Solvent Extraction of Metal Ions with Carboxylic Acids

Solvent Extraction of Metal Ions with Carboxylic Acids A. Equilibrium Treatment 

As stated earlier the polymeric species are often involved in the extraction of metal carboxylates. Therefore, the extraction equilibrium is sometimes more complicated than in the chelate extraction system. As is evident from the following treatment, it is advantageous and often indispensable to study the total metal concentration in the organic phase [Eq. (8)] instead of the conventionally utilized distribution ratio of the metal [Eq. (7)]. 

When a y-merized metal carboxylate of the composition MjAaHA (nj = a — h) is responsible for the extraction of a metal ion MB + with a carboxylic acid HA, the extraction equilibrium is written as  

The distribution ratio (D) of the metal between the organic and aqueous phases is given by 

According to Eq. (9), the conventional plot of log D against —log[H+] at a constant [(HA)2]D should yield a straight line with a slope of n only when j and aM are equal to unity. For the polymeric extracted species, the distribution ratio, D, depends not only on [H+] and [(HA)2]Q but also on the metal ion concentration. Therefore, the plot according to Eq. (9) yields a curve (Fig. 1). As shown in Fig. 1, the plot falls on the straight 

---

In the solvent extraction of metal ions with carboxylic acids, it is indispensable to have information about the partition of the carboxylic acid between the aqueous and organic phases. The carboxylic acid is known to dimerize in nonsolvating solvents. 

---