Adsorción de metales pesados en agua usando carbón activado modificado mediante tratamiento ácido
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Date
2024
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Universidad de Concepción
Abstract
La contaminación de agua con metales pesados representa un gran problema al medio ambiente y a los seres humanos debido a la toxicidad de estas especies. En la zona norte de Chile se presentan altas concentraciones de cobre, cadmio y plomo en ríos que abastecen agua potable. Dentro de las técnicas de remoción de estas especies en agua, la adsorción mediante carbón activado es una de más las efectivas. La adsorción de metales pesados en carbón activado ocurre principalmente en grupos funcionales oxigenados. La introducción de estos grupos en la superficie del carbón activado se realiza mediante tratamientos ácidos.
El objetivo general de este trabajo es evaluar el efecto de la modificación superficial con ácido nítrico de un carbón activado en la adsorción de cobre, cadmio y plomo en agua. Se ensayaron tres métodos distintos de acidificación de la superficie mediante los siguientes equipos: placa calefactora, baño María y rotavapor. Se modificó un carbón activado obtenido de neumáticos fuera de uso, con ácido nítrico 5M por 3 horas a 60°C. Se seleccionó como procedimiento óptimo el uso del rotavapor ya que permite mantener la solución de ácido nítrico y carbón activado en rotación constante y producir una mezcla homogénea. El material original (DMAC) y el modificado (DMAC-HNO3), fueron caracterizados mediante adsorción-desorción de N2 a 77K, punto de carga cero, espectroscopía infrarroja por transformada de Fourier (FTIR) y mediante análisis termogravimétrico y espectroscopia de masa (TGA-MS). Para comparar el porcentaje de remoción de ambos adsorbentes se realizaron test de adsorción en solución monocomponente (solo un metal en solución). El DMAC-HNO3 se sometió a ensayos de equilibrio y cinéticos en solución mono y multicomponente. Los datos experimentales fueron ajustados a modelos de isotermas (Langmuir, Freundlich, Temkin y Dubinin-Radushkevich) y a modelos cinéticos (pseudo-primer orden, pseudo-segundo orden, Elovich y difusión intrapartícula).
El DMAC-HNO3 obtuvo un área superficial de 988 m2 g-1, siendo caracterizado como mesoporoso. Se comprobó el aumento de grupos carbonilos y ácidos carboxilos en la superficie del adsorbente luego del tratamiento con ácido nítrico. Por otro lado, se demostró un incremento del porcentaje de remoción de los metales en solución monocomponente empleando el DMAC-HNO3 en comparación a DMAC; Pb(II) aumentó de 94,19% a 99,03%, Cu(II) de 27,90 ± 1,10% a 85,85 ± 0,44% y Cd(II) 5,95 ± 0,03% a 49,97± 3,14%. La isoterma de adsorción en solución monocomponente de los tres iones se ajustó al modelo de Freundlich. En solución multicomponente, el modelo de Freundlich se ajustó satisfactoriamente a los datos experimentales de Cu(II), mientras que, los datos experimentales de Cd(II) y Pb(II) no se ajustaron a ningún modelo. La cinética del Cu(II) en solución monocomponente se ajustó al modelo de pseudo-segundo orden, mientras que Cd(II) y Pb(II) fueron mejor representados por el modelo de Elovich. La cinética en solución multicomponente de los tres iones fue mejor representada por el modelo de Elovich. Esto indica que el mecanismo limitante de la velocidad es la quimisorción de cada metal sobre la superficie del carbón activado. Por otra parte, se obtuvo una disminución de las capacidades
III
de adsorción de los tres metales en solución multicomponente. El estudio de la selectividad en solución multicomponente demostró que el material DMAC-HNO3 es selectivo hacia Cu(II), obteniendo el siguiente orden de remoción: Cu(II) > Pb(II) > Cd(II).
A partir de estos resultados se comprueba la efectividad del tratamiento con ácido nítrico en la adsorción de metales pesados, no obstante, se sugiere profundizar en el proceso de adsorción mediante el estudio de variaciones de pH y las condiciones de modificación con ácido nítrico, que permita obtener capacidades de adsorción mayores en solución multicomponente.
