Sorption characteristics of an economical sorbent material used for removal radioisotopes of cesium and europium

Application study for the evaluation of sorption characteristics of sawdust as an economical sorbent material used for decontamination of radioisotopes cesium and europium from aqueous solution has been carried out in the present work. In this respect, sawdust (untreated and treated by HNO₃) has been prepared from the commercial processing of wood for furniture production. Pore properties of the activated carbon such as BET surface area, pore volume, pore size distribution, and pore diameter were characterized by N₂ adsorption and DFT software. Radiotracer method onto sawdust from aqueous solutions was studied in a batch technique with respect to pH, contact time, temperature. The kinetics of adsorption of Eu³⁺ and Cs⁺ have been discussed using five kinetic models namely, pseudo-first-order model, pseudo-second-order model, Elovich equation, intraparticle diffusion model, and modified Freundlich equation that have been tested in order to analysis the experimental data. Kinetic parameters and correlation coefficients were determined. It was shown that the second-order kinetic equation could describe the sorption kinetics for two metal ions. The metal uptake process was found to be controlled by intraparticle diffusion. Thermodynamic parameters, such as ΔH, ΔG and ΔS, have been calculated by using the thermodynamic equilibrium coefficient obtained at different temperatures. The obtained results indicated that endothermic nature of sorption process for both ^152+154Eu and ¹³⁴Cs onto sawdust.     

Reduction of palladium(II) monoglycinate complexes at rotating disc palladium electrode in acid media

Reduction of palladium(II) glycinate complexes in strongly acid 0.5 M NaClO₄ solutions (pH 0.6 and 1.0) with variable palladium(II) complex and free glycine concentration was studied by the taking of cyclic voltammograms at palladium rotating disc electrode. It is shown that it was a chelate monoglycinate palladium(II) complex that was present in all studied solutions and underwent the reduction. The diffusion coefficient of the chelate monoglycinate palladium(II) complex D = (6.5 ± 0.5) × 10⁻⁶ cm²/s was determined from the limiting diffusion current of the complex reduction. The monoglycinate palladium(II) complex reduction occurred in the double-layer segment of the palladium charging curve; it was not complicated by hydrogen adsorption at electrodes. The palladium(II) complex reduction half-wave potential was determined (E _1/2 = ∼0.300 to 0.330 V (SCE)). It is shown that the decreasing of the number of ligands coordinated by palladium via nitrogen atom facilitates the complex reduction process. In particular, the reduction potentials of palladium(II) complexes with different ligand number at palladium electrode shifted markedly toward negative potentials in the series: Pdgly⁺ < Pd(gly)2 < Pd(gly)₄²⁻.     

Preconcentration procedure trace amounts of palladium using modified multiwalled carbon nanotubes sorbent prior to flame atomic absorption spectrometry: 1st Nano Update

A method for preconcentration of palladium at trace level on modified multiwalled carbon nanotubes columns and determination by flame atomic absorption spectrometry (FAAS) has been developed. Multiwalled carbon nanotubes (MWCNTs) were oxidized with concentrated HNO₃ and the oxidized multiwalled carbon nanotubes were modified with 5-(4′-dimethylamino benzyliden)-rhodanine, and then were used as a solid sorbent for preconcentration of Pd(II) ions. Factors influencing sorption and desorption of Pd(II) ions were investigated. The sorption of Pd(II) ions was quantitative in the pH range of 1.0–4.5, whereas quantitative desorption occurs with 3.0 mL 0.4 mol L^?1 thiourea. The amount of eluted palladium was measured using flame atomic absorption spectrometry. The effects of experimental parameters, including sample flow rate, eluent flow rate, and eluent concentration were investigated. The effect of coexisting ions showed no interference from most ions tested. The proposed method permitted a large enrichment factor (about 200). The relative standard deviation of the method was ±2.73% (for eight replicate determination of 2.0 μg mL^?1 of Pd(II)) and the limit of detection was 0.3 ng mL^?1. The method was applied to the determination of Pd(II) in water, road dust, and standard samples.     

