Question

Name the reagent used in the leaching of gold.

• A. Carbon
• B. Iodine
• C. Sodium cyanide
• D. Carbon monoxide

Answer 1

The correct option is C

Sodium cyanide

The explanation for the correct option:

Option (C): Sodium cyanide

• Gold is usually found in low proportions in the form of mined ore. Differentiating gold from other minerals in the ore is essential.
• Because gold is a soluble mineral, it must be separated from other minerals. As a result, sodium cyanide can be added, forming a complex ion with the gold molecules.$\underset{\mathrm{Gold}}{4\mathrm{Au}\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{cyanide}}{8\mathrm{NaCN}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Sodium}\mathrm{gold}\mathrm{cyanide}}{4\mathrm{NaAu}{\left(\mathrm{CN}\right)}_2\left(\mathrm{s}\right)}+\underset{\mathrm{Sodium}\mathrm{hydroxide}}{4\mathrm{NaOH}\left(\mathrm{l}\right)}$
• The ore is crushed and ground. If the gold-bearing ore also contains other metals or sulfide minerals, it will require additional treatment before being leached.
• Gold is combined with sodium cyanide to create soluble gold.
• Because gold is soluble after the leaching process, it may move freely through the membrane whereas the remainder of the ore cannot.
• Hence, it is the correct option.

The explanation for the incorrect options:

Option (A): Carbon

• Carbon is an abundant element. Diamonds and graphite are examples of pure carbon, although they may also combine with other elements to form molecules.
• Under normal circumstances, carbon is quite inert.
• Inks and paints are made from amorphous carbon. It is also utilized in the manufacture of batteries. The lead-in your pencils is made of graphite. It is also required in the process of steel-making.

Option (B): Iodine

• Iodine is a chemical element with the atomic number $53$. Under typical conditions, it exists as a semi-lustrous, non-metallic solid, making it the heaviest of the stable halogens.
• Iodine is present in two forms i.e. non-radioactive and radioactive forms. Iodine is used to disinfect surfaces and storage containers, as well as in skin cleansers and bandages and for water purification.

Option (D): Carbon monoxide

• Carbon monoxide is a combustible gas that is colorless, very toxic, odorless, and tasteless. It is less dense than air.
• Carbon monoxide is an important industrial chemical. It is commonly utilized as a fuel in industrial processes in the form of producer gas or water gas. The gas can also be used as a reducing agent.
• The gas is also used in the Fischer-Tropsch process, which produces hydrocarbons.

Therefore, Sodium cyanide is used in the leaching of gold.