The ability of the back-fill and the host rock materials to take up radioisotopes like 241Am, 85,89Sr and 137Cs has been examined as a function of contact time, pH, amount of sorbent, sorbate concentration, and the presence of complementary cations. A batch technique using actual borehole water from the granite formation has been utilized. In general, the uptake of nuclides by bentonite is much higher than that with granite. The sorption order of nuclides on bentonite is Am>Cs>Sr. The presence of complementary cations, Na+, K+, Ca2+ and Mg2+ depresses the sorption of Cs and Sr on bentonite. The sorption data have been interpreted in terms of Freundlich and Langmuir isotherm equations. Utilizing the Langmuir isotherm equation, the monolayer capacity, Vm,and the binding constant, K, have been evaluated. The change in free energy for the sorption of nuclides on bentonite has also been calculated.
The extraction behavior of yttrium and trivalent lanthanoids has been investigated from thiocyanate solutions using bis(2,4,4-trimethylpentyl)octylphosphine
oxide (CYANEX 925) in xylene as an extractant by tracer techniques. The results demonstrate that these trivalent metal ions
are extracted as M(SCN)3•3CYANEX 925. The equalibrium constants of the extracted complexes have been deduced by non-linear regression analysis. The
extraction behavior of trivalent lanthanoids and yttrium was found to be ambiguous since the distribution ratios of these
metal ions are nonmonotinic function of atomic number (La<Y<Pm<Tm<Ho<Eu<Yb<Lu). The separation factors between these trivalent
metal ions have been calculated and compared with commercially important extraction systems like tributylphosphate (TBP),
trioctylphosphine oxide (TOPO), octy(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and di-2-ethylhexyl phosphoric
acid (DEHPA). The possibilities for separating yttrium from trivalent lanthanoids has also been discussed.
Benzene solution of dihexyl N,N-diethyl-carbamoylmethyl phosphonate (CMP) has been used for the extraction of Pm(III) from 0.2 to 6.0M HNO3. High extraction of Pm(III) was observed between 2 to 4M HNO3. The species extracted in the organic phase were Pm(NO3)3.3CMP and Pm (NO3)3 (3-n) CMP.nTBP when the extractants were CMP and CMP+TBP, respectively. Pm could be efficiently backextracted from both organic phases by pH 2.0 HNO3 solution.
Extraction of Am(III) by dihexyl N,N-diethylcarbamoylmethyl phosphonate (CMP) in benzene from nitric acid solutions (pH 2.0 to 6.0M) has been studied. High extraction of Am(III) by CMP from 2–3M HNO3 was observed. The species extracted was found to be Am(NO3)3·3CMP. The extraction was also done with mixtures of CMP+TBP and CMP+TOPO, where mixed species were extracted in the organic phase. The back-extraction experiments gave an efficient back-extraction of Am(III) by pH 2.0 (HNO3) from the loaded CMP+TBP phase but a poor back-extraction from the loaded CMP+TOPO phase. The loading of Nd(III) by mixture of CMP and TBP was 50% of the CMP concentrations at a total Nd(III) concentration of 0.182M. The thermodynamic parameters of Am(III) extraction by a mixture of CMP and TBP were evaluated by temperature variation method, which suggests that the two-phase reaction is stabilized by enthalpy and opposed by entropy.
Batchwise uptake of Am(III), Pm(III), Eu(III), U(VI) and Pu(IV) by dihexyl-N,N-diethylcarbamoylmethylphosphonate (CMP) adsorbed on chromosorb (CAC) at nitric acid concentrations between 0.01 to 6.0M has been studied. The difference between the uptake behavior of Pu(IV) as compared to other actinides and lanthanides is discussed. The Am(III) and U(VI) species taken up on CAC were found to be Am(NO3)3·3CMP and UO2(NO3)2·2CMP, respectively. The equilibrium constants for the formation of these species have been evaluated and compared with those of similar species formed in liquid-liquid extraction. Batchwise loading of Pm(III) on CAC from 3.0M HNO3 has also been studied.
Authors:M. Reddy, A. Damodaran, J. Mathur, M. Murali, and R. Iyer
Mixed-ligand chelate extraction of trivalent lanthanides such as La, Eu and Lu and a trivalent actinide, Am into xylene with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP) and dihexyl-N,N-diethylcarbamoylmethylphosphonate (CMP) has been studied by tracertechniques. These trivalent metal ions are found to be extracted from 0.01 mol/dm3 chloroacetate buffer solutions as M(PMBP)3·HPMBP type self adducts with HPMBP alone and in the presence of CMP as M(PMBP)3·CMP (where M=La, Eu, Lu and Am) into the organic phase. The equilibrium constants of the above species are deduced by non-linear regression analysis. The synergistic constants of trivalent lanthanides do not increase monotonically with atomic number but have a maximum at Eu and that of Am was found to lie between that of La and Eu.
