Vacuum Distillation Additives In Addition To Lead Preparation Of Fifty-nine Purity Bismuth New Technology

With the development of science and technology, the demand for high-purity bismuth is more and more, and the studies on high-purity bismuth have drawn great attention of researchers. However, there are some problems which are needed to be resolved when the traditional vacuum distillation is used to obtain "5N" high-purity bismuth from "4N" rich bismuth, one of them is that to remove lead in vacuum furnace is very difficult. The primary aim of this paper is to obtain "5 N" high-purity bismuth through converting lead to lead compound to be removed by reagent addition in a vacuum furnace.Firstly, the present situation on the study of high-purity metals and the recent development on preparation of high-purity metals with vacuum distillation at home and abroad were reviewed in detail. The properties, uses and production situation of bismuth were also reviewed.Secondly, the feasibility of separation of impurities in rich bismuth and reagent (sulphur or chlorine) deleading with vacuum distillation was studied in theory. Thermodynamics studies show that by adding sulphur or chlorine, the lead can be converted to lead sulfide or lead chloride to be removed effectively. For sulphuring deleadization, it is favorable for the separation of bismuth sulfide and lead sulfide from bismuth in higher temperature. However, for the chlorinate dedeleadization, it is easier to separate bismuth chloride and lead chloride from bismuth. The content of other impurities in rich bismuth can be decreased to the level of "5N"high-purity bismuth by vacuum distillation. Dynamics studies show that in order to increase the productivity of equipments and obtain low cost and achieve more economic benefit, a suitable temperature and reasonable vacuum degree are needed when vacuum distillation is adopted to purify rich bismuth.And then, minitype experiment studies on reagent deleadization were carried out in the vacuum furnace. The influence of amount of reagent, distillation temperature, vacuum degree and distillation time on the effect of deleadization were investigated and an optimal technical condition was achieved as following (see Table 1): Table 1 The optimal technical condition of reagent deleadizationOn this condition, the content of lead in rich bismuth can be decreased from 30ppm to 0.21ppm (sulphuring deleadization) or 0.24ppm (chlorinate deleadization), which has reached the level of "5N" high purity bismuth.Studies on the influence of vacuum distillation on other impurities in metal bismuth by minitype experiment show that if temperature is between 1223K~1273K, remnant pressure is about 16 Pa, bismuth volatilization rate is more than 80%, the content of impurity in the condensate can reach the level of the "5 N" high purity bismuth except for copper, lead and iron and the bismuth content in the condensate is 99.9994%. According to this result, experiments on reagent deleadization were carried out. Results show that the content of lead reaches the level of the "5 N" high purity bismuth and the content of bismuth achieves to 99.9997%.Finally, a multilevel internal-heat type vacuum furnace that meets our study were proposed on the basis of above studies.