HOMOGENEOUS LIQUID - LIQUID EXTRACTION OF METAL CATIONS AT NEAR NEUTRAL PH.

摘要

Solvent extraction procedures are, for the most part, performed at low pH to prevent hydrolysis of the cations, the very condition which limits the concentration of the extracting ligand, an anion. At low pH the undissociated species is predominant and, therefore, the formation of extractable species is not favored. The cation of interest can be maintained in solution at near neutral pH by adding an auxiliary complexing agent to form a charged complex, and then the cation can be extracted into a non-polar solvent by equilibration with another complexing agent which forms a neutral complex. Thus, it is possible to maintain conditions of higher pH to favor the enolate ion form of chelating extractants, and the anionic form of the various monodentate complexing agents. This technique has been studied in conjunction with homogeneous liquid-liquid solvent extraction into propylene carbonate, which forms a homogeneous solution with an aqueous phase when heated above 71(DEGREES)C. Thus, extraction is achieved with heating and cooling upon which the phases separate. Also, propylene carbonate yields a homogeneous phase with water and ethanol in the ratio, propylene carbonate/water/ethanol 2:2:1; thus permitting direct comparison by, e.g., absorption spectrophotometry of aqueous phase, organic phase and calibration standards.;A method was developed to extract uranium from ores and fuel elements using homogeneous liquid-liquid solvent extraction.;Thenoyltrifluoroacetone chelates of Fe(III), Co(II) and Cu(II) have been extracted from an aqueous phase containing tartrate, at pH values from 6 to 8, into propylene carbonate by the homogeneous liquid-liquid extraction technique. The extractions were very rapid, and quantitative under optimum conditions. Iron(III) was also quantitatively and rapidly extracted with acetylacetone under these same conditions. Normal extraction technique into propylene carbonate and toluene also gave rapid and quantitative results for Fe(III)-TTA from this aqueous medium. These results, attributed to the significantly higher ratio of enolate ion, suggest an alternative mechanism for the synergic effect of various organic bases in TTA extractions. Acid-base reactions in the organic phase yield similar higher concentrations of enolate ion in the aqueous phase.