Concentration Questions in English

(B) The metal extracted by leaching with a cyanide is $Ag$ (or $Au$).
In the Mac-Arthur Forest process,silver $(Ag)$ or gold $(Au)$ ores are treated with a dilute solution of $NaCN$ in the presence of air $(O_2)$.
The chemical reaction is: $4M + 8CN^- + 2H_2O + O_2 \rightarrow 4[M(CN)_2]^- + 4OH^-$.
Subsequently,the metal is recovered by displacement using a more electropositive metal like zinc $(Zn)$: $2[M(CN)_2]^- + Zn \rightarrow [Zn(CN)_4]^{2-} + 2M$.

(B) In the froth flotation process,$pine \ oil$ is used as a frother,while $aniline$ or $cresol$ are used as froth stabilizers. $Xanthates$ are used as collectors,and $NaCN$ is used as a depressant. Therefore,the correct answer is $aniline$.

(A) The froth floatation process is used for the concentration (purification) of ores,especially sulphide ores.
It is based on the principle of the difference in wetting properties of gangue and ore particles in water and a frothing agent (ore particles are wetted by oil,while gangue particles are wetted by water).
Statement $I$ is correct as it is used for sulphide ores.
Statement $II$ is incorrect because roasting is a separate metallurgical process.
Statement $III$ is incorrect because relative density is the basis for hydraulic washing,not froth floatation.
Statement $IV$ is correct as it describes the fundamental principle of the process.
Therefore,$I$ and $IV$ are correct.

(D) Leaching is a process of concentration of ore based on the principle of relative or selective solubility.
In this process,the ore is treated with a suitable reagent that dissolves the ore but leaves the impurities (gangue) undissolved.
For example,in the extraction of $Al$ from bauxite ore $(Al_2O_3 \cdot 2H_2O)$,the ore is treated with $NaOH$ solution,which dissolves $Al_2O_3$ to form sodium aluminate,while impurities like $Fe_2O_3$ and $SiO_2$ remain insoluble.

(D) Froth-flotation is a process used for the concentration of sulphide ores.
$(i)$ Froth-flotation is indeed used for removing gangue from sulphide ores.
$(ii)$ Cresols and aniline are used as froth stabilizers.
$(iii)$ Sodium cyanide $(NaCN)$ is used as a depressant to separate $ZnS$ from $PbS$.
$(iv)$ Aniline is used as a froth stabilizer,not as a froth enhancer. Froth enhancers are substances like pine oil or fatty acids. Therefore,statement $(iv)$ is incorrect.

(B) The froth floatation process is based on the difference in the wetting properties of the ore and the gangue particles with water and oil.
Ore particles are preferentially wetted by oil,making their surface hydrophobic (water-repelling).
Because their surface is not easily wetted by water,they attach to the air bubbles and rise to the surface along with the froth.
Gangue particles are preferentially wetted by water and remain in the aqueous phase.

(D) Levigation,also known as gravity separation,is a physical method used for the concentration of ores. It involves separating lighter gangue particles from heavier ore particles by washing them in a current of water. In contrast,$Calcination$,$Smelting$,and $Roasting$ are metallurgical processes that require heating the ore.

(B) Leaching is a chemical process in which the powdered ore is treated with a suitable reagent that selectively dissolves the ore while leaving the impurities in an undissolved state.
Bauxite,which is the principal ore of aluminium $(Al_2O_3 \cdot 2H_2O)$,is concentrated using this method (Bayer's process).
In this process,bauxite is treated with an aqueous solution of sodium hydroxide $(NaOH)$.
Alumina dissolves to form soluble sodium aluminate,while impurities like ferric oxide $(Fe_2O_3)$,titanium oxide $(TiO_2)$,and silica $(SiO_2)$ remain undissolved.
The chemical reaction is: $Al_2O_3(s) + 2NaOH(aq) + 3H_2O(l) \longrightarrow 2Na[Al(OH)_4](aq)$.

