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Part C: Factsheets (continued)

Nickel and compounds

Substance name:	Nickel and compounds
CASR number:	7440-02-0
Molecular formula:	Ni
Synonyms:	Raney alloy, Raney nickel Nickel compounds covered by this article include: nickel acetate (CASR 373-02-4) nickel carbonate (CASR 3333-67-3) nickel carbonyl (CASR 13463-39-3) nickel chloride (CASR 7718-54-9) nickel hydroxide (CASR 12054-48-7) nickel nitrate (CASR 13138-45-9) nickel oxide (CASR 1313-99-1) nickel sulfate (CASR 7786-81-4) nickel subsulfide (CASR 12035-72-2)

Physical and chemical properties

Nickel is a silvery-white, hard, malleable, ductile and ferromagnetic metal, which is a good conductor of electricity and heat. It has an atomic number of 28 and an atomic mass of 58.7.

Melting point: 1453°C
Boiling point: 2732°C
Specific gravity: 8.9

Properties vary widely depending on the particular compound. Some physical properties for selected nickel compounds follow.

• Nickel acetate is a green powder that effloresces somewhat in air and has a light acetic acid odour.
• Nickel carbonate occurs as light green rhombic crystals or as a brown powder that decomposes before it melts.
• Nickel carbonyl is a volatile, yellow liquid with a musty odour.
• Nickel hydroxide occurs as a fine green powder, as green crystals, or as an amorphous black powder. Its melting point is 230°C and its vapour density is 3.2.
• Nickel oxide occurs as a green or black powder that becomes yellow when heated. Nickel oxide has a specific gravity of 6.7 and melts at 1960°C.
• Nickel sulfate is a yellow-green crystalline solid, it decomposes when heated and its specific gravity is 3.7.
• Nickel subsulfide is a pale yellowish-bronze, metallic, lustrous, crystalline solid.

Nickel metal is relatively resistant to corrosion. It dissolves in dilute mineral acids and is insoluble in concentrated nitric acid.

Water solubility of nickel compounds varies. Nickel acetate, bromide, chloride, iodide, nitrate and sulfate are soluble in water. Hydrated nickel (II) is the primary ion in aqueous solutions. Nickel oxides, hydroxides, sulfides, arsenide, chromate, carbonate, phosphate and selenide are water-insoluble. More properties for selected nickel compounds follow.

• Nickel acetate is soluble in acetic acid and water, and insoluble in alcohol. Nickel acetate decomposes before it melts, forming nickel oxide, and emits irritating fumes.
• Nickel carbonate is soluble in dilute acids and ammonia, and insoluble in hot water. It can react violently with iodine, hydrogen sulfide, or a mixture of barium oxide and air.
• Nickel carbonyl is flammable and explosive. It is slightly soluble in water, but soluble in organic solvents.
• Nickel hydroxide is soluble in acids and ammonium hydroxide, but is practically insoluble in water. It decomposes to nickel oxide and water when heated at elevated temperatures.
• Nickel oxide is soluble in acids, potassium cyanide and ammonium hydroxide solutions. It is insoluble in both cold and hot water, and caustic solutions. The black form of nickel oxide is chemically reactive, whereas the green nickel oxide form is inert and refractory.
• Nickel subsulfide is not soluble in water, or in organic solvents.

Common uses

The vast majority of nickel is used in alloys (more than 3000 nickel alloys have been identified), especially stainless steel and other metal alloys. Nickel is commonly alloyed with iron, copper, chromium, aluminium and zinc. Alloys are used in the making of metal coins and jewellery and, in industry, for making metal items. Nickel and nickel compounds are used for nickel electroplating, to colour ceramics, to make batteries, for permanent magnet materials, and as catalysts. Nickel is also used in manufacture of welding electrodes, flux cored wire and as an ingredient in mineral oil lubricant.

