Advanced Materials Research Vol. 825

Abstract: Mining and metallurgical treatments of sulphide ores are characterised by present significant losses of non-ferrous and precious metals as different types of waste. These elements are accumulated in heaps due to the lack of efficient technology for the recovery of the metals from metallurgical waste. The treatment of two types of industrial metallurgical waste (copper converter slag and old flotation pyrite tailings) containing non-ferrous and precious metals were examined in the laboratory. Leaching of the slag containing 2.74% Cu (as digenite, bornite, and free metal) and 2.49% Zn (as a ferrite ZnFe2O4 and silicate) by an Fe3+-containing solution was studied. The effect of various experimental parameters on the leaching dynamics of copper, zinc, and iron under batch conditions was investigated. The following experimental parameters were recommended: a pH of 1.5, a pulp density of 10% (w/v), a temperature of 70 °C, and an initial Fe3+ concentration of 15 g/L. Leaching under these conditions resulted in the solubilisation of 89.4% copper and 35.3% zinc within 2.5 hours. Percolation leaching of the pyrite tailings containing 0.29% Cu (as chalcopyrite), 0.26% Zn (as sphalerite), 0.00007% gold, and 0.00108% silver was also studied. Acidic percolation leaching and the resulting biooxidation lasting 134 days resulted in the solubilisation of 73.4% zinc and 50.8% copper. The recovery rates of gold and silver from the bioleaching residues by cyanidation were 57.2% and 50.7%, respectively. The data obtained in the present work may be used to estimate the operating parameters for the industrial-scale processing of non-ferrous and precious metals from mining and metallurgical waste.

Abstract: In Bioleaching, although it is already prove that chalcopyrite can be dissolved by microorganisms, a major task is to do it efficiently in economical terms at industrial scale. BioSigma Bioleaching Seeds (BBS) represents a biotechnological breakthrough for the production of bioleaching solutions on demand with high concentrations of biomining microorganisms. This innovation is mainly a product based on the encapsulation of BioSigma bioleaching microorganisms in a natural matrix of alginate. This technology gives the following operational advantages: 1. High concentration of inoculum. 2. Long period of inoculum storage (more than 1 year). 3. Reduction of volume and costs of transport of bioleaching solutions. 4. Homogeneous mineral inoculation; uniform inoculation of the ore using solid capsules. 5. Protection against toxic elements to retain the viability and activity of the bioleaching solutions. 6. Addition of additives for incorporation of nutrients or other molecules that enhance the activity. 7. Encapsulation of different bioleaching microorganisms producing specific "bioleaching seeds" for each biohydrometallurgical process. All the above advantages make this new technology a very attractive alternative to enhance bioleaching processes at on site operations and overcome stressful conditions for biomining microorganisms.

Abstract: Abstract. In this study, the arsenopyrite was used as representative of gold-bearing sulfides in Carlin-Type gold ores to test the ability of oxidation on them by P. chrysosporium. After shaking incubation for 20 days, the conversion rates of iron, sulfur and arsenic in arsenopyrite were 6.28%, 35% and 21.76%, which were 44.86, 2.98 and 48.36 times compared with the asepsis system, respectively. It indicated that the P. chrysosporium could improve obviously the biotransformation rate of arsenopyrite by its own metabolic activity. The electrochemical oxidation behavior of arsenopyrite in the leaching system without and with P. chrysosporium were detected with electrochemical technology. The results showed that the P. chrysosporium did not change the oxidation mechanism of arsenopyrite, but strong oxidizing environment, which was structured by its products-oxidative enzymes and hydrogen peroxide, could promote the transformation from Fe2+ to Fe3+. P. chrysosporium could significantly decrease pitting potential and improve polarization current of arsenopyrite electrode and then accelerate its corrosion process. These indicated that P. chrysosporium was an available microorganism for degrading and transforming sulfides. P. chrysosporium could break gold inclusion and improve gold leaching rate, and finally realized economical and efficient application of Carlin-type gold ores.

Abstract: Xiangshan uranium deposit is the largest volcanic rock type uranium ore in China. Great number of low grade uranium ore (U < 0.03%) was stacked in the tailings dam as a waste rock in more than 50 years of exploitation, resulted in uranium resources waste. Two group column bioleaching experiments (column AB) were carried on in order to investigate uranium recovery effect by microbial for the low grade uranium ore. The bacteria for the tests was a mixture mainly composed by Acidithobacullus ferrooxidans and Leptospirrillum ferriphilum, which was isolated from the uranium minerals of Xiangshan uranium deposit and domesticated with the mineral and leachate system. The average uranium content is 0.0123%, the particle sizes for column A and B is less than 25mm The Fe²⁺, Fe³⁺ and F^- average contents of the test minerals were 1.90%, 0.59% and 0.14% respectively. Results showed that uranium leaching rate calculated by uranium concentration of slag were 76.75%, 75.31% in 95days and 85 days of test column A, B respectively. Rate of acid consumption of column test A, B were 7.60% and 7.69% respectively. while the rate of acid consumption was usually more than 10% by acid leaching. These evidences suggested that microbial hydrometallurgical technology was had effective for the low grade uranium ore and significant on uranium recovery for the low grade uranium ores.

