Adsorption studies of cesium on potassium copper nickel hexacyanoferrate(II) from aqueous solutions

Adsorption of cesium from aqueous solutions on potassium copper nickel hexacyanoferrate(II) (KCNF) has been investigated in batch experiments and optimized as a function of concentration of acids, salts and adsorbate using a radiotracer technique. The results are presented in terms of distribution coefficient, K_d (ml·g^–1). The uptake of cesium obeys a Freundlich adsorption isotherm over the concentration range of 3.7 to 37 mmol·l^–1 with b values of 0.77, 0.68 and 0.56 at temperatures of 293, 313, 333 K, respectively. The Langmuir adsorption isotherm is followed in the concentration range of 15 to 75 mmol·l^–1 in the same temperature range. The values of limiting adsorption concentration (C_m) have been found to be 2.58, 2.44 and 2.32 mmol·g^–1. The heat of adsorption was calculated as 26.43 kJ·mol^–1. The influence of a number of anions and cations on cesium retention has also been studied. Column experiments have been performed and breakthrough have been obtained under different operating conditions. The low cesium capacity of 1.1 mmol·g^–1 has been obtained under dynamic conditions as compared to batch experiments. Desorption of cesium from the column has been achieved (45.4%) by nitric acid solution of 8M concentration at a flow rate of 0.5 ml·min^–1.     

Adsorption of traces of hafnium on manganese dioxide from acid solutions

Adsorption of hafnium on manganese dioxide from nitric and perchloric acid solutions has been studied and optimized with respect to shaking time, concentration of acid, oxide and metal. Maximum adsorption has been noticed from 0.1 mol · dm^–3 acid solutions in 20 minutes around 10^–5 mol · dm^–3 hafnium concentration. The adsorption of hafnium follows a Freundlich adsorption isotherm. Oxalate, thiosulfate, Na(I) and Al(III) from nitric acid and K(I) and Zn(II) from perchloric acid increase the adsorption, whereas all other anions and cations tested reduce the adsorption from both media Fe(III) and Sn(IV) significantly. Zn(II) and Co(II) show low adsorption affinity.     

Inorganic particulates in removal of toxic heavy metal ions

Adsorption behavior of zinc ions on hydrous zirconium oxide (HZO) in aqueous solution has been studied as a function of concentration (10^–2–10^–8M), temperature (303–333 K) and pH 3–8 of adsorptive solution applying radiotracer technique. The kinetics of adsorption follows first order rate law and agrees well with the classical Freundlich isotherm in the entire range of adsorptive concentration. The removal was found to be increasing with pH of the adsorptive solution while it was suppressed in the presence of acid concentrations. The overall process is found to be endothermic and irreversible in nature.     

Influences of salt concentration,loading and pH on strontium adsorption

The adsorption of Sr on clay which contains zeolites and montmorillonite mixtures was investigated in solutions of NaCl by means of a batch technique. Sr retention was reduced with increasing NaCl concentration from 5·10^–4 to 5·10^–1M. Distribution coefficients (K _d ) linearly increased with pH in the acidic region but they were almost independent of pH in neutral and alkaline solutions. By fitting the data of the Dubinin-Radushkevich (D-R) isotherm, the mean energies of adsorption and adsorption capacities of Sr at different pH values were calculated. The results showed that the mode of adsorption below pH 4.5 is ion exchange, while above that value a multilayer adsorption occurs. Adsorption data were fitted to the Freundlich isotherm and from empirical Freundlich parameters a site distribution function was calculated.     

