Trend evolution of physicochemical parameters and metals mobility in acidic and complex mine tailings long exposed to severe mediterranean climatic conditions: Sidi Driss tailings case (NW-Tunisia)

Abstract

Sidi Driss initial waste of ore valorization unity (WOVU) and mine tailings (acidic wastes) are interesting examples to study the evolution of mining wastes which had a relatively complex mineralogy and were exposed for a long time to severe erosion and dispersion. The evolution of physicochemical parameters and the concentrations and mobility of Cr, Ni, Cu, Pb, Mn, Fe and Zn were studied. Between 90 and 98% of metals in WOVU were bound to residual fractions. The organic matter in WOVU mineralization, direct and indirect oxidation of pyrite, hydrolysis of Fe3+ and SO2 and jarosite formation contributed to pH decrease and metal mobility increase. The oxidation-reduction environments in mine tailings mobilized between 42 and 69% of Pb, Zn and Mn versus the initial quantities of stable metals. The mechanical dispersion caused by the torrential water runoff and the wind, and the metal mobility contributed to the liberation of 7–19% of total metal quantities. The calculated Redistribution (Utf) and Relative Binding Intensity (IR) indexes showed that the Sidi Driss mine tailings released from 1.4 times (Fe) to 88.8 (Cu) times more available metal quantities and Mn and Pb (76.1 ≤ IR ≤ 77.1) significantly had the lowest binding intensity (more mobile), when compared to other metals (86.3 < IR < 96.5) (less mobile). Thus, it is urgent to make a correct plan and to stop all available metal fractions and elucidate all possible risks associated to tailings.