Analytical fractionation of aquatic humic substances by metal affinity chromatography on iron(III)-coated cellulose

The chromatographic fractionation of aquatic humic substances (HS) onto iron(III)-coated cellulose (Cell-Fe(III)) as a metal-loaded adsorbent is described, analogously to the separation principle of the well-established metal affinity chromatography (MAC). For that purpose the sorption of HS from different aquatic origin on that collector was characterized by their kinetics and equilibrium distribution coefficients Kd. Based on Kd values of 10³ to 10⁴,mL/g, and fast sorption kinetics a preparative HPLC procedure, using stepwise increased pH-values (pH 8–12.5, borate buffer) as an eluent, was developed for the fractionation of dissolved HS (up to 7 fractions of different amount). The fractions obtained by this MAC procedure from selected aquatic HS samples were different in their Cu(II) complexation capacity, absorbance ratio E_{265 nm}/E_{365 nm} and Fourier transform infrared spectra. Received: 14 June 1999 / Revised: 6 August 1999 / Accepted: 10 August 1999     

On-line fractionation and characterization of aquatic humic substances by means of sequential-stage ultrafiltration

A five-stage tangential-flow ultrafiltration (UF) device equipped with advanced membrane filters (molecular weight cut-off: 1, 5, 10, 50 and 100 kDalton) of the polyethersulfone type is described and applied for the analytical on-line fractionation of a series of aquatic humic substances (HS) originating from surface or groundwaters. Fractionation patterns of HS (6 fractions each) evaluated by this UF device exhibit their particular dependence on the HS concentration, the pH-value and the salt content of the sample (10 ml) to be analyzed. Fundamental parameters (e.g., washing volume) governing the molecular-size fractionation of HS by means of multistage UF are discussed, too. The fractionation of an aquatic reference HS (BOC 3/9.5) by means of the above UF procedure reveals considerable differences preferably characterized by the UV-VIS absorption ratio E₃₅₀/E₄₅₀ and metal complexing capacity (Cu(II)) of the produced fractions. Moreover, molecular spectroscopy investigations (FTIR, ¹H-NMR) of the fraction series of this HS indicate that carbohydrate substructures (preferably found in fractions >50 k Dalton) and aromatic ones (preferably in fractions <5 k Dalton) are unevenly distributed.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Characterization of aquatic humic substances and their metal complexes by immobilized metal-chelate affinity chromatography on iron(III)-loaded ion exchangers

The analytical fractionation of aquatic humic substances (HS) by means of immobilized metal-chelate affinity chromatography (IMAC) on metal-loaded chelating ion exchangers is described. The cellulose HYPHAN, loaded with different trivalent ions, and the chelate exchanger Chelex 100, loaded to 90% of its capacity with Fe(III), were used. The cellulose HYPHAN, loaded with 2% Fe(III), resulted in HS distribution coefficients K_d of up to 10^3.7 mL/g at pH 4.0 continuously decreasing down to 10^1.5 at pH 12, which were appropriate for HS fractionation by a pH-depending chromatographic procedure. Similar distribution coefficients K_d were obtained for HS sorption onto Fe(III)-loaded Chelex 100. On the basis of Fe-loaded HYPHAN both, a low-pressure and high-pressure IMAC technique, were developed for the fractionation of dissolved HS applying a buffer-based pH gradient for their gradual elution between pH 4.0 and 12.0. By coupling the Chelex 100 column under high-pressure conditions with an inductively coupled plasma mass spectrometer an on-line characterization of HS metal species could be achieved. Using these fractionation procedures a number of reference HS were characterized. Accordingly, the HA (humic acids) and FA (fulvic acids) studied could be discriminated into up to 6 fractions by applying cellulose HYPHAN, significantly differing in their Cu(II) complexation capacity but hardly in their substructures assessed by conventional FTIR. In the case of using Chelex 100 exchanger resin two major UV active HS fractions were obtained, which significantly differ in their complexation properties for Cu(II) and Pb(II), respectively.     

