Interactions of PbCl2 capture and CdCl2 capture by kaolin in the high-temperature PbCl2-CdCl2-Kaolin reaction system

Abstract

Using kaolin for capturing hazardous metals is an effective and promising technology. However, interactions of multiple-metals with kaolin are not been clearly understood. Interactions of PbCl2 capture and CdCl2 capture by kaolin in high-temperature PbCl2-CdCl2-Kaolin reaction system were investigated in a two-stage fixed bed at 800 °C. Capture efficiency considering kaolin dihydroxylation and Pb/Al or Cd/Al were used to evaluate capture performance of kaolin. The results showed that kaolin captured more PbCl2 or CdCl2 in the cases that kaolin captured PbCl2 and CdCl2 at the same time, kaolin captured CdCl2 after its first capture of PbCl2 and kaolin captured PbCl2 after its first capture of CdCl2 than in the case that kaolin only captured PbCl2 or kaolin only captured CdCl2. PbCl2 vapor promoted absorption of kaolin for CdCl2, and CdCl2 vapor also promoted adsorption of kaolin for PbCl2. Heavy metal capture effects were controlled by chemical kinetics due to small particle size of kaolin and short contract time between heavy metal chloride and kaolin. PbCl2 vapor or adsorption products on kaolin surface promoted capture effect of CdCl2 through inhibiting desorption rate of CdCl2. Adsorption products promoted eutectic melting of kaolin surface, and slightly melted kaolin surface exposed new layers with more active sites to continue reactions of kaolin with PbCl2 and CdCl2. Therefore, PbCl2 vapor in the gas flow promoted absorption of kaolin for CdCl2, and CdCl2 vapor also promoted adsorption of kaolin for PbCl2. The results can provide an important reference for Pb and Cd capture during MSW incineration.