Environmental investigation on the use of a phosphogypsum-based road material: Radiological and leaching assessment

The transformation of phosphate ore into phosphoric acid results in the generation of high volumes of phosphogypsum (PG), an industrial by-product largely stockpiled worldwide. This solution, considered as the least damaging to the environment, constitutes a risk for the receiving environment due to the presence of harmful impurities such as heavy metals and radionuclides which hinder its large-scale valorization. This paper presents an environmental characterization of Moroccan phosphogypsum and an investigation on the environmental performance of a new lime (L) - fly ash (FA) treated phosphogypsum based road material. The concentration of metallic trace elements (Cr, Pb, Ni, Zn, Cu) in raw phosphogypsum ranged between 0.2 and 243 ppm, while its radioactivity reached 970 Bq/kg for Ra-226. The environmental performance of the proposed new road material (40% PG, 42% FA, 18% L) was evaluated using radiological risk indices besides static and dynamic leaching tests. The results showed a radioactivity reduction up to 82%, and an immobilization of metallic trace elements ranging from 25 to 100%. The stabilization/solidification mechanisms involved in the lime - fly ash treatment would be responsible for the fixation of these contaminants within the newly formed matrix.