Characterization of aquatic humic substances and their metal complexes by immobilized metal-chelate affinity chromatography on iron(III)-loaded ion exchangers

The analytical fractionation of aquatic humic substances (HS) by means of immobilized metal-chelate affinity chromatography (IMAC) on metal-loaded chelating ion exchangers is described. The cellulose HYPHAN, loaded with different trivalent ions, and the chelate exchanger Chelex 100, loaded to 90% of its capacity with Fe(III), were used. The cellulose HYPHAN, loaded with 2% Fe(III), resulted in HS distribution coefficients Kd of up to 10(3.7) mL/g at pH 4.0 continuously decreasing down to 10(1.5) at pH 12, which were appropriate for HS fractionation by a pH-depending chromatographic procedure. Similar distribution coefficients Kd were obtained for HS sorption onto Fe(III)-loaded Chelex 100. On the basis of Fe-loaded HYPHAN both, a low-pressure and high-pressure IMAC technique, were developed for the fractionation of dissolved HS applying a buffer-based pH gradient for their gradual elution between pH 4.0 and 12.0. By coupling the Chelex 100 column under high-pressure conditions with an inductively coupled plasma mass spectrometer an on-line characterization of HS metal species could be achieved. Using these fractionation procedures a number of reference HS were characterized. Accordingly, the HA (humic acids) and FA (fulvic acids) studied could be discriminated into up to 6 fractions by applying cellulose HYPHAN, significantly differing in their Cu(II) complexation capacity but hardly in their substructures assessed by conventional FTIR. In the case of using Chelex 100 exchanger resin two major UV active HS fractions were obtained, which significantly differ in their complexation properties for Cu(II) and Pb(II), respectively.     

Labile/inert metal species in aquatic humic substances: an ion-exchange study

Summary An ion-exchange procedure has been developed for the analytical fractionation of metals (e.g. Al, Co, Cu, Fe, Mn, Ni, Pb, Zn) forming labile/inert complexes with aquatic humic substances (HS) isolated (XAD 2, XAD 8, ultrafiltration) from bog, forest, ground and lake water. Using 1-(2-hydroxyphenylazo)-2-naphthol groups immobilized on cellulose (Cellulose HYPHAN) as chelating collector (batch and column procedure, resp.) for reactive metal fractions in dissolved HS, the kinetics and the degree of separation (referred to the total metal content) serve for the operational characterization of the metal lability. According to the separation kinetics (96 h), mostly the reactivity order Mn>Zn>Co>Pb>Ni>CuAl>Fe is observed for the above metals in HS, resulting in recoveries of >98% for Mn and Zn, but strongly varying for the other metals (e.g., 44–95% Cu, 18–84% Fe). By means of cellulose HYPHAN four metal fractions (e.g. Cu) can be distinguished kinetically: (a) about 50% of Cu freshly complexed with HS are directly exchanged (2nd order kinetics, k=0.275 1 · mol^–1 · s^–1) followed by (b) a less labile fraction (20–30%) of 1st to 2nd order exchange; (c) a hardly reactive fraction (5–10%) revealing uniform half times t_1/2 of 25 h closes the Cu exchange from HS. Moreover the Cu fraction (d), being exchange-inert in HS, amounts to 5–10% and increases by slow transformation processes of the formed HS/Cu species.     

Analytical fractionation of aquatic humic substances and their metal species by means of multistage ultrafiltration

