General Principles & Processes of Isolating Elemen

The common elements present in anode mud in electrolytic refining are antimony, selenium, tellurium, silver, gold, and platinum. These elements being less reactive, are not affected by CuSO₄ + H₂SO₄ solution and hence settle down under anode as anode mud.

At 673K, the value of G _{(CO, Co2)} is less than that of G _{(C, Co)}. Therefore, CO can be reduced more easily to CO₂ than C to CO. hence; CO is a better reducing agent than C at 673K.

The Gibbs free energy formation ( Δ_fG) of Cu₂S is less than that of H₂S and CS₂. Therefore, H₂ and C cannot reduce Cu₂S to Cu.

On the other hand, the Gibbs free energy formation of Cu₂O is greater than that of CO. hence, C can reduce Cu₂O to Cu.

C (s) + Cu₂O (s) → 2Cu (s) + CO (g)

Hence, the extraction of copper from its pyrite ore is difficult than from its oxide ore through reduction.

In the froth floatation method, the role of depressants is to prevent certain types of particles from forming the froth with the air bubbles. For example, NaCN is used as a depressant to separate lead sulfide ore (PbS) from zinc Sulphide ore (ZnS).NaCN forms a zinc complex Na₂ [Zn (CN)₄] on the surface of ZnS thereby preventing it from the formation of froth.

Copper can be extracted by hydrometallurgy but not zinc as per the below-given reason:

The E^o of zinc ( Zn²⁺/Zn = - 0.76V) is lower than that of copper (Cu²⁺/Cu = 0.34V). this means that zinc is a stronger reducing agent and can displace copper from a solution of Cu²⁺ ions.

Zn (s) + Cu²⁺ (aq) → Zn²⁺ + Cu (s)

In order to displace zinc by hydrometallurgy, we need stronger reducing agent like K ( E^o_K+/K = - 2.93V)

2K (s) + 2H₂O (l) → 2KOH (aq) + H₂ (g)

As a result, these metals cannot be used in hydrometallurgy to extract zinc. Hence, copper can be

extracted by hydrometallurgy but not zinc.

Below 1683K, the melting point of silicon, the Δ _fG^o curve for the formation of SiO₂ lies above the Δ _fG^o curve for MgO, so, at temperature below 1683 K, Mg can reduce SiO₂. On the other hand, above 1683 K, the Δ_fG^o curve for MgO lies above Δ_fG^o curve for SiO₂. Hence, at a temperature above 1683 K, Si can reduce MgO to Mg.

The reaction,

Cr₂O₃ + 2 Al → Al₂ O₃ + 2 Cr (ΔG⁰ = – 421 kJ)

Is thermodynamically feasible as is apparent from Gibbs energy value. The change in Gibbs free energy is

related to the equilibrium constant, k as

ΔG = - RT ln K

A certain amount of energy activation is required even for such reactions which are thermodynamically feasible, therefore heating is required.

ΔG = ΔH + S

Increasing the temperature increases the value of TΔS, making the value of ΔG more and more negative.

Therefore, the reaction becomes more and more feasible as the temperature is increased.

The method of leaching consists of treating the powdered ore with a suitable reagent which can selectively dissolve the ore but not the impurities. The impurities are filtered out and are recovered from the solution. For example, bauxite ore containing SiO₂, iron oxide, and titanium oxides impurities are concentrated by this method. Leaching is significant as it helps in removing the impurities like SiO₂, FeO₂, TiO₂, etc. from the bauxite ore.