Mond Process for Nickel

Mechanism — Two Temperature Stages:

Stage 1 (330–350 K / ~60°C): Impure Ni + CO gas: $Ni + 4CO \xrightarrow{330-350\text{ K}} Ni(CO)_4$

• Ni(CO)4 is volatile (boiling point 43°C) — easily collected as gas
• Impurities (Fe, Co, Cu) do not readily form stable volatile carbonyls at this temperature
• Ni(CO)4 vapour is pumped away from the impure solid

Stage 2 (450–470 K / ~180°C): Ni(CO)4 vapour heated: $Ni(CO)_4 \xrightarrow{450-470\text{ K}} Ni + 4CO$

• At higher T, the equilibrium reverses — Ni(CO)4 decomposes
• Pure Ni deposits on metal pellets/balls
• CO is recycled back to Stage 1

Net effect: Ni is transferred from the impure solid to the CO carrier and then deposited as pure metal. Impurities remain behind.

Van Arkel Method for Titanium

Mechanism — Iodide Carrier Cycle:

Stage 1 (~870 K / ~600°C): Impure Ti reacts with I2 vapour: $Ti + 2I_2 \xrightarrow{\sim 870\text{ K}} TiI_4$

• TiI4 is volatile — sublimes at ~150°C
• Impurities (e.g., C, N, O as TiC, TiN, TiO) do not form volatile iodides
• TiI4 vapour migrates to the hotter central zone

Stage 2 (~1700 K / ~1430°C, W filament): $TiI_4 \xrightarrow{\sim 1700\text{ K}} Ti + 2I_2$

• Pure Ti deposits on the hot tungsten filament as bright, crystalline, silvery metal
• I2 is regenerated and recycled (cyclic process)

Comparison Chart