This study is to assess the effect of magnesiumrich gangue dissolution on the ore containing chalcopyrite and carrollite from Democratic Republic of the Congo （DRC）. The ore contains 11.0 wt% magnesium and 2.4 wt% copper. When Mg^2＋ concentration is over 20 g·L^-1 after 2 months in column bioleaching, the redox potential of leachate keeps stable, much less than that when Mg2＋ concentration is below 20 g·L^-1. Meanwhile, the extractions of Cu^2＋ and Co^2＋ from chalcopyrite with carrollite obviously inhibited by Mg^2＋ concentration of over 20 g·L^-1 were investigated. The extraction of cobalt depends on chalcopyrite dissolved in column reactor. The growth and oxidation activity of bacteria are affected by high Mg^2＋ concentration （〉20 g·L^-1） in leachate of column reactor. As the rate of gangue dissolution depends on the amount of sulfuric acid, the decrease of the particle size relates to the increase of the total particle surface area and acid consumption. Therefore, the operation of pre-leaching for magnesium removal is not the most effective and economical way to solve the problem of magnesium-rich gangue minerals dissolution.
