Pyrite Particles Research Articles

Interaction of U(VI) with pyrite, galena and their mixtures: a theoretical and multitechnique approach

Pyrite and/or galena particles previously conditioned with U(VI) at pH 6 have been characterized by micro-Raman spectrometry, voltammetry, scanning electron microscopy and high resolution X-ray photoelectron spectroscopy. U3O8 is first formed on the sulphide surfaces via a redox process, then, if an excess of U(VI) remains in solution it is sorbed as UO3 and shoepite. Galvanic phenomena occur when the minerals are in mixture in a medium containing U(VI): galena particles are oxidized whereas U(VI) is reduced at the pyrite particle surface. The maximum amounts of fixed uranium are 0.4 mmol/g for pyrite and 0.1 mmol/g for galena and the 50:50 pyrite:galena mixture.

Identification of pyrite using 57Fe Mössbauer spectroscopy in core sediments from Erhai Lake, SW China combined with a series of acidic pre-treatments

A method has been developed for analyzing pyrite quantitatively in the sediments of Erhai Lake in southwest China using 57 Fe Mossbauer spectroscopy combined with a series of acidic pre -treatment s. Following a washing with an alkaline solution (0.1N Na OH), t he sediment samples were successively treated using HCl, HF, and then HCl (65 °C). The residue s thus prepared w ere analyzed for pyrite using 57 Fe Mossbauer spectrometry. The presence of pyrite was also confirmed in the acidic residues of the sediment s using sulfur K -edge X -ray absorption near edge structure . This method can be used to measure pyrite in aquatic sediments, especially when the con cent ration of pyrite is very low and the particles of pyrite are small or the crystallinity is low, and even in amorphous status . In addition, v ertical variation s of pyrite cont ent s are positively correlat ed with organic matter and negative ly correlat ed with hematite, superfine paramagnetic ferric iron and sedimen ta tion rate in the cored sediment from the Erhai L ake . All these geochemical indicators may also reflect environmental change s in sedimenta ry conditions and diagenesis.

Response of rough and acute surfaces of pyrite with 3-D approach to the flotation

This study presents a new 3-D approach to determine the morphological properties of pyrite particles by Brunauer — Emmett — Teller (BET) nitrogen gas adsorption and Permaran methods. The obtained parameters, which are surface roughness and acuteness, were correlated with the floatability of those mineral particles. The flotation performances of the pyrite particles ground in different mills were also evaluated by a Hallimond tube. The results showed that lower roughness and acuteness values caused higher flotation recoveries for the pyrite particles considered.

Single Particle Microelectrodes for Electrochemical Analysis of Sulfide Flotation Processes

The true electrochemical characteristics of sulfides found in industrial processes are of interest and as a result a relatively simple technique has been developed to study fundamental electrochemical interactions of individual particles measuring less than 100 microns in diameter. Cyclic voltammetry with sulphide mineral microelectrodes has been carried out on sulphide particles hand-picked from the concentrate and tailings products of an auriferous sulfide ore floated in air and nitrogen. These particles were found to be exclusively pyrite for the +53 micron fraction. Experimental results show no prominent differences in the electrochemical response of these pyrite particles from different flotation products but it appears that particle shape effects can contribute to pyrite losses in the tailings product.

The influence of pyrite pre-oxidation on gold recovery by cyanidation

The influence of pyrite pre-oxidation in alkaline solutions on gold recovery by cyanidation from Twin Creek refractory gold ore in which pyrite was identified as the major sulfide mineral has been investigated with the aid of electrochemical measurements, leaching experiments, and direct analysis of reaction products for selected residues. It was found that gold recovery by cyanidation in bottle roll experiments mainly depended on the extent of pyrite pre-oxidation. The rate of pyrite oxidation in alkaline solutions measured by electrochemical measurements, including chronoamperometry and linear sweep voltammetry, increased with an increase in pH, potential, and temperature. All alkaline reagents used for the electrochemical measurements, NaOH, NH 4OH, Na 2CO 3 and Ca(OH) 2, showed a similar effect on pyrite oxidation kinetics. However, the results of alkaline pre-oxidation for pyrite of the Twin Creek refractory gold ore suggested that NaOH and Na 2CO 3/Ca(OH) 2 were superior to Ca(OH) 2. Without pre-oxidation, cyanide leachable gold was found to be only 20% which could be increased to 70% under appropriate pre-oxidation conditions. At the same time, cyanide consumption decreased from 2.5 kg/t ore to 1.5 kg/t ore. Selected residues after pre-oxidation and cyanidation were examined by X-ray diffraction. Backscattered electron images of pyrite particles in these residues were taken. The reaction products at the surface of pyrite particles were found to be iron-, silicon-, and calcium-bearing compounds with variable amounts of sulfur as determined by X-ray energy dispersion analysis. Additionally, some mineral fines, such as aluminum and/or potassium-bearing minerals, were found to be present at the partially oxidized pyrite surface.

