Pyrite Leaching Research Articles

The electrochemistry of pyrite in chloride solutions

A detailed study of the anodic and cathodic behaviour of natural pyrite in acidic chloride solutions containing various oxidants has been conducted as part of an overall program on the fundamental aspects of the heap leaching of copper sulphide minerals.The stoichiometry of the anodic dissolution reaction depends on the potential in that it varies from less than 4F/mol Fe dissolved at potentials below 0.8 V(SHE) to 15F/mol Fe at potentials above about 1.0 V(SHE).The mixed potentials of pyrite in chloride solutions containing iron(III) are greater than those in the presence of copper(II) and both increase with agitation as a result of enhanced transport of iron(II) and copper(I) from the surface of the dissolving mineral. The mixed potentials are unaffected by the presence of dissolved oxygen confirming the low reactivity for the cathodic reduction of oxygen.The rate of anodic dissolution of pyrite in chloride solutions is independent of the acid and chloride concentration except at high chloride concentrations when the rate decreases slightly. The potential dependence of the anodic reaction roughly follows Tafel behaviour up to about 1.0 V but mechanistic conclusions are excluded due to the variable stoichiometry.Cathodic reduction of oxygen is some 30 times slower than that of 1 g/L iron(III). The reduction of copper(II) is also less significant in the leaching of pyrite due to the lower formal potential of the copper(II)/copper(I) couple than that of the iron(III)/iron(II) couple in concentrated chloride solutions.Comparative measurements have shown that pyrite will dissolve more slowly than chalcopyrite in chloride solutions and, this coupled to the low sulfate yield at low potentials, suggests that oxidation of pyrite as a source of heat in abiotic heap leaching is unlikely.

Pyrite oxidation with ozone: stoichiometry and kinetics

ABSTRACTOne of the most frequent causes of refractoriness in precious metals leaching is their occlusion or fine dissemination into a pyritic matrix. This study experimentally explores the acid leaching of pyrite with ozone, suggests the stoichiometry of the reaction, estimates its activation energy and defines the effect of the main variables on the leaching kinetics. The results of stoichiometry tests allow establishing that one mole of pyrite requires 7.7 moles of ozone to produce one mole of ferric ion and 2 moles of HSO4− ions. A decrease in the particle size, solution pH and solids’ concentration of the leaching system increases pyrite dissolution. The type of acid (nitric, sulphuric and hydrochloric) does not affect pyrite dissolution rate. Up to 60% of pyrite is dissolved when the optimal experimental conditions are employed (1 g pyrite (−25 µm), 800 mL of 0.18 M of H2SO4, 800 rev min−1, 1.2 L min−1 gas stream O2/O3 with 0.079 g O3 L−1 and 25°C). The apparent activation energy of the pyrite-ozone reaction is 14.92 kJ mol−1, and the absence of a passive layer on the pyrite surface and the linearity of the dissolution profiles suggest that the dissolution kinetics is controlled by the chemical reaction.

Origin and Geochemistry of Mine Water and its Impact on the Groundwater and Surface Running Water in Post-mining Environments: Zlatna Gold Mining Area (Romania)

In application at the Zlatna gold mining area (Apuseni Mountains, Romania), the correlation of water isotopes and geochemical data were successfully used to assess the genetic relationships between surface running water, groundwater and mine water, as well as to evaluate the mining effects on the surrounding environment after the cessation of mining operations. The majority of mine water sources display pH values between 4 and 5, i.e. acid mine water. The mine water characterized by slightly higher pH values (~6) interacts with ophiolitic rocks which have high pH buffering capacity. The neutral mine water (pH ~ 7) does not come into direct contact with reactive minerals, either because it is discharged from an exploration adit or because of the complete leaching of pyrite and other sulphides in old abandoned mining works. The later also shows low levels of heavy metals concentrations. Calcium is the dominant cation in mine water and in the majority of surface running water and groundwater sources, indicating the same mechanisms of mineralization. All mine water sources are $$\text{SO}_{4}^{2 - }$$ type and show very high $$\text{SO}_{4}^{2 - }$$ concentrations (6539 mg/l mean value). Surface and groundwater sources are classified either as $$\text{SO}_{4}^{2 - }$$ or as $$\text{HCO}_{3}^{ - }$$ type water. Linear correlation between δD and δ18O values indicates that all water sources belong to the meteoric cycle. Low δD and δ18O values of mine water (δD < −70‰; δ18O < −10‰) suggest snow melt and high-altitude precipitations as the main source of recharge. The mine water is less affected by the seasonal variation of temperature. In most cases, the variations in isotopic composition are within narrow limits (less than 1‰ for both δD and δ18O), and this result suggests well-mixed underground systems. Elevated concentration of sulphates, Zn and Fe in mine waters are the main issues of concern. For the study area, no relevant contamination of springs or phreatic water by mine water was revealed. On the contrary, surface running water is contaminated by mine water, and the negative effects of acid mine drainage occur mainly in the summer months when the flow of the surface running water decreases.

