Coprecipitation of 60Co from aqueous solutions with triethylenediamine complexes of d-element nitrates

Formation of complexes of Co²⁺ with triethylenediamine (CH₂-CH₂)₃N₂ (Q) in aqueous solution and coprecipitation of microamounts of ⁶⁰Co with triethylenediamine complexes of Cu²⁺, Ni²⁺, and Zn²⁺ nitrates were studied. Microamounts of ⁶⁰Co poorly coprecipitate with triethylenediamine complexes of Cu²⁺ and Zn²⁺ nitrates. At practically 100% precipitation of Cu²⁺ and Zn²⁺ from solutions in the form of the corresponding complexes, the degree of coprecipitation of ⁶⁰Co with these complexes does not exceed 15%. With the Ni²⁺ complexes formed from 10⁻¹ M aqueous solutions at the molar ratios Ni²⁺: Q = 1 : 1 and 1 : 2, the degree of coprecipitation of ⁶⁰Co is about 45 and 90%, respectively.     

Coprecipitation of 60Co with d element sulfides from aqueous solutions in the presence of EDTA

Coprecipitation of ⁶⁰Co microamounts from aqueous solutions with sulfides of d elements (Cu²⁺, Ni²⁺, Co²⁺) in the presence of 10^?2 M EDTA was studied. Under these conditions, the initial solution can be efficiently decontaminated from ⁶⁰Co by its coprecipitation with NiS. The degree of coprecipitation of ⁶⁰Co microamounts with NiS exceeds 95% at [Na₂S]: [Ni²⁺] = (5–10): 1.     

Recovery of 60Co from EDTA-containing aqueous solutions

The possibility of recovering radioactive cobalt from EDTA-containing aqueous solutions using oxidation (O₃) and photooxidation (UV/H₂O₂) methods was examined. The optimal amounts of reagents ensuring complete decomposition of EDTA and recovery of radioactive cobalt were determined. The procedures developed for oxidative decomposition of EDTA and for recovery of radioactive isotopes from aqueous media were tested with real liquid radioactive solutions.     

Coprecipitation of tellurium and molybdenum oxides from aqueous solutions

We report the preparation of mixtures of tellurium and molybdenum oxides of controlled composition through the precipitation of tellurous and molybdic acids from hydrochloric acid solutions of tellurium(IV) and molybdenum(VI) compounds. We have established general trends in the distribution of macrocomponents between the precipitate and solution and shown the feasibility of quantitative tellurium(IV) and molybdenum(VI) precipitation in a weakly acidic medium. After drying and calcination, the precipitates were tested as TeO₂-MoO₃ glass batches.     

Nucleation of solid solutions crystallizing from aqueous solutions

The study of nucleation and growth mechanisms of salts from aqueous solutions, as a function of supersaturation, is described using both macroscopic and microscopic experiments. In situ observations in a fluid cell in an atomic force microscope (AFM) reveal phenomena not accounted for in standard crystal-growth theories, specifically on the role of the crystal structure of the substrate in controlling spiral growth and two-dimensional nucleation. As a model example, the crystallization of two isostructural salts, BaSO(4) and SrSO(4), is described. The growth of solid-solution crystals is considerably more complex. The supersaturation of a given aqueous solution relative to a solid solution is different with respect to each solid composition, and it leads to the possibility that different compositions can simultaneously grow by different mechanisms on the same crystal face. Oscillatory compositional zoning is another consequence of the interplay between the thermodynamics and the kinetics of nucleation. The factors which control nucleation and growth of the solid solution (Ba,Sr)SO(4) from an aqueous solution are described. The predictions made from the theory are compared with direct observations of crystal growth in an AFM.     

Coprecipitation of radium with barium sulfate from salt solutions

Coprecipitation of radium with barium sulfate from highly concentrated NaCl solutions is studied, including the effects of the initial solution composition, alkaline reagent (CaO, NaOH), supporting electrolyte (NaCl) concentration, and pH. The process is promoted by high NaCl concentration in the initial solution, which is due to structural transformation and change in the sorption activity of the BaSO₄ precipitate in salt solutions. The results obtained were applied to recovery of radium from process solutions in chlorination of loparite concentrates.     

