Arsenopyrite (FeAsS) and realgar (As4S4) are two common arsenic minerals that often cause serious environmental issues. Centralised treatment of arsenic-containing tailings can reduce land occupation and save management costs. The current work examined the remediation schemes of tailings from Hunan Province, China, where by different tailings containing arsenopyrite and realgar were blended with exogenous slag zero valence iron (ZVI). Introducing Fe-oxidising bacteria (Acidithiobacillus ferrooxidans) recreates a biologically oxidative environment. All bioleaching experiments were done over three stages, each for 7 days and the solid phase of all tests was characterised by scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and selective extraction analyses. The results showed that the mixture group reduced arsenic release by 72.9–74.7% compared with the control group. The addition of 0.2 g ZVI clearly decreased arsenic release, and the addition of 4.0 g ZVI led to the lowest arsenic release among all tests. The decrease of arsenic released from the tailings was due to the adsorption and uptake of arsenic by secondary iron-containing minerals and Fe–As(V) secondary mineralisation. The addition of large amounts of ZVI reduced the arsenic detected in the amorphous Fe precipitates. Therefore, a low cost and integrated strategy to reduce arsenic release from tailings is to mix two typical tailings and apply exogenous slag ZVI, which can apply to the in situ remediation of two kinds or more arsenic-containing tailings.

Arsenopyrite (FeAsS), gudmundite (FeSbS) and the rarer Fe sulfosalts berthierite (FeSb2S4) and garavellite (FeSbBiS4), were investigated by Raman spectroscopy. Whereas (Sb,Bi)S3 pyramids are responsible for the Raman spectra of berthierite and garavellite, the spectra of gudmundite and arsenopyrite arise from the stretching and bending modes of (Sb,As)S units. Internal vibrations for berthierite and garavellite occur between 400 and 50 cm–1, and those of the gudmundite and arsenopyrite between 500 and 100 cm–1. The longer bond distances of the SbS3 groups readily explain the lower frequencies for berthierite in comparison with garavellite. Similarly, the greater mass and the longer bond distances of the Sb–S units also explain the lower frequencies observed for gudmundite relative to arsenopyrite.

A multidisciplinary approach has been used to study Au occurrences within pyrite and arsenopyrite in four refractory Au ores from Colombia, France (Le Châtelet and Villeranges) and Portugal (Neves Norte). The Au was characterized by optical and scanning electron microscopy and analysed using electron and ion microprobes to determine Au distribution, with particular attention to spectral interferences in electron and ion microprobes, background measurements in electron probes, and quantitative analysis using external standardization in ion probes. The ionic emission rate is proven to be dependent on the Au status; combined Au has a greater ion emission than metallic Au. Invisible Au occurrences are closely linked to As distribution. Gold bonding in arsenopyrite, examined by transmission electron microscopy, is shown to be dispersed within the FeAsS crystal structure. Typical growth patterns and As-Au diffusion zoning in pyrite and arsenopyrite may account for the very irregular distribution of Au in these minerals.

Surfaces of a natural sample of arsenopyrite (FeAsS) were oxidized by a range of inorganic oxidants, and the resultant surface alteration products studied using various spectroscopic techniques. The oxidants used were air during heating to relatively low temperatures (150°C), steam, ammonium hydroxide, hydrogen peroxide, and sulphuric acid. Electrochemical oxidation in water was also undertaken. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and spectral reflectance measurements, were used to characterize the surface compositions. New data are proposed for the binding energies of core electrons in arsenopyrite based on the fitted XPS spectra: 706.9 eV for the Fe 2p3/2 level, 161.2 eV for the S 2p level, and 40.7eV for the As 3d level. Spectroscopic analyses of the surfaces following oxidation indicated a range of iron oxides and hydroxides (Fe1−xO, Fe3O4, Fe2O3, FeOOH and Fe(OH)3), arsenic oxides (As2O3 and As2O5), sulphur and iron sulphates (FeSO4, Fe2(SO4)3). The relative proportions of the different phases present in the surface layer are related to the strength of the oxidant employed and, where relevant, the Eh/pH conditions prevalent during oxidation. The conclusions regarding the nature of the oxidation of arsenopyrite are discussed in relation to arsenopyrite extraction by flotation and leaching, and the breakdown of arsenopyrite in natural systems.

The (110) surfaces of arsenopyrite (FeAsS) and enargite (Cu3AsS4) have been modelled using a Density Functional Theory (DFT) plane-wave pseudopotential method (CASTEP) in order to better understand aspects of the geometric and electronic structures of these minerals, which have important implications for the release of arsenic in acid mine drainage environments. In this study, bulk calculations of these minerals have been conducted to give consistent geometries for surface models and to establish reference states for changes at the surfaces in these models. Surface structure experimental data for enargite were collected using low-energy electron diffraction which confirmed an unreconstructed 161 (110) lattice, with a and b values of 6.38±0.3 Å and 9.92±0.5 Å, respectively. Surface calculations demonstrate geometric and electronic relaxation of both arsenopyrite and enargite (110) surfaces. Changes in atomic positions, interatomic distances, Mulliken charges and electronic configurations are reported. Enargite has a surface energy of ∼0.02 eV/Å2 compared with arsenopyrite which has a surface energy of ∼0.11 eV/Å2, indicating that the enargite (110) surface is more energetically stable than that of arsenopyrite. The most stable surfaces are those which relax to restore the surface coordination and partial charge balance. For both minerals this is achieved by the formation of covalent bonds. Arsenic has the most positive Mulliken charge of all the surface atoms and is, therefore, predicted to be the most reactive atom at the arsenopyrite and enargite (110) surfaces. This implies that, according to these calculations, arsenic is most likely to react with oxidative species such as O2 and H2O in environments such as those associated with acid mine drainage, potentially releasing oxides and acids of arsenic into the environment.

