Name the chief forms of the occurrence of the following in the earth crust:
(a) aluminium, (b) calcium, (c) sodium, (d) lead.
(a) Aluminium: Oxides:
(i) CorundumAl2O3
(ii) DiasporeAl2O3.H2O
(iii) Bauxite Al2O3.2H2O
Halides: Cryolite Na3AlF6
Silicates:
(i) Feldspar KAlS3O8
(ii) Mica KAlSi3O10 (OH)2
(b) Calcium:Carbonate: Lime stone (CaCO3) marble, chalk, calcite and dolomite Sulphate : Gypsum, CaSO4 2H2O and anhydrite, CaSO4 Fluoride: Fluorspar, CaF2, Fluorapatite 3Ca3(PO4)2CaF2 Phosphate : Phosphorite, Ca3(PO4)2
(c) Sodium: Sodium chloride, NaCl
Sodium nitrate or chile salt petre NaNO3
Sodium carbonate Na2CO3 Borax Na2B4O7,10H2O.
(d) Lead: Anglesite, PbSO4 Cerussite PbCO3 Lanarkite, PbO, PbSO4.
Sodium metal cannot be obtained by the electrolysis of aqueous sodium chloride solution.
Write the chemical reactions involved in the extraction of metallic silver from argentite.
Silver ores and native gold have to be leached with metal cyanides. Suggest a reason for this.
Describe the principle of froth floatations process. What is the role of stabilizer and of a depressant? Give one example of each.
State briefly the principles which serve as basis for the following operations in metallurgy:
(i) Froth floation process.
(ii) Zone refinnting.
(iii) Refining by liquation.
What chemical principle is involved in choosing a reducing agent for gettting the metal from its oxide ore? Consider the metal oxides, Al2O3 and Fe2O3 and justify the choice of reducing agent in each case.