Removal of impurities from bismuth pickling solution using solvent extraction with TBP

This work proposes an extraction process for thorough removal of various impurities in crude bismuth. In the process, crude bismuth was pickled with nitric acid, and then the bismuth in the filtrate was extracted into the organic phase by TBP. After scrubbing with a saturated NaNO3 solution, stripping was carried out by NaOH solution, and a rod-shaped α-Bi2O3 precipitate was obtained. Increasing the concentration of NO3− and TBP and the ratio of Vo/Va could greatly increase the extraction efficiency of bismuth or the separation factor of impurities. Bismuth is extracted in the form of Bi(NO3)3·TBP, and the results of quantum chemical calculations indicated that both intermolecular forces and chemical bonds exist between the Bi(NO3)3 and TBP molecules. Thermodynamic analysis based on the Debye-Hückel equation under large ionic strength conditions showed that the extraction reaction is exothermic and proceeds spontaneously. Under the optimized extraction conditions, the extraction efficiency, elution efficiency, and stripping efficiency of bismuth were 98.5%, 0.55%, and 96.2%, respectively. All of the impurity elements were thoroughly removed after extraction. In particular, the separation factor βBi/M of M = Te, As, Cu, and Sb, which are prone to codeposition with bismuth during electrodeposition, were 160, 183, 982, and 359, respectively. The purity of α-Bi2O3 obtained by this method was as high as 99.95%