Density functional theory study on the formation mechanism of CaClOH in municipal solid waste incineration fly ash.

Municipal solid waste incineration (MSWI) fly ash is defined as a kind of hazardous waste because of its high levels of multiple pollutants. The main component of MSWI fly ash is CaClOH, and the characteristics have not achieved consensus. And density functional theory (DFT) was used to calculate the formation process of CaClOH in this study, which mainly included HCl adsorption on CaO (0 0 1) surface and Ca(OH)2 (0 0 1) surface and the surface reaction process. The reaction mechanism was investigated. The results showed that the maximum adsorption energies of HCl on CaO and Ca(OH)2 surfaces reached - 195.17 kJ/mol and - 83.48 kJ/mol, respectively, representing strong chemisorption. The chemisorption process was shown as the adsorption of H atom on O site, and the adsorption capacity was reflected in the adsorption range of O site. The significant electron density overlap between O site and H atom meant that a new chemical bond formed, which made the adsorption structure stable. The adsorption energy of multi-HCl adsorption on the crystal surfaces was not proportional to the number of HCl molecule, indicating that the adsorption processes were influenced by each other. After surface reaction, the H-Cl bond was broken completely, and the structure of CaO and Ca(OH)2 changed to new structures. According to transition state (TS) search, the formation of CaClOH had a higher priority, easier than that of CaCl2, explaining the presence of CaClOH in fly ash. The study provides helpful information for the solidification treatment of fly ash.

Synthesis, Characterization, and High-Temperature HCl Capture Capacity of Different Proportions of Potassium Fluoride-Doped CaMgAl Layered Double Hydroxides.

In this work, potassium fluoride-doped Ca-Mg-Al layered double hydroxides (CaMgAl-LDHs) were synthesized by a coprecipitation method, after which they were further used as strong adsorbents for HCl gas adsorption in a quartz reactor at high temperature. The physiochemical properties of the as-prepared KF/CaMgAl-LDHs and CaMgAl-LDHs were investigated by X-ray diffraction, thermogravimetric, scanning electron microscopy, energy-dispersive system, and Brunauer-Emmett-Teller. The HCl adsorption test showed that 25 wt % KF loading of the KF/CaMgAl-LDOs was the optimal adsorbent for HCl removal. The highest adsorption capacity of the KF/CaMgAl-LDH adsorbent was achieved with 0.2968 g at 600 °C, 500 ppm HCl concentration, and 0.5 g adsorbent. Furthermore, the microstructure of the adsorbents after the reaction revealed that the adsorbents were encapsulated by dense chloride. The adsorption process was mainly dominated by chemical adsorption, strong acid-base properties, specific surface area, and mesopore number.