Chemistry · Science General

Metallurgical Processes

1,403 Questions

This section explores key metallurgical processes including ore concentration, pyrometallurgy, and metal refining. It also covers corrosion and the properties of refractory materials. These chemistry questions are relevant for engineering and science entrance tests.

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Metallurgical Processes Questions

Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

An ore on heating in air forms $SO _{2}$. State the process that will be used for its concentration.

  1. Hydrautic washing

  2. Magnetic separation

  3. Froth floatation

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Whenever a metal sulphide is heated in air, sulphur dioxide is formed as one of the products. A sulphide ore is concentrated by the froth floatation process.

Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

In froth floatation process, gangue particles are wetted by pine oil.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Froth flotation is a process to purify sulfide ores, in presence of pine oil. The oil acts as hydrophobic agent and forms froth with hydrophobic impurities (gangue) which is skimmed off from the surface leaving behind the concentrated mineral.
Wet pine oil is used in froth flotation process because it does not have an affinity towards water (because of the hydrophobic chemicals as its constituents)and it attracts impurities which can be washed away.
Hence, it is true.
Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

Identify the principle behind the concentration of bauxite ore:

  1. magnetic property of impurities in white bauxite
  2. low specific gravity of $Al _2O _3$
  3. amphoteric nature of $Al _2O _3$
  4. high melting point of $Al _2O _3$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

An amphoteric compound is a compound that can react both as an acid as well as a base. For example, $ Al _{ 2 }{ O } _{ 3 } $. 

Hence, this principle is behind the concentration of bauxite ore. In this process $ Al _{ 2 }{ O } _{ 3 } $ first acts as an acid then as a base.

Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

The method used for the concentration of sulphide ores is:

  1. froth floatation

  2. smelting

  3. magnetic separatio

  4. gravity separation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. The principle of froth flotation process is that sulphide ores are preferentially wetted by the pine oil, whereas the gangue particles are wetted by the water. Hence the method used for the concentration of sulphide ores is froth flotation.

Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

Extraction of gold $\left( Au \right) $ involves the formation of complex ions '$X$' and '$Y$'.
        Gold ore $\underset { C{ N }^{ - },{ H } _{ 2 }O,{ O } _{ 2 } }{ \underrightarrow { \quad Roasting\quad  }  } \quad H{ O }^{ - }+'X'\quad \underrightarrow { \quad \quad \quad Zn\quad \quad \quad  } \quad 'Y'+Au$
'$X$' and '$Y$' are respectively

  1. $Au{ \left( CN \right) } _{ 2 }^{ - }$ and $Zn{ \left( CN \right) } _{ 4 }^{ 2- }$
  2. $Au{ \left( CN \right) } _{ 4 }^{ 3- }$ and $Zn{ \left( CN \right) } _{ 4 }^{ 2- }$
  3. $Au{ \left( CN \right) } _{ 3 }^{ - }$ and $Zn{ \left( CN \right) } _{ 6 }^{ 4- }$
  4. $Au{ \left( CN \right) } _{ 4 }^{ - }$ and $Zn{ \left( CN \right) } _{ 3 }^{ - }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Extraction of gold $(Au)$ involves the formation of complex ions $'X'$ and $ 'Y'. 'X'$ and $'Y'$ are $\displaystyle Au{ \left( CN \right)  } _{ 2 }^{ - }$ and $\displaystyle Zn{ \left( CN \right)  } _{ 4 }^{ 2- }$ respectively

 Gold ore $\displaystyle \underset { C{ N }^{ - },{ H } _{ 2 }O,{ O } _{ 2 } }{ \underrightarrow { \quad Roasting\quad  }  } \quad H{ O }^{ - }+\underset {'X'}{Au{ \left( CN \right)  } _{ 2 }^{ - }} \quad \underrightarrow { \quad \quad \quad Zn\quad \quad \quad  } \quad \underset {'Y'}{Zn{ \left( CN \right)  } _{ 4 }^{ 2- }}+Au \downarrow$

Note:
The complex X is water soluble.
More electropositive zinc displaces gold from complex.

Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

During leaching, gold is recovered from the solution by the addition of ______.

  1. zinc

  2. zinc oxide

  3. silver oxide

  4. zinc sulphide
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Gold is recovered from the solution by the addition of zinc.
$  2[Au(CN) _2]^- + Zn\rightarrow  [Zn(CN) _4]^{2+} +2 Au$
Note:
Gold ore is concentrated by leaching with sodium cyanide in presence of air.
$4Au +8CN^-+2H _2O +O _2 \rightarrow 4[Au(CN) _2]^-+4OH^-$

Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

In the process of extraction of gold,
1.) Roasted Au ore $+ \ CN^- _{(aq)} + O _2 \longrightarrow [X] + NaOH$

2.) $[X] + Zn \longrightarrow [Y] + Au$

  1. $X = [Au(CN) _2]^-, Y = [Zn(CN) _4]^{2-}$
  2. $X = [Au(CN) _4]^{2-}, Y = [Zn(CN) _4]^{2-}$
  3. $X = [Au(CN) _2]^-, Y = [Zn(CN) _6]^{4-}$
  4. $X = [Au(CN) _4]^-, Y = [Zn(CN) _4]^{2-}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
This reaction is an example of the Cyanide process (Mac Arthur Forrest Process) for extraction of metals like gold or silver.

