Search Results

You are looking at 81 - 90 of 2,205 items for :

  • "treatment" x
  • Chemistry and Chemical Engineering x
  • All content x
Clear All

Abstract  

The influence of preliminary annealing (at 400 and 1000 °C) and wet treatment (with 0.1M HCl; with 0.1M NaOH) of aluminum oxide on the separation efficiency of 68Ge-68Ga radionuclide chain was studied. The adsorption behavior of 68Ga daughter radionuclide was examined by desorption in order to find the best conditions for separation of both radionuclides. The effect of the preliminary annealing and wet treatment of alumina on the experimental generator columns was studied.

Restricted access

Abstract  

The presence of toxic heavy elements such as arsenic, cadmium and mercury in industrial wastewater and waterways is a serious pollution problem. The treatment of such contaminated water by conventional techniques, which often includes an ion-exchange or similar step, is expensive. This paper examines the use of natural materials such as hair, and certain plants, which are inexpensive, for the absorption and hence the clean up of heavy elements from polluted water. Our results show that these natural materials concentrate the heavy elements, in certain cases, to the extent of up to 500 fold or even better. The contact time required is of the order of several hours. The capacities of absorption vary from about 1 g/kg to about 5 g/kg for mercury, and are lower for arsenic and cadmium. The results show that with hair, nearly 10,000 liters of mercury contaminated water, a typical daily output from a 100 ton chlor-alkali plant, can be treated with about 1/2 kg of hair valued at about 25 cents. This makes the process extremely cost-effective compared to the conventional processes now in use.

Restricted access

Abstract  

Two kinds of feldspars, such as microcline and albite, were irradiated with g-rays of 250 Gy in 77 K and followed by ESR-measurements at 77 K. First ESR-spectra showed an Al-Oh+ center peak at a centeral part and hydrogen radical peaks having hyperfine (HF) splitting width of 50.2 mT. Second ESR-spectra measured after warming up to room temperature once showed eleven absorption peaks owing to an Al-Oh+-Al center, together with complete disappearance of H0-radicals. The Al-Oh+-Al signals in ESR-spectra showed similar dose response curves in both feldspars, giving almost linear relationships up to several hundred Gy and saturation behavior beyond 1 kGy. Thermal treatment of the feldspars induced an interesting appearance of two new hydrogen radicals in the ESR spectrum, which possess broader HF splitting in the ESR-spectra and relatively stable property at room temperature. The correlation of Al-Oh+-Al centers and the BTL intensities around 180 °C peak showed linear dependency. As a result, it is concluded that the Al-Oh+-Al centers should be main BTL-luminescence centers around the 180 °C peak in the feldspars.

Restricted access

Abstract  

This report describes the environmental sample treatment techniques for14C measurement with liquid scintillation counter. The groundwater sample of about 80 liters was collected from well and inorganic carbon was removed by acidification and recirculated gas stripping with the extraction efficiency of more than 98%. The biological samples were freeze-dried and combusted to carbon dioxide in high pressure combustion unit with a combustion efficiency of nearly 99%. The14CO2 in the stack effluents was collected by an air bubbler with a collection efficiency of more than 99% for a sampling time of two weeks. Sampling of14C in reduced form also has been done by passing the gases through a tube furnace with Pt/Al and Pd/Al catalyst. Active and passive sampling methods for atmospheric14C measurements were compared in detail, and it could be concluded that the uncertainty associated with passive sampling method was quite acceptable for environmental monitoring. The CO2 trapped in NaOH was precipitated as BaCO3, and subsequently reconverted to CO2 for environmental samples and transferred to Carbo-Sorb ETM for liquid scintillation counting. In case higher precision is the deciding factor, benzene synthesis would be employed with home-made benzene synthesizer.

Restricted access

Formation and filtration characteristics of solids generated in a high level liquid waste treatment process

II. Filtration characteristics of solids formed in simulated high level liquid waste

Journal of Radioanalytical and Nuclear Chemistry
Authors: Y. Kondo and M. Kubota

Abstract  

The filtration characteristics of solids generated in a simulated high level liquid waste (HLLW) were experimentally examined, when the simulated HLLW was processed according to the ordinary way of actual HLLW treatment process. The filtration characteristics of solids depended on the particle size. The phosphomolybdic acid, which was very fine particle with about 0.1 m diameter, made slurry a difficult-to-filter slurry, if the phosphomolybdic acid content (wt%) to the whole solids in a slurry exceeded 50 wt%. On the contrary, the zirconium compounds (zirconium molybdate and zirconium telluride) had positive effect on filtration characteristics because of their relatively large particle size of about 3 to 5 m. When the zirconium compounds content was above 50 wt%, slurry became a easy-to-filter slurry. A centrifugal sedimentation was discussed as a solid/liquid separation technique for very fine particles such as phosphomolybdic acid. The theoretical feed flow rate corresponded to 0.1 m diameter particles was about 20 l/h at the centrifugal acceleration of about 8000 G.

