Pyrite Surface Research Articles

Maximizing pollutant removal and greenhouse gas emission reduction in vertical flow constructed wetlands: an orthogonal experimental approach.

Owing to the impact of the effluent C/N from the secondary structures of urban domestic wastewater treatment plants, the denitrification efficiency in constructed wetlands (CWs) is not satisfactory, limiting their widespread application in the deep treatment of urban domestic wastewater. To address this issue, we constructed enhanced CWs and conducted orthogonal experiments to investigate the effects of different factors (C/N, fillers, and plants) on the removal of conventional pollutants and the reduction of greenhouse gas (GHG) emission. The experimental results indicated that a C/N of 8, manganese sand, and calamus achieved the best denitrification efficiencies with removal efficiencies of 85.7%, 95.9%, and 88.6% for TN, NH4+-N, and COD, respectively. In terms of GHG emission reduction, this combination resulted in the lowest global warming potential (176.8mg/m2·day), with N2O and CH4 emissions of 0.53 and 1.25mg/m2·day, respectively. Characterization of the fillers revealed the formation of small spherical clusters of phosphates on the surfaces of manganese sand and pyrite and iron oxide crystals on the surface of pyrite. Additionally, the surface Mn (II) content of the manganese sand increased by 8.8%, and the Fe (III)/Fe (II) and SO42-/S2- on pyrite increased by 2.05 and 0.26, respectively, compared to pre-experiment levels. High-throughput sequencing indicated the presence of abundant autotrophic denitrifying bacteria (Sulfuriferula, Sulfuritalea, and Thiobacillus) in the CWs, which explains denitrification performance of the enhanced CWs. This study aimed to explore the mechanism of efficient denitrification and GHG emission reduction in the enhanced CWs, providing theoretical guidance for the deep treatment of urban domestic wastewater.

Mechanism investigation of food waste compost as a source of passivation agents for inhibiting pyrite oxidation

Pyrite oxidation causes the generation of acid mine drainage (AMD), posing significant challenges in the management of sulfide tailings. Passivation agents such as humic acid have been tested to prevent pyrite oxidation. The potential of using humate rich food waste compost as a source of passivation agents to suppress pyrite oxidation was explored in this study. Batch leaching tests were conducted at room temperature, involved oxidatively leaching a pure pyrite and a pyrite-containing coal refuse sample, respectively, with and without adding the compost at acidic pH. The involved passivation mechanisms were investigated by solution leaching tests and spectroscopic (XPS) and microscopic (SEM) analysis of the pure pyrite sample and its leaching residues. Compared to the control, adding the compost led to the increases in solution pH, removal of the Fe2+/Fe3+ ions from the solutions by adsorption, and remarkable decreases (≥58 %) in sulfur concentration in both samples. Both SEM and XPS analysis indicated that a coating layer was successfully established on pyrite surface after being leached in the presence of the compost. The coating layer comprised a mixture of organic species (e.g., O-CO and N-H/C groups) and phosphate, potentially improving the likelihood of providing antioxidant protection over acidic pH. As a low-cost material, food waste compost can benefit the source control of AMD not only in terms of its surface passivation, but also its intrinsic alkalinity, metal immobilization, and low environmental risk.

Electrochemical Oxidation Mechanism of Pyrite in a Copper(II)-Citrate-Sodium Thiosulfate Composite System

