**4.3 Redox reactions**

This mechanism is highly valuable for certain ions which as product of the electron transfer type of reaction may directly precipitate or produce precursors for precipitation (**Figure 11**). The reduction of metals is somehow difficult to implement unless certain scrap of metallic wastes contain metals with low standard reduction potentials, also called less noble elements. If the metal is removed from the aqueous solution exhibits higher hydrolysis constants than the metal being released into the aqueous medium, the resulting pH of the solution should increase. One example of this would be the removal of polynuclear lead (II) ions by iron (II) ions [76–78].
