Indium Extraction from Sulfuric Acid Solutions in Systems with Poly(2-ethylhexyl)-phosphonitrile Acid

Abstract

Indium (III) extraction with poly(2-ethylhexyl)phosphonitrile acid (P2EHPNA, HX), di-(2-ethylhexyl)phosphoric acid (D2EHPA), as well as their mixtures with trialkylbenzylammonium chloride (TABAC) from sulfuric acid and zinc sulfate solutions in kerosene was studied. It has been shown that in a wide range of acidity (0.5–2.5 M H2SO4), the extraction capacity of P2EHPNA is much higher than that of D2EHPA. A significant increase in the extraction ability is explained by the absence of cyclic dimerization, characteristic of D2EHPA. Indium extraction decreases with an increase in the acidity of the aqueous solution. It was assumed that indium is extracted into the organic phase by a cation exchange mechanism with the formation of complexes InX3(HX)3n–3 and InX3(HX)2n–3, where HX is the monomer group of the extractant, and n = 2÷4. The introduction of TABAC into the organic phase containing P2EHPNA and D2EHPA leads to a strong decrease in the extraction ability of the reagents. The isotherm with 0.3 mol/dm3 of P2EHFNA in kerosene has a steep character. This makes it possible to extract almost completely (> 99%) in 1–2 steps with indium content of 0.5 g/dm3 in the initial solution. Since the stripping of In with mineral acids from P2EHPNA is impossible, its stripping was carried out with alkaline solutions of a complexing agent (polyhydric alcohol – sorbitol). It was shown that the degree of stripping with sorbitol solutions (2.0 M NaOH + 2.0 M sorbitol) is about 100% already in 3 minutes of phase contact. It has also been shown that when P2EHPNA in kerosene is used, not only almost complete strippig of indium with sorbitol solutions takes place, but also its noticeable concentration in re-extracts in one step (~ 35 g/dm3). At the same time, the phase separation was fast and high quality. It is obvious that the extraction systems with P2EHPNA is of interest for indium extraction from various technological solutions. This work was conducted within the framework of the budget project 0287-2021-0014 for Institute of Chemistry and Chemical Technology SB RAS using the equipment of Krasnoyarsk Regional Research Equipment Centre of SB RAS.