Cyanide process is used for the extraction of
(a) barium
(b) silver
(c) boron
(d) zinc

Q: Why is oxygen gas bubbled through the solution during leaching?

The reaction between silver sulfide and sodium cyanide is reversible. Oxygen is bubbled through to oxidize the sulfide ion to free sulfur (or sulfate), which removes the sulfide from the equilibrium and drives the reaction forward to form the soluble silver complex.

Q: Why do we use Zinc dust for the displacement step instead of another metal?

Zinc is used because it is more electropositive (more reactive) than silver and gold, meaning it has a higher tendency to lose electrons. It acts as a strong reducing agent, easily displacing silver from the cyanide complex. Zinc is also relatively cheap and forms a very stable cyanide complex itself.

Q: Can we use the cyanide process for extracting copper?

While copper does form stable cyanide complexes, it is not typically extracted this way. Copper ores are usually much more abundant and less valuable per gram than gold or silver, making the cyanide process economically unviable. Copper is generally extracted via smelting or cheaper acid leaching.

Q: What is the oxidation state of silver in the soluble complex?

In the complex $Na[Ag(CN)_2]$, the cyanide ligand has a charge of $-1$, and sodium is $+1$. To balance the overall neutral molecule, silver must be in the $+1$ oxidation state.

Q: Is the cyanide process dangerous?

Yes, sodium cyanide is highly toxic. The process must be strictly controlled in industrial settings to prevent cyanide from leaking into the environment or reacting with acids to form deadly hydrogen cyanide (HCN) gas.

Question

Cyanide process is used for the extraction of

Options:

(A) barium

(B) silver

(C) boron

(D) zinc

Sigma Percentile · Accepted Answer

### The MacArthur-Forrest Process

The extraction of noble metals like silver and gold requires a delicate and highly specific chemical approach. You cannot simply heat their ores with carbon like you would for iron. Instead, we rely on a brilliant hydrometallurgical technique known as the **Cyanide Process**, or the MacArthur-Forrest process.

This process is a beautiful two-step dance of coordination chemistry and redox reactions. Let's break down exactly how we coax pure silver out of a rock.

### Step 1: Leaching - Dissolving the Metal

Imagine you have a chunk of silver ore, such as argentite ($Ag_2S$). The silver is locked away in a solid sulfide matrix. Our first goal is to pull the silver out of the solid rock and into a liquid solution. We do this by treating the crushed ore with a dilute solution of sodium cyanide ($NaCN$) while continuously bubbling air (oxygen) through the mixture.

The reaction is as follows:

$$2Ag_2S + 8NaCN + O_2 + 2H_2O \longrightarrow 4Na[Ag(CN)_2] + 4NaOH + 2S$$

Why do we need oxygen? The oxygen acts as an oxidizing agent. It oxidizes the sulfide, which drives the reversible reaction forward. The silver ions bind with the cyanide ligands to form a highly stable, soluble coordination complex called **sodium dicyanoargentate(I)**, or $Na[Ag(CN)_2]$.

At this point, the silver is safely dissolved in the water, while all the rocky impurities (gangue) remain as solid waste. We simply filter the mixture, throwing away the dirt and keeping the precious silver-rich liquid.

### Step 2: Cementation - The Zinc Displacement

Now we have a liquid full of silver, but we want solid silver metal. How do we get it back? We use a chemical displacement trick called cementation. We add **zinc dust** to our clear solution.

Zinc is significantly more electropositive (more reactive) than silver. When zinc enters the solution, it acts as a powerful reducing agent. It forces its way into the cyanide complex, kicking the silver out:

$$2Na[Ag(CN)_2] + Zn \longrightarrow Na_2[Zn(CN)_4] + 2Ag \downarrow$$

As the zinc dissolves to form sodium tetracyanozincate(II), the silver is reduced from a $+1$ oxidation state back to its elemental $0$ state. It precipitates out of the solution as a fine, dark powder of pure silver metal, which can then be collected and melted down.

### Conclusion

The cyanide process is a masterclass in using complexation to selectively isolate a metal. Because of this specific chemical affinity, the process is perfectly suited for extracting **silver** (and gold). Therefore, the correct answer to our question is **silver**.

Animated Solution for Chemistry - General Principles and Processes of Isolation of Metals: Cyanide process is used for the extraction of

Select Answer:

Visualized Solution

$C y ani d e P r ocess$

$S t e p 1 : L e a c hin g$

$S o l u b l e C o m pl e x$

$S t e p 2 : D i s pl a ce m e n t$

$P r ec i p i t a t i o n$

$C o n c l u s i o n$

$T h e W a y F or w a r d$

The Sigma Insight: Principles of Metallurgy and Extraction

The MacArthur-Forrest Process

Step 1

Step 2

Conclusion

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