Water pollution by heavy metals represents a major problem to the environment and human beings due to the toxicity of these species. Rivers that supply drinking water in Northern Chile show high concentrations of copper, cadmium and lead. Among the methods for removal of heavy metals from water, adsorption onto activated carbon is considered one of the most effective. Heavy metals adsorption onto activated carbon is considered to mainly take place at oxygen containing functional groups. Acid treatment is used to introduce oxygen containing functional groups to the surface of the activated carbon. The main objective of this work is to investigate the effect of nitric acid surface modification of an activated carbon on the adsorption of copper, cadmium and lead from aqueous solution. Three different surface modification methods were tested using the following equipment: hot plate, water bath and rotary evaporator. An activated carbon based on end-of-life tires was treated with 5M nitric acid for 3 hours at 60°C. The rotary evaporator was selected as the optimal procedure since it can keep the nitric acid and activated carbon solution in constant rotation and produce a homogeneous mixture. The original material (DMAC) and the modified material (DMAC-HNO3) were characterized by N2 adsorption-desorption at 77K, point of zero charge, Fourier transform infrared spectroscopy (FTIR) and by thermogravimetric analysis and mass spectroscopy (TGA-MS). Adsorption tests were carried out in mono-component solution to compare the removal of both adsorbents. Equilibrium and kinetic tests were performed to evaluate the adsorption capacity of DMAC-HNO3 in mono and multicomponent solution. Experimental data were fitted to Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models and pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion kinetic models. The modified material resulted in a surface area of 988 m2 g-1 and a mesoporous structure. As a result of nitric acid modification, the amount of carbonyl groups and carboxylic acids on the surface of the adsorbent increased. There was an improvement in the percentage removal of metals in mono-component solution on DMAC adsorption compared to DMAC-HNO3 where Pb(II) increased from 94,19% to 99,03%, Cu(II) from 27.90 ± 1,10% to 85,85 ± 0,44% and Cd(II) 5,95 ± 0,03% to 49,97± 3,14%. The adsorption isotherm in mono-component solution of the three metals was best fitted to Freundlich model. The adsorption isotherm in multicomponent solution of Cu(II) was best fitted to Freundlich model, while Cd(II) and Pb(II) did not fit to any model. The kinetics of Cu(II) in monocomponente solution fit the pseudo-second order model, while Cd(II) and Pb(II) were best represented by Elovich model. The kinetics of three ions in multicomponent solution were best represented by Elovich model. This indicates that the rate limiting mechanism is the chemisorption of each metal on the activated carbon surface. On the other hand, adsorption capacities of the three metals decreased in multicomponent solution. The selectivity sequence of heavy metal adsorption in multicomponent solution was in the order Cu(II) > Pb(II) > Cd(II). V From these results, it was show that modified activated carbon treated with nitric acid effectively removes heavy metals from water, however, it is suggested to further investigate the adsorption process by studying pH variations and modification conditions with nitric acid, to obtain greater adsorption capacities in multicomponent solution.
Water pollution by heavy metals represents a major problem to the environment and human beings due to the toxicity of these species. Rivers that supply drinking water in Northern Chile show high concentrations of copper, cadmium and lead. Among the methods for removal of heavy metals from water, adsorption onto activated carbon is considered one of the most effective. Heavy metals adsorption onto activated carbon is considered to mainly take place at oxygen containing functional groups. Acid treatment is used to introduce oxygen containing functional groups to the surface of the activated carbon. The main objective of this work is to investigate the effect of nitric acid surface modification of an activated carbon on the adsorption of copper, cadmium and lead from aqueous solution. Three different surface modification methods were tested using the following equipment: hot plate, water bath and rotary evaporator. An activated carbon based on end-of-life tires was treated with 5M nitric acid for 3 hours at 60°C. The rotary evaporator was selected as the optimal procedure since it can keep the nitric acid and activated carbon solution in constant rotation and produce a homogeneous mixture. The original material (DMAC) and the modified material (DMAC-HNO3) were characterized by N2 adsorption-desorption at 77K, point of zero charge, Fourier transform infrared spectroscopy (FTIR) and by thermogravimetric analysis and mass spectroscopy (TGA-MS). Adsorption tests were carried out in mono-component solution to compare the removal of both adsorbents. Equilibrium and kinetic tests were performed to evaluate the adsorption capacity of DMAC-HNO3 in mono and multicomponent solution. Experimental data were fitted to Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models and pseudo-first order, pseudo-second order, Elovich and intraparticle diffusion kinetic models. The modified material resulted in a surface area of 988 m2 g-1 and a mesoporous structure. As a result of nitric acid modification, the amount of carbonyl groups and carboxylic acids on the surface of the adsorbent increased. There was an improvement in the percentage removal of metals in mono-component solution on DMAC adsorption compared to DMAC-HNO3 where Pb(II) increased from 94,19% to 99,03%, Cu(II) from 27.90 ± 1,10% to 85,85 ± 0,44% and Cd(II) 5,95 ± 0,03% to 49,97± 3,14%. The adsorption isotherm in mono-component solution of the three metals was best fitted to Freundlich model. The adsorption isotherm in multicomponent solution of Cu(II) was best fitted to Freundlich model, while Cd(II) and Pb(II) did not fit to any model. The kinetics of Cu(II) in monocomponente solution fit the pseudo-second order model, while Cd(II) and Pb(II) were best represented by Elovich model. The kinetics of three ions in multicomponent solution were best represented by Elovich model. This indicates that the rate limiting mechanism is the chemisorption of each metal on the activated carbon surface. On the other hand, adsorption capacities of the three metals decreased in multicomponent solution. The selectivity sequence of heavy metal adsorption in multicomponent solution was in the order Cu(II) > Pb(II) > Cd(II). V From these results, it was show that modified activated carbon treated with nitric acid effectively removes heavy metals from water, however, it is suggested to further investigate the adsorption process by studying pH variations and modification conditions with nitric acid, to obtain greater adsorption capacities in multicomponent solution.
Description
Tesis para optar al título de Ingeniero/a Civil Química
Keywords
Metales pesados, Carbón activado