OBTAINING BISMUTH AND ITS HIGH-PURITY COMPOUNDS

The process of metal bismuth dissolution in nitric acid was studied, and a comparison was made over environmentally friendly methods of obtaining bismuth nitrate solutions by the preliminary oxidation of bismuth, as well as by its dissolution in the presence of urea or ammonium nitrate. It has been shown that the dissolution of bismuth in the presence of ammonium nitrate at a molar ratio of ammonium nitrate to bismuth equal to 1.5-3.5 and a temperature of 70±5 °C allows eliminating the release of nitrogen oxides into the gas phase and obtaining a solution with a high concentration of bismuth. The feasibility of two-stage hydrolytic processing of a bismuth-containing nitrate solution in order to purify bismuth from impurity metals is shown. The first stage is the aqueous hydrolysis of a bismuth-containing solution by adding a bismuth nitrate solution to water heated to 60 °C at a volume ratio of water to bismuth-containing solution 9 : 1, and the second stage is additional precipitation of bismuth from the mother solution after aqueous hydrolysis by adding ammonium carbonate solution to reach pH 1 at a temperature of 55±5 °C. Based on the research carried out, ecologically safe technologies have been developed for the production of bismuth oxohydroxonitrate [Bi6O5(OH)3](NO3)5•3H2O and bismuth nitrate pentahydrate Bi(NO3)3•5H2O, as well as specially pure bismuth(III) oxide. As a result of the reduction of bismuth(III) oxide in molten sodium hydroxide containing sulphur at a temperature of 500 °C and at a ratio of bismuth(III) oxide/sodium hydroxide/sulphur equal to 1: 1.31: 0.20, high-purity metallic bismuth was obtained.