Nickel isotope fractionation during precipitation of Ni secondary minerals and synchrotron-based analysis of the precipitates

Nickel Isotope Fractionation As an Indicator of Ni Sulfide Precipitation Associated with Microbially Mediated Sulfate Reduction

“…The difference between the fractionation factors measured in this study and the magnitude of Ni isotope fractionation of −0.7 ‰ calculated in other NiS precipitation studies ,− can be quite surprising. However, it is important to note that, due to the complexity of the current experimental system, it is not possible to attribute the magnitude of the isotopic fractionation measured in this study to a single Ni sulfide precipitation process.…”

“…The data showed partitioning of light Ni isotopes in the solid phase compared to the initial solution, and enrichment in heavy isotopes of the residual aqueous Ni fractions. Enrichment in the heavier isotope associated with the aqueous fraction of Ni was observed in abiotic Ni sulfide precipitation experiments . Isotopic fractionation in abiotic NiS precipitation experiments was fit with a Rayleigh curve yielding a fractionation factor of ε = −0.73‰ .…”

“…Interactions between SRB and Ni might induce Ni isotope fractionation before the precipitation of sulfide phases occurs. Adsorption of dissolved Ni to the freshly precipitated Ni sulfides can also considerably affect the measured Ni isotope fractionation . Ni adsorption to minerals was documented to cause enrichment of heavy Ni isotopes in solution compared to the solid phases and to generate significant Ni isotope fractionation. − For example, in a recent study, adsorption of Ni to the mineral birnessite induced the largest fractionation factors observed for Ni to date (Δ 60 min‑aq ranging from −2.76‰ to −3.35‰) .…”

“…Despite this, Ni isotope measurements remain an underexploited tool in environmental applications. Studies on Ni isotope fractionation conducted on microbial activity, types of vegetation, , weathering, − adsorption, − and the formation of secondary minerals ,, have indicated that environmental processes induce significant Ni isotope fractionation, thus demonstrating the potential of Ni isotope analysis as a tool to trace Ni cycling in the environment.…”

“…For example, recent studies have shown a preferential uptake of lighter Ni isotopes by minerals during adsorption onto calcite (Δ 60 Ni min‑aq = −0.52‰) and birnessite (Δ 60 Ni min‑aq = −2.76 to −3.35‰) . Furthermore, research involving the precipitation of Ni-hydroxide, Ni-hydroxycarbonate, and Ni-sulfide has shown that lighter Ni isotopes are incorporated into the solid phases, resulting in fractionation factors ε = −0.40‰, −0.50‰, and −0.73‰, respectively …”