Role of sodium chloride and mineral matrixes in the chlorination and volatilization of lead during waste thermal treatment

Abstract

Knowledge of the transformation of lead (Pb) to volatile compounds could provide scientific basis for the control of its migration and pollution during waste thermal treatment. The effects and mechanisms of sodium chloride (NaCl) and mineral matrix compounds, which are ubiquitous in waste, on lead volatilization were studied. The results showed that the weight loss of the NaCl+PbO binary system exceeded NaCl mass fraction above its melting point, indicating that NaCl reacted with PbO in the absence of other substances. The reaction product was PbCl2, detected by synchrotron radiation based micro X-ray diffraction. NaCl can also act as a Cl-donor via solid–solid reaction, without Cl2 generation, at about 745°C in the NaCl+PbO+Al2O3 system or at 600–611°C in the NaCl+PbO+SiO2 system, producing PbCl2 in both cases. The minerals (Al2O3 and SiO2) promoted lead chlorination and volatilization at a lower reaction temperature. In these pure ternary systems below 850°C, the minerals did not inhibit lead volatilization by limiting diffusion or incorporating lead into the matrixes, which was momentous cognition for emission control. In summary, NaCl plays an important role in lead speciation, fate and transport during thermal treatment.