Removal of radionuclides from process streams - a survey

This report details the origin and control of radium 226, thorium 230 and lead 210 contamination of mill effluent streams from conventional and non-conventional milling of uranium ores, reviews the basic chemistry of the radionuclides as it relates to potential alternatives for control and presents these alternatives along with a summary of published cost data. The conclusions from the study indicate that the current technology, using sulphuric acid processing, solubilizes only a comparatively small quantity of the radionuclides, with the solid tailings containing approximately the same concentration as the original ore. Present technology does not provide for complete removal and isolation of the radionuclides. Current practice for control of thorium 230 in liquid effluents by neutralization is adequate to meet present Governmental guidelines. Radium in solution is presently being controlled by precipitation with barium chloride but levels of less than 3 pCi/L of soluble radium could be difficult if not impossible to achieve consistently by this treatment. A specification limit of 10 pCi/L would appear possible to achieve, but such a target level of 10 pCi/L for a total radium in tailings effluent will not be attained by simple settling of barium radium sulphate. Additional technology may be required although the use of flocculants appears promising. Indications are that the concentration of lead 210 in liquid effluent may exceed present guidelines. No specific control procedures are employed for lead 210. The leaching characteristics of the radionuclides from solid tailings are such that on mill shutdown, seepage and run-off will have to be treated to prevent environmental contamination. Alternatives include processing of tailings,toTeu,ge,tbe.rpdionuctie,..concentration or using different process technology that woul_be,ec,opomi, cally and environmentally acceptable for the processing and recovery of uranium from ores. These technologies are in the early stage of'development. A level of 50 pCi/g radium 226 in finaUta'hbilids,àeeàrs, attainablelinLpeactice; one prOcess produces a level of 10-20 pCi/g. Methods of isolating radrüM226Aare required for treating effluents from con; ventional m:i41l1Gl:)i ng _as.well as,from,alternative . _ pi bj of_isola.tiqg these radionuclides.