Removal of nitric oxide using combined Fe II EDTA and coal slurry in the presence of SO 2

Abstract Nitric oxide was removed by aqueous coal slurry containing FeIIEDTA in the presence of SO2 using a bubbling reactor. The effects of NO and O2 concentrations, temperature and pH on NO removal and coal pyrite leaching were studied. NO removal efficiency and coal pyrite leaching rate increased with the increase of NO concentration. The overall effect of high oxygen concentration is unfavorable to the removal of NO. The reduction rate of the complexed NO by coal pyrite increased with increasing temperature up to 60 °C, resulting in higher NO removal efficiency and coal pyrite leaching rate. Further increase in temperature was unfavorable to NO removal and coal pyrite leaching because the absorption of NO became the rate-determining step. The optimal pH was determined to be about 5.8. When pH was greater than 5.8, the reduction of FeIIEDTA-NO was inhibited, and therefore the NO removal efficiency decreased with further increase of pH. The reduction of FeIIEDTA-NO by coal pyrite played a significant part in coal pyrite leaching. Nevertheless, the leaching of coal pyrite was still controlled by chemical reaction.

Mechanical and chemical studies on EPS from Sulfobacillus thermosulfidooxidans: from planktonic to biofilm cells

Bacteria attach to minerals and form biofilms, which can initiate and enhance bioleaching. Extracellular polymeric substances (EPS) play a crucial role during the whole process. Little is known how the cell surface/EPS mechanically and chemically respond to transformation from planktonic to biofilm cells. In this study the attachment and biofilm formation by Sulfobacillus thermosulfidooxidans were followed during pyrite leaching. Adhesiveness and stiffness of the cell/biofilm and the pyrite surface were checked by atomic force microscopy (AFM) in force mapping mode under real living conditions. The EPS components were analysed by colorimetry, fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy. The results indicate that slimy and soft EPS heterogeneously accumulated in the biofilms and on the surface of pyrite to induce bacterial adhesion and form robust biofilms. After attaching to the pyrite surface, the cells started to change the components of their EPS. Huge amounts of humic substances were detected in the biofilm EPS.

Pyrite oxidation in column at controlled redox potential of 900 mV with and without bacteria

Comparisons on the bioleaching and sterile oxidation of pyrite were performed at controlled redox potential of 900 mV (vs. SHE) and different temperatures of 30 and 60 °C. For sterile experiments, the redox potential of irrigation solution was controlled by adding hydrogen peroxide solution (15 wt%), while the redox potential of irrigation solution for bioleaching was elevated by flowing through the packed bed in which bacteria were activated and colonized. The rate of pyrite bioleaching is faster than that of sterile oxidation at temperature of 30 °C. The reason is that the potential gradient of leaching solution in bioleaching column is much smaller than that in sterile column. The redox potentials of irrigation solution and leaching solution are similar for bioleaching; however, the redox potential difference of irrigation solution and leaching solution for sterile oxidation is about 150 mV. When temperature increases to 60 °C for sterile oxidation, the rate of pyrite leaching is faster than that of bioleaching at temperature of 30 °C, even though the redox potential gradient of leaching solution is great. The mineralogy analyses of pyrite residue were performed by scanning electron microscopy–energy-dispersive spectroscopy (SEM–EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses. The results confirm that pyrite oxidation might only occur at specific sites with high surface energy on surface and obeys the “indirect mechanism” whether there are bacteria or not. The pyrite oxidation rate is not inhibited by inert sulfur on residue surface at elevated redox potential. According to the conclusions, the way to accelerate pyrite oxidation is proposed.

