Early reprecipitation of sulfate salts in coal biodesulfurization processes using acidophilic chemolithotrophic bacteria.

This study evaluated the effect of three sulfate salt-based culture media on the reprecipitation of sulfur under the action of two types of bacterial inoculum, a pure strain of Acidithiobacillus ferrooxidans (ATCC 23270) and a consortium of this strain and Acidithiobacillus thiooxidans (ATCC 15494), in a biodesulfurization process for coal (particle size < 0.25 mm) from the 'La Guacamaya' mine (Puerto Libertador, Córdoba, Colombia). All of the experiments were periodically monitored, with measurements taken of pH, cell concentration, iron concentration, and pyrite oxidation. Additionally, mineralogical analyses were conducted on the initial and final coal samples, through scanning electron microscopy with an energy-dispersive X-ray spectrometer. The results showed that sulfate reprecipitation occurred primarily, and nearly entirely, during the first 3 days of the process. While all the treatments obtained high levels of mineral oxidation, the reprecipitation processes decreased in media with low concentrations of sulfate, leading to the higher final removal of inorganic sulfur. The bioassays revealed that after 15 days, the maximum pyrite oxidation (86%) and inorganic sulfur removal (53%) was obtained with the treatments using the Kos and McCready culture media. The bacteria evaluated were found to have a great ability to adapt to very simple culture media with minimal nutrient concentrations, and even with some nutrients absent (as in the case of magnesium).

Efecto del Tween ® 80 sobre la bioprecipitación de carbonato de calcio por Bacillus cereus / Effect of Tween ® 80 on calcium carbonate bioprecipitation mediated by Bacillus cereus

Resumen Se llevaron a cabo procesos de biosíntesis de carbonato de calcio, empleando una cepa de Bacillus cereus, aislada de los jardines de la Universidad Pontificia Bolivariana (Medellín, Colombia). Se evaluó el efecto disgregante del Tween® 80 a tres concentraciones: 0.00% p/v, 0.25% p/v y 0.50% p/v. Los experimentos se monitorizaron por 6 días con mediciones de pH y análisis mineralógicos a los precipitados finales por microscopía electrónica de barrido, difracción de rayos X y espectroscopia de infrarrojo con transformada de Fourier. El Tween® 80 tuvo un papel importante como desaglomerante de las estructuras de carbonato formadas por los microorganismos. Aunque los ensayos con el surfactante presentaron menor formación de precipitado, las concentraciones evaluadas no inhibieron el crecimiento bacteriano. Adicionalmente, este compuesto favoreció la formación de vaterita incrementando su proporción en comparación con la calcita (alrededor del 98%, utilizando Tween® 80 al 0.50% p/v).

Abstract This research presents the sprinkling effect of Tween® 80 for three concentrations (0.00% w, 0.25% w y 0.50% w) in a processes of calcium carbonate biosynthesis. The assays used a culture of Bacillus cereus, isolated from the gardens of the Universidad Pontificia Bolivariana (Medellin, Colombia). The experiments were monitored for 6 days measuring pH as well as through mineralogical analyses for precipitates using scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. Tween® 80 had an important role as deagglomerate, decreasing the precipitation of biomineralized-carbonate structures (generated by bacteria). It was also found that the evaluated concentrations did not inhibit the bacterial growth. Additionally, Tween® 80 favored the production of vaterite, increasing its ratio in comparison to calcite (around 98% by using 0.50% w of Tween® 80).

Comparación del potencial oxidativo de Acidithiobacillus ferrooxidans, en un proceso de biodesulfurización de carbón / Comparison of the oxidative potential of Acidithiobacillus ferrooxidans, in biodesulphurization process of coal

