Thesis REMOCIÓN DE ARSÉNICO Y COBRE DESDE SOLUCIONES DILUIDAS MEDIANTE EL USO DE ESFERAS DE ALGINATO CON INSCRUSTACIONES DE HIERRO EN POLVO
Date
2019
Authors
APABLAZA LOPEZ, ALEJANDRO CHRISTOFER
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Abstract
En Chile se generan una alta cantidad de desechos acuosos que contienen elementos nocivos para la salud humana como lo son el arsénico y el cobre. Para retirar estos elementos del agua se utilizan varias tecnologías, pero requieren muchos recursos. Necesitándose un proceso económico y amigable con el medio ambiente. Es por ello que el principal objetivo de este proyecto de título fue evaluar las variables que afectan la remoción de arsénico y cobre desde soluciones diluidas, mediante el uso de esferas de alginato dopadas con polvo de hierro. Estas variables fueron el pH, la velocidad de agitación, el porcentaje de hierro en las esferas, la inyección de oxígeno, la concentración de As y Cu en la solución, el tiempo, la temperatura y concentración de ácido sulfúrico en la elución de As, Cu y Fe. El trabajo experimental consistió en un sistema batch. Para las pruebas de remoción de arsénico y cobre se realizaron experimentos con porcentaje de hierro en las esferas entre 1% y 33%, porcentaje de oxígeno inyectado entre 0% y 100%, concentraciones de arsénico entre 0 y 5 mg/L, concentraciones de cobre entre 0 y 23 mg/L, temperaturas entre 10 y 60 ºC, con muestras de esferas de alginato dopadas de hierro secas con masa de 120 mg y un tiempo experimental de 360 minutos. Los resultados mostraron que para una concentración inicial de arsénico y cobre de 5 y 23 mg/L, respectivamente, el aumento en el pH incrementa la remoción de As y Cu, alcanzándose la máxima remoción de arsénico de 45,5 mg de As/g de hierro (91,2%) y de cobre de 93,7 mg de Cu/g de alginato (79,9%), a pH 5,5. En cuanto a la velocidad de agitación al incrementar esta, aumenta la remoción de As y Cu, hasta llegar a un máximo a las 250 RPM. Un aumento en el porcentaje de hierro en las esferas se traduce en una mayor remoción de arsénico, porque hay más hierro para remover As, pero menos alginato para remover el cobre. El mecanismo de remoción de arsénico consistiría en la reducción de arsénico a As(0) por parte del hierro, oxidándose el Fe y formando Fe2O3, depositándose el arsénico en el Fe0, además el óxido de hierro podría adsorber las especies de arsénico como se menciona en la literatura. Por su parte, el cobre es principalmente removido por intercambio iónico con el alginato. El oxígeno favorece la remoción de arsénico, mientras que disminuye la de cobre. Para concentraciones de cobre menores a 17 mg/L las esferas pierden su estabilidad física, mientras que al incrementar la concentración de arsénico la remoción de cobre se incrementa, desde 86,1 a 93,7 mg Cu/g de alginato, para 0 y 5 mg/L de As, respectivamente. A un mayor tiempo se alcanzaron mayores remociones de As y Cu, observandose el mismo efecto al incrementar la temperatura, alcanzándose remociones de 45,6 mg As/g de hierro y 108,8 mg Cu/g de alginato. Del análisis cinético se obtuvo que el modelo de pseudo segundo orden es el que mejor representa los resultados obtenidos, indicando que el paso limitante en la remoción de cobre es la reacción de intercambio iónico. Además fue calculada la energía de activación, teniendo un valor de 14,4 kJ/mol. Por su parte, la elución de As fue insignificante, mientras que el cobre y el hierro alcanzan la máxima elución con una concentración de H2SO4 de 0.0153 M, siendo esta de 71,6% y 62,3%, respectivamente.
