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

•One kind of binuclear rare earth complex with high catalytic activity was prepared.•Iron was effectively removed from kaolin using activated TD as the reductive agent.•The whiteness of calcined kaolin was notably raised after bleaching treatment.

A binuclear rare earth complex was prepared by using Ce3 + and Y3 + 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 Ce3 +:Y3 +: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%.