Pyrrhotite Surfaces Research Articles

XPS determination of the oxidation state of <sup>99</sup>Тс isotope absorbed on the surface of pirrhotite Fe<sub>n</sub>S<sub>n+1</sub> and stibnite Sb<sub>2</sub>S<sub>3</sub>

Sorption of pertechnetate on pyrrhotite FenSn+1 (I) and stibnite Sb2S3 (II) from distilled water was evaluated. The distribution coefficients were found to be 185 and 223 cm3/g, respectively. The XPS study of the chemical state of 99Tc absorbed on the surface of pyrrhotite and stibnite from aqueous solution of potassium pertechnetate (KTcO4) was carried out. It was found that Tc(IV) ions are present mostly on the surface of the studied samples, their concentration was 5.7 times higher on the surface of pyrrhotite compared to that on the surface of stibnite. A 13% admixture of Tc(VII) ions on the surface of pyrrhotite was observed.

Electrochemistry and DFT study of galvanic interaction on the surface of monoclinic pyrrhotite (0 0 1) and galena (1 0 0)

The electrochemical interaction between galena and monoclinic pyrrhotite was investigated to examine its impact on the physical and chemical properties of the mineral micro-surface. This investigation employed techniques such as electrochemistry, metal ion stripping, X-ray photoelectron spectroscopy, and quantum chemistry. The electrochemical test results demonstrate that the galena surface in the electro-couple system exhibits a lower electrostatic potential and higher electrochemical activity compared to the monoclinic pyrrhotite surface, rendering it more susceptible to oxidation dissolution. Monoclinic pyrrhotite significantly amplifies the corrosion rate of the galena surface. Mulliken charge population calculations indicate that electrons are consistently transferred from galena to monoclinic pyrrhotite, with the number of electron transfers on the mineral surface increasing as the interaction distance decreases. The analysis of state density revealed a shift in the surface state density of galena towards lower energy levels, resulting in decreased reactivity and increased difficulty for the reagent to adsorb onto the mineral surface. Conversely, monoclinic pyrrhotite exhibited an opposite trend. The XPS test results indicate that galvanic interaction leads to the formation of hydrophilic substances, PbSxOy and Pb(OH)2, on the surface of galena. Additionally, the surface of monoclinic pyrrhotite not only adsorbs Pb2+ but also undergoes S0 formation, thereby augmenting its hydrophobic nature.

Pyrrhotites in asteroid 162173 Ryugu: Records of the initial changes on their surfaces with aqueous alteration

The surface chemistry of pyrrhotites from intact particles directly collected from asteroid (162173) Ryugu was investigated by micro-Raman spectroscopy. The Raman peak characteristic to pyrrhotite was observed at around 115 cm−1 in Ryugu pyrrhotites, similar to freshly cleaved surfaces of terrestrial pyrrhotites. Additional Raman bands centered at around 220, 275, and 313 cm−1 with broadened features were also detected from the Ryugu pyrrhotites. The set of Raman bands at 220 and 275 cm−1 was assigned to typical Fe-S stretching vibrations of ν2 (225 cm−1) and ν1 (275 cm−1). These bands are not clearly observed in bulk crystals of pyrrhotite but appear in its nanoparticulate phase. These bands are ordinarily seen in amorphous monosulfides that formed under low oxygen fugacity (fO2) conditions in nature, indicating that the structural alteration of pyrrhotite surfaces occurred heterogeneously on the nanoscale under low fO2 conditions. Further, the Raman band at 313 cm−1 was attributed to a characteristic tetrahedral bonding of Fe(III) in the lattice of FeII1-3xFeIII1-2xS, followed by the local breakdown of the crystal lattice structures from planar bonding with Fe(II). In addition, some areas of the Ryugu pyrrhotite grains showed corroded structures with iridescence. Furthermore, assemblages of magnetite particles were also preferentially observed on small areas of the likely-dissolved pyrrhotite crystals in phyllosilicate matrices. These characteristic features in the Raman spectra and in corroded structures of Ryugu pyrrhotites record changes in the local environmental conditions via aqueous alteration. The corrosion of pyrrhotite crystals followed by the preferential formation of magnetite particles by asteroidal water is the likely product of dissolution of Fe(II) from the pyrrhotite surface and its oxidative precipitation in microchemical environments on the Ryugu parent body.

