Vapour Phase Refining – Mond’s Process, Van Arkel Process, Practice Problems and FAQ

What happens to ice if we heat it above 100 ^oC?

It will become a liquid and above 100 ^oC, it becomes vapour.

Can heating also transform metals into the equivalent vapour form?

Yes! There are some metals that, when heated to high temperatures, can be transformed into their vapours or into other volatile metal compounds. The possibility of refining those metals using their volatile molecules raises another question in this context. This concept page is focused on providing the answer to this intriguing question.

So let's start exploring right away!

TABLE OF CONTENTS

Vapour Phase Refining
Mond’s Process
Van Arkel Process
Practice Problems
Frequently Asked Questions – FAQ

Vapour Phase Refining

The basic principle behind vapour phase refining is that an impure metal is transformed into a volatile component (a complex of metal) that may be collected elsewhere. It is subsequently decomposed and the pure metal is recovered. Pure metals have a high density, high melting and boiling temperatures, and are good heat and electrical conductors.

There are two basic requirements for vapour phase refining.

A metal should form a volatile compound with a reagent.
The volatile compound should be easily decomposable for easy recovery.

The techniques that come under vapour phase refining are given below.

Mond’s Process
Van Arkel Process

Mond’s Process

Nickel is extracted from its sulphide ore by heating in the presence of excess oxygen followed by reduction with carbon. Nickel is found in association with other metals (impurities) which makes the extraction of pure Ni difficult. So, refining the nickel metal is necessary.

Refining of nickel occurs in two steps.

Step 1: Nickel is heated in a stream of carbon monoxide to form nickel tetracarbonyl complex [Ni(CO)₄]. [Ni(CO)₄] is highly volatile (boiling point 316 K). It is made by heating nickel powder to 330-350 K, in a stream of CO.

Step 2: Volatile [Ni(CO)₄] is decomposed at 450-470 K to give the pure metal and CO, which is recycled.

Van Arkel Process

This process generates small amounts of very pure metals (Ti, Zr, or Bi). Impurities of oxygen and nitrogen present along with a few other metals are removed by this process. When an impure element is heated with iodine, a volatile iodide is formed, such as $T i I_{4}, Z r I_{4}, o r B i I_{3} .$ . These are degraded by passing the gas through white-hot tungsten or tantalum filament heated by electricity. Iodine is recycled after the element is put on the filament. The filament conducts electricity better as additional metal is placed on it. To keep it white-hot, more electric current must be passed. As a result, the filament thickens and the metal is eventually recovered. A little amount of high purity metal is obtained after the tungsten core is distilled out of the centre.

Refining of zirconium using the Van Arkel process occurs in two steps.

Step 1: The crude metal is heated in an evacuated vessel with iodine.

Step 2: Metal iodide (ZrI₄) which is volatile in nature is decomposed on tungsten filament, when ZrI₄ is heated electrically at 1800 K.

Practice Problems

Q1. Which of the following metals is refined by Mond’s process?

A. Ni
B. Cu
C. Si
D. Ge

Answer: A

Solution:

High purity nickel is obtained using Mond’s process.

Refining of Cu is done using electrolytic reduction.

Si and Ge are obtained using zone refining.

So, option A is the correct answer.

Q2. Which of the following metals is refined by the Van Arkel process?

A. Ti
B. Zr
C. Bi
D. All of the above

Answer: D
Solution: Through Van-Arkel process, metals like Titanium (Ti), Zirconium (Zr), Bismuth (Bi), etc, can be refined.

So, option D is the correct answer.

Q3. What is the temperature at which [Ni(CO)₄] is decomposed?

A. 450-470 K
B. 1800 K
C. 330-350 K
D. 450-350 K

Answer: A
Solution: Volatile [Ni(CO)₄] is decomposed at 450-470 K to give pure nickel metal and CO, which is recycled.

So, option A is the correct answer.

Q4. Which impurities are removed in the Van Arkel process?

A. Nitrogen
B. Oxygen
C. Hydrogen
D. Both A and B

Answer: D
Solution: Impurities like oxygen and nitrogen present along with the few other metals are removed by the Van Arkel process.

So, option D is the correct answer.

Frequently Asked Questions – FAQ

Q1. Why are iodides of metals made in the Van-Arkel process?
Answer: The Van Arkel process is based on the fact that iodides are the least stable of all the halides. Being highly covalent, they can be easily decomposed to give pure metal.

Q2. Name some raw forms of nickel that can be used to get high purity nickel in the the Mond’s process?
Answer: Spongy nickel (obtained by reduction of process wastes or natural nickel ores), copper-nickel natural ores, converter mattes, anode scrap, alloys of copper-nickel-iron system, etc. are used as raw materials in the Mond’s process.

Q3. What are the uses of high purity Zirconium?
Answer: Zircon is a semi-precious gemstone that comes in a wide range of colours. Cubic zirconia is a synthetic gemstone made up of zirconium oxide. When cut, the colourless stones mimic diamonds. It is also used in cosmetics, food packaging and to make microwave filters. Because zirconium does not absorb neutrons, it is an excellent material for nuclear power plants.

Q4. How CO is produced in Mond’s process?
Answer:CO in Mond’s process is produced by passing steam through carbon, which forms a mixture of CO and H₂.

$H_{2} O (g) + C (s) \to C O (g) + H_{2} (g)$

Related Topics

Extraction of Crude Metal from Concentrated Ore	Extraction of Iron
Occurrence of Metals	Concentration of Ores
Zone Refining	Refining of Metals from Concentrated Ores