Direct reduction swelling behavior of pellets in hydrogen-based shaft furnaces under typical atmospheres

Hydrogen-based shaft furnace process is gaining more and more attention due to its low carbon emission, and the reduction behavior of iron bearing burdens significantly affects its operation. In this work, the effects of reduction degree, temperature, and atmosphere on the swelling behavior of pellet has been studied thoroughly under typical hydrogen metallurgy conditions. The results show that the pellets swelled rapidly in the early reduction stage, then reached a maximum reduction swelling index (RSI) at approximately 40%reduction degree. The crystalline transformation of the iron oxides during the reduction process was the main reason of pellets swelling. The RSI increased significantly with increasing temperature in the range of 850-1050℃, the maximum RSI increased from 6.66%to 25.0%in the gas composition of 100%H_(2). With the temperature increased, the pellets suffered more thermal stress resulting in an increase of the volume. The maximum RSI decreased from 19.78%to 17.35%with the volume proportion of H_(2) in the atmosphere increased from 55%to 100%at the temperature of 950℃.The metallic iron tended to precipitate in a lamellar structure rather than whiskers. Consequently, the inside of the pellets became regular, so the RSI decreased. Overall, controlling a reasonable temperature and increasing the H_(2) proportion is an effective way to decrease the RSI of pellets.

Porous silica synthesis out of coal fly ash with no residue generation and complete silicon separation

Ordered mesoporous silica materials exhibit enormous potential in industrial production.Since coal fly ash(CFA)is abundant in Si,it has become a green and promising way to utilize CFA by synthesizing porous silica materials.However,the stable crystalline structure of CFA limits the extraction of Si,and the residue is generated during the process of extracting Si.In this work,we proposed a no-residue method to synthesize ordered mesoporous silica out of CFA.Sodium carbonate(Na_(2)CO_(3))was used to reconstruct the crystals of the CFA,and the calcined mixture then directly reacted with the precipitators.This method combined the process of Si extraction and porous material synthesis.In this method,no residue was generated and the silicon in both amorphous and crystalline phases of CFA was fully utilized.By this method,the extraction efficiency of Si was increased from 31.75%to nearly 100%.The as-synthesized mesoporous silica had a highly-ordered pore structure with a space group of la-3d,a surface area of 663.87 m^(2)/g,a pore volume of 0.41 cm^(3)/g,and an average pore diameter of 2.73 nm.The mechanism of crystalline transformation and material structure formation were systematically studied.This method provides a new idea to dispose of CFA and synthesize porous silica materials.