Pyrite is an important gold carrier during gold leaching, but it is readily oxidized, which causes environmental problems such as acidic mine drainage. Thus, it is necessary to study the oxidation mechanism of pyrite in a gold-leaching electrolyte. The surface oxidation reaction of pyrite is a multi-electron transfer electrochemical oxidation process. Based on this, electrochemical technology was used to explore the electrochemical oxidation mechanism of pyrite in a Cu2+-Cit3−-S2O3 2− system. The surface oxidation products of the pyrite were characterized by Raman spectroscopy and X-ray photoelectron spectroscopy. The experiments showed that the thiosulfate concentration did not change the oxidation mechanism of pyrite at 0.30 V under the conditions of this experiment. Increasing the concentration and potential of thiosulfate accelerated the oxidation rate of pyrite. The electrochemical oxidation of pyrite in the Cu2+-Cit3−-S2O3 2− system occurred in two stages. At low potentials in a passivated state, the process was diffusion-controlled, and the surface oxidation rate was slow. When the potential exceeded 0.50 V, the passivation film on the surface was penetrated, allowing the oxidation reaction on the surface of pyrite to continue. The results of this experiment are useful for deepening the understanding of the oxidation mechanism of pyrite in electrolytes.

Regulating sulfur vacancies formation on mechanochemically modified pyrite to steer non-radical molecular oxygen activation for water purification

Ubiquitous pyrite (FeS2) in the earth’s crust features strong reducing capacity, presenting a promising alternative for molecular oxygen (O2) activation to facilitate water purification, but the interfacial electron transfer efficiency was remarkably retarded due to the existed passivation layer and limited reactive sites on the surface of pristine pyrite. Herein, we proposed an effective mechanochemical approach to unlock the potential of pyrite for O2 activation and refractory pollutant degradation. Compared to the inert pristine one, the ball milling-treated pyrite (BMPs) could achieve efficient sulfamethoxazole (SMX) degradation with a rate constant of 0.23 h−1. By a combination of characterizations, batch experiments, and density function theory (DFT) calculations, a clear panorama delineated the consecutive O2 adsorption and activation processes was established. Ball milling treatment could import rich sulfur vacancies (SVs) on pyrite, which unshifted the p-band center of adjacent S for improved O2 adsorption, also narrowed the band gap of BMPs to promote the interfacial electron transfer rate for O2 activation. Singlet oxygen (1O2) was identified as the dominant reactive species for SMX degradation, such non-radical oxidation feature rendered the system with remarkable activity and environmental robustness. Our work lay a foundation for constructing robust pyrite towards stable and efficient environmental remediation applications.

Influence and mechanism of new environmentally friendly depressant carboxymethyl-β-cyclodextrin on the flotation separation of chalcopyrite and pyrite

It is difficult to realize an effective separating of chalcopyrite and pyrite without using any depressants due to their similar physicochemical properties. Herein, a cyclic oligosaccharide carboxymethyl-β-cyclodextrin (CMCD) with carboxyl and hydroxyl groups was introduced for the first time as a novel environmentally friendly depressant for separating chalcopyrite from pyrite. The depression performance and adsorption mechanism of CMCD in the flotation separation of chalcopyrite and pyrite were investigated through micro-flotation experiments, molecular dynamics (MD) simulations, and a series of characterization tests. The flotation findings manifested that under weakly acidic conditions (pH=6.5±0.2), a high-quality copper concentrate with a copper recovery of 73.15 % and a grade of 28.06 % was obtained. CMCD exhibited superior inhibition of pyrite compared with other traditional inhibitors. The adsorption density of CMCD onto the pyrite surface was significantly higher than that of chalcopyrite, and the pre-treatment with CMCD hindered the attachment of sodium butyl xanthate (SBX) on pyrite but had a minor effect on chalcopyrite, as confirmed by contact angle, adsorption amount, and Atomic Force Microscope analyses. Moreover, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses robustly demonstrated that the carboxyl and hydroxyl groups in the CMCD molecule primarily reacted with the metal hydroxides on the pyrite surface through hydrogen bonding, leading to a more hydrophilic surface. MD simulations further confirmed at the molecular level that the affinity of CMCD for the pyrite surface was much greater than for chalcopyrite. In summary, CMCD shows promising potential as a depressant for separating chalcopyrite from pyrite.