Authors:M. Krishna, J. Arunachalam, M. Murali, Surendra Kumar, and V. Manchanda
The efficiency of immobilized moss as a bio-sorbent for the removal of 137Cs and 90Sr radionuclides from actual low-level radioactive waste (LLW) solutions was investigated. Preliminary batch experiments with
the moss (Funaria hygrometrica) for the sorption of Cs and Sr have shown a pH dependent binding trend from pH 1–13, with maximum binding between pH 5–10.
Time dependence of the batch studies showed that a contact time of 30 minutes was sufficient to reach equilibrium. Column
experiments for the sorption of Cs and Sr by moss after immobilizing in polymer silica matrix demonstrated that the sorbent
is capable of removing considerable amounts of Cs and Sr from actual LLW solutions under constant flow conditions. The adsorption
capacity was estimated to be 8.5 mg/g for Cs and 15 mg/g for Sr. These sorbed metal ions from the column could be leached
out using 0.20M nitric acid. The regenerated sorbent exhibited relatively the same initial binding capacity of both Cs and
Sr even after 3 cycles of reuse.
Authors:A. Saxena, R. Tomar, M. Murali, and J. Mathur
The sorption of 241Am, 233U and 137Cs from nitric acid solutions on a synthesized sodium potassium fluoro-phlogopite (SPFP) gel, structurally close to the fluorine mica mineral, has been studied. The synthesized gel was characterized by energy dispersive spectrometry, X-ray powder diffraction pattern, FTIR and thermogravimetric analysis and has a composition of Na0.5K0.5Mg3(Si3AlO10)F2.6H2O. Different parameters like contact time, acid concentration, amount of SPFP, metal ion concentrations, effect of competing cations, desorption of the nuclides from the loaded SPFP gel etc., were studied using batch technique. Also, the SPFP gel was loaded with Eu(III), U(VI) and Cs(I) and the amounts sorbed on the gel has been estimated by difference from the concentrations in the original solution and those remaining in the solution after loading. Na, K, Mg, Eu and U were estimated by ICP-AES and Cs by electrothermal atomization atomic absorption spectrometry. The exchange of Na, K and Mg with the loaded cations has been evaluated and discussed in the light of ion exchange and surface precipitate sorption mechanisms.
Authors:S. Murali, V. Natarajan, R. Venkataramani, and M. Sastry
An Electron Spin Resonance (ESR) study of radiation induced free radicals in the commonly used detergent powder (Surf), was conducted to examine its potential application for retrospective/high level dosimetry, including possible dating of the accidents. The radical ions present in the irradiated detergent powder were identified as arising predominantly from sodium tri poly phosphate (Na3P5O10) and sodium sulphate (Na2SO4). The physical mixture of sodium tri poly phosphate and sodium sulphate in 4:1 ratio was found to give an ESR response, similar to that of the detergent powder. These results suggest that the detergent powder can be used as a dosimeter in the 20 Gy to 18 kGy dose range, spanning over 3 orders of magnitude. The second derivative ESR spectra of the detergent powder irradiated to different doses showed that the relative yield of the radicals is independent of irradiation dose. The decay pattern of radicals when followed as a function of post irradiation days, lead to the idea about the contrasting decay characteristics of the radicals. From the ESR signals of the irradiated detergent samples, it is shown that radiation dose can be evaluated and the radiation incident can be dated with an accuracy of ±10%.
Authors:M. Murali, K. Michael, U. Jambunathan, and J. Mathur
Extraction, loading and stripping studies of Pu(IV) have been carried out using three phosphine oxides namely CyanexÒ-923 (cyn-923), CyanexÒ-925 (cyn-925) and TOPO in dodecane from nitric acid medium. All the three phosphine oxides have shown very high extraction of Pu. The order of extraction for Pu by these compounds is cyn-923 > TOPO - cyn-925. Loading of Pu (30.0 mg/l) in 3.0M HNO3 was carried out using 5% solution of each of the phosphine oxides in dodecane. It was found that even at an organic to aqueous phase ratio of 1:10, the loading of Pu is >96%. From the loaded organic phase, Pu could be almost quantitatively stripped using 0.1 or 0.5M oxalic acid. The extraction of Pu(IV) with cyn-925 has also been carried out from HCl, HNO3 or HClO4 (0.5 to 9.1M). The species extracted into the cyn-925/dodecane phase from 3.0M HNO3 or HCl media was found to be Pu(L)4.2 cyn-925 where L = NO3– or Cl–. Similar species were observed to be formed when dodecane was replaced by xylene, chlorobenzene or o-dichlorobenzene.