Sorption of 60Co from aqueous solutions on layered double hydroxides of Mg, Al, and Nd

Sorption of ⁶⁰Co from aqueous solutions of various compositions on layered double hydroxides (LDHs) of Mg, Al, and Nd in carbonate and hydroxide forms and on layered double oxides (LDOs) of Mg and Al was studied. ⁶⁰Co is poorly sorbed from aqueous nitrate solutions onto LDH-Mg-Al-OH. The ⁶⁰Co distribution coefficient K _d does not exceed 50 ml g^?1 at a phase contact time of 15 min and V/m = 50 ml g^?1. At the same time, ⁶⁰Co is efficiently sorbed from 10^?3?C10^?5 M aqueous Co(NO₃)₂ solutions onto LDH-Mg-Al and LDH-Mg-Nd with CO ₃ ^2? in the interlayer space. At a phase contact time of 15 min and V/m = 50 ml g^?1, K _d exceeds 2 × 10⁴ ml g^?1 for LDH-Mg-Nd and does not exceed 5 × 10³ ml g^?1 for LDH-Mg-Al. The ⁶⁰Co desorption from LDH-Mg-Nd-CO₃ into 0.05?C0.2 M solutions of Na₂CO₃, NaNO₃, (NH₄)₂C₂O₄, and Na₂H₂EDTA and into distilled water was studied. Na₂H₂EDTA is the most efficient desorbing agent. After 15-min contact of LDHMg(⁶⁰Co)-Nd-CO₃ with 0.1 and 0.05 M Na₂H₂EDTA solutions, the degree of desorption of ⁶⁰Co is ??100 and ??99%, respectively.     

Oxidation of U(III) with water in the course of precipitation of its solid compounds from aqueous solutions

U(III) was precipitated from solution as a yellowish-brown precipitate under the action of NH₄OH or Na₂B₄O₇ solutions at pH ～7.5. The electronic spectra showed the presence of substantial amounts of U(OH)₃ in the precipitate, decreasing within a few minutes. Therefore, pure U(OH)₃ can hardly be obtained. A brown precipitate is formed when a U(III) solution is added to an NH₄F solution. An X-ray phase analysis shows that anhydrous UF₃ is the only crystalline compound in the precipitate. The synthesis of U(III) phosphate was unsuccessful, because uranium was completely oxidized to U(IV). Thus, preparation of U(III) phosphate compounds from aqueous solutions is hardly possible.     

Preparation and reactivity of lead zirconate-titanate solid solutions produced by precipitation from aqueous solutions

A process for preparation of PZT by precipitation from butoxide precursors is described. The reactivity of the powders during low temperature firing (calcining) has been determined using weight loss, x-ray diffraction, and DTA-TGA techniques.     

The removal of phenolic compounds from aqueous solutions by organophilic bentonite

The adsorption of p-chlorophenol (p-CP) and p-nitrophenol (p-NP) on organophilic bentonite (dodecylammonium bentonite, DDAB) was studied as a function of solution concentration and temperature. The observed adsorption rates were found to be equal to the first-order kinetics. The rate constants were calculated for temperatures ranging between 25.0-35.0 degrees C at constant concentration. The adsorption energies, E and adsorption capacity, (qm), for phenolic compounds adsorbed to organophilic bentonite were estimated by using the Dubinin-Radushkevic equation. Thermodynamic parameters from the adsorption isotherms of p-CP and p-NP on organophilic bentonite were determined. These isotherms were modeled according to Freundlich and Dubinin-Radushkevic adsorption isotherms and followed the V-shaped isotherm category with two steps. The amount of adsorption was found to be dependent on the relative energies of adsorbent-adsorbate, adsorbate-solvent and adsorbate-adsorbate interaction.     

