Papers by Keyword: Pyrite

Abstract: Reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂), superoxide (O₂^-) and hydroxyl radicals (OH^.) are known to be formed on the surface of metal sulfides in aqueous solution under oxic and anoxic conditions. Consequently bacteria which have not been adapted to their presence are metabolically inhibited [1], presumably due to the presence of these ROS. Pyrite-grown cells of Acidithiobacillus ferrooxidans^T, in contrast to iron (II)-grown cells, were able to oxidize iron (II)-ions or pyrite after 24 h starvation and contact with 1 mM externally added H₂O₂. In this study, similar results were obtained with Acidiferrobacter sp. SPIII/3. However, Acidithiobacillus ferrivorans SS3 showed the highest tolerance towards contact with H₂O₂, while Leptospirillum ferrooxidans DSM 2391 was most sensitive. Similar results were obtained after exposure to defined doses of gamma radiation, which cleaves water molecules and generates ROS. In this study members of the three aforementioned genera of mineral-oxidizing bacteria were compared regarding their ability to survive, colonize pyrite and to oxidize iron (II)-ions after exposure to different concentrations of H₂O₂. Pyrite colonization was studied after exposure to endogenous ROS formed on pyrite or after external addition of H₂O₂ using confocal laser scanning microscopy (CLSM).

Abstract: Ferric sulfate is a very useful reagent for mineral leaching and metal recovery. Ferric sulfate may be used as an oxidative leaching agent for uranium, zinc, copper, nickel and other ores. Ferric ion is a modestly strong oxidant. Similarly, the use of ferric co-precipitation to stabilize arsenic, selenium and other species is in wide use. The demand for ferric sulfate for this application is increasing. Pyrite and pyrrhotite represent minerals that are widely available as sources of soluble iron to provide ferric sulfate for leaching and for iron co-precipitation. The use of biological processes for oxidation of pyrite is well established. However, the common goal is to use biological oxidation to liberate a valuable material (eg. Gold locked in arsenopyrite or pyrite). Much less attention has been paid to production of soluble iron for leaching of other minerals or for use as a precipitant. The use of chemical processes such as atmospheric and pressure oxidation may also be used to generate ferric sulfate from iron sulfide minerals. In this paper the use of biological and chemical processing for production of ferric sulfate will be reviewed and discussed.

Abstract: Refractory sulfide ores are ubiquitous resources of gold around the world. It was demonstrated that biooxidation pretreatment of refractory whole ores could be conducted in heaps. The effectiveness of column biooxidation of off-balance gold ores from Bakyrchik and Bolshevik deposits (northeast Kazakhstan) containing pyrite and arsenopyrite was examined in the laboratory. Bakyrchick ore contained 1.5% of pyrite, 3% of arsenopyrite and 4.5 g/t of gold. Bolshevik ore contained 1% of pyrite, 1% of arsenopyrite and 10.7 g/t of gold. The recovery rates of gold from the Bakyrchik and Bolshevik ores by direct cyanidation were 4.5% and 8.2%, respectively. Representative samples of each ore were processed in air-lift percolators. A bioleaching experiment was performed in duplicate. The enrichment culture was obtained from the pyrite flotation wastes and used as an inoculum. Bioleaching was conducted for 60 days at ambient temperature (20-25°C). The recovery rates of gold from the bioleaching residues of Bakyrchik and Bolshevik ores by cyanidation were 21.0% and 48.5%, respectively. The results obtained in the present work may be used to estimate perspectives of heap bio-oxidation for the recovery of gold from these sulfide ores.

Abstract: An in situ characterization has been carried out for several active systems (sulfuric acid, ferric iron, 9k medium and bioleaching solutions) to investigate the bioleaching process of natural pyrite using electrochemical noise (ECN) technique. Spectral noise impedance spectra obtained from power spectral density (PSD) plots for the different systems were compared. It has been observed that the bioleaching system obtained the lowest noise resistance Rsn 0.101MΩ. The reaction mechanism was proposed based on experimental data analysis. The bioleaching process of natural pyrite has been identified as the main function of bio-battery reactions, which distinguishes from the chemical oxidation reaction for the ferric ion and 9k solutions.

Abstract: The experimental results of flotation of pure tetradymite and pyrite show that HL-1 is an efficient collector for tetradymite flotation. Comparing to the butyl xanthate, HL-1 has stronger collector ability and higher selectivity. It solves the common problem of the separation of tetradymite and pyrite. The difference of adsorption quantity is consistent with results of the single mineral flotation test. Through the measurements of adsorption, zeta-potential, and FTIR spectral analysis, the flotation mechanism of tetradymite with HL-1 has been discussed. It is concluded that the adsorption of HL-1 on tetradymite surface is chemical adsorption through the dithiocarbamate group of the collector chelating the Bi (III) of tetradymite to form metal complex.

