Interaction of radium with freshwater sediments and their mineral components. I.

The radiotracer method has been used for investigation of the adsorption and desorption of traces of radium on ferric hydroxide and quartz under conditions similar to those prevailing in waste and surface waters. The effects of pH, liquid to solid ratio, ionic strength and presence of Ca²⁺ or SO ₄ ^2- ions have been studied. It has been concluded that at pH less than 7 and at concentration of suspended sediments (of common composition) less than 100 mg·1^–1 ferric hydroxide and quartz have negligible effect on the state and migration of radium in surface waters. Radium adsorbed on quartz can be easily desorbed with dilute solutions of hydrochloric acid or sodium chloride.     

Adsorption characteristics of traces of radium on membrane filters,glass and polyethylene

Adsorption of radium was studied on glass and polyethylene from aqueous solutions containing 8–40 pg·dm^{–3 224}Ra and on membrane filters, glass and polyethylene bottles from waste and river waters containing 2–170 pg·dm^{–3 226}Ra. The adsorption from aqueous solutions was determined as a function of pH and composition of the solutions and interpreted as due to ion exchange of Ra²⁺ ions for counter ions in the electric double layer on glass and polyethylene or due to chemisorption of RaSO₄ (RaCO₃) ion pairs on glass. Borosilicate glass adsorbed radium substantially more than polyethylene. The adsorption of dissolved forms of radium from the waste and river waters during storage and membrane filtration of the waters was negligible, but a significant loss of particulate forms of radium was sometimes observed during the storage. It has been recommended to separate dissolved and particulate forms of radium soon after the sampling and to prefer polyethylene to glass as container material for storage of dissolved forms of radium.     

Interaction of radium with freshwater sediments and their mineral components

Radiotracer method has been used for investigation of the adsorption and desorption of traces of radium on kaolinite and montmorillonite under conditions similar to those prevailing in waste and surface waters. It has been found that adsorption depends on the pH and ionic strength of the solution, and the character of these dependences is different for kaolinite and montmorillonite. Sulfates at concentration 60 mg·l^–1 have negligible effect on the adsorption. Montmorillonite represents better adsorbent for radium than kaolinite, but both minerals may significantly affect the form and migration of radium in surface waters, if present as (major) components of freshwater sediments. Radium can be quantitatively desorbed by 1M HCl from kaolinite but not from montmorillonite. The desorption by 0.1M NaCl is generally lower and depends on the pH during the preliminary adsorption. Mechanisms of radium adsorption on both minerals and the character of the adsorption sites are discussed.     

Comparison of the specific adsorption of sulfate (HSO<Subscript>4</Subscript><Superscript>−</Superscript>) ions on Cr and Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>

The specific adsorption of sulfate ions on powdered Cr was studied by a radiotracer technique using ³⁵S-labeled sulfuric acid in low concentration (c<10^–3 mol dm^–3) in the presence of a large excess of perchlorate supporting electrolyte. The pH and concentration dependence were determined. On the basis of a comparison of the results obtained for Cr₂O₃ and Cr, it can be assumed that, similar to other metals, the overall sorption behavior of Cr is determined by the protective oxide film present on the surface.     

Study of the immobilization of226Ra

A study of the immobilization for²²⁶Ra waste has been carried out. Cement-based concrete was used as a matrix for the solidification of radium waste. The experimental results show that the cement mixture with water/cement between 0.46–0.54 has higher strengh (above 20 MPa), and the compressive strength was not reduced by addition of 1% barite or the radium waste (RaSO₄) into the concrete solid.Sponsored by the National Nuclear Corporation of China.     

Interaction of radium with freshwater sediments and their mineral components

Radiotracer method has been used for investigation of the adsorption and desorption of traces of radium on muscovite and feldspar (albite) under conditions similar to those prevailing in waste and surface waters. The effects of pH, liquid to solid ratio, time, ionic strength (Na⁺) and presence of Ca²⁺ or SO ₄ ^2? ions have been studied. It has been concluded that both minerals can significantly affect the fate and migration of radium in surface waters if present as major components of bottom sediments or as suspended solids in concentrations of several milligrams per liter or higher. Muscovite can absorb radium even from moderately acidic waters. Radium adsorbed on muscovite and albite cannot be easily released upon an increase of the salinity of ambient water. However, almost complete desorption can be achieved with 1M HCl. Mechanisms of radium adsorption on both minerals and character of the adsorption sites are discussed.     

