PURPOSE: To regenerate a white clay matter excellent in adsorbability by feeding a waste clay containing an oil matter to an air tight rotary kiln and dry distilling the oil matter in a non-oxidizing atmosphere under a specific firing temp. and residence time to separate the oil matter therefrom.

CONSTITUTION: The waste clay containing the oil matter is fed to the rotary kiln to separate the oil matter by dry distilling in the non-oxidizing atmosphere at the firing temp. of 300-700°C for the residence time of ≤200min. As the rotary kiln, an indirect heating type rotary kiln is suitable and particularly an FM rotary kiln (U-turn kiln) having excellent volumetric efficiency is preferable. As the non-oxidizing gas, a gas having no oxidizing property such as nitrogen, argon, hydrogen, hydrocarbon, steam, carbon dioxide or the like is used. As a result, a black and brown clay matter having excellent adsorbability is recovered. In this case, the clay is finishing-fired at 400-800°C if a white clay is required to rise the commercial value.