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Studies of surface properties of Na- and La-montmorillonites
Thermogravimetry Q-TG, sorptometry, porosimetry and AFM methods
Abstract
This paper presents possible applications of thermal analysis, sorptometry and porosimetry to study physico-chemical properties of Na- and La-montmorillonite samples, especially for determination of total surface heterogeneity. The quasi-isothermal thermogravimetric (Q-TG) mass loss and its first derivative (Q-DTG) curves with respect to temperature and time obtained during programmed liquid thermodesorption under quasi-isothermal conditions have been used to study adsorbed layers and heterogeneous properties of the Na- and La-montmorillonites. Calculations of the desorption energy distribution functions by analytical procedure using mass loss Q-TG and differential mass loss Q-DTG curves of thermodesorption under quasi-isothermal conditions of polar and non-polar liquid vapours preadsorbed on a material surface are presented. Parameters relating to porosity of samples were determined by sorptometry, mercury porosimetry and atomic force microscopy (AFM). From nitrogen sorption isotherms from sorptometry and porosimetry methods, the fractal dimensions of montmorillonites have been calculated. Moreover, a new approach is proposed to calculate fractal dimensions of materials obtained from Q-TG curve; this is compared with values obtained by the above methods. The total heterogeneous properties (energy distribution function and pore-size distribution functions) of samples studied were estimated. The radius and pore volume of the tested samples calculated on the basis of thermogravimetry, sorptometry and porosimetry techniques were compared and good correlations obtained.
Abstract
Divalent transition metal nitroprussides form a family of microporous materials which lose their crystallization water (coordinated and zeolitic) below 100°C and then remain stable up to above 150°C. The dehydration process of representative samples in their stable phases was studied by thermo-gravimetry (TG) and differential scanning calorimetry (DSC). The copper complex dehydrates in a single step through a practically irreversible process. For cadmium and cobalt complexes the water evolution on heating takes place in two stages. The first one, where only zeolitic waters are removed, is dominated by a diffusion mechanism while, during the loss of the strongly bonded waters (second stage) the material framework effect is added. The involved activation energy and its dependence on the conversion degree were estimated evaluating the thermo-gravimetric data according to an isoconversion model.
Summary The disposal of used automotive tires has caused many environmental and economical problems to most countries. We propose the use of rice husk as filler for increasing the value of recycled tire rubber. Thermal degradation of both components and their sintering mixtures is presented in this paper. Thermal decomposition of rice husk occurs in various steps in the temperature range between 150 and 550°C. This complex process is the result of the overlapping of thermal decomposition of the three major constituents common in all lignocellulosic materials, i.e., hemicellulose, lignin and cellulose. Hemicellulose is degraded at temperatures between 150 and 350°C, cellulose from 275 to 380°C and lignin from 250 to 550°C. The degradation process of major constituents of scrap tires or their composites is observed at temperatures between 150 and 550°C. For composites, the addition of rice husk (maximum 25%) produces an increase in the mass loss rate. This effect is higher as the amount of rice husk increases. However, the degradation initial temperature of elastomeric matrix is not affected with addition of rice husk. Apparent kinetic parameters were also studied by the isoconversional Friedman method. We observed that the addition of rice husk produces a decrease in apparent activation energy for low conversions (up to 0.6). For higher conversions this decrease was not so clearly observed.
Abstract
The preparation and characterization of a Mexican organo clinoptilolite-heulandite mineral as well as the evaluation of its sorption properties for cadmium and cobalt are presented. The mineral was modified with different concentrations of hexadecyltrimethyl-ammonium bromide (HDTMA), the resulting materials were characterized by electron microscopy, IR spectroscopy, BET surface analysis, X-ray diffraction and their cation exchange capacities were determined. The cobalt and cadmium uptake was carried out in different concentrations. Neutron activation was used to measure the sorption of cobalt and cadmium. Organo zeolitic mineral samples were obtained with different surface characteristics compared with the original material and it was found that the retention of cobalt and cadmium by the organo zeolite diminishes due to the presence of HDTMA.
Abstract
Zinc oxide targets irradiated with high energy protons at the Los Alamos Meson Physics Facility (LAMPF) contain a number of radioactive spallation products in quantities large enough to warrant recovery. This paper describes methods for recovering7Be,46Sc, and48V from such targets and offers suggestions on possible ways to recover additional isotopes. The proposed methods are based on traditional precipitation and ion exchange techniques, are readily adaptable to hot cell use, and produce no hazardous waste components. The products are obtained in moderate to high yields and have excellent radionuclidic purity.
Abstract
The precipitation of uranyl ion with 2-hydroxy-1-naphthaldehyde /2H–1N=HL/ was studied. The solid complex /orange crystals/ was characterized by IR, UV-Vis spectra. Uranium was determined as U3O8 after calcination of the complex at 850°C /37.78% U experimental, 36.64% U calculated for C22H14O6U, UO2L2/. Using a statistical experimental design, the best conditions for quantitative precipitation were obtained. A gravimetric method for the determination of UO 2 2+ is proposed by weighing the complex after drying at 110°C.
Abstract
Radium isotopes were measured in groundwater near a radioactive storage facility with contained pasty residues from monazite and industrial processing sealed in concerete reserouirs. The concentration of radium isotopes in the water was slightly higher than found in the normal drinking water. The measured228Ra to225Ra ratio in the groundwater is not compatible with calculations of radium isotopes ingrow and docay in cake II for different elapsed times, leaving mesothorium cake as the most likely source of contamination.
Abstract
Inductively Coupled Plasma Mass Spectrometry ICP-MS has been applied to the characterisation of various nuclear waste forms. Long-lived radionuclides can be determined with similar sensitivities. The installation of an ICP-MS in a glove box and applications and limitations of the methods to nuclear materials, with especial emphasis on isobaric interferences are described.
Abstract
It is well known that phosphate rock contains a small amount of uranium. During the production of phosphate fertilizers, most uranium present is found in the phosphate fraction. Uranium was determined in the 70–200 ppm range in the phosphate rock and the final products by nuclear and classical methods.