The adsorption behaviour of microamounts of radium on inorganic ion exchangers

The radiochemical method has been used for investigation of the adsorption of radium on eighteen inorganic ion exchangers. The distribution coefficient of radium obtained are as follows: barite 2955, celestite 2420, BaSO₄ 4350, BaCrO₄ 5245, Ba₃(PO₄)₂ 5775, MnO₂·nH₂O 1681, La₂O₃·nH₂O 4150, Zerolit S/F 2920, etc.Presented at the International Conference on Nuclear and Radiochemistry, Beijing, Sept. 1–5, 1986.     

Indirect radiotracer study of the adsorption of chromate ions on γ-Al2O3 and direct study of the adsorption of sulfate ions on Cr2O3 using 35S-labelled H2SO4

The specific adsorption of sulfate ions on Cr₂O₃ was studied by a radiotracer technique using ³⁵S-labelled sulfuric acid in low concentrations (c<10^–3 mol dm^–3) in the presence of a large excess of perchlorate supporting electrolyte. The pH and concentration dependence were determined. It was found that the extent of adsorption is determined by the protonation of the surface sites, similar to other oxides studied previously. A comparison of Cr₂O₃ and Al₂O₃ in this respect shows that the protonation of the former takes place at significantly lower pH values than that of the latter. The indirect radiotracer study of the adsorption of chromate on Al₂O₃ was carried out using labelled sulfate ions as indicator species. The results obtained show that the adsorption strength of chromate species is very low in comparison to sulfate ions and a regular Langmuir-like adsorption behaviour can be observed. It is believed that the observations presented may contribute to a better understanding of the behaviour of surface layers with a mixed oxide content. Electronic Publication     

ESR study of electron interaction in a Tc/Al2O3 system

An investigation was made into the nature of paramagnetic centers in a Tc/Al₂O₃ system under varying conditions as to heat treatment and technetium content, and in O₂ and CO adsorption environments. It was found that in the case of reduction at 573 K Tc²⁺ ions and, conceivably, other ionic forms developed and stabilized on the carrier surface. After reduction at 973 K two types of electron center appeared, whose concentration increased as reduction was prolonged. Signals were observed in the low fields (3–20 mT) of the ESR spectra having g₁ 13.5 and g₂>30, which could be assigned to free charge carriers in a cluster of metal atoms or ions. Adsorption of O₂ at 300 K caused O ₂ ^– ion radicals to form on the surface of the reduced Tc/Al₂O₃ samples, both electron centers and technetium ions constituting the electron donors. In the case of CO adsorption paramagnetic (CO) ₂ ^– particles appeared on the Tc/Al₂O₃ samples after prolonged exposure. On reaction with O₂ two types of O ₂ ^– ion-radical with differing thermal stability were formed.Institute of Physical Chemistry, Russian Academy of Sciences, Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 1972–1978, September, 1992.     

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.     

Voltammetric evaluation of the electrode material on the oxidation of cyanide catalyzed by copper ions

The cyanide oxidation on vitreous carbon (VC), stainless steel 304 (SS 304) and titanium (Ti) was investigated through a voltammetric study of cyanide solutions also containing copper ions. Results showed that cyanide oxidation occurs by means of a catalytic mechanism involving adsorbed species as CN^–, Cu(CN)₄^3– or Cu(CN)₄^2– depending on the electrode material. It was observed that on VC, the adsorption of Cu(CN)₄^3– controlled the oxidation rate. Instead, for SS 304 and Ti, the adsorption of CN^– controlled the global process. However, in all cases, the adsorption of Cu(CN)₄^3– on the electrode surface was required for the catalytic oxidation of CN^–. Voltammetric experiments for solutions containing cyanide oxidation products, such as cyanogen (CN)₂ and cyanate (CNO^–), confirmed that the adsorbed species mentioned above controlled the catalytic oxidation of CN^– depending on the electrode material. A voltammetric identification of the oxidation products showed that cyanogen, (CN)₂ tended to adosorb on VC, while the formation of cyanate, CNO^– predominated on SS 304.     

