Study of inhibition effect of Ca2+ on phosphorus-contained active groups in coal

In order to study the mechanism of delaying coal spontaneous combustion through CaCl2 and improve inhibition effect, the chemical reactions between CaCl2 and coal have been studied. This research includes the study of ligand structure, formed by combination of Ca2+ and phosphorus (P)-contained active structure of coal, molecular frontier orbital, stabilization energy, natural bond orbital, Mulliken population, and charge transfer. All the calculations are performed with the Gaussian03 program. The calculation results indicate that bidentate, tridentate, and quadridentate ligands can be formed through the chemical reaction between Ca2+ and P-contained active groups in coal. During the generation of the complexes, stabilization energy becomes higher and the energy gap of frontier molecular orbital becomes lower, making a stable complex formed. After the formation of those complexes, the contribution of -PH2 group in the P-contained active structure is greatly reduced in the molecular frontier orbital. The orbital energy level increases dramatically, improving the stability of the active structure and retarding oxidation reaction.