Natural radionuclides content and radon exhalation rate from brazilian phosphogypsum piles

Abstract

Phosphogypsum is a waste of the wet-acid process for producing phosphoric acid from phosphate rock. For every ton of phosphoric acid obtained, from the reaction of phosphate rock with sulphuric acid, about four tons of phosphogypsum are produced. The level of radioactivity present in the phosphogypsum, among other impurities, prevents its reuse for a variety of purposes. Large quantities of phosphogypsum have been produced worldwide. In 2006, the annual production was estimated to be about 170 million tons. Brazilian annual production of phosphogypsum reaches 5.5 million tons. Brazil, like other countries that produce phosphate fertilizer, tries to find solutions for the safe applications of phosphogypsum, in order to minimize the impact caused by its disposal. Most of the worldwide phosphogypsum is stockpiled, posing environmental concerns. The monitoring of air and groundwater pollution, radon exhalation rate and direct exposure to gamma radiation for workers should be considered. The aim of this study is to evaluate the natural radionuclides content and the radon exhalation rate from phosphogypsum piles from Ultrafertil and Fosfertil fertilizer industries. Samples of this material were analyzed by gamma ray spectrometry for their radionuclide content. Radon exhalation rate was measured by the activated charcoal collector method. A theoretical model for radon exhalation calculation, suggested by UNSCEAR, was applied in order to corroborate the experimental results.