Distribution of Natural Radionuclides, Rare Earth Elements, Metals and Metalloids in a Phosphogypsum Stockpile

Abstract

A first detailed study of phosphogypsum (PG) from a stockpile in Barreiro (Portugal) was performed aiming for a better characterization of this industrial waste deposit, considering its enhanced content in natural radionuclides and toxic metals, making it a potential contamination source to the Tejo estuary. Whole samples and aggregates of these wastes resulting from phosphate industries were analysed by neutron activation, gamma-spectrometry, X-ray diffraction and scanning electron microscopy. This work clearly shows that a significant chemical heterogeneity in the PG occurs due to the existence of aggregates with different compositions randomly distributed. Among these aggregates, the dark grey ones have high concentrations of Sc, Cr, Zn, Ga, Ba, REE, Ta, W, Th and U and the highest concentrations of 226 Ra and 210 Pb. The separation of these dark aggregates prior to any application of the PG would lead to a safer reuse of these wastes. The chemical patterns, including the REE distribution with a significant negative Ce anomaly, found in PG, are certainly related with the geochemical signatures of the phosphate rocks used as raw material. This PG stockpile may play a significant role as a radioactive source in the Tejo estuarine environment.

Carbon Footprint Analysis on Phosphoric Acid Production Using Wet Process at PT Petrokimia Gresik

“…The raw material for the wet process is phosphate rock, common in mines in China, Middle Eastern, and North African countries [2]. This phosphate rock contains small amounts of heavy metals and radioactive elements, which are carried into the wet process by-product, namely phosphogypsum [3]. Apart from that, this industry is also energyintensive.…”

Behaviour of heavy metals and natural radionuclides in the mixing of phosphogypsum leachates with seawater

“…Phosphogypsum (PG) is a by-product from the manufacturing fertilizer industry generated during the production of phosphoric acid (H3PO4), mainly composed by gypsum (CaSO4•2H2O), but also contains high levels of pollutants such as heavy metals, acids, natural radionuclides, and some others trace elements (Rentería-Villalobos et al, 2010;Madruga et al, 2019) which may be leached. Globally, about 300 Mt of PG are produced every year (Yang et al, 2016) but only 15% of this amount is recycled, being mainly disposed by dumping in large stacks, usually placed in coastal zones close to the factories (Sanders et al, 2013;El Samad et al, 2014).…”