A new method for the spectrophotometric determination of pertechnetate with tris(1,10-phenanthroline)iron(II) ion

A new spectrophotometric determination of technetium has been developed by means of the solvent extraction of tris(1,10-phenanthroline)iron(II) ([Fe(phen)₃ ²⁺]) with pertechnetate into nitrobenzene. The concentration of technetium can be determined by measuring the characteristic absorbance at 516 nm (=11,700M^–1·cm^–1) in the organic phase. An important feature of the proposed method is that the concentration of pertechnetate can be determined without complicated processes such as the reduction of pertechnetate and the subsequent formation of a colored chelate.     

Extraction of pertechnetate by triphenyltin chloride and trioctyltin chloride

The extraction of pertechnetate in form of ionogene associates with triphenyltin and trioctyltin cations into chloroform, benzene, toluene and nitrobenzene was studied. As aqucous phases solutions of^99mTcO ₄ ^? in deionized water and in diluted solutions of NaCl, HCl, NaNO₃, HNO₃ NaClO₄, HClO₄ and NaOH were used. Concerning the organic phases, at the use of triphenyltin chloride the extractibility of pertechnetate increases in the sequence: toluene «chloroform, benzene nitrobenzene and approximately in the sequence: NaOH<NaCl, HCl<NaNO₃<H₂O<NaClO₄ concerning aqueous phases. For trioctyltin chloride in chloroform the extractibility of TcO ₄ ^? increases approximately in the sequence of aqueous phases: NaOH<HCl, NaNO₃, NaClO₄, NaCl«H₂O and in nitobenzene in the sequence NaOH<NaClO₄<HCl<NaNO₃, NaCl«H₂O. The extractibility for trioctyltin chloride is in general slightly lower as compared with triphenyltin chloride. The results of the extraction are presented in the form of graphical plots of technetium distribution ratio (D _Te′ logD _Tc) or extraction yield (E _Tc, %) against concentration of the investigated component in aqueous or organic phase. In some of the systems of the systems studied practically quantitative extraction of pertechnetate into organic phase has been achieved.     

Determination of technetium-99 from complex matrix

This paper reports an approach that can be used for efficient separation and determination of ⁹⁹Tc (as pertechnetate) after contamination of the environment by nuclear materials. The samples were decomposed by fusion in a mixture of potassium hydroxide and potassium nitrate. After fusion, technetium remains as the pertechnetate anion (TcO₄ ^?). The technetium was isolated from the sample by technique combining solvent extraction, anion exchange, then, again, solvent extraction. After separation, ⁹⁹Tc was measured by isotope-dilution mass spectrometry with ⁹⁷Tc as spike. This method yielded nanogram detection limits for ⁹⁹Tc.     

Preparation of Tc-HA complex by displacement of thiourea from the hexakis(thiourea-S)technetium(III) complex

The complexation of technetium with humic acid is usually done by a reduction of pertechnetate by Sn²⁺ ions. A Tc-HA complex can be scavenged in a Sn-HA complex, if tin is present as reductant. The main aim of the study was a preparation of the Tc-HA complex without impurities of Sn ions or other metal reductant, which was performed by a ligand exchange with hexakis(thiourea-S)technetium(III) under nitrogen atmosphere at pH 5.5. The [Tc(tu)₆]³⁺ complex was prepared from TcO₄ ^- in acidic solution with thiourea as a reductant. Presence of the Tc-HA complex and other technetium species was determined by gel chromatography, paper chromatography and dialysis. Yield of Tc-HA complex was about 80% and reaction mixture contains about 20% of technetium dioxide, which is a side product of ligand-exchange.     

Extraction of pertechnetate anion as a ligand in metal complexes with tributylphosphate

The extraction of the pertechnetate anion has been investigated in the systems tributylphosphate (TBP)—solvent (carbon tetrachloride, n-heptane, chloroform)—metal salt (uranyl nitrate and chloride, thorium nitrate)—ammonium salt. In the absence of a metal, the solvates HTeO₄. iTBP (i=4) are extracted, while in the presence of uranium and thorium, the distribution of technetium corresponds to the formation of the mixed complexes: UO₂(NO₃)(TeO₄)·2TBP, UO₂Cl(TcO₄)·2TBP and Th(NO₃)₃ (TcO₁)·2TBP. The effective constants of the reactions H⁺+TcO ₄ ⁻ +i(TBP)_org←(HTcO₁·iTBP)_org, and (ML_n·2TBP)_org+TcO ₄ ⁻ ←(ML_n−1TcO₄·2TBP)_org+L were established in the above systems. The extraction of pertechnetate ion is more effective when it is coordinated to a cation solvated by TBP than the extraction in the form of pertechnetate acid solvated by TBP.     

