Pyrite Particle Size Research Articles

Catalytic and galvanic effects of pyrite on ferric leaching of sphalerite

The catalytic and galvanic effects of pyrite on the dissolution kinetics of a zinc sulfide concentrate in an acidified ferric sulfate medium were assessed. The effects of particle size, oxidant concentration (ferric ion), and amount of pyrite added with respect to the original amount of zinc concentrate was explored, while temperature (70°C), hydrogen potential (pH=1.0) and agitation speed (600rpm) of the leach solution were held constant. A process based on the galvanic coupling between pyrite and sphalerite at solution potentials above 500mV to ensure rapid and complete sphalerite dissolution in a ferric sulfate medium is proposed. As a result, the highest zinc extraction in the shortest possible time was obtained through minimizing the formation of a passivating film, which inhibits further reaction, and by a synergetic effect between pyrite and sphalerite. The rate of zinc leaching was considerably improved by doping with pyrite in the presence of Fe3+. The results have demonstrated that it was possible to achieve 98.9% zinc extraction with doping pyrite in 6h and 85% zinc extraction without pyrite in 7h, both results being for a fine grain size. Ferric leaching reached 75% Zn extraction with doped pyrite and 70% without it, both in 7h using a coarse grain size. Scanning electron microscopy (SEM) images show a passivating layer on the sphalerite surface after ferric leaching without pyrite, while in presence of pyrite this layer was not observed and the pyrite surface was not attacked. The galvanic interaction between pyrite and sphalerite particles can be explained by the difference between their Fermi energies and the electrochemical potential of the solution. During this process pyrite remains mostly unleached, acting as a redox catalyst (electron-accepting) for sphalerite (electron-donating) dissolution. This diminishes the typical passive behavior of sphalerite in a ferric solution enhancing considerably the kinetics of sphalerite. This confirms that the difference between the rest potentials of pyrite and sphalerite is the driving force that improves zinc dissolution. For an industrial hydrometallurgical operation, using an appropriate sphalerite-pyrite concentrate does not necessarily represent a significant cost because the ore contains both sulfides.

Synthesis, characterization, and application of pyrite for removal of mercury

Abstract Pyrite has been demonstrated to be an excellent adsorbent for removing mercury in many studies. But most of them used natural pyrites that were grinded to micro-scale size or even larger. This study investigated methods to produce near nano-scale pyrite particles. Iron (III) chloride and sodium hydrosulfide were used as the source chemicals to synthesize pyrite. Several aging methods, including hydrothermal, ultrasonic and microwave irradiation, were studied in order to reduce the pyrite particle size. SEM/EDS and TEM/EDS analysis showed that microwave irradiation was the most effective way to produce small pyrite crystals close to the nano-scale. Results of batch kinetic experiments revealed that 0.1 g/L pyrite was able to remove about 90% Hg(II) in the first 5 min and all Hg(II) has been removed after 12 h, although some release of mercury to the solution was observed after 5 min. The release could be due to the formation of soluble Hg complexes or by other reactions that tended to increase pH. The mercury loading batch tests showed that the capacity of pyrite for adsorption of Hg(II) could reach 900 μmol Hg(II)/g FeS2. The presence of salts (0.01 M sodium sulfate and sodium nitrate) decreased the removal efficiency.

Heterogeneous Fenton process by natural pyrite for removal of a textile dye from water: Effect of parameters and intermediate identification

The ability of natural pyrite particles in the degradation of C.I. Reactive Orange 29 (RO29) solution by heterogeneous Fenton (pyrite/H2O2) process was studied. X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy analysis were performed to characterize the pyrite particles. The decolorization efficiency of the RO29 by pyrite/H2O2 process was obviously influenced by pyrite particle size, suspension pH, initial concentrations of H2O2 and RO29, and pyrite dosage. Decolorization efficiency of 94.4% was resulted at the initial RO29 concentration of 10 mg/L, H2O2 concentration of 3 mM, catalyst dosage of 3 g/L, pH of 2 and reaction time of 120 min. Decolorization efficiency through pyrite/H2O2 process was not decreased significantly even after five successive cycles because of the low release (0.6 mg/L) of pyrite iron in each decolorization cycle. Plausible degradation pathway of RO29 was proposed by using gas chromatography–mass spectroscopy analysis.

