Molten lithium nitrate-potassium nitrate eutectic: the reaction of bismuth compounds

Abstract

Bismuth(III) chloride reacted in pure molten lithium nitrate-potassium nitrate eutectic, initially forming insoluble bismuth oxychloride from 210° C, and then substituting oxide for chloride from 425° C to give more complex oxychlorides. Melts containing potassium nitrite caused the same Lux-Flood acid-base reactions, though at lower temperatures, but melts containing potassium chloride stabilised bismuth(III) in solution until higher temperatures were reached. Acidic melts containing potassium pyrosulphate reacted, but caused little difference in the bismuth(III) reactions. However, with the weaker Lux-Flood acid, potassium dichromate, chromate was substituted for chloride at higher temperatures, bismuthyl chromate being formed from bismuthyl chloride. In basic melts containing sodium hydroxide, the initial bismuthyl oxychloride precipitate was converted to bismuth(III) oxide at higher temperatures, or higher hydroxide concentrations. However, when both the latter became even larger (e.g. at 500° C for 48 h, Bi : OH = 1:14.5) lithium orthobismuthate(V) was formed. Less extreme conditions for the formation of the bismuthate(V) were required when the melt was made basic with sodium peroxide, and when bismuth(III) nitrate was substituted for the chloride. Sodium bismuthate(V) was not stable in pure nitrate eutectic, decomposing to bismuth(III) oxide and lithium bismuthate(III).