The Liquid-Liquid Extraction of Alkali Metals as Their Poly-Iodides

Abstract It has been known that alkali metal ions can be extracted into nitrobenzene as their poly-iodides, but the extraction has not been attempted for various salts of alkali metals except in the case of their iodides. In this research ammonium iodide and elemental iodine were preferentially added to the extraction system in order to convert various alkali metal salts into poly-iodides. Ammonium iodide should be larger than the equivalent amount to an alkali metal present in an aqueous solution. The ratio of free iodine to ammonium iodide is an important factor; when the ratio is more than three, a higher distribution ratio is obtained. The ratio of iodine to iodide in the organic phase after the extraction is estimated to be six; therefore, the extracted species seems to be heptaiodide. The extractability of alkali metals increases in the order: Li–Na–K–Rb–Cs, and the distribution ratio decreases with the increase in the amount of metal ions taken in. Back extraction is achieved by shaking the organic phase with 10 m nitric acid. The separation factor between the metals is too low for them to be separated from one another.