Study on continuous crystallization and purification of bismuth from Pb-Bi alloy

Abstract

The crude bismuth obtained from the smelting of bismuth concentrate and bismuth-containing by-products contains 5~20% lead, which needs to be removed during the refining of crude bismuth. Due to the similar physical and chemical properties and metallurgical behaviour of lead and bismuth towards each other, it is not easy to be separated by conventional methods. Although the conventional process of chlorination of crude bismuth to remove lead can meet the requirements of the refining process, the amount of chlorinated slag produced is large and the safety of chlorine gas is difficult to control, making it difficult to achieve clean production. In this paper, single-factor experiments and semi-industrial experiments for the separation and purification of bismuth from Pb-Bi alloy were carried out by continuous crystallization method, and the results showed that the bismuth content of Pb-Bi alloy was increased from 90.24% to 98.98%, the direct yield of bismuth was 87.37%, the metal recovery rate was 99.84%, the The slag production rate was 0.62%. In comparison with existing processes and studies, the method is low cost, clean and efficient, has a wide treatment range, can be operated continuously, and can be easily industrialised and promoted. Theoretically, the method combined with the vacuum distillation process to treat Pb-Bi alloys with bismuth content greater than 55.5% can obtain 99.99% of bismuth products.