The molecular-size fractionation of aquatic humic substances (HS) and their metal species by means of a novel sequential-stage ultrafiltration (UF) device equipped with five appropriate ultramembranes (1, 5, 10, 50 and 100 kD) is described. First of all, the concentration dynamics of macromolecules, particulary HS, during five-stage UF and its subsequent washing step has been modelled. Based on these results, the fractionation of aquatic HS (from ground and bog water) by means of multistage UF has been optimized for an analytical scale (10 ml sample, 1 mg/ml HS, 10 ml washing solution, pH 6.0). The molecular size-distribution of selected aquatic HS (BOC 1/2 from the "DFG-Versuchsfeld Bocholt", VM 5 from "Venner Moor", Germany) studied by five-stage UF exhibited strong systematic influences of the procedure used for their isolation. The molecular-size distribution of HS obtained by on-line UF and gel permeation chromatography (GPC) showed a satisfactory agreement in the range 1-50 kD. Moreover, when interrupting multistage UF for > 48 h a slow transformation in the HS samples has been found as gradually additional HS fractions of < 1 kD have been formed. Besides unloaded HS molecules, the molecular-size distribution of freshly formed metal species of HS (1.0 mg metal/g HS of Al(III), Cd(II), Cu(II), Fe(III), Mn(II), Ni(II), Pb(II), Zn(II), each) has been characterized by multistage UF as a function of pH-value, degree of loading and complexation time. Metal determinations as carried out by flame AAS, showed that considerable metal fractions in HS especially are present in molecules > 50 kD, which seemed to be rather acid-inert. With complexation times of < 2 days a transient shift of the molecular size distribution of both HS and their metal species (e.g., Al(III), Fe(III) to higher values (> 10 kD) has been found.     

Reduction of mercury(II) by tropical river humic substances (Rio Negro)-Part II. Influence of structural features (molecular size, aromaticity, phenolic groups, organically bound sulfur)

The influence of structural features of tropical river humic substances (HS) on their capability to reduce mercury(II) in aqueous solutions was studied. The HS investigated were conventionally isolated from Rio Negro water-Amazonas State/Brazil by means of the collector XAD 8. In addition, the isolated HS were on-line fractionated by tangential-flow multistage ultrafiltration (nominal molecular-weight cut-offs: 100, 50, 30, 10, 5 kDa) and characterized by potentiometry and UV/VIS spectroscopy. The reduction of Hg(II) ions to elemental Hg by size-fractions of Rio Negro HS was assessed by cold-vapor AAS (CVAAS). UV/VIS spectrometry revealed that the fractions of high molecular-size (F₁>100 kDa and F₂: 50-100 kDa) have a higher aromaticity compared to the fractions of small molecular-size (F₅: 5-10 kDa, F₆: <5 kDa). In contrast, the potentiometric study showed different concentration of functional groups in the studied HS fractions. The reduction of Hg(II) by aquatic HS fractions at pH 5 proceeded in two steps (I, II) of slow first order kinetics (t_1/2 of I: 160 min, t_1/2 of II: 300 min) weakly influenced by the molecular-size, in contrast to the differing degree of Hg(II) reduction (F₅>F₂>>F₁>F₃>F₄>>F₆). Accordingly, Hg(II) ions were preferably reduced by HS molecules having a relatively high ratio of phenolic/carboxylic groups and a small concentration of sulfur. From these results a complex ‘competition’ between reduction and complexation of mercury(II) by aquatic HS occurring in tropical rivers such as the Rio Negro can be suggested.     

Mass spectrometric investigations of the kinetic stability of chromium and copper complexes with humic substances by isotope-labelling experiments

Isotope-labelling exchange experiments were carried out to investigate the kinetic stability of Cr(III) complexes with humic substances (HS). To compare the results with those of an ion, not expected to form kinetically stable HS complexes with respect to its electron configuration, Cu(II) was investigated under the same conditions. HS solutions of different origin were therefore spiked with ⁵³Cr(III) or ⁶⁵Cu(II) after saturation of HS with chromium and copper of natural isotopic composition. In fractions of metal/HS complexes with different molecular weight, obtained by ultrafiltration and HPLC/ICP-MS using size exclusion chromatography (SEC), respectively, the isotope ratios of chromium and copper were determined by ICP and thermal ionisation mass spectrometry. Distinct differences in the isotopic composition of chromium were found in the permeate of the ultrafiltration compared with the corresponding unseparated solution, which indicates kinetically stable Cr(III)/HS complexes. On the other hand, the copper isotopic composition was identical in the permeate and the unseparated solution, which shows that a total exchange of Cu²⁺ ions took place between free and HS complexed copper ions. The SEC/ ICP-MS experiments also resulted in a different isotopic distribution of chromium in the chromatographically separated complexes whereas the copper complexes, separated by SEC, showed identical isotopic composition. The kinetic stability of Cr(III)/HS complexes could be explained by the d³ electron configuration of Cr³⁺ ions, a fact which is well known from classical Cr(III) complexes, and influences substantially the mobility of this heavy metal in the environment. Received: 7 December 1998 / Revised: 25 March 1999 / Accepted: 27 March 1999     

