Mond process

Spheres of nickel made by the Mond process

The Mond process, sometimes known as the carbonyl process, is a technique created by Ludwig Mond in 1890 to extract and purify nickel. The process was used commercially before the end of the 19th century. This process converts nickel oxides into pure nickel.

This process makes use of the fact that carbon monoxide combines with nickel readily and reversibly to give nickel carbonyl. No other element forms a carbonyl compound under the mild conditions used in the process.

This process has three steps:

1. Nickel oxide reacts with Syngas at 200 °C to give nickel, together with impurities including iron and cobalt.

NiO(s) + H₂(g) → Ni(s) + H₂O(g)

2. The impure nickel reacts with carbon monoxide at 50–60 °C to form the gas nickel carbonyl, leaving the impurities as solids.

Ni(s) + 4 CO(g) → Ni(CO)₄(g)

3. The mixture containing nickel carbonyl (and synthesis gas) is heated to 220–250 °C, resulting in decomposition back to nickel and carbon monoxide:

Ni(CO)₄(g) → Ni(s) + 4 CO(g)

Steps 2 and 3 illustrate a chemical transport reaction, exploiting the facts that (1) carbon monoxide and nickel readily combine to give a volatile complex and (2) this complex degrades back to nickel and carbon monoxide at higher temperatures. The decomposition may be engineered to produce powder, but more commonly an existing substrate is coated with nickel. For example, nickel pellets are made by dropping small, hot pellets through the carbonyl gas; this deposits a layer of nickel onto the pellets.

This process has also been used for plating nickel onto other metals, where a complex shape or sharp corners made good results difficult by electroplating. Although the results are good, the toxicity makes it impractical as an industrial process. Such parts are now plated by electroless nickel plating instead.

See also

• carbonyl metallurgy

Further reading

• [1]