Extraction of Copper from Scrap Copper Chemistry Notes
Extraction of Copper from Scrap Copper :
→ Hydrometallurgy: In this method, impure metal ore is converted into its soluble complex. Again it is displaced by some strong reducing metal by which pure metal is obtained. Here it is leached out using acid and hydrogen gas is passed hence it is known as water metallurgy or hydrometallurgy.
→ In low grade copper ores, percentage of copper is very low. It is leached out using acid/bacteria due to which copper ions come into the solution. The solution is treated with scrap iron or hydrogen gas, Copper ions are reduced to copper metal.
→ We know that in electrochemical series, reactivity of zinc metal is more than iron. Hence reduction will be faster in case zinc scraps are used. But zinc is expensive metal than iron so using iron scraps will be advisable and advantageous.
Extraction of Elements by Oxidation-Reduction Method :
→ Extraction of non-metals is carried out by this method. For example : chlorine from sea water or concentrated aqueous solution of NaCl which is also known as Brine’. On electrolysis, chlorine is easily extracted from it. Reactions of electrolysis are:
→ At anode, as the potential of water is less in comparison with Cl–(aq), priority should be given but due to over voltage of oxygen at anode, oxidation of Cl– takes place first. Ionic reaction is as follows:
2Cl–(aq) + H2O(l) → 2OH–(aq) + H2(g) + Cl2 (g), ∆G° = + 422 kJ
→ With the help of formula ∆G = -nFE°, value of E° for this reaction is 2.2 volt. Hence, for electrolysis in above reaction it will require an external e.m.f. that is greater than 2.2 V. An extra e.m.f. is required to overcome some other hindrances.
→ If molten NaCl is taken as electrolyte in place of Brine then Na metal is produced at cathode and NaOH does not form because here water is not present.
→ In this way, extraction of gold and Silver involves leaching of metal with NaCN. This is also an oxidation reaction after that displacement (reduction) is done by zinc metal.