Assessment of tailings stability and soil contamination of Kef Ettout (NW Tunisia) abandoned mine

Abstract

The abandoned mining wastes still represent one of the significant environmental hazards. Kef Ettout tailings is one example that was exposed to severe ambient conditions and must be assessed to determine its potential risks. The initial mine wastes, the tailings, and agricultural soils were investigated. The results showed that the winds and runoff water distributed the potentially toxic metals and the alkaline pH of tailings and soils, the carbonate, and TOC content controlled the metal bioavailability. About 22% of Pb and 70 and 98% of Zn and Cd, respectively, were leached from tailings. Despite the initial wastes were richer in Zn (1.5 times) than in Pb, the tailings kept much more Pb (1.6 times) than Zn. In agricultural soils, the mean concentrations of Pb, Zn, and Cd were 69, 141, and 1.8 mg kg−1, respectively. The enrichment factor and geoaccumulation index showed that more than 75% of soils were considered strongly contaminated. Speciation results indicated that about 97% of initial wastes metals were bounded to residual fractions. However, in tailings, 9–30, 4–10, and < 6% of Pb, Zn, and Cd, respectively, were in stable forms. Redistribution index (Utf) and relative binding intensity (IR) of metal tailing had confirmed that the tailings continued to provide more Zn quantity than Pb and Cd. In soils, the highest percentages of Pb and Zn were closely associated with organic matter, the Cd was significantly bounded to the exchangeable fraction, and the mean decreasing factor mobility order was Cd (66) < Pb (73) < Zn (78). Therefore, this tailings type must be rehabilitated to limit its risks, particularly of Zn.