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Summary  

A comprehensive sampling of organic and conventional oranges was carried out in Bebedouro, an important citrus producing region of Brazil. The soils, leaves and fruits of the variety Valencia (Citrus sinensis [L.]Osbeck) budded on Rangpur lime (Citrus limonia Osbeck) were analyzed. The chemical characterization was accomplished by instrumental neutron activation analysis (INAA). Indications for a difference between organic and conventional orange juices and leaves were obtained by applying univariate and multivariate statistical analysis. There were differences between samples for Br, Co, Cs, La and Rb from both systems.

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The large scale manufacture of sodium chromate is carried out by heating finely ground chromite ore mixed with sodium carbonate and lime in air. The essential reaction leading to the formation of sodium chromate is
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$2Cr_2 O_3 + 4 Na_2 CO_3 + 3 O_2 \xrightarrow{{\Delta {\rm H}_{R^0 } }}4Na_2 CrO_4 + CO_2$$ \end{document}
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Abstract  

Rotating disc reactor (RDR) was constructed to conduct gas–liquid–solid reactions with controlled reagent transfer from gaseous to liquid phase. The concept is based on continuous formation of thin liquid films at a surface of rotating discs where the mass transfer proceed in diffusion–convective way. The reactor was employed to run precipitation reaction of CaCO3 via carbon dioxide absorption in lime slurry. During each reaction pH changes and Ca2+ concentration in time were measured. Disc rotations and gas flows were changed during the experiment and their influence on the obtained CaCO3 powders has been examined and fully discussed.

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Abstract  

Oil shale ashes from the PAMA demonstration power plant in the Negev region of Israel are produced by fluidized bed combustion (700–850C) under short residence time. The FED is organic-rich calcareous raw material rich in carbonate rather than clays. Thus it is important to ascertain whether the calcite in the ashes is original natural calcite from the raw material or the product of recarbonation of lime. Three groups of ashes from the power plant, Ash Cooler (AC), Fly Ash (FAS) and Boiler Bank (BB) were examined using XRD, FT-IR, SEM and isotope analysis methods. The recarbonated calcite is distinguished from the natural original by smaller crystal size, lower degree of crystallinity and the presence of impurities. High negative δ13C values in oil shale ashes are explained by assuming recarbonation of lime with CO2 originating from the combustion of the organic matter of the raw oil shale. Fly Ash, FAS, and BB, produced from organically-rich FED, contain more recarbonated calcite than bottom ash, AC. This observation can be explained by the larger grains of the AC, which do not reach the highest temperature area, and thus most of the original calcite does not decompose.

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Abstract  

The sintering and the structure of clinkers, modified by the introduction of different ionic forms of sulfur and phosphorus into the raw mix, were examined. One reference synthetic mixture and 25 modified mixtures were prepared by mixing the reference sample with 0.5, 1.0, 1.5, 2.0 and 2.5%w/w of chemical grade CaSO4, CaS, Ca3(PO4)2, CaHPO4 and Ca(H2PO4)2. Free lime content in all samples was measured. The sintering reactions in samples were recorded by means of differential thermal analysis. The texture of the clinkers was examined using a scanning electron microscope and EDX. It is concluded that, despite of their relatively low doping concentration in the raw mix, P and S affect considerably its reactivity and the texture of the clinker. The various ionic forms of the same element (SO4 2-, S2- for S, PO4 3-, HPO4 2- and H2PO4 - for P) exhibit a different and unequivocal effect on the reactivity of the synthetic raw mix and on the texture of the corresponding clinkers. S (in both forms) and P (added as HPO4 2-) are mainly dissolved in the melt and they have a positive effect on the burnability of the raw mix. P (added as PO4 3- or H2PO4-) is preferentially accumulated in belite. In this case further stabilization of β-C2S occurs and the binding of the free lime is hindered.