Interactions of the extremely acidophilic archaeon Ferroplasma acidiphilum with acidophilic bacteria during pyrite bioleaching

Bioleaching has been applied as a successful technique for metal recovery from various mineral sources like low-grade ores, waste materials and tailings. Mixed cultures of bioleaching microorganisms have a high performance in mineral dissolution. Thus far, microbial interactions in bioleaching communities are poorly understood. In this paper, the acidophilic archaeon Ferroplasma acidiphilum and the bacteria Leptospirillum ferriphilum and Sulfobacillus thermosulfidooxidans were chosen to study their interactions during pyrite leaching. The initial attachment to pyrite and pyrite leaching efficiency of pure and mixed populations were investigated. The data indicate: (i) attachment and bioleaching efficiency of L. ferriphilum was reduced in the presence of F. acidiphilum. However, the combination of F. acidiphilum and S. thermosulfidooxidans showed increased leaching, although the initial attachment rate was reduced, when compared to pure cultures. Thus, synergistic or antagonistic interactions may exist between F. acidiphilum and S. thermosulfidooxidans or F. acidiphilum and L. ferriphilum, respectively; (ii) pre-established biofilms of L. ferriphilum inhibited initial attachment to pyrite by cells of F. acidiphilum and did not promote pyrite leaching by F. acidiphilum. In contrast, inactivated biofilm cells of S. thermosulfidooxidans enhanced pyrite bioleaching by F. acidiphilum; (iii) adhesion forces of cells to an AFM tip (Si3N4) seemed to be not correlated to attachment and bioleaching capacity; and (iv) lectins were applied to show and distinguish single species in mixed biofilm populations. Physical contact between cells of S. thermosulfidooxidans and F. acidiphilum was visible.

Anodic oxidation of iron(II) and copper(I) on various sulfide minerals in chloride solutions

A comparative study of the electrochemical oxidation of iron(II) and copper(I) ions on selected sulfide minerals in concentrated chloride solutions has been carried out as part of a broader study of the kinetics of the leaching of chalcopyrite, covellite, enargite and pyrite under chloride heap leaching conditions. Mixed potential, cyclic voltammetric and potentiostatic measurements have been made using rotating disk electrodes of massive mineral samples. For comparative purposes, arsenopyrite and platinum electrodes have also been used under the same conditions. The mixed potentials of the various minerals in solutions containing 4mol/L sodium chloride, 0.1mol/L hydrochloric acid and 0.05mol/L iron(II) or 0.05mol/L copper(II) ions at 25°C are all governed by the potentials of the redox couples with the exception of chalcopyrite in solutions of iron(II) for which the mixed potential is lower than the equilibrium potential of the iron(III)/iron(II) couple.Cyclic voltammetry conducted at potentials positive to the mixed potentials at slow sweep rates has shown variable reactivity of the minerals for oxidation of both iron(II) and copper(I) ions. Oxidation of copper(I) occurs readily on all minerals with the limiting current density observed on all with the exception of chalcopyrite for which the limiting current is not reached even at relatively large overpotentials. Partial passivation of the oxidation of copper(I) is observed at potentials above about 0.7V on covellite. Oxidation of iron(II) is slower than that of copper(I) on all minerals and the limiting current density is only observed on pyrite. Partial passivation of the oxidation of iron(II) is observed with all other minerals at potentials above 0.65 to 0.75V.Quantitative measurements of the rates of oxidation at the mixed potentials have been obtained from linear polarization measurements and the results compared with previously published data on the cathodic reduction of iron(III) and copper(II) on these mineral surfaces. The rate constant varies by about an order of magnitude within the mineral group for both iron(II) and copper(I) oxidation and the rates of oxidation on platinum are higher for both couples than for the mineral electrodes. The ratio of the rate of copper(II) reduction to iron(III) reduction is significantly greater for the minerals containing copper than for those without copper.The effect of illumination with light of wavelength 405nm on the rate of anodic oxidation of iron(II) on chalcopyrite has been evaluated and no positive effects that can be attributed to semi-conducting effects have been observed.

