Question

Purity of copper produced by fire refining is about ___________ percent.

• A. 99.3
• B. 99.9
• C. 98.7
• D. 97.3

Hint:

Differentiate between the two main refining methods for copper:

• Fire Refining: Removes O, S, and reactive metals. Purity \(\sim\)99.5%. Precious metals (Au, Ag) remain.

• Electrolytic Refining: Removes almost all impurities, including precious metals which are recovered from the anode slime. Purity > 99.95%.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Copper refining involves several stages to increase its purity. Blister copper, the product of the copper converter, has a purity of about 98.5-99.5%. It contains dissolved oxygen and other metallic impurities.

Fire refining is a pyrometallurgical process used to remove most of the oxygen and some easily oxidizable impurities. It is often a preliminary step before final electrolytic refining.

Step 2: Detailed Explanation:
The fire refining process has two stages:

• Oxidation: Air is blown through the molten blister copper. Impurities that are more reactive than copper (like Fe, Zn) are oxidized and form a slag. Sulfur is removed as SO\(_2\) gas.

• Reduction (Poling): After oxidation, the copper is saturated with oxygen (as Cu\(_2\)O). This oxygen is removed by bubbling a reducing gas (like natural gas) through the melt or by stirring with green wood poles ("poling").
The product is called "tough-pitch copper". This process cannot remove impurities that are less reactive than copper, such as gold, silver, nickel, and selenium. Therefore, while it significantly purifies the blister copper, it cannot achieve very high purities like 99.9%. A typical purity for fire-refined copper is in the range of

99.2% to 99.7%.
The value of

99.3% fits well within this range.

• 99.9% is typical for electrolytic refining.

• 98.7% is a typical purity for blister copper before refining.

• 97.3% is too low.

Step 3: Final Answer:
The purity of copper produced by fire refining is typically about 99.3 percent.