Extraction of copper and zinc from their oxides - class-XII

The various reaction involved in extraction of copper from cuprous oxide are:
$2FeS+3O _2 \rightarrow 2FeO+2SO _2$
$FeO+SiO _2 \rightarrow FeSiO _3$
$2Cu _2S+3O _2 \rightarrow 2Cu _2O+2SO _2$
$2Cu _2O+Cu _2S \rightarrow 6Cu+SO _2$
The solidified copper obtained has blistered appearance due to the evolution of $SO _2$ and so it is called blister copper.

Partial reduction of Sulphide ores gives copper oxide which further reacts with copper sulphide to show an auto reduction.

Blister copper is a form of a impure copper which is obtained in self reduction process during bessemerization.

During the extraction of copper from cuprous oxide $(copper[I]oxide)$ the ore is heated in a reverberatory furnace after mixing with silica. In the furnace, iron oxide, slag of iron silicate and copper is produced in the form of copper matte. This contains $Cu _2S$ and $FeS$.

Zinc is refined by distillation under reduced pressure or electrolytic method. Distillation is very useful for low boiling metals like zinc and mercury. The impure metal is evaporated to obtain the pure metal as distillate.

The volatile impurities associated with zinc spelter are Cd and As and the non-volatile impurities are Fe and C.

$2 Cu + O _2\xrightarrow {(\Delta)} 2CuO$
(x)                            (y)
Brown & Bright         Black
$CuO + H _2 \rightarrow Cu + H _2O$

In this process, air is blown through molten copper matte in a Bessemer converter. Bessemerisation is also used to convert pure iron to steel.

Reaction:
$ZnO + C \rightarrow Zn + CO$

$2Cu _{2}S + 3O _{2} (g)\xrightarrow {\triangle} 2Cu _{2}O + 2SO _{2}(g)$
$2Cu _{2}O + Cu _{2}S\xrightarrow {\triangle} 6Cu(S) + SO _{2}(g)$.

$ZnO(s) + C(s) \rightarrow Zn(s) + CO(g)$
Metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon.

The balanced chemical reaction for extraction of zinc from its ore by roasting of zinc ore is;

In the electrometallurgy of $Al$, graphite is used as anode as oxygen being a non-metal is liberated at the anode and the reoxidation of $Al$ into $Al _2O _3$ is avoided.

In the extraction of copper, the self-reduction reaction of Copper taking place in a Bessemer converter is as follows:

Reduction of zinc oxide is done by carbon, not by self reduction.

Sphalerite ((Zn,Fe)S) is a chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron.
Extraction of Zinc follows:
Roasting followed by reduction with carbon; then electro-fining of Zn.

Hydrometallurgy:
In this process, desired metal is extracted from its solution by addition of more electro positive metal.
But there are very few metals which are more electro positive than Zn so it can not be extracted by hydrometallurgy

In the extraction of copper, following methods are used
froth floatation
roasting
smelting
bessemerisation and 
electrolytic refining

Blister copper is refined by poling process where it removes impurity in form of $SO _2$ and $As _2O _3$.

During the roasting of sulphide ore of Cu, $Cu _2O$ and $Cu _2S$ formed where they react with each other to produce Cu metal.

In the extraction of copper, raw material used for the Bessemer converter is matte ($Cu _2S+FeS (little)$), where matte is formed in the blast furnace.

The commercial metallurgical process for the formation of metallic copper from the sulphide ore involves oxidation of $Cu _2S$ to $Cu _2O$  and auto reduction of a mixture of $Cu _2S$ and $Cu _2O$ to copper metal.

The refining process of blister copper is known as polling.
The $Cu _2O$ impurities are present in the copper metal.
In presence of heat of molten metals, the green logs liberate hydrocarbon gases which reduce copper oxide into copper.

During roasting of copper pyrite ore: 

The sulphide ore of copper is heated in the air until a part is converted to oxide and then further heating in the absence of air to let the oxide react with unchanged sulphide.

The sulphide ore of copper is heated in air until a part is converted to oxide and then further heating in the absence of air to let the oxide react with unchanged sulphide.
Self-reduction of CuS to Cu can be carried out in either Bessemer converter or Pierce-Smith converter.
$2Cu _2S+3O-2 \rightarrow 2Cu _2O + 2SO _2$
$2Cu _2O+Cu _2S \rightarrow 6Cu+SO _2$
This is the final step in Bessemer converter.

Copper matte contains Copper Sulphide $Cu _2S$, iron sulphide $(FeS)$ with some amount of silica.