Effect of lead ions treatment on the flotation behavior of lime-depressed pyrite in a butyl xanthate system

Pyrite is often found alongside other sulfide minerals and is typically suppressed by lime during industrial flotation to selectively enrich with other valuable minerals. Given the continuous depletion of mineral resources, recycling these suppressed resources has become necessary. Consequently, the reactivation of lime-depressed pyrite is crucial for its recovery via flotation. This study investigated the lead (Pb) nitrate to activate lime-depressed pyrite. Various analytical techniques, including micro-flotation tests, zeta potential measurements, contact angle measurements, ultraviolet–visible spectrophotometry, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM-EDS) were employed to investigate the activation mechanism of Pb2+ on lime-depressed pyrite. The treatment with Pb2+ resulted in a significant enhancement in the recovery of lime-depressed pyrite flotation, achieving a maximum recovery of 98.33 %. Analysis through zeta potential, XPS, and SEM-EDS revealed that Pb species reacted with lime-depressed pyrite surfaces to form Pb-S and Fe-O-Pb species. This reaction enhanced the active sites and adsorption of collectors on lime-depressed surfaces, consequently increasing the hydrophobicity of the pyrite particles.

Galvanic interaction between galena and pyrite with dithiothreitol and its effects on flotation performance

With the advancement of green mine construction and the increasing difficulty of lead–sulphur resources, the traditional lime high-alkalinity lead–sulphur separation technology has exposed many shortcomings. In this study, based on the galvanic interaction of galena and pyrite, an environmental-friendly depressant dithiothreitol (DTT) was used to separate pyrite and galena under low alkalinity. In addition, the mechanism of DTT was revealed by electrochemical, ion dissolution, contact angle, zeta potential and DFT calculation. The results indicated that the galvanic interaction between galena and pyrite promoted the oxidation of galena and the dissolution of Pb2+ from the surface of galena, and Pb2+ would be adsorbed on the pyrite surface and increase the floatability of pyrite. DTT could selectively depress pyrite at low alkalinity. The interaction mechanism of DTT was that DTT could weaken the galvanic interaction of galena and pyrite and complex lead ions. In addition, DTT was adsorbed on the pyrite surface through the Fe-S bond, and the pre-adsorbed DTT hindered the adsorption of DDTC on the pyrite surface, thus the pyrite flotation was depressed.

Inhibition of acid rock drainage with iron-silicate or phosphate film: in rainy and submerged environments.

Iron phosphate-based coating and iron silicate-based coating were used to inhibit the oxidation of sulfide minerals in rainy and submerged environments. The inhibiting effectiveness of coating agents on the oxidation of iron sulfide minerals was investigated using pyrite and rock samples resulting from acid drainage. The film formed with both surface-coating agents was identified by pyrite surface analysis. It was also confirmed that the formation of coatings varies depending on the crystallographic orientation. The inhibitory effects under rainy and submerged conditions were investigated using column experiments. Submerged conditions accelerated deterioration compared to that under rainy conditions. Iron phosphate coating had a significantly better oxidation-inhibitory effect (84.86-98.70%) than iron silicate coating (56.80-92.36%), and at a concentration of 300mM, H+ elution was inhibited by more than 90% throughout the experiment. Furthermore, methods for effective film formation were investigated in terms of producing Fe3+; (1) application of coating agents mixed with oxidant (H2O2), (2) application of coating agent after the use of the oxidant. In a rainy environment, applying iron phosphate-based coating using the sequential method showed oxidation inhibition effects for cycles 1-9, whereas applying the mixed material showed effects for cycles 9-13. The use of a surface-coating agent after applying an oxidant did not inhibit oxidation. The surface coating agent and the oxidizing agent should be applied as a mixture to form a film.

