Page 195 - 00. Complete Version - Progress Report IPEN 2014-2016

Nuclear Science and Technology | Progress Report 195

Naturally Occurring one. An experimental procedure was estab-
Radioactive Materials lished for the sequential determination of the

and Environmental radionuclides in the leachate. The concentra-
238
228
226
tion of the radionuclides U, Th, Ra, Ra,
232
Radiological Impact 210 Pb and Po in PG from the two provenanc-
210
es varied from 86 Bq·kg1 to 352 Bq·kg1. The
Lixiviation of natural radionuclides concentration of the radionuclides 226 Ra and
and heavy metals in tropical soils 228 Ra showed compliance with the limits ad-
amended with phosphogypsum opted by CNEN, for the safe use of phospho-
gypsum in agriculture. The concentration of
The Brazilian phosphate fertilizer is obtained As, Cd, Cr, Ni, Se, Hg and Pb in phosphogyp-
by wet reaction of the igneous phosphate rock sum were below the limits adopted by Bra-
with concentrated sulphuric acid, giving as fi- zilian Ministry of Agriculture, Livestock, and
nal product, phosphoric acid, and dehydrated Supply (MAPA), for the safe use of PG in agri-
calcium sulphate as a by-product, aka phospho- culture. The available fractions of the radionu-
226
228
gypsum (PG). PG is stored in stacks at open air. clides Ra, Pb, Po and Ra in soils and soil
210
210
Part of this PG has been used in agriculture as amended with PG varied from 0.05% to 1.2%.
soil amendment, mainly due to the character- For U and Th, the available fractions were
232
238
istics of CaSO4, which improves the root pen- lower than 0.05%. The metals showed avail-
etration in soil. It provides calcium in the soil able fractions in soils and soil amended with
depth, reduces the aluminium saturation, con- PG from 0.05% to 1.07%. The results obtained
tributes to the deepening of the plant root sys- for the concentration of the radionuclides and
tem and favours the absorption of water and metals in the available fractions were low, giv-
nutrients. However, the presence of radionu- ing evidence that, even when these elements
clides and metals put restrictions on the use are present in the PG, they do not contribute
of PG in agriculture. To assure a safe applica- to an enhancement of their content in water.
tion of PG, it is important to estimate the lix- It can be concluded that the utilization of Bra-
iviation of radionuclides and metals present zilian phosphogypsum as soil amendment is
in it. The main objective is to study the avail- viable, concerning the availability of the met-
ability of natural radionuclides, important in als and radionuclides studied.
terms of radiological protection ( 238 U, 232 Th,
226 Ra, 228 Ra, 210 Pb and 210 Po), and metals (As,
Cd, Cr, Ni, Se, Hg and Pb), present in the Bra-
zilian PG used in agriculture. For this purpose,
an experimental protocol was conducted in
the laboratory, in which columns filled with
Brazilian typical sandy and clay soils and PG
were percolated with water, to achieve a mild
extraction of these elements. The availabili-
ty of the radionuclides and metals was eval-
uated by measuring the total concentration
in the soil amended with PG and the concen-
tration in the leachate, to establish the ratio
Figure 1. Phosphogypsum stack outdoors at Vale Fer-
between the available fraction and the total tilizantes in Uberaba, MG, in 2016.