A comprehensive investigation of the continuous oxidation of pyrrhotite by micromolar hydrogen peroxide in near neutral and acidic solutions

Pyrrhotite oxidation poses a big threat to water environment duo to its high potential for generating pollutants. Hydrogen peroxide, commonly found in natural water at micromolar concentrations, possesses much more aggressive oxidation ability than oxygen and can complicate the pyrrhotite oxidation process. Here, the effects of micromolar H2O2 on the biotic and abiotic oxidation of pyrrhotite were examined at pH 1.93 and 6.45, respectively. Pyrrhotite oxidation was much more severe in acidic solutions compared to near neutral solutions. Jarosite with a high Fe/S molar ratio was widely detected in the precipitate collected in acidic solutions, and the introduction of external H2O2 influenced the crystallinity of jarosite. A layer of iron-deficient iron-sulfur oxide formed on the surface of pyrrhotite prevents its continuous oxidation, and the presence of Acidithiobacillus ferrooxidans enhanced this situation by promoting the release of Fe from the pyrrhotite. Additionally, the presence of external micromolar H2O2 also determined the elemental state on pyrrhotite surface, as it found that the contribution of Fe3+ and S (S4+ and S6+) species on pyrrhotite surface increased with the increase of H2O2 concentration in the solutions, especially in the presence of Acidithiobacillus ferrooxidans.

Activation Mechanism of Fe2+ in Pyrrhotite Flotation: Microflotation and DFT Calculations.

In industrial manufacturing, pyrrhotite(Fe1-xS), once depressed, is commonly activated for flotation. However, the replacement of CuSO4 is necessary due to the need for exact control over the dosage during the activation of pyrrhotite, which can pose challenges in industrial settings. This research introduces the use of FeSO4 for the first time to efficiently activate pyrrhotite. The impact of two different activators on pyrrhotite was examined through microflotation experiments and density functional theory (DFT) calculations. Microflotation experiments confirmed that as the CuSO4 dosage increased from 0 to 8 × 10-4 mol/L, the recovery of pyrrhotite initially increased slightly from 71.27% to 87.65% but then sharply decreased to 16.47%. Conversely, when the FeSO4 dosage was increased from 0 to 8 × 10-4 mol/L, pyrrhotite's recovery rose from 71.27% to 82.37%. These results indicate a higher sensitivity of CuSO4 to dosage variations, suggesting that minor alterations in dosage can significantly impact its efficacy under certain experimental conditions. In contrast, FeSO4 might demonstrate reduced sensitivity to changes in dosage, leading to more consistent performance. Fe ions can chemically adsorb onto the surface of pyrrhotite (001), creating a stable chemical bond, thereby markedly activating pyrrhotite. The addition of butyl xanthate (BX), coupled with the action of Fe2+ on activated pyrrhotite, results in the formation of four Fe-S bonds on Fe2+. The proximity of their atomic distances contributes to the development of a stable double-chelate structure. The S 3p orbital on BX hybridizes with the Fe 3d orbital on pyrrhotite, but the hybrid effect of Fe2+ activation is stronger than that of nonactivation. In addition, the Fe-S bond formed by the addition of activated Fe2+ has a higher Mulliken population, more charge overlap, and stronger covalent bonds. Therefore, Fe2+ is an excellent, efficient, and stable pyrrhotite activator.

Effect of Electrochemical Interaction between Chalcopyrite and Hexagonal Pyrrhotite on Flotation Separation

