Abstract
This work presents results obtained using gamma spectrometry measurements of phosphogypsum samples on a non-fractionated (native) and fractionated phosphogypsum byproduct. The phosphogypsum was divided into particles size fractions within the range of < 0.063, 0.063–0.090, 0.090–0.125, 0.125–0.250, and over 0.250 mm and analyzed after reaching radioactive equilibrium using high-resolution gamma spectrometry technique. It was found that there is no significant differentiation between 226Ra distribution among particular grain size fractions of this material; however, tendency for preferential retention of radionuclides in particular grain size fractions is observed. The detailed analysis of results revealed that radium is preferentially retained in smaller grain size fractions, whereas lead and thorium in coarse fractions. The results indicate that overall 226Ra activity concentrations between particular fractions of phosphogypsum vary globally between − 34 and + 47% regarding non-fractionated material, and for 210Pb activity concentration, fluctuations are found between − 26 up and + 38%. Presumably, the mechanism of radium incorporation into gypsum phase is based on a sequence of radium bearing sulfate phases formation followed by a surface adsorption of these phases on the calcium sulfate crystals, whereas for lead and thorium ions, rather incorporation into crystal lattice should be expected as more likelihood process.
Highlights
Phosphogypsym (PG) is a hydrated calcium sulfate, CaSO4· xH2O, a byproduct generated during wet process of phosphoric acid (H3PO4) production
Presented results clearly show that there is no significant differentiation between 226Ra distribution among particular grain size fractions of this material; obvious tendency for preferential retention of radionuclides in particular grain size fractions is observed
The secondary object of this work was an analysis of the existing disequilibrium between main radioactive contaminants in phosphogypsum and their progenies used for quantification of radionuclides in PG
Summary
Phosphogypsym (PG) is a hydrated calcium sulfate, CaSO4· xH2O, a byproduct generated during wet process of phosphoric acid (H3PO4) production. It is produced during digestion of phosphate rocks of igneous or sedimentary origin by concentrated sulfuric acid. Phosphoric acid plants have generated about 5 billion metric tons of phosphogypsum, among which 70– 90% are deposited in the form of piles (Hilton 2006) This figure is increasing of about 100 to 280 million tons each year (Koopman et al 1999; Parreira et al 2003; Reijnders 2007; Biegańska et al 2013). PG is classified as the NORM residue (Naturally Occurring Radioactive Material), and its utilization in industry is limited to roughly 15% of the total amount produced
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