V. Mikulaj

Membrane extraction in preconcentration of some uranium fission products

Theoretical comparison of the equilibria and kinetics of solvent extraction (SX) and emulsion liquid membrane extraction (MX) was performed using the distribution ratios at the outer inner boundaries of liquid membrane. Enhancement factors, pertraction factor (p) and mulitplication factor (N), were proposed to express efficiency of the MX technique. The extraction of cesium, strontium, cobalt(II), uranium(VI), cerium(III) and technetium(VII) was investigated from this point of view. The most perspective systems are those with chelating agents (e.g. di-2-ethylhexyl-phosporic acid and 8-hydroquinoline), especially at low concentrations (substioichiometric amounts), with which high enhancement factors can be achieved. The results with the ion-exchange systems (bis(1,2-dicarbollyl)-cobalt(III) and quaternary ammonium salts) may be interpreted as indicating some surface barriers which prevent the transport of ions. 20 references, 14 figures, 6 tables.

Radiochemical analysis of90Sr in milk, soil and plants by solvent extraction

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.

Coprecipitation of 15-crown-5 ether complexes of lead and strontium with tungstosilicic acid

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.

Precipitation separation of lead and calcium, strontium, barium from acidic solutions using crown ether and tungstosilicic acid

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 (βPb/βM), what can be used for determination of more precise constant stability βM.

An emulsion membrane extraction of strontium and its separation from calcium utilizing crowns and picric acid

The selective separation ability of the cyclic crowns, known for liquid-liquid extraction, e.g. alkali metals, is found to be effective for emulsion membrane extraction. 18-C-6, DB-18-C-6, DC-18-C-6 crowns were used as carriers. The co-transport of the ionic pair SrL2+. 2A through the membrane has been studied. Calcium was considered as a main competing ion. Even in the case of 20-fold preconcentration, there have been found conditions under which the pertraction process can reach Sr/Ca separation factors of about 500 and the yield of strontium is high (95–98%). The presence of calcium up to 1000-fold excess has no influence on the yield of strontium (1.10−5M). The calcium content in the isolated emulsion was caused by second emulsification of the outer solution. The influence of potassium on strontium pertraction has been studied and some transport data of Cs and Y have been obtained.

SORPTION-DESORPTION OF RADIOCESIUM ON VARIOUS SORBENTS IN PRESENCE OF HUMIC ACID

In general, the amount of radiocesium sorbed by the five sorbents with 0.01 mol·dm−3 NaCl was in order zeolite > NiFeCN−SiO2 > montmorillonite > aerogel > silica gel. Addition of humic acid solution to the sorbents depressed the sorption of cesium by all sorbents, except for NiFeCN−SiO2 was not seen, with the greatest effect showing to the aerogel. The presence of humic acid resulted in an enhanced desorption of cesium from zeolite, NiFeCN−SiO2 and to a lesser extent from montmorillonite and silica gel. The order of cesium retention following desorption for both sorbent and sorbent/humic-acid mixtures was zeolit > NiFeCN−SiO2 > montmorillonite > silica gel. The presence of humic acid resulted in decreasing of distribution coefficient values for both sorption and desorption processes.

Determination of239, 240Pu in environmental samples from surroundings of the atomic power station Jaslovske Bohunice

The development of a rapid and reproducible method for the separation of plutonium from soil samples is described. Tetravalent plutonium is extracted from 8M HNO3 into 30% Aliquat-336/toluene mixture. Uranium and thorium are removed with nitric and hydrochloric acid washes. Plutonium is backextracted with HCl−H2C2O4 and HCl−HF solutions. Plutonium is coprecipitated with NdF3 and filtrated onto a 0.1–0.2 μm membrane filter to prepare a source for α-spectrometry. The chemical yields of separation are about 50–60%.

Coprecipitation of radium with calcium and strontium from acid solutions using crown ether and tungstosilicic acid

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.

PRECIPITATION SEPARATION OF STRONTIUM AND CALCIUM FROM ACIDIC SOLUTIONS USING CROWN ETHER AND TUNGSTOSILICIC ACID

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 (²SR/²ca) 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.

Pertraction of strontium in bulk liquid membrane systems using crown ether as a carrier

The rate of pertraction of Sr2+ by 18-crown-6 (18-C-6) ether and picric acid in bulk liquid membrane systems containing various surface-active substances depends not only on the concentration of 18-C-6 and picric acid but also on the presence of various surface-active substances.