Advanced Materials Research Vols. 20-21

Abstract: In this paper, a central composite design was applied to optimize the bioleaching of iron from a kaolin sample containing 2.2% iron impurity by Aspergillus niger isolated from pistachio shell. The strains were inoculated into 500 ml flasks containing 100 ml media consisted of (g/l): sucrose 120; NH4NO3 0.45; KH2PO4 0.1; MgSO4.7H2O 0.3; FeSO4.7H2O 10-4; ZnSO4.7H2O 25×10- 5. The effects of initial pH, sugar and spore concentrations on iron removal extent were investigated. The two-level factorial design points were pH 2 and 5, sugar conc. 70 g/l and 130 g/l, spore conc. 9×107 and 35×107 spores/l. Also, the increase of dissolved iron, oxalic acid concentration, changes in pH value, and sugar concentration were registered. Consequently, after 10 days, the iron concentration of the best condition reached to 179.3 ppm that means 38.8% of the total iron content is removed. Furthermore, the data analysis showed that all the factors are significant, and the iron removal extent increases by increasing the initial pH to 4.4, sucrose content to 93.8 g/l, and spore concentration to 305.5 spores/μl, but further increase in each factor value has negative effect on the response.

Abstract: Bioleaching of pre-treated spent refinery catalyst was performed using sulfur and iron oxidizing bacteria separately. Both the mixed cultures were grown at various concentration of either ferrous sulfate or elemental sulfur. Bioleaching process was conducted by varying the reaction time, effect of substrates and effect of catalyst amount. Under the most favourable transport conditions examined, (5g/L spent catalysts, 10g/L ferrous sulfate, reaction time 7 days) the mixed iron oxidizing bacteria were able to recover Ni, V, and Mo of 90, 80 and 54 % respectively. Higher catalyst and ferrous sulfate concentration showed decline result in recovery of Mo and V. Ni showed consistent results throughout the series of experiments (88 to 90% recovery). The mixed sulfur oxidizing bacteria were observed to be more effective than the iron oxidizing bacteria. The sulfur oxidizing cells were able to recover Ni, V and Mo of 88, 94 and 46 % respectively (spent catalysts 50g/L, elemental sulfur of 2% (w/v), reaction time 7 days). The oxidation of elemental sulfur to sulfate could play a vital role for extraction of the metals.

Abstract: Bioleaching is technology applicable to iron extraction from low-grade non-metallic raw materials. Bioleaching of quartz sands and feldspars involves the action of heterotrophic bacteria. Impurities include fine – grained limonite, goethite, hematite or mica were removed by the reductive dissolution of Fe3+ in linked with the silicate mineral destruction. Heterotrophic bacteria produced organic acids that are able to solubilize Fe oxide and silicates but require organic carbon as a source of energy. Molasses is a relatively inexpensive carbon source used for various industrial fermentations and contains also other nutrients that accounted for the enhancement of iron dissolution in this study. The admixture of pigments in molasses coloured the samples, but the discoloration could be removed by the addition of NaClO following the bioleaching step. The feasibility of the bioleaching treatment has to be tested specifically to each type of silicate raw materials. The Fe content in the quartz sands and feldspar samples by the biological leaching decreased as much as 60% and by subsequent using of electromagnetic separation of feldspars, the decrease of Fe content in 74% was achieved. However, the application of magnetic separation of quartz sands after bioleaching resulted in total iron removal of 93 % and in such combined way prepared product contained 0.024 % of Fe2O3. Achieved results on iron removal point to the fact that combination of leaching and magnetic separation enables to obtain product usable in glass and ceramic industry.

Abstract: Iron oxidizing bacteria Acidithiobacillus ferrooxidans, iron reducing bacteria Acidiphilium spp. and their mixture were applied for leaching of iron impurities from quartz sand. The bacterial leaching was carried out in order to decrease the amount of colouring iron oxides and to improve the technological properties of the raw material. Mineralogical analysis confirmed the presence of siderite, iron-bearing muscovite and various amorphous and crystalline forms of iron oxides occurring both free and coating siderite and quartz particles. Mössbauer spectroscopy revealed various oxidation and magnetic states of iron ions, with the prevalence of reduced ionic species. Highest extraction of iron was achieved with pure culture of iron-reducing bacteria with ferrous iron as dominant species in the leaching liquor. Surprisingly, iron oxidizing bacteria caused passivation of the surface of iron-bearing minerals, resulting in the depression of iron leaching in comparison with abiotic control. Ferric iron was major species in the leaching solution containing the mixed culture of iron-oxidizing and iron-reducing bacteria. The mixture was far less efficient in iron extraction than pure culture of iron-reducing bacteria.

