Tag: general principles of metallurgy

Questions Related to general principles of metallurgy

Identify the principle behind the concentration of bauxite ore:

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

  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 $Al _2O _3$

Show answer
Correct Option: C
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.

The method used for the concentration of sulphide ores is:

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

  1. froth floatation

  2. smelting

  3. magnetic separatio

  4. gravity separation

Show answer
Correct Option: A
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.

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

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

  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 $Zn{ \left( CN \right) } _{ 3 }^{ - }$

Show answer
Correct Option: A
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.

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

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

  1. zinc

  2. zinc oxide

  3. silver oxide

  4. zinc sulphide

Show answer
Correct Option: A
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.
$4Au +8CN^-+2H _2O +O _2 \rightarrow 4[Au(CN) _2]^-+4OH^-$

Which of the following is commonly used to produce foam in froth floatation process?

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

  1. Pine oil

  2. Cresol

  3. NaCN

  4. Xanthate

Show answer
Correct Option: D

Which of the following ore is best concentrated by froth flotation method ?

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

  1. Galena

  2. Cassiterite

  3. Magnetite

  4. Zinc blende

Show answer
Correct Option: A,D
Explanation:

Galena ($PbS$) and zinc blende ($ZnS$) are sulphide ores. Cassiterite $SnO _{2}$ (oxide ore), and Magnetite $Fe _{3}O _{4}$ (oxide ore) are not sulphide ore. The froth flotation process is used to concentrate sulphide ores, based on preferential wetting properties with frosting agent and water.

Hence option $A$ and $D$ are correct.

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

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

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Froth flotation is selective separating the hydrophilic particles from hydrophobic. It is used for copper and lead sulfide ores. It is the preferential wetting of ore with pine oil to remove gangue or impurities.

Minerals from which metals can be preferably extracted are called :

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

  1. Ores

  2. Source

  3. Alloy

  4. None of these

Show answer
Correct Option: A
Explanation:

$\Rightarrow$ Minerals occur naturally in the Earth.

$\Rightarrow$ The minerals from which the metals are extracted without loss is called ores.
Example:
Many minerals are there for Aluminium extraction. But Bauxite extraction is of low cost. So Bauxite is only called ore of Aluminium. But remaining are only minerals.

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

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

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

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

Show answer
Correct Option: A
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 $Y = [Zn(CN) _4]^{2-}$

Froth floatation process used for the concentration of sulphide ore:

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

  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

Show answer
Correct Option: A,B,C,D
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.