Nickel is a metallic element with a silvery color and a lustrous surface. It is found in large amounts in nature and is the fifth most common of all elements on Earth. However, most of the nickel is concentrated in the core of the planet and can't be extracted.
Nickel has numerous uses and hundreds of thousands of products are made from it. Most of them are used in the transport, aerospace, marine, military and construction industries. It is mainly found in the composition of alloys, since it can make steel resistant to rust and high temperatures when combined with chromium and other metals. These alloys are suitable for the manufacture of medical tools, chemical equipment, pots and pans, kitchen sinks, building elements or food processing machinery.
Most of the nickel extracted in the world is used to make stainless steel, around 65% of the total amount. Of the remaining amount, another 20% is needed for other alloys, both steel and non-ferrous. These special alloys have niche uses in the aerospace or military industry. Nickel plating uses another 9%, while 6% is used in various ways: to produce coins and electronic items. It is required by the batteries that power most portable items as well as electric cars. Nickel can be replaced by other metals but only at a much higher cost.
Despite its abundance, nickel is rarely found on the surface of the Earth. This is because the pure metal is very reactive and interacts immediately with oxygen. However, the metal becomes chemically stable when combined with iron. This explains both why nickel is found in iron ores and the reason why stainless steel can be produced by mixing these two metals.
When added to many metal alloys, nickel offers superior strength and resistance to corrosion. In addition, these alloys become very malleable and easily ductile, so they can be used to produce sheets, wires, rods or tubes.
The existence of nickel was known for a long time but it was only extracted for the first time by Baron Axel Fredrik Cronstedt in 1751. Under the name of baitong, or white copper, it was mentioned in Chinese records as early as 1500 BC. This alloy was probably made of nickel and silver. In the 15th century, German miners from Saxony tried in vain to extract copper from nickel ores. After many failures, they gave the metal the name kupfernickel, meaning 'the devil's copper'. This was probably a reference to the high content of arsenic in the ores, a toxic metal with deadly effects.
James Riley was the first who discovered that an addition of nickel could make steel stronger and he presented his findings to the Iron and Steel Institute of Great Britain in 1889. In the same period, significant nickel deposits were found in Canada and New Caledonia. As a result, nickel suddenly became a highly prized alloy metal due to its obvious benefits.
More ore deposits were found in Russia and South Africa in the early 20th century, which allowed the large scale extraction of nickel for the first time. During the two world wars, the demand for steel increased significantly, as well as the need for nickel in alloys.
There are currently 23 countries in the world where nickel is mined, and 25 countries have the capacity to smelt the metal. The most common ores are pentlandite, pyrrhotite, millerite and other sulphides, which include around 1% of the pure metal. Lateritic ores limonite and garnierite, which also contain iron, are richer in nickel, with a content of up to 4%.
Nickel can be purified in various ways, depending on the type of ore. Many nickel ores are sulphides, which are extracted from deep underground deposits. These are found in Russia and Canada and tend to be very expensive to mine, since a lot of work is required. The upsides of these ores is the cheap separation process, while lateritic ores like those in New Caledonia are more expensive to purify. Another benefit of the sulfide ores is the higher overall value, since they also contain other rare elements that can be separated.
There are several methods to process sulphide ores, such as hydrometallurgical extraction, froth flotation or magnetic processing. The result is nickel oxide or nickel matte, with a metal content between 40 and 70%. The Sherritt-Gordon Process is used to further purify these intermediate products.
The cheapest processing technique for nickel sulphide is the Mond Process, also known as Carbonyl. A volatilization kiln is used to process a mixture of nickel sulphide and hydrogen. At a temperature of 60 C°, it comes in contact with carbon monoxide. The result is a gas, nickel carbonyl, which then binds to the surface of nickel pellets that are pre-heated. A heat chamber is used to bring these pellets to the right size. Pure nickel powder can also be produced through this technique, if a higher temperature is used.
Lateritic ores contain large amounts of iron, so a pyro-metallic method is usually needed for their purification. A rotary kiln furnace is used to purify them in advance, in order to remove the moisture that can be up to 40%. The resulting nickel oxide is transformed into pure Class I metal and nickel suflate in electric furnaces that volatize it at very high temperatures, between 1360 and 1610 C°.
Smelters that process lateritic ores usually end up with ferronickel as the final product, due to the very high content of iron. After impurities like carbon, silicon or phosphorous are eliminated, ferronickel can be directly used by steel manufacturers.
The presence of nickel as a trace mineral of the body has been known for some time. Even if its role is not well understood, the human body includes around 10 mg of nickel in total. Some animals, like chickens and rats, need nickel as an important nutrient and develop serious diseases if they have a deficiency. As a result, most studies of nickel have focused on these species.
