A chloride salts medium was evaluated in biodesulfurization processes of a Colombian coal (2.34% total sulfur: 1.34% as pyritic, 0.90% as organic and 0.10% from sulfates), employing a consortium of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The process was carried out at three pulp concentrations (9.09%, 16.67% and 23.08%) and was compared with assays under similar conditions but containing modified T&K medium. All the tests were determined by measuring changes in soluble iron, pH, redox potential and microbial populations approach. Original and treated coal was analyzed by scanning electron microscopy with an energy-dispersive X-ray (SEM-EDX). For bioassays with chloride salts medium, the results showed above 70% of pyritic sulfur oxidation after 12 days, regardless of pulp concentration in contrast with results obtained for bioassays with a T&K modified medium where pulp concentration had influence and the pyrite oxidation was lower (below 55%).