In Chile, a high amount of aqueous waste is generated that contains elements harmful to human health such as arsenic and copper. Several technologies are used to remove these elements from water, but they require many resources. Needing an economic and friendly process with the environment. That is why the main objective of this project was to evaluate the variables that affect the removal of arsenic and copper from diluted solutions, through the use of alginate spheres doped with iron powder. These variables were the pH, the speed of agitation, the percentage of iron in the spheres, the injection of oxygen, the concentration of As and Cu in the solution, the time, temperature and concentration of sulfuric acid in the elution of As, Cu and Fe. The experimental work consisted of a batch system. For the arsenic and copper removal tests, experiments were carried out with iron percentage in the spheres between 1% and 33%, percentage of oxygen injected between 0% and 100%, arsenic concentrations between 0 and 5 mg/L, concentrations of copper between 0 and 23 mg/L, temperatures between 10 and 60 ºC, with samples of dried doped iron alginate spheres with a mass of 120 mg and an experimental time of 360 minutes. The results showed that for an initial concentration of arsenic and copper of 5 and 23 mg/L, respectively, the increase in pH improve the removal of As and Cu, reaching the maximum removal of arsenic of 45.5 mg of As/g of iron (91,2%) and copper of 93.7 mg of Cu/g of alginate (79.9%), at pH 5.5. Regarding the speed of agitation to increase this, improve the removal of As and Cu, until reaching a maximum at 250 RPM. An increase in the percentage of iron in the spheres results in a greater removal of arsenic, because there is more iron to remove As, but less alginate to remove copper. The mechanism of arsenic removal would consist in the reduction of arsenic to As(0) by the iron, oxidizing of the Fe and forming of the Fe2O3, the arsenic is depositated in the Fe0, in addition the iron oxide could adsorb the arsenic species as mentioned in the literature. For its part, copper is mainly removed by ion exchange with alginate. Oxygen favors the removal of arsenic, while that of copper decreases. For copper concentrations lower than 17 mg/L the spheres lose their physical stability, while increasing the concentration of arsenic the copper removal increases, from 86.1 to 93.7 mg Cu/g of alginate, for 0 and 5 mg/L of As, respectively. To a higher time a greater removal of As and Cu was achieved, while the same effect was observed when the temperature was increased, removing 45.6 mg As/g of iron and 108.8 mg Cu/g of alginate. From the kinetic analysis it was obtained that, the pseudo second order model is the one that best represents the results obtained, indicating that the limiting step in the removal of copper is the ion exchange reaction. In addition, the activation energy was calculated, having a value of 14.4 kJ/mol. On the other hand, the elution of As was insignificant, while copper and iron reached the maximum elution with a H2SO4 concentration of 0.0153 M, this being 71.6% and 62.3%, respectively.
In Chile, a high amount of aqueous waste is generated that contains elements harmful to human health such as arsenic and copper. Several technologies are used to remove these elements from water, but they require many resources. Needing an economic and friendly process with the environment. That is why the main objective of this project was to evaluate the variables that affect the removal of arsenic and copper from diluted solutions, through the use of alginate spheres doped with iron powder. These variables were the pH, the speed of agitation, the percentage of iron in the spheres, the injection of oxygen, the concentration of As and Cu in the solution, the time, temperature and concentration of sulfuric acid in the elution of As, Cu and Fe. The experimental work consisted of a batch system. For the arsenic and copper removal tests, experiments were carried out with iron percentage in the spheres between 1% and 33%, percentage of oxygen injected between 0% and 100%, arsenic concentrations between 0 and 5 mg/L, concentrations of copper between 0 and 23 mg/L, temperatures between 10 and 60 ºC, with samples of dried doped iron alginate spheres with a mass of 120 mg and an experimental time of 360 minutes. The results showed that for an initial concentration of arsenic and copper of 5 and 23 mg/L, respectively, the increase in pH improve the removal of As and Cu, reaching the maximum removal of arsenic of 45.5 mg of As/g of iron (91,2%) and copper of 93.7 mg of Cu/g of alginate (79.9%), at pH 5.5. Regarding the speed of agitation to increase this, improve the removal of As and Cu, until reaching a maximum at 250 RPM. An increase in the percentage of iron in the spheres results in a greater removal of arsenic, because there is more iron to remove As, but less alginate to remove copper. The mechanism of arsenic removal would consist in the reduction of arsenic to As(0) by the iron, oxidizing of the Fe and forming of the Fe2O3, the arsenic is depositated in the Fe0, in addition the iron oxide could adsorb the arsenic species as mentioned in the literature. For its part, copper is mainly removed by ion exchange with alginate. Oxygen favors the removal of arsenic, while that of copper decreases. For copper concentrations lower than 17 mg/L the spheres lose their physical stability, while increasing the concentration of arsenic the copper removal increases, from 86.1 to 93.7 mg Cu/g of alginate, for 0 and 5 mg/L of As, respectively. To a higher time a greater removal of As and Cu was achieved, while the same effect was observed when the temperature was increased, removing 45.6 mg As/g of iron and 108.8 mg Cu/g of alginate. From the kinetic analysis it was obtained that, the pseudo second order model is the one that best represents the results obtained, indicating that the limiting step in the removal of copper is the ion exchange reaction. In addition, the activation energy was calculated, having a value of 14.4 kJ/mol. On the other hand, the elution of As was insignificant, while copper and iron reached the maximum elution with a H2SO4 concentration of 0.0153 M, this being 71.6% and 62.3%, respectively.
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Keywords
ESFERAS DE ALGINATO , HIERRO EN POLVO , REMOCION DE ARSENICO , REMOCION DE COBRE