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Poling – Poling, Examples, Practice Problems and Frequently Asked Questions

Poling – Poling, Examples, Practice Problems and Frequently Asked Questions

Since copper has been used so often for millennia, most people come into contact with it every day without ever realising it. Every aspect of human life, from biology to building materials, depends on copper. Here are some specifics on some of the contemporary uses for copper: Copper alloys are used to make jewellery because they improve the elasticity, flexibility, hardness, colour, and corrosion resistance of pure copper. The most often used building materials in the plumbing and electrical industries continue to be copper wire, tubing, and piping.

Do you know what the pure form of copper is?

The purest form of copper is commonly referred to as copper blisters.

How do we obtain pure copper, though?

Poling is a technique used to purge copper of impurities. On this concept page, poling will be covered in more detail.


TABLE OF CONTENTS

  • Poling – Introduction
  • Poling – Examples
  • Why is the Reduction in this Process Known as Poling?
  • Practice Problems
  • Frequently Asked Questions – FAQ

Poling – Introduction

Poling is a metallurgical process used to remove impurities from metals like copper, which includes copper oxide (CuO), and tin, which includes stannic oxide (SnO2), a type of contaminant in both copper and tin.

The crude metal is refined twice in a reverberatory furnace, typically in the form of molten blister copper. By gently blowing air through the molten metal, iron oxides and sulphur dioxide are created in the first stage, which removes the sulphur and iron.

2FeS+3O22FeO+2SO2+Heat

Cu2O+FeSCu2S+FeO

While the gaseous sulphur dioxide leaves the furnace through the off-gas system, the iron oxides are scraped or skimmed from the top of the copper as slag.

FeO+SiO2FeSiO3 slag

The second stage (reduction or poling) starts after the initial oxidation stage is finished.

This includes reacting the oxygen in the copper oxide with a reducing agent, typically natural gas or diesel (although ammonia, liquid petroleum gas, and naphtha can also be used). The product is copper metal.

2Cu2S+3O22Cu2O+2SO2

Cu2S+2Cu2O6Cu+SO2+Heat

After the completion of the reaction, the molten metal is poured into sand moulds. As the metal cools, the dissolved sulphur dioxide escapes. Some of the sulphur dioxide gas bubbles are trapped during the solidification and give a blister-like appearance to the metal. Therefore, the copper metal obtained by this process is called blister copper. It contains about 1% impurity. Blister copper is purified by the electrolytic refining process.

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Poling – Examples

  1. Conversion of lead sulphide to lead oxide

2PbS + 3O2  2PbO+SO2

2PbO + PbS 3Pb +SO2 

  1. Conversion of mercury sulphide to mercury oxide

2HgS + 3O2  2HgO+SO2

2HgO + HgS  3Hg +SO2 

Why is the Reduction in this Process Known as Poling?

The reduction process in the extraction of copper is known as Poling. This is because, in the past, wooden poles were made from newly cut ("green") trees. The reducing agent in these poles was syrup. The pole releases a gas that converts cuprous oxide to copper due to the heat of the copper. The term "poling" originated from the use of these poles.

 


Practice Problems

Q1. What is the reducing agent used in the given reaction?

2HgS + 3O2  2HgO+2SO2

A. SO2
B. O2
C. HgS
D. None of these

Answer: C

Solution:

The oxidation state of S in HgS = x

+2+x=0

x=-2

The oxidation state of O in HgO = y

+2+y=0

y=-2

The oxidation state of O in O2 = a

a=0

The oxidation state of S in SO2 = b

b-4=0

b=+4

The oxidation state of O decreases from 0 to -2. Hence, O in O2 is reduced and acts as an oxidising agent.

The oxidation state of S increases from -2 to +4. Hence, S in HgS is oxidised and acts as a reducing agent.

So, option C is the correct answer.

Q2. What is the oxidising agent used in the given reaction?

2PbS + 3O2  2PbO+SO2

A. PbS
B. PbO
C. O2
D. None of these

Answer: C

Solution:

The oxidation state of S in PbS = x

 

+2+x=0x=-2

 

The oxidation state of O in PbO = y

 

+2+y=0y=-2

 

The oxidation state of O in O2 = a

a = 0

The oxidation state of S in SO2 = b

 

b-4=0b=+4

 

The oxidation state of O decreases from 0 to -2. Hence, O in O2 is reduced and acts as an oxidising agent.

The oxidation state of S increases from +2 to +4. Hence, S in PbS is oxidised and acts as a reducing agent.

So, option C is the correct answer.

Q3. In the anode furnace, by gently blowing air through the molten metal, which oxides are created in the first stage?

A. FeO and SO2
B. SO2
C. FeO
D. SiO2

Answer: A

Solution: In an anode furnace, the raw metal is refined twice, usually into molten blister copper. Iron oxides and sulphur dioxide are produced in the first stage, which eliminates the sulphur and iron, by gently blowing air through the liquid metal.

2FeS+3O22FeO+2SO2+Heat

Hence, both FeO and SO2 are produced in the first stage.

So, option A is the correct answer.

Q4. Which of the following are steps of metallurgy?

A. Ore concentration.
B. Extraction of metals from concentrated ore.
C. Metals that are impure are refined or purified.
D. All of these

Answer : D

Solution: In metallurgy, the first process is crushing ore into a fine powder in a crusher or ball mill. The concentration of minerals is the process of eliminating contaminants from ore. The metal is extracted from the concentrated ore. Following that, impure metals are refined in metallurgy. As a result, all the processes given in the options are related to metallurgy.

So, option D is the correct answer.


Frequently Asked Questions – FAQ

Q1. Why is the history of metallurgy significant?
Answer:
 Since the Bronze Age, metallurgy has increasingly had an impact on human society, and this is especially true in the present Steel Era, when a wide variety of objects and constructions are made of metal. We could only use stone, bone, and wood tools if there were no metals at all.

Q2. What distinguishes the terms flux and gauge?
Answer: 
Flux is a chemical that is added to molten metal in order for it to combine with impurities and form slag, which can then be removed as trash. In general, ores are polluted by earthy impurities, which are known as gauges.

Q3. What exactly are copper blisters?
Answer:
After poling, the molten metal is poured into sand moulds. As the metal cools, the dissolved sulphur dioxide escapes. Some of the sulphur dioxide gas bubbles are trapped during the solidification and give a blister-like appearance to the metal. Therefore, the copper metal obtained by this process is called blister copper. It contains about 1% impurity. Blister copper is purified by the electrolytic refining process.

Q4. Why do we need to refine metals?
Answer: 
The final step in the impurity removal process is refining. Metals cannot be employed in daily life applications if they are used in crude form because their tensile strength is too low and other major properties of metals have deteriorated.


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