Optimization of the use of carbon paste electrodes (CPE) for electrochemical study of the chalcopyrite

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Oxidation of chalcopyrite by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans in shake flasks

Chalcopyrite oxidation was evaluated with two acidophilic thiobacilli that are important in bioleaching processes. Acidithiobacillus thiooxidans in pure culture did not oxidize CuFeS2 but oxidized externally added S in the presence of CuFeS2. Acidithiobacillus ferrooxidans released Cu2+ and soluble Fe from chalcopyrite, and the time course lead to a gradual passivation of chalcopyrite whereby Cu2+ dissolution leveled off. Fe3+ acted as a chemical oxidant in CuFeS2 leaching and was reduced to Fe2+. Parallel bacterial re-oxidation of Fe2+ contributed to a high Fe3+/Fe2+ ratio and an increase in redox potential. Chemical oxidation of chalcopyrite was slow compared with A. ferrooxidans-initiated solubilization. X-ray analysis revealed new solid phases: (i) jarosite, found in solids from A. ferrooxidans cultures and in chemical controls that initially received Fe2+ or Fe3+, and (ii) S-0, found mostly in iron-amended A. ferrooxidans culture and the corresponding chemical controls. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

Effect of Na-chloride on the bioleaching of a chalcopyrite concentrate in shake flasks and stirred tank bioreactors

Oxidative dissolution of chalcopyrite at ambient temperatures is generally slow and subject to passivation, posing a major challenge for developing bioleaching applications for this recalcitrant mineral. Chloride is known to enhance the chemical leaching of chalcopyrite, but much of this effect has been demonstrated at elevated temperatures. This study was undertaken to test whether 100-200 mM Na-chloride enhances the chemical and bacterial leaching of chalcopyrite in shake flasks and stirred tank bioreactor conditions at mesophilic temperatures. Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and abiotic controls were employed for the leaching experiments. Addition of Na-chloride to the bioleaching suspension inhibited the formation of secondary phases from chalcopyrite and decreased the Fe(III) precipitation. Neither elemental S nor secondary Cu-sulfides were detected in solid residues by X-ray diffraction. Chalcopyrite leaching was enhanced when the solution contained bacteria, ferrous iron and Na-chloride under low redox potential (< 450 mV) conditions. Scanning electron micrographs and energy-dispersive analysis of X-rays revealed the presence of precipitates that were identified as brushite and jarosites in solid residues. Minor amounts of gypsum may also have been present. Electrochemical analysis of solid residues was in concurrence of the differential effects between chemical controls, chloride ions, and bacteria. Electrochemical impedance spectroscopy was used to characterize interfacial changes on chalcopyrite surface caused by different bioleaching conditions. In abiotic controls, the impedance signal stabilized after 28 days, indicating the lack of changes on mineral surface thereafter, but with more resistive behavior than chalcopyrite itself. For bioleached samples, the signal suggested some capacitive response with time owing to the formation of less conductive precipitates. At Bode-phase angle plots (middle frequency), a new time constant was observed that was associated with the formation of jarosite, possibly also with minor amount or elemental S, although this intermediate could not be verified by XRD. Real impedance vs. frequency plots indicated that the bioleaching continued to modify the chalcopyrite/solution interface even after 42 days. © 2013 The Authors.

Bacterial and chemical leaching of chalcopyrite concentrates as affected by the redox potential and ferric/ferrous iron ratio at 22 degrees C

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Oxidative dissolution of chalcopyrite by Acidithiobacillus ferrooxidans analyzed by electrochemical impedance spectroscopy and atomic force microscopy

The microbiological leaching of chalcopyrite (CuFeS2) is of great interest because of its potential application to many CuFeS2-rich ore materials. However, the efficiency of the microbiological process is very limited because this mineral is one of the most refractory to bacterial attack. Knowledge of bacterial role during chalcopyrite oxidation is very important in order to improve the efficiency of bioleaching operation. The oxidative dissolution of a massive chalcopyrite electrode by Acidithiobacillus ferrooxidans was evaluated by electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). A massive chalcopyrite electrode was utilized in a Tait-type electrochemical cell in acid medium for different immersion times in the presence or absence of bacterium. The differences observed in the impedance diagrams were correlated with the adhesion process of bacteria on the mineral surface. (C) 2004 Elsevier B.V. All rights reserved.