Abstract: Contact angle measurement is a simple and quick method that expresses the surface wettability. Resulting values vary and depend on many factors that significantly affect the interpretation of results. In this paper a set of seventeen samples from different deposits with different genesis were subjected to a statistical evaluation, to determine the optimal number of measurements needed to obtain the desired standard deviation.

Abstract: Pyrite composition characteristics can reflect its physical and geochemical formation backgrounds, also are the important parameters to further discuss the genesis of minerals and ore deposit. In this paper, major and trace elements of 13 pyrite samples from Dabaoshan polymetallic ore deposit were analyzed using EPMA, the results suggest that S/Fe atomic ratio of pyrite in dacitic porphyries were similar with reference standard value, however that ratio in granodioritic porphyries is 2.051, which is slightly higher than the reference standard value; trace elements Cu, Zn and Pb show the characteristic of high oxygen fugacity settings, the Co content in pyrite was significantly lower than that of Ni, and Co/Ni is far less than 1, all the evidences show the characteristics of sedimentation-reformation ore deposit.

Abstract: The application of microwave technique in the roasting pyrite which contained little arsenic was described. The characteristics of microwave absorption of pyrite were investigated. The results indicated that pyrite was a good absorbent of microwave and heated rapidly to high temperature by microwave flied in a short time, causing decomposition and oxidization to removal the sulfur and arsenic. The effects of microwave irradiation time and sample mass on the removal efficiencies of sulfur and arsenic with microwave power of 4 kW and 6 kW were investigated. The big microwave power could shorten the time for removal of sulfur and arsenic. Finally iron concentrate contained 64.52% Fe, S<0.1%, As<0.094% were obtained.

Abstract: Adsorption of sodium cyanide on pyrite particle surface was studied. And influences of adsorbing time, dosage of pyrite, and pH on adsorbing effect were investigated. IR spectra, SEM, EDS and Element Area Scanning of samples before and after adsorption were measured. Results showed that adsorption of sodium cyanide on pyrite particle surface is a fast adsorbing process. As soon as adsorbing time is 1 min, adsorbing equilibrium is reached. At the condition of concentration of NaCN 24mg/L, adsorbing time 5min, and stirring rate 2000r/min, when dosage of pyrite particles is 5g/L, adsorbing rate is up to 80%, and at the time adsorbing capacity is the largest, 381.4mg/g. When pH is within 8.0-11.0, pH has little influence on adsorbing effect. IR and EDS results showed that at the particle range of-45μm is 93%, the surface of pyrite particles is easy to be oxidized and hydroxylated. S atoms on the surface of pyrite lattice are oxidized, while Fe atoms on the surface of pyrite lattice are hydroxylated. There exists hydrogen bond function between CN^- and OH^-, and there exists monomolecular chemical bond function between CN^- and pyrite. And-Fe (CN)_n^m-(n<6) is produced on the surface of pyrite, thus the superficial properties of pyrite is changed.

Abstract: In the bioleaching of mineral sulphides under the catalytic action of At. ferrooxidans, ferrous ion oxidation and sulfides/sulfur solubilization uses oxygen as the final electron acceptor. Also, under anaerobic conditions, At. ferrooxidans can alternatively catalize the oxidation of sulfur or reduced inorganic sulfur compounds (RISC) using ferric iron as electron acceptor [1]. The formation of Fe (II) from pyrite and covellite in the ferric anaerobic bioleaching with A. ferrooxidans, has been studied and well documented [2,3]. The requirements of ferric iron as electron acceptor for the anaerobic growth of At. ferrooxidans on elemental sulfur has been demonstrated and a linear relationship was obtained between the concentration of ferrous iron accumulated in the cultures and the increase in cell density [4]. It has been suggested a possible role in the solubilization of metals from sulfide ores involving the participation of the enzyme sulfur (sulfide): Fe (III) oxidoreductase [5]. Bacterial growth of At. ferrooxidans has also been reported in the oxidative anaerobic respiration using hydrogen as electron donor and ferric iron as electron acceptor [6]. Anaerobic reduction of ferric iron and ferrous iron production from pyrite by At. ferrooxidans has been demonstrated [2], however there are no reports about bacterial growth using this mineral. In this work, we studied the anaerobic bioleaching of pyrite with the aim to determine if At. ferrooxidans is capable to anaerobic growth on pyrite using ferric iron as electron acceptor.