Mubar Madrid,chapter 2. For these analyses, standards with an identical matrix were used. Temperature effect indicates an activation energy of The synthesis method was selected from the works published by Dutrizac et al. But if the arsenic is present as a separate phase, like scorodite or a similar phase, its chemical behavior will be different from that of the jarosite, and the dissolution of the arsenic will be able to occur under acidic conditions, which are common in the jarosite deposits. Sergio Pinedo Fuenzalida The solids examination by EDS after the induction period indicates the presence of a reaction front with an unreacted arsenical natrojarosite core and a gel halo of iron exgractiva with adsorbed arsenate. The values of the dependence of energy in NaOH medium were of The solid residues are amorphous, and do not evolve into crystal phases under the conditions of alkaline decomposition herein studied as observed in Figure 4.
|Published (Last):||17 June 2014|
|PDF File Size:||13.5 Mb|
|ePub File Size:||5.47 Mb|
|Price:||Free* [*Free Regsitration Required]|
Tugar Patricio Proust Crovetto Alkaline reactivity is characterized by the removal of sulfate and sodium ions from the lattice and by the formation of a gel consisting of iron hydroxides with adsorbed arsenate. There are few works on the dissolution and stability of such compounds, making the data insufficient for evaluating the real environmental risk caused by the improper disposal of the generated precipitates.
SEM analysis indicated the formation of a reaction front. The pH of the solution was constantly measured, and the experiments were designed so that the reactant concentrations would be constantly adjusted. Arsenic cannot be cietica destroyed, and can only be changed into different forms or transformed into soluble compounds in combination with other elements, such as iron.
In Ca OH 2 medium, a similar procedure was applied: Besides, in both media, t ind is independent kos the particle size Figure 9which confirms that the activation process is a phenomenon occurring at levels of molecular thickness, involving only the initial surface.
The WHO World Health Organization establishes, through its guidelines, that the maximum admissible content of arsenic in potable water should be reduced from 0. According to the previously stated, the stoichiometry of metaurgia process can be expressed according to the following reaction: Introduction The arsenic pollution of water is considered a problem of catastrophic proportions.
Thus, the use of innovative techniques for the elimination of arsenic is an important subject. Samuel Navarrete Cifuentes The alkaline decomposition of the arsenical natrojarosite is characterized by the removal of sulfate and sodium ions from the lattice and their diffusion to the solution, while a gel of iron hydroxide with adsorbed arsenate is formed.
Dependence of the conversion period Figure 10 shows the particle size effect on the decomposition rate of the arsenical natrojarosite. Carlos Carlesi Jara Jefe de Docencia. Formamide, N-Methylformamide, and N-Methylacetamide at The concentration of sulfates and sodium progressively increases, while simultaneously, the reflection intensities of the arsenical natrojarosite decrease until disappearing.
Dependence of the induction period. In any case, this could be a period where active sites are created until a reaction front is established. Gretchen Lapidus Lavine According to the previously stated, several experiments were carried out in order to observe the evolution of the solids at different conversion values. Barcelona,chapter Treatment technologies are available and most of them have been developed for the removal of arsenic at an industrial scale in water treatment plants.
For these analyses, standards with an identical matrix were used. Therefore, in this case, the rate constants are inversely proportional to the square of the initial diameter d 0. Oscar Jaime Restrepo Baena The experimental data are consistent with the spherical particle model with decreasing core and chemical control.
However, since it is a common phenomenon in the decomposition of this type of compounds, the induction period has not been eliminated in this research work, and its dependence on OH — concentration, temperature and particle size have been determined. N-methylformamide-water mixtures at It is important to note that, during the alkaline decomposition process, arsenic was not detected in the samples analyzed by AAS and ICP. The arsenic pollution of water is considered a problem of catastrophic proportions.
This induction period exponentially decreases as the temperature rises, and was independent of the initial particle size in the studied range. Recently, it has been drawn attention to the jarosite-type compounds as a means to control the arsenic in water. The study provides the kinetics and nature of the decomposition reaction topology, reaction rates and dependence of the reaction on variables such as medium concentration, temperature and particle size.
A point rarely metalhrgia in literature, but important when interpreting a kinetic study, regards morphology and particle size. In order to study the stoichiometry of the reaction, samples of arsenical natrojarosite were treated for long periods with NaOH and Ca OH 2. This kind of dependence is related to the chemical control; therefore, it is incompatible with the control by metalurtia of reactants through the layer of the product.
Catalina Vargas vice presidenta. Vice Presidente abasagoi adsl. It seems that the arsenic contained in the natrojarosite structure studied in this work does not have a significant influence on the reaction rate compared to a natrojarosite without arsenic.
This is due to the different coordination environments in the position of the cations or to the substitution of SO 4 2- by oxoanions formed by these elements AsO 4 3-CrO 4 Jessica Gallardo secretaria de finanzas. Therefore, jarosites containing arsenic have an environmental importance, not only as a means to control the As in water, but it is also well known that the hydrometallurgical industries, mainly the zinc industry, use jarosite precipitation as a means to control iron, sulfates and alkaline metals among others.
The end of the induction period was identified by a change in the surface color of the solid, which went from yellow to orange. Figure 10 shows the particle size effect on the decomposition rate of the arsenical natrojarosite.
The decomposition of the arsenical natrojarosite presents an induction period and a conversion period. Related Posts.
Cinética de procesos metalúrgicos
CINETICA DE LOS PROCESOS DE LA METALURGIA EXTRACTIVA