Papers by Keyword: Moderate Thermophiles

Abstract: Pyrometallurgical copper final slag was subjected to leaching by means microbial cultures of three different groups based on their optimum temperature for growth and activity: mesophilic and moderate thermophilic bacteria, and extreme thermophilic archaea. The leaching experiments were performed by the shake-flask technique and in agitated bioreactors under batch and continuous-flow conditions. The effect of the most essential factors (particle size, pulp density, pH, aeration) on this process was studied. The highest rates of extraction of the non-ferrous metals (Cu, Zn, Co) and iron were achieved by means of some archaea but at relatively low pulp densities (5 – 10%). Some moderate thermophilic bacteria were the most efficient at the higher pulp densities (15 – 20 %). The, leaching by some mesophiles at pH 3.0 – 3.5 was also very attractive since it was connected with high extractions of these metals (about 85 – 92% at 20% pulp density), much lower acid consumption and low solubiliation of fayalite which resulted in the production of pregnant solutions suitable for the recovery of the dissolved non-ferrous metals.

Abstract: Leaching of a pyritic and a pure chalcopyrite concentrate was carried out in stirred tank reactors in the absence and presence of a mixed culture of moderately thermophilic microorganisms at 45°C and pH 1.5. To study the effect of microbial activity on copper dissolution, the abiotic experiments were performed under accurately controlled redox potential conditions to reproduce the same oxidising conditions recorded during the bioleaching experiments. X-ray photoelectron spectrometry (XPS) was used to study the surface of chalcopyrite chips leached for different durations. The results showed that the microorganisms in cases of both concentrates did not have any effect in the copper leaching efficiency other than oxidation of ferrous to ferric ions. Biooxidation of elemental sulphur did not improve the leaching efficiency and bulk and surface jarosite had no negative effect on dissolution. A composite layer composed of mainly elemental sulphur and iron-oxy-hydroxide was found to be responsible for the hindered dissolution.

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%.

Abstract: Marine hydrothermal polymetallic sulfide ores contain high amounts of valuable metals such as Cu, Pb, Zn, Au, Ag, as well as In, Ge, Bi, and Se. Samples from a site in the Indian Ocean were taken during a BGR ship cruise, crushed and sieved for bioleaching experiments to reveal the extraction of the various metals. Chalcopyrite was the main mineral, the total copper content was 38.5 %wt. Comparative bioleaching with mesophilic, moderate thermophilic and thermophilic acidophilic iron- and sulfur-oxidizing bacteria and archaea was investigated. Batch culture experiments were conducted at 2% (w/v) pulp density in shake flasks in the presence of Acidithiobacillus ferrooxidans, Acidiphilium sp. and Acidithiobacillus thiooxidans as mesophiles (30°C), a mixed culture of moderate thermopilic iron- and sulfur oxidizing bacteria (50°C) and the thermophile Acidianus brierleyi (70°C). The results after four weeks showed most effective dissolution of copper in the presence of A. brierleyi (up to 4.3 g/l), compared with moderate thermophiles and mesophiles (3.3 g/l and 2.5 g/l, respectively). Furthermore, the bioleaching performance was approved with dissolved iron concentrations. Conclusively, an increase in temperature from 30 °C to 70 °C had a major impact on bioleaching efficiency. Copper and iron extraction efficiency occurred in the order thermophiles, moderate thermophiles, mesophiles.

Abstract: Moderately thermophilic bioleaching of a pyritic chalcopyrite concentrate was mimicked in an electrochemical vessel. The bioleaching was carried out for 28 days at 45°C with 2.5% (wt/vol) solid content at pH 1.5. Data from the redox potential development was used to program a redox potential controller in an electrochemical vessel to reproduce the same leaching conditions in the absence of microorganisms. Despite precipitation of iron as jarosite and formation of elemental sulphur in the electrochemical experiment, the copper recoveries were almost the same in both experiments.

Abstract: Stirred tank reactor (STR) leaching of non-ferrous metals from copper smelting slag was conducted using biogenic Fe³⁺ solution containing H₂SO₄. The solution was initially obtained through biooxidation of FeS₂+S° by using a moderately thermophilic microbial culture such as Sulfobacillus thermosulfidooxidans at 45°C and was applied as lixiviant in STR leaching experiments. The effect of pH, pulp density, temperature and initial Fe³⁺ concentration on leaching behavior of Cu, Fe, Zn and Ni from the slag were investigated. The presence of high concentration of Fe³⁺ ions was found to promote the leaching of copper and nickel while inhibiting the leaching of zinc and iron. Process pH was considered as the most significant parameter and the optimum leaching results were obtained at pH 1.8 with low fayalite dissolution and jarosite precipitation. During the leaching at this pH (1.8), 25% (w/v) pulp density and 65°C temperature in presence of 20 g/L initial Fe³⁺ concentration, maximum extraction of Cu (90%) and Ni (85%) was observed in 4 hours whereas Fe extraction was minimum (19%). A schematic flowsheet of multistage leaching process was proposed. The result obtained from multistage batch leaching experiments will be step forward for continuous stirred tank reactor leaching for industrial scale implementation.

Abstract: The focus of this paper is on the development of a bioleaching process for the treatment of complex polymetallic concentrates, containing chalcopyrite, sphalerite, galena and silver, using a moderately thermophilic culture operating around 45°C. Initial development R&D work and subsequent research for process improvements carried out in bench-scale piloting facilities will be discussed.