B. D. Symeopoulos

A comparative study of neodymium sorption by yeast cells

Abstract An approximate comparison of neodymium sorption at pH=1.5, between the well studied Saccharomyces cerevisiae and three other related microorganisms ( Kluyveromyces marxianus , Candida colliculosa and Debaromyces hansenii ) was made. Although big differences were not observed, a slightly higher neodymium uptake was attained by the latter three kinds of yeasts. Their adsorption isotherms, varying the initial metal concentration from 10 to 200 mg/L, at constant ionic strength (I=0.1 mol/L), could be fitted equally well, either to Langmuir or Freundlich adsorption model. Their estimated values of qmax and Kf, which are related to adsorption capacity, ranged from 10−12 mg/g and 0.90–1.2 respectively. The corresponding Scatchard plots suggest two types of bonding sites for all yeast studied and common receptor sites between C. colliculosa and D. hansenii . It is also discussed, the feasibility of using all these microorganisms, as potential detoxification tools, wherever contamination of foodstuffs by radionuclides, seems to be probable.

Spontaneous precipitation of barium sulfate in aqueous solution

The formation of barium sulfate scale in oil wells and in several industrial processes in which water supersaturated with respect to this salt is used, is often a serious cause of energy losses. The spontaneous precipitation in aqueous solutions containing relatively high barium and sulfate concentrations was investigated in the present work. In our experiments the supersaturation of the solutions was chosen so that an induction period preceded the onset of precipitation. In all cases the induction time was found to be inversely proportional to the solution supersaturation and the rates of the subsequent precipitation were higher the higher the solution supersaturation. The stability domain of the barium sulfate system was not affected by the barium: sulfate molar ratio which ranged from 0.01to ca. 100. The dependence of the induction time on the initial barium concentration was linear and irrespective of the molar ratio of barium: sulfate the same slope was obtained. The slope may be related to the size of the critical nucleus. The kinetic data obtained suggested a surface-controlled, polynuclear mechanism. On the basis of this model a value of 86 mJ m–2 was obtained for the surface energy of the precipitaing solid phase.

Significance of age, temperature, and aeration of yeast cell culture for the biosorption of europium from aquatic systems

The Eu(III) uptake from aqueous solutions by Saccharomyces cerevisiae, Kluyveromyces marxianus, and Debaromyces hansenii was studied as a function of the growth temperature, supply of air flow during the cultivation process, and the age of cells. Our results revealed that exponential phase cells and the optimum temperature of growth resulted in a higher metal uptake, while aeration did not have any significant effect on the uptake. These traits make the proposed bisorbents desirable for clean-up processes due to easy access and low cost, as well as low time- and low energy-consuming optimal conditions as specified in this study. The reason why younger cells grown close to the optimal temperature show higher metal removal capacity is related to qualitative and quantitative alterations of their membranes’ content in fatty acids and carboxyl groups mainly.

The use of radioanalytical methods in nucleation and crystal growth studies. The barium sulphate system

Abstract The spontaneous precipitation of barium sulphate in aqueous solutions was followed by counting the 131Ba specific activity in the aqueous phase. The main advantages of this method were the increased sensitivity and the possibility of monitoring the process to a larger extent in comparison with other techniques. Kinetics parameters including the size of the critical nucleus and the surface energy of the precipitating solid were estimated according to the model for polynuclear growth.

Neodymium sorption by clay minerals and zeoliferous rocks

The sorption of neodymium from its aqueous solutions (concentration range approx. 10–450 mg l−1) by montmorillonite, kaolinite and a clinoptilolite-containing rock has been investigated, using147Nd as radioactive tracer and γ-ray spectrometry. The neodymium uptake by montmorillonite was found to be much higher than of the other two materials in the whole investigated concentration range. However, in the case of montmorillonite and zeoliferous rock, the uptake ability is lower than that allowed by the measured CEC values and can be described by Langmuir-type equations. In the case of kaolinite, the observed higher than CEC-allowed uptake values could be attributed to sorption by mechanisms other than ion-exchange. The corresponding data obey a Freundlich-type sorption equation. Among the three geological materials investigated, montmorillonite exhibits the highest perspectives of application for the treatment and disposal of neodymium and trivalent actinides in nuclear industry.

Monotonic transfer annealing kinetics associated with an oscillatory phenomenon in51Cr(III)-doped potassium chromate

The monotonic kinetics of isothermal yield of51Cr(VI) in51Cr(III)-doped potassium chromate reveals a common mechanistic scheme with that of neutron irradiated K2CrO4, including two first order processes during the examined first hour. One of them is fast and the other very slow, but both seem to be controlled by two thermal coefficients.

Temperature and dose effect in the oscillatory transfer annealing of51Cr3+ in K2CrO4

Radiochromium doped potassium chromate exhibits partly an oscillatory exchange between trivalent and hexavalent states of the51Cr during isothermal treatment. Thermodynamically dissipative structures created by51Cr/III/ interstitials give rise to rythmic increase and decrease of the transferred yield to the parent lattice. A temperature effect has been noticed on the oscillations by increasing mainly the frequency while a dose effect increases the frequency for the same temperature and decreases the amplitudes. The last is due probably to the elimination of available51Cr/III/ interstitials after radiation annealing. The Volterra-Lotka model is used to explain the oscillatory exchange of51Cr.

Radioanalytical monitoring of the formation of barium sulfate in aqueous solutions

The formation of barium sulfate in aqueous media causes problems of insoluble scale formation. On the other hand, the coprecipitation of uranium and transuranium elements with barium sulfate has been suggested for the determination of these elements in environmental monitoring processes. Therefore, the study of barium sulfate crystal growth is required. The investigations done so far suffer from the low sensitivity of the analytical methods used. In the present work we have overcome this problem by using131Ba for the preparation of supersaturated solutions. Thus kinetics parameters such as induction time and precipitation rates were measured. The polynuclear mechanism was found to be operative at high and the spiral growth at low supersaturations.

Studies on the separation of Ra(II), U(VI) and Eu(III) from aqueous solution using MnO2-resin

The applicability of MnO2-resin for the selective separation of Ra(II) from aqueous solutions containing also U(VI) and Eu(III) has been investigated as a function of solution pH and salinity. The measurements were performed by LSC for radium and by spectrophotometry for uranium and europium, using Arsenazo-III. According to the experimental results the maximum chemical recovery of the MnO2-resin for Ra(II) is observed in the pH range between 5 and 7 and selective separation of Ra(II) from aqueous solutions can be triggered by adjusting solution pH and salinity.

Oscillatory annealing behaviour of three neutron irradiated inorganic crystalline compounds

Abstract In the present work a detailed form of the isothermal annealing behaviour of two cobalt(III) complexes ( cis - and trans -[Co(en) 2 Cl 2 ]NO 3 ) and (NH 4 ) 2 CrO 4 irradiated in the crystalline state by neutrons is presented. The kinetic analysis based on the experimentally obtained curves was done by a semiempirical equation used before in the investigation of oscillating reactions. In the case of chromates the oscillatory kinetics was directly confirmed by the consistent results obtained from two independent and commonly used radioanalytical techniques. Similarities between the observed kinetics and literature reports, concerning similarly treated crystalline lattices, suggest that the driving force is a common property of the defect-containing lattices. Oscillating reactions such as the observed, are predicted by the theory of irreversible processes.