Effects of brief milling and acid treatment on two ordered and disordered kaolinite structures

The structural characteristics of well-ordered kaolinite (K1) and poorly ordered kaolinite (K2) after the ¼ h milling procedures, continuing acid activation with 2 M hydrochloric acid and intercalation ability with urea were assessed. Kaolinite samples were examined by X-ray powder diffraction, thermogravimetry, infrared spectroscopy analysis and specific surface area measurement. Kaolinite K1 contained a slightly higher portion of particles <2 μm (38 vol.%) than K2 (31 vol.%) increasing after jet milling (to 92 vol.% and 54 vol.%, respectively), but decreasing slightly after ball milling (to the 37 vol.% and 26 vol.%, respectively). The acid treatment contributed to a narrower particle size distribution, increased value of the surface area and dehydroxylation temperature and improved the structural order of poorly ordered kaolinites. Maximum surface area SSA = 45 m2g− 1 was measured for K2 after ball milling and treatment with hydrochloric acid. Treatment of kaolinites with hydrochloric acid supports their ability to intercalate urea and exfoliate, while the mechanical millings adversely affected intercalation urea. The SSA 9.8 and 20.5 m2g− 1 of K1 and K2, respectively, changed after: (1) exfoliation to 21.0 and 34.1 m2g− 1, respectively, (2) jet milling and exfoliation to 38.0 and 42.0 m2g− 1, respectively, (3) ball milling and exfoliation to 20.3 and 34.4 m2g− 1, respectively, and (4) ball milling, acid treatment and exfoliation to 40.3 and 46.7 m2g− 1, respectively.

► Ball milling preserved disordered structure.
► Jet milling contributed to translation defects between adjacent layers.
► Hydrochloric acid treatment after grinding improved structural order.
► Hydrochloric acid treatment supports intercalation of urea and exfoliation.