Uptake of Tm(III) ions onto polyurethane foam from H2O - ethanol mixture containing 1-(2-pyridylazo)-2-naphthol (PAN)

Summary The sorption of microquantities of Tm(III) ions on washed polyurethane foam (PUF) from a mixture of aqueous solution and ethanol containing PAN was examined. The maximum sorption of 3.18^. 10^-6M solution of Tm(III) ions was observed at pH 8 with 30-minute equilibration time. The optimum ratio of aqueous-ethanol phase for the sorption of Tm(III) ions was found to be 3:1 v/v, respectively. The sorption rate of metal ions on PUF is followed a first order kinetics and obeyed the equation for an intra particle diffusion process. The equilibrium concentration data of Tm(III) ions could be described satisfactorily by several adsorption isotherms. The Freundlich adsorption isotherm constants 1/nand K_Fare 0.66±0.02 and (5.7±0.3)^. 10^-3mol^. g^-1, respectively. The Langmuir isotherm constants for monolayer coverage (Q) and binding strength of sorption (b) are (2.5±0.7)^. 10^-5mol^. g^-1and (1.6±0.1)^. 10⁴l^. mol^-1, respectively. The sorption capacity derived from Dubinin-Radushkevich (D-R) isotherm is (1.7±0.2)^. 10^-4mol^. g^-1and the sorption free energy (E) is 9.8±0.2 kJ^. mol^-1indicating chemisorption phenomena. The thermodynamic parameters indicate that the sorption of Tm(III) ions onto PUF is endothermic, entropy driven and spontaneous in nature.     

Analytical fractionation of aquatic humic substances and their metal species by means of multistage ultrafiltration

The molecular-size fractionation of aquatic humic substances (HS) and their metal species by means of a novel sequential-stage ultrafiltration (UF) device equipped with five appropriate ultramembranes (1, 5, 10, 50 and 100 kD) is described. First of all, the concentration dynamics of macromolecules, particulary HS, during five-stage UF and its subsequent washing step has been modelled. Based on these results, the fractionation of aquatic HS (from ground and bog water) by means of multistage UF has been optimized for an analytical scale (10 ml sample, 1 mg/ml HS, 10 ml washing solution, pH 6.0). The molecular size-distribution of selected aquatic HS (BOC 1/2 from the DFG-Versuchsfeld Bocholt, VM 5 from Venner Moor, Germany) studied by five-stage UF exhibited strong systematic influences of the procedure used for their isolation. The molecular-size distribution of HS obtained by on-line UF and gel permeation chromatography (GPC) showed a satisfactory agreement in the range 1–50 kD. Moreover, when interrupting multistage UF for > 48 h a slow transformation in the HS samples has been found as gradually additional HS fractions of < 1 kD have been formed. Besides unloaded HS molecules, the molecular-size distribution of freshly formed metal species of HS (1.0 mg metal/g HS of Al(III), Cd(II), Cu(II), Fe(III), Mn(II), Ni(II), Pb(II), Zn(II), each) has been characterized by multistage UF as a function of pH-value, degree of loading and complexation time. Metal determinations as carried out by flame AAS, showed that considerable metal fractions in HS especially are present in molecules > 50 kD, which seemed to be rather acid-inert. With complexation times of < 2 days a transient shift of the molecular size distribution of both HS and their metal species (e.g., Al(III), Fe(III) to higher values (> 10 kD) has been found.     

