Chemistry of Iron Cobalt and Nickel

CHEMISTRY OF IRON, COBALT AND NICKEL

Group VIIIB in the periodic system are divided into 3 sub groups. That vertically called triad transition. In the modern periodic system, this third triad transition was given new classification, namely no. 8, 9, and 10. But the tendency of properties especially their chemical properties horizontally have more similarities than vertically. So it is grouped again into 3 groups of horizontal, each consisting of 3 elements. Iron, cobalt, and nickel are an element contained horizontally in the transition group VIIIB. These elements tends to have similar properties so that they can mix and form an alloy. This essay will briefly discusses about the history, abundance, isolation, properties, uses, iron, cobalt and nickel alloys and its compound namely the oxides; the metallates; the sulfides, selenides and tellurides; the halides and oxohalides; and the complexes.

History of Iron, Cobalt and Nickel

Iron beads dating from around 4000 BC were no doubt of meteoric origin, and later samples, produced, by reducing iron ore with charcoal, were not cast because adequate temperature were not attainable without the use of some form of  bellows. Instead, the spongy material produced by low temperature reduction would had to be shaped by prolonged hammering. It seems that iron was first smelted by the Hittites in Asia. Minor sometime in the third millennium BC, but the value of the process was so great that its secret was carefully guarded and it was only with the eventual fall of the Hittite empire around 1200 BC that the knowledge was dissapear and the “ Iron Age” began. The name “iron” is Anglo Saxon in origin (iren, cf. German Eisen). The symbol is Fe and words such as “ferrous” derive from Latin ferrum, iron. (Greenwood et al., 1997:1070).

            Although harldy any metallic cobalt was used until the twentieth century, its ores have been used for thousand of years to impart a blue color to glass and pottery. It is present in Egyptian pottery dated at around 2600 BC and Iranian glass beads of 2250 BC. The source of the blue colour was recognized in 1735 by the Swedish chemist G.Brandt, who isolated a very impure metal, or “regulus”, which he named “cobalt rex”. In 1780 T.O. Bergman showed this to be a new element. Its name has some resemblance to the Greek word for “mine” but is almost certainly derived from the German word Kobold for “goblin” or “evil spirit”. The miners of northern European countries thought that the spitefulness of such spirits was responsible for ores which on smelting (Greenwood et al., 1997).

            An alloy of nickel was known in China over 2000 years ago, and Saxon miners were familiar with the reddish-coloured ore, NiAs, which superficially resembles Cu₂O. These miners attributes their inability to extract copper from this source to the work of the devil and named the ore “Kupfernickel” (Old Nick’s copper). In 1751 A. F. Cronstedt isolated an impure metal from some Swedish ores, and identifying it with the metallic component of Kupfernickel, named the new metal “nickel”. In 1804 J.B. Richter produced a much purer sample and so was able to determine its physical properties more accurately (Greenwood et al., 1997).

Abundance and Distribution of Iron, Cobalt, and Nickel

            In the earth’s crustal rocks, iron metal can be found about 6.2% or 62000 ppm, it is the fourth most abundant element after oxygen, silicon, and aluminium; and the second most abundant metal. Its also widely distributed, as oxides and carbonates, of which the chief ones are haematite (Fe₂O₃),  magnetite (Fe₃O₄), limonite (2Fe₂O₃.3H₂O)and siderit  (FeCO₃).  Iron pyrite (FeS₂) is also common but is not used as a source of iron because of the difficulty in eliminating the sulfur. The distribution of iron has been considerabely influenced by weathering. Leaching from sulfide and silicate deposits occurs readily as FeSO­₄ and Fe(HCO₃) respectively. In solution, these are quickly oxidized, and even mildly alkaline conditions cause the precipitation of iron (III) oxide. Because of their availability, production of iron ores can be confined to those of the highest grade in gigantic operations (Greenwood et al., 1997:1071).

Most of our stone and soil contain an iron. Iron isotopes are mainly used in nutritional studies, with Fe-57 and Fe-58 being the two most commonly used Fe isotopes. Studies have included iron-loss by human adolescents, conditions for effective iron absorption, interventions for anemia and genetic iron control. The Fe-54 isotope is used for the production of radioactive Fe-55 which in turn is used as an electron capture detector and in X-ray fluorescence. Fe-56 can be used for the production of radioactive Co-55 which is used as a tumor seeking agent in bleomycin. An iron ore that able to be an material must contain the high persentage of iron compound.

