Extraction of metals chemistry

Extraction of metals

Topics

• Introduction.• Reactivity series.• Enrichment of ores.• Extracting metals low,

middle,& top of series.• Refining of metals.

Introduction• Some Metals Are Found In Earth Crust In Free State

And Some In Form Of Their Compounds.• The Metals At Bottom Of Activity Series Are Least

Reactive & Are Found In Free State. Eg: Gold,silver,copper Ect.

• The Metals At Top Of Activity Series As( K, Na, Ca, Mg, Al) Are Very Reactive.

• The Metals At Middle Of Activity Series As (Zn ,Fe ,Pb , Cu) Are Moderately Reactive And Found In Crust Mainly As Oxides, Sulphides, Or Carbonates.

Reactivity Series

• This Is Reactivity Series Where K, Na, Ca, Mg &Al Are Electrolysis.

• Zn, Fe, Pb, Cu Are Reduction Using Carbon.

• Ag, Au Are Found In Native State.

KNaCaMgAlZnFePbCuAgAu

Enrichment of ores

• Ores Mined From The Earth Are Usually Contaminated With Large Amounts Of Impurities Such As Soil, Sand Etc.Is Called Gangue.

• The Processes Used For Removing The Gangue From Ore Is Based On Differences B/W The Physical Or Chemical Properties Of The Gangue & The Ore.

Extracting metals low in series• Metals Low In Series Are Very Unreactive.• Oxides Of These Metals Can Be Reduced To

Metals By Heating Alone.Eg:when Cinnabar Is Heated In Air , First It Is Converted Into Mercuric Oxide. Then It Is Reduced To Mercury On Further Heating.

• 2hg(s) +3o2(g)2hgo(s)+ 2so2(g) 2hgo(s)2hg +O2

Extracting metals from middle of series• Metals In Middle Of Series Are Moderately Reactive.• They Are Present As Sulphides & Carbonates.• Prior To Reduction, Metal Sulphides & Carbonates

Must Be Converted Into Metal Oxides.• When Sulphide Ores Are Converted Into Oxides By

Heating Strongly In Presence Of Excess O2 Is Known As Roasting.

• When Carbonates Ore Is Changed In Oxides By Heating Strongly In Limited Air Is Known As Calcination.

Chemical reaction of roasting and calcination of zinc ores

• Roasting:• 2zns(s) +3O2 (G) 2zno(s) + 2SO2 (G)• Calcination:• Znco3(s) Zno(s) + Co2(g)• The Metal Oxides Are Then Reduced To

Corresponding Metals By Suitable Reducing Agents As Carbon. Eg: When Zinc Oxide Is Reduced To Metallic Zinc.

• Zno (S)+ C(s) Zn(s)+ Co(g)

Reduction agents• Besides Using Carbon (Coke) To Reduce Metal

Oxides To Metal, Sometimes Displacement Reactions Can Also Be Used In Reduction.

• The Highly Reactive Metal As Na, Ca, Al, Ect. Are Used As Reducing Agents As They Can Displace Metals Of Lower Resistivity From Their Compounds.

• For Eg: When Manganese Dioxide Is Heated With Aluminium Powder :

• 3mno2(s) + 4al(s)3mn +2al2o3(s) +Heat

Substances Getting Oxidized & Reduced

• These Displacements Reactions Highly Exothermic In Nature.

• The Amount Of Heat Produced Is So Large That Metals Are Produced In Molten State.

Thermit Reaction

• The Reaction Of Iron(iii) Oxide[fe2o3 ] With Aluminium Is Join Railway Tracks Or Cracked Machine Parts This Is Known As Thermit Reaction.

• The Reaction For Thermit Reaction Is:

• Fe2o3[s] + 4al[s] 3mn(i) +2al2o3(s) + Heat

Extracting metals from top of series

• These Metals Are Very Reactive.

• They Cannot Be Obtained By Their Compounds While Heating By Carbon. For Eg: Carbon Cannot Reduce The Oxide Of Sodium, Magnesium, Calcium, Aluminium Ect. It Is Because They Have More Affinity Of O2 Than CO2 .

Extracting metals from top of series

• These Metals Are Obtained From Electrolytic Reduction. For Eg:

• Na, Mg, Ca Are Obtained By The Electrolysis Of Their Molten Chlorides.

• The Metals Are Deposited At The Cathode (Negatively Charged Electrode) .And Cl Is Liberated At Anode (Positively Charged Cathode)

Refining Of Metals

• Metals Are Produced By Various Reduction Process Which Are Not Very Pure.

• They Contain Impurities Which Must Be Removed To Obtain Pure Metals.

• The Most Widely Used Method For Refining Impure Metals Is Electrolytic Refining .

Electrolytic refining

• Many Metals Such As Cu, Zn, Sn, Ag, Au Etc Are Refined Electrolytically.

• The Impure Metal Is Made Anode & A Thin Strip Of Pure Metal Is Made Of Cathode .

• Solution Of Metal Salt Is Used In Electrolyte.

Electrolytic refining

• On Passing The Current Through The Electrolyte, The Pure Metal From The Anode Dissolves Into The Electrolyte.

• An Equivalent Amount Of Pure Metal From The Electrolyte Is Deposited On The Cathode.

• The Soluble Impurities Go Into The Solution, Whereas, The Insoluble Impurities Settle Down At The Bottom Of The Anode And Are Known As Anode Mud.

THANK YOU

BY:NIM

ESH BHATIA

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