Advanced Materials Research Vol. 825

Abstract: The fungus Phanerochaete chrysosporium has been proven to biotransform refractory gold ores, leading to increase in gold recovery. This transformation has been attributed to enzymes secreted by the microbe. This paper reports the findings of preliminary investigations aimed at assessing the use of hydrogen peroxide and cell-free extracts from the fungus, P. chrysosporium, to effect biotransformation of sulphidic refractory gold ores. The investigations show that the total dissolved arsenic, iron and sulphur in solution were up to 5.2 wt%, 0.9 wt% and 6.0 wt% respectively from flotation concentrate after 72 hrs of treatment. Analysis for sulphide sulphur in the residual solids of the gold concentrate indicated about 25 wt% oxidation within 24 hours of treatment. In general, cell-free decomposition of the samples did not increase beyond 24 hours of contact time, possibly due to exhaustion of the active components. Gold extraction by cyanidation increased by 24% after 24-hr treatment with the cell-free extracts. Comparatively, cell-free (in vitro) treatment recorded 66% overall gold recovery as against 61% for whole cell (in vivo) after 72 hours of treatment. These initial results indicate clearly that in vitro processing is a promising alternative to in vivo processing of refractory gold ores using P. chrysosporium.

Abstract: Mesophilic bacteria were enriched from samples collected from acid mine drainages in La Carolina (San Luis, Argentina). Two enrichments, E1 and E2, showed suitable rates for iron or sulphur oxidation, respectively. Both enrichments were characterized by FISH analysis. They were mainly composed by Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans respectively. Studies with both, mixed and individual enrichments, showed biooxidation (measured as iron solubilisation) of a refractory gold-bearing pyrite ore from Hualilán (San Juan, Argentina). Pyrite and sphalerite were the main mineral species in the ore with 7% w/w and 8% w/w of iron and zinc and approximately 25 ppm of gold. Leaching experiments (2% w/v ore, 1.8 initial pH, 180 rpm and 30°C) were carried out with the addition of different alternative energy sources (6.67 g/L sulphur powder, 1 g/L ferrous iron, 0.02% w/v yeast extract). Redox potential, pH, ferrous iron concentration and total Fe and Zn were measured regularly. A 100% of iron leaching (after 28 days in the best experimental condition) was observed in some of the cultures. In other systems high zinc release was obtained (100% of dissolution after 28 days in the best experimental condition). Our results strongly suggest that under the correct operating conditions, biooxidation pre-treatment can be used to recover zinc as a subproduct of gold extraction from refractory ore.

Abstract: In batch cultures, the presence of nitrate inhibited iron (II) oxidation by iron (II)- or tetrathionate-adapted Acidianus (A.) brierleyi and Sulfolobus (S.) metallicus cells and tetrathionate oxidation by iron (II)-adapted A. brierleyi cells. Tetrathionate-adapted cell lines of A. brierleyi and S. metallicus oxidised tetrathionate in the presence of up to 40 mM nitrate but cell numbers were lower than those in uncontaminated tests. The results of the bioleaching tests indicated a possible window of enhanced copper extraction in the presence of 2030 mM nitrate that might be exploited in tank bioleaching. The build up of nitrate above 40 mM in bioleaching solutions must be avoided

Abstract: Geomimetics, taking lessons from natures biogenic mineralization mechanisms, can provide powerful tools for advancing biohydrometallurgical processing. Microbial transformations are largely responsible for the Mn oxides found in nature. In this research biogenic birnessite was produced by a manganese-oxidizing fungus, Paraconiothyrium sp. WL-2, at pH 6.5 under room temperature, and characterized by XRD and TG-DTA. Abiotic (chemically synthesized) acidic birnessite was also prepared hydrometallurgically and subjected to a similar battery of characterization techniques. Following thermal treatment the sorption characteristics of these two materials were compared. The biogenic precursor showed several advantages to produce more effective Li-ion sieve than the chemically synthesized precursor. First, a shorter calcination period was required to produce Li₄Mn₅O₁₂ without other phases; second, a greater content and higher crystallinity of H₄Mn₅O₁₂ were obtained from the biogenic precursor. These advantages might be caused by poorer crystallinity and around 20 wt% organic matter in biogenic birnessite. While sorption density of Li⁺ in mmol/g was basically dependent on contents of H₄Mn₅O₁₂ phase, the unique morphologies and sorption density were maintained with biogenic precursor even after repetition of sorption/desorption of Li⁺.

Abstract: The copper extraction yield from thermophilic bioleaching of chalcopyrite depends on temperature, pH, and the oxidation-reduction potential (ORP), the activity of the thermophile used, as well as on the different genetic type of the chalcopyrite used. The bioleaching characteristics of chalcopyrite from marine volcanic type and porphyry type, and the influence of genetic type on microbial community were studied. The results indicated that the bioleaching of chalcopyrite is controlled by the ORP rather than by the pH. The thermophiles composition of marine volcanic type bioleaching was Metallosphaera cuprina and Sulfobus sp HB59. Metallosphaera cuprina was the dominate bacteria during porphyry chalcopyrite bioleaching. The different leachability between marine volcanic type and porphyry type is attributed to their nature which caused by genetic type.

