Strontium forms a compound of composition (SrL)2A·nH2O with low solubility (5.0·10–6 mol Sr·dm–3) in the presence of 18-crown-6 (L) and tungstosilicic acid (H4A) in acid media, as has been found by radiometric precipitation titration. Formation of the compound with limited solubility was used for separation of strontium and calcium from 1 mol·dm–3 HCl. It is possible to separate strontium in the range from trace to 6 mmol·dm–3 in the presence of calcium with its concentration up to 0.2 mol ·dm–3 and the recovery determined was 95% of Sr and 5% Ca or 90% of Sr and 4% Ca, respectively. The ratio of Sr/Ca depends on the stability constants ratio of metal-L (⊃SR/⊃ca) in the case of gradual addition of L. Potassium up to the concentration of 0.05 mol·dm–3 does not influence recovery of strontium.
A universal and fast method of90Sr determination in environmental matrices (raw and dried milk, plants, soils) has been elaborated. Solvent extraction method of daughter90Y by tributyl phosphate was used. The method of strontium determination is compatible with determination of other transuranic elements (americium, plutonium) and there is no need to check the chemical yield of strontium.
It was found that lead reacts with 18-crown-6 (L) and tungstosilicic acid (H4A) in acidic solutions and a compound with low solubility is formed what was confirmed by radiometric titration methods. Coprecipitation of complexion cation of PbL2+ with similar complexion cations of calcium, strontium and barium was studied. Formation of low soluble salts was utilized for separation of Pb from Ca, Sr and Ba from 1 mol·dm–3 HNO3. The ratio of Pb/Ca, Pb/Sr and Pb/Ba in the precipitation or separation factors Spb/M undoubted depends on the ratio of the stability constants of lead and metals with 18C6 (
M), what can be used for determination of more precise constant stability
Standard Gibbs energies of transfer of cesium ion from water to nitrobenzene and nitrobenzene-carbon tetrachloride mixture have been evaluated from electrochemical measurements. From the results the conclusion can be drawn that with increasing dielectric permitivity of organic mixed solvents the value of the Gibbs transfer energy of Cs+ ion decreases.
Authors:V. Mikulaj, P. Rajec, A. Švec, N. Cuong, and V. Ahn
A continuous extraction device for preconcentration of metals with light phase internal recycle has been developed. This system was used for preconcentration of cobalt and uranium from 20–30 dm3 samples with 10.8 dm3/hours feed rate. The emulsion membranes were created of surfactants and LIX 64 N (for cobalt) or di-2ethylhexyl-phosphoric acid (for uranium) as a carrier to control stability and permeability for long time periods. The results from continuous extraction of cobalt and uranium using the device constructed have shown the possibility to reach 100–200-fold preconcentration of metals with high yield (min. 92%).
Authors:P. Rajec, V. Švec, V. Mikulaj, and R. Hanzel
Lead as well as strontium form low solubility compounds of composition (ML2)2A·nH2O, (M=Pb2+, Sr2+), in the presence of 15-crown-5 (L) and tungstosilicic acid (H4A) in acid media as found by radiometric precipitation titration. “Sandwich” structure of crown-ether complexes of lead and
strontium could be expected due to the small size of cavity of 15-crown-5. Coprecipitation of PbL2/su2+ with crown complexes of strontium cation after adding tungstosilicic acid was studied in 0.01 mol·dm−3 HNO3. A significant influence of H+ cation in 1 mol·dm−3 HNO3 on coprecipitation of lead was observed. Formation of HL+ complexes by protonisation of 15-crown-5 competes to the formation of ML22+ complexes (approximately twenty percent of 15-crown-5 are used for creation of HL+ complexes). Formation of low solubility salts was utilised for separation of lead from strontium in 0.01 mol·dm−3 HNO3. The ratio of constant stability of lead and strontium β‘ with 15-crown-5 in 0.01 mol·dm−3 HNO3 was calculated. The separation factor S(Pb/Sr) depends on the ratio of stability constants βPbL2/βSrL2 The precipitation method can be used for separation of metals with high constant stability with crown ethers from solutions
containing other metals in the case of gradual addition of crown.
Authors:P. Rajec, V. Mikulaj, P. Husarčik, and V. Švec
The coprecipitation of radium with strontium or calcium, 18C6 and tungstosilicic acid was studied. It was determined that radium is coprecipitated with Ca and Sr and mixed compounds are fomed. It was also find the yield of Ra depends on the ratio of stability constants of metals present in a solution with 18C6. The stability constant of Ra with 18C6 was determined using a precipitation method.
Authors:V. Mikulaj, P. Rajec, A. Švec, and J. Macková
Transport of strontium through supported hollow fiber dichlorobenzene liquid membranes has been studied. The possible mechanism of strontium transport with 18-crown-6 ether as a carrier and picrate as co-counter-ion as well as the construction of a pertraction device with on-line radiometric detection of strontium using85Sr tracer is described. Preliminary results of strontium pertraction in a recycling and one-pass mode with different concentrations of crown are shown.
Authors:F. Macášek, R. Kopunec, V. Mikulaj, P. Rajec, and A. Švec
Membrane extraction is treated as an analogue of solvent extraction in three-phase distribution systems. Its advantages and drawbacks are discussed with respect to separation and preconcentration of radionuclides, fission products of uranium and uranium itself.
Authors:F. Macášek, V. Mikulaj, P. Rajec, R. Čech, L. Mátel, R. Kopunec, J. Kuruc, and A. Švec
Radiolytical decomposition of phenol was investigated at60Co gamma irradiation (1–2 Gy·s–1, 10 kGy) of pre- and continuously aerated aqueous solutions at concentrations of phenol 1–100 mg· ·dm–3 and in the presence of sodium hydroxide, sulphuric acid, sodium and ferrous sulphate, formaldehyde, 2-propanol,n-hexane, xylene, benzene, and commercial gasoline. From the decomposition rate at doses 50–400 Gy, a phenomenological model of linear relation between the dose acquired for 37% decomposition (D37), initial concentration (g·m–3) of phenol (p0) and of an admixture (s0) was confirmed in the formD37=52ftr(p0+feqs0), wheref's are constants which can be attributed to the relative transformation resistance of phenol towards the OH radicals in given matrix (ftr, for pure waterftr=1) and relative acceptor capacity of competing substrate (feq). In real wastewaters, the efficient decrease of phenols content may be substantially lower than that in model solutions, obviously due to radiation oxidation of aromates, as proved by irradiation of aqueous solutions of benzene. Technical and economical feasibility of the process is discussed.