[Introduction]
Gallium and indium are typical critical metals and have been employed as raw materials for advanced industry. Nevertheless, they do not form their own ores deposits in primary source and are produced as by-products from zinc and aluminum ores [1,2]. Their similar chemical properties make their separation difficult. The new extraction reagents such as tris(2-hydroxybenzyl)amine [3], aminophosphonic acid [4,5], thioglycolate [6], calixarenes [7,8], and tripodal compounds [9], were applied for their separation. In this work, we have newly prepared monoamido-monocarboxy phenanthroline (PTACA) derivatives with different amido side chains to investigate the extractive separation of aluminum group and other metals.
[Experimental]
2-Monoamido-9-monocarboxy-1,10-phenanthroline derivatives with different amido side chains have been prepared from dimethyl derivatives by 7 steps. The obtained compounds were identified by infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, and thin-layer chromatography.
The extraction study was performed using a conventional batchwise method. The organic phase was prepared by dissolving the extraction reagent in diluent to the desired concentration. The aqueous phase was prepared by dissolving each metal chloride at a concentration of 0.10 mM in 0.10 M HCl or 0.10 M NaCl. The two aqueous solutions were mixed arbitrarily to adjust the pH values. Equal volumes of both the organic and aqueous phases were mixed and shaken (150 rpm) for an adequate time at 30 °C. After phase separation, the pH values and metal concentrations were determined using a pH meter and inductively coupled plasma atomic emission spectrophotometry, respectively.
[Results and Discussion]
Compared with commercially available Versatic Acid 10 (VA10), PTACA derivatives exhibited extremely high extraction ability owing to tetradentate framework. Five hundred milli molar of VA10 exhibited Fe3+ extraction around pH 2.5 without any extraction of Al3+, Ga3+, and In3+, whereas only 5 mM PTACA derivatives exhibited complete extraction of In3+ even at pH 1, partially extraction of Fe3+, and without any extraction of Al3+ and Ga3+ with extremely high separation efficiency for In3+. This selectivity was caused by size discriminating property of coordinating site organized by phenanthroline framework and the attached amido and carboxy groups. Extraction and separation efficiencies were related to amido side chains of PTACA probably owing to steric hindrance of amido side chains.
The extraction equations of Fe3+ and Ga3+ (In3+ extraction was too good to be evaluated, while Al3+ extraction was poor to be evaluated) were determined by slope analysis as follows;
M3+ + HR + 2Cl- ⇌ MRCl2 + H+
And extraction equilibrium constants of Fe3+ and Ga3+ with PTACA derivatives were estimated.
[Conclusion]
2-Monoamido-9-monocarboxy-1,10-phenanthroline (PTACA) derivatives with different amido side chains were prepared to investigate the extractive separation of aluminum group metals and trivalent iron. PTACA derivatives exhibited high extraction ability and separation efficiency In3+ owing to size discriminating effect of phenanthroline framework and the attached amido and carboxy groups.
[References]