Abstract: Ferrous sulfate was added to batch cultures of Sulfobacillus (Sb.) acidophilus, Sb. thermosulfidooxidans and Sb. sibiricus during growth on tetrathionate. Soluble ferrous ion and polythionate concentrations were used as a measure of substrate utilisation. Sb. thermosulfidooxidans switched from utilising polythionates to exclusively oxidising ferrous ions, only then oxidising the remainder of the polythionates. Sb. sibiricus and Sb. acidophilus did not cease polythionate oxidation but utilised both substrates concurrently after ferrous ion addition. None of the cultures tested exhibited preferential polythionate utilisation, even though they were utilising polythionate prior to the addition of ferrous ions.

Abstract: Cobalt, having many diverse and critical uses, is an essential metal in today's society. However, the recovery of cobalt is difficult due to its associated mineral characteristics. A biohydrometallurgical process has been developed for cobalt recovery from low grade refractory carrollite. After direct oxidation for 6 days, 96.51 % Co and 26.32 % Cu were extracted from the ore using a pulp density of 10 %. The bioleaching solution contained 22.62 gL^-1 ferric iron while the concentration of cobalt was only 0.83 gL^-1. Therefore, a goethite deironization process was then conducted. Different conditions, such as pH value, temperature, standing time and oxidant concentration were studied in detail. The results showed that when the pH value was 4.0, oxidation temperature was 70 °C, standing time was 1 h, and oxidant concentration was 8%, then the iron removal and the loss of cobalt were 99.9 % and 0.5 %, respectively. The goethite precipitate had good filterability. The sum recovery of cobalt in the whole extraction process attained more than 95 %. The biohydrometallurgy process for the recovery of cobalt has economic and environmental advantages over the other methods.

Abstract: In heap bioleaching iron and/or sulfur oxidising microorganisms are used to facilitate the oxidation of base metal sulfides in ore, thereby liberating the metal ions (e.g. Cu²⁺) into the leach solution. The heap performance is consequently strongly influenced by the contacting of the leach solution and the ore particles. In this study two setups were used to examine irrigation from a single drip emitter, one of the most common methods of heap irrigation. The distribution of liquid, microbial colonisation and mineral recovery in a bioleach of a 132kg “ore slice” of agglomerated ore were monitored using sample ports positioned along the breadth and height of the box over a period in excess of 500 days. A specialist magnetic resonance imaging (MRI) method which is insensitive to the metal content of the ore was subsequently used to examine the effect of flow rate and particle size distribution on the liquid flow into a smaller bed. Overall the lateral movement of the liquid increased with bed depth, though preferential flow was evident. The majority of the liquid flow was in the region directly below the irrigation point and almost no liquid exchange occurred in the areas of lowest liquid content at the top corners of the samples. This had a significant impact on the local leaching efficiencies and microbial colonisation of the ore. The MRI studies revealed at steady state, the majority (~60%) of the liquid flowed into established large channels. There was minimal exchange with low liquid content regions (presumably stagnant liquid) despite their accounting for more than 16% of the total liquid hold-up. The effect of increasing the flow rate was to retard lateral liquid distribution while slightly increasing the liquid hold‑up in large channels in the region below the irrigation point. Hence poor lateral liquid distribution in drip irrigation was identified as a significant disadvantage of the method.

Abstract: The dissolution of metal sulfides is controlled by their solubility product and valence bond theory, pyrite and chalcocite have different electronic nature of the valence energy band, with which the electrolyte may exchange electrons during dissolution reaction, so they have different principals of dissolution. Pyrite which has a higher rest potential is galvanically protected, while chalcopyrite which has a lower rest potential is preferentially leached. Pyrite is intentionally added to the leaching of chalcocite concentrates, we investigated the influence of pyrite to chalcocite weight ratio, solution pH , Eh and the presence of bacteria on assisted leaching of chalcocite concentrates. The leaching solution redox potential, pH, iron, copper and bacteria were monitored, leached residue was collected and analysed to understand leaching mechanism. We found that chalcocite leaching efficiency is enhanced with pyrite:chalcocite weight ratio increased.

Abstract: This paper describes bioleach test work performed in continuously operated bench-scale reactor systems on a nickel-copper containing sulphide concentrate at 45 and 70°C, respectively. Optimisation of the process focused on determining the effects of process parameters such as residence time, grind size and feed solids concentration on the leach kinetics, metal extractions and performance of both the moderate thermophile and thermophile cultures. The results showed that nickel recoveries in excess of 96% could be achieved using a moderate grind size and leach temperatures, whereas ultrafine grinding and higher operating temperatures were required to achieve Cu extractions in excess of 93%.