Chemistry · Science General

Metallurgical Processes

1,436 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.

Pyrometallurgy furnacesMetal refining techniquesCorrosion protection methodsOre concentrationAuto reduction process

Metallurgical Processes Questions

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.

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

Iron ores are concentrated by:

  1. froth floatation method

  2. magnetic separation method

  3. amalgamation method

  4. none of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Iron ores are concentrated by magnetic separation method.
In  magnetic separation method, ferromagnetic and nonmagnetic particles in the ore are separated by an electromagnetic separator.

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

Chemical method used in concentration of ore is known as ___________.

  1. bleaching

  2. leaching

  3. roasting

  4. calcination
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Leaching is a chemical method of concentration of ores. It involves the treatment of the ore with a suitable reagent so as to make it soluble while impurities remain insoluble. The ore is recovered from the solution by suitable chemical method. Copper is recovered from chemical solutions by leaching processes such as solvent extraction.

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

In Bayer's process, the crushed ore is treated with ______ .

  1. hot concentrated caustic soda (NaOH)

  2. cold dilute caustic soda (NaOH)

  3. hot concentrated caustic potash (KOH)

  4. cold dilute caustic potash (KOH)
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Bayer's process is the industrial refining process to refine bauxite to produce alumina. In this process, the crushed ore is treated with hot concentrated caustic soda (NaOH).

Multiple choice chemistry non-metals introduction to non-metals occurence of metals occurrence of metals and non metals

 Copper is extracted from sulphide ore using the method:

  1. Carbon reduction

  2. Carbon monoxide reduction

  3. Auto reduction

  4. None of these
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The copper can be extracted from its sulphide ore by the auto reduction process.
The ore is reduced by heat alone.
 
$Cu _2S + O _2 \rightarrow 2Cu + SO _2$

The copper and the oxygen have been reduced (decrease in oxidation state). The sulphur has been oxidised (increase in oxidation state). The reducing agent is the sulphide ion in the copper(I) sulphide.

Hence, the correct option is $C$
Multiple choice chemistry non-metals introduction to non-metals occurence of metals occurrence of metals and non metals

 In the extraction of copper from copper pyrites, iron is removed as:

  1. $FeSO _4$
  2. $FeSiO _3$
  3. $Fe3O _4$
  4. $Fe _2O _3$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The copper ($II$) ions in the copper pyrite are reduced to copper ($I$) sulphide (which is reduced further to copper metal in the final stage).
The iron in the copper pyrite ends up converted into an iron ($II$) silicate slag which is removed.
$CuFeS _2 + SiO _2 + 4O _2 \rightarrow Cu _2S + 2FeSiO _3 + 3SO _2$
Multiple choice chemistry non-metals introduction to non-metals occurence of metals occurrence of metals and non metals

 Silica is added to roasted copper ore during extraction in order to remove:

  1. cuprous sulphide

  2. ferrous oxide

  3. ferrous sulphide

  4. cuprous oxide
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Silica is added during smelting in order to remove iron oxides from copper sulphide and oxides. During roasting the iron sulfides react with oxygen (in air or oxygen enriched air) to produce iron oxides (mainly as $FeO$, but with some magnetite $(Fe _3O _4))$ and sulfur dioxide. 
Copper sulfide and iron oxide can mix, but when sufficient silica is added, a separate slag layer is formed. 
The slag forming reaction is:
$FeO + SiO _2 \rightarrow FeO.SiO _2$
Slag is less dense than matte, so it forms a layer that floats on top of the matte.