The recycling of high-purity selenium from selenium-tellurium alloy scraps of xerographic photoreceptors and its manufacturing process have been carried out to remove tellurium by the following three processes (1) Selective separation of selenium as selenium dioxide by oxidizing roasting at high temperature, 600℃. (2) Selective leaching of selenium dioxide from selenium dioxide and tellurium dioxide mixture and reduction of selenium dioxide by SO_2 gas at a solution temperature of 80℃. (3) Selective distillation of selenium at low pressure. The first step was carried out using Te 10wt% selenium-tellurium alloy to vaporize selenium dioxide gas and leave tellurium dioxide solid in the reservoir. The selenium dioxide deposited in the condenser was analyzed and the high concentration of tellurium in selenium dioxide was observed due to the mixed Se-Te vapors such as SeTe, Se_2Te, SeTe_2,Se_3Te, Se_2Te_2 and Se_4Te. Also the formation of mixed oxide vapors should be expected. The second step was based on the large difference of solubility of each oxide in water, i. e. selenium dioxide has a solubility of about 100,000 times higher than tellurium dioxide. But leaching resulted in poor separation than that expected from the solubility data. The reason for the high solubility of tellurium dioxide was explained by the low pH of the solution and the formation of Te_2O_3-SeO_4 ion pairs in the concentrated selenious acid solution. The reduction of selenious acid solution with SO_2 gas was monitored by a platinum electrode and the electrode was found to determine the end point of the reduction following the ORP changes of Se/SeO_3^ to S/SO_3^. Concentration of tellurium in the SO_2 reduced selenium was made less than 1ppm by high temperature (80℃) solution reduction. The last purification step consisted of selective distillation. The liquid-vapor equilibrium was established and the theoretical plates were calculated to be 7 to obtain 99.9999wt% selenium from 99.9wt% selenium. The SO_2 reduced selenium was purified by low pressure distillation
