Extractability of the metal chelate:

The extractability of the metal chelate is affected by its solubility characteristics in organic solvents. If a methyl group on the molecule of chelating agents is substituted by a benzene ring, an increased solubility of metal chelate in non- polar solvents is observed. Generally, introduction of a hydrophobic group in the chelating molecule favours the transfer of its metal chelate in the organic phase. If the coordination number requirements of the metal in the metal chelate are satisfied by the water molecules, the chelate is poorly extracted in non-polar solvents. An increased extraction of these chelates is observed by oxygen containing diluents, polar in nature such as ketones, esters and alcohols. This increased extraction of metal chelates is attributed to their ability to replace water molecule in the metal chelate. Such a cooperative effect of a chelating agent and a solvent with solvating properties to enhance the extraction of metal will be dealt under the head of "synergistic extraction". The well-known reagents under the head of chelating agents are β -diketones, dithizone, 8- hydroxyquinoline, monoximes, dioximes, nitrosophenols, nitrosoarylhydroxylamines, hydroxamic acids and dithiocarbamates. Some of the acidic chelating agents commercially available in the market for the hydrometlurgical operations are LlX63, LlX64N, LlX65N, LlX70, SME-529, P-5000 series (hydroxyoximes); Kelex 100 (oxine derivative) and Hostarex DK16, LlX 54, X 151 ( β -diketones).