A vacuum distillation system was used to separate the extractant and white oil by using the difference in boiling points between the extractant and white oil. The low-boiling extractant is separated from the mixed liquid in a gaseous form by heating and heating, and then condensed and sent to the extractant storage tank for recycling. The remaining high-boiling white mineral oil in the system is processed by the white oil to be refined. Transfer to white oil storage tank.