On the mechanism of the electrochemical reduction of TcO 4 −1 ion on platinum cathode in sulphuric acid solutions

Electroreduction of oxygen-containing anions of the elements of VII group of periodic table, in particular, technetium is a very complicated process. The structure of electron shells of technetium 4d⁶ 5s¹ (s^9/2), allows some oxidation states from +7 to −1, and shows the tendency to hydrolysis, disproportionation and to complex formation. Heptavalent state with d⁰-electron configuration and low tendency to reduction is characteristic for technetium and rhenium. We have studied the products of electroreduction of ion TcO ₄ ⁻ from sulphurous acid solutions of pertechnetate on platinum cathode using electrophoresis, methods of classic preparation chemistry, electron and vibratory spectroscopy. As a result we have succeeded in the isolation of the products of electrochemical reactions, identification and explaining some features of the process connected with the formation of metalic technetium and intermediate complex forms of reduced technetium.     

Feed Adjustment Chemistry for Hanford 101-SY and 103-SY Tank Waste: Attempts to Oxidize the Non-Pertechnetate Species

More than 50% of the technetium in Hanford 101-SY and 103-SY tank waste is not pertechnetate (TcO₄ ^–). These non-pertechnetate species (TcN) are stable, soluble, reduced complexes of technetium. In order to remediate these waste, it will be necessary to oxidize these species to TcO₄ ^–. For radioanalytical purposes, oxidation requires digestion in Ce(IV)/16M HNO₃. Many oxidants are ineffective. Sodium peroxydisulfate, sodium peroxydisulfate/silver(I), and ozone oxidize all of the technetium species to pertechnetate.     

Efficient phase transfer of pertechnetate with bicyclic guanidinium compounds

Extraction of pertechnetate with bicyclic guanidinium compounds has been studied in the KTcO₄-buffer-H₂O/ligand-trichloromethane system. Extraction data of guanidinium ligands have been compared with trialkylmethylammonium (Aliquat 336), tetraphenylphosphonium and tetraphenylarsonium chloride. The lipophilicity of extractants investigated was determined by RP-HPLC. The efficiency of pertechnetate extraction correlates with the lipophilicity of the guanidinium compounds. 1:1 complex formation in the organic phase was observed. The influence of hydroxide, chloride and bicarbonate on the pertechnetate extraction has been investigated. Pertechnetate is extracted with great preference over OH⁻, Cl⁻ and HCO₃ ⁻, ions.     

Preparation of technetium metal by thermal treatment under argon/H<Subscript>2</Subscript>O

A new method for the preparation of Tc metal from pertechnetate is described. Metallic technetium was prepared from TcO₄⁻ by initial reduction in dry argon atmosphere at 300 °C followed by a wet argon atmosphere in the presence of carbon between 700 and 910 °C. The higher temperature conditions in the presence of H₂O and carbon form H₂ and CO, which can drive the reduction of TcO₂. This method was applied to the recovery of pertechnetate sorbed on anion-exchange resins resulting in the formation of Tc metal microspheres. The resulting Tc was characterized by XRD analysis and SEM.     

Ion exchange and solvent extraction of the thiourea complex cation of technetium-99 from mineral acid solutions

Sorption of macroamounts of the technetium thiourea complex cation by a cation exchange resin was studied in HNO₃ and HClO₄ solutions as a function of the concentration and reaction time for pertechnetate with thiourea. The distribution ratio reaches the value of 10³ and may be even higher (>10⁴) when sorption proceeds from a solution of the solid complex in dilute perchloric acid. The complex cation is extracted from 0.25–1M HNO₃ with solutions of the bis(1,2-dicarbollyl)cobalt(III) anion in nitrobenzene—chloroform (1:1), log D=2.75−2.95 being obtained. The preconcentration and separation of technetium on cation exchangers from dilute mineral acids would seem to be one field of application.     

Investigation on technetium species in ground water and migration through clay columns

Speciation of technetium in ground water has been studied for understanding the migration behaviour of this radionuclide in deep geological formations. A combination of free-liquid electromigration, ion exchange, solvent extraction, coprecipitation and dialysis methods has been applied. Both oxic and anoxic conditions have been employed. Systems studied include leaching of sodium borosilicate glass spiked with⁹⁹Tc and^95mTc followed by its passage through glauconitic sand columns, and dialysis of TcO₂ with ground water, sodium chloride, and humic acid solutions. Results indicate the presence of the pertechnetate, TcO ₄ ⁻ , ion as the dominating species.     

Solvent extraction of heptavalent technetium

An extraction study was performed on technetium in its highest oxidation state as a function of nitric acid concentration at 25, 50 and 70 °C. A long chain amine (tri-n-octylamine TOA) and an organophosphorus solvent (TBP) have been investigated. Addition of NH₄NO₃ has a salting-out effect on the extraction of TBP in the aqueous phase and therefore decreases the distribution coefficient for heptavalent technetium. The mechanism of extraction is discussed in the light of the results obtained.     

Solvent extraction of technetium in urine with TBP

The solvent extraction of technetium from urine with TBP has been investigated. The distribution ratio of technetium was determined as a function of HCl concentration and reaction time. The distribution ratio in the HCl-TBP system containing urine is consistently lower than that without urine. The chemical forms of technetium in urine, analyzed by paper chromatography, indicated that pertechnetate was reduced in the presence of HCl and that the reduction of pertechnetate was enhanced by urine. The observed decrease in the distribution ratio was attributed to the enhanced reduction of pertechnetate by urine.     

