Concentration Questions in English

(A) The froth flotation method is primarily used for sulfide ores. $Chalcopyrite$ $(CuFeS_2)$ is a sulfide ore,therefore this method is used for its concentration.

(A) Iron pyrites is $FeS_2$,which is a sulfide ore.
Froth flotation is the standard method used for the concentration of sulfide ores.

(D) Leaching is a process of extraction where the ore is treated with a suitable reagent which dissolves the ore but not the impurities.
$1$. Gold $(Au)$ and Silver $(Ag)$ are extracted by leaching with dilute solutions of $NaCN$ or $KCN$ in the presence of air $(O_2)$.
$2$. Aluminum $(Al)$ is extracted from bauxite ore $(Al_2O_3 \cdot 2H_2O)$ by leaching with a concentrated solution of $NaOH$ (Bayer's process).
Since all three metals are extracted using leaching,the correct answer is $D$.

(D) Magnetic separation is used when either the ore or the impurities are magnetic in nature. $Fe_3O_4$ (Magnetite) is strongly magnetic and is concentrated using this method. While $Fe_2O_3$ (Hematite) is also magnetic,$Fe_3O_4$ is the classic example for magnetic separation.

(D) Bauxite ore often contains $SiO_2$,$Fe_2O_3$,and $TiO_2$ as impurities.
When $SiO_2$ is the major impurity,Serpeck's process is used.
In this process,bauxite is heated with coke and nitrogen at $1800 \ ^\circ C$ to form aluminium nitride $(AlN)$,while $SiO_2$ is reduced to silicon $(Si)$ which volatilizes.
$Al_2O_3 + 3C + N_2 \rightarrow 2AlN + 3CO$
$SiO_2 + 2C \rightarrow Si + 2CO$
The $AlN$ is then hydrolyzed to produce pure alumina.

(B) The correct answer is $B$. In the froth floatation process,the ore particles are preferentially wetted by oil (pine oil),which makes their surface hydrophobic (water-repellent). Consequently,they are not easily wetted by water and attach to the air bubbles,causing them to float to the surface with the froth.

(C) $(C)$ Levigation or gravity separation is based on the difference in the densities of the ore particles and the gangue particles. In this process, the ore particles are heavier than the earthy or rocky gangue particles, allowing them to be separated by a stream of water.

(D) Froth Floatation Process is generally used for the concentration of sulphide ores based on the differential wetting properties of ore and gangue particles with oil and water.
However,$Argentite$ $(Ag_{2}S)$ is an exception as it is concentrated by chemical leaching (MacArthur-Forrest cyanide process).
The chemical reactions involved are:
$Ag_{2}S + 4NaCN \rightarrow 2Na[Ag(CN)_{2}] + Na_{2}S$
Silver is subsequently recovered by displacement using $Zn$:
$2Na[Ag(CN)_{2}] + Zn \rightarrow Na_{2}[Zn(CN)_{4}] + 2Ag$

(A) The froth floatation method is primarily used for the concentration of sulphide ores because sulphide ores are preferentially wetted by oil,while gangue particles are wetted by water.
$1$. Malachite: $Cu(OH)_2 \cdot CuCO_3$ (Carbonate ore)
$2$. Magnetite: $Fe_3O_4$ (Oxide ore)
$3$. Siderite: $FeCO_3$ (Carbonate ore)
$4$. Galena: $PbS$ (Sulphide ore)
Since $PbS$ is a sulphide ore,it is best concentrated by the froth floatation method.

(A) In the froth flotation process,$NaCN$ is used as a depressant to separate $ZnS$ from $PbS$.
$NaCN$ selectively prevents $ZnS$ from forming froth by forming a soluble complex,$Na_2[Zn(CN)_4]$,while $PbS$ remains unaffected and forms froth.
Therefore,$NaCN$ acts as a depressant for $ZnS$.

(B) Galena $(PbS)$ is a sulfide ore.
Sulfide ores are typically concentrated by the froth flotation process.
In this process,the ore particles are wetted by oil and float with the froth,while the gangue particles are wetted by water and settle down.

