Advanced Materials Research Vol. 825

Abstract: Copper sulphide ore containing 0.37% Cu, with chalcopyrite as the main copper-bearing mineral, was leached in percolation columns containing 20 kg of ore crushed to minus 20 mm at different temperatures 18, 50 and 70°C. The columns were inoculated with cultures of mesophilic, moderately thermophilic and extremely thermophilic chemolithotrophic bacteria, respectively. Different variants of leaching with respect to the composition of the leached solution and the rate of irrigation of the ore were applied at each of the temperatures above-mentioned. The best results were achieved at leaching carried out at 70°C, with periodic additions of ferric ions, nutrients and bacterial cells by leach solutions prepared in a separate BACFOX-type unit, and by application of enhanced aeration of the ore by air enriched in CO₂. 82.1% of the copper was leached in this way within a period of 230 days, while the highest Cu extraction achieved at 18°C was 28.0% and that at 50°C was 55.4%, within the same period of time.

Abstract: The economic importance of copper production in Chile has prompted the study of new strategies for the optimal management of mineral resources, including processing of low grade ore and even processing tails (processed ore). Currently, heap bioleaching is the most convenient technology to treat low grade copper sulphide ores bearing chalcopyrite, chalcocite and covellite. Covellite is a secondary copper sulphide occurring in copper sulphide deposits and it is also formed by acidic dissolution of chalcocite. In leaching processes, the main factors influencing the dissolution of covellite are the electrochemical potential (Eh) and temperature.This work aimed at assessing the effect of different concentrations of total iron (3.0 and 6.0 g/L) and temperatures (30 and 50°C) in the bioleaching of covellite contained in a low grade copper ore and the same ore after a previous process of bioleaching at ambient temperature. Initial composition of low-grade ore was chalcocite (0.58%), chalcopyrite (0.56%), covellite (0.30%) and pyrite (2.73%), while the processed ore contained chalcopyrite (0.47%), covellite (0.28%), chalcocite (0.10%) and pyrite (3.32%). Covellite was mostly dissolved (>90%) in both unprocessed and processed ore, independently of the temperature and total iron concentrations. However a higher total copper recovery was achieved in tests performed at 50°C due to higher dissolution of primary ores, especially in unprocessed ore. The microbial activity was confirmed by Most Probable Number (MPN) analyses of iron and sulfur oxidizing microorganisms. The microbial population was dominated by Acidithiobacillus spp. in tests operated at 30°C, while in tests operated at 50° Sulfobacillus spp. were the most abundant organisms.

Abstract: Bioleaching experiments of phosphorus from low grade fluorapatite ore containing 8.2% P₂O₅ and from fluorapatite concentrate containing 29.8% P₂O₅ were carried out in shake flasks. Elemental sulphur was supplemented as an energy source for acid generation. Mixed and pure acidophilic bacterial cultures consisting of iron-and/or sulphur-oxidizing bacteria Acidithiobacillus ferrooxidans, A. thiooxidans and Leptospirillum ferrooxidans were used in the experiments. These acidophiles are commonly used in bioleaching of sulphide minerals, but their application on phosphorus bioleaching has been limited. Phosphorus leaching was shown to be a pH-dependant phenomenon. Phosphorus leaching yields of up to 97% and 28% were obtained in 3 weeks for low grade fluorapatite ore and concentrate, respectively. These results indicate a potential for applying bioleaching for phosphorus extraction from low grade materials.

Abstract: Rapid technological advancement and the relatively short life time of electronic goods have resulted in an alarming growth rate of electronic waste which often contains significant quantities of toxic and precious metals. Compared to conventional chemical recovery methods, bioleaching has been shown to be an environmentally friendly process for metal extraction. In this work, gold bioleaching from electronic scrap material (ESM) was examined using batch cultures of the bacterium Chromobacterium violaceum which produces cyanide as a secondary metabolite. Gold was bioleached via gold cyanide complexation. The ESM was pretreated using nitric acid to dissolve the base metals (mainly copper) in order to reduce competition for the cyanide ion from other metals present in ESM. ESM was added to the bacterial culture after it reached maximum cyanide production during early stationary phase. Spent medium bioleaching using bacterial cell- free metabolites showed a higher gold recovery of 18%, compared to that of two-step bioleaching of 11% at 0.5% w/v pulp density of ESM. Gold bioleaching was further enhanced to 30% when the pH of the spent medium was increased to shift the equilibrium in favor of cyanide ions production. Spent medium bioleaching of pretreated ESM yield a higher gold recovery compared to two-step bioleaching at a pulp density of 0.5% w/v.