Material Balance Study of Adsorption of Organic Compounds

It was shown that the structure of a surface complex and the nature of an adsorption bond can be determined from the material balance of adsorption of H⁺and OH^–ions and organic compound. A calculation procedure was considered using adsorption of benzoic acid on silica gel and zirconia as examples. It was established that adsorption of benzoic acid on silica gel was accompanied by the release of H⁺ions resulted from the formation of surface hydrogen bonds, whereas adsorption on zirconia, by the substitution of OH^–ions in coordination sphere of Zr(IV).     

Interaction of sodium dodecylsulfate (SDS) with homoionic montmorillonites: adsorption isotherms and metal-ion release

The interaction of dodecylsulfate anions (DS^–) with homoionic Ca-, Mg-, Ni-, Cu-, Cd-, Pb- and Fe-montmorillonites were investigated. Mg- and Cd-montmorillonite do not adsorb DS^–, and an anion exchange at the edges of the clay mineral does not take place. Three different adsorption processes are identified on the other montmorillonites: i) Fe-montmorillonite is covered with amorphous iron hydroxide, and DS^–-anions are bound at positively charged sites. ii) On Ca- and Pb-montmorillonite DS^– is precipitated as Me(DS)₂. iii) On Ni- and Cu-montmorillonite DS^– forms ion pairs with the cations on the surface. In all cases DS^– is not bound above the CMC but the metal ions are mobilized from the surface either by solubilization of the precipitates or by formation of mixed micelles.     

Static and Kinetic Studies on the Adsorption Behavior of Sulfadiazene

To investigate the nature of interactive forces between sulfadiazene molecules and alumina surface the experiments were performed for the adsorption of sulfadiazene (SD) from its aqueous sulution onto the alumina surfaces at 25 ± 0.2°C and the influence of factors such as increasing concentration of SD (4.0–20.0 × 10^–3 mol cm^–3), the time required for adsorption equilibrium, pH (2.0–12.0) and temperature (5–45°C) of the adsorption medium, the presence of ions like Cl^–, SO^2– ₄ and PO^3– ₄ (0.01–0.30 M) and organic solvents (5% v/v) were observed on the course of adsorption of SD. Various adsorption and kinetic parameters such as adsorption coefficient, the rate constants for adsorption and desorption were also evaluated. The results of the above cited studies facilitated to formulate the mechanisms of interaction between SD and alumina surfaces. From application view point the present work may be a potential tool for an effective chromatographic separation of sulfa drugs from industrial effluents.     

Influence of Anions on Electrochemical Properties of Polypyrrole-Modified Electrodes

The influence of anions ClO₄ ^–, NO₃ ^–, Cl^–, SO₄ ^2–, and DDS^– (dodecyl sulfate) on the cyclic voltammetric response of polypyrrole-modified electrodes is studied. The change in the film composition is examined by electron probe microanalysis. It is established that essential changes in the shape of voltammograms take place during cycling if the anions are not sufficiently freely mobile in the polymer film and insertion of cations from the solution is necessary to guarantee electroneutrality of the system. Some differences between the mobility of Cl^– ions and ClO₄ ^– or NO₃ ^– ions are in good agreement with the results of semi-empirical quantum chemical calculations showing that the interaction of Cl^– and Br^– ions with pyrrole oligomers is stronger than that of NO₃ ^– or ClO₄ ^– ions. Nevertheless, it is established that the peak current determined from voltammograms increases linearly with the increase of the scan rate with very high correlation coefficient. It means that it is possible to describe the behavior of ClO₄ ^–, NO₃ ^– and Cl^– ions in the framework of the model of free ions. The redox behavior of the PPy films doped with anions of low mobility such as SO₄ ^2– and DDS^– depends essentially on the nature of cations in the test solution. It is found that the mobility of cations increases in the row Li⁺ < Na⁺ < K⁺ < Cs⁺. The mobility of DDS^– ions in the PPy in ethanolic solution is significantly higher and their electrochemical properties are quite similar to PPy|Cl or NO₃ ^– film in aqueous solution.     