All animal tissues include a small amount of nickel, which is also found in most foods. Very low amounts are present in human tissues as well and scientists have been unable to discover any area with a higher concentration so far. Nickel is not toxic to humans and it is found in all foods, as well as the Earth's crust, so it might play a key role in the metabolism. However, the gas nickel carbonyl is most likely poisonous.
The gastrointestinal tract is not effective in absorbing nickel, with under 10% of the total amount being digested. A molecule called nickeloplasmin carries the metal inside the body, in a bond with a protein. Excess nickel is eliminated in various ways: through excretion, urination and sweat. However, the kidneys can both eliminate nickel and keep it, which shows that it is needed by the body in some way.
Since nickel is so common, many foods contain it. Some of the highest concentrations are found in beans, such as split and green peas, soybeans or lentils. Walnuts, hazelnuts and other nuts are the richest in nickel. Oats, buckwheat, barley, and corn are all good sources of this metal among grains. It is also found in moderate concentrations in bananas, pears and other fruits and vegetables. Most fatty and animal foods have a poor content but it is found in oysters and herrings. Refined products are another poor source, probably because nickel enters a chemical reaction during processing.
The human body needs a supply of nickel but the amount is low. It is included for this reason in multi-vitamin supplements. The best natural sources are nuts, beans and chocolate.
While humans don't need a lot of nickel, it is essential for plants. Most plants include it, as well as foods derived from them, so it is found not only in fruits and vegetables but also in wine.
Nickel is also found in many common everyday items but scientists are not sure if we are able to assimilate nickel by coming in contact with them. Examples include kitchen tools, eyeglass frames, hair clips, pins, scissors, coins or costume jewellery. It is possible to absorb a small amount of metal by handling these objects. It is certain that some sensitive people can have an allergic dermatitis reaction after contact with them.
The role played by nickel in human biology is not well understood. The highest amounts of this metal are found in RNA and other nucleic acids, so scientists suspect it plays a role in the function of proteins or their structure. Some enzymes that are needed for the metabolism of glucose and help break it down include nickel. It might also be required for the production of human milk, since it appears to boost the production of prolactin.
Nickel is widely used in industry and can be considered one of the most important metals. It is a key ingredient of steel and other alloys but also commonly found in magnets and batteries. Stainless steel alloys consume most of the nickel mined in the world, around 65% of the total.
Alloys with a high content of chromium and nickel, while low in carbon, are known as austenitic steels. They are not attracted to magnets. These steels are grouped as 300 series stainless and they offer an excellent mix of good ductility and resistance to corrosion. Austenitic steels are considered some of the best quality stainless steels.
The reason for the special properties of austenitic stainless steels is their content of nickel. They have a crystal structure known as FCC (face-centered cubic), which looks like a cube with atoms on every corner and in the middle of every face. This structure is only possible when nickel is added to the alloy.
Nickel food supplements don't serve any clear purpose at the moment. High amounts of nickel might even be toxic, since increased levels have been found in people after conditions like burns, pregnancy toxaemia, heart attacks and strokes. However, the reason for these high amounts is not known, it might be a cause or a consequence of it. At the same time, there are also diseases associated with a low amount of nickel. Examples include kidney conditions, cirrhosis and psoriasis. However, attempts to treat these problems with an increased intake of nickel have failed. The only known effect of nickel in the body is an increased absorption of iron, which prevents conditions like osteoporosis and anemia.
Since the role of nickel remains largely unknown, there is no official recommended daily amount. A regular diet supplies between 200-750 mcg per day, so an average dose of 500 mcg is probably normal. Scientists estimate that the minimum daily amount of nickel would be between 50 and 100 mcg, if this metal was indeed found to play an important role. Food supplements don't commonly include nickel, since it is found in good amounts in normal food.
Metallic nickel and the trace amounts found in food are not toxic. However, the gas form nickel carbonyl is considered dangerous and can cause cancer. It is found in cigarette smoke, car exhaust and is produced by a number of industrial processes. It is generated by the reaction of nickel with carbon monoxide. When inhaled, this gas immediately causes toxic symptoms like nausea, vomiting or headache. In larger concentrations, it leads to vertigo. In time, the inhaled nickel builds up in the human lungs, increasing the risk of cancer of the nose, lungs or larynx. Some people are also allergic to the metal and can have local or systemic reactions to it. The reactions can be triggered by the nickel found in common items like jewellery, dental materials or even medical parts like heart valves of prosthetic joints.
No effects of nickel deficiency have been observed in humans so far. However, small mammals and birds need this metal and a lack of it can lead to serious problems, starting from dermatitis and depigmentation to slow growth, liver malfunction or severe reproduction deficiency. Humans can lose nickel through sweating, for example during intense exercises. Supplements of nickel might be required to compensate these losses, if nickel does indeed play a role in metabolism.