Identification of jarosite and other major mineral Fe phases in acidic environments affected by mining-metallurgy using X-ray Absorption Spectroscopy: With special emphasis on the August 2014 Cananea acid spill

Abstract

The sulfuric acid spill into the Sonora river, enriched in iron and copper ions from the Buenavista del Cobre mine (Cananea), gave way to the formation of various solid iron (Fe) phases. In this study, the mineral phases were identified by X-ray Absorption Spectroscopy (XAS) and bulk powder X-Ray Diffraction (XRD), and chemically through acid digestions for multielemental quantification, as well as a 3-step selective sequential extraction (SSE) to quantify the types of Fe oxide phases and the contribution of the associated elements. Jarosite was the only Fe mineral identified by XRD, but XAS allowed identification of jarosite with potentially toxic elements (PTEs) incorporated in its structure, making these elements less prone to leaching. In addition, very poorly crystalline phases such as schwertmannite and ferrihydrite were identified in several samples through XAS, which was confirmed by SSE. These phases are probably associated with PTEs. Other possible adsorbent Fe(III) minerals were also identified by XAS, such as maghemite and goethite; as well as mixed Fe(II)-Fe(III) minerals, such as green rust. It was possible to infer the influence of the acid spill on the different sampled areas through various Fe phases identified and/or the presence of gypsum. The influence was detected to be lower where the mineralogy was not associated to low pH and high sulfate concentrations. All precipitated Fe(III) phases downriver from the acid spill are known for their high retention capacities of PTEs either from incorporation into their structures and/or from surface adsorption, thus, contributing to the immobilization of the initial metal(loid) pollution caused by the acid spill. In addition, several other samples of mining-metallurgical wastes were analyzed by the same three techniques, suggesting many of the findings from the secondary Fe mineralogy of the Buenavista del Cobre mine acid spill as common processes occurring in mining-affected environments.