Mond process

These spheres of nickel metal were made with the Mond process.

The Mond process is a way to make pure nickel metal. It works because nickel easily reacts with carbon monoxide to make a volatile compound, while most other metals do not. It is an important example of a chemical transport reaction.

Process

The Mond process starts with impure nickel or nickel(II) oxide. This solid is treated with syngas, a mixture of carbon monoxide and hydrogen. Hydrogen is a reducing agent that chanegs the oxide to the metal:

NiO + H₂ → Ni + H₂O

The metal reacts with the carbon monoxide, making a coordination complex called nickel tetracarbonyl:

Ni + 4 CO → Ni(CO)₄

Nickel tetracarbonyl is volatile: it easily becomes a gas. When the carbonyl sublimes, impurities like cobalt or iron are left behind.

After it is separated from the impurities, the carbonyl gas is heated. At around 250 °C (482 °F), it breaks down back into the nickel metal and carbon monoxide:

Ni(CO)₄ → Ni + 4 CO

The purified nickel metal crystallises onto a prepared surface. This surface can be an object to be plated with nickel, or a small piece of nickel that grows to make a larger, purer ingot.

History

The Mond process is named for Ludwig Mond, who discovered nickel carbonyl in 1890. This was the first metal carbonyl discovered. Mond developed his discovery into the process that is now named after him. Mond patented it in 1898, and started the Mond Nickel Company to commercialise it.

Safety

The nickel tetracarbonyl made during the Mond process is very toxic. It is known to cause cancer and can be deadly if breathed in.