Pure cobalt is not found in nature, but compounds of cobalt are common. Small amounts of it are found in most rocks, soil, plants and animals. It is the 33^rd most abundant element and has been found in a variety of media, including air, surface water, leachate from hazardous waste sites, groundwater, soil, and sediment. Small amounts of metallic cobalt are present in meteorites but it is usually extracted from ore deposits worked in Canada, Morocco, Zaïre, Zambia, Russia, Australia, and Cuba. It is present in the minerals cobaltite (CoAsS), smaltite (CoAS₂), chloranthite, lemacite (Co₃S₄) and erythrite but also associated with copper and nickel as sulfides and arsenides

Cobalt is present in nature where it represents approximately 0.002% of the earth’s crust. Unlike its neighbors in the Periodic Table, iron, nickel, and copper, cobalt is not widespread in nature. It has an average abundance in Earth's crust of 25 parts per million (ppm); in ultrabasic rocks, where cobalt is most common, the average concentration is 110 ppm. Cobalt minerals may be concentrated by a range of geological processes to produce workable ores that typically contain 1,000–2,000 ppm. The isotope cobalt-60 (⁶⁰Co) is an artificially produced isotope used as a source of γ rays (its high energy radiation is useful for sterilisation in medicine and of foods).

Nickel is the seventh most abundant transition metal and the twenty-second most abundant element in the earth’s crust. It is aboout 99 ppm. It is commercially important ores are of two types:

1.      Laterites, which are oxide/silicate ores such as garnierite (Ni,Mg)₆Si₄O₁₀(OH)₈, and nickelliferous limonite (Fe,Ni)O(OH).nH₂O, which have been concentrated by weathering in tropical rainbelt in New Caledonia, Cuba and Queensland.

2.      Sulfides such as pentlandite (Ni,Fe)₉S₈, associated with copper, cobalt and precious metals so that the ores typically contain about 1.5% Ni. It can be found in the Canada, the former Soviet Union and South Africa (Greenwood et al., 1997:1145).

Nickel is composed of five stable isotopes, such as: ⁵⁸Ni, ⁶⁰Ni, ⁶¹Ni, ⁶²Ni and ⁶⁴Ni. Nickel-61 is the onlystable isotope of nickel which makes it useful for studies by EPR Spectroscopy. 

Isolation of Iron, Cobalt and Nickel

   It is not normally necessary to make iron in the laboratory as it is available commercially. Small amounts of pure iron can be made through the purification of crude iron with carbon monoxide. The intermediate in this process is iron pentacarbonyl, Fe(CO)₅. The carbonyl decomposes on heatingto about 250°C to form pure iron powder.

Fe + CO → Fe(CO)₅ (250°C) → Fe + 5CO

The Fe(CO)₅ is a volatile oily complex which is easily flushed from the reaction vessel leaving the impurities behind. Other routes to small samples of pure iron include the reduction of iron oxide, Fe₂O₃, with hydrogen, H₂.

Nearly all iron produced commercially is used in the steel industry and made using a blast furnace. Most chemistry text books cover the blast furnace process. In essence, iron oxide, Fe₂O₃, is reduced with carbon (as coke) although in the furnace the actual reducing agent is probably carbon monoxide, CO.

2Fe₂O₃ + 3C → 4Fe + 3CO₂

This process is one of the most significant industrial processes in history and the origins of the modern process are traceable back to a small town called Coalbrookdale in Shropshire (England) around the year 1773 (http://www.webelements.com/iron/).

            In 1995, world produce 20000 tonnes of cobalt, considerably below capacity. The major producing countries are Zaire, Zambia, Canada, Finland and former Soviet Union (Greenwood et al., 1997:1114).

Pure cobalt is produced when hydroxide and sodium hypochlorite (NaOCl) based on the reaction:

2Co²⁺_(as) + NaOCl_(as) + 4OH^-_(as) + H₂O → 2Co(OH)_3(s) + NaCl_(as)

Co(OH)_3(s) which is formed is heated to form oxide and then adding by carbon to form a pure metal.

