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90 ~ 80 70 60 :8 u 50 ~ ~ 40 cJ( 30 20 10 oI 60 The effect of spiking water on the filter paper alongside the Au(III) was also studied. Several authors have studied the beneficial effects of water on the extraction of metal ions in SF-C0 (6). The filter paper was spiked with different amounts of water (0 - 40 1-11) prior to extraction with each reagent. Again C 1 extracted none of the gold. The addition of water had a much smaller effect than pressure variation and for C2 and C4 actually decreased the amount of gold extracted by more than 16%. However, the opposite trend was observed for the ligand C3 where, the percentage extraction was seen to increase from ca 9% to ca 10% when 40 1-11 of water was spiked on to the filter paper prior to extraction. CONCLUSIONS AND FUTURE WORK Extraction of gold(III) by the fluorinated calix[4]arene thiourea derivative is demonstrated on an analytical scale using supercritical CO2. No organic solvent modification is needed. High extraction percentages were obtained and as found by other workers in the field of metal extraction by SFE, it is expected that quantitative extraction is achievable through the incorporation of additional washing steps to recover gold after each SFE run. Other fluorinated calix[4]arenes, functionalized on the lower rim with thiol and thioamide groups, were much less efficient. No extraction of gold is possible when Au(O) is used, unless an oxidant is added to the extraction cell. Addition of Fe(III) in acidic solution onto reduced gold in the extraction cell, does however revive the extraction of gold. Further work is in progress on selectivity, reagent recovery and metal release, and on the use of these promising fluorinated reagents for the extraction of gold from geological and material sources. ACKNOWLEDGEMENTS Research grant support from Enterprise Ireland through the Basic and Strategic Research Programmes is gratefully acknowledged, as is the support in-kind of industrial partners. ABOUT THE AUTHORS Jeremy D Glennon is a graduate of the National University of Ireland, having obtained BSc and PhD degrees in chemistry from University College Dublin. He is director of the Advanced Separations Group in 0: 80 100 120 Temperature / °C Figure 4 Effect oftemperature on the SFE ofgold from filter paper at a pressure of400 atm using synthesized fluorinated tetrameric calixarenes (20 mg reagent, 40pl Au(Ill) standard, 30 min static, 15 min dynamic) With the optimum temperature of 60°C, the pressure was then varied between 200 and 400 atm (Figure 5). No extraction of gold was again recorded with C1; however, some gold was extracted with C2 (ca 17%) and C3 (ca 9%) at the optimum conditions, 60°C, 200 atm and 60°C and 400 atm, respectively. Much higher extractions were recorded with the thiourea calix[4]arene, C4. All of the C4 reagent was observed to be removed from the extraction cell during SFE carried out at 400 atm. 2 ...... C3 ...... C4 2 90 ~ 80 70 ...... C4 ...... C3 0: 60 sg 50 Jj 40 cJ( 30 2 20 10 o'--==,*~::=IIt::::::=--+-_--+-_---I 200 250 300 350 400 450 Pressure / atm Figure 5 Effect ofpressure on the SFE ofgold using synthesized fluorinated tetrameric calixarenes at their optimum temperatures (40pIAu(Ill)standard, 20mgligand, 30 min static, 15 min dynamic) Analytical Chemistry at University College Cork (fji;} ColdBulletin1999,32(2) 57PDF Image | Carrying Gold in Supercritical C02
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