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Help! Purification of bauxite (edexcel)

could someone please tell me the basic outline of the purification of bauxite (for AS)? says on the specification we need to know how its purified before its used in electrolysis
thanks!
Reply 1
Avatar for RMIM
RMIM
9
haber process 400c 200atm iron catalyst

ostwald, Hno3
1. 4NH3+ 5O2 <---> 4NO + 6H20
900c 4-10atm platinum/rhodium cat
2. 2NO + O2 <---> 2NO2
3. NO2 + O2 + H2O <--> 4HNO3

contact proess, H2SO4
1. S + O2 ---> SO2
2. SO2 + O2 ----> SO3
425c 2atm catalyst: vanadium(V)oxide

<<SO3 +H2O--> H2SO4 but this is not done as a hard to condense mist is formed>> so

3. SO3 + H2SO4 ---> H2S2O7 (99.5%) (OLEUM)
4. H2S2O7 + H20 ---> 2H2SO4 (98%)

Aluminium. Bauxite (Al2O3.XH2O amphoteric + FE2O3basic + SiO2)
1.Bauxite crushed and hot 10% solution os NaOH added.
2. Iron oxide does not react as its basic. SiO2 is weakly acidic but has giant atomic structure so it does not reach. Al2O3 will react as it amphoteric

3. solids are filtered off leaving sodium aluminate
4. carbon dioxide blown in giving aluminum hydroxide
5. aluminum hydroxide heated to give AL2O3.XH2O again.

AL2O3.XH20 is dissloved in cryolite to lower melting point from 2000c to about 900c.
This is then electrolised in a cell lined with carbon acting as the cathode and carbon anodes that are lowered in.

Cathode Al3+ + 3e --> Al
Anode 2O^2- ----> O2 + 2e this oxygen reacts with carbon anode C+O2-->CO2

--
electrolysis of brine
titanium anode: 2Cl- ----> CL2 + 2e
steel cathode: 2H+ + 2e ---> H2

(all the answers were taken from edexcel past papers, i hope i did not make any mistakes - double check)
Reply 2
Avatar for fait
fait
Here you go:

fait
Purification of Bauxite:

Ore is crushed and heated to 170c with 10% NaOH. Aluminimum Oxide reacts to form [Al(OH)4]-

The impurites (iron, titanium oxides are filtered off) which produces lakes of red mud which are enviromental hazards.

Carbon dioxide is blown into the solution containing aluminiate ions to form aluminimum hydroxide:

[Al(OH)4]- (aq) + C02 (g) --------> Al(OH)3 (s) + HCO3- (aq)

Precipation of Al(OH) 3 is heated to 1200c where it decomposes to anhydrous aluminimum oxide:

2Al(OH)3 (s) -----> Al2O3 (s) + 3H20 (l)

Hope that helps. :smile:
Reply 3
Avatar for RMIM
RMIM
9
I dont think we need to know any equations (so why learn them) for edexcel apart from

Cathode Al3+ + 3e --> Al
Anode 2O^2- ----> O2 + 2e this oxygen reacts with carbon anode C+O2-->CO2

but do check all the past papers
Yes, in AQA at least this is all you need to know:

Al3++3e−=>Al Al^{3+} + 3{e^-} => Al at the Cathode.

and

2O2−=>O2+2e− 2O^{2-} => O_2 + 2{e^-} at the Anode.
Reply 5
Avatar for Mrs.Gladiator
Mrs.Gladiator
OP
thanks a lot, that really helps :smile:
My pleasure. Unless you weren't talking to me... :s-smilie:

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