The mechanism of electrochemical interaction between chalcopyrite and hexagonal pyrrhotite was analyzed via electrochemical interaction, copper ion concentration testing, and X-ray photoelectron spectroscopy (XPS) characterization. Besides, the effect of electrochemical interaction between the two minerals on the flotation separation was investigated using the mineral flotation tests, adsorption capacity tests, and a microcalorimetric test. Our research results showed that chalcopyrite had higher electrochemical activity than hexagonal pyrrhotite, and when the former acted as an anode during the electrochemical interaction of the two, the corrosion current density was three times higher than that when it acted alone, and the surface oxidation corrosion was intensified. At the same time, the interaction between the two minerals was accompanied by a large number of copper ions dissolved and adsorbed on the surface of the hexagonal pyrrhotite, so that adsorption of butyl xanthate intensified, adsorption increased, and flotation recovery increased by 5%–20%. However, owing to the increase in metal defects and the generation of hydrophilic sulfate, the surface of chalcopyrite hindered the adsorption of butyl xanthate on its surface, and the flotation recovery decreased by nearly 10% compared with that before the occurrence of the electrochemical interaction. This action also significantly weakened the inhibition effect of lime on hexagonal pyrrhotite and increased the difficulty of the flotation separation of the two minerals. The research results of this study provide theoretical guidance for the flotation separation of copper–sulfur ores containing pyrrhotite.

Application of ultrasonic pre-treatment for flotation separation pyrrhotite from chlorite

The strengthen separation mechanism of pyrrhotite and chlorite by ultrasonic pre-treatment was revealed through ICP measurements, XPS measurements, SEM analyses, Zeta potential measurements, turbidity analyses, microscopic observation, adsorption capacity measurements, FTIR analyses and contact angle measurements. The results showed that ultrasonic pre-treatment can promote the dissolution of iron oxide particles on pyrrhotite surface and the desorption of iron ions adsorbed on chlorite surface in mixed minerals, which caused Zeta potential and point of zero charge(PZC) negatively shift on pyrrhotite/chlorite surface and convert mutual attraction energy to mutual repulsive energy, thus weaken the hetero-aggregation and enhance the separation between pyrrhotite and chlorite. Ultrasonic pre-treatment can optimize the adsorption capacity of butyl xanthate(BX) and the surface wettability on pyrrhotite surface, however, it has little effect on BX adsorption and wettability on chlorite surface, hence ultrasonic pre-treatment also can strengthen the separation of pyrrhotite from chlorite. Then the flotation experiment of artificial mixed pyrrhotite and chlorite was carried out, the results show that the recovery of pyrrhotite increases from 77.50 % to 81.72 % and the content of MgO decreases from 6.57 % to 5.74 % by the reaction of ultrasonic pre-treatment. Which further proof that ultrasonic pre-treatment can enhance the flotation separation of pyrrhotite from chlorite.

Prospects of pulp aeration for the cleaner production of pyrrhotite-rich type copper sulfide ore: Mechanism and application

Mineral extraction is facing increasingly severe challenges in terms of environment protection and cost reduction. Abundant of lime and sulfuric acid were consumed in the traditional high alkaline process (HAP) to extract chalcopyrite and iron sulfides. In this study, pulp aeration process (PAP) was proved a low-cost and environment friendly method in the processing of a pyrrhotite-rich type copper sulfide ore. Flotation results confirmed that pulp aeration was able to selectively depress pyrrhotite and pyrite flotation under ML8 system, thus 3000 g/t lime was cancelled during copper flotation stage, and around 4000 g/t sulfuric acid was saved during the subsequent sulfur flotation stage due to the low initial pulp pH. In the novel PAP, the directly production cost decreased by 4.34 RMB/t, besides, approximately 3.6 kg carbon dioxide and other waste could be reduced indirectly. Mechanism research revealed that pulp aeration oxidized the surface of pyrrhotite and pyrite, which further depressed the subsequent ML8 adsorption. However, the adsorption of ML8 on chalcopyrite was stable enough and it was unaffected by pulp aeration. Overall, pulp aeration was an environment friendly and cost-effective method for the separation of high-pyrrhotite type copper sulfide ore, which possessed broad industrial application prospects.

