Loading capacity of an extractant:

Loading capacity of an extractant is the maximum amount of the metal ion that can be extracted by the extractant. It is usually expressed in terms of metal extractant mole ratio. For the determination of loading capacity, please refer to sub-Sec. 3.3.3 on "Effect of Metal Ion Concentration."

The loading capacity is determined at specific aqueous and organic phase conditions. In the organic phase, the extractant concentration is kept constant. In the aqueous phase, the molarity of the acid/ pH is kept constant and the concentration of the metal ion is varied. With the increase in the metal ion concentration, there is an increase in concentration of the metal ion in the organic phase.

There is a linear relationship between [M]_aqueous and [M]_organic up to a point. But when the organic phase gets saturated, there is no further increase in the concentration of the metal ion in the organic phase. These curves are known as extraction isotherms.

The molar ratio of metal to extractant at the loading conditions can be computed. From this data, the loading capacity of the extractant is found out.