Two-dimensional natural pyrite crystals and their formation

AbstractTwo-dimensional pyrite crystals (40–80 µm wide and 2–3 µm thick) and large thin crusts are reported from the mudstones from the Carboniferous coal basin in Poland. Crystals occur on a flat surface, originally probably a crack in the rock, and are composed of uniform particles (150–200 nm wide). A hypothetical pathway of the formation of 2D pyrite crystals is presented: (1) formation of pyrite particles (or monosulphide precursors) in the suspension introduced onto the surface of the crack, and forming a film with a smooth meniscus at the air/suspension interface on the rock substrate; (2) thinning of the suspension film due to the water loss, increase of particle concentration, and formation of the first monolayers; (3) growth leading to the formation of thin crystals complying with pyrite crystallography.

Pyrite oxidation by Acidithiobacillus ferrooxidans bacteria

The kinetic model of pyrite particle dissolution by the action of bacteria Acidithiobacillus ferrooxidans in a shaken Erlenmeyer flask was presented. The model agreed well with the experimental data for the extracted iron and the number of cells in the liquid phase. The specific growth rate of the adsorbed cells was evaluated (?A = 1,6 d-1) by fitting the experimental data to the model curve. Also, the relevance of the two proposed mechanisms for the bacterial dissolution of sulphide (direct and indirect) was discussed, indicating that the indirect one was dominant. The adsorption process of A. ferrooxidans to the pyrite surface was well correlated by a Langmuir type isotherm.

Sorption Process for Copper Recovery from Effluents of Mining Enterprises by Granulated Pyrite-Bearing Wastes

The sorption process is proposed for copper recovery from waste effluents of mining enterprises by applying the old condensed granulated pyrite-bearing concentrates with obtaining sulfide product of 4.5% in copper content, amenable to pyrometallurgical processing. Copper is precipitated on pyrite particles as a low-temperature modification of β-chalcosine. The sorption parameters are determined, the process flowsheet is developed, as well as technical and economical factors of “underdump” water treatment in the Sibai open pit are calculated.

Acid leaching and dissolution of major sulphide ore minerals: processes and galvanic effects in complex systems

AbstractThe kinetics and mechanisms of dissolution of the major base metal sulphide minerals, pyrite, chalcopyrite, galena and sphalerite in acidic (chloride) media have been investigated. Minerals were ground in air, then dissolved in air-equilibrated solutions at pH 2.5, while monitoring the redox potential. Solution samples were analysed by ICP-AES and HPLC, and surfaces of residual sulphides analysed using XPS. Dissolution of aerial oxidation products on pyrite particles in the first 15 min apparently led to a sulphur-rich surface, and was followed by slower dissolution of pyrite itself, driven by oxygen reduction, and resulting in net production of protons. Chalcopyrite dissolution resulted in a Cu, S-rich (near) surface layer, accompanied by net consumption of protons. Apparently incongruent dissolution of galena and sphalerite may reflect the formation of elemental S at the surface. The rates of dissolution of chalcopyrite, galena and sphalerite in the presence of pyrite were determined, respectively, as 18, 31 and 1.5 times more rapid than in single-mineral experiments. These data were consistent with galvanically-promoted mineral oxidation of the other sulphides in the presence of pyrite. In the case of galena, the experimental data suggested extensive release of Pb ions and development of a sulphur-rich surface during galvanically-promoted dissolution.