Abstract: The sphalerite-pyrite oxidation by Acidithiobacillus ferrooxidans was studied to analyze how the formation of the elemental sulfur layers occurs around sphalerite grains. Two possible mechanisms of formation have been raised. One mechanism corresponds to the formation of sulfur pseudomorphs where, both, iron and zinc have been leached of the sphalerite, whereas compound sulfur is oxidized, in situ, to elemental sulfur, leaving an unreacted core of sphalerite that remains in the center. Another mechanism consists in the dissolution of iron, zinc and sulfur presents. When the attack by Fe3+ as by H+ broken the S-metal bonds, sulfur is then oxidized to a series of sulfur intermediate compounds. These compounds in solution then are oxidized to elemental sulfur, which precipitates on sphalerite grains.

Abstract: An experimental campaign was conducted for monitoring the formation of hydrocarbon gaseous compounds during bioleaching of copper sulphide ores with mesophilic microorganisms. Three different mineral samples were used: a pyrite concentrate, a chalcopyrite concentrate and a copper sulphide ore rock from El Teniente mine containing 1 % copper. Mineral samples were bioleached in 250 ml shake flasks containing 100 ml of basal medium inoculated either with a pure strain of Acidithiobacillus ferrooxidans or a natural bacteria consortium obtained from the acid leaching of El Teniente ore in columns. Each sealed system shake flask was fed with a flow of synthetic air and the exit stream was passed through a column containing an adsorbent material and next through a water trap as to avoid back air contamination from the environment. Compounds present in the adsorbent material after 90 days of bioleaching were analysed using a gas chromatography mass spectrometry technique with a procedure that detects 162 different hydrocarbon gaseous compounds (SGH). Results showed that the bacterial communities in copper sulphide bioleaching results in the formation of some hydrocarbon gaseous compounds, mainly various types of methyl benzene and branched alkanes. The formation of these organic compounds is likely to be related to the presence of heterothrofic microorganisms present in the natural populations.

Abstract: Bioleaching of the copper flue dust emanating from smelters at Sarcheshmeh Copper Complex has been studied. At the present, the dust is sent back to the smelter, which reduces its efficiency. In this study, a continuous system including a feed tank and two-stage aerated stirred tank bioreactors was established. Mixed mesophile bacteria with different amounts of the dust containing 35% of copper mainly in the form of sulfide minerals were used. The effects of pulp densities, residence times and temperatures on the final copper recovery and redox potential were experienced. Despite the copper concentrates bioleaching, the process of dust bio-treating was net acid consuming. Lower pulp densities resulted in a stable redox potential in both reactors. However, increasing the pulp density to 7%, was created an unstable redox potential in the first bioreactor especially at lower temperatures. Final copper recoveries were calculated for pulp densities of 2%, 4% and 7%, were 91.8%, 90.3% and 87.6% with residence times of 2.7, 4 and 6 days respectively. The promising results indicated that bioleaching is a feasible process that can be applied to copper flue dusts.

Abstract: In this study, the viscosities and conductivities of bioleaching solution were determined by Ubbelohde viscometer and conductivity meter, respectively. The mean ionic activity coefficients, relative partial molar free energies of copper bioleaching solution at above experimental temperatures ranging from 298 K to 313 K have been calculated. Simultaneously, these characters of copper bioleaching solution were compared with and without mesophilic bacteria. The experimental data showed that the viscosities and thermodynamic properties for bioleaching solution would be crucial to minimize the third phase formation so as to increase extraction efficiency.

Abstract: Based on the bioleaching mechanism and electrochemical studies of covellite, the dissolution rate of covellite mineral is accelerated through increasing the redox potential (Eh) of the leach. In the present work, some methods were adopted to enhance the bioleaching of covellite concentrate (collected from Zijinshan copper mine, Fujian province, China) by adding different oxidants such as pure pyrite, ferric ions and H2O2. The goal of this study was to provide appropriate operating parameters for the industry application and increase the efficiency of the bioleaching of copper mine. The results showed that the optimal way to increase the redox potential (Eh) level was the addition of pure pyrite. This method could effectively raise the Eh of bioleaching process while the effect of environmental change was negligible. It could quicken the leaching process and enhance the final copper recovery through the addition of pyrite by 1:1 or 1:2 ratio of covellite concentrate to pyrite.

Abstract: In heap bioleaching the dissolution of gangue minerals from igneous ore materials can lead to the build-up of considerable concentrations of Mg and Al sulphates in the recycled leach solution. This may interfere with microbial ferrous iron oxidation, which drives the oxidation of the target minerals. The kinetics of the oxidation process have been well studied for Leptospirillum and Acidithiobacillus species in tank systems. Although not directly comparable, kinetic parameters derived for tank systems do apply also for heap bioleach conditions. In the present study the effect of solution concentrations of Mg and Al as sulphate at individual concentrations of 0 to 10 g/L and combined concentrations 0 to 16 g/L each has been investigated in continuous culture using Leptospirillum ferriphilum. Increasing the concentrations of the salts increasingly depresses the rate of ferrous iron oxidation and also shifts the viable range more and more into the low potential region. Al significantly reduces the amount of carbon maintained in the reactor (assumed to be commensurate with biomass), whereas Mg actually enhances it at low concentrations. In both cases, however, the rate is always depressed. The results indicate that heap cultures are likely to perform sub-optimally in those operations where build-up of dissolved gangue minerals is not controlled.