An eco-friendly depressant derived from grape seed extract (GSE) as depressant for flotation separation of pyrite from chalcopyrite under low-alkalinity conditions

This study explores the selective depression mechanism of pyrite by proanthocyanidins (PC) during chalcopyrite-pyrite flotation separation. The selective inhibition effect of inhibitor PC was examined through flotation experiments. The depression mechanism of PC on pyrite was analyzed employing X-ray photoelectron spectroscopy (XPS) analysis, selective adsorption tests, adsorption experiments, contact angle measurement, and zeta potential measurement. The artificial mixed mineral flotation test of chalcopyrite-pyrite at a ratio of 1:12 was conducted under pH 7, PC concentration of 75 mg/L, and PAX concentration of 18.75 mg/L. The copper concentrate exhibited a recovery rate of 88.97%, with a copper grade of 29.43%. The sulfur grade in copper concentrate was 40.35%, and the pyrite recovery rate was 1.97%. PC can be used as a potential depressant of pyrite. adsorption experiments and Zeta potential measurement indicated that PC treatment significantly impeded PAX adsorption on the pyrite surface, as confirmed by XPS test results and Ion adsorption analysis.

In-situ groundwater remediation of contaminant mixture of As(III), Cr(VI), and sulfanilamide via electrochemical degradation/transformation using pyrite

Electrochemical advanced oxidation processes (EAOPs) are effective in removing persistent contaminants from groundwater. However, their practical applicability depends significantly on various site-specific characteristics. Therefore, the primary objective of this investigation was to study the feasibility of EAOPs and pyrite, which is a sulfide mineral, to effectively remove the mixture of arsenic (As (III)), chromium (Cr (VI)), and sulfanilamide in groundwater. We conducted a comparison of three systems: (1) EAOP alone, (2) pyrite alone, and (3) a combined EAOP and pyrite system. In EAOP alone, sulfanilamide was effectively oxidized (80%), while the electrochemical transformation of As(III)/Cr(VI) into As(V)/Cr(III) was limited. In just the pyrite system, As(III), Cr(VI), and sulfanilamide were adsorbed onto the surface of pyrite (60%, 20%, and 18%). Neither the EAOP nor the pyrite system alone could effectively treat the contaminants mixture. Nonetheless, the combined system completely removed As(III), Cr(VI), and sulfanilamide by the synergistic reaction. This could be attributed to the formation of green rust, a natural adsorbent mineral produced as a reaction of dissolved iron, generated via electrochemical pyrite oxidation, with the groundwater electrolyte (e.g., CO3 or SO4). This system harmonized the combined approach of EAOP and pyrite to effectively eliminate both organic and inorganic contaminants. Environmental implicationA paper proposed electrochemical oxidation (EO) with pyrite to remove both organic and inorganic contaminants from groundwater. The removal performance of the combined system was evaluated, and the synergistic mechanism was revealed. The combination of EO and pyrite with synergistic removal effectively removed the mixture of both contaminants. This could be attributed by the formation of green-rust by electrochemical activation for pyrite. Compared to the single system of EO and pyrite alone, the combined system with EO and pyrite improved removal performance. Results suggested that the combined system could be used for green groundwater remediation.

Exploration of sodium thiosulfate for leaching of cobalt-containing pyrite: A DFT study

The paper presents the theoretical calculation results of exploratory research relating to the leaching of cobalt-containing pyrite using sodium thiosulfate as a lixiviant. It is well known that density functional theory (DFT) calculations can qualitatively evaluate the exchange of matter and energy between the mineral system and the surroundings, which greatly expands the breadth and depth of leaching process. Thus, DFT method was used to determine the effectiveness of sodium thiosulfate (Na2S2O3) as a lixiviant for the leaching of cobalt-containing pyrite in this study. The analyses of DFT calculations illustrated that thiosulfate can be well adsorbed on the surface of cobalt-containing pyrite due to the formation of S-Fe and O-Co bonds between the S 3p orbital and O 2p orbital in sodium thiosulfate and the Fe 3d orbital and Co 3d orbital in cobalt-containing pyrite. Analysis of crystal orbital Hamilton population (COHP) indicated that Fe-S and S-Co bonds became longer when the thiosulfate adsorbed on the surface of the cobalt-containing pyrite, resulting in the weakening of interactions between S and Fe or Co atoms. Overall, the findings suggested that sodium thiosulfate was a promising lixiviant，favored the dissolution of Fe and Co.

