Characterization and assessment of chemical modifications of metal-bearing sludges arising from unsuitable disposal

► Ettringite-gypsum sludges were characterized using sequential extraction. ► The dissolution of ettringite was modeled using the program PHREEQC. ► U, Ca, SO42− and F are present in the water-soluble fraction of the samples. ► Due to unsuitable disposal one sample underwent modifications to its structure. ► This finding was confirmed by the modeling of ettringite dissolution.