(A) $X$: Magnetic separation is used when either the ore or the impurities are magnetic in nature. This method is used for the concentration of $FeCr_2O_4$.
$Y$: Froth floatation process is suitable for sulfide ores. It is based on the difference in wetting properties of the ore and gangue with water and oil. This method is used for the concentration of $Ag_2S$.
$Z$: Gravity separation is based on the difference in densities of the ore particles and impurities. This method is used for the concentration of $Al_2(SiO_3)_3$.

(D) Smelting is not a method of concentration of ores; it is a method of extraction of metal.
Concentration of ores (or beneficiation) involves removing gangue from the ore,such as gravity separation,froth flotation,and electromagnetic separation.
Smelting is a process of extraction of metal in its molten state by using a reducing agent in the presence of a flux,typically used for oxides of metals like $Pb$,$Zn$,$Fe$,and $Cu$.

(C) In the froth-floatation process,the mineral particles are wetted by oil and the gangue particles are wetted by water.
Collectors like pine oil,fatty acids,and xanthates are used to enhance the non-wettability of the mineral particles.
Palm oil acts as a collector in this process,as it makes the mineral particles water-repellent (hydrophobic) so that they can attach to the air bubbles and rise to the surface as froth.

(A) Collectors are organic substances that increase the non-wettability of the mineral particles with water,allowing them to attach to air bubbles in the froth flotation process. $Sodium \ ethyl \ xanthate$ is a widely used industrial collector.

(B) The principle involved in the $Froth \text{ } floatation$ method is the difference in the wetting properties of the ore and the gangue particles.
The sulphide ore particles are preferentially wetted by oil,while gangue particles are preferentially wetted by water.

(A) The impurity $FeCr_2O_4$ (chromite) is magnetic in nature. Therefore,the magnetic separation process is used to concentrate the ore.

(D) The beneficiation or concentration of sulphide ores is typically achieved using the $Froth \ flotation \ method$.
In this process,a suspension of the powdered ore is made with water,and collectors (like pine oil or xanthates) and frothers are added.
The sulphide particles are preferentially wetted by the oil and rise to the surface with the froth,while the gangue particles are wetted by water and settle at the bottom.

(A) The correct answer is $A$ because copper pyrites $(CuFeS_2)$ is a non-magnetic ore.
$B$ (Pyrolusite,$MnO_2$),$C$ (Chromite,$FeCr_2O_4$),and $D$ (Cassiterite,$SnO_2$) are magnetic ores,and thus they are concentrated using electromagnetic separation.

(A) Bauxite $(Al_2O_3 \cdot 2H_2O)$ is an important ore of aluminium containing impurities like $Fe_2O_3$,$SiO_2$,and $TiO_2$.
In the Bayer's process,the crushed ore is treated with a concentrated solution of sodium hydroxide $(NaOH)$ at high temperature and pressure.
This dissolves the aluminium oxide present in the bauxite to form soluble sodium aluminate $(NaAlO_2)$,while the impurities remain insoluble.
The chemical reaction is: $Al_2O_3 \cdot 2H_2O + 2NaOH \rightarrow 2NaAlO_2 + 3H_2O$.
Thus,$NaOH$ is the reagent used in the Bayer's process.

(D) . The froth flotation process is based on the difference in the wettability of different minerals. The metallic sulphide particles are preferentially wetted by oil,while the gangue particles are wetted by water.
$B$. Sodium ethyl xanthate,$C_2H_5OCS_2Na$,acts as a collector. Collectors attach themselves to the mineral grains via polar groups,making the minerals water-repellent so they pass into the froth.
$C$. $NaCN$ acts as a depressant in the separation of $ZnS$ and $PbS$. It forms a soluble complex with $ZnS$ $(Na_2[Zn(CN)_4])$,preventing it from floating,while $PbS$ forms froth.
Since all statements are correct,the answer is $D$.

(B) The $Serpek$ process is used for the purification of bauxite ore $(Al_2O_3 \cdot 2H_2O)$ containing silica $(SiO_2)$ as an impurity.
In this process,the bauxite ore is heated with coke $(C)$ and nitrogen $(N_2)$ at a high temperature of about $1800 \ ^\circ C$.
The chemical reaction involved is: $Al_2O_3 + 3C + N_2 \rightarrow 2AlN + 3CO$.
Here,$AlN$ (aluminum nitride) is formed,and silica is reduced to silicon,which volatilizes off.
Therefore,the chemicals used in the $Serpek$ process are $C + N_2$.

