Microstructure Study On Ferrous Dust Carbonation Pellets

The macro properties of ferrous dust carbonation pellets are determined by themicroscopic structure factors, such as grain shape, cemented form, distribution of poresize, and porosity. Revealing the change regularity of microscopic structure by studyingmicroscopic structure of carbonation pellets can provide the theoretical evidence forferrous dust recycling and carbon dioxide capture.Based on the carbonation and fractal theory, the microstructure of green pelletsmade in different CaO ratio and pelletizing times and that of carbonation pellets made indifferent reaction temperatures and CO₂partial pressures were investigated by opticalmicroscope and scanning electron microscope etc. Quantificational analysis was made onthe influence of these technical parameters on the pore structure by mercury intrusionporosimetry and fractal theory.The experimental study results show as follows:1)Ca（OH）₂gel spheric granules are stacked together and attached to the surface offerrous dust irregularly. With the CaO content rising, the gel granules are bondedtogether to form gel frame structure, the pelletizing effect of the mixture is improvedeffectively. The number of gel pores is increased, the porosity is reduced gradually, thecritical pore size, the most pore size and pore size distribution are moved to smaller pore,with the complexity of the pore structure increasing, the fractal dimension is increased2)With the pelletizing time lengthening, the granules are arranged selectively andpore size becomes smaller, then the number of smaller pores is increased, and theporosity is decreased significantly, the complexity of pore structure is exacerbated, so thefractal dimension is increased.3)The rising of the reaction temperature is favorable toward the carbonationprocess and thus improve the conversion rate. There are lots of tiny flocculent or globularCaCO₃microlites on the surface of lime gel granules, which form a bonded bridge insome pores. The fill effect of CaCO₃microlite causes a series of changes on porestructure, for instance, the critical pore size, the most pore size and pore size distributionto smaller pores. The smoothness of pore channel surface can be improved，the porosityis decreased, the pore structure tends to be regular and simple, and the fractal dimensionis reduced.4)With CO₂partial pressure increasing, gas internal diffusion is strengthened, thecompactness is enhanced by the bonded bridge from CaCO₃microlite. The pore sizedistribution is moved to smaller pore, the complexity of pore structure is reduced, fractaldimension shows a drop.As can be seen from the above, these technical parameters have significant impactson pellets microscopic structure. And it is suggested that it is workable to study the porestructure of pellets because the study of microscopic structure can provide theory forcarbonation pellets actual production.