The use of phosphogysum in crops cultivated at the Cerrado Region

Phosphogysum is a byproduct of the chemical reaction called the 'wet process', whereby sulfuric acid is reacted with phosphate rock to produce the phosphoric acid needed for fertilizer production. The Brazilian production of this material is around 4.5 millions of tons per year, which is stacked in piles at the same place where it is produced. Researches accomplished in several countries around the world have demonstrated the potential use of this product as an agricultural source of calcium and sulfur, and as a conditioner for soils that contain high levels of sodium. In Brazil, these studies are focused mainly in the application of phosphogysum in the Cerrado region, the main agriculture front line of the country. Taking into account the presence of natural radionuclides in this material and the fact that the mobility and bioaccumulation of these elements can vary significantly with changes in climate, a research project has been conducted by a partnership of the Brazilian Commission of Nuclear Energy (CNEN) and the Agriculture Department of Federal University of Vicosa in order to investigate the radiological impact of the use phosphogysum in crops cultivated at the Cerrado region. For this purpose a set green house experiments have been conducting in two types of soil (one with clay and the other with sandy loam in texture) to determine the transfer factor of natural radionuclides (238U, 232Th, 226Ra e 228Ra) from soil to two forage crops (soy beams and lettuce). The present paper presents the preliminary results of this study, including the organic matter content, granulometric distribution and P, K, Ca, Mg and Al concentration in soil samples, the mineralogical characterization and radioactivity concentration in both, phosphogysum and soils samples. The measurement of 232Th concentration has been carried out by neutron activation analysis, 238U by delayed neutron counting technique, 226Ra and 228Ra by the method of radiochemical separation. (author)