Nickel in Periodic Table
Nickel (Ni), chemical element, silvery, malleable, ductile, ferromagnetic transition metal of Group 9 (VIIIB) of the periodic table, used in making alloys with iron and other nonferrous metals. The metal nickel has incomplete d-orbital in their atom and ions. Therefore, it is a transition metal with only one important oxidation number or state +2.
The face-centered cubic crystal lattice, nickel has chemical symbol Ni, atomic number 28, atomic weight 58.69, melting point 1455°C, boiling point 2730°C, and valence shell electronic configuration [Ar] 3d7 4s2. It is a hard silvery metal that is very malleable and ductile and easily rolled down or polished. The ferromagnetic properties and Courie point of cobalt (375°C) less than that of cobalt and iron. The compact metal is quite resistant to air and water molecule but strong heating in the air produces little amount of oxide.
History and Occurrence
The name of the metal nickel is derived from the German word devil spirit. In the 17th century, a mineral having the appearance of cuprite but could not be smelted to obtained copper. Metallurgists decided that the ore was dominated by the evil spirit of the mountain copper devil or Kupfer-nickel. The confusion regarding the mineral persists until 1751. In 1751, Baron Axel Fredrik Cronstedt extracts copper from the copper devil or Kupfer-nickel mineral in the Swedish village of Los. Even sometime after, scientists believed that nickel was a mixture of cobalt, iron, arsenic, and copper, and the doubts were finally resolved by scientist T Bergmann in 1775.
On Earth, nickel is the twenty-second most abundant element in the earth’s crust and seventh among the transition elements. It occurs most often in combination with sulfur, iron, and arsenic in the mineral-like nickeline. It has five naturally occurring isotopes like 58Ni, 60Ni, 61Ni, 62Ni, and 64Ni with several radioactive isotopes (atomic mass ranges 48 to 78). The nickeliferous limonite, (Fe, Ni)O(OH), and garnierite (Ni, Mg)6Si4O10(OH)8 are the main ores of the metal. Indonesia and Australia have the biggest reserves of the metal. Garnierite is found in New Caledonia, Cuba, Brazil, and Queensland. The most important single deposit of nickel is found in countries like Sudbury, Canada, Russia, and South Africa.
Extraction and Purification
Nickel is mainly extracted from the sulfide ore which contains about 3 percent of Ni, 1.5 percent of copper, and precious metals like gold, silver, platinum. The main steps for extraction of metal, concentrated sulfide ore magnetically or selective floatation. The concentrated sulfide ore subject to a series of roasting and smelting with the addition of silica and limestone. The mate rich Ni and Cu sulfide separated by solid-phase which is then extracted by Mond process or electrolytically.
Mond Carbonyl Process
In the mond process, the Ni-Cu sulfide is roasted to oxidize to their oxides. The oxides leaching with hot dilute sulfuric acid, the most of copper oxide dissolves out as CuSO4. The oxide is now reduced with hydrogen in water gas at about 300 to 350°C. The impure nickel is now converted to volatile tetracrbonyl by the action of CO at atmospheric pressure and around 50°C. The pure form of nickel is obtained by decomposing metal tetracarbonyl.
In the electrolytic process, the nickel-copper mate is roasted in a multiple hearth roaster to form their respective oxides. Most of the copper oxide is leached out with hot dilute sulfuric acid. The residue is further reduced with coke that contains 65 percent of Ni, and 30 percent of Cu, and 3 to 8 percent of sulfur and iron residue. Electrolysis is carried out with nickel sulfate solution as an electrolyte and Ni-electrode or cathodes on which the pure metal is deposited.
Properties and Compounds
Some physical and chemical properties like density, melting point, and boiling point of nickel given above the picture. The compact metal is quite resistant towards air and water but finely divided nickel very reactive and pyrophoric. It is slowly attacked by dilute hydrochloric acid and sulfuric acid but dissolves readily in dilute nitric acid and aqua regia. Practically, it is unattacked by caustic alkalies. It reacts slowly with fluorine at ordinary temperature. Heated nickel catches fire in chlorine or bromine and also combines with phosphorus, arsenic, or antimony.
In the +2 state, nickel forms a wide range of simple compounds like oxide (NiO), hydroxide (NiOH), halides sulfide (NiS), carbonate (NiCO3), cyanide (NiCN), and complex compounds. It is the only metal from first transition elements that form halides in a +2 oxidation state. The chemistry of nickel above +2 state forms some poorly understand oxides and some complex compounds. The only important simple compounds of the metal are Ni2O, 2H2O, and NiO(OH) which has a crystalline solid form. No simple halides above +2 states are known, although Ni(III) fluoride has been prepared in the impure form which is marginally stable at 25°C
Uses of Nickel
The metal is used mainly in the form of alloys like Monel metal, nickel silver, nichrome, alnico with iron, and other nonferrous metals. A small part of Ni increasing the quality of cast iron. For example, 0.25 to 0.45 percent of nickel in steels increases the mechanical properties and corrosion resistance properties. 68 percent of nickel from global production uses for making stainless steel. The metal is used in many industrial and consumer products like stainless steel, magnets, rechargeable batteries, electrical plating, etc.
The alloy, alnico is used for making permanent magnets like horseshoe magnet. The metal is used for making electrical cells like alkaline iron-nickel and cadmium nickel cells, gas diffusion electrodes for alkaline fuel cells, and as a chemical catalyst for hydrogenation of oils and hydrocarbon in organic chemistry. The common chemical catalyst for this purpose is Raney Nickel, a highly active form of the metal prepared by dissolving aluminum from the alloy NiAl3 with alkali.
Biological application of nickel
The natural biological application of nickel was established only in 1975 with the discovery of the metal in the enzyme jack bean urease. The enzyme is present in a number of plants, eubacteria, archaebacteria, and fungi. The enzyme contains an uncommon oxidation state like +2 with a redox reaction inactive unit containing octahedral nickel which acts as a Lewis acid. The redox-active nickel centers are present in other enzymes like Hydrogenase, CO dehydrogenase, methyl-S-coenzyme M reductase found mainly in bacteria.