The following reaction takes place in Bessemer converter :

Auto reduction process is used in the preparation of Cu, Hg and pb etc.

Zinc blende (ZnS) is first roasted to form zinc oxide (ZnO), which is then reduced to zinc metal using carbon (coke).

The chemical formula of malachite is $Cu _2CO _3(OH) _2$. Hence the composition is $CuCO _3.Cu(OH) _2$.

Copper is mainly extracted from copper pyrites. After the concentration of its ore by froth flotation process, the ore is roasted in a current of air to remove arsenic, antimony and much of sulphur.

Cuprite is an oxide mineral composed of copper(II) oxide ($Cu _2O$), and is a minor ore of copper. It can yield small gemstones.

Copper is extracted from the ore copper pyrite by smelting in a blast furnace. The flux used is  $SiO _2$ and slag formed is $FeSiO _3$.

Copper is obtained from its one by process of self reduction or intoreduction.
$Cu _2S+2Cu _2O \rightarrow 6Cu+SO _2$

Chemical formula of willemite is Zn₂SiO₄

$\underset{\displaystyle chloroform}{CHCl _3}\overset{\displaystyle 6[H]; Zn/H _2O}{\underset{\underset {\displaystyle -ZnCl _2}{-HCl}}{\displaystyle \rightarrow}}\underset{\displaystyle methane}{CH _4}$.
Chloroform on reduction with Zn and HCl gives dichloromethane $(CH _2Cl _2)$.

Spelter zinc is an alloy of equal parts copper and zinc, i.e. a brass, used for hard soldering and brazing, or as an alloy, containing lead, that is used instead of bronze.

Polling is a metallurgical method employed in the purification of copper which contains cuprous oxide as an impurity. 

Copper matte is a mixture of cuprous sulphide (Cu2S) and ferrous sulphide (FeS). These are sulphides of copper (I) and iron (II).

In extraction of copper:
In final step electrolytic refining process is used to 99.99% pure copper metal.

During the Bessemerisation process, the sulphide ores of less electropositive metals are heated in air to convert part of the ore into oxide or sulphate which then react with the remaining sulphide ore to give the metal and sulphur dioxide.
Copper sulphide is partially oxidised to cuprous oxide which futher can react with remaining copper sulphide to form copper and sulphur dioxide.
$2Cu _{2}S+3O _{2} \rightarrow 2Cu _{2}O+2SO _{2}$
$Cu _{2}S+2Cu _{2}O \rightarrow 6Cu+SO _{2}$
This process is also called  autoreduction process or air reduction process. 

Blast of air converts $Cu _2S$ partly into $Cu _2O$ which reacts with remaining $Cu _2S$ to give molten copper. The copper so obtained is called "Blister copper" because, as it solidifies, $SO _2$ hidden in it escapes out producing blister on its surface

• The chemical formula of copper matte is $Cu _2S+FeS$. It is a combination of copper sulphide and iron sulphide.
• It is a phase in which extracted metal is converted into crude metal which is a final product.
• $80-70\%$ of copper matte is used $80-95\%$. $5- 17\%$ metallic copper, $Fe-Co$ alloy etc are used.
  

Spelter Zn is purified by both distillation and electro fining process(here we get more pure Zn).

Smelting is used to produce a metal from its ore. This includes iron extraction from iron ore, copper extraction, and other base metals from their ores like lead and zinc. 

Blister copper contain $Cu _2O$ as impurity and is refined by poling process. 

Self-reduction of CuS to Cu can be carried out in either Bessemer converter or Pierce-Smith converter.
$2Cu _2S+3O-2 \rightarrow 2Cu _2O + 2SO _2$
$2Cu _2O+Cu _2S \rightarrow 6Cu+SO _2$

Self-reduction of CuS to Cu can be carried out in either Bessemer converter or Pierce-Smith converter.

Lead metal is purified by electrolysis in a similar manner to copper, the electrolyte is Lead $(II)$ hexa Fluorosilicate $PbSiF _6$. The given statement is True.

Pine oil acts as foaming agent. It stabilizes the froth.
Sodium ethyl xanthate (also potassium ethyl xanthate) acts as collectors.
They coat the ore particles.

(A) Froth floatation method is used for concentration of sulphide ores such as galena $(PbS)$, zinc blende $(ZnS)$ and copper pyrites $(CuFeS _2)$.

Silica is added to roasted copper ores during smelting in order to remove $FeO$ (ferrous oxide) as $FeSiO _3$ (slag).