Application of cone packing model in extraction: Pt.1

Synergistic effect in trinary system: substrate1 + substrate2 + extractant, is reported with the extraction for uranyl ion in mixed acetate and chloride substrates by applying cone packing model. Based on the cone packing model, ligand packing around the uranyl equatorial plane should be neither overcrowded nor undercrowded. The sum of ligand's Fan Angle (FA) around the uranyl equatorial plane provides a useful criterion for estimating steric crowding. Whereas FAS of UO2(OAc)2(TBP)2, UO2(OAc)2TBP, UO2Cl2(TBP)2 and UO2Cl2(TBP)3 are 204, 164, 164 and 203 deg respectively, none is favourable to form stable extracted complexes. FAS of UO2(OAc)Cl(TBP)2 is l84 deg indicating the most favorable packing. Therefore synergistic effect based on the formation of extracted complex UO2(OAc)Cl(TBP)2 in mixed acetate and chloride solution was predicted. The above speculation was confirmed by extraction of uranyl ion in the substrates of sodium acetate-acetic acid and ammonium chloride. Keeping the total concentration of substrates constant, synergistic extraction is found at l:3 acetate to chloride ratio which shifts a little on changing concentration of the uranyl ion from 3.97 x 10-4 mol·dm-3 to 2.06 x 10-2 mol·dm-3. The extracted complex was proved to be mostly UO2(OAc)Cl(TBP)2 by using the slope method and analysing the uranyl and chloride concentration in organic phase. Variation of the distribution coefficient of synergistic effect with the pH of the medium was studied. The similiar effect was found with other oxtractants and diluents