Solid State Phenomena Vol. 262

Abstract: Gradually bio-metallurgy technology is becoming an irreplaceable new technology. The nickel-bearing tailings in Jilin, China contains Ni 0.13 %, Cu 0.03%, Co 0.01%, S 15.20%, Fe 6.30%. A comparative study of the HQ0211 bacteria, indigenous bacteria (after the domestication named ZXJE511 bacteria) and acid pool leaching revealed that the local species ore leaching was preferably the best way. At pH 2.0, room temperature (about 23°C), pulp density 20%,the Ni, Co and Cu leaching rates were 70.08%, 40% and 57.67 % , respectively ,after 38 days of bioleaching, proving the superiority of the bacterial leaching of Ni, Co, Cu from tailings. Biological leaching tailings solved the problem of the conventional methods which could not be addressed by acid leaching. This technology is environmentally friendly and can make maximum use of the resources, thereby avoiding the waste of the resources.

Abstract: In an attempt to investigate the use of bacteria and their metabolites as bioflotation reagents for environmentally friendly mineral processing, laboratory cell flotation tests were carried out using copper sulfide ores bearing a high content of pyrite, which were mixed with a biosurfactant-producing mixotrophic bacterium as bioflotation reagents. The interaction of bacterial cells and their metabolic products with the sulfide ores resulted in the alteration of the surface chemistry of both ores and bacterial cells as evidenced by FTIR and SEM-EDS observations as well as surface tension and contact angle measurements. The change in the surface properties of the sulfide ores in turn enabled the bacterium to function as flotation bioregeants in the flotation of copper sulfide ores as a function of bacterial cell concentration, conditioning time, flotation time and pH. Overall, the bacterium and its metabolites as bioreagents yielded flotation recoveries which might be attributed to the multi-function of the bacterium as depressant, collector and frother. Thus, the bacteria tested in this study could potentially be used as flotation bioreagents, providing an alternative to conventional flotation reagents.

Abstract: Previous agglomerate-scale heap bioleaching studies have outlined the variations in cell numbers of the liquid and attached phases during colonisation of sterilised ore by a pure culture. In this study, a mixed mesophilic culture was used in agglomerate-scale columns containing non-sterilised low-grade copper ore. Over a six - month period, columns were harvested at various intervals to provide snapshots of the metal distribution and the quantity, location, and ecological variations of mineral-oxidizing microbes within the ore bed. The initial colonisation period in this experiment was dissimilar to previous work, as the indigenous community was retained within the ore-bed throughout acid agglomeration. The overall colonisation phase lasted for approximately 1,000 hours until cell concentrations stabilised. In each column, less than 0.05% of the total cells were found in the leachate, 15-20% in the interstitial phase and the remaining ~80% were attached to the mineral surface. Once cell numbers had stabilised, interstitial cell concentrations were approximately 2,000× greater than those in the leachate. This difference persisted for the duration of the experiment. Copper concentrations in the two liquid phases generally decreased over time, but were on average 50× higher in the interstitial phase. Iron concentrations were more stable, but again were 30× higher in the interstitial phase. This demonstrates that that the difference in cell concentration between the leachate and interstitial phases cannot be explained through diffusion gradients within the system as it is much greater than those observed for the dissolved metals. It also shows that the specific environmental conditions of the interstitial and attached cells are very different to those inferred through analysis of leachates alone.

