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Part of INC-06 — General Principles & Processes of Isolation of Elements

Concentration Methods: Principles and Reagents

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1. Hydraulic Washing (Gravity Separation)

  • Principle: Density difference
  • Method: Ore fed into sloped trough with flowing water; heavy ore settles, light gangue washes away
  • Used for: Dense oxide ores (haematite, cassiterite, SnO2)

2. Magnetic Separation

  • Principle: Difference in magnetic susceptibility
  • Method: Crushed ore passed over/near rotating magnetic roller/drum; magnetic fraction deflected
  • Used for: Chromite (FeCr2O4) from non-magnetic gangue; wolframite from cassiterite

3. Froth Flotation (Most NEET-Important)

  • Principle: Difference in wettability — sulphides are hydrophobic, gangue is hydrophilic
  • Setup: Ore + water + pine oil; compressed air blown in
  • Reagents and roles:
ReagentRoleExample
Pine oilCollector — makes sulphide hydrophobicPine oil for ZnS, PbS
Frother (pine oil/cresol)Stabilizes froth bubblesPine oil dual role
DepressantMakes specific ore hydrophilic (selectively suppresses)NaCN for ZnS
ActivatorReactivates depressed mineral if neededCuSO4 for ZnS
  • NaCN as depressant for ZnS–PbS mixture: ZnS+4NaCN→Na2[Zn(CN)4]+Na2SZnS + 4NaCN \rightarrow Na_2[Zn(CN)_4] + Na_2S ZnS surface becomes hydrophilic → sinks; only PbS floats

4. Chemical Leaching

  • NaCN for gold: 4Au+8NaCN+2H2O+O2→4Na[Au(CN)2]+4NaOH4Au + 8NaCN + 2H_2O + O_2 \rightarrow 4Na[Au(CN)_2] + 4NaOH Recovery: 2Na[Au(CN)2]+Zn→Na2[Zn(CN)4]+2Au2Na[Au(CN)_2] + Zn \rightarrow Na_2[Zn(CN)_4] + 2Au
  • NaOH for bauxite (Bayer's): Al2O3+2NaOH→2NaAlO2+H2OAl_2O_3 + 2NaOH \rightarrow 2NaAlO_2 + H_2O Fe2O3 is filtered off (does not dissolve in NaOH)

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Concentration Methods: Principles and Reagents — Notes | NoteTube