Low grade copper sulfide ore bioleaching in a new bioreactor.

Although the application of biological techniques in the sulfide minerals leaching to obtain valuable metals is an important technological advance, the relatively slow kinetics of the bio-oxidation still limits its commercial application, however, the research for constant improvement under optimal conditions continues. Microorganisms are capable of performing their role with great efficiency under optimal conditions. Bioreactor designing seeks to maintain certain environmental conditions as to favour efficient microbial growth such pH, temperature, oxygen, carbon dioxide dissolution, stirring speed, and others. In an aerobic process such as bioleaching the optimum oxygen transference is extremely difficult to achieve, because oxygen scarcely dissolves in water. Although the oxygen transference usually is facilitated by agitation, which is also required to mix the nutrients and maintain homogeneous solution, this agitation should be limited because of the high power consumption, and the damage the microorganisms subjet to excessive shear may undergo. In order to improve biooxidation kinetics, we designed a new bioreactor, which combines elements of the stirred tank and the airlift reactor, and introduces innovative elements, to their effective use in biohydrometallurgy. The new bio-reactor called RELBA was designed and build-up in the Universidad Nacional Autonoma de Mexico (UNAM) laboratories. It controls dissolved O-2 among other parameters and it prevents shear. Bioleaching tests of the ore, containing 0.135% Cu and 3.07% Fe, were performed in the orbital incubator and in the RELBA bio-reactor at 35 degrees C using a mixed strain of Acidithiobacillus caldus, Acidihiobacillus thiooxidans and Leptospirillum ferriphilum. These results confirm the advantages of the new bioleaching reactor and that jarosite formation is prevented in the bioleaching process.