Abstract: This study is prompted by the high leaching efficiency of Zijinshan copper bio-heap leaching industrial plant. Bioleaching columns with 100 mm diameter and 1 m height were used to investigate copper bioleaching at different operating conditions. Elevated temperature, high total iron concentration and high acidity significantly increased copper leaching rate as determined by solution and residue assays. At 60 °C with 50 g/L iron (initial Fe³⁺/Fe²⁺ gram ratio 2.5), pH 1.0 and no aeration, copper extraction was achieved 90% after 60 days. However, at 30°C, 5 g/L total Fe, pH 1.5 and no aeration, copper extraction reached 80% and 85% after 90 and 200 days, respectively. Real-time PCR assay showed that only 10⁵ cells/ml and 2×10⁵ cells/g are in solution and on the ore surface at the condition of 60 °C 50 g/L iron and pH 1.0, respectively. In addition, a similar leaching rate was observed in the tests with and without inoculation. The column without inoculation was directly irrigated with acid mine drainage (AMD). Our results indicate high copper leaching efficiency at extreme conditions for mineral oxidizing bacteria. Inoculation and aeration are not necessary in Zijinshan copper mine bio-heap leaching process.

Abstract: Low grade copper ores containing chalcopyrite are increasingly used for copper recovery via biomining. Since metal sulfide oxidation is an exothememic process, bioleaching activity can be measured due to the heat output by microcalorimetry, which is a non-destructive and non-invasive method. The bioleaching activity of pure cultures of Sulfolobus metallicus, Metallosphaera hakonensis and a moderate thermophilic enrichment culture on high grade chalcopyrite was evaluated. Chalcopyrite leaching by microorganisms showed a higher copper recovery than sterile controls. Chemical chalcopyrite leaching by acid produced heat due to the exothermic reaction, the heat output was increased while metal sulfide oxidation by microorganisms.

Abstract: In this paper, the bioleaching behavior of three pyrites from different geological origins (high-temperature hydrothermal, low-temperature hydrothermal and coal sedimentary) by L. ferriphilum was studied. The internal structure of three pyrite samples were investigated using optical microscope. The results show that the physical characteristics and internal structures of pyrites from different geological origins are different, and this causes the divergences of their bioleaching behavior. High-temperature hydrothermal pyrite (n-type semiconductor tested) is not almost dissolved and the leaching rate is only 0.58%, while the leaching rate of low-temperature hydrothermal pyrite and coal sedimentary pyrite (both of p-type semiconductor tested) are 15.25% and 27.50% respectively. The Leica optical microscope test of p-type semiconductor pyrites indicates that coarse particle of low-temperature hydrothermal pyrite is crystallized well and sedimentary pyrite consists of fine-grained crystal with poor crystallinity. This was suggested to cause the divergences of the bioleaching rate of both p-type semiconductor pyrites. In view of mineralogy, the semiconductive type of pyrite is the primary factor affecting its bioleaching. Furthermore, the different internal structure of pyrites will further have an influence on bioleaching for the same semiconductive type.Key words: pyrite; bioleaching; L. ferriphilum; geo-genetic

Abstract: Laboratory scale (7 L) reactors, inoculated with the L. ferriphilum dominated BIOX inoculum, were used to test the stability of the community under controlled conditions. Further, the effect of increased temperature, solids loading and pH fluctuations on the bioleaching performance and community structure were studied. Both performance and community structure remained stable under controlled conditions (41.5°C, 20% solids loading, 7 day residence time). Increasing the solids loading to 31% did not significantly affect performance or community structure. An increase in temperature (2°C every 10 days) did not have a significant effect up to 48°C, but the increase from 48°C to 50°C resulted in the loss of L. ferriphilum and a decrease in leaching performance. A more gradual increase (1°C increments) from 48°C to 50°C resulted in a stable community, dominated by Ac. cupricumulans and Acidithiobacillus caldus. A similar shift in community structure was observed when the pH fell below pH 0.8, but this was transient and L. ferriphilum recovered dominance upon adjustment to a pH > 1.0. A further increase in temperature to 52°C resulted in the loss of At. caldus and the emergence of Sulfobacilli. However, leaching performance under these conditions was poor, despite the presence of over 10 g/L ferric iron. In addition, yeast extract was required to maintain high cell numbers at 52°C. This work has identified a selection of conditions under which the community in BIOX reactors could evolve dynamically towards those communities currently observed in commercial operations.

Abstract: Effect of microorganisms and nickel sulfide ore before and after bioleaching on the emulsification was investigated. The emulsion stability was evaluated by the disengagement time or the production rate of crud. The results indicate that no crud formed and the disengagement time of system was prolonged with increasing bacteria density. And a large number of bacteria dispersed at the water-oil interface and aqueous phase and rarely existed in organic phase. The influence of bacteria on the emulsion stability was attributed to the structural characteristics and the mass transfer viscosity. And the emulsion with nickel sulfide ore after bioleaching was more stable, characterized as higher production rate of crud and lower light transmittance of aqueous phase, because bacteria alter the surface properties of minerals and increase particles’ hydrophilicity.

Abstract: Solvent extraction (SX) used for the recovery of copper is a primary low-cost hydrometallurgical process applied extensively in cases like commercial bioleaching operations. Bioleaching solutions during SX treatment are exposed to important concentrations of organic extractants, a step that has a detrimental impact on microbial activity. The following work studies and determines the effect of this exposure on the re-establishment of growth and activity of different bioleaching microorganisms after contact and phase separation. Different bioleaching iron and sulfur -oxidizing microorganisms were tested. After contact with an industrially utilized organic extractant (LIX 84IC as extractant and Oxform SX12 as solvent), cultures were grown and their substrate utilization monitored. Acidithiobacillus ferrooxidans showed only a slight increase in doubling time without significant latency period. On the contrary, for both Sulfobacillus species studied, S. thermosulfidooxidans and S. thermotolerans, were strongly impacted showing important lag phases before growth could take place. Additionally, the SX reagent showed disruption of cell walls and protein liberation during contact with all the different strains studied.