Cobalt also is obtained by heating its ore (cobaltite) to produce the cobalt oxide. That compound is then heated with aluminum to free the pure cobalt metal by the following reactions:

 

           

Production for nickel is complicated and dependent on the particular ore involved. Therefore only be sketched in outline. In this case of nickel the oxide ores are not generally amenable to concentration by normal physcical separations and so the whole ore has to be treated. (Greenwood et al., 1997:1145)

Nickel occurs more abundantly than cobalt but only a few deposits are economically useful for extraction. The metal is obtained by heating with sulphur compounds to give the sulphide, which is roasted to form the oxide. And then, it is reduced directly by heating with the coke or dissolved to give a solution containing nickel (II) from which nickel  can be deposited electrolytically. The metal obtained by reduction cab be purified by the Mond process. It is heated to 320 K with carbon monoxide to give the pure volatile tertacarbonyl Ni(CO)₄. And then when heated to 500 K gives the pure metal and carbon monoxide is recorvered (Chambers & Holliday, 1975:405)

Ni + 4CO  Ni(CO)₄

Reduction that occurs in this process only a portion of the iron that can be tied into slag, and most are still in the form of ferro-nickel alloy. In this case to separate the iron from the nickel smelter is added to the reaction of some sulfur-containing materials (Gypsum or Pyrite). Because of differences in iron and nickel holding capacity of the oxygen and sulfur, so the process is obtained which is an alloy metal FeS and Ni₃S₂ and most of the iron can be slagged.

The resulting metal was still contain more than 60% Fe and the subsequent metal that remains in the liquid state continue to be processed again in the converter. Converter processes given the added material to the silicon oxide slag the iron. The results of slag still contain nickel converter is high enough, so the slag is usually in the back on the smelting process (resmelting). The next process is in the roast to separate metal sulfur. Nickel oxide obtained from the subsequent reduction roasting with charcoal added material (charcoal), in order to get the nickel metal.

Properties of Iron, Cobalt and Nickel

Iron is a silvery, lustrous metal but chemically active. After a short time in moist air it changes from silvery to rusty as reddish-brown FeOOH is formed. Water and soluble electrolytes such as salt accelerate the reaction. Iron with symbol Fe has atomic number of 26. At ground sate, electron configuration of Fe is [Ar]3d⁶4s². The physical properties of iron are shown in the following table.

Density			7.87 g cm–3
Molar volume			7.09 cm3
Melting point			1811 K
Boiling point			3134 K
Specific heat cp at 298 K			449 J K–1 kg–1
Molecular Weight			55.85 gmol-1
Electronegativity			1.7 eV
Electron Affinity			15.7 kJ mol-1
Electrode potential M2+ + 2e             M M3+ + e               M2+			-0,44 +0,74
Magnetic characterization			Ferromagnetic
Thermal conductivity Wm–1K–1
173 K	273 K	373 K	573 K	973 K
99	83.5	72	56	34
Coefficient of linear expansion K–1
100 K	293 K	500 K	800 K
5.6 · 10–6	11.8 · 10–6	14.4 · 10–6	16.2 · 10–6
Resistivity nm
78 K	273 K	373 K	573 K	973 K	1473 K
7	89	147	315	855	1220

Table 1. Physical Properties of Iron

Source: Per Enghag, 2004: 169

Several chemical properties of iron are:

1.      With hot water vapor can react to produce hydrogen gas, but wit cold water cant no react.

3Fe_(s) + 4H₂O_(g) → Fe₃O_4(s) + 4H_2(g)

2.      Iron will corrosion and the color change to brown if react with wet air.

4Fe_(s) + 3O_2(g) + nH₂O → 2Fe₂O₃.n H₂O

3.      If it is burned with  sulfur will form iron (II) sulfides (FeS).

Fe_(s) + S_(s) → FeS_(s)

4.      With halogen group will form FeX₃ (X=F, Cl, Br, dan I) compound, except with iodium will form FeI_2.

5.      Reaction with acid

a.       Reaction with hydrochloric acid to produce hydrogen gas and iron (II) chloride.

Fe_(s) + HCl_(aq) → FeCl_2(aq) + H_2(g)

b.      Reaction with dilute sulfuric acid will form H₂ gas but with concentrated sulfuric acid will produce SO₂ gas. It can be occurred because besides acidic, sulfuric acid also acts as an oxidizing agent.

As the acid:

Fe_(s) + 2H⁺_(aq) → Fe²⁺_(aq) + H_2(g)

As oxidizing agent:

Fe_(s) + SO₄^2-_(aq) + 4H⁺_(aq) → Fe²⁺_(aq) + SO_2(g) + 2H₂O_(l)

c.       Reaction with nitric acid

With dilute nitric acid will form NO and NO₂ gas, but with concentrated nitric acid will produce NO₂ gas. It can be occurred because the oxidizing properties of concentrated nitric acid stronger than dilute nitric acid.

