Inorganic Synthesis

Cobalt metal preparation

Theory:

The first row transition elements are usually produced from their ores. The composition of the ores differs from one to another element. If the ore is composed mostly of an oxide (such as iron ore) it can be directly reduced to form pure element. Otherwise it is terrified to convert carbonates and sulfides  to an oxide or a mixture of the oxides. Cobalt ore is represented by minerals cobaltite (CoS2), erythrite (Co3(AsO4)2·8H2O) and others. Most of the world´s production comes from Congo, Africa where large deposits of cobalt minerals are found [1].

Procedure I:

2Al + 3CoCl2 → 2AlCl3 + 3Co

Cobalt(II) chloride hexahydrate (7.14 g, 30 mmol) was dissolved in 40mL of distilled water. The solution was heated to 85°C and aluminium powder (0.54 g, 20 mmol) was added in portions with stiring. The colour of the solution continually changed from deep red to bright pink, almost colourless. The cobalt metal precipitated as black powder. It was filtered and poured into solution of sodium hydroxide in order to dissolve unreacted aluminium. Then it was decanted and filtered. The filtrate was washed with distilled water and dried at 50°C. Yield: 74.26%.

mix

Procedure II:

CoCl2.6H2O + Na2CO3 -> CoCO3 + 2NaCl
3CoCO3 + 1/2 O2 -> Co3O4 + 3CO2
Co3O4 + 4H2 -> 3Co + 4H2O

An equimolar amount of sodium carbonate solution was added into a solution of cobalt(II) chloride. Pink cobalt(II) carbonate precipitate was filtrated out using Buchner´s funnel and dried it in an oven at hundred degrees of celsius. After the powder was completely dry, the temperature was raised up to 250 °C to decompose the carbonate into cobalt(II,III) oxide and carbon dioxide. A colour change from pink to almost black is observed. An apparatus for hydrogen generation was set up using a three-neck round-bottom flask and a few gas-washing bottles attached to a quartz tube where cobalt(II,III) oxide was placed in a ceramic boat. The three-neck round-bottom flask was filled with zinc metal and a separatory funnel containing hydrochloric acid was attached to the flask. Droping the acid onto the metal produced hydrogen gas. When all oxygen was pushed out from the apparatus, the quartz tube was tempered with a Bunsen burner for about 20 minutes. At the end of the quartz tube, condensing droplets of water were observed as a side-product of the reaction. Yield: 83-85 % (based on Co3O4).

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Cobalt(II) carbonate [photo: Gemchina.com]

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Cobalt (II,III) oxide [photo: Michal Hegedus]

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Water droplets on the wall of the quartz tube [photo: Michal Hegedus]

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Half reduced cobalt(II,III) oxide [photo: Michal Hegedus]

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Pure cobalt metal powder [photo: Michal Hegedus]

Literature:

[1] 10 top Cobalt-producing Countries. (2015, April 26). Retrieved May 24, 2016, from http://investingnews.com/daily/resource-investing/critical-metals-investing/cobalt-investing/top-cobalt-producing-countries-congo-china-canada-russia-australia/