Concentration of ore - class-XII

Leaching of low grade copper ores is carried out with acid or bacteria, when copper goes into solution as $Cu^{2+} _{(aq) }+ H _{2(g)}\rightarrow Cu _{(s)}+2H^+ _{(aq)}$ 

By using depressants or adjusting proportion of oil to water, selective prevention of one sulphide ore from coming to the froth is possible.

• Magnetic separation based on differences in magnetic properties of the ore components.
  
•  If either the ore or the gangue is attracted towards the magnetic field, then the separation is carried out by this method. 
• For example, iron ores are attracted towards the magnet, hence, non–magnetic impurities can be separated from them using magnetic separation.
• Here, Haematite, Magnetite, and Sidderite are iron ores and hence magnetic separation can be used to separate them.
• Malachite is a Copper ore and hence magnetic separation can't be used to concentrate it.

• Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water.
• It is possible to separate two sulphide ores by adjusting the proportion of oil to water or by using ‘depressants’.
•  In the case of an ore containing $ZnS$ and $PbS$, the depressant used is $NaCN$. It selectively prevents $ZnS$ from coming to the froth but allows $PbS$ to come with the froth.

• Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water
  
• Among the given options Zinc blend ($ZnS$) is the only sulphide ore and hence Froth floatation process is used for its concentration.
• Hence, option B is the right answer.

Leaching is a process where ore is soluble and impurities are insoluble, widely used extractive metallurgy technique which converts metals into soluble salts in aqueous media.
Bauxite, SIlver and gold ores are usually soluble in some solvents and hence leaching is used to concentrate them.
Hence, option $B$ is the correct answer.

Froth floatation process is used for the sulphide ores. In this method, wetting of the ore by an oil takes place. 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.

This method is used for those metals whose ore gets preferably wetted by the oil and the gangue by the water. The sulphide ores preferably wetted by the oil and the gangue with the water.

This method is used for those metals whose ore gets preferably wetted by the oil and the gangue by the water. The sulphide ores preferably wetted by the oil and the gangue with the water.

In froth flotation process, pine oil is usually added to the suspension of the powdered ore. Pine oil enhance non-wettability of the mineral particles.

Here answer is option B

In the leading of ${ Ag } _{ 2 }S$ (silver sulphide) with $NaCN$, a stream of air is passed because reversible nature of reaction between ${ Ag } _{ 2 }S$ and $NaCN$ and to oxidise ${ Na } _{ 2 }S$ formed into ${ Na } _{ 2 }{ SO } _{ 4 }$ and sulphur.

Froth flotation relies on the difference in surface properties between ore and gangue. Ore particles are preferentially wetted by oil (hydrophobic), while gangue particles are wetted by water (hydrophilic).

Leaching is a process in which the ore is dissolved in a suitable solvent, where the impurities remain undissolved. This method is used in the extraction of $Ag$ from Argentite where is, the ore is dissolved in sodium cyanide solution.

Froth flotation method is used for the concentration of sulphide ores. 

Generally sulphide ores are concentrated by "Froth floatation" and cinnabar(HgS) is a sulphide ore.

Sodium ethyl xanthate is used as collector in froth floatation process.

During concentration of Tin stone separation of wolframates of $Fe({II})$ and $Mn({II})$ is based on the fact $SnO _2$ is diamagnetic and both $FeWO _4$ & $MnWO _4$ are paramagnetic so magnetic separation method is used for concentration of ore.

As impurity $FeCr _2 O _4$ contains iron so magnetic-separation process is used.

NaCN (Sodium Cyanide) is used as a depressant in the froth flotation of sulphide ores to prevent one specific sulphide (like ZnS) from floating while allowing another (like PbS) to float.

Hydrometallurgy involves the extraction of metals from their ores using aqueous solutions. The displacement of silver from a cyanide solution by zinc is a classic example of this process.

Collectors (like xanthates) are used to make the mineral particles water-repellent (hydrophobic) so they attach to air bubbles, whereas frothers are the agents that actually stabilize the froth.

Chief ore of copper is copper pyrite ($CuFeS _{2}$). It is a sulphide ore and sulphide ores are concentrated by froth flotation method.

(A) Froth floatation process used for the concentration of sulphide ore is based on the difference in wettability of different minerals. The metallic sulphide particles of ore are preferentially wetted by oil and the gangue particles by water.
(B) Froth floatation process used for the concentration of sulphide ore uses sodium ethyl xanthate, $C _{2}H _{5}OCS _{2}Na$ as collector. Other examples of collector include ethyl xanthate and potassium ethyl xanthate. They attach themselves to the grains of mineral by polar groups so that minerals become water repellent and pass on into the froth.
(C) Froth floatation process used for the concentration of sulphide ore uses NaCN as depressant in the mixture of ZnS and PbS when ZnS forms soluble complex and Pbs forms froth. Other depressant used is KCN.
Depressants depress the floating property of one of the components of the ore and help in the separation of different minerals present in the same ore.
Thus, all of the above statements are correct.

