Nickel

Typical wastewaters

• nickel electroplating and electroless nickel rinse water Ni²⁺, held through the hydroxide window by ammonia, citrate, EDTA and hypophosphite in electroless rinses; 3.98 daily maximum and 2.38 mg/L monthly average
• chemical sector effluent total nickel 5.0 to 50 µg/L after precipitation and solids separation
• textile dyeing and leather tanning (metal complex dyes) nickel from metal complex dyes; 0.2, 0.1 and 0.05 mg/L by ZDHC level

1 · Identity

Symbol, number

Ni, 28

Oxidation states in water

+2 only: Ni(H₂O)₆²⁺ is the predominant form in natural water at pH 5 to 9, with hydroxide, sulfate, bicarbonate, chloride and ammonia complexes formed to a minor degree in that range (WHO background document 2021); nickel leached from plated fittings is in the same form. Ni(OH)₂ and NiCO₃ are far less soluble than the salts, and the sulfides less still (WHO). 0 as the metal and its alloys, which release Ni²⁺ by passive leaching rather than corrosion.

Note

The element entry gives the green salts, the hydroxide that precipitates in alkali and the ammine and cyanide complexes; the chapter uses them. Nickel has no redox chemistry in water, so no oxidation step helps or hinders removal.

2 · Occurrence in water

Natural sources

Dissolution from nickel bearing strata, above all ultramafic and laterite terrain; acid rain increases nickel mobility in soil and so in groundwater (WHO). Pristine surface water is near the analytical limits.

Anthropogenic sources

Leaching from nickel or chromium plated taps and from stainless steel pipe, well casing and fittings, the primary source in drinking water (WHO); nickel plating and electroless nickel rinse waters, stainless steel pickling, nickel refining and smelting (Sudbury), batteries, nickel catalysts, and metal complex dyes in textile dyeing (ZDHC lists nickel among heavy metals from raw materials such as metal complex dyes); the ledger's mining, chemical and textile chapters carry the plant level figures.

3 · Speciation

Across the pH of natural water nickel is the hexaaqua ion and its weak ion pairs; it is not hydrolysed at neutral pH, not adsorbed strongly, and passes conventional treatment as a dissolved cation. In alkali it precipitates as Ni(OH)₂, with the minimum solubility at high pH (about 10 to 11 in the textbook curves), so hydroxide precipitation runs higher than for copper or zinc and the effluent must be neutralised afterwards. Nickel sulfide is far less soluble and sulfide precipitation reaches lower residuals. The plating chemist's problem is complexation: ammonia, citrate, EDTA and the hypophosphite bath of electroless nickel hold Ni²⁺ in solution through the hydroxide window, so complexed rinses need breaking (oxidation, sulfide, or a chelating resin) before precipitation.

Solubility

Ni(OH)₂ controls in alkaline treatment and NiS in sulfide treatment; both far below the salts. No solubility products quoted because the sources read print none.

Hydrolysis

Weak; NiOH⁺ is minor below pH 9 (WHO), so nickel salts are only faintly acidic in water.

Complexation

Minor with the natural ligands (OH⁻, SO₄²⁻, HCO₃⁻, Cl⁻, NH₃) in the pH 5 to 9 range (WHO); strong with ammonia, EDTA and citrate in process baths; organically bound in food. Humic substances improve coagulation removal (WHO).

Precipitates

Ni(OH)₂ (treatment), NiCO₃ and basic carbonates, NiS (sulfide treatment and sediments), nickel co-precipitated in Fe(OH)₃ and Al(OH)₃ flocs and in calcium carbonate softening sludge.

4 · Role in treatment

5 · Removal and control

6 · Analytics

Sampling pitfalls

The sample defines the answer: first draw after overnight stagnation from a chromium plated tap can be a hundred times the flushed value (WHO: up to 490 µg/L against low values after flushing). State the stagnation time. Acidify to pH below 2; nickel is stable in solution, so the usual loss is adsorption on unacidified container walls. Bottled water surveys used detection limits of 1.9 to 25 µg/L, which decides what 'not detected' means.

