Search Results

You are looking at 21 - 30 of 58 items for :

  • "manganese oxide" x
  • Refine by Access: All Content x
Clear All

Abstract  

A comparison of strontium sorption on synthetic inorganic ion exchangers and zeolites from 0.01M CaCl2 solution, sea water and an artificial foodstuff fluid has been carried out in batch and column experiments. It was found that some adsorbents among the groups manganese dioxides, mixed titanium-manganese oxides, antimony-based materials and synthetic zeolites had the highest selectivity to strontium (K d>1000). These adsorbents are interesting for further investigation concerning their use for radiostrontium decontamination of foodstuffs (if nontoxic), as well as for analytical purposes.

Restricted access

Abstract  

The removal of Ce(III) from aqueous solutions by hydrous manganese oxide (HMO) and hydrous stannic oxide (HSO) was studied as a function of concentrations (10−2−10−7 mol·dm−3) and pH (1.2–10.0) by using the radiotracer technique. The effects of co-ions and irradiation of HMO and HSO were also studied. The uptake of Ce(III) fitted well with the Freundlich adsorption isotherm. No significant desorption of pre-adsorbed Ce(III) in the studied temperature range (303–333 K) indicates that both the solids may be good adsorbents for the removal of Ce(III).

Restricted access

Abstract  

Recently, model free kinetic analysis of sinusoidal modulated TG-curves has been presented. In this contribution we compare the activation energies resulting from model free analysis of modulated TG-curves and from Vyazovkin's model free kinetic analysis of non-modulated TG-curves. We used polytetrafluorethylene and manganese oxide as samples. As a result we find, that both methods deliver similar activation energies for polytetrafluorethylene. However, the activation energies of manganese oxide deviate substantially. The main purpose of kinetic analysis is its potential for predictions of the temporal behavior of materials under certain thermal conditions. Analysis of modulated TG-curves allows a model free determination of the temperature dependence of the activation energy. However, in order to make predictions, one still has to rely on kinetic models such as e.g. first order kinetics. This is in contrast to Vyazovkin's approach, which allows a model free description of kinetic processes in terms of a conversion dependent activation energy. This function can then be used to make kinetic predictions without any further assumptions with respect to reaction models. In this paper we further discuss this fundamental difference.

Restricted access

Abstract  

Bio-availability of radionuclides in soil is influenced by their chemical form and association with different geo-chemical phases. The solid phase speciation of aged90Sr,137Cs,239Pu and241Am in three common agricultural soil types was investigated using separate extractions with seven reagents. Six of these are commonly used to determine radionuclide association with readily exchangeable forms, carbonates, iron and manganese oxides and organic phases. Trimethyl-chlorosilane was also included because of its ability to extract radionuclide-humate complexes from soil. The extract from this part of the study was subsequently subjected to ultra-filtration to determine the association of radionuclides with different molecular size fractions. The results from this speciation study are discussed in terms of availability for plant uptake.

Restricted access

Abstract  

Composite ion-exchange resins were prepared by coating copper-ferrocyanide (CFC) and hydrous manganese oxide (HMO) powders on polyurethane (PU) foam. Polyvinyl acetate/Acetone was used as a binder. The foam was loaded with about five times its weight with CFC and HMO powders. The distribution coefficients of CFC-PU foam and HMO-PU foam for cesium and strontium respectively were estimated. Under similar conditions the HMO-PU foam showed higher capacity as well as better kinetics for removal of strontium than CFC-PU foam for Cs. The pilot plant scale studies were conducted using a mixed composite ion-exchange resin bed. About 1000 bed volumes could be passed before attaining a DF of 10 from an initial value of 60–80. The spent resin was digested in alkaline KMnO4 and the digested liquid was fixed in cement matrix. The matrices were characterized with respect to compressive strength and leach resistance.

Restricted access

Abstract  

A rapid method has been developed for the de termination of214Pb and214Bi in natural waters by alpha-spectrometric measurement of214Po. Well water was filtered on a membrane filter impregnated with manganese oxide and followed by direct alpha-spectrometric analysis. A prominent alpha peak was assigned to214Po, which should be supported by the longer lived parents214Pb and214Bi. The activity ratios between214Pb and214Bi adsorbed on the filter were determined by using the change of activity of214Po as a function of counting period after the filtration. The adsorbed yield of214Pb was also determined from the growth of the alpha-peak due to210Po from a210Pb tracer added in the original water. The results indicated that the amount of214Pb was in radioactive non-equilibrium state with the Rn-222 dissolved, while the activity ratios of214Bi/214Pb showed on increasing tendency with the storage period of the water.

