The study area is located in Cartagena-La Union Mining District, SE Spain. 2500 years of mining has generated large quantities of waste materials and silt ponds affecting 1500ha. The semi-arid climate causes high evapo-transpiration rates, which concentrate salts at the soil surface. Soil columns and surface samples were taken and described, and efflorescence salts were also collected. Electrical conductivity, pH, redox potential, sulphates, total and soluble heavy metals were analyzed.

The results show extremely acidic spoils that range from 1.85 – 2.0 pH. However, specific areas containing efflorescence salts may have pH values as low as 1.2. Salt crusts were taken and analysed using XRD, SEM/EDS, and XRF to establish their mineralogical composition. Results show the presence of epsomite (MgSO4•7H2O), hexahydrite (MgSO4•6H2O), millosevichite (Al,Fe)2(SO4)3, wupatkiite (Co,Mg,Ni)Al2(SO4)4•22H2O, starkeyite (MgSO4•4H2O), gypsum (CaSO4•2H2O), bassanite (CaSO4•).5H2O), langbeinite (KBaFe2(PO4)3), jarosite (K(Fe3S04)2(OH)6) and copiapite (Fe,Mg)Fe4(SO4)6(OH)2•20H2O.

This study investigated the effect of soluble salts movement through the soil system during spring and summer in these abandoned mining zones. In the winter, increased precipitation leaches the salts from the surface layer. This is followed by subsequent upward migration and salt crystallization in the dry season. These salts create potential health risks through lixiviation and transport of heavy metals that are derived through acid mine drainage caused by sulphide weathering in the mining zones. The high solubility of these salts causes an increased risk of heavy metal contamination to surface and groundwater, and human, animal, and plant health. In addition, in the dry season, these heavy-metal laden salt crusts may be transported by wind, increasing the health risk.

These conditions may be similar to other former mining areas, creating the same environmental problems. As a consequence these results should be considered when we are trying to implement reclamation actions at these contaminated sites.