Abstract
The mining industry in Chile concentrates in the northern part of the country, mostly covered by desert landscapes, including the Atacama Desert and its adjacent areas. Their arid and semi-arid climates cause the predominance of eolian weathering on tailing surfaces. The tailing dust transported by wind is a main factor of metal contamination in the vast areas surrounding mining waste repositories. In this context, we studied with Brunauer-Emmett-Teller (BET) analysis the microstructural characteristics of tailings from the Domeyko and Delirio impoundments exposed to wind erosion under contrasting humidity regimes. Both sites are located near urban areas and have been abandoned for more than 30 years. Pyrite together with other sulfides trigger the acidification of the system and the activation of the dissolution processes. The proportion between pyrite, pH compensating silicates such as feldspars and water available in the adjacent pores controls the development of three main alteration patterns in the tailings column. Unaltered feldspars, secondary iron hydroxides or jarosite dominate in the mineral makeup of the matured tailings. Considering BET characteristics, those mineralogical clusters differ by the reactive surface area that links directly to the volume of micropores and mesopores. Microstructural features like bottleneck, plate and cylindrical pores correspond to the specific alteration patterns. Cylindrical pores do not form in the Feldspar cluster, but they are common in samples of the Jarosite cluster. Otherwise, bottleneck-shaped pores, typical for the tailings not affected by chemical transformations, are rare in the Jarosite cluster. Both bottleneck and cylindrical pores are not found in the sulfate crusts. At the more acidic levels, typical for the Jarosite cluster, the smallest pores are destroyed reducing the reactive surface area. The plate-shaped pores formed in goethite store toxic metals. On the other hand, in the Jarosite cluster, gypsum shares microstructural features linked to the adsorption of hazardous elements. The development of sulfate crusts inhibits the reactivity and shields the tailing surfaces affected by the acid weathering, although sulfate minerals may accumulate toxic metals in their structure. The BET analysis complements the chemical, mineralogical and granulometric properties of abandoned mining waste deposits and improves our understanding of the eolian transport of tailing dust in desert climates.