Process for the selective recovery of transition metals from organic residues

Process for the selective recovery of transition metals from an organic stream having a boiling point higher than or equal to 340° C. and containing transition metals which comprises the following steps:

• a. melting up to the liquid state said organic stream and possibly a first extractor if solid, where said first extractor consists of an ionic liquid or a mixture of two or more ionic liquids, wherein said ionic liquid contains a quaternary ammonium salt or a quaternary phosphonium salt as cation and an anion with chelating properties as anion;
• b. feeding to a first liquid-liquid extraction unit working at a temperature of at least 150° C. said molten organic stream and said first extractor, optionally melted, and carrying out the liquid-liquid extraction, obtaining a liquid mixture containing an ionic liquid, or a mixture of two or more ionic liquids, and the metals;
• c. after extraction, cooling at a temperature comprised between 0° C. (zero degrees centigrade) and 70° C. said liquid mixture, which after cooling is biphasic, and subsequently sending the biphasic mixture to a first liquid-solid separation unit, to separate a liquid phase that contains ionic liquids and metals, and a metal-depleted solid phase;
• d. after the first separation, the separated metal-depleted solid phase is optionally sent to a washing unit to which a solvent is fed, so as to eliminate the residual ionic liquid by keeping it into the solvent and obtaining a washed metal-depleted solid;
• e. sending the separate liquid phase containing ionic liquids and metals into a liquid-solid precipitation and separation unit and adding a counter-solvent, thereby obtaining a solid phase containing the metals and a liquid flow containing counter-solvent and ionic liquids,
• wherein the anion is selected from salicylate, thiosalicylate, acetate, citrate, oxalate, malonate, dicyanoamide, and glutarate, and
• wherein in the extraction step, in addition to the ionic liquid, an extracting agent selected from the group consisting of thiocarbazones, thiocarbamides, mercaptobenzenes and aromatic carboxylic acids containing a thiol group is used.