Abstract: Pyrrhotite ores are always mingled with very finely disseminated gold and other precious metal particles, which raise the disposal of such refractory ores to bacterial leaching level. In this paper, the bioleaching tests of pyrrhotite were carried out in Erlenmeyer flasks with moderately thermophilic Leptospirillum ferriphilum (at 40°C) and extremely thermophilic Acidianus manzaensis (at 65°C). The effects of bacterial strains, temperature, and acid tolerance on the extraction of iron were investigated, and the bioleaching residues were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that high temperature and low pH have important positive effects on the dissolution of iron under abiotic control, and extreme thermophilies are unsuitable for leaching pyrrhotite. As the pH value rapidly increased to above 4.4 and amounts of sulfur and goethite were generated at the initial stage during the process of bioleaching by A. manzaensis, the cell concentration dramatically declined. In comparison, more than 44% extraction of iron was achieved in the presence of L. ferriphilum after four days of leaching. At the end of bioleaching, jarosite, sulfur and goethite, which could effectively block bioleaching process, were detected on the surface of residues by using XRD and SEM.

Abstract: Spent hydrotreating catalyst is a major solid waste from the petroleum industry. Although bioleaching of these wastes has been reported, research to date has focused on mesophiles. Bioleaching of industrial wastes by thermophiles has not been investigated. The bioleaching ability of thermophilic archaea Acidianus brierleyi was examined and compared with the commonly used mesophile Acidithiobacillus thiooxidans to establish the potential for high temperature leaching of spent catalyst. Spent Ni-Mo catalyst embedded in an alumina matrix containing substantial amounts of coke (i.e. carbonaceous deposits and volatile foulants) was used in this study. Decoking (i.e. removal of these deposits) as a pre-treatment and its effect on the leaching characteristics were examined. Spent catalyst is considered a hazardous waste since the toxic metal concentration exceeded the regulatory limit for land disposal and failed the toxicity characteristic leaching procedure (TCLP) test. Bioleaching with A. brierleyi and At. thiooxidans reduced the heavy metal leachate concentration to below regulated levels for safe waste disposal. Leaching efficiencies of 31% Al, 65% Ni and 44% Mo were achieved for coked catalyst using spent medium from At. thiooxidans. With decoked catalyst and spent medium from A. brierleyi, higher leaching efficiencies of 76% Al, 98% Ni and 93% Mo were attained. These results demonstrate the feasibility and the higher efficacy of spent medium leaching of decoked catalyst by acidophilic thermophiles.

Abstract: Copper sulphide ore bioleaching processes are currently under full development in Chile and worldwide, for treatment of: secondary sulphide in heaps [1], low-grade ores in dumps, and concentrates in reactors at high temperatures [2]. Abundant knowledge is available in the literature and great experience has been gathered about the behavior of mesophilic microorganisms and their application in bioleaching of sulfides in heaps and dumps [, as well as, about the behavior of extreme thermophilic microorganisms in reactors [. However, there is little information about the behavior of some moderately thermophilic microorganisms in the dissolution of chalcopyrite and pyrite at 45oC [. This is the case of S. acidophilus, a gram-positive rod shaped that often forms endospores and grow at temperature optima, generally between 45 and 55°C. It has been characterized as a chemolithoheterotrophic bacteria that obtains energy from the oxidation of ferrous iron or from reduced sulfur compounds and that utilizes yeast extracts as a carbon source [. S. acidophilus was isolated by Golovacheva and Karavaiko [ and described by Norris et al. [. Limited literature exists about its participation in bioleaching processes. In this work, we present experimental results obtained from the bioleaching of chalcopyrite and pyrite with S. acidophilus at 45°C, and compare them with those obtained with At. ferrooxidans at 30°C.

Abstract: Bioleaching of secondary and low grade copper ores in heaps and/or dumps is to day a well established technology. However, there is still a strong need to improve the copper leaching rates and recoveries currently reached at plant level in order to increase the economic outcome and range of application of this technology. This work presents a conceptual model which helps to elucidate when a bioleaching process is controlled either by biological, chemical or transport phenomena. This model, mathematically simplified but scientifically well grounded, it is expected will facilitate discussions among biologists, metallurgists and process engineers to develop collaborative approaches to improve this technology integrating different expertise.

Abstract: Mining operations today face a difficult challenge in terms of water availability, with most of these deposits located in arid areas where fresh water is scarce. This is especially relevant for bio-mining operations where not only the source but the water quality can be a decisive factor for its successful utilization. This research evaluates the metallurgical and microbiological performance of an adapted chloride and copper-resistant mixed culture during the leaching (laboratory scale columns) of a secondary copper sulfide at different chloride concentrations. Up to 6 g/l chloride all columns established Eh potentials over 750 mV with complete oxidation of ferrous iron in the PLS showing well established microbial activity. Copper recovery in solution, along with a high redox potential, was established faster in the mesophilic column but leveled off quickly over time. Copper extraction showed that the 6 g/l chloride column has the highest metallurgical performance (83% CuT) with 4 extra points of copper recovery over the 1.5 g/L and 3 g/l Cl^- columns. These results are a good indication that comparable copper recovery rates –to the ones achieved using fresh water- can be reached in the presence of important chloride concentrations by way of using the use of a suitable and well adapted microbial population. The related process and chloride-resistant culture have been patented under the following ID N°: EP2313534/US0201095.

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.