Combined Sulfidation and Vacuum Distillation for the Directional Removal of Hazardous Mercury from Crude Selenium

Abstract

In this work, an innovative process involving directional sulfurization–vacuum distillation is proposed to effectively remove trace levels of mercury impurities from crude selenium. First, a reaction between sulfur and mercury is used to break the strong chemical Se-Hg bond to achieve the sulfide mineralization of mercury. Second, selenium and mercury are separated by vacuum distillation based on a difference in volatility. Thermodynamic analysis confirms the feasibility of this method. The experimental results show that the sulfidation reaction potential energy of different sulfidizing agents is in the order S > Na2S > FeS, and the optimum conditions are determined to be the following: a sulfidation temperature of 473 K and time of 30 min, and vacuum distillation experimental parameters of 503 K, 60 min, and 10–20 Pa system pressure. The overall experimental results show that the maximum removal of mercury is 97.49%. The content of mercury in the refined selenium was reduced from 0.32% to 0.0088% in the volatile matter. The results have practical value for the separation of selenium and mercury from hazardous wastes.