Labile complexes of trace metals in aquatic humic substances: Investigations by means of an ion exchange-based flow procedure

The lability/inertness of heavy metals bound in aquatic humic substances (HS) has been characterized by means of ligand exchange with cellulose-immobilized triethylenetetramine-pentaacetic acid (TETPA) applying a flow system. On the basis of high metal distribution coefficients, K_d of 10³ to 10⁴ (ml/g) on cellulose TETPA even in slightly acidic HS solutions, labile and inert metal fractions in HS are characterized by their different kinetics and degree of phase exchange in small TETPA columns. For traces of metals bound to dissolved HS, the lability order Cd Mn(II)>Zn>Pb>Co>Ni>Cu is revealed. Systematic variation of environmentally relevant parameters shows the strong influence of the pH value and the ratio of metal loading/complexing capacity on the metal lability in HS. Surprisingly, in the case of freshly formed HS/Ni and HS/Cu complexes, slow transformation processes occur which lower their initial lability by one order of magnitude and supposedly increase their thermodynamic stability.Dedicated to Prof. Dr. F. Huber, Department of Chemistry, University of Dortmund, on the occasion of his 65th birthdayOn leave from Department of Analytical Chemistry, Institute of Chemistry, UNESP, Campus de Araraquara, CEP 14800-900, C. P. 355-Araraquara, SP, Brasil     

Quantification of carbohydrate structures in size fractionated aquatic humic substances by two-dimensional nuclear magnetic resonance

Two-dimensional phase sensitive C,H correlation spectra were successfully applied to the quantification of carbohydrate substructures in aquatic humic substance (HS) fractions obtained by tangential flow multistage ultrafiltration (TFMSTUF) of a selected bog water HS (HO13, German Research Program DFG-ROSIG) as well as a river HS (Suwannee River Fulvic Acid Reference of the International Humic Substances Society, IHSS). It turns out that after size fractionation the HS samples give very well resolved C,H-correlation spectra which offer a great potential for substructure quantification. Details of the combined substructure quantification technique, novel in HS characterization, are presented. The results of the combined procedure point out that carbohydrate moieties predominantly occur in higher molecular mass fractions (> 10 kDa) of isolated HS.     

Quantification of carbohydrate structures in size fractionated aquatic humic substances by two-dimensional nuclear magnetic resonance

Two-dimensional phase sensitive C,H correlation spectra were successfully applied to the quantification of carbohydrate substructures in aquatic humic substance (HS) fractions obtained by tangential flow multistage ultrafiltration (TFMSTUF) of a selected bog water HS (HO13, German Research Program DFG-ROSIG) as well as a river HS (Suwannee River Fulvic Acid Reference of the International Humic Substances Society, IHSS). It turns out that after size fractionation the HS samples give very well resolved C,H-correlation spectra which offer a great potential for substructure quantification. Details of the combined substructure quantification technique, novel in HS characterization, are presented. The results of the combined procedure point out that carbohydrate moieties predominantly occur in higher molecular mass fractions (> 10 kDa) of isolated HS.     

Separation of Y from Sr by zirconium vanadate gel ion-exchanger sorbent: kinetics and thermodynamic study

A new zirconium vanadate (Zr–V) ion-exchanger was synthesized and characterized for fast and selective separation procedure of ⁹⁰Y from ⁸⁹Sr. The method was based on ⁹⁰Y(III) sorption from aqueous HCl solution containing ⁸⁹Sr(II) onto Zr–V gel exchanger. The kinetics of Y(III) sorption from HCl solution by Zr–V exchanger was subjected to Weber–Morris, Lagergren, Bhattacharya and Venkobachar, and Bt models. Initially, the uptake of Y(III) onto the exchanger was fast followed by kinetically first-order sorption with an overall rate constant, K _Lager = (3.55 ± 0.03) × 10^?4 min^?1. Film and intraparticle transport are the two steps that might influence Y(III) sorption. The negative values of ΔG of ⁹⁰Y retention dictate that, the process is a spontaneous. The negative values of ΔH and ΔS reflect the exothermic nature of ⁹⁰Y(IIsorption and the random uptake of ⁹⁰Y(III) onto Zr–V sorbent. Zr–V exchanger offers unique advantages of ⁹⁰Y(III) retention over conventional solid sorbents in rapid and effective separation of traces of ⁹⁰Y(III) from Sr. The exchanger was successfully packed in column for an effective separation of ⁹⁰Y.     