Degradation of p-chloroaniline by pyrite in aqueous solutions

The degradation of p-chloroaniline (PCA) in aqueous solution by pyrite was studied. The effects of different parameters such as pyrite particle size, pH and pyrite dosages on the degradation of PCA were examined in batch experiments. The rate of PCA degradation increased with increased pyrite dosage and with decreased pyrite particle size from 20 to 200 mesh in aqueous solutions. Results showed that PCA degradation accelerated with lowering initial pH. In addition, the efficacy of PCA degradation by pyrite was higher with oxygen presence as compared to without oxygen. The role of reactive oxygen species (ROS) produced by pyrite in the system was also investigated. In particular, superoxide radical (O2−) produced by pyrite was instrumental in producing more H2O2, which favored the degradation reaction. The results of this study give new insights into the mechanism of the reactivity of pyrite toward environmental contaminants.

Study on the purification property of pyrite and its spectra on the processing of metal-bearing wastewater

The purification property of pyrite was discussed by using in situ attenuated total reflection-Fourier transform infrared spectroscopy. Results showed that there might be dissolution–adsorption precipitation equilibrium of heavy metals on the surface of pyrite, which is dependent on the surface oxidation of pyrite and the neutralization reaction of carbonate within pyrite. If there was excessive carbonate within pyrite, the “dissolution” of metals would be less than that of the “adsorption precipitation,” making pyrite exhibit its purification property. Based on this property, pyrite was used to process simulated wastewater containing Pb2+, Hg2+, Cd2+, Cr(VI) and Cu2+. Results showed that the efficiencies of metal removal exceeded 96%. In addition, reflectance spectroscopy and absorption spectroscopy were also utilized to investigate the simulated metal-bearing wastewater treatment process. Analysis by diffused reflectance infrared Fourier transform spectroscopy confirmed that the superficial hydroxyl groups in pyrite reacted with metal ions during the wastewater treatment process. Reflectance spectroscopy in the visible region was used to characterize the variation in particle size and specific surface area of pyrite during the wastewater treatment process, which explained its increasing activity when reutilized. Further, analysis by absorption spectroscopy and X-ray photoelectron spectroscopy indicated that the process involved when using pyrite for the treatment of Cr(VI)-containing wastewater was an adsorption–precipitation process.

Effect of grinding parameters on the rheology of pyrite–heptane slurry in a laboratory stirred media mill

The influences of wet ultra-fine grinding parameters on the rheological behavior of pyrite–heptane slurry in a laboratory stirred media mill were investigated with solid concentration, dispersant dosage, grinding time and carbon numbers of organic acid as dispersant. The results reveal that when the solids concentration is increased from 64 wt% to 79 wt%, the rheological behavior of slurry with 1 wt% of stearic acid transforms from Bingham characteristic to the pseudoplastic one with a yield stress. The Casson model fits well for the experimental data. And the apparent viscosity of the pyrite–heptane slurry increases exponentially with increase solid concentration at a given shear rate. The increase of viscosity is propitious to reduce the particle size of pyrite. When the solid concentration is 64 wt%, stearic acid is superior to octadecanol for the reduction of the slurry viscosity, and the slurry with 1 wt% of stearic acid possesses the best flowability. The extrapolated Bingham yield stress with dispersant almost stays constant when the dosage is over 2 wt%. Besides, the rheological behavior and particle size are also related to the grinding time and carbon numbers of organic acids as dispersant.