• Nickel acetate is used mainly as a mordant in the textile industry, and as a hydrogenation catalyst. It is also used as an intermediate in the formation of other nickel compounds, as a sealer for anodised aluminium, and in nickel electroplating.
• Nickel carbonate is used as a chemical intermediate for nickel oxide, nickel powder, and nickel catalysts. It serves in electric components, such as vacuum tubes and transistor cans. It is used as a catalyst to remove organic contaminants from wastewater or potable water. It is used in the preparation of coloured glass, in the manufacture of certain nickel pigments, as a neutralising compound in nickel electroplating solution, and in the preparation of many specialty nickel compounds.
• Nickel carbonyl is used in refining nickel ore, forming nickel films and coatings, as a catalyst in various chemical reactions, and in glass plating.
• Nickel hydroxide is used in nickel-cadmium batteries and as a chemical intermediary for nickel catalysts and nickel salts. The hydrogenation of finely powdered newspaper with a nickel hydroxide catalyst converts cellulose feed materials to liquid hydrocarbon fuels, with a high yield.
• Nickel oxide is used in fuel cell electrodes, the production of active nickel catalysts, electroplating, and colouring and decolourising glass. It is also used in the manufacture of nickel salts that can be used to make refined nickel oxide. It is used in nonmetallic resistance thermometers or thermistors, which are temperature-sensitive semiconducting ceramics.
• Nickel subsulfide is produced in nickel refineries and used in the manufacture of lithium batteries.
• Nickel sulfate is used in coatings for camshafts, in oil and in general drilling equipment.

Sources of emissions

Point sources

Combustion of coal and other fossil fuels leads to release of nickel to the atmosphere. Other sources of atmospheric nickel include emissions from mining and refining operations, steel production, nickel alloy production, electroplating, and municipal waste incineration. Sources of nickel in water and soil include wastewater from municipal sewage treatment plants. Nickel oxide has been identified in residual fuel oil and in atmospheric emissions from nickel refineries.

Diffuse sources

A minor source of atmospheric nickel is windblown dust. Sources of nickel in water and soil include stormwater run-off, soil contaminated with municipal sewage sludge, and groundwater near landfill sites.

Natural sources

Nickel is an abundant element. It is naturally found in soils, waters, and foods, and is emitted from volcanoes. It occurs in the environment mainly in combination with arsenic, antimony and sulfur. A large source of nickel lies in the seabed. Metallic nickel is found alloyed with iron in many meteors and the earth's core is believed to contain substantial quantities. Commercially important nickel ores are garnierite, pyrrhotite and millerite.

Mobile sources

Vehicles running on petrol and diesel fuel can contribute to nickel emissions to the atmosphere.

Consumer products that may contain nickel and compounds

Coins, jewellery, nickel-cadmium batteries, some paints and ceramics, magnetic tapes, computer components, goods containing stainless steel (sinks, cooking utensils, cutlery).

Health effects

How might I be exposed to nickel and compounds?

Major sources of exposure for most people are by eating food and drinking water that contain natural amounts of nickel. Breathing cigarette smoke or smoking tobacco is another way of being exposed to nickel. Skin contact with nickel can occur when handling coins, touching other nickel-containing metals, or wearing nickel jewellery. Elevated levels of nickel may be encountered near industries using nickel and/or nickel compounds. Occupational exposure can occur in industries using nickel in various forms.

By what pathways might nickel and compounds enter my body?

Nickel and compounds can be inhaled or ingested. They can also pass through the skin.

Health guidelines

National Occupational Health and Safety Commission (NOHSC) defines nickel and compounds as hazardous:

• TWA (eight-hour time weighted average) exposure limit in the workplace:
  • 1mg/m³ for nickel metal
  • 1 mg/m³ for nickel sulfide roasting (fume and dust) (as Ni)
  • 0.05 ppm (0.12 mg/m³) for nickel carbonyl
  • 0.1 mg/m³ for soluble nickel compounds (as Ni).