Cathodic reduction of iron(III) and copper(II) on various sulfide minerals in chloride solutions

A comparative study of the electrochemical reduction of iron(III) and copper(II) ions on selected sulfide minerals in concentrated chloride solutions has been carried out as part of a broader study of the kinetics of the leaching of chalcopyrite, covellite, enargite and pyrite under chloride heap leaching conditions. Mixed potential, cyclic voltammetric and potentiostatic measurements have been made using rotating disk electrodes of massive mineral samples. For comparative purposes, arsenopyrite, platinum and gold electrodes have also been used under the same conditions. The mixed potentials of the various minerals in solutions containing 4.2mol/L sodium chloride, 0.1mol/L hydrochloric acid and 0.054mol/L iron(III) and/or 0.047mol/L copper(II) ions at 25°C vary with time depending on the mineral reactivity. The difference between the mixed potentials and the solution potentials provide qualitative indications of mineral reactivity to dissolution with iron(III) or copper(II) as oxidants.Cyclic voltammetry conducted at potentials negative to the mixed potentials at slow sweep rates after the mixed potential measurements has shown variable reactivity of the minerals for reduction of iron(III) and copper(II) ions. The data has been analysed in terms of electrochemical kinetics using a modified Butler-Volmer approach that takes into account mass transport of the oxidized and reduced species and anodic oxidation of the minerals. The electrochemical rate constant derived from a fit of the data to the rate equation shows that all the minerals have greater reactivity for the reduction of copper(II) than iron(III) ions.The rate constant varies by about an order of magnitude within the mineral group for both iron(III) and copper(II) reduction and the rate of reduction on platinum and gold electrodes are higher for both couples than for the mineral electrodes. The ratio of the rate of copper(II) reduction to iron(III) reduction is significantly greater for the minerals containing copper than for those without copper.The observed influence of mass transport on the cathodic currents close to the mixed potentials for the reduction of copper(II) on platinum, pyrite and enargite has been quantitatively explained in terms of the effect of mass transport on the surface concentration of copper(I).An attempt has been made to correlate the kinetic data with published data on the semi-conducting properties of the metal sulfides. With the exception of covellite (which is not considered a semiconductor), the formal potentials of the copper(II)/copper(I) and iron(III)/iron(II) couples fall within the bandgaps of the metal sulfides and there does not appear to be any correlation between the energy levels of the couples in solution relative to the conduction bands of the sulfides and the reactivity for electron transfer to the metal ion couples. The effect of illumination with light of wavelength 405nm on the cathodic currents has been demonstrated to be due to thermal and not photocurrent effects.

Influence of Sulfobacillus thermosulfidooxidans on Initial Attachment and Pyrite Leaching by Thermoacidophilic Archaeon Acidianus sp. DSM 29099

At the industrial scale, bioleaching of metal sulfides includes two main technologies, tank leaching and heap leaching. Fluctuations in temperature caused by the exothermic reactions in a heap have a pronounced effect on the growth of microbes and composition of mixed microbial populations. Currently, little is known on the influence of pre-colonized mesophiles or moderate thermophiles on the attachment and bioleaching efficiency by thermophiles. The objective of this study was to investigate the interspecies interactions of the moderate thermophile Sulfobacillus thermosulfidooxidans DSM 9293T and the thermophile Acidianus sp. DSM 29099 during initial attachment to and dissolution of pyrite. Our results showed that: (1) Acidianus sp. DSM 29099 interacted with S. thermosulfidooxidansT during initial attachment in mixed cultures. In particular, cell attachment was improved in mixed cultures compared to pure cultures alone; however, no improvement of pyrite leaching in mixed cultures compared with pure cultures was observed; (2) active or inactivated cells of S. thermosulfidooxidansT on pyrite inhibited or showed no influence on the initial attachment of Acidianus sp. DSM 29099, respectively, but both promoted its leaching efficiency; (3) S. thermosulfidooxidansT exudates did not enhance the initial attachment of Acidianus sp. DSM 29099 to pyrite, but greatly facilitated its pyrite dissolution efficiency. Our study provides insights into cell-cell interactions between moderate thermophiles and thermophiles and is helpful for understanding of the microbial interactions in a heap leaching environment.