Colorimetric determination of palladium (II) by means of promazine hydrochloride

In acetate buffer medium palladium(II) ions form with promazine hydrochloride (PM) two complexes: an orange one of a formula [Pd(C₁₇H₂₀N₂S)]²⁺ (λ_max = 460 nm, ε = 4.5 × 10³, at 20 °C and pH = 2) and a violet one of a formula [Pd(C₁₇H₂₀N₂S)₂]²⁺ (λ_max = 540 nm, ε = 8.8 × 10³ at 20 °C and pH = 2).The values for instability constants determined by Bjerrum's method amount to pK₁ = 3.95; pK₂ = 3.07; pβ₁ = 3.95; pβ₂ = 7.02, respectively.A colorimetric method of the determination of palladium(II) has been elaborated. The method consists in a measurement of the absorbance of the violet complex of palladium(II) with promazine hydrochloride at λ = 540 nm. The method permits the determination of 2–17 μg Pd/ml with an error of ±2%. The time of the determination is 20 min. Iron(III), Ce(IV), Pt(IV), V(V), Cr(VI), and HNO₃ interfere with the determination.     

Sorption of aqueous palladium onto synthetic hydroxyapatite

The sorption of Pd(II) on hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) has been studied at 25 °C as a function of pH, in 0.01 M NaClO₄, and 0.01 and 0.025 M Ca(ClO₄)₂ aqueous background electrolytes and Pd(II) concentration (9.3 to 47 ??M), trying to minimize some types of reactions, such as solid dissolution of and metal precipitation. The radiotracer palladium, ¹⁰⁹Pd, obtained by neutron irradiation, has been used to calculate the palladium??s distribution coefficients K _d between aqueous and solid phase. A mathematical treatment of results has been made by ion-exchange theory in order to interpret palladium sorption onto treated solid. For this, we take into account the existence of active sites at the hydroxyapatite surface, and the aqueous solution chemistry of palladium as well as the effect of phosphate anions from solid dissolution. The results can be explained as evidence of sorption of the species PdOH⁺, and of a mixed hydroxo complex of Pd²⁺ like (XCaO^?)?CPdOH⁺·nH₂O fixed onto {??Ca?COH} surface sites of the hydroxyapatite.     

Catalytic kinetic spectrophotometric determination of trace amounts of palladium with dahlia violet after separation and preconcentration on sulphydryl dextran gel

A sensitive and selective kinetic catalytic spectrophotometric method has been described for the determination of trace amounts of palladium(II). The method is based on the catalytic effects of palladium(II) on the reduction reactions of Dahlia Violet with sodium dihydrogen hypophosphite (NaH₂PO₂) in a sulfuric acid medium. Under optimal conditions, trace amounts of palladium(II) can be determined. A good linear range has been obtained in the concentration range of Pd(II) over 0.001–0.028 μg/mL with a detection limit of 5.9 × 10⁻¹⁰ g/mL. The method has been successfully applied to the determination of palladium(II) in ore and soil samples. The relative standard deviation was less than 5.0% (n = 11). The coexisting ions were eliminated by preconcentration and separation on sulphydryl dextran gel with satisfactory results. The text was submitted by the authors in English.     

Uncertainty of determination of palladium in road dust sample by inductively coupled plasma mass spectrometry

The determination of palladium in a road dust sample taken close to the highway (w _Pd=450 ng g⁻¹) was carried out by the ICP-MS method after sample decomposition by aqua-regia. Analyses were evaluated by two methods: external calibration accompanied with mathematical correction of spectral interferences (EC) and isotope dilution measurement after separation of Pd by extraction to dibutyl sulfide solution (ID). In both cases, the uncertainties and accuracy of results were investigated. Although in the case of ideally homogeneous sample the repeatability of EC results (11 ng g⁻¹ Pd) was somewhat lower than those of ID results (16 ng g⁻¹ Pd), the uncertainties of results of both techniques were almost the same and they reached the level of 19 ng g⁻¹ Pd. The main uncertainty source of the EC method is represented by the correction of spectral interferences. In case of real non-homogeneous sample, the main uncertainty component represents the soil sampling. The uncertainty of results (approx. 75 ng g⁻¹ Pd) only slightly exceeded the repeatability (approx. 70 ng g⁻¹ Pd). The accuracy of results was proven by analyses of CRM TDB–1 Diabas Rock (in case of ID) and by the standard addition method (in case of EC).     

