Lixiviación por agitación de concentrado de cobre proveniente de la compañía minera San Geronimo en ambientes ácidos
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2018
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es
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Universidad Andrés Bello
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Licencia CC
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Resumen
La lixiviación es una etapa tradicional e indispensable en el proceso productivo de cobre metálico a partir de minerales oxidados y sulfurados, sin embargo, la cantidad de óxidos es cada vez menor y tenderá a desaparecer en los próximos diez años; por otra parte, el tratamiento de los sulfuros por vía pirometalúrgica tradicional constantemente tiene costos operacionales más altos, y las normas ambientales son cada vez más estrictas respecto de las emisiones de gases fugitivos e impurezas, lo que ha motivado el desarrollo de técnicas que permiten aprovechar la capacidad ociosa generada en el tratamiento hidrometalúrgico, y así desarrollar procesos continuos, a menor costos y más sostenibles.
Es así como un grupo de estudiantes y académicos de la Universidad de Santiago de Chile, del cual formé parte, está investigando y desarrollando un nuevo proceso de lixiviación continua de concentrados sulfurados de cobre. En este estudio se investigó, mediante pruebas experimentales a escala laboratorio, el consumo de diferentes reactivos lixiviantes de tipo ácido, la distribución másica del cobre y sus impurezas (Fe, As, Si y S), se realizó además un análisis termodinámico y cinético, junto con las posibles soluciones a problemáticas operacionales surgidas durante el estudio; estas pruebas se llevaron a cabo con una temperatura de 293,15 K, presión atmosférica, razón solido:liquido de 0,081, velocidad de agitación de 125,66 (rad/s) y pH de 1 para la pulpa, aunque variándolo en algunas pruebas experimentales y el D80 para el concentrado de 95 (μm).
La oxidación de los minerales sulfurados de cobre resultó ser gobernada por un control de tipo difusional, en donde, una parte del azufre resultante bloquea la capa límite de la partícula, impidiendo la difusión del reactivo lixiviante hacia la superficie del mineral, como resultado, las recuperaciones metalúrgicas optimas fueron en promedio de 14,61% a los 918 (s). Además, en el proceso, se observó una alta dependencia del ácido y del oxígeno, de este último, solo reaccionó en promedio el 0,05% del estequiométrico. Adicionalmente, la problemática
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difusional se solucionaría aumentando la cantidad de oxígeno en el sistema, debido a que el azufre que rodea a las partículas del mineral reaccionaría para formar ácido sulfúrico.
Los resultados concernientes al comportamiento de los reactivos lixiviantes indicaron que el mejor agente es el ácido sulfúrico, puesto que tiene la más alta recuperación metalúrgica, de 17,47% a los 1.100 (s), además posee la más baja tasa de consumo de protones, vale decir, que de cada 6,77 moles de protones agregados, 1 (mol) va destinado a disolver 1 (mol) cobre de los minerales sulfurados; igualmente, considerando que la calcopirita es el mineral de mayor abundancia en este concentrado de cobre, el ácido sulfúrico es el que mejor lo disuelve. Finalmente, de todos los compuestos moleculares estudiados, los formados con sulfato prevalecen sobre los otros en su estabilidad.
Durante la lixiviación, el arsénico y el silicio forman, reversiblemente, ácido tetraoxoarsénico (V) (H3AsO4) y ácido trioxosilícico (IV) (H2SiO3), respectivamente, los cuales tienen la capacidad de disolver todos los minerales sulfurados de cobre detectados, siendo responsables, en conjunto, del 3,825% del total de cobre recuperado en promedio. Por otra parte, el agua de mar cumple la función de mejorar el potencial de lixiviación, beneficiando a los minerales cuyas valencias para el cobre son de +1.
Los reactivos de flotación arrastrados por el concentrado tienden a aumentar su tensión superficial durante la lixiviación, es más, gracias a los gases generados, los hace difícilmente coalescentes, por lo cual, se catalogaron como un problema a solucionar; por su parte, la tostación de concentrados de cobre logró eliminarlos por completo. Por otro lado, la lixiviación de la calcina logró una recuperación de 98,36% como consecuencia de trasformar los minerales sulfurados a oxido de cobre (II).
Los resultados del estudio señalan una variedad de líneas investigativas, con el fin de desarrollar una novedosa tecnología de producción de cobre metálico a partir de minerales sulfurados, como remplazo de aquellas tradicionales existentes en la actualidad.