7 · Regulatory limits

Limits change, and many are set locally. Treat these as the published values to start from, not as your compliance target: check the standard in force at your site and the numbers written into your own permit.

8 · Health and environmental effects

Toxicity

Food dominates intake; water matters where it is polluted, where natural nickel is mobilised or where plated taps and stainless steel leach (WHO). TDI 13 µg/kg body weight from a BMDL₁₀ of 1.3 mg/kg per day for post-implantation loss in a two generation rat study with an uncertainty factor of 100. Inhaled nickel compounds are carcinogenic (IARC Group 1) and metallic nickel possibly so (2B), but there is no evidence of carcinogenicity by the oral route. Oral nickel can elicit systemic contact dermatitis in sensitised people; the acute LOAEL is 4.3 µg/kg, against which a glass of water at 80 µg/L gives a margin of exposure of about 16 (WHO fact sheet).

Bioaccumulation

Not addressed as a concern in the sources read; nickel in food is organically complexed and nickel does not biomagnify in the way mercury does.

Ecotoxicity

US EPA aquatic life criteria (1995, hardness 100 mg/L as CaCO₃): freshwater 470 µg/L acute and 52 µg/L chronic, saltwater 74 and 8.2 µg/L; the EU annual average EQS of 4 µg/L bioavailable is the tighter working ceiling in Europe.

Flags

• The Ni(OH)₂ minimum solubility pH and the ammine complex are cited to Metcalf and Eddy chapter 6 and Stumm and Morgan chapter 6 from memory of the text, not re-read this session.
• The precipitation equations are written here; the CWW BREF names hydroxide and sulfide precipitation without printing them.
• No seawater or municipal wastewater nickel concentration was read; the 2021 WHO background document read was the May 2021 public review draft, not the final WHO/HEP/ECH/WSH/2021.6 (iris.who.int returned 403).
• Plating rinse and pickling effluent concentrations were not read; only the limits are quoted.
• EU law was read on legislation.gov.uk mirrors because eur-lex did not respond; the eur-lex urls are kept for consistency.
• Abu Dhabi values cover two media (marine 0.1 mg/L, sewer 10 mg/L); other GCC states not read.
• Standard Methods and ISO method numbers other than those in the sources read (EPA 200.8, ISO 17294-2 and the methods the WHO documents cite) are quoted from memory and were not confirmed this session.

Gaps

• No seawater, municipal wastewater or raw plating effluent nickel concentration was read.
• No solubility products or complex stability constants are quoted; the textbooks were not re-read.
• Reverse osmosis and lime softening for nickel are not covered because no read source gives figures for them.
• The EU textiles BAT conclusions (2022/2508) were not read for a nickel BAT-AEL.
• EU law was read on legislation.gov.uk mirrors; the final 2021 WHO background document was not reachable.
• Other GCC discharge standards (Saudi, Oman, Qatar) were not read.
• The chelating resin equation is written in the resin convention from the mechanism WHO describes; the document names the resin type without a stoichiometry.
• The nickel carbonate equation is cited to Metcalf and Eddy chapter 6, from the chapter, not re-read.

Sources

Identity

Name and symbol

Nickel, Ni

Atomic number

28 protons

Position

group 10 · period 4 · d-block · transition metal

CAS number

7440-02-0

Atomic structure

Atomic mass

58.6934 u

Electron configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁸
[Ar] 4s²³d⁸

Electrons per shell

2, 8, 16, 2

Valence electrons

10 ns and (n-1)d

Physical properties

State at room temperature

Solid

Melting point

1,728 K (1,454.85 °C)

Boiling point

3,186 K (2,912.85 °C)

Density

8.912 g/cm3

Appearance

Lustrous, metallic, and silver with a gold tinge

Thermal conductivity

90.9 W/(m·K)

Electrical resistivity

69.3 nΩ·m at 20 °C

Electrical conductivity

14.43 MS/m

Crystal structure

face-centered cubic

Molar heat capacity

26.07 J/(mol·K)

Chemical properties

Oxidation states

+3, +2

Electronegativity

1.91 (Pauling Scale)