Froth Flotation: The process is based on the principle of preferential wetting of ore particles by the oil and gangue by water. In this process, sodium ethyl xanthate is used as a collector. 

(A) The concentration of ore involves physical and chemical methods. Froth floatation method is the physical method for the separating mineral from the gangue.
(B) It  is based on the difference in wettability of different minerals.
The metallic sulphide particles of ore are preferentially wetted by oil and the gangue particles by water.
(C) Froth floatation process used for the concentration of sulphide ore.
(D) In this method impurities sink to the bottom and the ore particles rise to the surface alongwith the froth.

The chemical treatment of the ore for concentration is done  when ore is required in very pure form .
This method is used for the purification of bauxite ($Al _2O _3$ an ore of aluminum ) which contains ferric oxide, titanium oxide and silica as impurities.
It is also used for the treatment of gold, silver and copper.

In differentiation flotation, zinc sulphate is depresses zinc sulphide and PbS forms froth copper sulphate activate depressed lead sulphide. Froth is made by blowing oxygen. Thus, all the given statements are correct.

Froth flotation is a process of  concentration. Froth floatation process is suitable for sulphide 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 $FeCr _2O _4$.

The bauxite is purified by the Bayer Process. First the ore is mixed with a hot concentrated solution of sodium hydroxide. The $NaOH$ will dissolve the oxides of aluminum and silicon but not other impurities such as iron oxides, which remains insoluble. The insoluble materials are removed by filtration.This method is called the chemical method.

In the froth floatation process, for the benefaction of ores, the ore particles float because their surface is not easily wetted by water. This method is base on the difference in the wetting properties of ores and gangue particles with the water and oil.

Leaching involves the treatment of the ore with a suitable reagent to make it soluble while impurity remains insoluble. The ore is recovered from the solution by suitable chemical method.

Froth floatation process is used to concentrate sulphide ores. In some cases, sulphide ores of copper, zinc and lead concentration are brought by this method. It is the referential wetting of the ore by an oil. A strong current of air is blown through the suspension producing a heavy froth e.g. Galena $(PbS)$ is associated with Sphalerite $(ZnS)$ and Pyrite $(FeS)$.

Froth floatation process is based on the principle that the metallic sulphide particles of ore are preferentially wetted by oil and the gangue particles by water.
Sulphide ores being lighter are easily wetted by oil to come on the surface of solution with froths during froth floatation process, leaving behind heavy matter of gangue wetted by water.
Sulphide ores are usually dressed by froth floatation process.

During concentration of sulphide ores by froth floatation process potassium ethyl xanthate is added.
Ethyl xanthate, potassium ethyl xanthate and similar compounds compounds behaves as collector and attaches themselves by polar groups to ore particles making that hydrophobic and i.e., why ore particles are passed into froth.

The given statement is false as magnetic ores are separated by magnetic separation method.

In the field of extractive metallurgy, mineral processing, also known as ore dressing, is the process of separating commercially valuable minerals from their ores. 

Pine oil enhances non-wettability of the mineral particles. So, it is used as frothier in froth-flotation process.

Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. Any physical and chemical process by which low grade ores are concentrated is called froth flotation.

Scarp Iron is a magnetic substance whereas others are not. So, they are separated by Magnetic Separation.

Chromite is $[Fe(CrO _{2}) _{2}]$
Magnetic separation depends on its difference in the magnetic separation of the ores and gangues.

Enrichment of ore means concentration or purification of ore. It can be done by hydraulic washing, magnetic separation, chemical separation.

Whenever a metal sulphide is heated in air, sulphur dioxide is formed as one of the products. A sulphide ore is concentrated by the froth floatation process.

An amphoteric compound is a compound that can react both as an acid as well as a base. For example, $ Al _{ 2 }{ O } _{ 3 } $. 

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 $(Au)$ 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.

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

Xanthates are commonly used as collectors in the froth flotation process to increase the hydrophobicity of the ore particles, which helps in forming the froth.

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.

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.

$\Rightarrow$ Minerals occur naturally in the Earth.

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.

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. 

(A) Sodium ethylxanthate acts as collector and not frother.

$\displaystyle 4Au+8KCN+2H _{2}O+O _{2}\rightarrow 4KAu(CN) _{2}+4KOH$
$\displaystyle 4Au+16KCN+6H _{2}O+3O _{2}\rightarrow 4KAu(CN) _{4}+12KOH$
$a = 4$      $ b = 8$       $c = 2$      $ d = 1$        $e = 4$               $f = 4$
$u = 4$     $ v = 16$       $ w = 6$       $ x = 3$     $ y = 4$           $ z = 12$ 

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.

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.

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.

Bayer's process is used for the concentration of aluminium ore, bauxite. In this process, the impurities like iron oxide and silica are removed.

Concentration of ore is also k/a enrichment of ore or one dressing. All the method depend on some difference in physical or chemical properties of gangue.

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).