Study of the behavior of iodine and rhenium during oxidative roasting of lead cake

Abstract

Oxidative roasting aims to convert rhenium into a water-soluble form, followed by leaching into solution and subsequent sorption–desorption steps to obtain ammonium perrenate. It was found that the presence of iodine significantly affects the technological parameters of rhenium extraction during sorption and desorption stages, reducing the ion-exchange capacity for rhenium due to the simultaneous transition of iodide and perrenate species into solution. The main objective of this study was to determine the technological parameters that ensure effective separation of iodine and rhenium during oxidative roasting. Experimental data showed that the maximum transfer of rhenium (up to 95.6%) into water-soluble compounds occurs at 300–400 ℃, when iodine compounds have not yet volatilized. At temperatures above 400 ℃, iodine sublimates mainly as PbI₂, accompanied by a decrease in rhenium extraction efficiency. It was experimentally established that, under optimal roasting conditions, rhenium is concentrated in the solid phase as perrenates and iodides, ensuring almost complete dissolution during subsequent leaching. The volatilisation of iodine at elevated temperatures leads to the decomposition of rhenium iodides and the formation of insoluble metallic phases, thereby negatively affecting extraction.