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Luna-Sánchez, Rosa María; González, Ignacio; Lapidus, G.T.

doi:10.1023/a:1021262503128

Cited by 11 publications

(13 citation statements)

References 9 publications

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“…[31] The inset of Figure 4 3 and Ag 3 SbS 3 were measured at 2.14, 2.09, 2.03, 2.00 and 1.97 eV, respectively. Energy gaps for proustite and pyrargyrite are similar to those reported in the literature (2.11 eV and 1.93 eV at 300 K, respectively).…”

Section: Spectroscopic Measurementsmentioning

confidence: 99%

On the Reactivity of Sulfosalts in Cyanide Aqueous Media: Structural, Bonding and Electronic Aspects

2010

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The reactivity of the ruby silver minerals proustite (3Ag(2)S⋅As(2)S(3)) and pyrargyrite (3Ag(2)S⋅Sb(2)S(3)) was studied with two types of electrodes: a carbon-paste electroactive electrode (CPEE) and a paraffin-impregnated graphite electrode (PIGE). Polycrystalline samples of α-Ag(2)S (acanthite), As(2)S(3) (orpiment), Sb(2)S(3) (stibnite), Ag(3)AsS(3) (proustite), Ag(3)SbS(3) (pyrargyrite), and three samples of the proustite-pyrargyrite solid solution series were synthesized from pure elements by a solid-state reaction method. Phase identification of samples was carried out by XRD and chemical homogeneity was checked by SEM-EDS. Besides, sulfosalts were characterized by diffuse reflectance spectroscopy (DRS). Flat-band and formal potentials of sulfosalts were determined by the Mott-Schottky method and differential pulse abrasive stripping voltammetry, respectively. Band structure, bonding and solid-state structure are considered to investigate the oxidation and reduction of the solids. A ligand-to-metal charge transfer (LMCT) transition from the AsS(3) (or SbS(3)) group to Ag is related to ease of reducing the pyrargyrite-proustite series. Despite the increase in the amount of As (Sb) in Ag(3)SbS(3) (Ag(3)AsS(3)), reactivity is similar due to the similarity of the solid-state structures, and the same oxidation states of S, As, Sb and Ag species in the lattice. However, the nature of the pnictogen (As or Sb) changes the position of the conduction and valence band edges and modulates the reactivity of the pyrargyrite-proustite series. Anodic dissolution occurs by hole transfer from the top of the valence band that is formed mainly by the states of the AsS(3) and SbS(3) groups. Meanwhile, silver reduction occurs by electron transfer from the Ag 5s orbitals located at the bottom of the conduction band. The difficulty in dissolving proustite and pyrargyrite in cyanide is related to the presence of pyramidal AsS(3) and SbS(3) groups in these sulfosalts.

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Section: Spectroscopic Measurementsmentioning

confidence: 99%

On the Reactivity of Sulfosalts in Cyanide Aqueous Media: Structural, Bonding and Electronic Aspects

2010

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“…[2][3][6][7] However, the behavior of the silver ions in this situation completely differs from when the silver is found in the mineral. 8 This is due to the fact that the silver ions contained in minerals may be present in phases that retard or accelerate their release, while the addition of ions to the solution does not result in the formation of phases that behave in the same manner as the mineral. For that reason, it is necessary to study the electrochemical behavior directly in the silver sulfide or in the corresponding mineral.…”

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confidence: 99%

A Comparative Study of Silver Sulfide Oxidation in Cyanide Media

Luna-Sánchez¹,

González

Lapidus³

2003

J. Electrochem. Soc.

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In the present research, the differences in the oxidation behavior of a high purity acanthite concentrate and silver sulfide ͑analytical reagent͒ in cyanide media were examined using two methods: electrochemical ͑Evans diagrams͒ and chemical ͑stirred tank reactor͒. On one hand, the kinetics of acanthite oxidation were determined to be mixed reaction-diffusion controlled, while, on the other, the analytical reagent oxidation was found to be solely diffusion controlled. The construction of the Evans diagrams was performed using the current vs. potential values of silver sulfide oxidation and oxygen reduction, obtained with direct pulse chronoamperometry on carbon paste electrodes. Analysis of these diagrams allowed calculation of the system's reaction velocity, which corresponded to 8.8 ϫ 10 Ϫ10 mol cm Ag 2 S Ϫ2 s Ϫ1 . When cyanidation was performed on a sulfide concentrate ͑1.4% acanthite͒, a normalized reaction velocity, several orders of magnitude lower, was obtained, even after compensating for the effects of diffusion. An analysis of the reactions involved, both in the electrochemical and the leaching systems, showed a notable difference between the two, reflected by dissimilar interfacial hydroxide ion concentrations. This difference in the chemical atmosphere questions the validity of employing Evans diagrams to describe the leaching kinetics in certain systems. Also, this study established that, for both systems, the aqueous phase lead ions accelerated silver sulfide oxidation because they acted as sequestering agents for hydroxide and/or sulfide ions.Cyanidation is still by far the method most employed in industry to extract gold and silver from their minerals, despite the environmental restrictions associated with it. Even though this method has been extensively studied and applied, doubts still exist regarding the reaction mechanism between silver sulfide and oxygen. 1-5 Two different techniques have been employed to study this process: in chemical and electrochemical systems. In the former, mineral concentrates are leached in stirred tank reactors, obtaining an estimate of the time that is required to extract the silver. The principal disadvantage of this type of research 4 is that it does not allow the direct elucidation of the chemical processes which take place during leaching. Consequently, it is difficult to identify the controlling phenomenon of the reaction, or the effect of solution parameters on the mechanism.In electrochemical systems, a major part of the work in cyanidation has been performed on gold and silver in their metallic forms. 1-3,5-6 However, it has been observed in practice that the behavior of metallic silver greatly differs from that of silver when it is present as a sulfide. In order to simulate the effect of those ions which are generally found associated with silver in its different mineralogical phases, studies have been performed with the addition of ions ͑sulfide and lead, among others͒ to the leaching solution. 2-3,6-7 However, the behavior of the silver ions in this situa...

