Instrumental neutron activation analysis, gamma spectrometry and geographic information system techniques in the determination and mapping of rare earth element in phosphogypsum stacks

Phosphogypsum is a by-product from the phosphate fertilizer industry, disposed in huge stacks in open-air storage areas. Its use in agriculture may be a solution to decrease these stacks, because, among its other uses, phosphogypsum can be used as a soil amendment to provide calcium and sulphur for major crops. However, it contains rare earth elements (REE) from its raw material. The objective of this study was to determine the concentrations of REE in phosphogypsum stacks Imbituba (southern Brazil) in order to verify the possibility of contamination in the surrounding of the stacks due to the disposal and to ensure the safe use of phosphogypsum in agriculture. Samples of phosphogypsum were collected and REE were determined by neutron activation analysis and gamma spectrometry. There was no leaching of the REE through the profile of the stacks, which suggests that the occurrence of REE in the phosphogypsum is associated with the formation of sulphates, carbonates, fluorides and phosphates. The results indicate that application of phosphogypsum from Imbituba to agricultural soils can contribute to increase the concentration of rare earth elements in the cultivated soils, but these are not available to plant uptake.