Leaching is an essential and traditional stage in the productive process of metallic copper from oxidized and sulfidized minerals, however, there is fewer and fewer amount of oxides that will tend to disappear within the next ten years; on the other hand, the treating of sulphides by traditional pyrometallurgy usually has higher operative costs, and the environmental regulations are increasingly strict with respect to fugitive emissions of gases and pollutants, which has motivated the development of techniques that allow to take advantage of the idle capacity generated during the hydrometallurgical treating, so then developing continuous processes, at lower costs and more sustainable. That's why a group of students and academics of Universidad de Santiago de Chile, which I was part of, is investigating and developing a new continuous leaching process of copper sulphides. This group investigated, by experimental proofs at laboratory scale, the consumption of different acid type leaching reagents, mass distribution of copper and its impurities (Fe, As, Si and S), also it was performed a kinetic and thermodynamical analysis, together with possible solutions to operative problems arisen during this study; all these proofs were performed at a temperature of 293.15 K, atmospheric pressure, solid:liquid ratio of 0.081, stirring speed of 125.66 (rad/s) and pH equivalent to 1 for the pulp, although being modified during some experimental proofs, and D80 for the concentrate of 95 (μm). Copper oxidation resulted being governed by a diffusion type control, where, a part of resultant sulphur blocks the boundary layer of the particle, preventing the diffusion of the leaching reactive to the particle surface, as result, optimal metallurgical recoveries were 14.61% at 918 (s). In addition, during the process, a high dependency between acid and oxygen was observed, on regard the last one, only reacted an average of 0.05% of stoichiometric amount. What's more, the problem of diffusion would be solved just by increasing the system oxygen 18 quantity, due to the sulphur surrounding mineral particle, would react to form sulfuric acid. Results concerning to the behaviour of the leaching reagents indicated that sulfuric acid is the best, due to it has the higher metallurgical recovery, of 17.47% at 1100 (s), additionally has the lower proton consumption ratio, this is, every 6.77 mol of protons added, 1 mol is for dissolving 1 mol of copper from the sulfidized minerals, also, considering chalcopyrite is the most abundant mineral in this copper concentrate, sulfuric acid is the one that better dissolves it. Finally, out of all the studied molecular compounds, sulphates prevail over the others in stability. During leaching, arsenic and silicon form, in a reversible way, arsenic acid (H3AsO4) and orthosilicic acid (H2SiO3), which have the capability to dissolve all the detected sulfidized copper minerals, being together responsible for an average 3.825% of the recovered copper. On the other hand, sea water has the role of improving the leaching potential, benefitting minerals whose copper valences are +1. Flotation reagents still present on the concentrate, lead to an increase of surface tension during leaching, moreover, it becomes hardly coalescent due to the generated gases, so it has been catalogued as a problem to solve; for its part, roasting of copper concentrates succeeded in eliminating the completely. Furthermore, leaching of calcine achieved a recovery of 98.36% as consequence of transforming sulfidized minerals to copper oxide (II) The results of this study point out a wide range of investigation lines, with the aim of the development a new production technology of metallic copper from sulfidized minerals, as replacement of those traditional existing nowadays.
Leaching is an essential and traditional stage in the productive process of metallic copper from oxidized and sulfidized minerals, however, there is fewer and fewer amount of oxides that will tend to disappear within the next ten years; on the other hand, the treating of sulphides by traditional pyrometallurgy usually has higher operative costs, and the environmental regulations are increasingly strict with respect to fugitive emissions of gases and pollutants, which has motivated the development of techniques that allow to take advantage of the idle capacity generated during the hydrometallurgical treating, so then developing continuous processes, at lower costs and more sustainable. That's why a group of students and academics of Universidad de Santiago de Chile, which I was part of, is investigating and developing a new continuous leaching process of copper sulphides. This group investigated, by experimental proofs at laboratory scale, the consumption of different acid type leaching reagents, mass distribution of copper and its impurities (Fe, As, Si and S), also it was performed a kinetic and thermodynamical analysis, together with possible solutions to operative problems arisen during this study; all these proofs were performed at a temperature of 293.15 K, atmospheric pressure, solid:liquid ratio of 0.081, stirring speed of 125.66 (rad/s) and pH equivalent to 1 for the pulp, although being modified during some experimental proofs, and D80 for the concentrate of 95 (μm). Copper oxidation resulted being governed by a diffusion type control, where, a part of resultant sulphur blocks the boundary layer of the particle, preventing the diffusion of the leaching reactive to the particle surface, as result, optimal metallurgical recoveries were 14.61% at 918 (s). In addition, during the process, a high dependency between acid and oxygen was observed, on regard the last one, only reacted an average of 0.05% of stoichiometric amount. What's more, the problem of diffusion would be solved just by increasing the system oxygen 18 quantity, due to the sulphur surrounding mineral particle, would react to form sulfuric acid. Results concerning to the behaviour of the leaching reagents indicated that sulfuric acid is the best, due to it has the higher metallurgical recovery, of 17.47% at 1100 (s), additionally has the lower proton consumption ratio, this is, every 6.77 mol of protons added, 1 mol is for dissolving 1 mol of copper from the sulfidized minerals, also, considering chalcopyrite is the most abundant mineral in this copper concentrate, sulfuric acid is the one that better dissolves it. Finally, out of all the studied molecular compounds, sulphates prevail over the others in stability. During leaching, arsenic and silicon form, in a reversible way, arsenic acid (H3AsO4) and orthosilicic acid (H2SiO3), which have the capability to dissolve all the detected sulfidized copper minerals, being together responsible for an average 3.825% of the recovered copper. On the other hand, sea water has the role of improving the leaching potential, benefitting minerals whose copper valences are +1. Flotation reagents still present on the concentrate, lead to an increase of surface tension during leaching, moreover, it becomes hardly coalescent due to the generated gases, so it has been catalogued as a problem to solve; for its part, roasting of copper concentrates succeeded in eliminating the completely. Furthermore, leaching of calcine achieved a recovery of 98.36% as consequence of transforming sulfidized minerals to copper oxide (II) The results of this study point out a wide range of investigation lines, with the aim of the development a new production technology of metallic copper from sulfidized minerals, as replacement of those traditional existing nowadays.
Notas
Tesis (Ingeniero Civil en Metalurgia)
Palabras clave
Lixiviación, Cobre, Pruebas