Valorization of Phosphogypsum Using Fly Ash and Silica: Radiological Mitigation and Enhanced Rare Earth Element Recovery for Cleaner Production

The by-product of phosphoric acid, phosphogypsum (PG) is commonly stockpiled because of its radiological and chemical limitations. This study investigates the valorization of PG using fly ash and silica additives during the production of phosphoric acid (WPA) aiming to increase the physicochemical characteristics, decrease the radionuclide, and recover the rare earth element (REE). Under simulated industrial conditions, experimental trials were run with the Moroccan phosphate rock (PR) with the additive dosage optimised according to SiO2/F molar ratio. It has been found that additions of fly ash (34 kg/t PR) and silica (8.5 kg/t PR) substantially enhance the crystallinity of PGs and reduce the 226Ra content by almost 30%. Moreover, fly ash addition increases selective leaching of REEs to phosphoric acid and the transfer efficiencies of La, Ce and Nd are significantly increased. The two-purpose approach converts two industrial by-products, PG and fly ash, into useful products, which promote waste reduction, cleaner production, and circular economy goals.