Biomass Production and Inoculation of Industrial Bioleaching Processes

Abstract

Microbial activity inleaching processes accounts for 4% of today’s copper produced in the world. Factorsrelated with lesser overall metal recoveries, no recovery of precious metalsand molybdenum in comparison with conventional concentration/smelting &refining technologies and the high prices of metals inhibit the use of bioleachingat a larger scale. In order to increase bioleaching rates and overall metal recoveries,continuous inoculation of the ore with a leaching solution containing specific adaptedconsortium of microorganisms, allows an early expression of microbial activity,reducing 2-3 fold the time required by ore native bearing microflora to grow.This leaching solution concentrated in microorganisms can be produced by meansof bioreactors operated in continuous regime. Unfortunately biomining microorganisms have a very low duplication timewhen comparing to common microbes like E.colior B. subtilis, that forces the useof huge volume bioreactors in the case of conventional bioreactors, to ensurethe growth of microorganisms have sufficient residence time. To overcome thisproblem, we have designed a very efficient air-lift bioreactor (Patent Registration No. CL 48319), that can be used at industrial operations for the production ofsolutions with a high concentration of biomining microorganisms, for theinoculation of bioleaching heaps, with lesser residence time in comparison toconventional bioreactors. Ourbioreactor has an internal recirculation for producing sulfide-ore bioleachingsolutions, with a phase-separating and solids-recirculation system, without theneed to impel the suspension containing the solids towards the bioreactor withpumps, using diatomaceous earth, ferric precipitates and/or elemental sulfur asa solid support to immobilize iron and/or sulfur-oxidizing microorganisms. Dependingon the source of energy supplied for the growth of the microorganisms, thebioreactor can produce either a solution concentrated in ferric ions andiron-oxidizing bacteria or sulfur oxidizing bacteria. In order to validate ourbioreactor design at industrial scale, a trial was carried out in an air-liftbioreactor of 35 m3 nominal capacity, which is part of a biomassplant located in Radomiro Tomic Division of CODELCO. In this article, theresults of the test proving the advantages and satisfactory design of ourbioreactor for producing continuously iron-oxidizing bacteria and sulfuroxidizing bacteria for inoculation and irrigation of heaps and dumps are shown.