The first-principles plane-wave pseudopotential method is used to study the electronic and chemical structures of pyrite (FeS2) and arsenopyrite (FeAsS). The results indicate that an antibonding interaction occurs between Fe and As atoms in arsenopyrite. This interaction results in the Fe atom being repelled towards the S atom to stabilize antibonding orbitals, causing a larger S–Fe–S angle in arsenopyrite than in pyrite and a distortion in the arsenopyrite structure. In arsenopyrite, Fe–Fe distances are alternately long and short. The low spin density of the Fe d electrons supports this configuration in arsenopyrite. However, electron density calculations indicate that there is negligible electron density present between Fe atoms. This result indicates that cation-anion interactions are dominant in arsenopyrite. The pyrite Fe 3d orbital is split below the Fermi level, whereas the arsenopyrite Fe 3d orbital is not split, which can be attributed to the stronger interatomic bonding effects between Fe and S atoms in pyrite compared to arsenopyrite. It is found that the d-p orbital interactions between Fe and S atoms lead to bonding-antibonding splitting in both pyrite and arsenopyrite. However, the bonding effects between pyrite Fe and S atoms are stronger than in arsenopyrite. In arsenopyrite, the bonding interaction between the As 4p and Fe 3d orbitals is very weak, while the antibonding effect is very strong. The p-p orbital interaction is the dominant effect in As–S bonding. Frontier orbital calculations indicate that the Fermi levels of pyrite and arsenopyrite are notably close to each other, resulting in similar electrochemical activities. Orbital coefficient results show that the pyrite Fe 3d and S 3p orbitals are the active orbitals in the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), respectively. In the case of arsenopyrite, Fe 3d orbitals are very active in both the HOMO and LUMO. Moreover, the activity of the As 4p in the HOMO is greater than S 3p, whereas the opposite situation occurs in the LUMO. Based on these results, As atoms could be one of the active sites for the oxidation of arsenopyrite. In addition, separation of arsenopyrite and pyrite could be achieved by utilizing the difference in chemical reactivities of iron in the two minerals.

The distribution of Au and associated trace elements in pyrite and arsenopyrite from late Archean Hutti and Hira-Buddini orogenic gold deposits, eastern Dharwar Craton, southern India was investigated by laser ablation-inductively coupled plasma-mass spectrometry. X-ray element maps acquired by electron probe microanalyser reveal oscillatory zoning of Co and As indicating the crystallization of pyrite and arsenopyrite in an episodic fluid flow regime in which fluid salinity fluctuated due to fault-valve actions. The absence of any relationship between Au and As in pyrite obviate the role of As in the incorporation of Au into pyrite, particularly here and may be generally the case in orogenic gold deposits. On the other hand, positive correlations of Au with Cu, Ag and Te suggest possible influence of these chalcophile elements in the enhanced gold concentrationin sulfides. Pb-Bi-Te-Au-Ag bearing micro-particles (<2 μm) are observed exclusively in micro-fractures and pores in arsenopyrite. The absence of replacement features and element gradient suggests direct precipitation of Pb, Bi, Te, Au and Ag from a fluid that was unreactive towards arsenopyrite. An intermittent fall in fluid pressure caused by the fault-valve action would have resulted in the sporadic precipitation of Au, Pb, Ag, Bi and Te.

An unworked quartz vein-hosted gold deposit occurs in the Clew bay area of County Mayo, western Ireland. The veins are late-Caledonian in age and transect greenschist-facies poly-deformed Silurian quartzites. The veins contain disseminated arsenopyrite that may be a primary mineral source for elevated levels of arsenic (As) found in groundwater samples recovered from wells related spatially to the gold deposit. Levels from 5 to 188 μg/L (significantly above the 7.5 μg/L threshold for safe drinking water) have been detected. A series of element distribution maps using a scanning electron microscope (Hitachi model S-4700) linked to an energy-dispersive spectrometer (INCA® Oxford Instruments) and mineral distribution maps generated by QEMSCAN® (Quantitative Evaluation of Minerals by Scanning electron microscopy) were used to map the distribution of the primary arsenopyrite and related secondary As-bearing phases. Laser Raman microspectroscopy was used to identify the secondary As-bearing phases. 'Island weathering' of primary arsenopyrite together with hydrated pseudomorphs of arseniosiderite, pharmacosiderite and scorodite after arsenopyrite are recorded. Circulating groundwater hydrates the primary arsenopyrite, providing the release mechanism that forms the secondary As-bearing phases that occur as microfracture infills together with muscovite and biotite. The textural relationships between the primary and secondary As minerals indicate their potential as mineral sources of As that could enter transport pathways leading to its release into groundwater.