Study of the dynamic lixiviation of 226Ra from phosphogypsum by an automatic system previous radiometric detection

Abstract

The phosphogypsum (PG) is a by-product from phosphate fertilizer industry, it is produced in large amount, and contains naturally radionuclides, principally 226Ra and these decay products. The lixiviation study of the radionuclides from PG has great industrial and environmental importance due to the reutilization possibilities. A study of dynamic lixiviation of 226Ra in PG samples was carried out with an automatic system composed by a lab-on-valve and multisyringe flow injection analysis. Artificial rainwater at two different pH (5.4±0.2 and 2.0±0.2), was used as leaching agent. The PG sample was placed in a designed column, and the leaching agent passed through the column at a flow rate of 3.5 mL min-1.Eightleaching fraction of 30 mL each one were recollected. Each leaching fraction was analyzed in an automatic system for the extraction/pre-concentration of 226Ra, which is absorbed on manganese dioxide formed on cellulose beads. Then, 226Ra is eluted with hydroxylamine and finally co-precipitated with barium sulfate. The 226Ra activity was measured with a low background proportional counter. The specific activities of the leaching are between 28 and 12 Bq Kg-1 from artificial rainwater at pH 2, and in the range of 16 and 10 Bq Kg-1 at pH 5.4. The sum of eight fractions reached up to 52% of the total 226Ra content in the PG sample, which is to highlight considering that re-absorption processes not occur in dynamic lixiviation. This methodology was validated by analyzing a PG reference material (MatControl CSN-CIEMAT 2008).