Mobility of 232Th and 210Po in red mud

The valorization of industrial by-products such as red mud became a tempting opportunity, but the understanding of the risks involved is required for the safe utilization of these products. One of the risks involved are the elevated levels of radionuclides (in the 100-1300 Bq/kg range for both the U-238 and Th-232 decay chains, but usually lower than 1000 Bq/kg, which is the recommended limit for excemption or clearance according to the EU BSS released in 2013) in red mud that can affect human health. There is no satisfactory answer for the utilization of red mud; the main current solution is still almost exclusively disposal into a landfill. For the safe utilization and deposition of red mud, it is important to be able to assess the leaching behaviour of radionuclides. Because there is no commonly accepted measurement protocol for testing the leaching of radionuclides in the EU a combined measurement protocol was made and tested based on heavy metal leaching methods. The leaching features of red mud were studied by methods compliant with the MSZ-21470-50 Hungarian standard, the CEN/TS 14429 standard and the Tessier sequential extraction method for Th-232 and Po-210. The leached solutions were taken to radiochemical separation followed by spontaneous deposition for Po and electrodeposition for Th. The 332 +/- 33 Bq/kg Th-232 content was minimally mobile, 1% became available for distilled water 1% and 6% for Lakanen-Ervio solution; the Tessier extraction showed minimal mobility in the first four steps, while more than 85% remained in the residue. The Po-210 measurements had a severe disturbing effect in many cases, probably due to large amounts of iron present in the red mud, from the 310 +/- 12 Bq/kg by aqua regia digestion, distilled water mobilized 23%, while Lakanen-Ervin solution mobilized similar to 13%. The proposed protocol is suitable for the analysis of Th and Po leaching behaviour.