Statistics in identifying factors that control the geochemical distribution of potentially polluting elements over a tailings pond surface: a case study.

Abstract

The study shows how the statistical approach can provide information on the factors and processes that control the geochemical distribution of elements at the surface of an abandoned tailings pond. In this regard, the case study of a waste deposit resulting from the ore processing plant of Fundu Moldovei was carried out. The facility was concentrating Cu, Pb, and Zn from the polymetallic sulfide ores of the Fundu Moldovei-Leșu Ursului mining district (Romania). The statistics indicate three types of waste, showing specific properties: (i) Waste of the beach, rich in soluble fraction (14.4%) and secondary minerals (e.g., jarosite, ferricopiapite, magnesiocopiapite, pickeringite, and clay minerals). The latter and the related high contents of Al, K, Fe, Co, Ni, Cu, Pb, and Zn are controlled by the water evaporation and subsequent transient pH (2.6-3.5) of the leachates accumulated as puddles. The lower pH and scarce soluble fraction favor a rise in the Cu and Zn contents, while Al, K, Fe, and Co are noticeable at a higher pH when the soluble fraction is abundant. (ii) Waste of the upper dam slope, marked by intense oxidation and a meager occurrence of secondary minerals precipitated from highly acidic pore leachates (average pH of 2.55), namely, jarosite, ferricopiapite, magnesiocopiapite, and coquimbite. The surface waste contains more pyrite and is coarser because of the fine particle removal during rainfall. Unlike the beach waste, in the upper dam tailings, Al, K, Fe, Co, Cu, Pb, and Zn seem to relate mainly to the primary minerals (muscovite, chlorite, and pyrite). (iii) Downslope dam waste is less acidic (average pH of 3.75) than that of the upper slope; it contains secondary minerals stable at a higher pH (e.g., gypsum, apjohnite, dietrichite, clay minerals, and schwertmannite). Calcium, Mn, and Cd are more abundant in the dam waste. They originate from both primary and secondary minerals (e.g., muscovite, chlorite, gypsum, ferricopiapite, and magnesiocopiapite) and correlate with the coarser waste.