Effect of pH, ionic strength, foreign ions, fulvic acid and temperature on 109Cd(II) sorption to γ-Al2O3

The sorption of Cd(II) from aqueous solution on γ-Al₂O₃ was investigated under ambient conditions. Experiments were carried out as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic acid and temperature. The results indicated that the sorption of Cd(II) was strongly dependent on pH and ionic strength. At low pH, the sorption of Cd(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on γ-Al₂O₃ surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms at three different temperatures. The thermodynamic data (ΔG ⁰, ΔS ⁰, ΔH ⁰) calculated from the temperature dependent sorption isotherms suggested that the sorption of Cd(II) on γ-Al₂O₃ was an spontaneous and endothermic process.     

Removal of natural uranium from water produced in the oil industry using Algerian bentonite

Batch sorption experiments have been carried out to remove natural uranium (NORM) from water obtained together with crude oil and natural gas, using Algerian bentonites. The effect of some important factors such as S/L ratio, pH, initial concentration, particle size was evaluated and a kinetic study performed. The value of the distribution coefficient (K _d) at equilibrium for natural uranium varied from 30 to 600 cm³·g⁻¹ and 50 to 1100 cm³·g⁻¹ (∼10% margin error) using natural bentonite and drilling bentonite, respectively. The isotherms showed that the data are consistent with both Freundlich and Langmuir models.     

Sorption behavior of Co(II) on γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> in the presence of humic acid

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The extent of sorption of divalent metal cations is controlled by a number of factors including cosorbing or complexing. In this work, the effects of pH, humic acid HA/Co(II) addition orders, ionic strength, concentration of HA, and foreign cations on the Co(II) sorption on γ-Al₂O₃ in the presence of HA were investigated. The sorption isotherms of Co(II) on γ-Al₂O₃ in the absence and presence HA were also studied and described by using S-type sorption model. The experimental results showed that the Co(II) sorption is strongly dependent on the pH values, concentration of HA, but independent of HA/Co(II) addition orders, ionic strength, and foreign cations in the presence of HA under our experimental conditions. The results also indicated that HA enhanced the Co(II) sorption at low pH, but reduced the Co(II) sorption at high pH. It was hypothesized that the significantly positive influence of HA at low pH on the Co(II) sorption on γ-Al₂O₃ was attributed to strong surface binding of HA on γ-Al₂O₃ and subsequently the formation of ternary surface complexes such as ≡S-OOC-R-(COO⁻) _x Co^2−x . Chemi-complexation may be the main mechanism of the Co(II) sorption on γ-Al₂O₃ in the presence of HA.     

Modified analcime loaded with zincon as a useful material for the separation and preconcentration of trace palladium and its determination by third-derivative spectrophotometry

This work assesses the potential of natural analcime zeolite as a sorbent for the preconcentration of palladium. Palladium is quantitatively retained on modified analcime zeolite loaded with zincon using the column method in the pH range from 2.5 to 3.5 at a flow rate of 1 mL/min. The palladium complex was removed from the column with 5.0 mL of dimethylsulfoxide (DMSO) and determined by third-derivative spectrophotometry. The detection limit is 0.03 μg/mL (signal-to-noise ratio = 3) in the final solution. Since it is possible to retain 0.15 μg of palladium from 600 mL of solution passing through the column, elution with 5.0 mL of DMSO gives a detection limit of 0.25 ng/mL for palladium in the initial aqueous solution. The calibration curve is linear over the range 0.1 to 5.0 μg/mL of palladium(II) in the final solution with a correlation coefficient of 0.9996. Seven replicated determinations of 5.0 μg of palladium in 5.0 mL dimethylsulfoxide gave a mean d ³ A/dλ³ (peak-to-peak signal between λ₂ = 625 and λ₁ = 654 nm) of 0.64 with a relative standard deviation of 1.2%. The sensitivity of the method (d ³ A/dλ³) is 0.5843 mL/μg of palladium(II) from the slope of the calibration curve. The interference of a large number of anions and cations has been studied and the optimized conditions developed were utilized for the determination of trace palladium in various synthetic and water samples. The text was submitted by the authors in English.     

