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

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

  1. Galena

  2. Cassiterite

  3. Magnetite

  4. Zinc blende
Reveal answer Fill a bubble to check yourself
A,D Correct answer
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.

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

Minerals from which metals can be preferably extracted are called :

  1. Ores

  2. Source

  3. Alloy

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

In the equation,


$4M + 8 CN^- + 2 H _2O + O _2 \longrightarrow 4[M(CN) _2]^- + 4 OH^-$

the metal M is:

  1. Copper

  2. Silver

  3. Gold

  4. Zinc
Reveal answer Fill a bubble to check yourself
B,C Correct answer
Explanation

Cyanide process, also called Macarthur-Forrest Process, method of extracting silver and gold from their ores by dissolving them in a dilute solution of sodium cyanide or potassium cyanide. 


The process was invented in 1887 by the Scottish chemists John S. MacArthur, Robert W. Forrest, and William Forrest.

$4Ag + 8 CN^- + 2 H _2O + O _2 \longrightarrow 4[Ag(CN) _2]^- + 4 OH^-$


$4Au + 8 CN^- + 2 H _2O + O _2 \longrightarrow 4[Au(CN) _2]^- + 4 OH^-$


Hence options B & C 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