Extractants Containing Carbon-Oxygen Bonds:

As mentioned earlier, the extractants of this class are essentially ethers, ketones and alcohols. They are electron donating reagents but alcohol being amphoteric, exhibits both donor and acceptor properties. These extractants did receive attention during the earlier part of development of metal extraction chemistry. Diethyl ether and diisopropyl ether were at one time very favoured extractants for metal halides and halometallic complexes. They were also used as extractants for metal nitrates resulting into the development of separation technology for nuclear fuel reprocessing. Metal sulphates and percholates are generally nonextractable into these solvents. Only one ketone, methyl isobutyl ketone (MIBK) has been used commercially for the extraction of metals.

It has been shown that inorganic salts, soluble in water immiscible oxygen bearing organic solvents, are usually weak electrolytes or they involve a complex ion. The main characteristic of extraction from aqueous halide solutions by oxygen containing solvents is the extraction of protonated metal complex anions, preferentially singly charged ones, (H⁺.FeCl₄^-). An equally important feature of the system is the high extractability of essentially covalent metal halides. The striking difference between the two is that the halo complexes are extractable into oxygenated solvents only while the halides can be transferred into nonpolar hydrocarbons also. With some restrictions due to aqueous complex chemistry of metals in halide solutions, higher extractions are observed for monovalent complex anions of bivalent and trivalent transition metals. Inspite of pronounced complexing tendencies of bivalent metals, the high charge on the complex MX ₄^2- prevents their extraction into relatively high dielectric constant solvents such as butanol and octanol.