Nickel isotope fractionation during laterite Ni ore smelting and refining: Implications for tracing the sources of Ni in smelter-affected soils
Abstract
Nickel isotope ratios were measured in ores, fly ash, slags and FeNi samples from two metallurgical plants located in the Goias State, Brazil (Barro Alto, Niquelandia). This allowed investigating the massdependent fractionation of Ni isotopes during the Ni-laterite ore smelting and refining.
Feeding material exhibits a large range of delta Ni-60 values (from 0.02 +/- 0.10 parts per thousand to 0.20 +/- 0.05 parts per thousand, n = 7), explained by the diversity of Ni-bearing phases, and the average of delta Ni-60(feeding materials) was found equal to 0.08 +/- 0.08 parts per thousand (2SD, n = 7). Both delta Ni-60 values of fly ash (delta Ni-60 = 0.07 +/- 0.07 parts per thousand, n = 10) and final FeNi produced (0.05 +/- 0.02 parts per thousand, n = 2) were not significantly different from the feeding materials ones.
These values are consistent with the very high production yield of the factories. However, smelting slags present the heaviest delta Ni-60 values of all the smelter samples, with delta Ni-60 ranging from 0.11 +/- 0.05 parts per thousand to 0.27 +/- 0.05 parts per thousand (n = 8).
Soils were also collected near and far from the Niquelandia metallurgical plant, to evaluate the potential of Ni isotopes for tracing the natural vs anthropogenic Ni in soils. The Ni isotopic composition of the non-impacted topsoils developed on ultramafic rocks ranges from -0.26 +/- 0.09 parts per thousand to -0.04 +/- 0.05 parts per thousand (n = 20).
On the contrary, the Ni isotopic composition of the non-ultramafic topsoils, collected close to the plant, exhibit a large variation of delta Ni-60, ranging from -0.19 +/- 0.13 parts per thousand up to 0.10 +/- 0.05 parts per thousand (n = 4). This slight but significant enrichment in heavy isotopes highlights the potential impact of smelting activity in the surrounding area, as well as the potential of Ni isotopes for discerning anthropogenic samples (heavier delta Ni-60 values) from natural ones (lighter delta Ni-60 values).