Adsorption study on PGM elements by AlHCF from nitric acid solution

Mishima, Ria ; Tachioka, Sotaro*; Inaba, Yusuke*; Harigai, Miki*; Matsumura, Tatsuro  ; Watanabe, Shinta*; Onoe, Jun*; Nakase, Masahiko*; Takeshita, Kenji*

In Japan, the final disposal of high level liquid waste (HLLW) will be done after vitrification into borosilicate glass and then disposed into deep underground. In this vitrification process, there are some concerns. The first concern is precipitation of platinum group metals (PGMs) in the melter due to their low solubility into borosilicate glass. The second concern is the formation of yellow phase caused by Mo content. The final concern is the generation of huge number of vitrified glasses and the requirement of wide space needed for final disposal. Among many kinds of extractants and adsorbents for separation of such metal ions, metal hexacyanoferrate (HCFs) were reported to have an ability to adsorb PGMs. The objective of this study is to elucidate the adsorption behavior of aluminum hexacyanoferrate (AlHCF) for various metal ions and understand the relation between elution and adsorption. The effect of synthetic and workup conditions on PGM and Mo adsorption from simulated HLLW (sHLLW) was surveyed. Also, the relationship between adsorption of metal ions and elution of the AlHCF was studied. The synthesized AlHCF showed adsorption performance for PGMs and Mo in simulated HLLW. As a result of an adsorption test with a Pd single component solution to investigate the adsorption mechanism, the eluted element ratio was Fe:Al = 1:4 in the Pd adsorption test. However, the element ratio was Fe:Al = 3:4 in the original AlHCF. Therefore, it was suggested the existence of not only Pd adsorption, but also resorption and stabilization mechanisms.