Electrochemical and XPS investigations on the galvanic interaction between pentlandite and pyrrhotite in collectorless flotation system

Pentlandite and pyrrhotite are ubiquitously symbiotically aggregated with each other, and the galvanic interaction between them inevitably occurs in flotation process. However, there were few detailed researches regarding this galvanic interaction and its effect on the surface oxidation of pentlandite and pyrrhotite that has been reported. In this work, the galvanic interactions and its influence on the surface oxidation and collectorless flotation behaviors of pentlandite and pyrrhotite were systematically researched at pH 8.5. Results of electrochemical measurements showed that pentlandite had a higher OCP value than pyrrhotite, indicating that pentlandite would act as the cathode, while pyrrhotite acted as the anode in the galvanic couple. Compared to the minerals oxidized solely, a more passivated surface was found for both pentlandite and pyrrhotite. ICP-OES and XPS analyses demonstrated that in the presence of pyrrhotite, a thicker iron oxide/hydroxide film was obtained with a decrease in the species of sulfate and nickel oxide/hydroxide on pentlandite surface. For pyrrhotite, within the galvanic interaction, the oxidation and metal dissolution of pyrrhotite was accelerated. However, the hydrogen ion generated in the anodic reaction would hinder the precipitation of iron oxide/hydroxide and sulfate on pyrrhotite surface. Micro-flotation results further confirmed that the galvanic interaction between pentlandite and pyrrhotite significantly affected their collectorless flotation behaviors, which was also affected by the relative content ratio between them. This work systematically studied the galvanic interaction and its role in the surface oxidation in pentlandite/pyrrhotite collectorless flotation system, which could also provide reference for the further study on complex Ni-bearing sulfide minerals flotation.

The utilization of BHA and SBX collector mixture for the flotation of moderately oxidized pyrrhotite

The benzohydroxamic acid (BHA) and sodium butyl xanthate (SBX) mixture was used as a collector for the flotation of moderately oxidized pyrrhotite (MOP) in this work. Microflotation results revealed that the flotation recovery of MOP was not very high with the addition of individual SBX or BHA collector, but significantly improved using a mixed collector of SBA/BHA, the maximum flotation recovery of could reach 88.55%. Zeta potential measurement revealed that the surface charges of MOP were negatively moved after the addition of mixed SBX/BHA compared to adding SBX or BHA alone, revealing a much stronger interaction between the collector mixture and MOP surface, leading to the improvement of MOP floatability. The FTIR spectra analysis revealed that the synergistic effect of SBX/BHA was attributed to the interaction between BHA and MOP, which could reduce the hydrophilic Fe(OH)3 on the pyrrhotite surface, allowing more adsorption of SBX onto the generated fresh unoxidized surfaces.

A novel sulfur-containing ionic liquid collector for the reverse flotation separation of pyrrhotite from magnetite

To improve the quality of the iron concentrate, the efficient separation of pyrrhotite from magnetite has always been an important beneficiation objective. In this paper, a novel collector of sulfur-containing ionic liquid (SCIL) was synthesized by using the isobutyl xanthic acid with N-tetrabutyl quaternary ammonium salt, and its molecular structure was characterized by 1H NMR, 13C NMR and FTIR analysis. The SCIL was used as a flotation collector for the first time to selectively separate pyrrhotite from magnetite by reverse flotation. Its flotation performance and adsorption mechanism on pyrrhotite or magnetite were investigated by microflotation tests, FTIR spectra, zeta potential measurement, XPS analysis and MDS. The microflotation results demonstrated that the SCIL has excellent collecting ability and selectivity for pyrrhotite against magnetite, compared with the traditional collector of sodium butyl xanthate (SIBX). Specifically. the flotation test results of mixed mineral shown that the S grade was reduced from 25.72 % of feed to 2.92 % of concentrate using SCIL as the collector, confirming its high efficiency. The analyses of zeta potential measurement and FTIR spectra indicated that SCIL was chemisorbed onto the pyrrhotite surface. The XPS results further confirmed that the CS bond of SCIL could be associated with S sites of the pyrrhotite surface, and Fe sites of the pyrrhotite surface might react with the CN or the CS bonds of SCIL. MDS further indicated that the adsorption of SCIL onto the pyrrhotite surface was much stronger than the SIBX.

