Documents found
-
8581.More information
In this paper the author proposes certain distinctions between the respective roles of mothers and educators. Differences between mothering and education are described within seven dimensions: 1) role limits; 2) affective intensity; 3) attachment; 4) rationality; 5) spontaneity; 6) objectivity; 7) extent of responsibility. The author recommends the maintenance of the important objectives of educational programs for parents. The complementary nature of the role of parents and that of teachers should be recognized.
-
8582.More information
There is an important concern about the problems occuring with wastes elimination, specially the industrial liquid wastes. Te face the problem of organic aqueous wastes coming front various branches of industry, the WPO® (wet peroxide oxidation) process was developed at the laboratory. In the WAO process (wet air oxidation), which uses gaseous oxygen, the limiting step is usually oxygen transfer. In this new process, this problem is suppressed by using a liquid oxidising agent (hydrogen peroxide). This process is adapted from the classical Fenton's reaction and iron salts are used as the catalyst in order to promote the formation of •OH radicles which are the main active species. But the reaction is carried out at about 120 °C; so, a very significant TOC (total organic carton) removal efficiency is obtained (60 to 90 %) in comparison with the low efficiency of the classical Fenton's reagent (typically 25 % at room temperature).Significant amounts of free fatty acids are formed during the reaction. They are namely oxalic, malonic, succinic and acetic acids, which are common by products obtained during audition of most industrial organic pollutants. In order to comply with the regulations requirements, it was necessary to improve the efficiency of the original process. It was also very important to obtain an efficient elimination at a temperature not greater than 100 °C in order to avoid to pressurize the treatment reactor. This could be obtained by using new catalysts which are described in this paper.Because of the related field, precious metals like Pt and potentially toxic ones like Cr were not considered. One needs a treatment process as cheap and as reliable as possible. So, only Fe, Cu, Co, Ni and Mn were used as salts in order to test their calalytic activity in the treatment by hydrogen peroxide of a synthetical mixture of oxalic, malonic, succinic and acetic acids (O, M, S, A). The experimental device is a stirred tank reactor where the organics and the catalyst are batch loaded. It is continuously fed, for 1 hour, with hydrogen peroxide. The total amount injected is 1.5 the stoechiometric amount. In table 1, it can be seen that any metal has a satisfactory activity when used alone (TOC removal efficiency cannot exceed 22 %). In table 2, it is clear that, in soma cases, the association of two or three metals with each other can lead to very important synergetic effects. When using a mixture of Fe, Cu and Mn, the removal efficiency can increase to 91 %. This Fe/Cu/Mn catalyst is studied with further details in table 4. It appears to have its best efficiency at about 100 °C because of a parasitic decomposition of the peroxide at higher temperatures. For an organic mixture coutaining 5 g TOC/l, 100 ppm of each metal is a convenient concentration. This new catalyst still needs an acidic pH, from 3 to about 5, but the dependency is not so strict than with Fe alone (original process) which needs a value from 3 to 3.5. In addition, it was observed that the treatment time could be easily reduced (down to 45 minutes) as well as the amount of peroxide injected.Very similar results have been obtained with synthetic solutions of pollutants and with real industrial ones, thus establishing the ability of the Fe/Cu/Mn mixture to catalyse the oxidation of a large variety of species and not only carboxilic acids. The difference between the efficiency of this new catalyst and the conventional one is shown in table 5. Figures 1 and 2 are related to an Industrial WPO® unit which is commonly used with the conventional catalyst (Fe). It has been possible to improve its efficiency by using the new one without any significant modification. The Fe/Cu/Mn catalyst can be easily separated alter reaction (coprecipitation effect). Thus, the treated water meets the regulation requirements and the recovered catalyst can be easily resolubilized and recycled.
Keywords: Eaux usées industrielles, oxydation à haute température, peroxyde d'hydrogène, pollution organique réfractaire, réactif de Fenton, synergie catalytique, Industrial wastewaters, high temperature oxidation, hydrogen peroxide, refractory organic pollution, Fenton 's reagent, synergetic effect, catalysis
-
-
8584.More information
This article is about the international relations of Latin America between 1950-1980. No systematic account of such history is attempted here. Rather attention is paid above all to the main thrust of such history. In this study it is argued that most dominated countries have very little capacity to affect the general and most fundamental structures of the World System. These countries tend to be mere object of history. There foreign policies to a very large extent contribute to the reproduction of the World System. Indeed it is one of the functions they must assume as far as the development of the system is concerned. But given the fact that underdeveloped countries are also subject of history, they do not submit passively to such a general law of social system. Their foreign policies are sometimes designed to modify the International Division of Labor "or their place within it" and with it the distribution of power without however drastically changing or upsetting the inner logic of the World System. It is within such an approach that one must study the international role of dominated countries in general and of the Latin American states in particular.
-
-
-
-
8588.
-
8589.
-