Study on the Performance of a Novel Highly Stable Nano-Hydroxyapatite Gel Foam to Inhibit Coal Spontaneous Combustion

The preparation of gel foams with high stability for inhibiting coal spontaneous combustion remains a huge challenge. In this paper, a highly stable gel foam (SCTH) was developed by introducing nano-hydroxyapatite (HAP) into gel foam system (sodium alginate/calcium L-lactate/tannic acid/composite forming agent). The effects of HAP on the foam performances of SCTH were analyzed. The results showed that HAP could improve the stability of SCTH by forming hydrogen bonds, metal ion bonds with the system and interfacial barriers. After 100 days, SCTH without HAP had only 44.8% of the foam volume remaining. The SCTH with 1.2 wt% HAP had 80% of the volume remaining. In addition, the SCTH had better safety. Thermogravimetric analysis showed that the SCTH could improve the maximum weight loss rate temperature, and increase the residual weight of the coal after thermal decomposition. The coal temperature-programmed oxidation experiment showed that the SCTH could increase the temperature of coal entering the rapid oxidation stage from 120 to 190 degrees C, and the CO inhibition rate was 85.3% at 200 degrees C. Fire suppression experiment showed that the SCTH could reduce the temperature of burning coal by 81.9% within 10 min, thus achieving rapid fire suppression. X-ray photoelectron spectroscopy analysis showed that the SCTH could more effectively reduce the total content of C=O and -COO in coal and block the chain cycle reaction of coal. This work presents a new design idea for using multifunctional nanoparticles to prepare highly stable gel foams with excellent inhibition performance of coal spontaneous combustion.