Influence of pyrite surface defects on xanthate adsorption: A density functional theory perspective

Many scholars have studied the adsorption behavior of various ions and agent molecules on pyrite surfaces based on density functional theory (DFT) calculations, however, the adsorption behavior of pyrite by surface defects has been relatively less studied. In this study, we try to produce defects on the surface of pyrite by hydration and study them systematically. The effects of pyrite surface defects on the molecular adsorption of xanthates were investigated on the atomic scale by combining DFT calculations, and AFM observation methods, respectively. The results indicate that oxygen molecules can indirectly participate in hydration reactions and promote crystal defect generation. In addition, the absence of coordination intensifies the electron transfer of pyrite, which favors the formation of new coordination with xanthates, and the adsorption energy is also reduced. Defects lead to an increase in the number of xanthate molecules at the adsorption site, and the adsorption capacity is also enhanced. The adsorption morphology was analyzed by AFM measurements to confirm the DFT calculation results. The complex interfacial system of sulfide ores was investigated, and it was found that the hydration process of sulfide ores generates surface defects, which further promote xanthate molecules adsorption. The results extend the traditional electrochemical adsorption theory of sulfide ores and provide theoretical support for the study of the molecular dynamics adsorption process on the surface of sulfide ores.

Effects of sulfur‐ and Fe‐deficient defects on the decomposition of hydrogen peroxide H2O2 on pyrite surface

AbstractThere is still a lack of research on the effect of the S and Fe vacancy on the adsorption mechanism of peroxide (H2O2) on the pyrite surface. In this work, the adsorption of H2O2 molecules on the perfect and defective pyrite surface is simulated based on density functional theory (DFT). The results indicated that the adsorption energy of H2O2 molecules on the S‐vacancy surface is relatively lower than that on the perfect surface and dissociative adsorption entirely occurs, while the adsorption behavior of H2O2 molecules on the S‐rich pyrite surface has not occurred. When the H2O2 molecules are adsorbed on the Fe‐rich pyrite surface, two products appear, one with two OH− species and the other with an H2O molecule and an O atom. The analysis of the transition state (TS) found that the dissociation of the H2O2 molecule producing two OH− species that bond with two Fe atoms is more likely to occur. In addition, based on the coordination chemistry, it is demonstrated that Fe atoms are more reactive around an S vacancy than on a perfect surface.

Activation flotation of lime-depressed pyrite with carbon dioxide: Performances, mechanism and pilot-scale application

Activation flotation of lime-depressed pyrite by sulfuric acid (H2SO4) is usually accompanied by safety hazards and environmental pollution. Exploring eco-friendly, economical and effective activator to replace H2SO4 holds great significance for the sustainable development of mining industry. In this study, carbon dioxide (CO2) as a potential activator was applied in activation flotation of lime-depressed pyrite. Micro-flotation experiments results showed CO2 significantly improved the floatability of pyrite, and a maximum recovery of 93.94% was achieved under optimal operating conditions. The activation mechanism was investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Results indicated the depression of pyrite by lime was attributed to the formation of iron oxide/hydroxide species and calcium film, and CO2 effectively eliminated these hydrophilic compounds from the surface of pyrite, thus promoted the adsorption of xanthate onto the pyrite surface. Moreover, the anodic oxidation of xanthate on pyrite and the influence of CO2 on this process were investigated by cyclic voltammetry measurements. It was found that xanthate oxidation to form dixanthogen was more likely to occur in the presence of CO2, and this reaction replaced pyrite surface oxidation as the dominant anodic process. Finally, pilot-scale experiments were successfully conducted and the recovery of pyrite reached 93.18%, surpassing the ore dressing index of using H2SO4 as activator in actual production at the same period. Moreover, the concentration of sulfate ions in mineral processing wastewater was significantly reduced, and the annual cost of activator can be saved by 0.52 million RMB. The new process of activation flotation pyrite with CO2 has prospects for large-scale application in terms of activation performance, cost-effectiveness and environmental impact.