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“…For the electrode, with slope = −1.04 × 10 15 and area, A = 0.1295 cm 2 we obtain a doping density of 4.05 × 10 17 cm −3 . This value corresponds to a relatively low doping level and accounts for the small conductivity values.…”

Section: Conductivity Estimate-mentioning

confidence: 85%

“…14 Pyrargyrite synthesized by a solid state route and its solid solutions of intermediate compositions covering Ag 2 S, Sb 2 S 3 and Ag 3 SbS 3 were studied electrochemically in aqueous cyanide solutions in the context of Ag extraction from Ag 3 SbS 3 and Ag 3 AsS 3 . 10 In acid media, we are aware of two preliminary reports of pyrargyrite: one for mined powder in 25 mM sulfuric acid 15 that does not include photoelectrochemistry, and our own report of synthesized material in 0.1 M acetic acid. 16 In this paper, we present the solid synthesis of phase-pure pyrargyrite and its photoelectrochemical properties in acid media along with the complimentary material characterization by electron microscopy and X-ray photoelectron spectroscopy.…”

mentioning

confidence: 99%

Photoelectrochemical Study of Pyrargyrite in Acid Media

Parajuli

Chhetri

Barakoti

et al. 2015

J. Electrochem. Soc.

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Silver antimony sulfide (Ag 3 SbS 3 , pyrargyrite) was synthesized by a solid state route from silver, antimony and sulfur powder precursors under an argon atmosphere. The product was characterized by powder X-ray diffraction (XRD) and found to be Ag 3 SbS 3 pyrargyrite alone, with a bandgap (E g ) of 2.0 eV. We analyzed the ground sample by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The bulk composition was found to be consistent with stoichiometric ratios. Surface characterization by X-ray photoelectron spectroscopy (XPS) indicates that the surface is depleted of Ag and S with an excess of Sb. Surface oxygen was found to be predominantly bound to Sb. The electrochemical and photoelectrochemical behavior of films on fluorine-doped tin oxide was compared to the behavior of bulk electrodes prepared from pieces of pyrargyrite grown under Ar. The films' photoelectrochemical behavior was consistent with a p-type material with the conduction band aligned to reduce H + in acid media. The photocurrent showed evidence of states with energies in the forbidden region that were localized at the surface and filled in the dark. Under illumination, photogenerated holes oxidized these surface states and caused recombination. On platinized films, electrons from H 2 oxidation filled these states. Materials with photocatalytic activity in the visible region of solar spectra are of fundamental and practical interest. In applications for solar energy conversion such as water splitting, there is a need for stable materials that can perform electrochemical reactions.1 Since the first report on water splitting with TiO 2 , 2 the development of materials with lower bandgap, E g , than the ca. 3 eV of TiO 2 (e.g., for anatase E g = 3.2 eV) 3,4 has remained a challenge. Although significant progress has been made (e.g., Refs. 5-7) this remains a challenge because as well as E g , the valence band (VB) and conduction band (CB) must be aligned to enable the reaction of interest while the material must be stable. 8 In this paper, we present the preparation of phase-pure pyrargyrite, a material reported 9-11 to be p-type with E g = 2.0 eV. We propose that this material is of interest for water splitting because the conduction band is aligned for H + reduction to H 2 . Pyrargyrite is a naturally occurring silver ore. Its crystal structure has been studied from mined samples;12 natural crystals present high conductivity due to Ag ion mobility 13 with relatively low activation energy (ca. 0.5 eV). 12,13 This is one example of simple Ag-containing sulfosalts 12 that have received increasing attention because of their ionic conductive properties. 14 Pyrargyrite synthesized by a solid state route and its solid solutions of intermediate compositions covering Ag 2 S, Sb 2 S 3 and Ag 3 SbS 3 were studied electrochemically in aqueous cyanide solutions in the context of Ag extraction from Ag 3 SbS 3 and Ag 3 AsS 3 . 10In acid media, we are aware of two preliminary reports of pyrargyrite: one for mined powder in 2...

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Untitled

Cited by 11 publications

References 9 publications

On the Reactivity of Sulfosalts in Cyanide Aqueous Media: Structural, Bonding and Electronic Aspects

On the Reactivity of Sulfosalts in Cyanide Aqueous Media: Structural, Bonding and Electronic Aspects

A Comparative Study of Silver Sulfide Oxidation in Cyanide Media

Photoelectrochemical Study of Pyrargyrite in Acid Media

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