Dissolution kinetics of natural FeS 2 in carbon tetrachloride and water-carbon tetrachloride media saturated by chlorine

The dissolution kinetics of natural pyrite samples in Cl 2-saturated carbon tetrachloride and water-carbon tetrachloride media have been investigated. The effects of pyrite particle size, reaction time, temperature, stirring speed and water-to-carbon tetrachloride ratio were studied. The dissolution rate of pyrite in these media increased with increase in temperature and decrease in particle size. In water-carbon tetrachloride medium, the rate was independent of the stirring speed. However, in carbon tetrachloride medium alone, the increase in the stirring speed significantly increased the dissolution rate. The experimental data were analyzed on the basis of unreacted shrinking core model. It has been found that the dissolution is controlled by diffusion through the ash layer in carbon tetrachloride and that it is chemically-controlled in water-carbon tetrachloride medium. The activation energies for the diffusion- and the chemically-controlled steps were 32.3 and 22.3 kJ mol −1, respectively.

Kinetics of pyrite oxidation in aqueous suspension by nitric acid

The kinetics of pyrite oxidation in aqueous suspension by nitric acid has been investigated. The effects of pyrite particle size (75–90, 106–125, 180–250, 250–425, 425–850 μ), reaction time (0–12 600 s), nitric acid concentration (5–30° by weight), temperature (13–80°C), and speed of stirring (5–20 s −1), were studied. The sulfur in the FeS 2 was oxidized to sulfate and elemental sulfur during the leaching. Most of the oxidized pyritic sulfur was found in the solution as sulfate. All of the elemental sulfur was oxidized to sulfate as the reaction progressed to completion. The leaching rate was independent of stirring speed. The kinetic parameters were determined based on the shrinking core model. The apparent activation energies for the leaching of pyrite were found to be 52 kJ mol −1 in the 25° HNO 3 and 25 kJ mol −1 for the temperature range 13–40°C and 28 kJ mol −1 for temperature range 50–80°C in the 10% HNO 3.

PYRITE PARTICLE SIZE DISTRIBUTION AND PYRITIC SULFUR REDUCTION IN CRUSHED COALS: A PRELIMINARY REPORT

ABSTRACT Six bituminous coals were ground to 28, 100, and 400 mesh x 0, and examined by optical automated image analysis (AIA) to estimate their pyrite particle size distributions and degree of liberation (DOL). These data were used to determine the feasibility of estimating specific-gravity-based pyritic sulfur reduction by AIA methods. Preliminary results indicate that further research is warranted. A review of the progress is presented.

Kinetics of the chlorination of pyrite in aqueous suspension

The kinetics of chlorination of pyrite in aqueous suspension have been investigated. The effects of pyrite particle size (106–125, 125–150, 150–180, 180–250, 250–425 μm), reaction time (0–14400 s), temperature (13–60°C), and speed of stirring (5–20 s −1) were studied. The experimental data were analyzed on the basis of the unreacted shrinking core model. The rate-controlling step was found to be the chemical reaction between chlorine and pyrite for the temperature range 13–35°C, but the diffusion of chlorine through the fluid film for the temperature range 40–60°C. The activation energies for the chemical- and diffusion-controlled cases were calculated as 36.7 and 3.7 kJ mol −1 respectively.

Determination of pyrite particle size distribution in coal by merging analyses of size distributions at different microscopic magnificiations: Optimum allocation of number of observations to different size groups

In the characterization of particle size distributions, it is often useful to measure the size of smaller particles using optical magnifications that are higher than the magnifications used to measure relatively large particles. This results in an examination of a smaller area in the sample specimen. This paper considers the question of how many fields should be microscopically analysed at different k magnifications to arrive at an efficient estimate of the mean particle diameter (by count). The resolution of this question depends upon the following three factors: 1, the relative sizes of areas scanned under different magnifications; 2, the expected number of particles of a given size range per optical field under a given magnification; and 3, the standard deviation within each size range scanned under the same magnification. A formula is provided for the optimum allocation of field counts at each magnification when measuring particle sizes in various size ranges. Numerical examples are also provided. The discussion in this paper is illustrated by reference to the measurement of pyrite particle sizes in a given coal. It is well known that the size distribution of pyrites in coal influences the potential amount of sulphur reduction that can be achieved by physical coal cleaning methods.