Enhanced flotation separation pyrrhotite from serpentine by fluid force field

The strengthening effect of fluid force field on the flotation of pyrrhotite from serpentine was revealed through XPS measurements, ICP measurements, zeta potential measurements, turbidity analyses, microscope observation, adsorption capacity measurements and flotation kinetics methods. The results showed that fluid force field can promote the shedding of pyrrhotite surface material(Fe2O3, SO42-, Fe2+and Fe3+), expose more S0 and form fresh pyrrhotite surface; fluid force field can cause Zeta potential and point of zero charge(PZC) negatively shift on pyrrhotite/serpentine and reduce the value of mutual attraction energy between them, then weaken the hetero-aggregation between serpentine and pyrrhotite; fluid force field can promote the adsorption of butyl xanthate(BX) on pyrrhotite surface, then improve the recovery rate of pyrrhotite from serpentine. By the reaction of fluid force field, the turbidity of artificial mixed minerals slurry increased from 154NTU to 168NTU, the adsorption capacity of BX on pyrrhotite surfaces increased from 0.78 mg/g to 1.08 mg/g, the recovery of pyrrhotite increased from 79.14 % to 82.67 %, and the recovery of serpentine decreased from 23.74 % to 19.43 %. The results of flotation kinetics showed that kinetic model 2 can well reflect the flotation kinetics of pyrrhotite without pre-stirring, while model 1 can well reflect the flotation kinetics of pyrrhotite after pre-stirring by stirring tank.

Reconstruction of pyrrhotite fracture surfaces

The interpretation of core level Synchrotron photoemisison spectra (SPES) collected from a pristine fracture surface of monoclinic pyrrhotite (Fe7S8), as a function of photon energy, has identified the three distinct surface species. The Fe 2p photoemission spectra show the Fe in pyrrhotite is high spin FeII in octahedral co-ordination. Comparison of bulk and surface sensitive spectra did not identify any changes due to the broad nature of the high spin Fe 2p spectra. However, the sulfur spectrum shows an undercoordinated monosulfide at 160.8 eV, a disulfide (161.7 eV) and polysulfide species (163.2 eV) at the surface. This indicates stabilisation of the surface involves reconstruction and results in chemical transformation of sulfur species. A high binding energy tail that extends to 167 eV has been attributed to ligand to metal charge transfer satellites (LMCT) and supported by the pre-edge features observed in Fe L2,3 and S L2,3 near edge X-ray absorption fine structure (NEXAFS). An accurate fit for the bulk pyrrhotite sulfide spectrum has been estimated by comparing spectra with different surface sensitivities, and thereby an accurate fitting method has been developed for the monoclinic pyrrhotite S 2p spectrum. This method may be used for future photoemission spectra to improve the analysis of similar samples and provide a basis for interpretation of pyrrhotite samples during mineral processing and environmental conditions.

Metallurgical byproducts application aimed at improving ore concentration efficiency at Talnakh Concentrator

Talnakh Concentrator processes the mixture of high-grade and cupriferous ores to produce copper and nickel-pyrrhotite concentrates via the process implemented in 2016. Since 2018, pursuing a comprehensive use of raw materials, Talnakh Concentrator proceeded with reconcentration of low-nickel pyrrhotite product to produce low-grade reflotation concentrate (0.8–1.2% of nickel) sent to Nadezhda Metallurgical Plant named after B.I. Kolesnikov (hereinafter, NMP) for hydrometallurgical processing. Testing of Copper Plant’s byproducts application was aimed at increasing nickel recovery as a result of the nickeliferous pyrrhotite surface activation by copper ions. It is impractical to apply blue vitriol, traditionally used for this purpose, as it leads to a significant decrease in technical and economic performance due to an increase in operating costs for reconcentration. The Copper Plant products, such as decopperized electrolyte and a coppernickel solution from PGM Concentrator were tested as activators. These products contain not only residual amount of copper ions, but also a substantial quantity of sulphuric acid. The study showed that Copper Plant’s solution application increased the amount of nickel recovered to the product of reconcentration and improved the product pyrrhotite content that favorably effected its subsequent pressure oxidation leaching. Application of the copper-nickel solution from PGM Concentrator is considered to be the best option due to a higher ratio of copper ions to sulphuric acid. Solutions applied during nickel-pyrrhotite flotation at Talnakh Concentrator were also studied. The authors simulated the initial composition alteration of Talnakh Concentrator’s feed with an increase in a share of cupriferous ore, containing much less pyrrhotite than high-grade ore. It was found out that if the feed contained critical amount of cupriferous ore, application of Copper Plant’s solutions contributed to maintenance of sulphur content in the nickel-pyrrhotite concentrate of Talnakh Concentrator that provided energy potential required for the appropriate thermal conditions of NMP’s smelting vessels.

