QUANTITATION OF CATION BINDING BY SILICA-GEL BOUND THIAMACROCYCLES AND THE DESIGN OF HIGHLY SELECTIVE CONCENTRATION AND PURIFICATION COLUMNS FOR PALLADIUM(II), GOLD(III), SILVER(I), AND MERCURY(II)

The macrocycles 1,4-dithia-19-crown-6 (T(2)19C6) and 1,4,7,10-tetrathia-18-crown-6 (T(4)18C6) were chemically bonded to silica gel. Binding constants (K) for the interaction of Pd2+, Au3+, Ag+, and Hg2+ with the immobilized macrocycles were determined using a strongly complexing anion or NH3 so the concentration of uncomplexed cation would be low enough to prevent quantitative loading of the column. Binding constants for Cu2+, Fe3+, and other base metals were at least 10 orders of magnitude less than constants for Pd2+, Au3+, Ag+, and Hg2+. Values of K were higher for T(4)18C6 than T(2)19C6. Immobilized thiamacrocycles effectively removed Au(III) and Pd(II) from 1 L of 1 M HCl and 1 M FeCl3. The gold and palladium were then eluted in 10 mL of a thiourea solution. Parts per billion analyses of Au(III) and Pd(II) performed by using this preconcentration step were within 5% of the expected value. Similar analyses for Hg2+ and Ag+ were performed in NO3- matrices. Au(III), Ag(I), and Pd(II) were separated with purities of 99.9% by binding them to the macrocycle column and selectively eluting with Br-, then I-, and finally ethylenediamine. In another experiment, palladium was removed from an industrial silver electrolyte solution with 99.9% purity in one pass through the column.