Mechanism of Oxidation of Pyrite, Chalcopyrite and Bornite During Flash Smelting

The oxidation processes of pyrite, chalcopyrite and bornite were studied under simulated flash smelting conditions. The influence of temperature, in the range from 733 to 1473 K and of oxygen partial pressure (3.5 and 21 kPa) on the degree of sulphide particle oxidation was determined. It was established that under the same conditions, the highest degree of oxidation was achieved for pyrite particles and the oxidation of bornite particles was the slowest process.It was established with electron probe microanalysis (EPMA) that migration of iron ions towards the reaction surface took place during sulphide particle oxidation on flash smelting. This process considerably influenced the path of phase transformations in the oxidizable particles.Based on the experimental results, a dependence has been found between the shape of reacted particle and the degree of particle phase transformation. Mechanisms have been proposed for pyrite, chalcopyrite and bornite oxidation in flash smelting, on the basis of results obtained.The adequacy of mechanisms proposed was tested by investigating the shaft product taken from the flash smelting furnace (Pirdop, Bulgaria) obtained when sulphide copper blend was smelted to a matte containing 55% of Cu.On a étudié les processus d’oxydation de la pyrite, de la chalcopyrite et de la bornite sous des conditions simulées de fusion flash. On a déterminé l’influence de la température, dans la gamme de 733 à 1473 K, et de la pression partielle de l’oxygène (3.5 et 21 kPa) sur le degré d’oxydation de particule de sulfure. On a établi que, sous les mêmes conditions, le plus haut degré d’oxydation est obtenu pour les particules de pyrite alors que l’oxydation des particules de bornite est le processus le plus lent.On a établi au moyen d’analyse par microsonde électronique (EPMA) que la migration des ions de fer vers la surface de réaction a lieu pendant l’oxydation de la particule de sulfure au moment de la fusion flash. Ce processus influence considérablement la route des transformations de phase des particules oxydables.Basé sur les résultats expérimentaux, on a trouvé une dépendance entre la forme d’une particule ayant réagi et le degré de transformation de phase de la particule. On propose des mécanismes d’oxydation de la pyrite, de la chalcopyrite et de la bornite dans la fusion flash, sur la base des résultats obtenus.On a évalué l’adéquation des mécanismes proposés en étudiant le produit de la cuve pris du four de fusion flash (Pirdop, Bulgarie) obtenu lorsqu’un mélange de sulfure et de cuivre était fondu en une matte contenant 55% de Cu.

Quantitative determination of modal content and morphological properties of coal sulphides by digital image analysis as a tool to check their flotation behaviour ☆

An efficient depression of coal sulphides in the flotation process means a healthier environment and may be essential for the sustainability of a coal operation. Nitric and ferric oxidative pre-treatment of coal pyrite have been tested to improve pyrite depression, and the results are compared with those from the process of raw, not pre-treated coal. The removal indexes point to nitric pre-treatment as the best, but depression is still low. The microscopic study of feed and products, coupled to Digital Image Analysis (DIA) in all the cases, provide important clues to understand the behaviour of pyrite, which can be related to quantitative parameters, such as the exposition ratio (ER), and to qualified interpretation of the textures. Pyrite shows in the first float an unexpected hydrophobic behaviour, which is due to its occurrence as framboids, or porous particles which may be intergrown with organic matter and behave as coal. In general, the flotation results can be predicted from the DIA-data, e.g. depression of liberated pyrite into the tailings, increased by oxidative pre-treatments by 300% (ferric) or by >400% (nitric); or concentration of middlings with lower pyrite ER in the floats. DIA is an efficient tool to obtain some important quantitative informations which otherwise would be inaccessible (e.g. the morphological data on >1,000,000 pyrite particles for this study), and its use should be enhanced to check ore processing.

Evolutions of structure, composition and optical absorption behavior of pyrite films formed by sulfurating iron

The crystal structure, crystallite morphology, film composition and absorption properties were investigated for the pyrite films sulfurated from iron films. The pyrite particles nucleate mainly from the transitional phases of iron sulfides formed in the films during 673 K sulfurating while the pyrite particles nucleate directly from the iron bisulfides formed in the films during 773 K sulfurating. There are higher sulfur contents and more obvious grain propagation in the film sulfurated at 773 K than in that sulfurated at 673 K. By prolonging sulfuration time at 673 K, the optical absorption edge tends to increase and approaches the ideal value as sulfurated over 20 h. Low absorption edges exist in the films sulfurated at 773 K.