Coprecipitation of microamounts of radionuclides on chitosans of various molecular weights in solutions

Coprecipitation of ²³³U, ²³⁹Pu, ²⁴¹Am, ¹⁵²Eu, ⁹⁰Sr, ⁹⁰Y, and ⁶⁰Co on chitosans of various molecular weights (MW) was studied. Low-molecular-weight chitosan (LMWC) with MW of 5 kDa (5 × 10³ g mol⁻¹) proved to be a more effective coprecipitant than high-molecular-weight chitosan (HMWC) with MW of 700 kDa (7 × 10⁵ g mol⁻¹). With HMWC, the degree of coprecipitation (α) was 80% for ¹⁵²Eu and ⁹⁰Y, 99% for ²³³U and ²⁴¹Am, and 85% for ²³⁹Pu. For ⁶⁰Co, α monotonically increased with an increase in the chitosan concentration in solution and reached 40% at [HMWC] = 5 g l⁻¹. For ⁹⁰Sr, α did not exceed 3% in the entire examined range of chitosan concentrations. With LMWC, the α values for An, ¹⁵²Eu, and ⁹⁰Y differed insignificantly (92–99%). For ⁶⁰Co and ⁹⁰Sr, α increased to 40% in the range of chitosan concentrations from 0 to 1 g l⁻¹. The presence of inorganic salts in solution considerably decreases α of UO₂²⁺ with chitosans but does not noticeably affect the behavior of Am, Pu, and Eu. The effect of salts on the efficiency of ²³³UO^2/2+ coprecipitation on HMWC decreases in the order Na₂SO₄ > NaCl > Na₂CO₃ > NaNO₃ > Na₃PO₄. Based on the results obtained, a procedure suitable for expedition conditions was developed for preconcentration of Pu from seawater on chitosan, with simultaneous separation of Pu from U, for radioecological monitoring of natural waters. The specific activity of Pu in samples of near-bottom seawater of gulfs of the Novaya Zemlya archipelago was (150–170) ± 20 mBq m⁻³. The results are well consistent with the published data.     

Cast iron deterioration with time in various aqueous salt solutions

The changes with time in the corrosion rate and corrosion current density on a cast iron electrode in various aqueous salt solutions have been carried out using total immersion test and potentiostatic polarization curves. The concentration of salts taken is expected to be present in potable water. The relative behaviour of these salts towards corrosion has also been studied, which is found to be different from previous studies. The total immersion test parameters viz. weight loss, corrosion rate as well as potentiostatic parameters, open circuit potential,I _corr, Tafel slopes, corrosion rate, have been calculated by standard methods. Besides these the relative increase in corrosion rate with time as well as the percentage to which corrosion rate should be decreased so as to provide protection towards corrosion have also been calculated. It was found that KCl and NaCl are major contributors than MnSO₄, Pb(NO₃)₂, KI and KBr. The relative increase in corrosion is high in KBr, KI, NaNO₃, CaCl₂, and less in Pb(NO₃)₂, NaHCO₃ and CaCO₃ test solutions. For the reliability of results the data has been statistically analysed.     

Uranium(III) in aqueous solutions: Preparation,properties, synthesis of solid compounds

Published data on the preparation procedures, stability, and complexation of U(III) in aqueous solutions are summarized and correlated. Reactions with inorganic and organic free radicals studied by the flash radiolysis method, the spectroscopic properties, the extraction and ion-exchange behavior of U(III), and methods for isolation of solid U(III) compounds from aqueous solutions are discussed.     