Cesium sorption on mylonite

As part of the laboratory support program for the field migration experiment at the Grimsel Test Site (GTS) in the Swiss Alps, the sorption behaviour of cesium on Grimsel mylonite was studied. Batch sorption experiments were carried out in N₂ atmosphere (<3 ppm O₂). The adsorption isotherms were reversible and non-linear for cesium concentrations of between 3.2·10^–8 and 5.0·10^–4M. Two different sites appear to be involved in sorption depending on whether Cs loading was high (10^–6–10^–3 meq/g) or low (10^–7–10^–6 meq/g). At low Cs loadings adsorption was considered to occur mainly at the crystal edges of mica particles. Selectivity coefficients for exchange between cesium and potassium were calculated for different Cs loadings. It was suggestd that by varying the potassium concentration of the solution and by making some assumptions, a K_d value for cesium at the migration site could be estimated. Data were fitted to both Freundlich and Dubinin-Radushkevich isotherms. The empirical Freundlich parameters enabled a site distribution function to be calculated and a mean energy of sorption of about 12 kJ/mol was found using Dubinin-Radushkevich isotherms approach.     

Adsorption of cesium on a composite inorganic exchanger zirconium phosphate - ammonium molybdophosphate

The applicability of zirconium phosphate-ammonium molybdophosphate (ZrP-AMP) for the efficient removal of cesium from aqueous acidic solutions by adsorption has been investigated. The adsorption data analysis was carried out using the Freundlich, Dubinin-Raduskevich (D-R) and Langmuir isotherms for the uptake of Cs in the initial concentration range of 3.75^.10^-5-7.52^.10^-3 mol^.dm^-3 on the ZrP-AMP exchanger from nitric acid medium. The mean free energy (E) values for the adsorption of Cs were obtained from the D-R isotherm. Equilibrium adsorption values at different temperatures have been utilized to evaluate the change in enthalpy, entropy and free energy (ΔH°, ΔS°, ΔG°). The adsorption of cesium on the ZrP-AMP exchanger was found to be endothermic. This revised version was published online in August 2006 with corrections to the Cover Date.     

New understanding of the nature of OH adsorption on Pt(1 1 1) electrodes

The adsorption of hydroxyl on Pt(1 1 1) single crystal electrodes from aqueous acidic solutions is carefully reinvestigated. The effect of small additions (10⁻⁸–10⁻⁵ M) of chloride and bisulphate anions on the OH adsorption region in perchloric acid solution has been studied. Two regions can be differentiated in the voltammetric profile, that behave differently after the addition of the foreign anion. The initial broad adsorption process is unaffected until the highest concentration is attained. However, the sharper peak at higher potentials is affected even at the lower anion concentration. Since mass transport limitations allow to discard the anion adsorption as the main process giving this peak, we propose that the two processes are due to the dissociative adsorption of two different kinds of water, that are affected by the anion in a different way. From this idea, a new model, based on the Frumkin adsorption isotherm, is proposed, which gives an excellent fit of the experimental results.     

Biosorption of americium-241 by Saccharomyces cerevisiae

The biosorption of radionuclide ²⁴¹Am from solution by Saccharomyces cerevisiae (S. cerevisiae), and the effects of experimental conditions on the adsorption were investigated. The preliminary results showed thatS. cerevisiae is a very efficient biosorbent. An average of more than 99% of the total ²⁴¹Am could be removed by S. cerevisiae of 2.1 g/l (dry weight) from ²⁴¹Am solutions of 17.54–4386.0 mg/l (2.22 MBq/l–555 MBq/l) with adsorption capacities of 7.45–1880.0 mg/g biomass (dry weight) (0.94 MBq/g–237.9 MBq/g). The adsorption equilibrium was achieved within 1 hour and the optimum pH ranged 1–3. No significant differences on ²⁴¹Am adsorption were observed at 10–45 °C, or in solutions containing Au³⁺ or Ag⁺, even 2000 times above ²⁴¹Am concentration. The relationship between concentrations and adsorption capacities of ²⁴¹Am indicated the biosorption process should be described by the Freundlich adsorption isotherm.     