Diffusion of ionic species labeled with35S in various aqueous electrolyte solutions at 25°C

Composite diffusion coeffcients have been measured for the various species labeled with³⁵S which are present in a number of aqueous solutions due to the introduction of the labeled material as³⁵SO ₄ ^2– . The solutions were of two components consisting of water and either sodium sulfate. The diffusion coeffcient measured for sodium chloride solutions is similar to literature data for the corresponding diffusion in sodium sulfate solutions. The results for sulfuric acid and ammonium hydrogen sulfate have been interpreted using literature data for the relative concentrations of the hydrogen sulfate and sulfate ions to obtain estimates for the diffusion coefficents of those ions. The results for perchloric acid, regarded as representing the diffusion coefficient of the hydrogen sulfate ion, have a much different concentration dependence to that observed for the estimates for that ion in sulfuric acid and ammonuim hydrogen sulfate. The difference is attributed to the effect of the perchlorate ion on the water structure.     

Adsorption of Cl? ions on electrodeposited rhodium black layer (rhodized electrode) at low concentrations

The adsorption of Cl^– ions on rhodium black layer (rhodized electrodes) was studied by radiotracer technique at low Cl^– ion concentrations (c10^–5 mol dm^–3) in 1 mol dm^–3 H₂SO₄ supporting electrolyte. The specific adsorption of Cl^– ions was treated in terms of partition between solution phase and electrodeposited Rh black layer. The potential dependence of the partition coefficient is determined.     

A comparison of the surface properties of lignin and sulfonated lignins by FTIR spectroscopy and wicking technique

The comparison of the FTIR spectra indicated that the sulfonation without caused changes in the main structure of lignin and only in the lignin chains. The surface properties, e.g. the surface free energy and related components, e.g. the Lifshitz–van der Waals and Lewis acid–base interactions components, of lignin and lignosulfonates, LGSs, with different ions, e.g. Na⁺–, Mg²⁺–, and Ca²⁺–, studied and compared by wicking technique indicated that the surface free energy of lignin is lower than that of all used LGSs. This suggests that the sulfonation can enhance the surface property for lignin by increasing of the Lifshitz–van der Waals component and Lewis base component of lignin.     

The ESR Study of O2 – Radical Anion Formation during Adsorption of an NO + O2 Mixture and O2 on ZrO2 and (0.1–2.0)% MoO3/ZrO2

The influence of conditions of the preliminary thermal treatment of ZrO₂, ammonia and methanol adsorption, and MoO₃ supporting on O₂ ^– formation during the adsorption of an NO + O₂ mixture was studied. The interaction of O₂ ^– with different molecules was studied. Adsorbed ammonia and methanol, as well as supported Mo⁶⁺ ions, were shown to inhibit this reaction. The involvement of the Zr⁴⁺ and O^2– Lewis sites in the reaction was concluded. The interaction of ammonia and methanol with the O₂ ^– radical anions changed the g tensor parameters and decreased the thermal stability of O₂ ^– in the case of methanol. O₂ ^– radical anions were formed on the reduced (0.1–2.0)% MoO₃/ZrO₂ samples during the interaction of O₂ with the Mo⁵⁺ ions in the octahedral configuration. As in the case of O₂ ^– formation during NO + O₂ adsorption on ZrO₂, the radical anions were localized in the coordination spheres of the coordinately unsaturated Zr⁴⁺ ions. A change in the MoO₃ content of the samples from 0.1 to 0.5% led to an increase in the amount of O₂ ^–, whereas a change from 0.5 to 2.0% led to a decrease in the O₂ ^– amount due to the screening of the Zr⁴⁺ ions by oxo complexes and polymolybdates.     

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.