ABSTRACT
In hydrometallurgical processing, the role of solvent extraction reagents is predominant among many factors to improve extraction and separation efficiencies. Ten requirements have been identified for industrial use of commercially available extractants,1-3 as follows:
1. High selectivity for the target ion 2. Direct extraction from leachate without pH adjustment 3. Sufficiently fast extraction rate 4. Reversible extraction and easy stripping 5. High solubility of the extractant and its metal complex in suitable
diluents (organic solvents) 6. Chemically long-term stability for use (stability to radiation in nuclear
waste solution is also required)
3.1 Introduction ............................................................................................... 81 3.2 Macrocyclic Ligands .................................................................................. 82
3.2.1 Structures and Names of the Compounds ..................................... 82 3.2.2 Characteristics of Calixarenes ....................................................... 83
3.3 Molecular Design of Calixarene Compounds for Metal Extraction ......... 85 3.4 Research on Metal Cation Extraction with Calixarene Derivatives .......... 88 3.5 Conclusions .............................................................................................. 120 References ......................................................................................................... 120
7. Low loss of the extractant to the aqueous phase 8. Clean and quick phase separation with minimal entrained carryover 9. Low price for commercial use 10. Safe for operation (nontoxicity, low volatility, nonflammability)
Although various kinds of extractants have been prepared and examined and even brought into industrial use, no extractant has been found that satisfies all of the above requirements. Thus, in actual practice, compromises must be accepted, leaving considerable opportunity for improvement through dedicated research. The most important factor among the 10 requirements is the first: high selectivity for a given target ion. Conventional preparation of the extractants has been carried out by introducing functional groups for extraction of a target ion, together with adequately long alkyl chains and phenyl groups for high lipophilicity and minimal solubility loss to the aqueous phase.