Ionisation energy

7.64 eV
1st 737.1, 2nd 1,753, 3rd 3,395 kJ/mol

Electron affinity

1.156 eV

Atomic radius

empirical 124, covalent 124, van der Waals 163 pm

Ionic radius

Ni²⁺ 69 low spin; Ni³⁺ 56 low spin; Ni⁴⁺ 48 low spin; Ni³⁺ 60 high spin pm

Reactivity

A group 10 transition metal ([Ar] 3d8 4s2) of the iron triad; chemically reactive in principle, but a passivating oxide layer makes bulk nickel slow to react with air and resistant to corrosion even when red hot, so it is used for plating and alloys.

with water

Does not react with water; nickel and copper-nickel alloys resist sea water and are used in desalination plant tubing.

with oxygen, air

Large pieces react only slowly with air because a nickel oxide film forms and stops further attack; the oxide is not conveniently made by heating the metal in oxygen: $\ce{2 Ni + O2 -> 2 NiO}$

with acids

Reacts with most dilute acids to give hydrogen and green nickel(II) salts; nickel sulfate is made in bulk by dissolving the metal in sulfuric acid: $\ce{Ni + H2SO4 -> NiSO4 + H2}$

with halogens

Forms the dihalides NiF2, NiCl2, NiBr2 and NiI2, solids with octahedral nickel; nickel(II) chloride is the commonest, usually made from the metal and hydrochloric acid: $\ce{Ni + Cl2 -> NiCl2}$

Typical compounds

• NiSO₄ nickel(II) sulfate electroplating salt, as hexa- and heptahydrate
• NiCl₂ nickel(II) chloride commonest halide; green aquo ion in water
• NiO nickel(II) oxide from heating the hydroxide, carbonate or nitrate
• NiO(OH) nickel oxide hydroxide cathode of nickel-cadmium and nickel-metal hydride cells
• Ni(CO)₄ nickel carbonyl toxic volatile carbonyl of the Mond refining process
• (Fe,Ni)₉S₈ pentlandite the main sulfide ore, Sudbury

Occurrence, production and use

Crustal abundance

8.4×101 milligrams per kilogram

Oceanic abundance

5.6×10-4 milligrams per liter

Occurrence and sources

Nickel is found as a constituent in most meteorites and often serves as one of the criteria for distinguishing a meteorite from other minerals. Iron meteorites, or siderites, may contain iron alloyed with from 5 percent to nearly 20 percent nickel. Nickel is obtained commercially from pentlandite and pyrrhotite of the Sudbury region of Ontario, a district that produces about 30 percent of the world's supply of nickel.

Other deposits are found in New Caledonia, Australia, Cuba, Indonesia, and elsewhere.

• pentlandite and pyrrhotite (iron nickel sulphides) magmatic sulphide deposits of Canada (Sudbury), Russia, Australia and the United States; 35 percent of identified resources (USGS); iron meteorites carry 5 to nearly 20 percent nickel
• garnierite and other laterite ores tropical weathering crusts of Indonesia, the Philippines, New Caledonia, Australia and Brazil; 54 percent of identified resources
• seafloor manganese crusts and nodules, tailings about 10 percent of resources in hydrothermal and seafloor deposits and 1 percent in tailings

Extraction, production

Smelting of sulphide concentrate and hydrometallurgy of laterite

Sulphide concentrate is smelted to matte and refined to class 1 nickel; laterite is smelted to ferronickel and nickel pig iron or leached at high pressure with acid to mixed hydroxide and sulphate intermediates (the route of Indonesia's growth). The sources name the routes but no reaction, so no equation is written. World mine production about 3.7 million tonnes in 2024 (estimate); scrap supplied about 54 percent of United States apparent consumption.

Uses

Nickel is a hard, corrosion resistant metal. It can be electroplated onto other metals to form a protective coating. Finely divided nickel is used as a catalyst for the hydrogenation of vegetable oils. Adding nickel to glass gives it a green color. A single kilogram of nickel can be drawn into 300 kilometers of wire. Nickel is also used to manufacture some types of coins and batteries.

