Iron removal from kaolin using binuclear rare earth complex activated thiourea dioxide

Abstract A binuclear rare earth complex was prepared by using Ce 3 + and Y 3 + as the central ion, and acetyl acetone (Hacac) as the ligand. Thiourea dioxide (TD) had strong reductive properties and good bleaching performance on kaolin after being activated by the complex. The concentrations of TD and the activator were fixed at 30 g/L and 0.6 g/L respectively, and the influences of raw material proportion, solution pH and reaction time on the activating efficiency of TD were investigated. The results show that TD reached its optimum activating efficiency after activation with the complex prepared under the conditions: the molar ratio of Ce 3 + :Y 3 + :Hacac = 1:1:7, solution pH = 7, and reaction time = 3 h. The highest reductive potential of TD could reach up to − 662 mV under the mild conditions (T = 25 °C, pH = 7.2). The influence of the dosage of activated TD on the bleaching effect of kaolin was characterized by colorimeter, XRD, SEM and EDS. The results show that the bleaching effect of kaolin reached the highest when the dosage of activated TD was 0.5 wt% (relative to the mass of kaolin). The calcined whiteness index of kaolin was raised from 82.6% to 88.7%.