Structural, optical and electrical properties of polycrystalline pyrite (FeS 2) films obtained by thermal sulfuration of iron films

Iron films deposited by magnetron sputtering were annealed in 80 kPa sulfur vapor at 673 and 773 K for different times. The structural, optical and electrical properties were determined. Pyrite particles formed at 673 K reveal an aggregate morphology evolved from some transitional iron sulfides. With increasing annealing time, the crystallites become distinguishable and the aggregate morphology tends to disappear. The pyrite grains formed at 773 K have more uniform distribution and show more obvious propagation with annealing time than those formed at 673 K. The values of electrical resistivity of the films prepared at both temperatures and optical absorption edge of the film prepared at 673 K significantly increase with annealing time. The films prepared at 673 K generally have higher optical absorption edges, lower electrical resistivity, higher carrier concentration and lower charge mobility than those prepared at 773 K. Film bulk integrity, residual iron amount and grain boundary area could be considered as the factors responsible for the film property changed with annealing temperature and time.

Characterisation of sphalerite and pyrite flotation samples by XPS and ToF-SIMS

The surface analytical techniques of X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) have provided information on the type and concentration of species on the surface of sphalerite and pyrite particles in flotation concentrate and tail samples, but also on their distribution on each particle and across particles of different sizes. From this surface analytical study, a more accurate interpretation of the flotation results of sphalerite and pyrite minerals in a mixed mineral system could be made as a function of the concentrations of copper sulphate activator and xanthate collector, and particle size. In particular, it was found that sphalerite particles reporting to the concentrate are larger in size and contain less iron hydroxide on their surface than particles reporting to the tail. As for the pyrite particles, their lower recovery than the sphalerite particles is the result of a larger proportion of iron hydroxide on their surface inhibiting copper and collector adsorption.

In situ capping design of a pyrite cinder pile in the St. Lawrence river for metal containment

AbstractA pile of pyrite cinders discharged from a former manufacturing facility rest upon the bottom of the St. Lawrence River adjacent to Clark Island. In situ capping was the selected remedy to control both the fine particle resuspension that produced a red mud cloud in the water, commonly formed on windy days, and the soluble metals concentrations originating from the pyrite pile. Metal mass balances around the pile allowed estimates of the pre‐capping release rates. Elevated concentrations above the pile were observed for eight metals; these included iron, lead, mercury, selenium, arsenic, copper, cadmium, and zinc. After iron, the highest concentration in the pyrite particles were cadmium and zinc present in the 1,000 mg/kg range. Mercury was the lowest at the 10 mg/kg level in the pyrite solids. For iron the soluble release rate was estimated to be 0.08 g/s, and the particle release was 0.8 to 1.2 g/s. A 30 cm cap consisting of particles 19 to 40 mm in diameter is proposed for the site. Its placement covers a ten‐hectare area and is expected to isolate the fine pyrite particles and prohibit their resuspension into the water column. Design estimates of steady state flux reduction efficiencies range from a low of 99.21 percent for iron to a high of 99.96 percent for copper. Breakthrough times to achieve these steady state flux reductions range from 100 to 3,800 years and metal porewater concentrations at 5 cm below the cap surface are estimated to be reduced by 83 percent. Although soluble metals will continue to be released from the pile zone, the flux of all the metals will be significantly reduced. © 2002 Wiley Periodicals, Inc.

Application of numerical modelling for prediction of the influence of power density on microwave-assisted breakage

The influence of electric field strength on the microwave treatment of ore is elucidated. The ore consisted of a microwave-absorbing mineral in a low-absorbing matrix, and the influence of electric field strength was assessed by numerical simulation. Simulations were undertaken using finite difference modelling techniques for a theoretical 15×30 mm sample of calcite host rock containing 10 vol.%, 1-mm 2 particles of pyrite. The simulations modelled the microwave heating, thermal conduction, expansion, thermally induced fracturing and strain softening and, finally, uniaxial compressive strength to predict the effect of microwave heating on the strength of the ore material. Standard correlations were then used to develop specific comminution energy verses t 10 relationships for the treated and nontreated samples. It is shown that microwave power density is vital to the fracturing of the rock, and it is suggested that by utilising high power densities, the microwave fracturing of rock to reduce grinding energy requirements may be economically viable.

