The mercury removal mechanism of selenium mercury material by soda roasting

Abstract

In the present work, Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were employed in the investigation of roasting mechanism, roasting dynamic model, control step of soda roasting process of selenium–mercury material. The results indicated that at the beginning of the roasting process, the control step might be interface chemical reaction for the first 30 min, and the kinetic equation might be 1−(1−R)⅓ = Kt with a activation energy E1 = 40.50 kT/mol. However, as the roasting proceeded, internal diffusion gradually became the control step for 90–135 min, and the kinetic equation might be 1−⅔R−(1−R)⅔ = Dt with a activation energy E2 = 6.75 kT/mol. The SEM analysis of the roasted selenium–mercury materials indicated that the dynamic model of soda roasting attributed to the shrinkage model was reasonable. Combined with the results obtained by SEM and EDS of the roasted selenium–mercury materials, we concluded that the addition of too much Na2CO3 might lead to the formation of molten crystalline phase in the inner of the roasted selenium–mercury materials, changing the mercury removal mechanism of the roasting process. Meanwhile, Se had a tendency to segregate at where the content of Na was relatively high. In order to study the mechanism of diffusion, Na2O2 of 9% was added to one of the samples. According to the results, we concluded that the diffusion of products (such as HgxOy) from the inside of the raw material was the control step of internal diffusion.