Enhancement of Biofilm Formation on Pyrite by Sulfobacillus thermosulfidooxidans

Bioleaching is the mobilization of metal cations from insoluble ores by microorganisms. Biofilms can enhance this process. Since Sulfobacillus often appears in leaching heaps or reactors, this genus has aroused attention. In this study, biofilm formation and subsequent pyrite dissolution by the Gram-positive, moderately thermophilic acidophile Sulfobacillus thermosulfidooxidans were investigated. Five strategies, including adjusting initial pH, supplementing an extra energy source or ferric ions, as well as exchanging exhausted medium with fresh medium, were tested for enhancement of its biofilm formation. The results show that regularly exchanging exhausted medium leads to a continuous biofilm development on pyrite. By this way, multiply layered biofilms were observed on pyrite slices, while only monolayer biofilms were visible on pyrite grains. In addition, biofilms were proven to be responsible for pyrite leaching in the early stages.

Biofilm formation and interspecies interactions in mixed cultures of thermo-acidophilic archaea Acidianus spp. and Sulfolobus metallicus

The understanding of biofilm formation by bioleaching microorganisms is of great importance for influencing mineral dissolution rates and to prevent acid mine drainage (AMD). Thermo-acidophilic archaea such as Acidianus, Sulfolobus and Metallosphaera are of special interest due to their ability to perform leaching at high temperatures, thereby enhancing leaching rates. In this work, leaching experiments and visualization by microscopy of cell attachment and biofilm formation patterns of the crenarchaeotes Sulfolobus metallicus DSM 6482T and the Acidianus isolates DSM 29038 and DSM 29099 in pure and mixed cultures on sulfur or pyrite were studied. Confocal laser scanning microscopy (CLSM) combined with fluorescent dyes as well as fluorescently labeled lectins were used to visualize different components (e.g. DNA, proteins or glycoconjugates) of the aforementioned species. The data indicate that cell attachment and the subsequently formed biofilms were species- and substrate-dependent. Pyrite leaching experiments coupled with pre-colonization and further inoculation with a second species suggest that both species may negatively influence each other during pyrite leaching with respect to initial attachment and pyrite dissolution rates. In addition, the investigation of binary biofilms on pyrite showed that both species were heterogeneously distributed on pyrite surfaces in the form of individual cells or microcolonies. Physical contact between the two species seems to occur, as revealed by specific lectins able to specifically bind single species within mixed cultures.

Aluminum-Enhanced Coal Pyrite Leaching during SO2 Removal with Coal Slurry

During SO2 removal from flue gas by coal slurry scrubbing, coal pyrite sulfur can be simultaneously reduced. But satisfactory coal pyrite conversion cannot be achieved under normal scrubbing conditions. In the present work, aluminum oxide and aluminum sulfate were tested as additives to enhance the leaching of coal pyrite during SO2 removal in a bubbling reactor. It was found that adding aluminum oxide or aluminum sulfate into the coal slurry could increase the coal pyrite conversion and SO2 removal efficiency. The leaching process could be described by the reaction-controlled shrinking core model. Based on the facts that both aluminum and ferric irons can exist in aqueous solution in the form of sulfate and hydroxide complex ions, it was deduced that the attraction between the oppositely charged ions might promote the coal pyrite leaching reactions, suppress the formation of passive Fe solid products, and increase the concentration of soluble complexed Fe(III) which also acted as coal pyrite oxidant.

Microbial communities from different subsystems in biological heap leaching system play different roles in iron and sulfur metabolisms.

