Analysis of the iron coatings formed during marcasite and arsenopyrite oxidation at neutral-alkaline conditions

• Published in: Geologica acta Vol. 11; no. 4; pp. 465 - 481
• Main Authors: Asta Andrés, Maria Pilar, Pérez López, R., Román Ross, G., Illera, V., Cama, Jordi, Cotte, M., Tucoulou, R.
• Format: Journal Article
• Language: English
• Published: Universitat de Barcelona 01-12-2013; Geologica Acta; Institut de Ciències de la Terra "Jaume Almera"; Universitat de Barcelona (UB), Geociències Barcelona (Geo3BCN), Institut de Diagnosi Ambiental i Estudis de l'Aigua (IDAEA), Universitat Autònoma de Barcelona (UAB)
• Subjects: Arsenopyrite; basic pH; Chemical engineering; Chemical engineering research; Chemical properties; Identification and classification; Iron; Iron phases; Marcasite; Neutral; Oxidation-reduction reaction; Pyrites; Sulphide oxidation; Sulphide oxidation. Iron phases. Arsenopyrite. Marcasite. Neutral-basic pH; Spain; Marcasite; Sulphide oxidation; Iron phases; Arsenopyrite; Neutral-basic pH
• ISSN: 1695-6133; 1696-5728
• DOI: 10.1344/105.000002062

In order to study the nature of the precipitates formed on arsenopyrite and marcasite after reacting with neutral to alkaline solutions, a combination of techniques including Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS), X-ray Photoelectron Spectroscopy (XPS) and synchrotron-based techniques such as micro-X-Ray diffraction (µXRD) and Micro-X-ray Absorption Near Edge Structure (µXANES) have been used. The results showed that the oxidation of marcasite and arsenopyrite under neutral to alkaline conditions leads to the formation of an Fe rich coating which seems to prevent the oxidation of these sulphides. SEM observations confirmed the presence newly-formed phases after the sulphides reaction under the studied conditions. XPS analysis showed that iron, sulphur and arsenic in the case of the arsenopyrite are in oxidized states in the sulphide surfaces. The microscale analysis of the S and Fe speciation performed by µXANES suggested that due to the sulphide oxidation an increase in the oxidation state of those elements took place together with an increase of the sulphate content in the surface layer (grain boundary). Micro-X-ray diffraction results indicated that goethite (a-FeOOH) is the only crystalline newly-formed phase when the reaction occurs at pH 12 whereas at lower pH the products formed on the sulphide surfaces seem to be poorly crystalline and they do not contribute to the diffraction effects in the XRD diagrams.