(B) Silver and gold are extracted by the cyanide process (Mac Arthur - Forrest process). After the preliminary crushing and concentration by froth floatation process,the ore (crushed auriferous rocks in the case of gold) is leached with a dilute $(0.4 - 7\, \%)$ solution of sodium cyanide made alkaline by adding lime and kept agitated by a current of air. Silver (or gold) passes into the solution as argentocyanide (or aurocyanide).
It is based on the fact that gold/silver dissolves in a dilute solution of sodium cyanide in the presence of atmospheric oxygen with the formation of a complex cyanide.
Reaction:
$4Au + 8NaCN + 2H_2O + O_2 \rightarrow 4Na[Au(CN)_2] + 4NaOH$
$Ag_2S + 4NaCN \rightarrow 2Na[Ag(CN)_2] + Na_2S$
Silver is obtained by reaction with $Zn$:
$2Na[Ag(CN)_2] + Zn \rightarrow Na_2[Zn(CN)_4] + 2Ag$

(A) In the Bayer's process for leaching bauxite $(Al_2O_3 \cdot 2H_2O)$,the ore is treated with concentrated $NaOH$ solution at $473-523 \ K$ and $35-36 \ bar$ pressure.
$Al_2O_3 \cdot 2H_2O(s) + 2NaOH(aq) + H_2O(l) \to 2Na[Al(OH)_4](aq)$
Here,$X$ is sodium tetrahydroxoaluminate,$Na[Al(OH)_4]$.
When $CO_2$ gas is passed through this solution,$Al(OH)_3$ precipitates out,which on heating gives hydrated alumina $(Al_2O_3 \cdot xH_2O)$.
$2Na[Al(OH)_4](aq) + 2CO_2(g) \to 2Al(OH)_3(s) + 2NaHCO_3(aq)$
$2Al(OH)_3(s) \xrightarrow{\Delta} Al_2O_3 \cdot xH_2O(s) + (3-x)H_2O$
Thus,$X$ is $Na[Al(OH)_4]$ and $Y$ is $Al_2O_3 \cdot xH_2O$.

(B) In the froth-floatation process,froth stabilizers such as cresols and aniline are added to stabilize the froth and enhance the non-wettability of the mineral particles.

(B) In the froth flotation process,collectors like pine oil,fatty acids,and xanthates are added to the suspension of powdered ore in water to make the mineral particles preferentially wetted by oil. Froth stabilizers like cresols and aniline are added to stabilize the froth. Therefore,the statement that aniline is a froth stabilizer is correct. Zincite $(ZnO)$ is an oxide ore,not a carbonate ore. Titanium is refined using the Van Arkel method,not zone refining. Sodium cyanide $(NaCN)$ is used in the leaching process for the extraction of silver.

(B) The froth floatation process is a method used for the concentration of sulphide ores.
It is said that the idea of this process was inspired by a fisherwoman who noticed that sulphide minerals,being hydrophobic,float on water while gangue particles sink,similar to how oily substances float on water.
Thus,$X$ is a fisherwoman and $Y$ is the concentration of ores.

(B) Bayer's process is specifically used for the purification of Bauxite $(Al_2O_3 \cdot 2H_2O)$ ore when the main impurity present is Silica $(SiO_2)$.
In this process,the ore is treated with a concentrated solution of $NaOH$ at high temperature and pressure.
$Al_2O_3$ dissolves to form soluble sodium aluminate,while $SiO_2$ also dissolves to form sodium silicate.
However,the process is designed to separate the alumina from the impurities,particularly silica,which is the most common impurity in Bauxite.

(B) Serpeck's process is used for the purification of bauxite ore containing silica $(SiO_2)$ as an impurity.
In this process,the bauxite ore is heated with coke $(C)$ and nitrogen $(N_2)$ at a temperature of about $1800 \ ^\circ C$.
The chemical reaction is: $Al_2O_3 + 3C + N_2 \rightarrow 2AlN + 3CO$.
The aluminum nitride $(AlN)$ formed is then hydrolyzed to produce aluminum hydroxide,which is further calcined to get pure alumina $(Al_2O_3)$.