The microbial communities are important for minerals decomposition in biological heap leaching system. However, the differentiation and relationship of composition and function of microbial communities between leaching heap (LH) and leaching solution (LS) are still unclear. In this study, 16S rRNA gene sequencing was used to assess the microbial communities from the two subsystems in ZiJinShan copper mine (Fujian province, China). Results of PCoA and dissimilarity test showed that microbial communities in LH samples were significantly different from those in LS samples. The dominant genera of LH was Acidithiobacillus (57.2∼87.9%), while Leptospirillum (48.6∼73.7%) was predominant in LS. Environmental parameters (especially pH) were the major factors to influence the composition and structure of microbial community by analysis of Mantel tests. Results of functional test showed that microbial communities in LH utilized sodium thiosulfate more quickly and utilized ferrous sulfate more slowly than those in LS, which further indicated that the most sulfur-oxidizing processes of bioleaching took place in LH and the most iron-oxidizing processes were in LS. Further study found that microbial communities in LH had stronger pyrite leaching ability, and iron extraction efficiency was significantly positively correlated with Acidithiobacillus (dominated in LH), which suggested that higher abundance ratio of sulfur-oxidizing microbes might in favor of minerals decomposition. Finally, a conceptual model was designed through the above results to better exhibit the sulfur and iron metabolism in bioleaching systems.

Leaching of pyrite in cupric chloride solution

Pyrite (FeS2 ) is the most abundant sulphide mineral in the world and may contain significant amounts of gold locked in its structure. Traditionally, pyrite has to be oxidized in order to break down the mineral matrix for better gold liberation by e.g. roasting, pressure leaching and bioleaching [1]. Due to environmental and health concerns, as well as public opinion, alternative methods are developed to replace gold cyanide leaching, which has been the preferred gold leaching process. Gold is known to form a stable complex with chloride as [AuCl4 ]- or [AuCl2 ]-. In chloride leaching of pyrite in the presence of [Cu2+ ] which acts as a catalyst/oxidant, the pyrite structure can be simultaneously broken down and the gold dissolves into a solution from which it can be later recovered [2, 3]. In this study, dissolution of the pyrite concentrate in cupric chloride solutions was investigated. The effect of cupric ion concentration (16, 32 g/L), temperature, (60, 75, 90 °C), chloride ion concentration (50, 150 g/L), pH (1, 1.5) and mixed chloride-bromide ion concentration (75+75 g/L) on pyrite dissolution were studied during 6 hour batch leaching experiments. Redox potentials between 0.495-0.511 V vs. Ag/AgCl resulted in pyrite dissolution of 31-34%, whereas redox potentials between 0.523-0.573 V vs. Ag/AgCl resulted in 45-68% pyrite dissolution.

Direct Detection of Fe(II) in Extracellular Polymeric Substances (EPS) at the Mineral-Microbe Interface in Bacterial Pyrite Leaching.

We herein investigated the mechanisms underlying the contact leaching process in pyrite bioleaching by Acidithiobacillus ferrooxidans using scanning transmission X-ray microscopy (STXM)-based C and Fe near edge X-ray absorption fine structure (NEXAFS) analyses. The C NEXAFS analysis directly showed that attached A. ferrooxidans produces polysaccharide-abundant extracellular polymeric substances (EPS) at the cell-pyrite interface. Furthermore, by combining the C and Fe NEXAFS results, we detected significant amounts of Fe(II), in addition to Fe(III), in the interfacial EPS at the cell-pyrite interface. A probable explanation for the Fe(II) in detected EPS is the leaching of Fe(II) from the pyrite. The detection of Fe(II) also indicates that Fe(III) resulting from pyrite oxidation may effectively function as an oxidizing agent for pyrite at the cell-pyrite interface. Thus, our results imply that a key role of Fe(III) in EPS, in addition to its previously described role in the electrostatic attachment of the cell to pyrite, is enhancing pyrite dissolution.