Statistical relationship between pyrite grain size distribution and pyritic sulfur reduction in Ohio coal

This paper presents a statistical relationship between the pyrite particle size distribution and the potential amount of pyritic sulfur reduction achieved by specific-gravity-based separation. This relationship is obtained from data on 26 Ohio coal samples crushed to 14 × 28 mesh. In this paper a prediction equation is developed that considers the complete statistical distribution of all the pyrite particle sizes in the coal sample. Assuming that pyrite particles occurring in coal have a lognormal distribution, the information about the particle size distribution can be encapsulated in terms of two parameters only, the mean and the standard deviation of the logarithms of the grain diameters. When the pyritic sulfur reductions of the 26 coal samples are related to these two parameters, a very satisfactory regression equation ( R 2 = 0.91) results. This equation shows that information on both these parameters is needed for an accurate prediction of potential sulfur reduction, and that the mean and the standard deviation interact negatively insofar as their influence on pyritic sulfur reduction is concerned.

Observations on low-temperature oxidation of minerals in bituminous coals

Mineral matter in three naturally weathered coals from Pennsylvania strip mines and in two laboratory-oxidized coals has been characterized by 57Fe Mössbauer spectroscopy, scanning electron microscopy and other techniques to determine mineralogical trasnformations that occur in coals during weathering. Pyrite was found to be the most readily oxidized mineral, forming a variety of iron sulfates initially and geethite eventually. The iron sulfates formed were different in the two laboratory-oxidized coals, despite identical oxidation treatments. Calcite disappeared from one calcite-rich coal with increasing oxidation, but was not replaced by an equivalent amount of gypsum. A severely weathered strip-mine coal was enriched in calcium, which was dispersed through the oxidized macerals. Extended X-ray absorption fine-structure spectroscopy indicated that this dispersed calcium was most likely present as salts of carboxylic acids. Siderite was suprisingly resistant to oxidation at room temperature. Less direct evidence indicates that clay minerals also take part in the alteration to some extent. The coals oxidized in the laboratory showed alteration behavior that differed in a number of respects from that of the strip-mine coals. For example, iron sulfates were much less common in the latter coals; also, the formation of geothite appeared to be controlled to a large extent by the pyrite particle size in the strip-mine coals, but not in the laboratory-oxidized coals. The oxidation of an individual pyrite grain is not only a function of general conditions (temperature, humidity, oxygen partial pressure), but also the immediate local (< 1 mm) chemistry, as a variety of iron sulfates were observed in the coals, often in close proximity. Also, assemblages of gypsum and goethite were observed in otherwise slightly oxidized coal, which indicates that the alteration of pyrite and calcite, when in close contact, proceeds most rapidly.

Evaluation of Pyrite Particle Size, Shape, and Distribution Factors

Abstract The microstructure of coal is determined and characterized by combined scanning election microscope-energy dispersive analysis techniques. Microstructural information on a micrometer-size scale is correlated with microchemical information developed by energy dispersive X-ray microanalyses to establish the presence and distribution of pyrite, the primary sulfur-bearing inorganic phase in coal. Other complementary analytic techniques are also used. This study evaluates particle size, shape, and distribution factors which bear on decisions to try to remove additional sulfide particles to reduce the sulfur content. Subsamples are obtained from complete channel samples or sources such as raw material prepared as appropriate to the major methods of coal conversion. Data from specimens from strip and shaft mines in Iowa provide the primary information to be reported. Conventional chemical analyses for these coals show an approximate range of 3-7 weight percent for total sulfur and 2-4.5 weight percent f...