Nickel - Ni
Nickel (Ni) is a silvery transition metal used in stainless steel, corrosion-resistant alloys, batteries, plating and catalysts. Its chemical form matters for health and environmental assessment. In water treatment, dissolved nickel ions, complexes and nickel-bearing particles can require different removal approaches.
Chemical properties · Applications · Nickel in water and treatment · Health effects · Environmental effects
| Symbol / atomic number | Ni / 28 |
|---|---|
| Standard atomic weight | 58.6934(4) |
| Group / period / block | 10 / 4 / d |
| Electron configuration | [Ar] 3d8 4s2 |
| Electronegativity (Pauling) | 1.91 |
| Density | 8.90 g cm−3 at room temperature |
| Melting point | 1455 °C |
| Boiling point | 2913 °C |
| Covalent radius | 0.117 nm |
| Non-bonded radius | 0.197 nm |
| Common oxidation state in compounds | +2; other oxidation states also occur |
| Naturally occurring isotopes | 58Ni, 60Ni, 61Ni, 62Ni and 64Ni |
| First ionisation energy | 737.1 kJ mol−1 |
| Discovery | Axel Cronstedt, 1751 |
Physical and atomic data follow the Royal Society of Chemistry; atomic weight, natural isotopes and discovery follow CIAAW. Atomic weight is dimensionless; the corresponding molar mass is approximately 58.6934 g mol−1. The number in parentheses indicates uncertainty in the final digit. Ionic radii depend on oxidation state, coordination and spin state.
Nickel: properties and occurrence
Nickel is a workable metal with useful corrosion and heat resistance. Performance depends on the alloy and service environment rather than on the element alone. Nickel occurs in sulfide deposits, including pentlandite, and in laterite ores formed by weathering. These deposit types require different processing routes.
Some nickel minerals contain sulphur or arsenic; the composition of an ore or residue matters when assessing its hazards. Axel Cronstedt identified nickel as a distinct element in 1751.
Applications of nickel
- Stainless steel and other alloys: nickel is combined with iron, chromium and other elements to obtain useful mechanical and corrosion properties. Not all stainless steels contain the same nickel content.
- Special alloys: nickel-chromium heating alloys can also contain silicon, manganese and iron. Nickel-based superalloys are used in demanding high-temperature equipment.
- Marine equipment: suitable copper-nickel and nickel-copper alloys are used in seawater service, including some desalination installations. Grade and water chemistry govern suitability.
- Other uses: nickel is used in rechargeable batteries, coatings, coinage and chemical catalysts.
Nickel in water and water treatment
See Nickel in water (Ni + H2O) for related information, and the drinking-water FAQ for general water-quality background.
Sources and chemical forms
Weathering can introduce nickel naturally. Metal processing, plating and other wastewater streams can add nickel, while water-contact fittings can contribute nickel to drinking water. Source control and suitable materials are therefore relevant alongside treatment.
Dissolved nickel commonly occurs as Ni(II), either as free ions or complexes. Nickel can also be associated with suspended particles. pH, ligands and solids influence mobility and removal, so total nickel alone does not describe every treatment-relevant form.
Removal and process selection
- Hydroxide precipitation: alkaline dosing can form nickel-bearing solids. Clarification and filtration then separate those solids from water. The operating pH must be established for the actual stream.
- Ion exchange: suitable resins can capture dissolved nickel, including in groundwater treatment. Competing ions, resin selectivity and breakthrough affect performance.
- Coagulation and filtration: may assist removal in some waters, depending on pH, coagulant dose and nickel form. Particle filtration alone should not be assumed to remove dissolved nickel.
Complexing agents in industrial streams can keep nickel in solution and hinder precipitation. Jar tests or pilot trials should establish achievable residuals and separation performance. A single pH value cannot guarantee complete removal from every water.
Removal transfers nickel to sludge, spent media or regenerant. Characterise and manage these residual streams, and monitor treated water against the applicable drinking-water, discharge or process specification.
Health effects of nickel
Exposure and allergy
People encounter nickel through food, water, air and skin contact. An essential nutritional role in humans has not been established. The US Institute of Medicine did not set a Recommended Dietary Allowance or Adequate Intake for nickel. General dietary reference information should not be interpreted as a recommendation to take nickel supplements.
Nickel is a common cause of allergic contact dermatitis, for example after contact with nickel-releasing jewellery. In sensitised individuals, oral nickel exposure can also trigger eczema flare-ups, known as systemic contact dermatitis. This differs from the effects of inhaling industrial dust or fumes.
Nickel compounds and metal
IARC classifies nickel compounds as carcinogenic to humans (Group 1) and metallic nickel as possibly carcinogenic to humans (Group 2B). Occupational studies underpin evidence for cancers of the lung and nasal passages. These hazard classifications do not imply that all exposure routes, materials or doses carry the same risk.
Breathing nickel-containing dust or fumes can cause respiratory effects. Nickel carbonyl is a particularly hazardous compound in certain industrial processes and should not be described simply as “nickel gas”. Exposure assessment and controls need to reflect the actual chemicals and work being performed.
Drinking-water and food risk assessments address oral exposure separately from occupational inhalation. Nutritional reference values, workplace air limits and water-quality limits serve different purposes and are not interchangeable.
Environmental effects of nickel
Nickel moves between dissolved forms, particles, soils and sediments. Binding to solids can reduce mobility, but does not make nickel permanently immobile. Environmental conditions and chemical form influence availability to organisms.
Nickel has biological functions in plants and some other organisms, yet excessive exposure can be harmful. Plants can accumulate nickel, and some species accumulate particularly high amounts. This should be distinguished from biomagnification through a food chain: uptake by a plant alone does not establish increasing concentrations at each trophic level.
Assessment of a discharge should consider the receiving environment and bioavailable fraction as well as total nickel. Treatment changes nickel's form or location; it does not destroy the element.
Nickel page last reviewed: by Lenntech.
Back to the periodic table of elements.
Sources and further reading
- RSC: nickel properties, uses and history.
- CIAAW: nickel atomic weight and isotopes.
- USGS: nickel deposits and applications.
- IARC: nickel and nickel compounds.
- UKHSA: nickel exposure, allergy and cancer classifications.
- ATSDR: nickel and public health (2024).
- EFSA: nickel in food and drinking water (2020).
- WHO: nickel drinking-water fact sheet.
- EPA: metal-products wastewater treatment and precipitation (PDF).
- Institute of Medicine: dietary reference assessment, including nickel.