ИСТИНА

Technologies of rare earth elements (REE) separation are once again attracting attention in view of government’s plans to restore REE industry in our country. Liquid extraction with various phosphorus containing extragents dominated in this field for decades. But the main trend in hydrometallurgy is a turn to sorption and chromatographic separations as more effective, universal and eco-friendly. The restoration of REE industry gives a good chance to build it on the basis of innovative sorption technologies. Among sorbents which can be used for this purpose chemically modified silica looks very promising. Such sorbents are widely used as stationary phases in HPLC and in biotechnology and pharma for isolation and purification of proteins, biologically active compounds, medicines, etc. There are precedents of the use of silica with attached organic ligands in hydrometallurgy, in particular, for separation of platinum metals. In this work we studied two types of silica based sorbents with chemically attached aminocarbonic and aminophosphonic ligands. REE are sorbed on I and II in slightly acidic media at pH > 2, sorption increases with the increase of pH. For II sorption occurs also in high acidic solutions due to complexation with phosphoryl moiety. Sorption on I strongly depends on ionic strength of the solution decreasing with its increase. It may be explained by the variation of surface stability constants due to electrostatic interaction between ionized functional groups. Selectivity of sorption of different REE on I perfectly corresponds to the ratio of their stability constants with N-substituted iminodiacetic acid. In contrast to divalent non-ferrous metals, ions of REE form different complexes with attached iminodiacetic acid. Their ratio depends on the distance between attached ligands and therefore on the sorption capacity of sorbent. We have shown that selectivity of sorption can be enhanced by lowering of sorption capacity. Sorption of REE on sorbents I and II proceeds rather fast, within 30 min, but considerably slower than in the case of non-ferrous metals due to low rate of REE complex formation. The increase of temperature is one more instrument to increase the performance of REE separation.