Experimental study on the influence of transition metals on coal spontaneous combustion

In order to analyze the influence of transition metals on the spontaneous combustion characteristics of coal,the compound of three metal ions,Fe,Mn and Cu,with high content in coal,are selected to add to the coal for experimental research.Firstly,the parameters of ignition temperature,quality change,apparent activation energy and heat release of coal are analyzed by thermogravimetry and differential scanning calorimetry.Then,the influence of three metal ions on coal spontaneous combustion is analyzed by the release of indicator gas in the oxidation process.Finally,the influence of three metal ions on active groups in the low-temperature oxidation process of coal is analyzed by infrared spectroscopy.The experimental results show that Fe²⁺and Cu²⁺reduce the ignition temperature of coal samples by 23 ℃ and 20 ℃ respectively,reduce the activation energy of coal oxygen reaction,and increase the oxidation heat release of coal samples by 324.1 J/g and 42.6 J/g,indicating that Fe²⁺has the strongest promotion effect on coal spontaneous combustion,and Cu²⁺ has a significant impact on the early stage of coal natural oxidation.However,Mn²⁺has little effect on characteristic temperature,heat release and gas release during spontaneous combustion.The infrared spectrum test show that Fe²⁺and Cu²⁺ accelerated the reaction of the active structures of -COOH,-CH₃,-CH₂- and -OH during the low-temperature oxidation of coal,while the catalytic effect of Mn²⁺ is weak.This is because Cu²⁺ has stronger oxidizing activity than Mn²⁺,and Fe²⁺will be reduced to Fe³⁺with stronger oxidizing ability to promote the coal oxygen reaction at the same time of catalytic reaction.The results of this study can provide theoretical support for the prevention and control of coal spontaneous combustion.