Australian Drinking Water Guidelines (NHMRC and ARMCANZ 1996):

• Maximum of 0.02 mg/L (ie 0.00002 g/L).

What effect might nickel and compounds have on my health?

This depends on how much nickel a person has been exposed to, for how long, the nature of the nickel compound, and the person's current state of health. A small amount of nickel is probably essential for humans, although a lack of nickel has not been found to affect people's health. An allergic skin reaction is the most common adverse health effect. This may occur in people who are sensitive to nickel as a result of jewellery or other products containing nickel coming into direct contact with the skin. Once a person is sensitised, further contact with nickel will produce a reaction, most commonly a skin rash at the site of contact (dermatitis). Less frequently, some sensitised people may have asthma attacks following exposure to nickel. Some people may react when they ingest food, drink water or breathe dust containing nickel. People who are not sensitive to nickel must ingest very large amounts of nickel to show adverse health effects.

Exposure to nickel salts can cause 'nickel itch', which causes burning and itching sensations in the hands, followed by abnormal redness of the skin and nodular eruption on the finger webs, wrists and forearms. Nickel salts act as emetics when swallowed. Nickel dust is irritating to the eyes, nose and throat. The lungs can be affected, including chronic bronchitis, reduced lung function, and lung cancer, as well as nasal effects, including rhinitis, nasal sinusitis, nasal mucosal injury. Sinus cancer has been observed in workers who breathed high levels of nickel while working in nickel refineries or nickel processing plants. Asthma disorders have been linked to nickel platers exposed to nickel sulfate and welders exposed to nickel oxides. Nickel and its compounds, nickel carbonate, nickel carbonyl, nickel hydroxide and nickel sulfate, are classified by the NOHSC as a Category 3 carcinogen (substance that causes concern for humans owing to possible carcinogenic effects but in respect of which the available information is not adequate for making a satisfactory assessment). Nickel oxide and nickel subsulfide are classified by the NOHSC as a Category 1 carcinogen by inhalation (substance known to be carcinogenic to humans). Nickel carbonyl is classified as a Category 2 reproductive toxicant (substance that should be regarded as if it causes developmental toxicity to humans).

Environmental effects

Environmental fate

Finely divided particles of nickel and nickel compounds are mainly carried by air. Both natural sources and human activity contribute to the atmosphere, with input from both stationary and mobile sources. Various dry and wet precipitation processes remove particulate matter as wash-out or fallout from the atmosphere, with transfer to soils and waters. Soilborne nickel may enter waters by surface run-off or by percolation into groundwater.

Nickel occurs naturally in surface waters from the weathering of minerals and rocks. Once nickel is in surface and groundwater systems, physical and chemical interactions (complexation, precipitation/dissolution, adsorption/desorption, and oxidation/reduction) will determine its fate. Under normal conditions, nickel is overwhelmingly associated with abundant iron and manganese particles that precipitate and absorb free nickel ions. Much of the nickel in the environment is, therefore, found in soils and sediments. Organic material in polluted environments will keep nickel soluble.

Environmental transport

Nickel can be transported as particles released into the atmosphere or as dissolved compounds in natural waters.

Environmental guidelines

Australian Water Quality Guidelines for Fresh and Marine Waters (ANZECC 1992):

• Freshwater: maximum of 0.015 mg/L (0.000015 g/L) to 0.15 mg/L (0.00015 g/L) (depending on water hardness)
• Marine waters: maximum of 0.015 mg/L (ie 0.000015 g/L).

What effect might nickel and compounds have on the environment?

Very small amounts of nickel have been shown to be essential for normal growth and reproduction in some species of animals. Nickel and its compounds can have high acute and chronic toxicity to aquatic life. Nickel toxicity to aquatic organisms is determined by water hardness: the softer the water, the higher the toxicity. There is not enough information to evaluate or predict the short-term and long-term effects of nickel and its compounds to plants, birds or land animals. Nickel does not appear to bioaccumulate in fish, plants or animals used for food.

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