Advanced Materials Research Vols. 71-73

Abstract: The objective of this work is to evaluate the acidic and biological leaching of tailings containing Ni/Cu from a flotation and smelting plant. Acidithiobacillus ferrooxidans, strain LR, was used for bioleaching at pH 1.8 and chemical controls were run parallel to that. The acidic leaching was done within 48 hours at pH 0.5 and 1.0. In the slag inoculated flasks the redox potential was high (600 mV), thus indicating oxidative bacterial activity, however, the obtained results after 15 days showed only around 13% Ni and 8% Cu extractions, which were not different to those of the controls. For the flotation tailings bioleaching extractions were approximately 45% for Ni and 16% for Cu while differing figures were obtained for the chemical controls. These were 30% and 12% respectively. Here we could observe that the presence of bacterial activity led to a higher solubility of Ni. Acid leaching of slag showed higher nickel and copper extractions: 56% and 24% respectively at pH 0.5 and 21% and 11% at pH 1.0. However, the acid consumption was 320 and 150 Kg/ton of slag, respectively, both much higher than in bacterial assays. These results indicated that Ni and Cu solubilization from the slag is acid dependent no matter the redox potential or ferric iron concentration of the leaching solution. For flotation tailings, acid treatment showed extractions of 23% for Ni and 16% for copper at pH 0.5 and 22% and 28%, respectively at pH 1.0. The acid consumption was also higher: 220 and 120 Kg/ton, at pH 0.5 and 1.0, respectively. Based on own findings we could observe that acid leaching is found to be more effective for slag, though the acid consumption is much higher, while for the flotation tailings, bacterial leaching seems to be the best alternative.

Abstract: Indirect bioleaching is a biotechnology that presents important advantages when apply to bioprocessing of zinc and zinc polymetallic concentrates such as high metals recovery, fast kinetic of 4-5 hours to get full metals extraction, sulphur oxidation to elemental sulphur (avoiding sulphuric acid generation, while pyrite mineral remains untouched), and use of conventional reactors (aeration is not required) and normal process equipments. On the other hand, the development of high-efficiency bioreactors for ferrous iron bio-oxidation based on flooded fixed-bed model has opened the way to succeed in the potential commercial application of this innovative bio-hydrometallurgical technology, being especially attractive to benefit zinc and lead bulk or polymetallic concentrates containing other valuable metals like silver. In addition, a great variety of concentrates is feasible to be processed, e.g. in the range of 15% to 60% Zn and Pb metals content. That aim, within European Biomine project, for the first time in biohydrometallurgy field, indirect bioleaching technology applied on Zn/Pb polymetallic concentrates has been demonstrated in continuous in an integrated pilot plant at Tecnicas Reunidas’ (TR) R&D Centre in Madrid (Spain) producing electrolytic SHG zinc plates. Overall zinc recovery in the integrated pilot facility after more than 300 operating hours has been above 95% thanks to the ability and good performance of the ZincexTM technology (solvent extraction and electrowinning), in which obtaining of SHG electrolytic zinc is fully guaranteed with high current efficiency (above 93%) and good deposit morphology. In definitive, a profitable marriage between indirect bioleaching process and ZincexTM technology has been successfully demonstrated in TR facilities at pilot plant scale, and main results of such integrated pilot plant operation are presented in this paper.

Abstract: Chilean copper production has been growing in the last 20 years reaching an annual production of 5,557,000 tons of Cu in 2007. For each ton of copper produced, about 200 tons of sterile and low grade ore and 100 tons of tailings are discharged in the environment. Most of these wastes contain significant amounts of sulphide minerals, mainly pyrite, and once submitted to weathering, may produce acid mine drainage. On the other hand, the high price of copper raised the interest for processing by leaching the low grade ore deposited in large dumps. An important part of these mining wastes and low grade ores is located in the Andes, where the mean temperature is usually ~5°C or less. The rate at which bioleaching reactions occur is directly related to the temperature at which the microorganisms (bacteria and archaea) develop. A temperature decrease causes both a decrease of the rate of the involved chemical reactions and a decrease or inhibition of microbial growth. In this work we present the results of the isolation of microorganisms from an old tailing deposit, exposed at low temperatures (5oC) during most of the winter. The isolated microorganisms initially showed a low capacity to oxidize 3g/L Fe(II) sulfate at pH 1.6, and tetrathionate 0.01 M, with an initial pH 4 both at 5oC. However, after successive cultures, microorganisms showed a slow capacity to oxidize both substrates, as well as the sulphide contained in the tailings samples. The terminal Restriction Fragment Length Polymorphism (tRFLP) of the isolated cells grown in basal medium containing Fe(II) showed a nearly pure culture of Acidithiobacillus ferrooxidans. The present study indicates that, even at very low temperatures, microorganisms play an important role in the generation of acid mine drainage and in the oxidation and leaching of sulphide ores.

Abstract: Geochemical modeling program PHREEQC was used to simulate generic bioleaching processes. Carbonate minerals (e.g., calcite) dissolve in acid solution, increasing the solution pH and Ca concentration while the concentration of CO2 may be controlled by the equilibrium with the atmospheric CO2. Non-oxidative dissolution of Fe-monosulphides was demonstrated to release H2S and increase the pH. In the absence of ferric iron precipitation (goethite), the oxidation of pyrite decreased the solution pH from 2 to ~1.4, while the oxidation of Fe-monosulphide and chalcopyrite increased the solution pH to ~3.2-3.4. Assuming equilibrium precipitation of goethite, oxidative leaching decreased the solution pH for all three minerals from pH ~2 to ~0.9-1.2. Adjustment of the solution pH to 1.8 or 2.0 with KOH with concurrent equilibrium precipitation of K-jarosite resulted in low dissolved iron concentrations.

