Iron removal from kaolin using thiourea dioxide: Effect of ball grinding and mechanism analysis

This study reports a series of experiments conducted to evaluate the suitability of thiourea dioxide (TD) under ball grinding, in leaching out iron-bearing impurities from two raw kaolin samples. The bleaching mechanism of kaolin was investigated. The results show that the combined application of ball grinding (at 400 rpm) and AlCl3 (0.5 wt%) could give the highest bleaching efficiency, wherein the Fe2O3 content decreased from 1.34% to 0.76% for Beihai kaolin, and 2.05% to 1.42% for Xingzi kaolin, corresponding to an increase of 4.98 and 12.12 percentage points, respectively. The values are acceptable in the ceramics industry. Through ball milling, the intrinsic stratiform structure of the kaolinite was gradually destroyed, the resultant particles became finer, and specific surface area was increased. The Al3 + ions added could fill the vacancy of Fe3 + on the kaolinite lattice, promoting the leaching out of Fe3 +. The results obtained from X-ray energy-dispersive spectroscopy and X-ray fluorescence spectroscopy conform well to the theoretical analysis.