	Figure 1 Iron (copyright from http://images-of-elements.com/iron.php at May 18th, 2013)

 

Cobalt is a bluish silvery metal with magnetic properties similar to those of iron. Its salts give glass a beautiful deep-blue color. Cobalt with symbol Co has atomic number of 27. At ground sate, electron configuration of Fe is [Ar]3d⁷4s². The physical properties of cobalt are shown in the following table.

Density			8.90 g cm–3
Molar volume			6.62 cm3
Melting point			1768 K
Boiling point			3200 K
Specific heat cp at 298 K			421 J K–1 kg–1
Molecular Weight			58.932 gmol-1
Electron Affinity			63.7 kJ mol-1
Magnetic characterization			Ferromagnetic
Thermal conductivity Wm–1K–1
173 K	273 K	373 K	573 K	973 K
130	105	89	69	53
Coefficient of linear expansion K–1
100 K	293 K	500 K	800 K
6.8 · 10–6	13 · 10–6	15 · 10–6	15.2 · 10–6
Resistivity nm
78 K	273 K	373 K	573 K	973 K	1473 K
9	56	95	197	480	885

Table 2. Physical Properties of Cobalt

Source: Per Enghag, 2004: 669

The chemical properties of cobalt are; (a) cobalt is less reactive element. It combines slowly with oxygen in the air, but does not catch fire and burn unless it is in a powder form; (b) reacts with most diluted mineral acids to produce hydrogen gas. It does not react with water at room temperatures; (c) forms the complex compounds, (d) in water solution exist as Co²⁺ (red colored), and (e) resistance to the corrosion, and (f) Co³⁺ is not stable, but its complexes are stable in solution and in solid state, and (g) dissolves in diluted mineral acids.

	Figure 2 Cobalt ( copyright from http://images-of-elements.com/cobalt.php at May 18th, 2013)

 

Nickelis a moderately lustrous, silvery metal, and extensively used in alloys. It is a malleable and ductile metal, ferromagnetic up to 354°C.  Iron meteorites contain metallic iron with up to 20% nickel. The main nickel source is the mineral pentlandite. Nickel with symbol Ni has atomic number of 28. At ground sate, electron configuration of Ni is [Ar]3d⁸4s². The physical properties of nickel are shown in the following table.

Density			8.90 g cm–3
Molar volume			6.59 cm3
Melting point			1728 K
Boiling point			3186 K
Specific heat cp at 298 K			444 J K–1 kg–1
Molecular Weight			58.69 gmol-1
Electron Affinity			112 kJ mol-1
Magnetic characterization			Ferromagnetic
Thermal conductivity Wm–1K–1
173 K	273 K	373 K	573 K	973 K
113	94	83	67	71
Coefficient of linear expansion K–1
100 K	293 K	500 K	800 K
6.6 · 10–6	13.4 · 10–6	15.3 · 10–6	16.8 · 10–6
Resistivity nm
78 K	273 K	373 K	573 K	973 K	1473 K
5.5	62	103	224	400	-

Table 3. Physical Properties of Nickel

Source: Per Enghag, 2004: 687

The combination of nickel, chromium and iron produce stainless steel (stainless steel) are widely applied to kitchen utensils (spoons, and cooking equipment), home ornaments and buildings, and industrial components. At room temperature, nickel can not be attacked by air or water. Some of the reactions of nickel:

1.         Very slow to react with hydrochloric acid or dilute sulfuric acid

2.         Reacts rapidly with dilute nitric acid, but with concentrated nitric acid, noickel is passive.

Hydrochloric acid (both dilute and concentrated) and dilute sulphuric acid dissolve nickel with the formation of hydrogen:

Ni + 2H⁺ ® Ni²⁺ + H₂ ­

Ni + 2HCl ® Ni²⁺ + 2Cl^- + H₂ ­

These reaction accelerate if the solution is heated. Concentrated, hot sulphuric acid dissolves nickel with the formation of sulphur dioxide.

