Evolution of the waste generated along the cleaning process of phosphogypsum leachates

Abstract

“The generation of acidic leachates from phosphogypsum (PGL) stacks is a global problem due to their high pollutant concentrations (As, Cr, Cd, Cu, Ni, Zn, F-, PO43-, SO42-, 210Po and 238,234U). The cleaning treatment of the PGL by neutralization with alkaline reagents is a proper option for removal of pollutants by (co)-precipitation. This study is focused on the characterization of the wastes generated along the cleaning process of PGL using CaCO3 and Ca(OH)2 with the aims of diagnosis for their valorization. In addition, a chemical modelling was performed to obtain a general guide on the precipitation behavior (cleaning) of the chemical species when the pH is increased. The main finding was that the fluorine is removed from dissolution as fluorite at pH around 3, precipitating with some gypsum. Nevertheless, calcium phosphate dominates the precipitated phase during the alkaline treatment, where monetite and brushite are the prevailing species formed at neutral pH range and fluorapatite in more basic conditions. These species contain very high concentrations of toxic chemical species and 238U-series radionuclides (mainly 238U-isotopes and 210Pb). Therefore, it is needed to design a valorization process for these two generated wastes, which could contribute to the circular economy and the improvement of the environmental conditions of the PG stacks surroundings.”