Presence of Masking Agents in the Aqueous Phase:

The role of masking agents in solvent extraction has been discussed in sub-Sec. 3.3.5. Their presence can be made use in carrying out separations which are otherwise difficult to achieve. This amounts to the fact that the presence of the masking agent can improve upon the separation factor. It has been mentioned earlier that the masking agent forms sufficiently strong complexes with the interfering metals to prevent their reaction with the extractant either altogether or raise the pH of extraction to a value below which the metal of interest can be extracted quantitatively without interference. The presence of masking agent is known to slow down the rate of extraction due to slower kinetics of formation of the complex. The applicability of a particular masking agent to an extraction system of interest can be gauged by considering the complex forming constants of both the masking agent and the extracting agent. Masking agents have been used successfully mostly in chelating extraction systems. There are numerous examples and only a few are cited here.