(C) The froth floatation process is a method used for the concentration of sulphide ores.
It is based on the principle of the difference in the wetting properties of the ore and the gangue particles with water and oil.
Sulphide ores are preferentially wetted by oil (pine oil),while gangue particles are preferentially wetted by water.

(D) The froth floatation process is primarily used for the concentration of sulphide ores.
Among the given options,$Cu$ (Copper) is commonly found as a sulphide ore,such as copper pyrites $(CuFeS_2)$.
Therefore,the froth floatation process is used for the concentration of copper ore.

(A) Haematite $(Fe_2O_3)$ is an oxide ore of iron.
Since it is a heavy oxide ore,it is concentrated by the gravity separation method (also known as hydraulic washing or levigation).

(C) Electromagnetic separation is a method used for the concentration of ores where either the ore or the impurities are magnetic in nature.
Cassiterite $(SnO_2)$ is the ore of tin. It is often associated with magnetic impurities like wolframite ($FeWO_4$ and $MnWO_4$).
Since the impurities are magnetic,electromagnetic separation is used to remove them from the non-magnetic cassiterite ore.

(B) The process of removal of unwanted materials from the ore is known as ore concentration.
Froth floatation,electromagnetic separation,and gravity separation are common methods used for the concentration of ore.
Smelting,on the other hand,is a metallurgical process used for the extraction of metal from the concentrated ore by heating it,not for the concentration of the ore itself.

(B) Chemical leaching (specifically the $Baeyer's$ process) is used for the concentration of bauxite $(Al_2O_3 \cdot 2H_2O)$.
$Copper$ $pyrite$ $(CuFeS_2)$ is concentrated by the froth flotation method.
$Cassiterite$ $(SnO_2)$ is concentrated by hydraulic separation (gravity separation) because it is heavier than the siliceous gangue.
$Galena$ $(PbS)$ is also concentrated by the froth flotation method.

(D) The process used for the concentration of sulphide ores is the $Froth \ Floatation$ method. In this process,the ore particles are preferentially wetted by oil (pine oil),while the gangue particles are wetted by water.

(C) Rutile $(TiO_2)$ is non-magnetic,while chlorapatite $(Ca_3(PO_4)_2 \cdot CaCl_2)$ is magnetic. Therefore,they are separated by the $Magnetic \ separation \ method$.

(D) . The froth floatation process is based on the difference in wettability of different minerals. The metallic sulphide particles are preferentially wetted by oil,while the gangue particles are wetted by water.
$B$. Sodium ethyl xanthate $(C_2H_5OCS_2Na)$ acts as a collector. It attaches to the mineral grains via polar groups,making them water-repellent so they pass into the froth.
$C$. $NaCN$ is used as a depressant to separate $ZnS$ and $PbS$. It forms a soluble complex with $ZnS$ $(Na_2[Zn(CN)_4])$,preventing it from floating,while $PbS$ remains in the froth.
Therefore,all the given statements are correct.

(B) In the froth floatation process,$NaCN$ acts as a depressant for $ZnS$ by forming a water-soluble complex,$Na_2[Zn(CN)_4]$.
The reaction is: $ZnS + 4NaCN \rightleftharpoons Na_2[Zn(CN)_4] + Na_2S$.
This prevents $ZnS$ from forming froth,while $PbS$ remains unaffected and can be floated.

(B) Leaching is a process of concentration of ores where the ore is dissolved in a suitable solvent.
For argentite $(Ag_2S)$,leaching is carried out using a dilute solution of sodium cyanide $(NaCN)$ in the presence of air.
The chemical reaction is:
$Ag_2S + 4NaCN \xrightarrow{\text{Air}} 2Na[Ag(CN)_2] + Na_2S$.
Then,the $Na_2S$ is oxidized to $Na_2SO_4$ by air to prevent the reverse reaction.

(B) depressant is a substance added to the froth flotation process to selectively prevent one mineral from forming a froth.
In the case of a mixture of $ZnS$ and $PbS$,$NaCN$ acts as a depressant for $ZnS$.
It reacts with $ZnS$ to form a soluble complex,$Na_2[Zn(CN)_4]$,which prevents $ZnS$ from forming a froth.
The chemical reaction is: $ZnS + 4NaCN \rightarrow Na_2[Zn(CN)_4] + Na_2S$.
Consequently,$PbS$ is left to form the froth,allowing for the separation of the two minerals.

