Occurrence, properties and pollution potential of environmental minerals in acid mine drainage

Abstract

This paper describes the occurrences, the mineralogical assemblages and the environmental relevance of the AMD-precipitates from the abandoned mine of Valdarcas, Northern Portugal. At this mining site, these precipitates are particularly related with the chemical speciation of iron, which is in according to the abundance of mine wastes enriched in pyrrhotite and pyrite. The more relevant supergene mineralogical assemblages include the following environmental minerals: soluble metal-salts, mainly sulphates, revealing seasonal behaviour, iron-hydroxysulphates and iron-oxyhydroxides, both forming ochre precipitates of poorly and well-crystalline minerals. Pollution potential of the most highly water soluble salts was analysed in order to evaluate the environmental effect of their dissolution by rainfall. Laboratory experiments, carried out with iron and aluminium sulphates, demonstrated the facility to release metals, sulphate and acidity upon dissolution. Regarding the ochre precipitates, composed by several less soluble iron (III)-minerals, the spatial distribution on the nearby aqueous system as well as the proportion of Jarosite, Schwertmannite and Goethite in the mixtures gave information about the halo's contamination promoted by the AMD emerging from the waste-dumps.

Eliciting Drivers of Community Perceptions of Mining Projects through Effective Community Engagement

“…It is an acidic leachate with high concentrations of heavy metals and sulfate that result from the oxidation of sulfidic minerals. AMD can severely contaminate surface and ground-water, as well as soils [74][75][76]. For example, at the Summitville gold mine in Colorado, AMD polluted seventeen miles of the Alamosa River, severely impacting aquatic life.…”

Impacto das drenagens ácidas das minas de Regoufe e Rio de Frades (Geoparque Arouca) na qualidade de água superficial

“…Depois do início da atividade extrativa, uma grande quantidade de sulfuretos fica exposta às condições superficiais, tendendo a desintegrar-se quimicamente e formam-se novos compostos, até que se restabeleça o equilíbrio com o meio (e.g., BANKS et al, 1997;VALENTE & GOMES, 2009). Desta forma, os sulfuretos ficam expostos à ação conjunta do oxigénio, da água superficial e subterrânea e de bactérias oxidantes catalisadoras, ocorrendo uma série de reações químicas de que resultam ácidos e outros compostos químicos, constituindo a denominada drenagem ácida de minas (DAM).…”

“…Estas águas ácidas provenientes da drenagem de uma mina, embora aparentemente límpidas, podem produzir uma série de situações de impacto negativo ao misturarem-se com águas naturais, havendo alteração na qualidade das águas e, consequentemente, efeitos nefastos sobre a manutenção do ecossistema fluvial circundante (e.g., BANKS et al, 1997;FAVAS & CONDE, 2000;VALENTE & GOMES, 2009;FAVAS et al, 2012).…”

Dissolution Kinetics of Sulfate from Schwertmannite Under Variable pH Conditions

“…Sulfide minerals (Eq. 1) in coal-mining districts and massive sulfide mines are oxidized upon interaction with ground or rain water, atmospheric oxygen, and/or bacterial activities (Valente and Gomes 2009). In addition to SO 4 2-, high concentrations of Fe(III) are also released, which can itself oxidize pyrite, or be removed from the aqueous phase as ferric hydroxy-sulfates (Toran 1987 …”