Selective recover of bismuth by amide extractant from chloride leaching of lead anode slime and the mechanism

Solvent extraction has been identified as a highly effective method of overcoming the challenges associated with separating Pb and Bi. This study aimed to determine the separation and purification requirements for the acid leaching solution from lead anode slime. The study proposes a separation process utilising N218 as the extractant. By optimising the extraction conditions and implementing a six-stage countercurrent extraction method, the extraction of Bi^{3 +} was improved, achieving an extraction efficiency of 99.32 %. Pb²⁺ impurities were removed through a three-stage cross-flow washing process using BiCl₃+HCl, successfully achieving the effective separation of bismuth and lead. Following hydrochloric acid stripping and electrodeposition treatment, the resulting bismuth purity was found to be 99.99 %, indicating a high degree of purity. This research addresses the challenges of separating bismuth from toxic metals such as lead and antimony. The study proposes a coordination structure with a 3:1 stoichiometry (N218:Bi) for the complex formed between the amide extractant and Bi³⁺ in a perchlorate system. And proton participation is involved. In contrast to the 1:1 or 2:1 coordination modes of amides reported in other metal systems in the existing literature, this 3:1 coordination pattern has been reported for the first time in this Bi³ ⁺ extraction system. It reveals that the inhibitory effect on the amide extraction system intensifies with increasing radius of the alkali metal cations, and elucidates the underlying mechanism.