REACTION BETWEEN [PdCl4]2- AND 5,5-DIMETHYL-2-THIOXOIMIDAZOLIDIN-4-ONE

Abstract

The reaction between 5,5-dimethyl-2-thioxoimidazolidin-4-one (H2L) and [PdCl₄]^2- has been studied in aqueous solution by potentiometric and spectrophotometric measurements. In the presence of the palladium salt, H₂L is completely monodeprotonated (HL^?); from spectrophotometric measurements, only two complexes having 1:1 and 1:2 Pd/ligand mol ratios have been identified. Potentiometric titrations, carried out on solutions with 1:1, 1:2, 1:3 and 1:4 metal/ligand mol ratios, show that these complexes must be formulated as Pd(HL)₂ and [Pd₂(HL)₂(μ-H₂O)(μ-OH)]⁺. Ionization constants of the pure ligand and formation constants of the complexes give pH distribution curves of the various species and the spectra of the two complexes. From MeOH, S-coordinated Pd(H₂L)_nCl₂ (n = 2–4) complexes have been separated in the solid state; from water, two complexes of formula Pd(H₂L)(HL)Cl and Pd(HL)Cl have been obtained with HL^? N,S-coordinated to the metal.     

Electroreduction kinetics and mechanism of palladium(II) glycinate chloride complexes on rotating palladium disk electrode

The electroreduction kinetics of Pd(Hgly)₂Cl₂ on rotating palladium disk electrode was studied by means of cyclic voltammetry. The double layer range of the palladium charging curve showed a single wave with the diffusion limited current I _d, which yielded the diffusion coefficient of Pd(Hgly)₂Cl₂ complex D = 6 × 10⁻⁶ cm²/s. The plotted direct and reverse voltammetric curves were linearized in coordinates E, log[I/(I _d − I)]. The slope of this line gave b _k factor evidencing the slow electrochemical step. When [Cl⁻] decreased from 1 to 0.2 M, E _1/2 potential shifted to positive values. This was accounted for by reversible cleavage of Cl⁻ ion from Pd(Hgly)₂Cl₂ complexes before the irreversible electrochemical step. The pulse galvanostatic experiment resulted in the double electrical layer capacity and roughness factors f of electrolytic palladium deposits. The calculated values of f from 60 to 310 were attributed to adsorption of glycine particles on the electrodeposited palladium surface, which promotes to increasing number of palladium microcrystal growing centers.     

Impact of environmental conditions on the sorption behavior of radionuclide 63Ni(II) onto hierarchically structured γ-MnO2

A novel hierarchically structured γ-MnO₂ has been synthesized using a simple chemical reaction between MnSO₄ and KMnO₄ in aqueous solution without using any templates, surfactants, catalysts, calcination and hydrothermal processes. As an example of potential applications, hierarchically structured γ-MnO₂ was used as adsorbent in radionuclide ⁶³Ni(II) treatment, and showed an excellent ability. The effects of pH, ionic strength, temperature, humic acid (HA) and fulvic acid (FA) on the sorption of radionuclide ⁶³Ni(II) to hierarchically structured γ-MnO₂ have been investigated by using batch techniques. The results indicated that the sorption of ⁶³Ni(II) on γ-MnO₂ is obviously dependent on pH values but independent of ionic strength. The presence of HA/FA strongly enhances the sorption of ⁶³Ni(II) on γ-MnO₂ at low pH values, whereas reduces ⁶³Ni(II) sorption at high pH values. The sorption of ⁶³Ni(II) on γ-MnO₂ is attributed to inner-sphere surface complexation rather than outer-sphere surface complexation or ion exchange. The thermodynamic parameters (ΔH ⁰, ΔS ⁰, ΔG ⁰) are also calculated from the temperature dependent sorption isotherms, and the results suggest that the sorption of ⁶³Ni(II) on γ-MnO₂ is a spontaneous and endothermic process.     