En este estudio se comparó la actividad oxidativa de dos cepas de Acidithiobacillus ferrooxidans en un proceso de desulfurización, empleando un carbón sub-bituminoso alto en azufre (2.30% de azufre total, con 1.06% pirítico, 1.10% orgánico y 0.14% de sulfatos), proveniente de la mina "La Guacamaya" ubicada en Puerto Libertador -Córdoba, Colombia. Se realizaron ensayos a nivel de erlenmeyer, la concentración de hierro total en la solución fue de 200 mg/L y 1200 mg/L respectivamente, empleando sulfato ferroso. El proceso fue monitoreado mediante mediciones periódicas de los principales factores físico-químicos implicados (pH, potencial de óxido-reducción (Eh), hierro en solución y concentración celular). Según los resultados obtenidos, la mayor eficiencia del proceso se logró, al trabajar con microorganismos compatibles con Acidithiobacillus ferrooxidans y una concentración de sulfato ferroso inicial de 1200 mg/L, el cual obtuvo la mayor tasa de oxidación de pirita (Py oxidada) (68%), así como, mejores condiciones en el medio lixiviante (pH: 1,47; Eh: 625 mV; 6.3×10(8) células/mL) en comparación con el cultivo axénico a las mismas condiciones (Py oxidada: 52%, pH: 1,63, Eh: 580 mV, 5.1×10(8) células/mL), después de 12 días de experimentación.

This study aimed comparing the oxidative activity of two strains of Acidithiobacillus ferrooxidans in a desulphurization process, using a sub-bituminous coal with a high sulfur content (2.30% total sulfur: 1.06% as pyritic, 1.10% as organic and 0.14% from sulfates) from "La Guacamaya" mine, located in Puerto Libertador - Cordoba, Colombia. Several assays were performed in Erlenmeyer flasks, the total iron concentration used in solution were 200 mg/L and 1200 mg/L respectively, using ferrous sulfate. The process was monitored by periodically measuring the main physicochemical factors involved (pH, Eh, cell population and iron in solution). According to the results obtained, the highest efficiency of the process was achieved by working with microorganisms compatible with Acidithiobacillus ferrooxidans and initial concentration of 1200 mg/l of ferrous sulfate, which had higher pyrite oxidation rates (Py oxidized) up to 68% and the best experimental conditions in the leaching medium (pH: 1,47; Eh: 625 mV; 6.3×108 cells/mL), in comparison with the axenic culture on the same conditions (Py oxidized: 52%; pH: 1,63; Eh: 580 mV; 5.1×108cells/mL), after 12 days of experimentation.

Efecto de la cisteína en un proceso de biodesulfurización de carbones en lecho empacado / Effect of cysteine in a biodesulfurization process of packed-bed coals

Se llevaron a cabo procesos de biodesulfurización de dos carbones colombianos ricos en azufre ("Mina Vieja" y "Vampiro"), en reactores de lecho empacado a nivel de erlenmeyer, utilizando un consorcio de Acidithiobacillus ferrooxidans (ATCC 23270) y Acidithiobacillus thiooxidans (ATCC 15494), evaluando la adición de cisteína a la solución lixiviante. Los ensayos fueron monitoreados por medidas de hierro en solución, pH y potencial redox. Adicionalmente, se hicieron análisis mineralógicos por difracción de rayos X (DRX) antes y después de los experimentos. Los ensayos sin adición de cisteína alcanzaron una oxidación de pirita de 45.3% y 57.9% para "Mina Vieja" y "Vampiro" respectivamente. Cuando se adicionó cisteína, la oxidación aumentó en 14.9% para "Mina Vieja" y 6.4% para "Vampiro". Por otra parte, todos los ensayos evidenciaron remoción de caolinita, debido a su interacción con el ácido sulfúrico del medio. Con base en los resultados obtenidos, los componentes del carbón influenciaron tanto crecimiento bacteriano como la eficiencia de la cisteína sobre el grado de pirita oxidada.

Biodesulphurization processes of a two sulphur-rich coals from Colombia ("Mina Vieja" y "Vampiro") were carried out at packed-bed reactors at erlenmeyer level, using a consortium of Acidithiobacillus ferrooxidans (ATCC 23270) and Acidithiobacillus thiooxidans (ATCC 15494). Cysteine addition were evaluated. The assays were monitored by measurements of iron content, pH, and redox potential. X-ray diffraction (XRD) were used to establish the mineralogy before and after the process. The assays without cysteine respectively reached a pyrite oxidation of 45.3% ("Mina Vieja") and 57.9% ("Vampiro") after 38 days. Cysteine addition improved pyrite oxidation by 14.9% ("Mina Vieja") and 6.4% ("Vampiro"). On the other hand, all the assays removed kaolinite by interaction with sulphuric acid of the media. In base to the results, coal compounds influence bacterial growth and affects the efficiency of cysteine over pyrite oxidation.