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One of the fundamental events in the formation of the medieval European continent was the transition to more complex organisational structures, even for the inhabitants of the territories beyond the Roman limes. The historical-social transformation movement of the western European world and the new multiethnic composition of the new Roman-Germanic societies were only two of the consequences of the collapse of the division between the highly-developed Mediterranean world and the areas not directly controlled by Rome where, however, stable socio-economic organisational forms had still developed, involving both the steppe and the Germanic populations. Even if it never was an insuperable boundary for all those who lived in the areas not under Roman control, the limes forever lost that ideological concept of barrier and border between two diverse and opposing worlds. The mechanism that caused such consequences involved very complex processes that, as they occurred, affected the environmental geographic conditions as well as the local traditions and ethnic affinities. The populations that continued to live in the areas beyond the Pannonian border introduced themselves into the stream of cultural transformations that arose in that part of the post-Roman European territories between Late Antiquity and the early medieval centuries. It would still be several centuries before this change would complete its natural cycle. In the end, the tribal societies disappeared and new social and cultural structures arose. This helped to spread new ways of using nature, new standards for social co-existence and a new vision of the world.

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Abstract  

A thermal analysis study on the reduction of iron oxide rich slags under different conditions is presented in this paper. The effects of important process variables such as time, temperature, lime-silica ratio, FeO level in slag etc. are discussed. It is shown that the mechanism of reduction by externally added graphite is different from that by a carbon saturated bath although the activation energy values are similar.

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Radium-226 in uranium mill tailings

I. Fate and consequent dissolution

Journal of Radioanalytical and Nuclear Chemistry
Authors: H. Steger and M. Legeyt

Abstract  

A study of the physical state of226Ra in uranium mill tailings was undertaken by Chemex Laboratories Ltd. under contract to NUTP. A test portion of a leached uranium ore was collected just prior to neutralization with lime and subjected to repetitive batch water leaching. The leachates were analyzed for barium, lead,226Ra, iron and sulphate. The experimental results suggest that226Ra is co-precipitated with lead sulphate during uranium leaching of the ore with sulphuric acid. The attainment of equilibrium conditions in the pore water of the leached ore then allows a re-proportioning of226Ra between solid lead and barium sulphates resulting in a depletion of226Ra in the outer layers of the crystals of solid lead sulphate and an enrichment in226Ra in the outer layers of solid barium sulphate.

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Abstract  

In this work, the pozzolanic and hydraulic properties of ashes originating from various sources were studied in model systems such as ash and ash-lime pastes. The sources of studied ashes were: fluidized combustion of brown coal, pulverized combustion of brown coal and pulverized combustion of hard coal. This article is a continuation of our previously published studies on cement pastes with mentioned ashes. The following experimental techniques were applied: calorimetry, thermal analysis (TG, DTG) and infrared absorption (IR). Previously drawn conclusions relating to the reactivity of ashes in an environment containing Ca2+ ions were confirmed. According to these conclusions, an ash originating from fluidized combustion of coal exhibited higher reactivity compared to other ashes from pulverized combustion. Pozzolanic and hydraulic properties of this ash were also confirmed. Differences in the behaviour of ashes originating from pulverized combustion of various types of coal in the presence of water and Ca2+ rich environment were demonstrated.

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Abstract  

Extensive use of pan, by one-tenth of world"s population, entails the evaluation of trace element contents in its ingredients. Radiochemical neutron activation analysis (RNAA) was developed and successfully employed to determine the concentration of 36 trace elements (essential, toxic and nonessential) in its four basic ingredients, leaf of betel pepper, betel nut, catechu and lime. The radiochemical separation methodology has significantly improved the detection limits of most of these elements due to suppression of Compton background. This study provides the base-line values of certain toxic and essential elements in these ingredients. The daily intake of essential and toxic elements through pan was estimated and compared with the recommended values. The cumulative intake of Mn is four times higher than the recommended value and that of toxic elements is well below the tolerance limits.

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