Removal of heavy metal ions from aqueous solutions using various low-cost adsorbents

The removal of single heavy metals Co and Zn from aqueous solutions using various low-cost adsorbents (Fe(2)O(3), Fe(3)O(4), FeS, steel wool, Mg pellets, Cu pellets, Zn pellets, Al pellets, Fe pellets, coal, and GAC) was investigated. Experiments were performed at different solution pH values (1.5-9) and metal concentrations (0.67-333 mg/l). The effect of solution pH on metal adsorption using Fe(2)O(3) and Fe(3)O(4) was significant, but was negligibly small using steel wool, Mg pellets, Fe pellets, and Al pellets over the entire pH range. Steel wool and Mg pellets were the most excellent adsorbents; for example, the removal of Zn and Co from dilute solutions (<35 mg/l) was greater than 94% at an adsorbent dose of 1.7 g/l. A mass transfer model, which involves two parameters tau (50% breakthrough time) and k (proportionality constant), was proposed to describe breakthrough data of Co in the fixed beds packed with steel wool and Mg pellets. The calculated breakthrough curves agreed well with the measured data (standard deviation < 6%). The value of tau decreased with increasing the flow rate. The effects of flow rates on the value of k and adsorption capacity are discussed.     

Coprecipitation of tellurium(IV), tungsten(VI), and lanthanum(III) hydroxides from aqueous solutions

We have investigated the coprecipitation of tellurium(IV), tungsten(VI), and lanthanum(III) hydroxides through the addition of aqueous ammonia to a mixture of tellurium dioxide, lanthanum oxide, and tungstic acid solutions in hydrochloric acid. The effects of initial solution composition and precipitation pH on the composition of the precipitate have been assessed. It has been shown that the composition of the precipitate is essentially identical to that of the starting solution if the relative contents of lanthanum and tungsten in the mixture are within 20 mol % and precipitation is ceased at pH 7.     

Coprecipitation of microamounts of Cs with ferrocyanides of various metals

Coprecipitation of microamounts of Cs with ferrocyanides of various metals, exhibiting a high sorption activity with respect to Cs ions, was studied. The distribution coefficients of ¹¹⁷Cs were determined in coprecipitation with the ferrocyanides in 0.1 M NaNO₃. The precipitated ferrocyanide was separated from solution by filtration through a Trumem metal-ceramic membrane. Cesium is recovered most efficiently with ferrocyanides of bivalent transition metals (Ni, Co, Cu, Fe, Cd).Translated from Radiokhimiya, Vol. 46, No. 5, 2004, pp. 444–445.Original Russian Text Copyright © 2004 by Milyutin, Gelis, Klindukhov, Obruchikov.     

Sorption of plutonium in various oxidation states from aqueous solutions on Taunit carbon nanomaterial

Sorption of Pu from weakly acidic and weakly alkaline solutions on Taunit carbon nanomaterial was studied. Under these conditions, both polymeric Pu(IV) and ionic Pu(V, VI) species are recovered from freshly prepared solutions. Also, Pu is efficiently sorbed from simulated groundwater after more than 10 months of storage. The Pu sorption in all the forms by carbon nanotubes is rapid and almost quantitative (95 ± 5%) at the sorbent-to-solution ratio of 1 : 80 g ml⁻¹. Plutonium preliminarily sorbed on Taunit can be efficiently immobilized in a magnesium potassium phosphate ceramic whose physicochemical properties meet the requirements of prolonged environmentally safe storage of long-lived radionuclides.     

Removal of ammonium from aqueous solutions with volcanic tuff

This paper presents kinetic and equilibrium data concerning ammonium ion uptake from aqueous solutions using Romanian volcanic tuff. The influence of contact time, pH, ammonium concentration, presence of other cations and anion species is discussed. Equilibrium isotherms adequately fit the Langmuir and Freundlich models. The results showed a contact time of 3h to be sufficient to reach equilibrium and pH of 7 to be the optimum value. Adsorption capacities of 19 mg NH(4)(+)/g were obtained in multicomponent solutions (containing NH(4)(+), Zn(2+), Cd(2+), Ca(2+), Na(2+)). The presence of Zn and Cd at low concentrations did not decrease the ammonium adsorption capacity. Comparison of Romanian volcanic tuff with synthetic zeolites used for ammonium removal (5A, 13X and ZSM-5) was carried out. The removal efficiciency of ammonium by volcanic tuff were similar to those of zeolites 5A and 13X at low initial ammonium concentration, and much higher than those of zeolite ZSM-5.