Sorption of cesium on montmorillonite and effects of salt concentration

The sorption behavior of cesium on montmorillonite type clay was studied by using radioactivity measurements. Concentrations of Cs⁺ ions ranged from 10^–6 to 10^–2M. Cesium retention reduced with increasing salt concentration which was varied between 10^–4 and 10^–1M. Selectivity coefficients K_Cs–Na for the exchange between Cs and Na were calculated for different equivalent fractions of Cs on the solid phase. Using theK _Cs–Na values, free energy change was found to be 7.8 kJ/mol. The data could be fitted to a Freundlich isotherm, and empirical Freundlich parameters enabled the generation of a site distribution function. By fitting the data to the Dubinin-Radushkevich (D-R) isotherm, a mean energy of sorption of 8.6 kJ/mole was calculated which corresponds to the energy of ion exchange reactions. The values of energy changes calculated by using two different methods were in good agreement.     

Adsorption studies of cesium on a new inorganic exchanger ammonium molybdophosphate-alumina (AMP-Al2O3)

The applicability of ammonium molybdophosphate-alumina (AMP-Al₂O₃) for the efficient removal of Cs from aqueous solution by adsorption has been investigated. The kinetics of adsorption of cesium ions has been studied by using radioanalytical procedure over a concentration range of 10⁻⁴−10⁻² mol.dm⁻³ and in the temperature range of 303–318 K. The results showed that the uptake follows the first order rate law with respect to cesium concentration and obeys Langmuir and modified Freundlich adsorption isotherm in the concentration range studied. Equilibrium adsorption values at different temperatures have been utilised to evaluate change in standard thermodynamic parameters (ΔH ⁰, ΔG ⁰ and ΔS ⁰). From the thermodynamic parameters it is found that the process is exothermic in nature.     

Kinetic study of Cr(VI) sorption on MnO2

The kinetics of adsorption of chromate ions has been investigated radiometrically over a wide range of concentration of chromate ions (10^–6–10^–2M) and temperature (303–323 K). The kinetics of the process follows essentially a first order rate law with respect to adsorptive concentration and obeys the Freundlich adsorption isotherm in the concentration range studied. In addition, the kinetics of desorption of the preadsorbed species also follows a first order rate law and the activation energy for desorption is greater than that of the adsorption process. On the basis of an adsorption kinetic study, the thermodynamic parameters have been calculated. Infrared spectroscopy has shown the chemical interaction of chromate ions on the surface of MnO₂.     

Adsorption of cesium using supermolecular impregnated XAD-7 composite: isotherms,kinetics and thermodynamics

As an effective cesium complex agent, calix[4]biscrown-6 (CBC) applied at a low cost way is of interest. In this study, CBC/XAD-7 was prepared by embedding CBC into XAD-7. Subsequently the as-prepared sorbent was used for the removal of cesium from aqueous solution as functions of HNO₃ concentration, contact time, temperature and initial cesium concentration. The results revealed that the nitric concentration influenced cesium adsorption by complex and protonation interaction. The most effective adsorption happened at the nitric concentration of 1.0 M. The adsorption isotherm well described with the Langmuir model illustrated a monolayer adsorption. Its maximum adsorption capacity was 24.4 mg/g in the 2 M nitric acid aqueous solution. The adsorption kinetics was in accordance with the pseudo-second order model, which indicated a chemisorption. The thermodynamic parameters demonstrated that the adsorption process was exothermal and spontaneous. In addition CBC/XAD-7 showed highly selective recognition toward cesium and good reusability. The study offered an economical and effective material for cesium removal.

     

Efficiency of succinylated-olive stone biosorbent on the removal of cadmium ions from aqueous solutions

