MINERALOGIA - SPECIAL PAPERS, 47, 2017 www.Mineralogia.pl MINERALOGICAL SOCIETY OF POLAND POLSKIE TOWARZYSTWO MINERALOGICZNE __________________________________________________________________________________________________________________________
Nickel isotope fractionation during weathering of ultrabasic rocks and Ni lateritic ores smelting Artur PĘDZIWIATR1,2, Jakub KIERCZAK2, Jarosław WAROSZEWSKI1, Gildas RATIÉ3, Cécile QUANTIN4, Emmanuel PONZEVERA5 1
Institute of Soil Sciences and Environmental Protection, Wrocław University of Environmental and Life Sciences, Grunwaldzka 53, 50-537 Wrocław, Poland,
[email protected], Institute of Geological Sciences, University of Wrocław, Pl. Maksa Borna 9, 50–204 Wrocław, Poland 3 Synchrotron SOLEIL, L’Rome des merisiers, Saint Aubin BP48, 91192 Gif sur Yvette Cedex, France 4 UMR 8148 GEOPS, Université Paris Saclay – Université Paris Sud - CNRS, Rue du Belvédère 504, 91405, Orsay Cedex, France, 5 IFREMER, Centre de Brest, Unité Géosciences Marines, 29280, Plouzané, France 2
Weathering of ultrabasic rocks under temperate climate leads to incomplete hydrolysis of silicates. On the contrary, complete hydrolysis observed under tropical conditions leads to the formation of lateritic profile with high Ni content. Therefore, laterites are extensively mined for Ni and used in metallurgical processes. The aim of our study is to determine Ni isotope fractionation during weathering of ultrabasic rocks under temperate climate and Ni lateritic ores smelting. The studied serpentine soils (Leptosol, Cambisol) formed under temperate climate are derived from serpentinized peridotite (the Szklary Massif) and serpentinite (Jordanów). The serpentinized peridotite has a lighter isotopic composition (δ60Ni) compared to serpentinite (0.13 ± 0.06‰ and 0.20 ± 0.06‰ respectively). Soil horizons in the Szklary Massif are isotopically lighter compared to the parent rock (Δ60Nisoil-rock up to -0.22‰). Similar trend is observed in Bw and BwC horizons in Jordanów except to the surface horizon (Δ60Nisoil-rock = 0.12‰). Nickel extracted by DTPA-CaCl2 in the Szklary Massif presents heavy isotopic composition compared to the soil (Δ60NiDTPA/CaCl2-soil up to 0.74‰), while in Jordanów, the Δ60NiDTPA/CaCl2-soil is more variable. The Ni isotope signature (δ60Ni) for Ni-bearing silicate ores from the Szklary Massif is 0.46 ± 0.05‰. Furthermore, δ60Ni for pyrometallurgical slags, a by-product of Ni laterites smelting ranges from – 0.22 ± 0.05‰ to 0.55 ± 0.06‰. Our results demonstrate that weathering of ultrabasic rocks could lead to the removal isotopically heavy pool of Ni (at least in the Szklary Massif) confirming previous results in other ultramafic areas. Furthermore, one may consider that decomposition of organic matter could be responsible for heavy isotope signature of soil from surface horizon in Jordanów. Moreover, other factors such as pedogenesis or types of Ni-containing secondary minerals may affect the biogeochemical cycle of Ni. The variability in δ60Ni in slags could reflect changes in smelting techniques and yields or stages of Ni smelting (Kierczak et al., 2009). References Kierczak, J. et al. (2009). The mineralogy and weathering of slag produced by the smelting of lateritic Ni ores, Szklary, Southwestern Poland. Can. Mineral. 47, 557–572.
35
