*Article* **Study on the Extraction and Separation of Zinc, Cobalt, and Nickel Using Ionquest 801, Cyanex 272, and Their Mixtures**

**Wensen Liu 1,2,3, Jian Zhang 3,4,5, Zhenya Xu 6, Jie Liang 1,\* and Zhaowu Zhu 2,3,4,\***


<sup>3</sup> National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Beijing 100190, China; zhangjian01@ipe.ac.cn


**Abstract:** Both Cyanex 272 (bis (2,4,4-trimethylpentyl) phosphinic acid) and Ionquest 801 (2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester) are commonly used for metal extraction and separation, particularly for zinc, cobalt, and nickel, which are often found together in processing solutions. Detailed metal extractions of zinc, cobalt, and nickel were studied in this paper using Cya-nex 272, Ionquest 801, and their mixtures. It was found that they performed very similarly in zinc selectivity over cobalt. Cyanex 272 performed much better than Ionquest 801 in cobalt separation from nickel. However, very good separation of them was also obtained with Ionquest 801 at its low concentration with separation factors over 4000, indicating high metal loading of cobalt can significantly suppress nickel extraction. Slop analysis proved that two moles of dimeric extractants were needed for one mole extraction of zinc and cobalt, but three moles were needed for the extraction of one mole nickel. A synergistic effect was found between Cyanex 272 and Ionquest 801 for three metal extractions with the synergistic species of *M(AB)* determined by the Job's method.

**Keywords:** solvent extraction; cyanex 272; ionquest 801; zinc; cobalt; nickel
