Use of Diluents for commercial applications:

One of the important cheap diluents for industrial use is kerosene particularly its 1600- 2000 C fraction. For commercial applications, particularly in hydrometallurgy, a range of diluents has been developed by major oil companies. In general, these diluents contain a mixture of paraffinic, aromatic and naphthenic hydrocarbons. The Excaid range from Exxon (Escaid 100, Escaid 110, Escaid 350), MSB 210, Shell 140, Shell R from Shell and Chevron Ion Exchange solvents speak of the variety of commercial diluents available.

In the earlier section, we have noticed that the diluents affect the extractability of an extractant to a great extent. It has become apparent that diluents are not as inert, as they might appear to be. Various workers have tried to correlate different properties of the diluents with the extraction efficiency of a system. The mechanism of the role of the diluent seems to be complex. One property of the diluent which has received special attention is its polar nature. In the extraction of rare earth nitrates with Aliquat 336, a decrease in the extraction of the metals with the polar nature of the diluent was observed. Similar effect was noticed on the extraction of anionic chloro species in tertiary amines. From different observations, one may conclude that the diluent affects the solvation of the extractant and hence, its extractive properties. Interaction between the diluent and the extractant lowers the free concentration. The effect of dielectric constant of the diluent in some other systems was observed and no straight correlation could be observed. It is difficult to ascribe the change in extraction solely to the dielectric constant. Other effects such as impurities, degree of aromacity, solubility of diluent in water, etc. may also be involved.

One thing clearly emerges out of the above discussion that the choice of a diluent for a particular process cannot be predicted, a priori. A diluent is usually picked up on the basis of the experimental data. Diluents are usually produced on industrial scale resulting in some variations in their composition. These variations and the presence of impurities may alter the behaviour of diluents.