Analytical application of polyurethane foam functionalized with quinolin-8-ol for preconcentration and determination of trace metal ions in wastewater

Quinolin-8-ol-bonded polyurethane foam (Ox-PUF) was synthesized by coupling the polyurethane foam matrix with oxine through an azo (-N=N-) group. The chromatographic retention behavior of Ag⁺, Pb²⁺, and Al³⁺ onto the Ox-PUF was studied. The extraction of Ag⁺, Pb²⁺, and Al³⁺ was accomplished within 15–20 min at pH ranges of 1–4, 4–6, and 6–12, respectively. The kinetics and thermodynamics of the sorption of tested metal ions onto Ox-PUF have been studied. The average values of ΔH, ΔS, ΔG; k ₁, k ₋₁, k′, and t _1/2 at 298 K were −28.7 kJ/mol, 210.1 J/(mol K), −6.74 kJ/mol, 0.095, 0.01, 0.113, and 7.184 min, respectively. The sorption capacities of the Ox-PUF were 0.16, 0.07, and 0.59 mmol/g for Ag⁺, Pb²⁺, and Al³⁺, correspondingly. The proposed method has been successfully applied to the preconcentration and removal of tested metal ions from wastewater. Recoveries between 80 and 99% were obtained (RSD ∼ 7). The text was submitted by the authors in English.     

Ethylenediamine and 1,10-phenanthroline biscyclometallated complexes of Pd(II) and Pt(II) based on 4,6-diphenylpyrimidine

Biscyclometallated [(M(N∧N))₂(μ-dphpm)](ClO₄)₂ and [(N∧N)Pd(μ-dphpm)Pt(N∧N)]Cl₂ complexes [M = Pd(II), Pt(II); (N∧N) ethylenediamine (En), 1,10-phenanthroline (phen); dphpm² — bisdeprotonated form of 4,6-diphenylpyrimidine)] have been characterized by the ¹H NMR, electronic absorption and emission spectroscopy, and also cyclic voltammetry methods. The lowest unoccupied molecular orbital (LUMO) of biscyclometallated complexes with ethylenediamine, responsible for low-energy photo- and electro-stimulated processes irrespective of the metal nature, is assigned to the π* orbital mainly localized on the pyrimidine part of the bridging ligand. In the case of complexes with phenanthroline chelating ligands, the replacement of one or two palladium metal centers [{Pd(phen)}₂(μ-dphpm)]²⁺ by platinum centers changes the LUMO nature of the complexes for the π* orbital mainly localized on the peripheral metal-complex fragment {Pt(phen)}.     

Oxygen desorption from polycrystalline palladium: Thermal desorption of O<Subscript>2</Subscript> from a chemisorbed layer of O<Subscript>ads</Subscript> in the course of the decomposition of PdO surface oxide and in the release of oxygen from the bulk of palladium

The desorption of oxygen from polycrystalline palladium (Pd(poly)) was studied using temperature-programmed desorption (TPD) at 500–1300 K and the amounts of oxygen absorbed by palladium (n) from 0.05 to 50 monolayers. It was found that the desorption of O₂ from Pd(poly), which occurred from a chemisorbed oxygen layer (O_ads), in the release of oxygen from a near-surface metal layer in the course of the decomposition of PdO surface oxide, and in the release of oxygen from the bulk of palladium (O_abs), was governed by repulsive interactions between O_ads atoms and the formation and decomposition of O_ads-Pd*-O_abs structures (Pd* is a surface palladium atom). At θ ≤ 0.5, the repulsive interactions between O_ads atoms (ɛ_aa = 10 kJ/mol) resulted in the desorption of O₂ from Pd(poly) at 650–950 K. At 0.5 ≤ n ≤ 1.0, the release of inserted oxygen from a near-surface palladium layer occurred during TPD in the course of the migration of O_abs atoms to the surface and the formation-decomposition of O_ads-Pd*-O_abs structures. As a result, the desorption of O₂ occurred in accordance with a first-order reaction with a thermal desorption (TD) peak at T _max ∼ 700 K. At 1.0 ≤ n ≤ 2.0, the decomposition of PdO surface oxide occurred at a constant surface cover-age with oxygen during TPD in the course of the formation-decomposition of O_ads-Pd*-O_abs structures. Because of this, the desorption of O₂ occurred in accordance with a zero-order reaction at low temperatures with a TD peak at T _max ∼ 675 K. At 1.0 ≤ n ≤ 50, oxygen atoms diffused from deep palladium layers in the course of TPD and arrived at the surface at high temperatures. As a result, O₂ was desorbed with a high-temperature TD peak at T > 750 K.     

