Impact of acid mine drainages on surficial waters of an abandoned mining site

Weathering of sulphide minerals produces a great variety of efflorescences of soluble sulphate salts, which significantly influence environmental pollution by acting as either sinks or sources for acidity and trace elements. This study aims to characterise surface waters impacted by mining activities in the Sierra Minera of Cartagena-La Union in southeastern Spain. Water samples were analyzed for trace metals (Zn, Cd, Pb, Cu, As, Fe), major ions (Na+, K+, Ca2+, Mg2+), and anions (F−, Cl−, NO3−, CO32−, SO42−), followed by an evaporation-precipitation experiment to identify salts formed from onsite water evaporation. Mineralogical analysis utilizing X-ray diffraction revealed that the area is heavily polluted due to historical mining activities, characterized by high trace element content, acidic pH, and supergene alterations of raw materials. Predominant minerals found in the acid mine drainage precipitates include magnesium, zinc, iron, and aluminium sulphates, alongside quantified minerals from the hexahydrite group, rozenite group, alunogen, and others such as coquimbite and copiapite, with gypsum being the sole representative of calcium sulphates. Insights gained from this study contribute to the understanding of the system's response to intermittent rainfall in a semiarid climate, suggesting that while the MINTEQ model could analyze mining-affected waters, simulations through evaporation provide more realistic results.