Base hydrolysis of halobis/8-quinolinolato/ oxotechnetium/V/ complexes

Reaction mechanism of base hydrolysis of halobis/8-quinolinolato/oxotechnetium (V) /TcOX (ox)₂ X=Cl and Br/ was investigated by means of solvent extraction and spectrophotometric methods. Furthermore, distribution coefficients of tris/acetylacetonato/technetium/III/, dichlorobis/8-quinolinolato/technetium/IV/ and TcOX/ox/₂ between chloroform and aqueous solutions were determined. In an alkaline solution, TcOX/ox/₂ decomposed to pertechnetate as a final product. On the basis of the established base hydrolysis, the respective rate constants were determined.     

Synthesis of tris(β-diketonato) technetium(III) and its adsorption behaviour on silica gel

Tris (benzoylacetonato) technetium(III) and tris (2-thenoyltrifluoroacetonato) technetium(III) were synthesized by the direct reduction of pertechnetate with dithionite in the presence of excess ligands. The geometrical isomers of the benzoylacetonate were further separated by means of a silica gel column chromatography. In the silica gel system, the adsorption distribution coefficient of the tris (-diketonato) technetium(III) decreases in the order of Tc(acac)₃>fac-Tc(bzac)₃>mer-Tc(bzac₃)>Tc(tta)₃.     

The determination of technetium-99 in seawater and marine algae

Technetium-99 is preconcentrated from acidified seawater containing a trace of bromine by adsorbing it as the pertechnetate ion on the anion exchanger Duolite A101D. After elution with 4 M nitric acid, it is purified from other radionuclides by scavenging with hydrous iron(III) oxide and extracting from 5 M sodium hydroxide medium into methyl ethyl ketone. The organic phase is then evaporated and technetium is electrodeposited from oxalic acid medium onto a bronze disc and counted with a low background β-counter. Overall recovery is > 90% and the precision is ±0.2 pCi l^-1 at a technetium level of 0.6–1.0 pCi l^-1. Concentrations of the radionuclide in the central Irish Sea were found to lie in the range 0.4–2 pCi l^-1. The same analytical scheme can be used for determining the element in nitric acid digests of marine algae.     

Structural studies on some antimonate exchangers

The possibility of simultaneous extraction of palladium and technetium from nitrate solutions was investigated using tri-n-octylamine (TOA) solutions in carbon tetrachloride as a heavy, non-flammable diluent. Conditions of technetium extraction being essentially known, the main attention was focussed on the extraction of palladium which was studied in dependence on the concentration of nitric acid, salts (nitrates, chlorides, nitrites), urea and palladium. A strong decrease of Pd extraction with 10% TOA in CCl₄ has been found above a palladium concentration of 10⁻⁴M but in the presence of chlorides and nitrites a satisfactory high distribution can be preserved. Both Tc and Pd extracted with TOA/CCl₄ can be stripped into dilute ammoniacal solutions. An extraction procedure for the simultaneous isolation of Pd (80% yield) and Tc (99%) from fission product waste solutions (0.20 g Tc and 0.17 g Pd/dm³ 0.5–1.0M HNO₃) is proposed.     

Kinetics and mechanism of the technetium(VII) oxidation of L-cysteine

Summary The pertechnetate ion oxidizes L-cysteine in strong acid to form yellow and violet (_max=430 and 550 nm) species. A reaction mechanism has been determined which satisfactorily accounts for all the experimental findings. The results obtained support the postulate that the yellow species is a technetium(V)-cystine complex and the violet a technetium(V)-cysteine complex. The rate constants and Arrhenius parameters are reported.     

Fast atom bombardment mass spectrometry of pertechnetate

Negative Ion Fast Atom Bombardment Mass Spectrometry is conducted on potassium pertechnetate evaporated onto a copper probe. The mass spectra of pertechnetate /TcO ₄ ^– / reveal the presence of mononuclear and polynuclear technetium oxo species which form general series Tc_nO _n+1 ^– ,...Tc_nO_n+4 with n=1 to 5. The polynuclear species are believed to be formed via gas phase reactions.     

Extraction of molybdenum and technetium with diamides of dipicolinic acid from nitric acid solutions

The concentration of molybdenum(VI) in dissolved spent nuclear fuel is comparable with the concentrations of Tc, and the minor actinides (Np, Am). Therefore it is of great interest to understand its behavior under conditions imposed by separation processes. The simultaneous extraction ability of ortho, meta, and para isomers of N,N′-diethyl-N,N′-ditolyl-dipicolinamide (EtTDPA) for molybdenum and technetium were investigated in a large range of nitric and hydrochloric acid conditions. Molybdenum shows no increase in extraction at higher concentrations of nitric acid giving a solvate number n=0 with all isomers of EtTDPA, while Mo shows great extractability from HCl. Technetium distribution ratios decrease with increasing concentrations of nitrate showing indication of ion exchange occurring between TcO₄ ⁻ and NO₃ ⁻ anions. Et(m)TDPA and Et(p)TDPA show the greatest extractability, with 60% of the total technetium extracted into the organic phase at 1M HNO₃.