Animated Solution for Chemistry - Metallurgy: Among statements (A)-(D), the correct ones are : (A) Limestone is decomposed to CaO during the extraction of iron from its oxides. (B) In the extraction of silver, silver is extracted as an anionic complex. (C) Nickel is purified by Mond's process. (D) Zr and Ti are purified by van-Arkel method.

Extraction and Refining

Metallurgy is not just about digging dirt out of the ground; it is a highly sophisticated symphony of chemistry designed to coax pure metals out of their natural, often stubborn, mineral states. In this problem, we are taken on a grand tour of four distinct metallurgical processes. Let's break down the chemistry behind each statement to see why they are all perfectly correct.

The Blast Furnace and Limestone

Imagine you are operating a massive blast furnace for the extraction of iron. You feed iron ore, coke, and limestone into the top. But why limestone? Iron ore often contains acidic impurities, primarily silica (). To remove this, we need a basic flux.

Limestone, which is calcium carbonate (), decomposes upon heating inside the furnace:

The resulting calcium oxide () is the basic flux we need. It reacts with the silica to form a molten, fusible slag of calcium silicate (), which floats on top of the molten iron and can be easily removed. Therefore, Statement A is absolutely correct.

Hydrometallurgy of Silver

How do we extract precious metals like silver? We use a technique called hydrometallurgy, specifically the Mac-Arthur Forrest cyanide process.

In this process, the crushed silver ore is leached with a dilute aqueous solution of sodium cyanide () in the presence of air. The silver dissolves by forming a soluble coordination complex:

If you look closely at the formula of the dicyanoargentate(I) ion, , it carries a net negative charge. This makes it an anionic complex. Thus, Statement B is also correct.

Mond's Process for Nickel

Once a metal is extracted, it often needs to be purified. For Nickel, we use a brilliant technique called Mond's process, which is a type of vapour phase refining.

Impure nickel is heated in a stream of carbon monoxide at around 330-350 K. This forms a highly volatile complex called nickel tetracarbonyl, leaving the solid impurities behind:

Later, this volatile gas is heated to a higher temperature (450-470 K) to decompose it, yielding pure nickel metal. So, Statement C is spot on.

For metals like Zirconium () and Titanium (), which need to be ultra-pure for space and nuclear applications, we use the van-Arkel method.

Similar to Mond's process, this is also a vapour phase refining technique. The impure metal is heated with iodine in an evacuated vessel to form a volatile metal iodide:

This volatile iodide is then decomposed on a white-hot tungsten filament at around 1700 K to deposit pure metal. This statement is perfectly correct as well.

Since we have carefully analyzed all four statements and found that A, B, C, and D are all factually correct based on standard metallurgical principles, the correct option is (a).