Effects of Galvanic Interaction between Chalcopyrite and Monoclinic Pyrrhotite on Their Flotation Separation

The galvanic interaction between chalcopyrite and monoclinic pyrrhotite and its effect on flotation separation were studied using monomineral flotation tests, adsorption capacity tests, X-ray photoelectron spectroscopy (XPS) characterization, and scanning electron microscopy (SEM) test. These results showed that the interaction promoted the reduction of O2 on the cathodic chalcopyrite surface and accelerated the generation of Fe(OH)3, which was not conducive to collector adsorption; hence, the flotation recovery decreased by 10–16%. On the other hand, galvanic interaction accelerated the oxidation of S on the anodic monoclinic pyrrhotite surface to S0 or SO42− and produced a large amount of H+, thus preventing the formation of Fe(OH)3. Meanwhile, the Cu2+ eluted from chalcopyrite surface activated monoclinic pyrrhotite; hence, the flotation recovery increased by 3–10%. Galvanic interaction reduced the floatability difference between the two minerals, and the separation difficulty was significantly increased. Even with an increase in the amount of lime, the separation could not be improved.

Bio-oxidation behavior of pyrite, marcasite, pyrrhotite, and arsenopyrite by sulfur- and iron-oxidizing acidophiles

The oxidation of sulfide minerals is of central importance due to the acid mine drainage (AMD) production. The bio-oxidation of pyrrhotite, pyrite, marcasite, and arsenopyrite was carried out with mesophilic bacteria (Acidithiobacillus ferrooxidans, A. thiooxidans, and Leptospirillum ferrooxidans) at 34 °C for 30 days. Bio-oxidation tests showed that marcasite has a high potential in producing AMD compared to pyrrhotite. Arsenopyrite has different behavior in the presence and the absence of additives (i.e., FeSO4·7H2O and sulfur). While the absence of additives increased the nickel and zinc dissolution, their presence increased the total iron dissolution. Sulfur and jarosite were observed on the surfaces of pyrrhotite and arsenopyrite. With the formation of these passivation layers, the continuous iron extraction is effectively suppressed. This study is helpful to comparatively evaluate the AMD production of sulfide minerals in an oxidizing environment and to study the effects of passivation layers on their biooxidation in different conditions.

Surface and interface analysis of iron sulfides in aqueous media using X-ray photoelectron spectroscopy of fast-frozen dispersions

Iron sulfides are important minerals and materials, whose surface properties are largely determined by the interface with aqueous phases. Here, natural pyrrhotite (Fe9S10) and pyrite (FeS2) were ground, reacted in water and acidic non-oxidative and oxidative ferric chloride and sulfate solutions, then centrifuged, fast-frozen and examined with X-ray photoelectron spectroscopy at –160 °C (cryo-XPS) in comparison with the samples thawed in vacuum, dried in vacuum or air and measured at room temperature (RT). The interfacial layers were composed mainly of ferric (hydr)oxides and aqueous iron salts as the reaction products rather than reactants; RT-XPS found the products modified due to dehydration, further reactions and redistribution over the surface. The cryo-XPS revealed plentiful surface Fe-S centers with various spin and oxidation states at pyrrhotite and pyrite, particularly in water, missed in conventional XPS. The surfaces of pyrrhotite and, much less, pyrite are enriched with polysulfide anions -S-Sn-S-, which partially volatilize at RT both under non-oxidative and oxidative conditions; the number n can be larger than 6 at pyrrhotite. It was concluded, nevertheless, that elemental sulfur insignificantly contributes to the spectra under the conditions employed. Pros and cons of the technique in the case study of iron sulfides are discussed.

