Assessment of the pollution potential of a special case of abandoned sulfide tailings impoundment in Riotinto mining district (SW Spain).

This work describes a special case of pollution potential assessment applied to an abandoned sulfide tailings impoundment located in the Riotinto mining district (Huelva), near the Tinto River. Three overlapping levels of discharged tailings were recognized in the impoundment, from deeper to upper: pale yellow to white, red, and brownish-yellow. Mineralogical, physical, and chemical characteristics of tailings, water leachates, water, and sulfate efflorescent salts were analyzed. The total toxic element content and the leachate concentration were respectively used to calculate two indices that support potential toxicity assessment: the Index of Contamination (IC) and the Hazard Average Ratio (HAQ). According to the IC values, all tailings samples showed a high potential for contaminating soils and sediments, especially the intermediate tailings with up to As (8.6 g kg-1), Pb (14.8 g kg-1), and Cu (1 g kg-1). Deeper tailings leachate was extremely saline and acidic, with a very high concentration of sulfates and toxic elements, exceeding the values: 2600, 980, 30, and 17 mg L-1 for SO4, Fe, Al, and Cu, respectively. For this reason, these deeper tailings were linked to the saline and acid seepage, and also to the sulfate acid efflorescences formed at the dike toe. In conclusion, the studied abandoned tailings impoundment is related with a high likelihood of polluting the environment, represented by very high IC and HAQ values. However, when the Tinto River is considered the receiving water body, the severity of the potential contamination must be judged as very low.

A new ranking scale for assessing leaching potential pollution from abandoned mining wastes based on the Mexican official leaching test.

Potentially toxic elements (PTEs) present in abandoned mining wastes (AMW) are of great concern because of potential risks to human health and ecosystems. Indices of contamination (IC) applied to mining wastes are calculated using the total concentration of PTEs and comparing them with regional geochemical backgrounds. However, determining the total content of heavy metals is insufficient to assess the hazard of mining wastes. Therefore, in addition to total concentration, the potential risk is also evaluated through water mobility of elements. Accordingly, leaching procedures are useful tools for the geochemical characterization of soluble constituents that are mobilized. In this study, the solubility of PTEs from different types of mining wastes is comparatively assessed using three standard leaching methods (European; U.S. Geological Survey and; Mexican). The Hazard Average Quotient (HAQ) was calculated to assess the potential Toxicity Factor (TF). TF is an indicator of the relative potential toxicity of wastes and is the basis for the classification of AMW. A comparative assessment provides evidence that there are no statistically significant differences in PTEs solubility by the three leaching methods and it was also found that the pH of the eluates was dictated by the type of waste. Results suggest that the IC gives an indicator of the potential contamination of soils and sediments by erosive processes, or a long-term measure, whereas TF assesses the possibility of contaminating water in the short term. The most significant finding is the new ranking scale of TF, as a function of HAQ, applied to the Mexican standard leaching test. This factor, together with other considerations relating to risk-generating processes, might then be applied in places having large amounts of recorded AMW, such as the Iberian Peninsula and Latin America, where effective management is required to rank sites, based on preliminary environmental and human risk assessment.

Geochemical anomalies for the determination of surface stream sediments pollution: case of Sierra de Cartagena-La Unión mining district, Spain.

This work explores the ability of the Spanish Geochemical Database to identify the existence of polluted stream sediments due to the presence of abandoned mine wastes. The mining district of Sierra de Cartagena-La Unión has been used as test area. A total of 18 abandoned tailings facilities were selected and samples were taken for analysis of the content in potential toxic elements. The results were contrasted with geochemical background values in order to identify which geochemical elements could entail anomalies potentially reflected in the Spanish Geochemical Database. For the study area, As, Cd, Pb, and Zn have been identified as potential toxic elements which can be used as geochemical indicators of sediment pollution processes originated in abandoned mine wastes. Furthermore, the correlation between Cd and Zn allows them to be considered as the best indicators of potential sediment contamination. The study of anomaly thresholds, through the analysis of accumulated frequencies of the contents of these elements in the sediments of the Spanish Geochemical Database, allows identifying sediments that may have been contaminated. A Mann-Whitney test contrasting the data of tailings, polluted sediments, and non-polluted sediments has been performed in order to verify differences among these types of samples. In addition, a geospatial analysis has demonstrated a very close relationship between contaminated sediments and the presence of mining wastes upstream. This methodology can be applied to any other mining region, to recognize the possible influence of pollution processes derived from the presence of abandoned mine wastes taking advantage of existing geochemical databases.