(B) Bauxite is the primary ore of aluminium,containing $30-60 \% \ Al_2O_3$,with impurities such as $SiO_2, Fe_2O_3$,and $TiO_2$.
When powdered bauxite is digested with a concentrated $NaOH$ solution at $473-523 \ K$ and $35-36 \ bar$ pressure,$Al_2O_3$ (amphoteric) dissolves to form sodium aluminate,and $SiO_2$ (acidic) dissolves to form sodium silicate.
$Fe_2O_3$ and $TiO_2$ are basic oxides and do not react with $NaOH$,remaining as insoluble residue.
Therefore,the pair of oxides that leaches out is $Al_2O_3$ and $SiO_2$.

(B) Leaching involves the treatment of the ore with a suitable reagent to make it soluble while impurities remain insoluble. After this,the ore is recovered from the solution by suitable methods.
The principal ore of aluminium,bauxite $(Al_2O_3 \cdot 2H_2O)$,usually contains $SiO_2$,iron oxides,and titanium oxides as impurities.
$Al_2O_{3(s)} + 2NaOH_{(aq)} + 3H_2O_{(l)} \rightarrow 2Na[Al(OH)_4]_{(aq)}$
$2Na[Al(OH)_4]_{(aq)} + CO_{2(g)} \rightarrow Al_2O_3 \cdot xH_2O_{(s)} + 2NaHCO_{3(aq)}$
The sodium silicate remains in the solution,and hydrated alumina is filtered,dried,and heated to give pure $Al_2O_3$.
$Al_2O_3 \cdot xH_2O_{(s)} \xrightarrow{1470 \ K} Al_2O_{3(s)} + xH_2O_{(g)}$

(C) Leaching is a process of concentration of ores where the ore is dissolved in a suitable solvent in which the ore is soluble but the impurities are not.
$Al$ (Aluminum) is primarily extracted from its ore,Bauxite $(Al_2O_3 \cdot 2H_2O)$,which is concentrated by the Bayer's process,a well-known method of leaching using a concentrated solution of $NaOH$.

(A) The given reaction is an example of cyanide leaching,which is used for the extraction of metals like $Ag$ and $Au$ from their ores.
In this process,the ore is treated with a suitable reagent (like $NaCN$ or $KCN$) to dissolve the metal in the form of a complex.
Levigation is a gravity separation process based on the difference in densities of the ore and gangue.
Froth flotation is a physical process used primarily for sulphide ores.
Liquation is a refining process used for metals with low melting points.

(B) $Bauxite$ is the chief ore of $Al$ that is concentrated by the leaching process (Baeyer's process).
$Haematite$ is concentrated by magnetic separation.
$Zinc$ $blende$ and $Calamine$ are concentrated by the froth floatation process.

(C) . This principle is valid for magnetic separation.
$B$. This principle is valid for gravity separation.
$D$. It is possible to separate two sulphide ores by adjusting the proportion of oil to water or by using depressants.
$C$. In the froth flotation process,the mineral particles are preferentially wetted by oil,while the gangue particles are wetted by water. Thus,option $C$ is the correct statement.

(D) Statement $I$ is incorrect because in Hall's process,silica is removed as sodium silicate $(Na_2SiO_3)$ by treatment with $Na_2CO_3$.
Statement $II$ is correct because Baeyer's process is used for red bauxite,which is contaminated with $Fe_2O_3$.
Statement $III$ is correct because in Serpeck's process,$Al_2O_3$ is heated with $C$ and $N_2$ to form aluminum nitride $(AlN)$.
The reactions in Serpeck's process are:
$Al_2O_3 + 3C + N_2 \xrightarrow{1800^{\circ}C} 2AlN + 3CO$
$AlN + 3H_2O \rightarrow Al(OH)_3 + NH_3$
$2Al(OH)_3 \rightarrow Al_2O_3 + 3H_2O$

(B) In the Bayer's process,the leaching of alumina is done by using $NaOH$.
$Al_{2}O_{3(s)} + 2 NaOH_{(aq)} \stackrel{150^{\circ}C, 35 \ atm}{\longrightarrow} 2 Na[Al(OH)_{4}] + 3 H_{2}O$
$2 Na[Al(OH)_{4}] + CO_{2} \rightarrow Al_{2}O_{3} \cdot x H_{2}O + 2 NaHCO_{3}$
$Al_{2}O_{3} \cdot x H_{2}O_{(s)} \xrightarrow{1470 \ K} Al_{2}O_{3(s)} + x H_{2}O_{(g)}$
So,the option $(b)$ is the correct answer.