Reduction-melting combined with a Na_2CO_3 flux recycling process for lead recovery from cathode ray tube funnel glass

摘要

With large quantity of flux (Na_2CO_3), lead can be recovered from the funnel glass of waste cathode-ray tubes via reduction-melting at 1000℃. To reduce flux cost, a technique to recover added flux from the generated oxide phase is also important in order to recycle the flux recovered from the reduction-melting process. In this study, the phase separation of sodium and the crystallization of water-soluble sodium silicates were induced after the reduction-melting process to enhance the teachability of sodium in the oxide phase and to extract the sodium from the phase for the recovery of Na_2CO_3 as flux. A reductive atmosphere promoted the phase separation and crystallization, and the teachability of sodium from the oxide phase was enhanced. The optimum temperature and treatment time for increasing the teachability were 700 ℃ and 2 h, respectively. After treatment, more than 90% of the sodium in the oxide phase was extracted in water. NaHCO_3 can be recovered by carbonization of the solution containing sodium ions using carbon dioxide gas, decomposed to Na_2CO_3 at 50℃ and recycled for use in the reduction-melting process.