Sorption of144Ce(III) and147Pm(III) on hydrated iron sesquioxide

The sorption of¹⁴⁴Ce(III) and of¹⁴⁷Pm(III) on hydrated iron sesquioxide suspension and the sorption of¹⁴⁴Ce(III) on hydrated iron sesquioxide in a laboratory column were studied. The dependence of the sorption on pH and time, the sorption isotherm, the temperature-dependence of sorption, and the effects of ionic strength on sorption and desorption were determined under static conditions. The maximum sorptions of¹⁴⁴Ce(III) and¹⁴⁷Pm(III) were reached at pH=7.4 (K_d=8.9·10⁵) and pH=9.1 (K_d=6.2·10⁵), respectively.     

Separation and determination of some trivalent metal ions using rhodamine B grafted polyurethane foam

The incorporation of rhodamine B into polyurethane foam matrix was prepared by mixing the rhodamine B with polyol (polyether) prior to the addition of diisocyanate reagent to form the polyurethane foam material. Rhodamine B grafted polyurethane foam (Rod.B-PUF) was found to be very suitable for the separation and preconcentration of trivalent metal ions e.g. bismuth (III), antimony (III) and iron (III) from thiocyanate solutions. Bismuth and antimony were separated from concentrated acid medium (1–6 M H₂SO₄). Iron (III) was separated from pH 1 to 3. The kinetics of sorption of the Bi (III), Sb (III) and Fe (III) onto the Rod.B-PUF was found to be fast, the extraction is accomplished from 5 to 10 min with average values of half-life of sorption (t_1/2) of 2.9 min. The average values of the Gibbs free energy (ΔG) for the sorption of metal ions onto Rod.B-PUF are ?6.6 kJ mol^?1, which reflect the spontaneous nature of sorption process. The sorption mechanism of the metal ion onto Rod.B-PUF was also discussed.     

The influence of humic acid on the pH-dependent sorption of americium(III) onto kaolinite

This work investigates the sorption of americium [Am(III)] onto kaolinite and the influence of humic acid (HA) as a function of pH (3–11). It has been studied by batch experiments (V/m = 250:1 mL/g, C _Am(III) = 1 × 10⁻⁵ mol/L, C _HA = 50 mg/L). Results showed that the Am(III) sorption onto the kaolinite in the absence of HA was typical, showing increases with pH and a distinct adsorption edge at pH 3–5. However in the presence of HA, Am sorption to kaolinite was significantly affected. HA was shown to enhance Am sorption in the acidic pH range (pH 3–4) due to the formation of additional binding sites for Am coming from HA adsorbed onto kaolinite surface, but reduce Am sorption in the intermediate and high pH above 6 due to the formation of aqueous Am-humate complexes. The results on the ternary interaction of kaolinite–Am–HA are compared with those on the binary system of kaolinite–HA and kaolinite–Am and adsorption mechanism with pH are discussed. Effect of different molecular weight of HA, with three HA fractions separated by ultrafiltration techniques, on the Am sorption to kaolinite were also studied. The results showed that the enhancement of the sorption of Am onto kaolinite at the acidic pH conditions (pH 3–4) was higher with HA fractions of higher molecular weight. Also, the Am sorption over a pH range from 6 to 10 decreased with decreasing molecular weight of HA.     