Abstract: A sulphide concentrate containing 31.4% total sulphur (in which 30.7% was sulphidic), 31.8% iron, 8.0% arsenic, 18.5 g/t gold and 32.9 g/t silver finely disseminated in pyrite and arsenopyrite as the most essential components was subjected to microbial pretreatment to expose the precious metals from the sulphide matrix. Three different types of microbial cultures were tested for their ability to oxidize the sulphides and to expose the precious metals for the subsequent chemical leaching: mesophilic chemolithotrophic bacteria with a temperature optimum for their growth and activity at about 32 – 37°C, moderate thermophilic bacteria with the relevant optimum at 53 – 59°C, and hyperthermophilic archaea at 75 – 84°C. The microbial pretreatment of the concentrate was carried out in reactors with mechanical stirring and enhanced aeration by air enriched in CO_2. It was found that sulphide oxidation of about 40 – 45 % was sufficient for achieving gold extraction higher than 90% during the subsequent leaching of the pretreated concentrate by different gold-solubilizing reagent (cyanide, thiourea, thiosulphate). The highest rate of sulphide oxidation was achieved by a mixed culture of hyperthermophilic archaea at 82°C but at relatively low pulp densities (within 7 – 9%). At higher pulp densities (within 10 – 25%) the highest rates were achieved by means of moderate thermophilic bacteria at 57 – 59°C.

Abstract: Present work deals with synthesis of copper nanoparticles at the room temperature, using two aqueous extracts prepared from green and dry leaves of Aloe vera and Geranium (Pelargonium graveolens). Finely cut leaves were placed in the flask with the distilled water. The mixture was boiled for 15 min at the temperature of 60°C. After boiling, the mixture was centrifuged and pure extract was used for copper nanoparticles synthesis. The source of copper ions was leaching solution obtained from the bioleaching of copper shale (Kupferschiefier) using chemolithotrophic bacteria such as Acidithiobacillus frerooxidans. The bioleaching procedure was performed in the column reactor.

Abstract: Biohydrometallurgy has broad application prospect in the treatment of low-grade nickel sulfide ore. However, quite a number of nickel sulfide deposits are associated with basic gangue minerals such as contain olivine, serpentine. The high basic gangue minerals will lead to a higher acid consumption and make it difficult to bioleach at pH below 2.5. It is crucial to improve processes and adapt bacteria with this kind of ore. This paper reviews the experimental researches and industrial applications for bioleaching of the high acid consumption nickel sulfide ores. It is suggested that bioleaching at elevated pH will have similar leaching rate compared with pH below 2.5, meanwhile the cost will be decreased remarkably due to a lower acid consumption and less dissolved impurity ions.

Abstract: Flotation tailings are hazardous due to physical and chemical instability and are currently considered one of the main pollution concerns of mining industry. Most of these tailings are fine-grained residues with low copper content (0.1-0.8%) and include toxic compounds, such as heavy metals, arsenic, and flotation reagents, among others. Another hazard is the generation of acid mine drainage (AMD) due to biological oxidation of tailings. On the other hand, low-grade ore is challenging the mining industry to commercially produce copper.The main objective of this work was to assess the use of flotation tailings and low-grade ore to produce a biologically-produced copper sulfide, as a product for further pyrometallurgical or fine chemistry processing. Low-grade ore and flotation tailings were first agglomerated at different proportions and leaching tests were performed in 1m columns, using either industrial or synthetic raffinate solution. Then, the PLS solution obtained from the column tests was subjected to selective precipitation of copper by using biogenic hydrogen sulfide (H₂S) generated by a mixed culture of neutrophilic sulfate reducing bacteria (SRB), enriched from sediments of Caracarani river (located at 4,600 m over sea level in northern Chile).Over 91% of the copper soluble present in the PLS was recovered as copper sulfide in 28 days, while ferrous iron, other metals and arsenic remained in solution. Analysis performed by XRD confirmed the presence of copper in the precipitate (58% as covellite). This work demonstrates the possibility to apply bioleaching and bio-precipitation technologies to treat tailings and low-grade copper ore to produce a high quality copper sulfide.