Ni + 2H₂SO₄ + 2H⁺ ® Ni²⁺ + SO₂ ­+ 2H₂O

Dilute and concentrated nitric acid dissolve nickel readily in cold:

            Ni + 2HNO₃ + 6H⁺ ® 3Ni²⁺ + 2NO ­+ 4H₂O

	Figure 3 Nickel ( copyright from http://images-of-elements.com/nickel.php at May 18th, 2013)

 

Uses of Iron, Cobalt and Nickel

Iron is the basic metal for the production of the steel family. This is very diversified and plays a crucial role in modern human life, from the load-bearing functions in large steel buildings and bridges to the small springs in precision mechanics, special steels for the surgeon’s scalpels to all steel components in household and kitchen (Per Enghag, 2004: 168).

Iron is an important micronutrient for living things. Iron largely stable in the metal bound with protein (metalloprotein), because the iron in a free state can cause the formation of free radicals that are toxic to cells. Iron is a major constituent of the survival of living beings and works as a carrier of oxygen in hemoglobin. FeSO₄ is used as a mineral source for therapeutic mineral deficiency/ iron deficiency and is used to make ink powder. Fe₃SO₄ used for textile dyeing and testing of aluminum.

But iron also has some weaknesses especially the corrosive properties.  Corrosion that mension before is an interaction between an iron with water and air. We can modify iron becomes a steel in order to make an iron uncorrosively, but ussualy has a high cost to do that. To minimalize the corrosive in iron there are several ways to do protection for iron from the water and air:

·         Painting the fence or bridge also everythink that made from an iron. Paint can protect iron from water and air because if we painted them, water and air can’t directly attract with water and air. The better paint that recomended to used is paint that contained lead and zinc.

·         Coat with plastic, for example on a plate rack

·         Coated with lead, for example on packaging cans

·         Coating with Zn, for example on iron pipe

·         Coating with chromium, for example, motors bumper

·         Coating with Mg, for example in the steel pipe in the ground 

·         Making bridge construction, tranports body, train rel, etc.

Cobalt is used as stainless steel and steel magnet. Because cobalt has positive value of E₀ so difficult to oxidize. . The artificially produced isotope ₆₀Co, where as an important source of light, and is extensively used as a radiotherapeutic agent. Cobalt-60 can emit gamma rays that kill viruses, bacteria, and other pathogenic microorganisms without damaging the product. Cobalt-60 is used for irradiating the cancer cells. With a controlled radiation dose given, the cancer cells will be killed, while normal cells will not be affected and will withstand the radiation.

Nickel is used on a large scale for the manufacture of stainless steel and other alloys that are corrosion resistant (used in all types of corrosive environments and also on our kitchen sinks) contains, as well as 18% chromium, also 8% nickel. It is also used to make coins; the US 5-cent coin (whose nickname is “nickel”) contains 25% nickel.

Alloys of Iron, Cobalt and Nickel

Alnico is an alloy containing Aluminum (Al), Nickel (Ni), Cobalt (Co) hence its name Alnico. But Alnico actually contains more than just these three elements. It also contains Iron and Copper with some versions also containing Titanium and even Niobium (the Titanium versions were sometimes called Ticonal, derived from the elements TiCoNiAl). Alnico magnets were developed in the 1930’s and was the first “Real” performance permanent magnets (the first “magnets”, called magnetic steels, were quickly replaced by the vastly superior Alnico).

Alnico is produced by either a sintering method or, more commonly, a casting method. The as cast or as sintered shape is acceptable for many applications but surfaces may need to be ground for a smoother surface finish. The as cast look has darkened edges with a slightly rough texture (due to the sand mold edges); a machined face of an Alnico magnet has a bright silvery metallic surface and is usually extremely smooth as it is often precision ground (http://www.alnico-info.com/).

The other alloy is kovar. Kovar is the alloy of iron, cobalt and nickel with a coefficient of thermal expansion similar to that of hard (borosilicate) glass. It is an alloy with 29% Nickel, 17% Cobalt and the remaining balance is Iron.This makes it especially suitable for uses which require a matched-expansion seal between metal and glass parts. Thus kovar finds wide usage in the electronics industry for metal parts bonded to hard glass envelopes for such devices as power tubes, x-ray tubes, etc., and other applications requiring glass-to-metal seals.

REFERENCES

Chambers & Holliday. 1975. Modern Inorganic Chemistry an Intermediate Text. London: Butterworth & Co Ltd.

Greenwood, N & Earnshaw, A. 1997. Chemistry of the Elements: Second Edition. Great Britain: Elsevier Ltd.

Enhag, Per. 2004. Encyclopedia of The Elements. Sweden: WILEY-VCH Verlag GmbH & Co. KgaA