Chemical functionalization of olive stone wastes with succinate linkers can potentially improve the performance of wastewater treatment technologies via enhanced adsorption and high affinity of the covalently attached succinate groups for heavy metals. In this study, a novel reusable adsorbent material based on agricultural waste has been synthesized by esterifying the lignocellulosic matrix of olive stones with succinic anhydride in toluene under basic conditions. Characterization of the as-prepared material by FTIR and solid-state MAS ¹³C NMR spectroscopies and TGA confirmed that the heterogeneous esterification has proceeded very efficiently to yield the succinylated-olive stone (S–OS). Subsequent alkaline treatment of S–OS with saturated NaHCO₃ aqueous solution led to the resulting sodic material (NaS–OS), which was subjected to batch experiments in order to evaluate its cadmium-removing efficiency from aqueous solutions at realistic concentrations of cadmium found in industrial effluents. The results obtained from the sorption characteristics have revealed that NaS–OS material is highly effective in removing cadmium from aqueous solutions, with a maximum uptake capacity of 200 mg g⁻¹ (1.78 mmol g⁻¹). The Langmuir isotherm model was found to fit adequately the equilibrium isotherm data. Cadmium adsorption occurs rapidly and the adsorption mechanism is a chemical sorption via ionic exchange between the adsorbate and adsorbent. Thermodynamic parameters were also evaluated from the effect of temperature studies. Regenerability of NaS–OS material was ascertained by quantitative desorption of cadmium with 1 M aqueous NaCl and the reusability of the matrix after five repeated cycles led to nearly no attenuation in its performance (less than 2% in the sorption capacity), indicating that repeated use of NaS–OS is quite feasible. Compared to other low-cost adsorbents utilized for the removal of Cd(II) from water/wastewater, NaS–OS shows higher sorption capacity. These results have important implications for the design of low-cost adsorbents based on agricultural wastes.     

Ion-exchangers in radioactive waste management Part XIV: Removal behavior of hydrous titanium oxide and sodium titanate for Cs(I)

The removal behavior of hydrous titanium oxide and sodium titanate for Cs(I) from aqueous solutions by radiotracers was studied. Batch experiments revealed that an increase in Cs concentration (10^–8 to 10^–2 mol·dm^–3), temperature (298 to 328 K) and pH (2.50 to 10.20) apparently enhanced the uptake of Cs(I) on hydrous titanium oxide whereas a high degree of uptake of Cs(I) on sodium titanate was almost unaffected by a change in adsorption temperature (298 to 328 K) and pH (2.50 to 10.20). Both systems follow Freundlich adsorption isotherm. Uptake of Cs(I) on hydrous titanium oxide obeys first order rate law. According to thermodynamic data the uptake is endothermic and apparently irreversible in nature.This revised version was published online in November 2005 with corrections to the Cover Date.     

Preparation and characterization of potassium copper nickel hexacyanoferrate(II) as an ion exchanger for cesium

Potassium copper nickel hexacyanoferrate(II) [KCNF] was prepared by treating potassium nickel hexacyanoferrate(II) with copper nitrate solution in 0.1M HNO₃. The resulting material was dried at various temperatures. Chemical analysis, i.r., thermal decomposition and surface property measurements were used to characterize the material. The adsorption of cesium from aqueous solutions on KCNF was investigated and optimized as a function of equilibration time and pH. The material dried at 110°C was found to be fairly stable in dilute acids, salt solutions, high doses of gamma-radiation and at high temperature. It also showed better surface properties and a high value of ion exchange capacity (2.25 mmol·g^–1) for cesium.     

Investigation of adsorption behaviour of mercury in microamounts on manganese dioxide from aqueous solutions

Adsorption of mercury onto manganese dioxide was studied in relation to the concentrations of electrolyte, adsorbent and adsorbate and foreign ions. Adsorption of other metal ions under similar conditions was also measured. Adsorption decreases with increasing electrolyte concentration. Thiosulfate, thiocyanate, iodide and all cations tested suppress the adsorption; the greater the ionic potential of cation, the weaker the adsorption of mercury. Adsorption follows the Freundlich-type isotherm over a wide range of mercury concentration (10^–7–10^–8 g·ml^–1). 98% of the adsorbed mercury can be eluted from the oxide column with 60 ml of 3M nitric acid solution.     