Bioleaching of Pyrrhotite with Bacterial Adaptation and Biological Oxidation for Iron Recovery

The microbially mediated recovery of valuable metals contained in mining waste presents an economical alternative to conventional hydrometallurgical processes. In order to investigate the effect of bacterial adaptation and biological oxidation on bioleaching, the microbially mediated bioleaching of a pyrrhotite sample from mine waste, with indigenous bacteria existing in acid mine drainage, was studied. The indigenous bacteria were sub-cultured repeatedly for iron adaptation, and Acidithiobacillus ferrooxidans was identified as the dominant member of the microbial consortium. The point of zero charge (PZC) of pyrrhotite sampled from mine waste was determined as 3.0. The performance of bioleaching by contact and non-contact biological oxidation was compared by conducting bioleaching under different initial pH (pHini) conditions (2.8 and 3.2). Negatively charged bacteria could be attached onto the pyrrhotite, which has a positive surface charge at lower pHini (2.8) than the PZC (3.0). Bacteria attachment and corrosion pits on the surface of the pyrrhotite residues were observed at pHini of 2.8. Under bacteria-adapted conditions, the leaching concentration of Fe (44.2 mg/L) at pHini of 2.8 was 2.1 times greater than that (21.3 mg/L) at pHini of 3.2. Under non-adapted bacteria conditions, the extent of Fe leaching was not significantly different between the pHini of 2.8 and 3.2. This could be attributed to the fact that the adapted bacteria could more easily attach onto the pyrrhotite surfaces at pHini 2.8, allowing contact biological oxidation during the bioleaching experiments. We demonstrate here that the bioleaching of pyrrhotite could increase Fe recovery through bacterial adaptation and contact biological oxidation.

The Depression and Adsorption Mechanism of Polyglutamic Acid on Chalcopyrite and Pyrrhotite Flotation Systems

The rejection of pyrrhotite and pyrite has become a long-standing problem in the copper ore industry. This paper describes the first successful depression and adsorption mechanism of a novel and non-hazardous reagent, polyglutamic acid (PGA), on pyrrhotite in the selective flotation of chalcopyrite with xanthate as the collector, making use of various laboratory-scale measurement techniques. The addition of PGA inhibited the flotation of pyrrhotite much more strongly than that of the chalcopyrite in a wide pH range. The prior addition of PGA achieved an improved selective flotation of chalcopyrite from pyrrhotite at pH 8, at which the grade and recovery of chalcopyrite in concentrate were over 80%. Surface measurement techniques including XPS spectral, IR spectral, zeta potential, and reagent adsorption analyses indicated that the PGA interacted differently with the two minerals, and had much greater affinity towards pyrrhotite than chalcopyrite. The presence of PGA blocked the electrochemical activity of the collector on the pyrrhotite surface and thus depressed its flotation, whereas the adsorption of the collector and its oxidation to dixanthogen were more effective on the chalcopyrite surface, indicating a weaker interaction of PGA with chalcopyrite. Our results suggest that the application of PGA could replace the toxic inorganic depressants in flotation technology, and could significantly reduce the environmental impacts of processing.

Water quality effects on bubble-particle attachment of pyrrhotite

In froth flotation, separation between the valuable and the gangue minerals comes as a result of the attachment of hydrophobic particles to air bubbles. Considering the importance of bubble formation and bubble-particle attachment, it is evident that the pulp phase facilitates the events for the most crucial requirements of successful flotation. Water forms the bulk of the pulp phase; and as a result of water scarcities in countries like South Africa, the need to recycle process water within mining operations is increasing. Hence it is of great importance to understand the effects of water quality on the vital sub-processes within the flotation process, particularly bubble-particle attachment. A novel attachment timer which allows for 396 opportunities for bubble-particle attachment was used for the bubble-particle attachments tests in this work. Three water qualities of increasing ionic strength were tested both in the presence and absence of a xanthate collector to see the effect of increasing ionic strength of synthetic plant water on the bubble-particle attachment probability. The attachment time measurements showed a general decrease in attachment probability as the ionic strength of the synthetic plant water increased both in the absence and presence of a collector. This result indicated that increasing the concentration of the ions present in synthetic plant water lowered the probability of pyrrhotite particles attaching to air bubbles. Further, adsorption studies showed that less xanthate adsorbs on the mineral surface at the highest ionic strength of synthetic plant water under study. This indicates that increases in the ionic strength of synthetic plant water hindered the xanthate adsorption on the pyrrhotite surface. Furthermore, an increase in the zeta potential of pyrrhotite with increasing ionic strength was reported, indicating cation adsorption on the mineral surface. The study presented shows a direct relationship between the zeta potential and attachment probability.