Escalado de un proceso de biooxidación de residuos de minería ricos en sulfuros usando reactores de tanque agitado
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Muñoz Echeverri, Laura María
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En este trabajo se presenta el escalado y evaluación del proceso de biooxidación de un residuo de minería aurífera (proveniente de la mina La Maruja, Marmato-Caldas), desde una escala de laboratorio hasta un nivel de planta piloto en reactores de tanque agitado. Para procurar el éxito del escalado, se realizó una caracterización mineralógica inicial del residuo y una adaptación del agente biológico, Acidithiobacillus ferrooxidans, al mineral. A escala de laboratorio se determinó el nivel más apropiado de agitación, y se evaluaron dos criterios de escalado seleccionados con base en las necesidades del proceso. A través de la caracterización mineralógica se estableció que la fase mineral predominante en el residuo fue la pirita con un 34.1% y el contenido de Fe y S ascendió a 24.9 y 28.7%, respectivamente; se observaron además partículas micrométricas de oro diseminadas en la superficie de los sulfuros indicando la refractariedad del mineral. Mediante una serie de cultivos sucesivos se obtuvo una cepa estable respecto a su actividad oxidativa y se eliminaron las fases de latencia en las cinéticas de biooxidación. Los ensayos preliminares en reactores indicaron que el intervalo de agitación idóneo para el proceso oscila entre 500 y 700 r.p.m, sobresaliendo 500 r.p.m por la reducción en el consumo de potencia. El criterio de escalado más adecuado fue velocidad en la punta del impulsor, el cual redujo el estrés hidrodinámico sobre el microorganismo y condujo a los más altos porcentajes de hierro y sulfatos disueltos. El escalado desde laboratorio hasta planta piloto, precisó del ajuste y/o cambio de ciertas condiciones con cada aumento en el volumen, particularmente la calidad del medio de cultivo y la relación inicial [células]/[mineral], algunos de estos cambios parecen haber afectado el arranque del proceso a nivel de planta piloto. A nivel de laboratorio (matraz y 5L) los porcentajes de hierro y sulfatos disueltos fueron de ≈22% y ≈25%, y mejoraron con el aumento en escala (27-29% y 30-32%). Si bien aún se requiere del ajuste de ciertos parámetros y condiciones, particularmente en planta piloto, en términos generales se encontró que el escalado del proceso de biooxidación de los residuos de La Maruja, presentó resultados promisorios que pueden ser tomados como punto de partida para la optimización del proceso y su implementación a escala comercial.
Abstract: This work presents the scale-up and the evaluation of the biooxidation process of mine tailings (coming from La Maruja mine in Marmato, Caldas (Colombia)) from laboratory to a pilot scale in stirred-tank reactors. To ensure a successful scaling, an initial mineralogical characterization of mine tailings and an adaptation of the biological agent (Acidithiobacillus ferrooxidans) to the mineral were carried out. The most appropriate level of agitation was established at laboratory scale. Additionally, two scaling criteria were selected and evaluated based on the process needs. Thanks to the mineralogical characterization it was established that the predominant mineral phase in the residue was pyrite (35.7%) with Fe and S reaching 24.9 and 28.7% respectively. Micron gold particles were observed in the mineral surface indicating refractoriness. By means of a series subcultures, a stable strain was obtained and the latency phases were eliminated in the biooxidation kinetics. Preliminary tests in reactors indicated that proper agitation rate is between 500 and 700 r.p.m, favoring 500 r.p.m because of lower power consumption. The most suitable scale-up criteria was speed at the tip of the impeller. Thus, reducing hydrodynamic stress on the microorganisms and generating the highest rates of diluted Fe and S. The scale-up from laboratory to the pilot plant requires adjusting and/or changing certain conditions every time the volume is increased, in particular, the culture medium and the initial relation [cells]/[mineral]. These changes may have affected the onset process at pilot plant level. At laboratory level, the percentage of ore biooxidation was significantly improved with an increase in the scale. While some parameters and conditions might still require some adjusting, particularly at the pilot level, the overall scale-up of the biooxidation process of mine tailings from La Maruja, produced promising results that can be taken as a starting point for process optimization and commercial implementation.
Abstract: This work presents the scale-up and the evaluation of the biooxidation process of mine tailings (coming from La Maruja mine in Marmato, Caldas (Colombia)) from laboratory to a pilot scale in stirred-tank reactors. To ensure a successful scaling, an initial mineralogical characterization of mine tailings and an adaptation of the biological agent (Acidithiobacillus ferrooxidans) to the mineral were carried out. The most appropriate level of agitation was established at laboratory scale. Additionally, two scaling criteria were selected and evaluated based on the process needs. Thanks to the mineralogical characterization it was established that the predominant mineral phase in the residue was pyrite (35.7%) with Fe and S reaching 24.9 and 28.7% respectively. Micron gold particles were observed in the mineral surface indicating refractoriness. By means of a series subcultures, a stable strain was obtained and the latency phases were eliminated in the biooxidation kinetics. Preliminary tests in reactors indicated that proper agitation rate is between 500 and 700 r.p.m, favoring 500 r.p.m because of lower power consumption. The most suitable scale-up criteria was speed at the tip of the impeller. Thus, reducing hydrodynamic stress on the microorganisms and generating the highest rates of diluted Fe and S. The scale-up from laboratory to the pilot plant requires adjusting and/or changing certain conditions every time the volume is increased, in particular, the culture medium and the initial relation [cells]/[mineral]. These changes may have affected the onset process at pilot plant level. At laboratory level, the percentage of ore biooxidation was significantly improved with an increase in the scale. While some parameters and conditions might still require some adjusting, particularly at the pilot level, the overall scale-up of the biooxidation process of mine tailings from La Maruja, produced promising results that can be taken as a starting point for process optimization and commercial implementation.