Page 48 - PR 2014 2016 07 Nuclear Science and Technology

190 Nuclear Science and Technology | Progress Report

Naturally Occurring experimental procedure was established for
Radioactive Materials the sequential determination of the radionu-

and Environmental clides in the leachate. The concentration of the
238
228
232
210
radionuclides U, Th, Ra, Ra, Pb and
226
Radiological Impact 210 Po in PG from the two provenances varied
-1
from 86 Bq · kg to 352 Bq · kg . The concen-
-1
Lixiviation of natural radionuclides tration of the radionuclides 226 Ra and 228 Ra
and heavy metals in tropical soils showed compliance with the limits adopted
amended with phosphogypsum by CNEN, for the safe use of phosphogypsum
in agriculture. The concentration of As, Cd, Cr,
The Brazilian phosphate fertilizer is obtained Ni, Se, Hg and Pb in phosphogypsum were be-
by wet reaction of the igneous phosphate low the limits adopted by Brazilian Ministry of
rock with concentrated sulphuric acid, giving Agriculture, Livestock, and Supply (MAPA), for
as final product, phosphoric acid, and dehy- the safe use of PG in agriculture. The available
drated calcium sulphate as a by-product, aka fractions of the radionuclides Ra, Pb, Po
210
226
210
phosphogypsum (PG). PG is stored in stacks and 228 Ra in soils and soil amended with PG
at open air. Part of this PG has been used in varied from 0.05% to 1.2%. For U and Th,
238
232
agriculture as soil amendment, mainly due to the available fractions were lower than 0.05%.
the characteristics of CaSO , which improves The metals showed available fractions in soils
4
the root penetration in soil. It provides calci- and soil amended with PG from 0.05% to 1.07%.
um in the soil depth, reduces the aluminium The results obtained for the concentration of
saturation, contributes to the deepening of the the radionuclides and metals in the available
plant root system and favours the absorption fractions were low, giving evidence that, even
of water and nutrients. However, the presence when these elements are present in the PG,
of radionuclides and metals put restrictions on they do not contribute to an enhancement of
the use of PG in agriculture. To assure a safe their content in water. It can be concluded that
application of PG, it is important to estimate the utilization of Brazilian phosphogypsum
the lixiviation of radionuclides and metals as soil amendment is viable, concerning the
present in it. The main objective is to study the availability of the metals and radionuclides
availability of natural radionuclides, important studied (Figure 30).
in terms of radiological protection ( U, Th,
232
238
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 availability
of the radionuclides and metals was evaluated
by measuring the total concentration in the
soil amended with PG and the concentration
in the leachate, to establish the ratio between
Figure 30. Phosphogypsum stack outdoors at Vale
the available fraction and the total one. An Fertilizantes in Uberaba, MG, in 2016.

Instituto de Pesquisas Energéticas e Nucleares