Reaction principle of replacing copper with reduced iron powder

The principle of iron displacement.

Since the standard potential of Fe2+/ Fe (-0.141V) is much lower than that of Cu2+ /Cu (0.330V), iron can thoroughly replace Cu2+ from copper solution into Cu, and in this reaction process, the iron consumption of theoretical production of 1kg copper is only 0.88kg. The reason for the big difference between theoretical and practical reaction is that.

1) The excess acid in the copper solution consumes the iron and then gives off the hydrogen

    Fe + 2H+ ——  Fe2+ + H2

2) Dissolved hydrogen in the copper solution will make the ferric ions generated by the replacement reaction continue to oxidize to ferric ions. The strong oxidizing ferric ions will be reduced to ferric ions by the iron powder, so it needs to consume another part of the iron.

    4H+  +  4Fe2+ + O2 ——  4Fe3+ + H2O

         2Fe3+  + Fe —— 3Fe2+

3) Fe3+ can also oxidize the formed Cu to Cu2+, thus increasing the iron consumption

     2Fe3+  + Cu ——  2Fe2+ + Cu2+

As can be seen from the above chemical reaction, in the method of replacing copper with iron, the main factors causing iron consumption are: acidity of the solution, oxygen content in the solution, etc.;Since the replacement reaction is carried out at the liquid-solid interface, the specific surface and contact time of iron powder are also important factors affecting the replacement. The reduced iron powder particles are larger than the surface and porous. In the replacement of copper, the reaction efficiency is higher than that of other solid iron particles.