One-step extraction of bismuth from bismuthinite in sodium carbonate–sodium chloride molten salt using ferric oxide as sulfur-fixing agent

Abstract

In view of serious shortcomings existing in the current bismuthinite metallurgical process, such as high energy consumption, low recovery rate of bismuth and low-concentrate SO₂ fume pollution, a clean process was proposed, which involves molten salt smelting of bismuthinite concentrate. Using Na₂CO₃–NaCl molten salt as reaction medium and Fe₂O₃ as sulfur-fixing agent, crude bismuth could be produced directly with high recovery—more than 97%—and high bismuth grade—around 90%. To identify the reaction mechanism, thermodynamic calculations and mechanistic experiments were performed and the results indicated that the reducing and sulfur-fixing reactions of Bi₂S₃ occurred easily and that sulfur was fixed mainly in the form of FeS. To regulate the bismuth extraction process, the effects of a range of parameters during the bismuthinite smelting were comprehensively investigated, including smelting temperature and time, dosage and composition of molten salts, dosage of coal powder. Confirmation experiments were also carried out and 79.63% of lead and 95.00% of silver were collected in the crude bismuth. This study is beneficial for the further optimisation of the bismuth glance smelting process and its potential application to other sulphide ore extractions.