Restricted access

Summary  

Sand filters are used as a filter bed in many ground water treatment plants to remove the physical contaminants and oxidation products. A build-up of radioactivity may take place on the granules, where iron and manganese oxides are deposited and form thin films on the surface of sand filter. The oxides of iron and manganese play an important role in adsorbing radium from ground water. The disposal of those granules makes a significant problem. A batch technique is used for solubilization of radium from sand filters in the presence of some organic acids, which act as reducing agents. These acids are formic acid, acetic acid, benzoic acid, succinic acid, oxalic acid, phthalic acid, and adipic acid. The data were obtained as a function of acidity, temperature, contact time and liquid/solid ratio particle size and shaking speed. It was found that oxalic acid was the best for radium removal. The effectiveness of these acids on radium removal was as follows: oxalic acid > phthalic acid > adipic acid > succinic acid > formic acid > acetic acid. The maximum removal obtained was 69.9% at 1M oxalic acid at 8 ml/g ratio. Reaction kinetics and mechanism parameters of the dissolution process were studied and compared with other published data.

Restricted access

Abstract  

210Pb activities were analyzed in surface sediments from the Coatzacoalcos River (Gulf of Mexico) to evaluate its distribution according to sediment grain size and in different geochemical compartments by using sequential extraction techniques. The geochemical fractionation experiments provided compatible results: by using the Tessier’s method [<cite>1</cite>] more than 90% of the 210Pb activity in the samples was found the residual fraction (primary and secondary minerals) and the remaining (<10%) in the iron and manganese oxides fraction of the sediments; whereas using the Huerta-Diaz and Morse method [<cite>2</cite>] the 210Pb content was found in comparative amounts in the reactive, the silicate, and the pyrite fractions (accounting together for >80%), and the rest was found in the residual fraction. The grain size fractionation analyses showed that the 210Pb activities were mostly retained in the clay fraction, accounting up to 60–70% of the 210Pb total activity in the sediment sample and therefore, it is concluded that the separation of the clay fraction can be useful to improve the analysis of low 210Pb content sediments for dating purposes.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: T. Hashizume, K. Terayama, T. Shimazaki, H. Itoh, and Y. Okuno

Abstract  

We succeeded in studying the mechanism of hydrogen added carbothermic reduction process of iron-manganese oxide by means of the new technique, simultaneous measurement of evolved gas analysis (EGA) and humidity sensor (HS). Water vapor evolved by the reduction with hydrogen can be detected by HS. Other gas was detected by TCD. Without carbon, the hydrogen reduction process was followed to the formation of the intermediate product between MnO and FeO and finally reduction to the mixture of MnO and Fe. With carbon, the intermediate products between MnO and FeO was formed at about 780 K. The methane was formed in higher temperature than 1073 K and the reduction with carbon proceeded mainly. At higher temperatures, methane decomposed to yield nascent carbon that tended to result in the acceleration of the reduction rate with carbon. The study is concerned with the mechanism of the hydrogen reduction of MnFe2O4 and the effect of without and with carbon on this reduction by means of combining EGA and HS.

Restricted access

Abstract  

The sorption behavior of the pertechnetate anion in various solid-solution systems under aerobic conditions and pH 1.3–12.5 has been investigated. Batch techniques were employed. On most of natural minerals only surface adsorption occurs. Rs-values were no larger than 2.0 ml · g–1. Adsorption on various natural minerals and rocks such as sandstone, basalt, granite, pyrite, peat and others are comparaed with the analogous processes on artificial inorganic sorbents: titanium oxides (thermoxide-34, thermoxide-3), crystaline cadmium sulfide, zirconium phosphate, and complex inorganic sorbents: antimony oxide — silicon oxide — phosphorus pentoxide, antimony oxide — silicon oxide — aluminium oxide, lithium oxide — manganese oxide — aluminium oxide — water, lithium oxide — titanium oxide —chromium oxide — water. For comparison the sorption of Tc on some organic sorbents was included. The solubility of Tc2S7 in water was measured to be 0.257 g/l. It has been shown that preliminary irradiation of sorbents such as sandstone, peat and humic acid by -rays with doses not less than 107 rad results in the decrease of Tc(VII) sorption.

Restricted access