Page 196 - 00. Complete Version - Progress Report IPEN 2014-2016

196 Nuclear Science and Technology | Progress Report

Availability of Po present in ogies adopted, giving evidence that, although
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phosphogypsum used in agriculture the radionuclides are present in the PG, they
are not available in the leachate.
The main phosphate industries in Brazil are re-
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sponsible for the production of 5.5 × 106 met- Availability of U and Th in the utilization
ric tons of a TENORM residue, phosphogypsum of phosphogypsum in agriculture
(PG) annually, which is stored in stacks. The
presence of radionuclides puts restrictions on Phosphogypsum (PG), a byproduct of the phos-
the use of PG in building materials and in soil phate industry, is classified as Technological-
amendments. The Brazilian regulatory body, ly Enhanced Naturally Occurring Radioactive
CNEN, ruled that PG would only be permitted Material (TENORM) or as a NORM waste. It is
for use in agriculture or in the cement industry obtained during the attack of the phosphate
if the concentration of Ra and Ra does not rock with sulfuric acid for the production of
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exceed 1 Bq·g1. In Brazil, PG has been widely phosphoric acid. PG presents in its composi-
used as soil amendment, to improve soil fertil- tion radionuclides of the natural U and Th de-
ity. To assure a safe utilization in agriculture, it cay series: mainly Ra, Ra, Th, Pb and
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is important to estimate the lixiviation of the 210 Po. The Brazilian producers stock the PG in
radionuclides in PG. The main objective is to dry stacks, posing risks to the surrounding en-
evaluate the availability of Po in the utiliza- vironment. Therefore, several studies were un-
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tion of PG in agriculture as soil amendment. dertaken to evaluate viable ways of its reuse.
An experiment was carried out, in which col- One possible solution to this problem is to re-
umns filled with sandy and clay Brazilian typ- use PG in agriculture as a soil conditioner. The
ical soils and PG were percolated with water, Brazilian regulatory body, CNEN, established
to achieve a mild extraction of determination exemption limits for the use of PG in agricul-
of Po. The technique used for the Po in the ture or cement industry: the Ra and Ra ac-
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samples of soil, soil + PG and PG was alpha tivity concentration should be below 1.0 Bq·g1.
spectrometry which is suitable for the mea- However, for its safe application, it is still nec-
surement of low activity of 210 Po in environ- essary to ensure that the radionuclides pres-
mental samples, since it presents high efficien- ent in the PG will not be available to the envi-
cy and sensibility. The concentration present in ronment. The availability of U and Th in
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the leachate was compared with the total con- samples of soils amended with PG through per-
centration of Po in soil, in the mixture soil + colation with water, by calculating the avail-
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PG and sole PG, in order to evaluate the avail- able fraction, was determined. This fraction
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ability of the activity concentrations of Po. was obtained by the ratio of the concentra-
The results obtained for 210 Po in the clay soil tion of the radionuclides in the leachate by a
were approximately 2.5 times higher than the radiochemical procedure based on a publica-
sandy soil. The results obtained for the radio- tion from International Atomic Energy Agen-
nuclides concentration in the PG varied from cy over the total concentration in the samples,
155 ± 11 to 346 ± 7 Bq·kg1 for Po. However, by Instrumental Neutron Activation Analysis
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the addition of PG to the soils studied did not and gamma spectrometry. The results demon-
represent any increase in the final activity con- strated that the available fraction of the radio-
centration. The results obtained for the activi- nuclides were in all cases lower than 0.2%. This
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ty concentration of Po in the leachate were indicates that the use of phosphogypsum as
close to the detection limits of the methodol- agricultural input does not contribute to in-

Instituto de Pesquisas Energéticas e Nucleares