Nickel is alloyed with other metals to improve their strength and resistance to corrosion. Nickel is alloyed with steel to make armor plate, vaults and machine parts. It is alloyed with copper to make pipes that are used in desalination plants. Very powerful permanent magnets, known as Alnico magnets, can be made from an alloy of aluminum, nickel, cobalt and iron.

It is extensively used for making stainless steel and other corrosion-resistant alloys such as Invar(R), Monel(R), Inconel(R), and the Hastelloys(R). Tubing made of copper-nickel alloy is extensively used in making desalination plants for converting sea water into fresh water.

Nickel, used extensively to make coins and nickel steel for armor plates and burglar-proof vaults, and is also a component in Nichrome(R), Permalloy(R), and constantan.

Nickel gives glass a greenish color. Nickel plating is often used to provide a protective coating for other metals, and finely divided nickel is a catalyst for hydrogenating vegetable oils. It is also used in ceramics, in the manufacture of Alnico magnets, and in the Edison(R) storage battery.

• Stainless steel and alloys: austenitic stainless steel and alloy steel; nichrome heating elements, copper nickel alloys for desalination plant, propeller shafts and turbine blades; coins stainless and alloy steel and nickel alloys typically account for more than 85 percent of United States consumption (USGS)
• Food and beverage: finely divided nickel on diatomaceous earth as the catalyst for hydrogenating vegetable oils to margarine and hardened fats, filtered off after the reaction (FDM BREF); nickel and compounds to water is a food chapter substance
• Chemicals: nickel catalysts for secondary reforming and methanation in ammonia plants; palladium or nickel catalysts for hydrogenating diolefins in aromatics plants; nickel formerly used in hydrogen peroxide working solution hydrogenation; spent nickel catalysts as a waste stream; nickel is discharged from phosphoric acid and pigment plants
• Pharmaceuticals and fine chemicals: metallisation of azo dyes with nickel to form chelated complexes; nickel catalysts for catalytic hydrogenation of nitro compounds, with removal of nickel from process waters as an OFC BREF technique
• Textiles: nickel bound in metal complex dyes (Cr, Cu, Ni) for wool and in some reactive dyes for cotton; the Textiles BREF lists nickel among the metals discharged from reactive dyeing
• Batteries and plating: nickel cadmium and nickel metal hydride batteries and lithium ion cathodes; electroplating, the second United States use after alloys
• Mining: nickel ore is a base metal ore of the MWEI BREF; nickel is listed among substances discharged from base metal, precious metal, iron ore, industrial mineral and uranium extraction

Safety, toxicity

Exposure to nickel metal and soluble compounds (as Ni) should not exceed 0.05 mg/cm3 (8-hour time-weighted average per 40-hour work week). Nickel sulfide fume and dust is recognized as being potentially carcinogenic.

GHS classification, signal word Danger

• H317 May cause an allergic skin reaction Sensitization, Skin
• H351 Suspected of causing cancer Carcinogenicity
• H412 Harmful to aquatic life with long lasting effects to the aquatic environment, long-term hazard
• H334 May cause allergy or asthma symptoms or breathing difficulties if inhaled Sensitization, respiratory
• H341 Suspected of causing genetic defects Germ cell mutagenicity
• H350 May cause cancer Carcinogenicity
• H360F May damage fertility Reproductive toxicity
• H372 Causes damage to organs through prolonged or repeated exposure Specific target organ toxicity, repeated exposure
• H250 Catches fire spontaneously if exposed to air Pyrophoric liquids
• H411 Toxic to aquatic life with long lasting effects to the aquatic environment, long-term hazard
• H370 Causes damage to organs Specific target organ toxicity, single exposure
• H360 May damage fertility or the unborn child Reproductive toxicity

Discovery and name

Discovered by

Axel Fredrik Cronstedt

Discovered

1751

First isolated

not in sources

Named by

not in sources

Origin of the name

after Nickel, a mischievous mine spirit in German mythology

Nickel is silvery white and takes on a high polish. It is hard, malleable, ductile, somewhat ferromagnetic, and a fair conductor of heat and electricity. It belongs to the iron-cobalt group of metals and is chiefly valuable for the alloys it forms.