Sorption of Am(III) on natural sediment: experiment and modeling

Release of long-lived radioactivity to the aquatic bodies from various nuclear fuel cycle related operations is of great environmental concern in view of their possible migration into biosphere. This migration is significantly influenced by various factors such as pH, complexing ions present in aquatic environment and sorption of species involving radionuclides on the sediments around the water bodies. ^241/243Am are two major radionuclides which can contribute a great deal to radioactivity for several thousand years. In the present study, ²⁴¹Am sorption on natural sediment collected from site near a nuclear installation in India, has been investigated under the varying conditions of pH (3–10) and ionic strength [I = 0.01–1 M (NaClO₄)]. The sorption of Am increased with pH of the aqueous medium [10% (pH 2) to ~100% (pH 10)], which was explained in terms of the increased negative surface charge on the sediment particles. There was marginal variation in Am(III) sorption with increased ionic strength (within error limits) of the aqueous medium suggesting inner-sphere complexation/sorption process. Sediment was characterized for its elemental composition and structural phases using Energy Dispersive X-Ray (SEM-EDX) and X-Ray Diffraction (XRD) techniques. Zeta-potential measurement at I = 0.1 M (NaClO₄) suggested that Point of Zero Charge (pH_PZC) was ~2, indicating the presence of silica as major component in the sediment. Kurabtov plot using sorption data as a function of pH at fixed I = 0.1 M (NaClO₄) indicated the presence of multiple Am(III) species present on the surface. Potentiometric titration of the suspension indicated the presence of mineral oxide like behavior and assuming a generic nature (≡XOH) for all types of surface sites, protonation–deprotonation constants and total number of sites have been obtained. The sorption data has been modeled using 2-pK Diffuse Double Layer Surface Complexation Model (DDL-SCM). ≡XOAm²⁺ has been identified as the main species responsible for the sorption profile.     

Adsorption profile of preheated Cr(III)-SCN complexes on polyurethane foam

The accumulation of preheated chromium(III)-thiocyanate complexes onto polyurethane foam (PUF) has been studied. The maximum sorption of Cr(III) (7.01^.10^-5M) is occurred at pH 2 from 1.2M thiocyanate solution in 10 minute agitation time using 7.25 mg/ml PUF. The sorption data have been investigated by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The Freundlich parameters 1/n = 0.31 and of K _F = 9.7^.10^-4 mol^.g^-1, Langmuir constants M = 7.03^.10^-5 mol^.g^-1 and of b = 1.5^.10⁵ l^.mol^-1 and of D-R constants, C _m = 1.91^.10^-4 mol^.g^-1, affinity coefficient b = -0.0023 mol^2.kJ^-2 and sorption energy E = 14.7 kJ^.mol^-1 have been evaluated. Thermodynamic parameters of enthalpy, entropy and Gibbs free energy suggest the endothermic and spontaneous adsorption of Cr(III)-SCN complex onto PUF at higher temperature. The influence of common anions and cations on the accumulation of chromium-thiocyanate on PUF and possible sorption mechanism of [Cr(SCN)₄]^- species on PUF is discussed.     

Biosorption of lanthanum from aqueous solutions using magnetic alginate beads

Magnetic alginate beads are potential biosorbent for sorption of lanthanum(III) from an aqueous medium. Batch experiments were carried out to study the equilibrium, kinetics, and thermodynamics of lanthanum sorption. The effects of initial solution pH, initial lanthanum concentration, and temperature on lanthanum sorption were investigated. The optimum pH value was defined to be 4. Kinetic and isotherm experiments were carried out at the optimum pH. It was enough to reach the adsorption equilibrium at 4 hours, and the maximum uptake capacity was (1.8 mmol g^?1) at 25°C. Uptake kinetics and sorption isotherms were obtained and modeled using conventional and simple equations: best results were respectively obtained with the pseudo-second-order rate equation and the Langmuir equation. The La(III) loaded magnetic alginate beads were regenerated using 0.1 M CaCl₂ without activity loss.