Abstract: Biodesulfurization of a high-sulfur and medium-ash coal product was carried out in a 5-m tall packed bed bioreactor using a mixed culture of iron- and sulfur- oxidizing microorganisms. The feed coal (4 tones) was obtained from a heavy media cyclone product from Takht-Zeitoon coal mine (Tabas, Iran) with a density of -1.4 g/cm³ and a grain size of 0.5-25 mm, having the ash and sulfur contents of 14.92% and 2.46%, respectively. The pilot scale process was performed in a semi-continuous mode with a solution injection rate of 2.5-4.5 lit/min/m², aeration rate of 4-12 m³/h/m² and solution pH of 1.7-2, over a period of 190 days. Iron and sulfate ions were controlled during the process in two 1500-L stirred tank reactors by goethite and gypsum precipitation processes, respectively. The column biodesphurization in a period of 170 days was followed by a washing step with HCl to remove sulfate precipitates. Results showed that the total sulfur and ash contents reached to 1.69% and 11.04%, respectively, which were corresponded to 31% sulfur removal and 26% ash removal. It was indicated that biodesulfurization has a good industrial potential to treat coarse-grained high sulfur coals.

Abstract: The goal of the present work was to compare the rates of pyrite oxidation by different microorganisms, representatives of the groups predominating in biohydrometallurgical processes. The experiments were conducted in flasks with 100 mL of the medium containing mineral salts, 0.02% of yeast extract, and 2 g of pyrite at 45°C on rotation shaker (200 rpm) for 30 days. Strains Acidithiobacillus caldus MBC-1, Sulfobacillus thermosulfidooxidans VKMV 1269^T, and Acidiplasma sp. MBA-1 were used in the study. Different combinations of the strains were used in the experiments (pure cultures of S. thermosulfidooxidans VKMV 1269^T, Aсidiplasma sp. MBA-1, A. caldus MBC-1, as well as mixed cultures S. thermosulfidooxidans VKMV 1269^T + A. caldus MBC-1, Aсidiplasma sp. MBA-1 + A. caldus MBC-1, S. thermosulfidooxidans VKMV 1269^T + Aсidiplasma sp. MBA-1). Iron concentrations in the medium were the highest in the variants “S. thermosulfidooxidans VKMV 1269^T + A. caldus MBC-1”, “Aсidiplasma sp. MBA-1 + A. caldus MBC-1”, and “Sb. thermosulfidooxidans VKMV 1269^T + Aсidiplasma sp. MBA-1” and achieved 3.8, 3.5, and 3.3 g/L, respectively. Iron concentration in sterile control as well as in the experiments with pure cultures of Aсidiplasma sp. MBA-1 and A. caldus MBC-1 were very low. It demonstrated that in these variants pyrite was almost not oxidized. In the experiment with the pure culture of S. thermosulfidooxidans VKMV 1269^T, the rate of oxidation was high during 10 d of the experiment but then the oxidation activity drastically decreased. The ferric iron concentration achieved a maximum of 1.8 g/L and then decreased, whereas the ferrous iron concentration began to increase. Revealed differences in pyrite oxidation rates can be explained by differences in the physiological properties between the microorganisms. Results of the present work suggest that different groups of microorganisms have different impact in pyrite biooxidation.

Abstract: This study investigated the biooxidation of a high-grade refractory gold ore from the Zarshouran mine (West Azarbaijan, Iran) in shake flasks and a stirred tank bioreactor (STBR) using a mixed culture of moderately thermophilic microorganisms. The influence of four critical parameters including, pH, biooxidation time, nutrient medium type and pulp density on the iron and arsenic extraction as well as gold cyanidation were evaluated in a full factorial design in shake flasks at 45 °C. Maximum iron extraction was obtained in M9K medium, pulp density of 5% (w/v), 15 days of biooxidation time and the pH of 1.6. Biooxidation in the STBR was carried out at the pulp densities of 10% and 20% (w/v), the pH of 1.7 in the M9K medium, in which dissolved oxygen, pH, redox potential, iron and arsenic concentrations were measured during the process. It was found that 61% decrement of sulphur content in the STBR led to recover 80% of gold, which was 43% higher than that in the conventional cyanidation process. It can be concluded that the oxidation of refractory arsenopyrite gold ore can achieved using a moderately thermophilic biooxidation culture.