To obtain fundamental data for developing an efficient recovery process of rare metals from grinding powder and cutting fragment of optical glass, the release of Nb, Ta, La, Gd and coexisting elements (Ti, Zr and Zn) was investigated under the conditions of a heating rate of 30 degrees C/min and terminal temperatures from 200 to 1000 degrees C in a Cl(2) gas stream. The release of Zn, Nb, Ti and La drastically increased above 700 degrees C and attained almost 100% at 1000 degrees C, while that of Zr attained to 10% above 800 degrees C. Carbon addition accelerated the volatilization, and the release of elements other than La and Gd reached 100% by 1000 degrees C. The release of La and Gd was only 2-3% in the temperature from 800 to 1000 degrees C. When the samples were heated at 700 degrees C for 120 min, Ta and Nb were selectively volatilized from solid phase without the release of La and Gd. Based on the experimental results, a three-step heat treatment process at 500, 700 and 1000 degrees C in a Cl(2) gas stream with carbon addition was proposed to recover the rare metals selectively from the optical glass.