Vaporization Mechanisms of Water-Insoluble Cs in Ash During Thermal Treatment with Calcium Chloride Addition

Abstract

The vaporization mechanisms of water-insoluble Cs in raw ash and Cs-doped ash during thermal treatment with CaCl addition was systematically examined in a lab-scale electrical heating furnace over a temperature range of 500-1500 °C. The results indicate that the water-insoluble Cs in the ash was associated with aluminosilicate as pollucite. Addition of 10% CaCl caused the maximum vaporization ratio of Cs in the raw ash to reach approximately 80% at temperatures higher than 1200 °C, whereas approximately 95% of Cs was vaporized at temperatures higher than 1300 °C when 30% CaCl was added. The formation of an intermediate compound, CsCaCl, through the chemical reaction of Cs with CaCl was responsible for Cs vaporization by means of the subsequent decomposition of this intermediate upon the increase in temperature. The indirect chlorination of Cs by the gaseous chlorine released from the decomposition of CaCl was insignificant. A high CaCl content in the resulting annealed products with 30% CaCl addition delayed the decomposition of CsCaCl and thus lowered the Cs vaporization ratio compared to that with 10% CaCl addition at 900-1250 °C. Thermal treatment with CaCl addition is a proposed method to remove Cs from Cs-contaminated incineration ash.

Effect of Atmospheres on Transformation of Heavy Metals during Thermal Treatment of MSWI Fly Ash: By Thermodynamic Equilibrium Calculation

“…Inductively coupled plasma-atomic emission spectrometry (ICP-AES) was used to determine the heavy metals in fly ash after digestion with HF-HNO 3 -HClO 4 . The detailed procedure of the acid digestion was introduced elsewhere [ 9 ]. The chemical composition as well as the heavy metal concentration are shown in Table 1 and Table 2 , respectively.…”

“…Heavy metal vaporization is aided by a high chlorine concentration [ 8 ]. This is because metallic chlorides have a higher boiling point than oxides, sulfides, and elements [ 9 ]. Furthermore, the mode of occurrence of chlorine is closely related to the heavy metal vaporization.…”

Pyrohydrolysis of CaCl2 Waste for the Recovery of HCl Acid upon the Synergistic Effects from MgCl2 and Silica

“…The thermodynamic databases applied included FactPS and FToxid. The output products include ideal gas, liquid phases, and solids phases …”

“…The changes in the atomic structure of the residues were further determined by CrystalMaker software . In addition, thermodynamic calculations were conducted in FactSage 6.4 . All these efforts were made to attain the mechanistic insights governing the co-pyrohydrolysis of CaCl 2 and MgCl 2 , and hence, to promote the HCl regeneration rate from this abundant, mixed waste.…”

“…18 In addition, thermodynamic calculations were conducted in FactSage 6.4. 19 All these efforts were made to attain the mechanistic insights governing the co-pyrohydrolysis of CaCl 2 and MgCl 2 , and…”