Activity concentration of natural radionuclides (238U, 226Ra, 232Th, 228Ra, 210Pb and 40K) in soil amended with niobium tailings

Abstract

The storage of tailing from anthropic activities like mining, which may contain radionuclide traces, is a problematic situation consequent from NORM industries activities and for which they seek alternatives. The study presented in this paper is related to carbonate deriving from niobium extraction. This carbonate is stored in dams, which can cause an increase in radionuclides and metals concentration, imposing restrictions on its use. To ensure the safe usage of the residue, it is assessed the activity concentration of 238U, 226Ra, 232Th, 228Ra, 210Pb and 40K in soil samples as well as mixture soil + carbonate, soil + carbonate + lime, soil + lime and soil. The techniques used were gamma spectrometry and instrumental neutron activation analysis. Activity concentration evaluation was performed before and after the tillage of lettuce (Lactuca sativa) and bean (Phaseolus vulgaris), and the soil-plant transfer factor was determined for lettuce. The study of radionuclides and metals availability in the soil solution is important for a better understanding of the mobility of contaminants in water/soil systems, in order to estimate the real environmental impact. Preliminary results show samples with niobium traces presented values within the recommended world values.