) to immobilize U(VI) in batch experiments. U(VI) immobilization was faster when exposed to H₂ than O₂ and stabilized at 94% for H₂ and 85% for O₂, respectively. The non-equilibrium data from the H₂ experiments were best simulated by a kinetic model consisting of pseudo-second-order adsorption (k_a = 2.87 × 10⁻³ g EPS·(mg U)⁻¹·min⁻¹), first-order bioreduction (k_b = 0.112 min⁻¹) and first-order desorption (k_d = 7.00 × 10⁻³ min⁻¹) and fitted the experimental data with R² of 0.999. While adsorption was dominant in the first minute of the experiments with H₂, bioreduction was dominant from the second minute to the 50^th min. After 50 min, adsorption was negligible, and bioreduction was balanced by desorption. This work also provides the first set of equilibrium data for U(VI) adsorption by EPS alone. The equilibrium experiments with O₂ were well simulated by both the Langmuir isotherm and the Freundlich isotherm, suggesting multiple mechanisms involved in the interactions between U(VI) and EPS. The thermodynamic study indicated that the adsorption of U(VI) onto EPS was endothermic, spontaneous and favorable at higher temperatures.     

Removal of cobalt(Ⅱ) ion from aqueous solution by chitosan-montmorillonite

Montmorillonite （MMT） modified with chitosan （CTS, molecular weight = S x 104） was applied to remove heavy metal cations by using Co2＋ as a model ion. An increase in MMT interlayer distance observed from X-ray diffraction indicates the intercalation of CTS into MMT. Together with the results of scanning electron microscopy and Fourier transform infrared spectroscopy, it was concluded that the composite material of CTS and MMT （CTS-- MMT） was prepared successfully. The mass ratio of CTS to MMT had a strong influence on the adsorption performance of CTS-MMT. The highest adsorption value of 150 mg/g was obtained over the composite material with CTS to MMT mass ratio of 0.25, which is much higher than those reported in other studies. The adsorption isotherms and kinetic results indicated that Co2＋ was adsorbed over CTS-MMT in a multilayer model, and the chemical sorption of Co2＋ was determined to be the rate-limiting step.     

Kinetics and equilibrium adsorption study of lead(II) onto the low cost adsorbent—Eupatorium adenophorum spreng

Adsorption of Pb(II) ions from aqueous solution onto a low cost adsorbent—the Eupatorium adenophorum spreng has been investigated to evaluate the effects of initial lead ion concentration, contact time, pH and temperature on the removal of Pb(II) systematically. The optimal pH value for Pb(II) adsorption onto the E. adenophorum spreng was found to be 5.0. Thermodynamic parameters such as standard Gibbs free energy (ΔG°), standard enthalpy (ΔH°), and standard entropy (ΔS°) were evaluated by applying the van’t Hoff equation, which describes the dependence of equilibrium constant on temperature. The thermodynamics of Pb(II) adsorption onto the E. adenophorum spreng indicated that the adsorption was spontaneous and endothermic. Langmuir and Freundlich isotherms were used to analyze the equilibrium data at different temperatures and the equilibrium data were found to fit Freundlich isotherm equation better than Langmuir isotherm. The adsorption was analyzed using pseudo-second-order kinetic models.