Inorganic ion-exchangers in radioactive waste management</p> </p>

Summary The uptake of indigenously synthesized amorphous stannic and zirconium phosphate was assessed for, one of the important fission fragment, cesium from aqueous solutions using a radiotracer technique. A virtual increase in sorptive concentration (from 1.0 ^. 10^-8 to 1.0 ^. 10^-2 mol ^. dm^-3) and pH (from 2.4 to 10.2) and temperature (from 303 to 333 K) enhanced the uptake of cesium on stannic phosphate. However, the extremely high degree of uptake of cesium on zirconium phosphate was almost unaffected with the dilution beyond 10^-5 mol ^. dm^-3 and pH (i.e., from 2.4 to 10.2) and temperature (from 303 to 323 K). Irreversible uptake occurring for these solids follow the Freundlich adsorption isotherm and the presence of several complexing agents viz., sulphate, phosphate, glycine and EDTA did not affect appreciably the uptake of cesium on zirconium phosphate but it did affect for stannic phosphate system. Both these solids showed good radiation stability towards a 11.1 GBq Ra-Be neutron source having neutron flux ca. 3.2 ^. 10⁶ n ^. cm^{-2 .} s^-1 and associated with a nominalg-dose of ca. 1.72 Gy/h, at least for the uptake of cesium.</p> </p>     

Modeling of iron adsorption on HTTA-loaded polyurethane foam using Freundlich,Langmuir and D-R isotherm expressions

The sorption of Fe(III) at low pH range from 1 to 4.5 on open cell polyether type HTTA-loaded polyurethane foam has been carried out using batch technique. The optimum shaking time for 2.5· 10^–4M solution of Fe(III) was found to be 30 minutes. The concept of macropore and micropore nature of polyurethane foam sorbent offers unique advantages of adsorption. Freundlich and Langmuir adsorption isotherms are followed at low concentration range from 1·10^–4 to 3·10^–4M solution of Fe(III). The Freundlich constant (1/n=0.46±0.013 andK=9.16±1.39 mg·g^–1) and Langmuir isotherm constants(M=21.78 mg·g^–1 andb=88.41±9.731·g^–1) were established. The sorption mean free energyE=12.22±0.09 kJ·mol^–1 and loading capacityC _m =145.21±6.1 mg·g^–1 were evaluated using Dubinin-Radushkevich isotherm, which suggested that the adsorption mechanism was chemisorption.     

Radiotracer technique in adsorption studies

Hydrous manganese oxide (HMO) was synthesized and its adsorption properties with respect to Ba(II) ions investigated as a function of contact time, adsorptive concentration, temperature and pH, using a radiotracer technique. The adsorption equilibrium is achieved quickly in ca. 30 min and the steady state values of adsorption at various concentrations (10^–2–10^–7M) agree well with the classical Freundlich isotherm. The adsorption increases with increasing pH and reaches a maximum followed by a plateau over a fairly wide pH range. The temperature markedly affects the extent of adsorption and the process is thermodynamically found to be irreversible.     

Radiolysis of aqueous cesium iodide

In hypothetical accident scenarios for Light Water reactors, the extent of release of iodine upon irradiation needs to be assessed for the purpose of evaluation of the applicable source term. In this context, an understanding of the behaviour of aqueous cesium iodide solutions subjected to high gamma-ray fluxes acquires significant importance. In the present work, gamma radiolysis of a cesium iodide solution (10^–2M I^–) with and without boron additive is investigated by irradiating with⁶⁰Co source at ambient temperature. Upon irradiation of the CsI solution, iodine is liberated, and the concentration of iodide in the KOH trap present in the radiolysis vessel increases with dose. The radiolytic products I ₃ ^– , IO ₃ ^– and H₂O₂ formed in the irradiated solution are also estimated and G values obtained are reported. G(I ₃ ^– ) and G(IO ₃ ^– ) are of the order of 10^–3 and 10^–4, respectively. G(H₂O₂) decreases with increase in dose. Addition of boron up to 200 ppm, does not appear to alter significantly the release fraction of iodine.