TY - THES

T1 - Mineralogy and leachability of V, Cr, Cu, Mo, Ni and F from natural rocks : six examples from Austria

AU - Berger, Maximilian

N1 - embargoed until 31-10-2020

PY - 2018

Y1 - 2018

N2 - Mined natural rocks used as construction material can be substituted by recycled materials and industrial aggregates, e.g., steel slags. The use of these materials is subjected to the Austrian Recycling Building Materials Regulation (RBV) and hence restricted by limits for total contents and leaching concentrations of several environmentally critical elements. Natural rocks are not subjected to such limits although they can be enriched in heavy metals as well. In this study, which is conducted within the project MiLeSlag (Mineralogy and Leachability of Steel Slags), six Austrian rock samples were investigated in terms of their mineralogy (optical microscopy) and their total and leachable contents of V, Cr, Cu, Mo, Ni and F (ICP-MS, IC, photometry). Chemical composition of the phases was determined by electron probe microanalyses (EPMA). The leachability of environmentally relevant elements from two samples was determined by pH-dependant leaching tests (EN 14429) and percolation tests (according to EN 14405). Hydrogeochemical modelling using LeachXSTM was applied to constrain the phases which control the leachability of those samples which were tested by EN 14429. Vanadium was present in two natural aggregate mixtures for road construction in concentrations of 60 and 258 mg/kg, respectively. In the mixture “diabase-greywacke” V was bound to titanite, in the mixture “amphibolite-breccia” to magnetite. One Mo-mineralised gneiss sample contains 49500 mg/kg Mo which is present as molybdenite. From this sample 2.5 mg/kg Mo were leached at neutural pH which is five times higher than the limit value for slags in road construction. A serpentinite sample contains 3011 mg/kg Cr exceeding all limits of the RBV. In this sample Cr is mainly present in chromian spinel but also in serpentine and chlorite. A small portion 0.24 mg/kg Cr was present as Cr(VI). Leaching of Cr accounted only for 0.003 mg/kg, which is below all limits of the RBV. Hydrogeochemical modelling confirmed that the extremely low leaching of Cr is controlled by the low solubility of the spinel phase. In the serpentinite sample, where Ni is incorporated in olivine and serpentine, total Ni contents of 2580 mg/kg and leaching concentrations of 1.1 mg/kg are clearly above the limit values for recycled and industrial aggregates. Contrary to hydrogeochemical modelling and mineralogical observations, the latter confirmeing the incorporation of both Ni and Cr (in serpentinite) and Mo (in gneiss) in mineral phases, percolation tests showed decreasing release of these elements over time which suggests desorption rather than dissolution as leachability controlling factor. However, clogging of pores by secondary mineral phases like iron hydroxides or clay minerals, might have decreased the release of these elements physically during the course of the percolation tests. In summary, this study demonstrates that heavy metals may not only be present in natural rocks used as raw materials in increased concentrations, but also can be leached in concentrations above limit values valid for industrial or recycled aggregates.

AB - Mined natural rocks used as construction material can be substituted by recycled materials and industrial aggregates, e.g., steel slags. The use of these materials is subjected to the Austrian Recycling Building Materials Regulation (RBV) and hence restricted by limits for total contents and leaching concentrations of several environmentally critical elements. Natural rocks are not subjected to such limits although they can be enriched in heavy metals as well. In this study, which is conducted within the project MiLeSlag (Mineralogy and Leachability of Steel Slags), six Austrian rock samples were investigated in terms of their mineralogy (optical microscopy) and their total and leachable contents of V, Cr, Cu, Mo, Ni and F (ICP-MS, IC, photometry). Chemical composition of the phases was determined by electron probe microanalyses (EPMA). The leachability of environmentally relevant elements from two samples was determined by pH-dependant leaching tests (EN 14429) and percolation tests (according to EN 14405). Hydrogeochemical modelling using LeachXSTM was applied to constrain the phases which control the leachability of those samples which were tested by EN 14429. Vanadium was present in two natural aggregate mixtures for road construction in concentrations of 60 and 258 mg/kg, respectively. In the mixture “diabase-greywacke” V was bound to titanite, in the mixture “amphibolite-breccia” to magnetite. One Mo-mineralised gneiss sample contains 49500 mg/kg Mo which is present as molybdenite. From this sample 2.5 mg/kg Mo were leached at neutural pH which is five times higher than the limit value for slags in road construction. A serpentinite sample contains 3011 mg/kg Cr exceeding all limits of the RBV. In this sample Cr is mainly present in chromian spinel but also in serpentine and chlorite. A small portion 0.24 mg/kg Cr was present as Cr(VI). Leaching of Cr accounted only for 0.003 mg/kg, which is below all limits of the RBV. Hydrogeochemical modelling confirmed that the extremely low leaching of Cr is controlled by the low solubility of the spinel phase. In the serpentinite sample, where Ni is incorporated in olivine and serpentine, total Ni contents of 2580 mg/kg and leaching concentrations of 1.1 mg/kg are clearly above the limit values for recycled and industrial aggregates. Contrary to hydrogeochemical modelling and mineralogical observations, the latter confirmeing the incorporation of both Ni and Cr (in serpentinite) and Mo (in gneiss) in mineral phases, percolation tests showed decreasing release of these elements over time which suggests desorption rather than dissolution as leachability controlling factor. However, clogging of pores by secondary mineral phases like iron hydroxides or clay minerals, might have decreased the release of these elements physically during the course of the percolation tests. In summary, this study demonstrates that heavy metals may not only be present in natural rocks used as raw materials in increased concentrations, but also can be leached in concentrations above limit values valid for industrial or recycled aggregates.

KW - Mineralogie

KW - Löslichkeit

KW - Schwermetalle

KW - Natürliche Gesteine

KW - Schlacken

KW - mineralogy

KW - hard rock

KW - heavy metals

KW - leaching tests

KW - slags

M3 - Master's Thesis

ER -