Nickel is an important industrial and battery metal that is also naturally present in rocks, ores, soils and waters. Its stable isotope composition can help distinguish potential sources while providing information on weathering, transport, retention and other processes affecting Ni in natural and industrial systems.
Nickel is widely used in stainless steel, high-performance alloys, electroplating and rechargeable batteries. At the same time, it is naturally enriched in particular geological environments and may also be released by mining, metallurgy, industrial activities and material degradation. Distinguishing between these contributions can therefore be important for both environmental investigation and material traceability.
Nickel occurs naturally in ultramafic and mafic rocks, sulfide deposits and lateritic weathering profiles. It can also be associated with Fe- and Mn-rich phases. Human activities including mining, ore processing, metallurgy, combustion and the manufacture or disposal of Ni-bearing products can introduce additional Ni into soils, waters, sediments and particulates.
Nickel has five stable isotopes, with ⁵⁸Ni and ⁶⁰Ni forming the principal pair used for stable isotope studies. Small but measurable isotope fractionations can develop during weathering, adsorption, mineral formation, biological processes and other reactions that redistribute Ni between different phases.
The δ⁶⁰Ni signature can complement concentration and elemental data by providing information on both Ni source and subsequent transformation. This is particularly useful where natural geological inputs coexist with mining, metallurgical or other anthropogenic contributions.
High-precision Ni isotope analysis requires complete sample digestion and strong purification because several matrix elements and molecular species can interfere with Ni masses. Purified Ni is measured by MC-ICP-MS, with instrumental and laboratory fractionation controlled using isotope standards, double-spike correction and sample-standard bracketing.
Preparation is adapted to the matrix. Geological samples can be digested using concentrated HF–HNO₃ mixtures, followed by aqua regia and HCl treatments to ensure complete dissolution and convert the sample into a form suitable for chromatographic separation.
Nickel is isolated from the surrounding matrix through selective chromatography. A modern workflow combines an AG50W-X8 cation-exchange column for bulk matrix removal with a small Ni-specific resin column for final purification of Ni.
Purified Ni is measured by multi-collector ICP-MS in medium-resolution mode. ⁵⁸Ni, ⁶⁰Ni, ⁶¹Ni and ⁶²Ni are collected simultaneously, while Fe is monitored to control the principal isobaric interference on mass 58.
A ⁶¹Ni–⁶²Ni double spike can be combined with sample-standard bracketing to correct isotope fractionation. Recovery, procedural blanks, residual matrix and reference materials are controlled before expressing the result as δ⁶⁰Ni.
Natural nickel comprises ⁵⁸Ni, ⁶⁰Ni, ⁶¹Ni, ⁶²Ni and ⁶⁴Ni.
High-precision isotope analysis has been demonstrated using samples containing only approximately 100–200 ng of Ni.
Near-quantitative recovery has been demonstrated using a low-blank DMG-free three-column purification procedure.
Very low whole-procedure Ni blanks have been achieved from digestion through chromatographic purification.
High-precision MC-ICP-MS measurements have been performed using approximately 100 ng g⁻¹ Ni solutions.
Long-term external reproducibility better than ±0.06‰ has been demonstrated for δ⁶⁰Ni measurements.
Geological powders in this mass range have been used for complete digestion, Ni purification and isotope analysis.
The method has been tested across reference materials spanning very low to highly Ni-rich geological matrices.
Analytical values are based on Quitté & Oberli (2006), Ratnayake et al. (2021) and Li et al. (2024). Together these studies establish quantitative Ni extraction, low-blank purification across diverse geological matrices and high-precision MC-ICP-MS analysis using interference control, double-spike correction and sample-standard bracketing. The exact digestion, purification chemistry, sample mass and required Ni quantity are adapted to the matrix and analytical objective. Quitté & Oberli (2006) → Ratnayake et al. (2021) → Li et al. (2024) →
Ni isotope interpretation combines source comparison with an understanding of the reactions that can fractionate Ni during weathering, transport and retention. The strongest interpretations therefore combine δ⁶⁰Ni with Ni concentration, mineralogy, geochemistry and well-characterised candidate sources.
Natural Ni-rich geology, mining residues, metallurgical materials and other anthropogenic inputs can contribute Ni to the same environmental system. Where their isotope signatures differ, δ⁶⁰Ni can help evaluate the relative compatibility of contaminated samples with these sources.
Chemical weathering redistributes Ni between primary minerals, secondary phases and dissolved waters. Because these transfers can fractionate Ni isotopes, δ⁶⁰Ni can help identify how nickel is released and transported through a weathering system.
Nickel can interact strongly with Fe and Mn oxides, clays and other reactive mineral surfaces. Isotope fractionation during these reactions can provide additional information on whether Ni is being transported, immobilised or redistributed within a contaminated environment.
A difference in δ⁶⁰Ni does not automatically indicate a different source. Weathering, adsorption, mineral formation and biological or chemical transformations may also modify the isotope signal. Robust interpretation therefore combines isotope measurements with geochemistry and well-characterised source materials.
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