Biofilm Formation of &lt;i&gt;Sulfobacillus&lt;/i&gt; &lt;i&gt;thermosulfidooxidans&lt;/i&gt; on Pyrite in the Presence of &lt;i&gt;Leptospirillum ferriphilum&lt;/i&gt;

In this study, initial attachment to and biofilm formation of Sulfobacillusthermosulfidooxidans DSM 9293T on pyrite in the presence of Leptospirillumferriphilum DSM 14647T were investigated. Interactions of S.thermosulfidooxidansT and L.ferriphilumT were studied by means of monitoring attachment behavior and biofilm formation on pyrite. Our preliminary results showed that 1): Pre-established biofilms of L.ferriphilumT had effects on attachment of S. thermosulfidooxidansT to pyrite; 2): physical contact between cells of L. ferriphilumT and S. thermosulfidooxidansT on pyrite were visible 3): Pyrite leaching by cells of S. thermosulfidooxidansT was inhibited by the presence of inactive cells of L.ferriphilumT.

Leaching kinetics of gold bearing pyrite in H2SO4–Fe2(SO4)3 system

Gold bearing pyrite leaching was conducted in H2SO4–Fe2(SO4)3 system at different reaction temperatures, with different ferric ion concentrations, sulfuric acid concentrations and stirring speeds. The leaching kinetics and mechanism were studied. When the temperature ranged between 30–75 °C, the pyrite leaching was mainly controlled by chemical reaction with positive correlation to the ferric ion concentration. The activation energy obtained from Arrhenius empirical formula is 51.39 kJ/mol. The EDS and XPS analyses suggest that the oxidation of sulfur within pyrite is through a series of intermediate stages, and eventually is oxidized to sulphate accompanied with the formation of element sulfur. This indicates a thiosulfate oxidation pathway of the gold bearing pyrite oxidation in H2SO4–Fe2(SO4)3 system.

Impact of mechanical activation and mechanochemical activation on natural pyrite dissolution

In this paper, a new pretreatment method was employed for the enhancement of pyrite mineral dissolution by using mechanochemical activation. The mechanochemical activation was carried out by co-milling of pyrite and iron powder for 20 and 50min. The XRD analysis indicated that a fraction of pyrite and iron phase remained and troilite (FeS) was formed as a new phase after 50min milling. In addition, the microstructural changes of mechanochemically and mechanically activated pyrite were investigated by Rietveld method. The results revealed that amorphization degree increased from 53% in mechanically activated pyrite for 50min to 83% in mechanochemically activated pyrite for 50min. The mechanochemical activation intensified crystallite size reduction of pyrite in comparison with mechanical activation. In spite of mechanical activation, the microstrain measures slightly reduced during mechanochemical activation due to mechanochemical reaction. Although, both the mechanochemical and mechanical activations of pyrite can enhance the dissolution of pyrite, total iron extractions in the 1M sulfuric acid leaching tests at ambient temperature increase from 1.12% for the initial pyrite to 21.22% for 50min mechanically activated pyrite leaching and then abruptly climb to 87.2% for 50min mechanochemically activated pyrite leaching.

Pretreatment of cyanided tailings by catalytic ozonation with Mn2 +/O3

The increasing amount of cyanided tailings produced as a by-product has gained significant attention in recent years because of the rapid development of the gold industry and extensive exploitation of gold mineral resources. The effective use of these secondary resources is becoming an important and urgent problem for all environmental protection staff. Manganese-catalyzed ozonation for the pre-oxidation of cyanided tailings was studied and the effects of Mn2+ dosage, initial sulfuric acid concentration, ozone volume flow, temperature and agitation speed on pretreatment were examined. The optimum reaction conditions were observed to be: ore pulp density 2.5%, agitation speed 700r/min, temperature 60°C, Mn2+ dosage 40g/L, ozone volume flow 80L/hr, initial sulfuric acid concentration 1mol/L, and reaction time 6hr. Under these conditions, the leaching rate of Fe and weight loss could reach 94.85% and 48.89% respectively. The leaching process of cyanided tailings by Mn2+/O3 was analyzed, and it was found that the leaching of pyrite depends on synergetic oxidation by high-valent manganese and O3, in which the former played an important part.