Abstract: In this study the effects of pH and temperature on iron solubility were predicted using the geochemical modelling code PHREEQC and the thermodynamic database WATEQ4F. The modelling results demonstrated that the solubility of secondary solid phases formed under acid bioleaching conditions decreases with increasing temperature and also with increasing pH. Modelling calculations showed that bioleaching solutions are typically supersaturated with respect to K-, Na-, NH4-, and H3O-jarosites and the precipitates are typically solid solutions containing their mixtures. Jarosite solubility modelling results were also compared with a data set from jarosite synthesis experiments. Model-derived temperature dependence of hydronium-jarosite correlated very well with the actual experimental data.

Abstract: The purpose of this study was to model, based on thermodynamic equilibrium constants, the effects of chloride and phosphate ion on the speciation of ferric iron in solution and on Fe(III)-precipitates. The thermodynamic modelling was based on the geochemical modelling code PHREEQC and the thermodynamic database WATEQ4F. Increasing phosphate levels (g per L range) increase the complexation of ferric ion with phosphate (FeH2PO42+) with a parallel decrease in ferric sulphate complex (FeSO4+) and release of sulphate as SO42- in solution. Chloride ion at comparable levels and under otherwise similar conditions had negligible effects on the speciation of soluble iron species. In the solid phase analysis, jarosite and goethite species declined with increasing phosphate levels, whereas chloride did not affect the relative proportions of secondary Fe(III) minerals in the solid phase. Saturation index values for jarosites and goethite were dependent on the temperature with the range of phosphate levels (0–20 g/L) examine in this study.

Abstract: Acidithiobacillus caldus and Leptospirillum ferriphilum cells grown in different energy substances (ferrous ion, sulfur and pyrite) were used. The adhesion of A. caldus and L. ferriphilum cells on pyrite and their effect on pyrite surface properties were studied by adsorption, zeta-potential and FT-IR methods, and the corrosion images of pyrite interaction with bacteria were examined using atomic force microscopy. Research showed that pyrite isoelectric point (IEP) after interaction with bacterial cells shifted towards cells isoelectric point, and the shift degree in case of interaction with A. caldus was observed to be much more pronounced than for interaction with L. ferriphilum, which can be due to higher affinity of A. caldus towards pyrite. The FT-IR spectra of pyrite treated with bacterial cells revealed the presence of the cell functional groups signifying cells adsorption. Although the adsorption density of A. caldus on pyrite was higher than that of L. ferriphilum, L. ferriphilum with strong ability to oxidize ferrous ion showed better leaching efficiency than A. caldus with strong ability to oxidize sulfur for pyrite leaching. The results demonstrated that more important of indirect action (L. ferriphilum) than direct action (A. caldus) on pyrite.Introduction Bacterial adsorption to minerals is an initial step in bacterial leaching for metal recovery [1]. It has been reported that bacterial adhesion is dependent not only on the biochemical properties of the organism but also on the interfacial properties of the various interfaces existing in a bioleaching system[2].The bacteria-mineral interactions result in the changes of their surface properties. The elucidation of their alternate will be beneficial for bioleaching processes. Both Acidithiobacillus caldus and Leptospirillum ferriphilum are known for their ability to inhabit acidic environments and derive energy from oxidation of inorganic substances with natural occurrence in ore deposits and acid mine drainage and high affinity towards sulfide minerals [3-5]. In this work, the alterations of surface properties of pyrite after interaction with L. ferriphilum and A. caldus are studied, and the changes in surface properties caused by bacterial adsorption are discussed with reference to bioleaching behavior of pyrite.

Abstract: Thermophilic micro-organisms are known to oxidise pyrite and other iron sulphide minerals resulting in the production of acidic ferric sulphate solutions. In this study, the leach liquors generated from such bacterial oxidation were aged through a forced hydrolysis process to yield various iron oxyhydroxides and sulphates. The forced hydrolysis was carried out under a pH range of 1.9 to 9.0. Upon completion of aging, the precipitates generated were characterised using powder X-Ray diffractrometry. The XRD analyses revealed a production of a variety of iron oxyhydroxides and basic iron sulphates. The nature of these precipitates was influenced by the pH conditions used during aging. Jarosite compounds were precipitated under acidic conditions, whilst aging under more basic conditions led to the precipitation of iron oxyhydroxides. These findings may find application in forecasting the phase boundary conditions for Fe(III) precipitation in biogeochemical processes and provide an insight into the tackling of problems associated with the treatment and management of acid mine drainage.

Abstract: This study examined bioleaching of uranium ore at different acid concentrations by a novel consortium culture combined with both mesophilic and moderately thermophilic acidophiles containing 4 species of bacteria and 1 species of fungus. Four plastic buckets were set up with uranium minerals at room temperature (about 27-32°C) at different acid concentration (6g/l and 15g/l) for acidification and initial pH of 1.6, 1.8 and 2.1 for bioleaching, respectively. Results showed that from a point of application in commercial uranium bioleaching, higher acidified concentrations of acid can shorten the duration and working cycles of uranium recovery, and a higher initial pH in bioleaching stage can reduce the usage of acid.

Abstract: The paper describes the evaluation of a new mixer system developed in conjunction with SPX Process Equipment for the BIOX® process. Five different impeller combinations were tested with a Lightnin A315 A340 combination given the best results. With this combination the overall power per unit were reduced and less air were injected into the test reactors and still obtain the same and even better oxygen mass transfer compared to the commercially used A315 impeller.