The Impact of Additives on the Formation and Leaching Characteristics of the Vitrified Slag

摘要

Plasma technology is a state-of-the-art technology to destroy various types of hazardous wastes. The vitrified slag can form in the process of plasma treatment of inorganic wastes and effectively stabilize and immobilize heavy metals, and its leaching rate is very low. In this paper, the impact of additives on the formation and leaching characteristics of the vitrified slag has been studied by a 30 kW DC plasma arc reactor system and rotating agitator, respectively. In the experiment, the mixtures of additives (SiO_2, Na_2CO_3, Na_2SiO_3 and CaO) and two types of fly ashes have been vitrified, and leaching rates of the vitrifies slag have been tested according to Identification standards for hazardous wastes ---- Identification for extraction toxicity (GB 5085.3-2007). XRD (X-ray diffraction) analysis results of the microscopic structures of the vitrified slag show they are amorphous. The impact of additives depend on the ration of O/Si (the ratio of the whole oxygen ions to the whole network former Si ions in the vitrified slag, range of 2～3) and the basicity (range of 0.2～0.8), which are the determinative factors in the formation of the vitrified slag. The bigger ratio of O/Si and the narrower peak width of the spectrum lead to the higher leaching characteristics and more unstable vitrified slag.