Question

Write the chemical reactions involved in the process of extraction of Gold. Explain the role of dilute NaCN and Zn in this process.

Answer 1

To answer this question the concepts in metallurgy should be known. Metallurgy is a process that is used for the extraction of metals to obtain them in their pure form. The compounds of metals mixed with rocks, soil, sand, and impurities are referred to as minerals. These minerals are called ores.

Complete step by step answer:
In presence of oxygen dilute NaCN is used for leaching gold. At first in the reaction between NaCN and gold sample, a cyanide complex of gold is formed. After this, Zn is used, zinc displaces the position of gold, and extract of gold metals is completed. Here NaCN acts as an oxidizing agent. And Zn acts as a reducing agent. The reactions are shown below,
$4Au(s) + 8C{N^ - }(aq) + 2{H_2}O(aq) + {O_2}(g) \to 4{[Au{(CN)_2}]^ - }(aq) + 4O{H^ - }(aq)$
$Zn(s) + 2{[Au{(CN)_2}]^ - }(aq) \to {[Zn{(CN)_4}]^{2 - }}(aq) + 2Au(s)$.

Additional information:
Let us discuss some theories,
1.Limestone: Limestone is an ore that contains large amounts of calcium carbonate. This calcium carbonate is used to extract Calcium from this ore.
2.Dolomite: Dolomite is just another type of limestone. These ores contain large quantities of Calcium and Magnesium.
3.Chalk: Chalk is also a type of limestone. As opposed to limestone, chalk does not contain calcium carbonate as the main compound instead, it contains another compound known as calcite, which is also used to extract calcium.
4.Feldspar: Feldspar ores are usually of two types – plagioclase and orthoclase. The first type contains large quantities of calcium and sodium, while the other is rich in potassium

Note: Gold is an element with symbol, Au. It is resistant to most acids and is a precious metal used for jewelry, coinage and other arts. Because of the softness of pure gold, it’s alloyed with base metals for making jewelry. Palladium-gold alloys are more expensive than those which are made using nickel.