(D) In the froth floatation method,collectors are used to enhance the non-wettability of the mineral particles.
$Sodium \ ethyl \ xanthate$ is a commonly used collector for sulphide ores.
It has a hydrophobic end (ethyl group) and a hydrophilic end (polar xanthate group),which helps the ore particles to attach to the air bubbles and float with the froth.

(B) Bayer's process is used for the concentration (beneficiation) of red bauxite,which contains iron oxide as the main impurity.
Serpeck's process is used for the concentration of white bauxite,which contains silica $(SiO_2)$ as the main impurity.
In Serpeck's process,the silica impurity is removed by heating with carbon and nitrogen: $SiO_2 + 2C + N_2 \rightarrow Si_3N_4 + 2CO$ (or simplified as $SiO_2 + 2C \rightarrow Si + 2CO$ in some contexts).
Therefore,process $X$ is Baeyer's process and impurity $Z$ is $SiO_2$.

(D) Chemical leaching (or hydrometallurgy) is a process used to extract metals from their ores by dissolving them in a suitable solvent.
$Al_2O_3 \cdot 2H_2O$ (Bauxite) is concentrated by the Bayer's process,which is a form of chemical leaching where the ore is treated with a concentrated solution of $NaOH$ to dissolve the alumina as sodium aluminate,leaving behind impurities like $Fe_2O_3$ and $SiO_2$.
Therefore,chemical leaching is specifically useful for the concentration of $Al_2O_3 \cdot 2H_2O$.

(D) Leaching of $Ag_2S$ is carried out by treating it with a dilute solution of $NaCN$ in the presence of air $(O_2)$ as an oxidizing agent.
The chemical reaction is:
$Ag_2S + 4NaCN \rightleftharpoons 2Na[Ag(CN)_2] + Na_2S$
Since the reaction is reversible,the presence of $O_2$ oxidizes the sulphide ion $(S^{2-})$ to sulphur or sulphate,shifting the equilibrium to the right:
$2Na_2S + 2H_2O + O_2 \rightarrow 4NaOH + 2S$
This forms a soluble complex,$Na[Ag(CN)_2]$.
Finally,silver is recovered by displacement using zinc:
$2Na[Ag(CN)_2] + Zn \rightarrow Na_2[Zn(CN)_4] + 2Ag \downarrow$

(A) In the froth flotation process,$NaCN$ is used as a depressant to selectively prevent $ZnS$ from forming a froth,while allowing $PbS$ to be concentrated.

(B) The Serpek process is used for the purification of bauxite ore $(Al_2O_3 \cdot 2H_2O)$ containing silica $(SiO_2)$ as an impurity.
In this process,the bauxite ore is heated with coke $(C)$ and nitrogen $(N_2)$ at a temperature of about $1800 \ ^\circ C$.
This reaction forms aluminum nitride $(AlN)$: $Al_2O_3 + 3C + N_2 \rightarrow 2AlN + 3CO$.
The aluminum nitride is then hydrolyzed to produce aluminum hydroxide,which is further calcined to get pure alumina $(Al_2O_3)$.

(C) The froth flotation method is primarily used for the concentration of sulphide ores.
$CuFeS_2$ (Copper pyrites),$Ag_2S$ (Silver glance),and $ZnS$ (Zinc blende) are sulphide ores and can be concentrated by this method.
$MnO_2$ (Pyrolusite) is an oxide ore,which is typically concentrated by gravity separation or magnetic separation,not by froth flotation.

(B) The froth flotation process is primarily used for the concentration of sulphide ores.
Among the given options,$HgS$ (Cinnabar) is a sulphide ore.
Therefore,it is concentrated by the froth flotation process.

(A) The ore of tin is $SnO_2$ (cassiterite). The impurity present is $FeCrO_4$ (iron chromite),which is magnetic in nature. Since the impurity is magnetic,it can be separated from the non-magnetic $SnO_2$ ore using the magnetic separation method.