Environmental Implications of Saline Efflorescence Associated with Metallic Mining Waste in a Mediterranean Region

Abstract

Salt efflorescences from metal sulphides and their waste are important drivers of pollution both in and around mining areas. However, little is known about these supergene minerals, particularly in the mining areas of the Mediterranean. This study aims to characterise saline efflorescences and their leachates from a Mediterranean mining area located in Southeast Spain. The physicochemical characteristics were determined using stereomicroscopy and compositional analysis, with the following techniques: XRD, WDXRF and TG-MS. Additionally, to assess the risk and potential mobility of their analytes, the samples were subjected to the leaching test DIN 38414-S4. The results showed that the salt efflorescences presented a wide range of crystalline habits and colours. Sulphates were by far the largest mineral group, followed by silicates, oxides and sulphides. Their geochemistry was dominated by elements such as S or Fe, although other potentially toxic elements such as Cd, As, Zn, Pb, Ni and Cu were also present. Due to their high metal(loid) concentrations, the salt crusts studied may act as sources of environmental contaminants, demonstrating that their leachates pose a considerable risk to soil and drinking water quality. An analysis of the correlations and provenances of the components of the salt efflorescences revealed the possible presence of some rare supergene minerals of great interest, such as cuprocopiapite and Pb-As-jarosite.