Reaction:

$Au + 8NaCN +2H _2O + O _2 \rightarrow 4Na[Au(CN) _2 ] + 4NaOH$

Gold is obtained by reaction with Zn:

$2Na[Au(CN) _2] + Zn \rightarrow  Na _2[Zn(CN) _4 ] +  2Au$


Therefore, $X = [Au(CN) _2]^-$ and $Y = [Zn(CN) _4]^{2-}$

Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

Froth floatation process used for the concentration of sulphide ore:

  1. is based on the difference in wettability of different minerals
  2. uses sodium ethyl xanthate ($C _2H _5OCS _2Na$) as a collector
  3. uses $NaCN$ as depressant in the mixture of $ZnS$ and $PbS$ when $ZnS$ forms soluble complex and $PbS$ forms froth

  4. uses pine oil as frothing agent
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
Explanation

Froth flotation is a process for selectively separating hydrophobic materials from hydrophobic. In some cases, for example, sulphides ores of copper, zinc and lead concentration is brought by this method. In this method, the advantage is taken of the preferential wetting of the ore by an oil.The finely ground ore is taken in a tank containing water and 1% of pine oil or turpentine oil.
A strong current of air is blown through the suspension, producing a heavy froth or foam on the surface.The metal sulphide is wetted by the oil but the gangues is not and the sulphide-oil mixture is carried to the surface by films of oil The froth is skimmed off, the gangue settles down on the bottom or remains underneath the froth. By this flotation method, it is possible to concentrate over 90% of a sulphite ore to 1/10 of its original bulk.
During the flotation process of some ores, these substances are added which activate or depress the flotation property of the minerals and thus help in the separation of minerals present in the ore. For instance, galena (PbS) is usually associated with sphalerite (ZnS) and pyrites ,NaCN.
Hence all options are correct.

Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

Select the correct statement(s) :

  1. Gravity separation method is used in concentration of oxide ore and carbonate ore

  2. Magnetic separation method is used for separation of non-magnetic rutile and magnetic impurity of chlorapatite
  3. $Fe _3O _4$ is magnetic and impurities non-magnetic
  4. $MnO _2$ is non-magnetic and impurities magnetic
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation
A) Gravity separation is an industrial method of separating two components, either a suspension, or dry granular mixture where separating the components with gravity is sufficiently practical: i.e. the components of the mixture have different specific weight. All of the gravitational methods are common in the sense that they all use gravity as the dominant force. The working principle is to lift the material by vacuum over an inclined vibrating screen covered deck.So by gravity separation we remove impurities present in oxides and carbonates there by oxides and carbonates are concentrated.

B) Magnetic separation is a process in which magnetically susceptible material is extracted from a mixture using a magnetic force. But non magnetic substances are not separated.

C) $Fe _3O _4$, is magnetic and impurities non-magnetic.

D) $MnO _2$, is magnetic substance.

Hence options A  &C are correct.
Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

All minerals are not the ore but all ores are minerals. The extraction of a particular metal depends upon several factors and overall it has to be convenient and economical.


Which of the following statement is true?

  1. Na-ethyl xanthate is used as frother exclusively.

  2. Levigation cannot be applied for sulphide in any condition.

  3. Froth floatation can be applied for non-sulphide ore also using suitable activator.

  4. Impurities like S and As are removed as elemental vapor in roasting.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

(A) Sodium ethylxanthate acts as collector and not frother.


(b) Levigation can be used for sulphide ore to remove majority of gangue when density difference is high.

(C) Froth floatation can be used for non-sulphide ores having sulphide impurities, and the ore is recovered by using suitable activator.

(D) During roasting, impurities such as S and As are removed as their volatile oxides $SO _2$ and $As _2O _3$, respectively.

Hence, only option C is true.

Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

Leaching method is used to concentrate the ores of:

  1. Gold

  2. Silver

  3. Aluminium

  4. All of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
Leaching
It involves treatment of ore with leaching agents (like NaOH, NaCN, KCN or other reagents) due to which ore becomes soluble and their impurities remain insoluble. The leaching Process is basically done in the extraction of Al from Alumina.
$Al _2O _3 + 2 NaOH \rightarrow 2NaAlO _2 +  H _2O$ + Impurities

If leaching process is done in case of Ag and Au with NaCN (0.4 to 0.8%) then the process is called as Mac-Arthur Forrest cyanide Process.
$Ag + NaCN \rightarrow NaAg(CN) _2 + $ Impurities
$Au + NaCN \rightarrow NaAu(CN) _2 + $ Impurities
Multiple choice chemistry principles of metallurgy concentration of ore concentration of ores general principles of metallurgy

The principle behind froth floatation is:

  1. preferential wetting of ore and gangue particles.

  2. difference is specific gravity of ore and gangue particles.

  3. magnetic properties of ore and gangue.

  4. electrical properties of gangue particles.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Froth flotation commences by comminution (that is, crushing and grinding), which is used to increase the surface area of the ore for subsequent processing and break the rocks into the desired mineral and gangue in a process known as liberation, which then has to be separated from the desired mineral. The ore is ground into a fine powder and mixed with water to form a slurry. The desired mineral is rendered hydrophobic by the addition of a surfactant or collector chemical. The particular chemical depends on which mineral is being refined. As an example, pine oil is used to extract copper. This slurry (more properly called the pulp) of hydrophobic mineral-bearing ore and hydrophilic gangue is then introduced to a water bath which is aerated, creating bubbles. The hydrophobic grains of mineral-bearing ore escape the water by attaching to the air bubbles, which rise to the surface, forming a foam or a scum (more properly called a froth). The froth is removed and the concentrated mineral is further refined.