Fluorescent powder was subjected to mechanochemical (MC) treatment using a planetary mill to control its structural change followed by selective leaching of Y and Eu with 1N HCl solution at room temperature. The crystal structure of the fluorescent powder tends to be transferred into disordered state by the MC treatment. It is possible to control the crystal disordered state by choosing the MC condition such as media size and rotational speed of the mill. The optimum condition gives us to improve the yield of Y and Eu, depressing the yield of La, Ce and Tb in the acid leaching. In the present experiment using 15 mm ball size, the preferable MC treatment would be conducted within about 20 minutes at 400rpm in mill rotational speed.