Enhance U(VI) reduction on natural pyrite surfaces by gamma irradiation

Pyrite with acid-washed surfaces is chemically inert toward aqueous U(VI) at routine conditions. Given that there is a strong radiation field in the nuclear waste repository, the impact of gamma irradiation on the interaction between aqueous U(VI) and natural pyrite was investigated. Three different natural pyrites, namely Si-, Pb-, and As-pyrites, were used for reactions with uranyl nitrate and uranyl acetate, and the focus was set on Si-pyrite. With an initial pH of ∼ 4.5 and ∼ 6.5, results showed that the solution pH increased mainly due to the reduction of nitrate or the decomposition of acetate caused by the gamma irradiation, while it decreased for the reaction with an initial pH of ∼ 9.0 after gamma irradiation due to the oxidation of aqueous Fe2+. Meanwhile, significant amounts of U(IV)/U(V) were formed on pyrite surfaces at these three pH conditions, demonstrating that gamma irradiation can greatly enhance the U(VI) reduction by pyrite. We proposed that the oxidizing ·OH radical generated by water radiolysis could react with pyrite, leaving the concomitant eaq− and ·H radicals to be effective reductants for aqueous U(VI) or the U(VI)-precipitate formed on pyrite surfaces. Conversely, the impact of gamma irradiation on the U(VI) reduction is insignificant at pH ∼ 3.0, mainly due to the quenching effect of eaq− by H+. Besides, carbonate has an inhibitive effect, because it is a quencher of eaq− and can form anionic complexes with U(VI). The presence of pyrite can also protect UO2 from γ-irradiation-induced oxidation.

Sulfur isotope and trace element geochemistry of sulfides from the unique Yaojialing Zn-Au-Cu deposit, Lower Yangtze River Metallogenic Belt, China: Implications for ore-forming process and exploration

The Yaojialing Zn-Au‑Cu deposit is a porphyry-skarn-epithermal vein-type compound deposit that consists of epithermal vein-type lead‑zinc‑silver orebodies, skarn Zn-Cu-Au orebodies, and porphyry CuAu orebodies from shallow level to depth. We decipher the source and metallogenic mechanism by studying the trace element and S isotopic compositions of sulfides (pyrite, sphalerite, chalcopyrite, and galena) from three types of orebodies. The collected pyrite can be divided into two types. PyI coexists with chalcopyrite, and PyII coexists with sphalerite or galena. In addition, PyI was further divided into PyIa (collected from porphyry copper bodies) and PyIb (collected from skarn copper bodies). PyII can be further divided into PyIIa (collected from skarn-type lead‑zinc ore body) and PyIIb (collected from vein lead‑zinc ore body in strata). Sphalerite and galena from skarn-type PbZn ore bodies and shallow vein-type PbZn ore bodies are named SpI and GnI, and SpII and GnII, respectively.Pyrite and sphalerite trace element thermometers revealed that the temperature of the ore-forming fluids decreased from 500 to 600 °C in the porphyry ore body to 300– 360 °C in the skarn ore body and then to 240– 280 °C in the shallow vein ore body. The decrease in the Co and Ni contents of pyrite collected from deep to shallow depths may indicate that meteoric water precipitated in the late ore-forming hydrothermal system. Rapid crystallization and variations in the physicochemical states (such as temperature, pH, fO2, and geochemical composition) of the fluids resulted in an obvious oscillating zone of euhedral PyI pyrite particles. It also affects the solubility of trace metal elements and leads to the selective entry of these elements into pyrite. PyII also shows obvious zonation characteristics rather than oscillating zonation, indicating that the growth rate of pyrite is relatively slow. Moreover, the relationships between the Au and As contents in the two types of pyrite are different. PyI is coupled, while PyII shows decoupling. We believe that this phenomenon is due to the high content of As in ore-forming fluid systems, which may inhibit the absorption of Au on the surface of pyrite rather than the decoupling of Au and As caused by rapid crystallization, based on the rapid increase in As content and non-oscillating zonation in PyII. According to the analysis of the sulfur isotopes of various sulfides, the solid evidences suggest that the ore-forming materials of each type of orebody in the Yaojialing deposit were mainly derived from magmatic-hydrothermal processes and that the fractionation of sulfur isotopes was the result of variations in physicochemical conditions caused by magma-hydrothermal evolution rather than the addition of foreign sulfur sources.

