Experimental Study on Bismuth Removal from Lead with Auxiliary Calcium Magnesium

The separation of lead from the impurity bismuth remains a significant challenge, with achieving effective separation being a critical bottleneck in the production of high-purity lead via the vacuum gasification method. This study focuses on lead as the primary subject of investigation, conducting both theoretical and experimental research on the auxiliary conversion of lead through vacuum gasification. The calculations of the Gibbs free energy indicate that, within the temperature range of 600 to 610 K, the impurity bismuth reacts completely with calcium and magnesium, resulting in the formation of the compound CaMg2Bi2. Under optimal experimental conditions, the bismuth compound CaMg2Bi2 is converted into BiCa2. Notably, BiCa2 is nonvolatile and remains in the crucible as a residue. The auxiliary calcium is entirely transformed into CaSe and CaTe, leading to a reduction in the calcium content of the volatile substances from 0.5% to 16 ppm. Similarly, the magnesium content in the volatiles decreases from 0.66% to 187 ppm. Ultimately, the bismuth content in the final product is reduced from 6 ppm to 1.4 ppm, achieving a removal rate of 76.6%, while the direct yield of metallic lead reaches 71%. This process effectively facilitates the separation of metallic lead from the bismuth impurities.