In situ sulfur K-edge X-ray absorption near edge structure of an embedded pyrite particle electrode in a non-aqueous Li +-based electrolyte solution

Changes in the composition of embedded pyrite (FeS 2) particle electrodes in 1 M LiClO 4 propylene carbonate solutions as a function of the applied potential have been examined in situ by S K-edge fluorescence X-ray absorption near edge structure (XANES), using a specially designed cell that minimizes attenuation of low energy X-rays. Pyrite electrodes that had been scanned from 3.0 V versus Li/Li +, i.e. close to the open circuit voltage, down to 1.0 V (fully discharged state, i.e. 4e −-reduction) and then half recharged (2e −-reoxidation) by scanning the potential in the positive direction up to 2.2 V versus Li/Li +, revealed features consistent with the presence of Li 2FeS 2, in agreement with in situ Fe K-edge results reported earlier by this research group. Moreover, only subtle changes were discerned between the in situ S K-edge XANES of the half-, and fully-recharged electrodes. This close resemblance may reflect similarities between the spectral signatures of Li 2FeS 2 and Fe 1− x S (pyrrhotite), which is the main product of the discharge reaction. Evidence for the formation of elemental sulfur and Li 2S, which are believed to be minor products of the reaction, was obtained from analysis of the first differential S XANES and selected difference spectra. The compositional variations of the embedded pyrite particles throughout the course of the electrochemical processes occur in the presence of a persistent sulfate coating.

The low-potential hydrophobic state of pyrite in amyl xanthate flotation with nitrogen

Research on the low-potential hydrophobic state of pyrite, with potassium amyl xanthate (PAX) as collector, is reported to help explain and understand the fundamental aspects of the N 2TEC flotation process, which was originally developed for the improved recovery of gold from refractory auriferous sulfide ores. Typically in the N 2TEC process, air is replaced by nitrogen as the flotation gas, and potassium amyl xanthate is used as collector for the reactive auriferous pyrite particles. The first N 2TEC flotation process was commissioned at Lone Tree in Nevada in March 1997 and has been in operation since that time. On the basis of electrochemically controlled contact angle measurements, the low-potential, low-pH hydrophobic state of pyrite has been examined as a function of flotation variables such as pH, gas-phase composition, collector concentration and pyrite potential.

Statistical comparison of hydrophobic and hydrophilic species on galena and pyrite particles in flotation concentrates and tails from TOF-SIMS evidence

A comparison of the amount of collector sodium diisobutyl dithiophosphinate (DBPhos) adsorbed on the surface of galena and pyrite has been investigated by time of flight secondary ion mass spectrometry (TOF-SIMS). Statistical comparison of spectra from both galena and pyrite particles showed that there was approximately 12 times more collector on galena compared to pyrite. Galena particles that reported to the concentrate showed statistically less calcium, lead hydroxide and oxy-sulphur species on their surfaces compared to tail particles. The major contributions that assisted the flotation of galena were the presence of hydrophobic DBPhos and PbDBPhos. Reduced collector adsorption and increased hydrophilic species concentrations inhibited the flotation of pyrite.

X-Ray analysis of riverbank sediment of the Tisza (Hungary): identification of particles from a mine pollution event

A serious heavy metal pollution of the Tisza River occurred on March 10, 2000, arising from a mine-dumping site in Romania. Sediment samples were taken from the main riverbed at six sites in Hungary, on March 16, 2000. The objective of this work was to distinguish the anthropogenic and crustal erosion particles in the river sediment. The samples were investigated using both bulk X-ray fluorescence (XRF) and thin-window electron probe microanalysis (EPMA). For EPMA, a reverse Monte Carlo method calculated the quantitative elemental composition of each single sediment particle. A high abundance of pyrite type particles was observed in some of the samples, indicating the influence of the mine dumps. Backscattered electron images proved that the size of particles with a high atomic number matrix was in the range of 2 μm. In other words the pyrites and the heavy elements form either small particles or are fragments of larger agglomerates. The latter are formed during the flotation process of the mines or get trapped to the natural crustal erosion particles. The XRF analysis of pyrite-rich samples always showed much higher Cu, Zn and Pb concentrations than the rest of the samples, supporting the conclusions of the single-particle EPMA results. In the polluted samples, the concentration of Cu, Zn and Pb reached 0.1, 0.3 and 0.2 wt.%, respectively. As a new approach, the abundance of particle classes obtained from single-particle EPMA and the elemental concentration obtained by XRF were merged into one data set. The dimension of the common data set was reduced by principal component analysis. The first component was determined by the abundance of pyrite and zinc sulfide particles and the concentration of Cu, Zn and Pb. The polluted samples formed a distinct group in the principal component space. The same result was supported by powder diffraction data. These analytical data combined with Earth Observation Techniques can be further used to estimate the quantity of particles originating from mine tailings on a defined river section.