Restricted access

Abstract  

Coupled TG-FTIR technique was used for identification of gaseous compounds evolved at thermal treatment of six coal samples from different deposits (Bulgaria, Russia, Ukraine). The experiments were carried out under dynamic heating conditions up to 900C at heating rates of 5, 10 or 50 K min–1 in a stream of dry air. The emission of CO2, H2O, CO, SO2, COS, methane, methanol, formic acid, formaldehyde, acetaldehyde, chlorobenzene was clearly identified in FTIR spectra of the samples studied. The formation of ethanol, ethane, ethylene and p-xylene, at least on the level of traces, was also identified. At the heating rate of 5C min–1 the temperature of maximum intensities of the characteristic peaks of COS was 270C, of formaldehyde, formic acid, ethane and methanol 330C, of SO2, CO, acetic acid, ethylene and p-xylene 400C and of chlorobenzene 500C. At 10C min–1 and 50C min–1 these temperatures were shifted, respectively, by 70–300C and 150–450C towards higher temperatures and the respective absorption bands in FTIR spectra were, as a rule, more intensive.

Restricted access

Abstract  

Perovskite oxides of composition (Sr1-xCax)(Fe0.5Co0.5)O3- were investigated for CO2 absorption properties and were proved to be useful as materials for CO2 absorption in the temperature range from 550 to 850 °C. The absorption rate of CO2 increased with Ca doping. The mechanical treatment of perovskite oxides for several minutes, especially for the oxides containing a small amount of Ca, was found to be effective for activating the oxides for CO2 absorption and for reducing the starting temperature of CO2 absorption by about 80 °C. However, it was not less effective to treat the oxides for a long time. The site distortion due to Sr and Ca ions at site A and the mixed valence states at site B were confirmed to be effective for CO2 absorption at high temperatures. During the absorption of CO2, a spinel compound was formed according to the following reaction: 2(Sr,Ca)(Fe,Co)O2.5 + CO2 (Sr,Ca)CO3 + (Sr,Ca)(Fe,Co)2O4.

Restricted access

Abstract  

Phase changes of iron containing solid wastes from steel mill pickling lines after thermal treatments were investigated aiming the determination of the appropriate conditions for its transformation to be useful for industrial raw materials. Above 275°C, the thermally treated wastes contain a mixture of α-Fe2O3 (hematite) and γ-Fe2O3 (maghemite) in different proportions, depending on the maximum heating temperature of the thermal treatment. Increasing the maximum temperature the maghemite participation is decreased through its transformation to hematite. Above 850°C hematite is the main constituent, suggesting that thermal treatment of the wastes in this temperature will give a product that could be used as red iron pigment.

Restricted access

Abstract  

Chemical treatment assumes an important role in the management of radioactive wastes as it is a simple technique and offers advantage in terms of handling of wastes thereby reducing the risk of mansievert exposure. Low level wastes (LLW) and intermediate level wastes (ILW) are generated in various facets of nuclear fuel cycle and have various chemical composition. A systematic study was carried out by using copper ferrocyanide and calcium phosphate precipitation methods for the removal of cesium and strontium, respectively. The supernatants were subjected to ultra filtration (UF) using a membrane having a pore size of 0.2 m. The decontamination factors (DF) at 2 and 24-hour intervals with and without UF were estimated. The DF obtained was in the range of 200–300 for cesium and 200 for strontium with LLW solution which has chemical characteristics similar to ground water. Two hours of settling is adequate for strontium before UF. In case of cesium there is no much change in the DF values by UF. However, the UF has helped in the solid — liquid separation as the flocks of copper ferrocyanide precipitate are feathery in nature. The effect of ionic strength and the presence of TBP on the removal efficiency of cesium and strontium have also been studied. DF are observed to be a function of ionic strength and are low in deionized water, in salt solutions containing 1 to 4M sodium nitrate and also in solutions of ILW. However, increasing the chemical dosing to two times of normal plant dosing has yielded a DF of about 200 for sodium nitrate solutions with respect to cesium removal. When the concentration of ammonium nitrate in the waste exceeds 0.1M, the DF reduces. Entrained TBP as well as soluble TBP reduces the removal efficiency of cesium. This paper deals with the experimental data and mechanism of the processes involved in the removal of cesium and strontium.

Restricted access

Abstract  

Thermal analysis was used to deduce the mechanism of resistance to enzymatic digestion by starches and to account for the extent of resistance at different enzymolysis reaction temperatures. Thermalanalysis was also used to determine the most productive treatment temperature for exploration of the effects of heat-moisture treatment of starches on their subsequent chemical and physical behavior, including enzyme digestibility. The starches were selected according to an experimental design based on a nontraditional description of genetically varied corn starches. As a result, each functional response to heat moisture treatments of the starches adjusted to different moisture contents could be assigned to the relevant causative structural factor in the experimental design.

Restricted access