Treating waste with waste: Lignin acting as both an effective bactericide and passivator to prevent acid mine drainage formation at the source

Acid mine drainage (AMD) induced by pyrite oxidation is a notorious and serious environmental problem, but the management of AMD in an economical and environmentally friendly way remains challenging. Here, lignin, a natural polymer and abundant waste, was employed as both a bactericide and passivator to prevent AMD formation. The addition of lignin to a mimic AMD formation system inoculated with Acidithiobacillus ferrooxidans at a lignin-to-pyrite weight ratio of 2.5: 10 reduced the combined abiotic and biotic oxidation of pyrite by 68.4 % (based on released SO42−). Morphological characterization of Acidithiobacillus ferrooxidans revealed that lignin could act on the cell surface and impair the cell integrity, disrupting its normal growth and preventing biotic oxidation of pyrite accordingly. Moreover, lignin can be used alone as a passivator to form a coating on the pyrite surface, reducing abiotic oxidation by 71.7 % (based on released SO42−). Through multiple technique analysis, it was proposed that the functional groups on lignin may coordinate with iron ions on pyrite, promoting its deposition on the surface. In addition, the inherent antioxidant activity of lignin may also be actively involved in the abatement of pyrite oxidation via the reduction of iron. Overall, this study offered a “treating waste with waste” strategy for preventing AMD formation at the source and opened a new avenue for the management of AMD.

Cleaner flotation separation of chalcopyrite from pyrite at low alkalinity: Based on calcium hypochlorite oxidative modification in acid mine drainage system

Efficient and clean flotation separation of copper-sulfur has attracted soaring interest in the beneficiation of sulfide ore. The objective of this work was to examine the influence of calcium hypochlorite (Ca(ClO)2) oxidative modification on the flotation separation of chalcopyrite from pyrite in acid mine drainage (AMD) system. A maximum recovery difference of 69.70 % between both minerals was observed under the recommended conditions (initial pH = 8.5 ± 0.2, [Ca(ClO)2] = 100 mg/L, [EX] = 32 mg/L, and the volume ratio of AMD to pure water = 1:1). A high-grade concentrate with 77.35 % Cu recovery and 29.01 % Cu grade was obtained, demonstrated by mixed-mineral micro-flotation experiments. Analysis of Cu and Fe ions influence indicated that low concentrations of Fe3+ and Cu2+ favored the selective separation of pyrite and chalcopyrite. Moreover, analysis of the pulp ion concentrations showed that Ca(ClO)2 promoted the dissolution of iron ions on the pyrite surface compared to chalcopyrite, thereby enhancing pyrite oxidation. The Ca(ClO)2 interacted more intensively with the pyrite surface, forming a passivated layer that impeded the adsorption of collector, as demonstrated by Zeta potential and contact angle results. The generation of hydrophilic products caused by oxidation on the pyrite surface, such as CaSO4, CaOH+, Fe(Ⅲ)–OOH, and/or Fe2(SO4)3 was confirmed by XPS analysis, further reducing the floatability of pyrite. Furthermore, local electrochemical impedance spectroscopy and scanning electron microscopy analyses further afforded favorable evidence for selective inhibition of pyrite by Ca(ClO)2 in the AMD system. This study provides a new approach to achieve cleaner separation of pyrite and chalcopyrite and offers new perspectives for AMD treatment solutions.

