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Chemistry > Metallurgy > Flashcards

Metallurgy Flashcards

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1
Q

metals are oxidising/reducing agent

A

reducing agents as they lose and donate electrons

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2
Q

define mineral

A

the compounds of various metals found in nature- associated with their earthly impurities are called minerals

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3
Q

define ore

A

naturally occurring minerals from which metals can be extracted profitably and conveniently

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4
Q

define metallurgy

A

large scale processes involved in the extraction of pure metals from their respective ores

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5
Q

define matrix/ gangue

A

rocky impurities including silica, mud, etc. associated with the ore

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6
Q

define flux

A

substance added to the ore to get rid of the matrix- forms a fusible compound SLAG

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7
Q

ores of aluminium

A
  1. bauxite (main)- hydrated aluminium oxide
  2. cryolite- sodium aluminium fluoride
  3. corundom- aluminium oxide
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8
Q

ores of zinc

A
  1. zinc blende (main)- zinc sulphide
  2. calamine- zin carbonate
  3. zincite- zinc oxide
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9
Q

ores of iron

A
  1. haematite (main)- iron 3 oxide
  2. magnetite- tri iron tetroxide
  3. iron pyrites- iron disulphide
  4. spathic iron ore- iron 2 carbonate
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10
Q

stages of extraction of metals

A
  1. dressing of ore/ concentration
  2. conversion of concentrated ore to oxide
  3. reduction of metallic oxides to its metal (impure)
  4. electro-refining of impure metal
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11
Q

dressing of ore

A

separation of ore from gangue
reason: to convert impure ore to pure concentrated ore

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12
Q

conversion of concentrated ore to its oxide

A

reason: to convert the pure concentrated ore to its oxide since oxides are easy to reduce

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13
Q

reduction of metallic oxide to its metal

A

reason: to obtain the metal, from the metallic oxide by reduction

method of reduction depends on position of metal in activity series of metals

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14
Q

electro-refining of impure metal

A

reason: to obtain the metal in its very pure form

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15
Q

methods of concentration

A
  1. hydrolytic
  2. froth floatation
  3. magnetic method
  4. chemical method
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16
Q

hydrolytic method/ gravity separation

A

separation of ore and gangue due to difference in density of particles

17
Q

magnetic separation

A

separation of magnetic ore from non magnetic gangue, or non magnetic ore from magnetic gangue

18
Q

froth flotation

A

separation of ore and gangue by preferential wetting
generally applied for sulphide ores

19
Q

chemical method of concentration

A

separation of ore and gangue by use of a chemical NaOH in Baeyer’s process during extraction of aluminium

20
Q

conversion of concentrated ore to oxide

A

done by
1. roasting (generally sulphide ores)
2. calcination (generally carbonate ores)

21
Q

define roasting

A

process of heating the concentrated ore in presence of excess air to a high temperature before it is reduced to a metal

22
Q

define calcination

A

process of heating the concentrated ore in a limited supply of air or in absence at a temperature just below its melting point or not sufficient to melt the ore

23
Q

metal at the top of activity series is..

A
  1. most easily oxidised
  2. most electropositive and most reactive
  3. can displace the metal below from its salt solution
24
Q

reduction of metallic ores to metal, processes

A
  1. electrolysis (K to Al)
  2. reducing agents (Zn to Cu)
  3. thermal decomposition (Hg and Ag)
25
Q

types of electrorefining

A
  1. distillation refining
  2. oxidation refining
  3. electrolytic refining
26
Q

dressing of ore- aluminium

A

bauxite is used
CHEMICAL METHOD
impure bauxite to pure aluminium oxide (alumina)

27
Q

reduction of oxide to metal- aluminium

A
  1. method- electrolysis
  2. process- Hall Heroult’s process
  3. conversion- pure alumina to pure aluminium
  4. reaction: electrolytic reduction
  5. electrolyte: mixture of fused alumina, cryolite, fluorspar (1:3:1)
  6. electrodes: inert graphite
28
Q

reason for use of cryolite and fluorspar

A

acts as a solvent for fused alumina, and also lower the melting point of the mixture, and increase conductivity of electrolytic mixture

29
Q

why doesn’t aluminium occur in free state

A

reactive metal

30
Q

function of sodium hydroxide

A
  1. bauxite is reacted with NaOH under pressure for 2 hrs
  2. impurities Fe2O3 and SiO2 remain unaffected since they are not amphoteric
  3. bauxite being amphoteric reacts with the base forming sodium aluminate and water, impurities separate out

hence NaOH is used during purification of bauxite

31
Q

define seeding

A

sodium aluminate salt is diluted in water, and extra aluminium hydroxide is added to it to further precipitate out the aluminium hydroxide

32
Q

electrolytic cell used during extraction of aluminium

A

rectangular steel tank with carbon lining
cathode: carbon lining of the cell
anode: thick graphite rods attached to copper clamps dipping into fused electrolyte

temp: 950 C
current: 100 A at 6-7 V

33
Q

GR: fused alumina is electrolytically reduced to aluminium

A

it is a highly stable oxide
aluminium has a high affinity for oxygen

34
Q

difficulties faced during electrolytic reduction of alumina

A
  1. fused alumina is a non electrolyte and has a high melting point
  2. large amount of electrical energy is required
  3. liberated Al can also volatize out and get wasted, so fusion temperature of the mixture is lowered
35
Q

why is a layer of powdered coke sprinkled over the electrolytic mixture

A
  1. prevents burning of carbon electrodes in the air
  2. minimizes heat loss by radiation
36
Q

why are the anode graphite rods continuously replaced

A
  1. oxygen released reacts with anode
  2. anode gets oxidised to CO which burns to give CO2 or escapes
  3. the anode is hence consumed and renewed periodically
37
Q

processes of electrolytic reduction and electrorefining

A

reduction: Hall Heroult’s process
refining: Hoope’s process

38
Q

define alloy

A

a substance prepared by adding other metals to a base metal in appropriate proportions to obtain certain desirable properties

39
Q

define amalgam

A

an alloy in which the base metal is mercury

Chemistry (9 decks)

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