The effect of chloride ions and A. ferrooxidans on the oxidative dissolution of the chalcopyrite evaluated by electrochemical noise analysis (ENA)

It is believed that the dissolution of chalcopyrite (CuFeS2) in acid medium can be accelerated by the addition of Cl- ions, which modify the electrochemical reactions in the leaching system. Electrochemical noise analysis (ENA) was utilized to evaluate the effect of the Cl- ions and Acidithiobacillus ferrooxidans on the oxidative dissolution of a CPE-chalcopyrite (carbon paste electrode modified with chalcopyrite) in acid medium. The emphasis was on the analysis of the admittance plots (Ac) calculated by ENA. In general, a stable passive behavior was observed, mainly during the initial stages of CPE-chalcopyrite immersion, characterized by a low passive current and a low dispersion of the Ac plots, mainly after bacteria addition. This can be explained by the adhesion of bacterial cells on the CPE-chalcopyrite surface acting as a physical barrier. The greater dispersions in the Ac plots occurred immediately after the Cl- ions addition, in the absence of bacteria characterizing an active-state. In the presence of bacteria the addition of Clions only produced some effect after some time due to the barrier effect caused by bacteria adhesion. © (2009) Trans Tech Publications.

Potassium Leaching as Affected by Soil Texture and Residual Fertilization in Tropical Soils

Potassium (K) leaching is affected by soil texture and available K, among other factors. In this experiment, effects of soil texture and K availability on K distribution were studied in the presence of roots, with no excess water. Soils from two 6-year field experiments on a sandy clay loam and a clay soil fertilized yearly with 0, 60, 120, and 180 kg ha-1 of K2O were accommodated in pots that received 90 kg ha-1 of K2O. Soybean was grown up to its full bloom (R2). Under field conditions, K leaching below the arable layer increased with K rates, but the effect was less noticeable in the clay soil. Potassium leaching in a sandy clay loam soil was related to soil K contents from prior fertilizations. With no excess water, in the presence of soybean roots, K distribution in the profile was significant in the lighter textured soil but was not apparent on the heavier textured soil.

Effect of water-bath post-polymerization on the mechanical properties, degree of conversion, and leaching of residual compounds of hard chairside reline resins

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Gene expression modulation by chalcopyrite and bornite in Acidithiobacillus ferrooxidans

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Differential proteomic analysis of Acidithiobacillus ferrooxidans cells maintained in contact with bornite or chalcopyrite: Proteins involved with the early bacterial response

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Aplicação de técnicas eletroquímicas no estudo da dissolução oxidativa da covelita (CuS) por Thiobacillus ferrooxidans

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Nitrate role in basic cation leaching under no-till

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrochemical noise analysis of chalcopyrite carbon paste electrodes by Acidithiobacillus ferrooxidans

The electrochemical response of chalcopyrite was studied using electrochemical noise analysis (ENA). The assay was carried out under constant aeration using 30 mL in two electrochemical cells containing iron-free mineral salts solution. These cells were initially monitored for 56 hours, After 72 hours, 7.25x 10(10) cells mL(-1) of A, ferrooxidans strain LR were added in both cells and monitored until 128 h. Subsequent to this period, 0.927 mmol L-1 of silver ions and 400 mmol L-1 of chloride ions were added each one separately. Both conditions were monitored until 168 hours. According to results obtained, it was observed that Cl- ions addition induced an accelerated corrosion process. However, there is a tendency of the system to reach the stationary state due to repassivation of the electrodic surface. In the other side, the Ag+ addition contributed for the maintenance of the oxidant atmosphere, in spite of controversial effect caused by considerable variations in the R-n values, resulting in a instability in the chalcopyrite reactivity.

The effects of bacterial leaching on metal partitioning in sewage sludge

The partitioning of Mn, Al, Zn, Cu and Ti ions in municipal sewage sludge was investigated before and after bioleaching processes effectuated by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Oxidation reduction potential increase and pH decrease were obtained as a result of bacterial activity. A less pronounced and constant decrease was obtained with A. ferrooxidans, whereas A. thiooxidans presented a lag phase before a steep pH decrease. Metal solubilization was accomplished in experimental systems supplemented with energy source, Fe2+ for A. ferrooxidans and S-0 for A. thiooxidans. Solubilization efficiency differed for each metal except for Al, and was relatively similar for either organism. Metal partitioning was conducted using five-step sequential extraction procedure before and after the bioleaching. The results indicated that Zn and Mn ions were mostly associated with the organic fraction, whereas Cu, Al and Ti ions with the sulphide/ residue fraction. The bioleaching process caused prompt solubilization of metals mostly associated with the more labile fractions (exchangeable, adsorbed and organically bound metals), whereas those associated to the less labile ones (EDTA and sulphide/residue fractions) were exchanged towards more labile fractions.