Separation of thorium from zirconium carbide waste is reported. The waste typically contains zirconium, yttrium, uranium, and thorium, along with other impurities including rare earth elements (REEs), iron, calcium, aluminum, hafnium, and titanium. The first step in the separation was selective leaching of zirconium, uranium, and most other impurities with HNO 3 −HF, leaving thorium and REEs as insoluble fluorides. The effective parameters such as HNO 3 and HF concentrations, temperature, and time were optimized for achieving the maximum leaching of zirconium and the minimum leaching of thorium, using central composite design and a multiple response optimization algorithm. Thorium and REEs were leached from the residual solid with H 2 SO 4 , followed by their precipitation with ammonia, dissolution of the precipitate in HNO 3 , and extraction of thorium with tri-noctylamine−kerosene. The factors affecting the extraction of thorium were optimized with respect to HNO 3 , TOA, diluent, V org /V aq , and extraction time. Using the above sample preparation and extraction methods, thorium could be extracted with an efficiency of 95.6%.