Inhibition photooxidation of pyrite under illumination via altering photogenerated carrier migration pathways: Role of DTC-TETA surface passivation

The oxidation of pyrite is the main cause of acidic mine drainage (AMD), which is a very serious environmental problem in numerous mining areas around the world. Previous studies have shown that passivation agents create a hydrophobic film on the surface of pyrite, effectively isolating oxygen and water. However, the presence of abundant sulfide minerals in tailings ponds may exacerbate AMD when exposed to solar radiation, due to the semiconductor properties of pyrite. It remains uncertain whether the current surface passivation coating can effectively prevent the oxidation of pyrite under light conditions. This paper is the first to investigate the passivation effect as well as the mechanism of surface passivation coating on pyrite under illumination from the perspective of materials science. The results demonstrated that the triethylenetetramine-bisdithiocarbamate (DTC-TETA) passivation coating on pyrite almost completely suppressed the photooxidation of pyrite under illumination by changing the migration path of photogenerated charge carriers. The formation of NC(S)2-Fe chelating groups provides atomic-level interface channels for DTC-TETA to transfer electrons to pyrite and creates a favorable reduction environment for pyrite. Besides, DTC-TETA coating greatly improves the electron-hole pairs recombination efficiency of pyrite, which significantly inhibits the photogenerated electron reduction of oxygen to generate reactive oxygen species (ROS). Moreover, DTC-TETA coating captures the photogenerated holes, avoiding direct oxidation of pyrite by holes. Density functional theory (DFT) calculations revealed that the DTC-TETA coating increases the adsorption energy barrier for oxygen and water. The results extend the existing knowledge on passivation mechanisms on pyrite and hold significant implications for the future screening, evaluation, and practical application of surface passivating agents.

Sulfur Vacancies in Pyrite Trigger the Path to Nonradical Singlet Oxygen and Spontaneous Sulfamethoxazole Degradation: Unveiling the Hidden Potential in Sediments.

Pharmaceutical residues in sediments are concerning as ubiquitous emerging contaminants. Pyrite is the most abundant sulfide minerals in the estuarine and coastal sediments, making it a major sink for pharmaceutical pollutants such as sulfamethoxazole (SMX). However, research on the adsorption and redox behaviors of SMX on the pyrite surface is limited. Here, we investigated the impact of the nonphotochemical process of pyrite on the fate of coexisting SMX. Remarkably, sulfur vacancies (SVs) on pyrite promoted the generation of nonradical species (hydrogen peroxide, H2O2 and singlet oxygen, 1O2), thereby exhibiting prominent SMX degradation performance under darkness. Nonradical 1O2 contributed approximately 73.1% of the total SMX degradation. The SVs with high surrounding electron density showed an advanced affinity for adsorbing O2 and then initiated redox reactions in the sediment electron-storing geobattery pyrite, resulting in the extensive generation of H2O2 through a two-electron oxygen reduction pathway. Surface Fe(III) (hydro)oxides on pyrite facilitated the decomposition of H2O2 to 1O2 generation. Distinct nonradical products were observed in all investigated estuarine and coastal samples with the concentrations of H2O2 ranging from 1.96 to 2.94 μM, while the concentrations of 1O2 ranged from 4.63 × 10-15 to 8.93 × 10-15 M. This dark-redox pathway outperformed traditional photochemical routes for pollutant degradation, broadening the possibilities for nonradical species use in estuarine and coastal sediments. Our study highlighted the SV-triggered process as a ubiquitous yet previously overlooked source of nonradical species, which offered fresh insights into geochemical processes and the dynamics of pollutants in regions of frequent redox oscillations and sulfur-rich sediments.