Abstract This study evaluated the biooxidation of pyrite contained in a Colombian coal (2.38 mm < particle size < 0.50 mm). The variables were cysteine concentration (0-600 mg/L) and culture type (pure Acidithiobacillus ferrooxidans (ATCC 23270) and a consortium of Acidithiobacillus thiooxidans (ATCC 15494) and Acidithiobacillus ferrooxidans). Pyrite oxidation for the assays without cysteine was 31.14% after 12 days. In the presence of pure A. ferrooxidans, oxidation increased by 8.18% in the assays containing 60 mg Cys/L. In contrast, the counterpart using the consortium exhibited a significant increase in redox potential, which improved oxidation by 28.44%. Since all the assays had a similar kaolinite removal (around 31.45%), and the experiments without cysteine did not show differences in behaviour, the A. thiooxidans-cysteine interactions might have been responsible for increasing Fe3+ regeneration, alleviating the toxic effect of Al3+ ion dissolution, thus improving pyrite oxidation. The consortium-cysteine-coal interactions contrasted with those proposed by other authors for A. ferrooxidans-cysteine-pure pyrite and A. thiooxidans-cysteine, indicating different metabolic pathways in the presence of inorganic and organic coal matrices. On the other hand, the biooxidation rate decreased for both cultures in the presence of 600 mg Cys/L, showing similar inhibition to that reported in the literature.

A un carbón proveniente del municipio de Puerto Libertador, Córdoba-Colombia (2.34% de azufre total, con 1.34% pirítico, 0.90% orgánico y 0.10% de sulfatos), se le aplicó un cultivo mixto de Acidithiobacillus ferrooxidans y Acidithio bacillus thiooxidans, con el fin de evaluar procesos de biodesulfurización en suspensión, a partir de variables que influyen en el proceso: concentración inicial de hierro y pH de la solución lixiviante, bajo dos configuraciones de tamaño de partícula: pasante malla 8 (-malla 8) y pasante malla 60 (-malla 60), acorde con la serie Tyler de tamices. Los procesos de biodesulfurización se evaluaron cada dos días, mediante mediciones de la concentración de hierro, pH, potencial de óxido-reducción y crecimiento celular, en la solución. A partir de los ensayos realizados, se alcanzaron oxidaciones de azufre pirítico por encima del 50%, después de 12 días de proceso. Se pudo constatar que tanto el tipo de carbón tratado, como de las condiciones evaluadas, inciden en el grado de lixiviación alcanzado. La mejor eficiencia del proceso se observó al utilizar concentraciones de hierro iniciales menores a 1200 ppm y un pH inicial entre 1.5 y 1.3.

Biodesulfurization process for Colombian coal (2.34% total sulfur: 1.34% as pyritic, 0.90% as organic and 0.10% from sulfates) from municipality of Puerto Libertador (Córdoba, Colombia) was carried out. A mixed culture of A. ferrooxidans and A. thiooxidans was used. The study was mainly focused on the influence of pH, and iron concentration in coal leaching pro- cess. Two mineral particle sizes were evaluated: less 8 mesh (-malla 8) and less 60 mesh (-malla 60), Tyler series. Biodesulfurization processes were determined by measuring changes in soluble iron, pH, redox potential and microbial populations approach. The results showed above 50% of pyritic sulphur oxidation after 12 days. Coal type and evaluated conditions influence in leaching process. Less to 1200 ppm of iron concentration and initial pH between 1.5-1.3, were considered to have critical roles in optimizing pyrite dissolution.