Hard pan formation on mining residuals

Abstract

Hard pan formation is a widespread natural phenomenon which is able to reduce erosion by wind and water, prevent water infiltration and air circulation due to particle agglutination and pore filling, and to accumulate high amounts of potentially toxic elements in secondary mineral and gel phases. The process is driven by capillary forces, occurs with different climates from the polar circle to the equator, and is depending on material composition, climate, and deposition history. The size of matrix flow cells and the development of focused rock drainage systems controls the effectiveness ofthis self-sealing process. lntroduction Hardpan formation is a widespread natural phenomenon. It is known from semi-arid to arid climates such as calcrete, silcrete, ferricrete, but has been observed also in humid and tropical areas. These crusts are in general characterized by reduction of pore volume and permeability, relative or absolute increase or depletion of certain elements as well as by the formation of characteristic mineral phases stable under these environmental conditions (Thornber et al. 1987). This natural phenomenon can be observed and characterized macro-and microscopically , chemically and geophysically already a few years after deposition on anthropogenic depositories like slagheaps, tailings, waste roclc, etc. (Blowes et al.