Which of the following is used in the extraction of silver? (a) \(\mathrm{NaCN}\) (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) (d) \(\mathrm{NaCl}\)

The cyanidation process is a metallurgical technique used for the extraction of gold and silver from ore. It involves treating the crushed ore with a dilute solution of sodium cyanide or potassium cyanide. The precious metals are leached from the ore into the solution. In the case of silver extraction, silver ions form complexes with the cyanide ions, allowing them to be dissolved in water. This process is particularly effective because it can extract silver from low-grade ores, making it economically viable.

During cyanidation, several reactions take place. The most important reaction for silver extraction is:
\[ \text{Ag} + 2\text{NaCN} + \text{O}_{2} + \text{H}_{2}\text{O} \rightarrow \text{Na}[\text{Ag}(\text{CN})_{2}] + 2\text{NaOH} \]
The silver reacts with sodium cyanide in the presence of oxygen and water to form a soluble silver-cyanide complex. This reaction is helped by the introduction of an oxidizing agent, which can be oxygen from the air or added as a compound like peroxide or cyanide itself in higher concentrations. Once the silver is in solution, it can be recovered by various methods, such as precipitation or electro-winning.

Sodium cyanide (\( \text{NaCN} \)) plays a crucial role in the cyanidation process as it is the chemical reagent that facilitates the leaching of silver from ore. As a simple salt formed from sodium and cyanide ions, it is highly soluble in water, which makes it effective in the process. Due to the toxicity of cyanide, there are strict regulations on its handling and disposal.

It's crucial for the successful extraction of metals that the concentration of sodium cyanide is carefully controlled. Too little and the process is ineffective; too much and it can become uneconomical or lead to environmental issues. Therefore, in a metallurgical context, sodium cyanide is both a valuable tool and a substance that must be managed with care to ensure the safety of workers and the environment.

Metallurgical processes encompass the various methods used to extract valuable metals from their ores. These processes can be pyrometallurgical, involving heat and chemical reactions to produce a pure metal, or hydrometallurgical, which involves aqueous solutions to leach metals from ores. The cyanidation process falls under the category of hydrometallurgy.

These processes are designed to achieve two main goals: the concentration of the metal within the ore (to make it more economically viable to extract), and the extraction of metals from the concentrated ore. The development of metallurgical techniques is driven by the pursuit of more efficient, cost-effective, and environmentally friendly methods of extraction. The extraction of silver using the cyanidation process illustrates the advancement of chemical metallurgy, enabling the mining industry to recover valuable metals from ores that might not otherwise be profitable.