Impact of environmental conditions on the sorption behavior of radionuclide <Superscript>60</Superscript>Co(II) on MnO<Subscript>2</Subscript>

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The removal of ⁶⁰Co(II) from wastewaters by MnO₂ was studied as a function of various environmental parameters such as shaking time, pH, ionic strength, foreign ions, and humic substances under ambient conditions. The results indicated that the sorption of ⁶⁰Co(II) on MnO₂ was strongly dependent on pH and ionic strength. At low pH, the sorption of ⁶⁰Co(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on MnO₂ surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of HA/FA enhances ⁶⁰Co(II) sorption at low pH values, whereas reduces ⁶⁰Co(II) sorption at high pH values. The Langmuir and Freundlich models were used to simulate the sorption isotherms of ⁶⁰Co(II) at three different temperatures of 298.15, 318.15 and 338.15 K. The thermodynamic parameters (ΔH ⁰, ΔS ⁰ and ΔG ⁰) calculated from the temperature dependent sorption isotherms indicated that the sorption process of ⁶⁰Co(II) on MnO₂ was endothermic and spontaneous.     

Sorption of hafnium on hydrous titanium oxide using radiotracer technique

The sorption of hafnium on hydrous titanium oxide (TiO₂·1.94 H₂O) has been studied in detail. Maximum sorption of hafnium can be achieved from a pH 7 buffer solution containing boric acid and sodium hydroxide using 50 mg of the oxide after 30 minutes shaking. The value ofk _d, the rate constant of intraparticle transport for hafnium sorption, from 0.01M hydrochloric and perchloric acid and pH 7 buffer solutions has been found to be 17 mmole·g^–1·min^–2. The kinetics of hafnium sorption follows Lagergren equation in 0.01M HCl solution only. The values of the overall rate constantK=6.33·10^–2 min^–1 and of the rate constant for sorptionk ₁=6.32·10^–2 min^–1 and desorptionk ₂=2.28·10^–5 min^–1 have been evaluated using linear regression analysis. The value of correlation factor() is 0.9824. The influence of hafnium concentration on its sorption has been examined from 4.55·10^–5 to 9.01·10^–4 M from pH 7 buffer solution. The sorption data followed only the Langmuir sorption isotherm. The saturation capacity of 9.52 mmole·g^–1 and of a constant related to sorption energy have been estimated to be 2917 dm³·mole^–1. Among all the additional anions and cations tested only citrate ions reduce the sorption significantly. Under optimal experimental conditions selected for hafnium sorption, As(III), Sn(V), Co(II), Se(IV) and Eu(III) have shown higher sorption whereas Mn(II), Ag(I) and Sc(III) are sorbed to a lesser extent. It can be concluded that a titanium oxide bed can be used for the preconcentration and removal of hafnium and other metal ions showing higher sorption from their very dilute solutions. The oxide can also be employed for the decontamination of radioactive liquid waste and for pollution abatement studies.     

Sorption of radiocobalt on a novel γ-MnO2 hollow structure: effects of pH, ionic strength, humic substances and temperature

A novel γ-MnO₂ hollow structure has been synthesized using a simple chemical reaction between MnSO₄ and KMnO₄ in aqueous solution without using any templates, surfactants, catalysts, calcination and hydrothermal processes. As an example of potential applications, γ-MnO₂ hollow structure was used as adsorbent in radionuclide ⁶⁰Co(II) treatment, and showed an excellent ability. The effect of pH, contact time, ionic strength, humic acid (HA)/fulvic acid (FA), and temperature was investigated using batch techniques. The results indicated that the sorption of ⁶⁰Co(II) on γ-MnO₂ was obviously dependent on pH values but independent of ionic strength. The presence of HA/FA enhanced the sorption of ⁶⁰Co(II) on γ-MnO₂ at low pH, whereas reduced ⁶⁰Co(II) sorption on γ-MnO₂ at high pH. The kinetic sorption of ⁶⁰Co(II) on γ-MnO₂ can be well fitted by the pseudo-second-order rate equation. The thermodynamic parameters (ΔH ⁰, ΔS ⁰, ΔG ⁰) were also calculated from the temperature dependent sorption isotherms, and the results suggested that the sorption of ⁶⁰Co(II) on γ-MnO₂ was a spontaneous and endothermic process. The sorption of ⁶⁰Co(II) on γ-MnO₂ was attributed to surface complexation rather than ion exchange.