Abstract: Coal spontaneous combustion poses a serious threat to mine safety, and the use of inhibitors represents a key approach for its prevention. Given the catalytic role of transition metal ions in coal during oxidation, this study employs the environmentally friendly chelating agent citric acid to suppress metal ion activity through complexation, systematically investigating the effects of citric acid mass fractions and the synergistic inhibition mechanisms on long-flame coal. Multiple characterization techniques, including temperature-programmed experiments, synchronous thermal analysis, FTIR, ESR, ICP-MS, XPS, low-temperature nitrogen adsorption, and SEM, were used to analyze macro and micro structural changes in coal samples treated with citric acid at different mass fractions. Results indicate that 5% citric acid provides the optimal inhibition effect, increasing the crossing-point temperature by 40.0 °C, reducing the CO release peak by 79%, and raising the thermal decomposition temperature (T₂) by 20.0 °C. Although citric acid treatments with mass fractions above 5% led to higher CO₂ generation due to citric acid pyrolysis, CO release still decreased by over 24.6%, indicating sustained suppression of the oxidation chain reaction. Mechanism analysis indicates that citric acid inhibits coal spontaneous combustion through a synergistic physicochemical effect.Chemically, ICP-MS and XPS results show that citric acid chelates Fe, Ca and other metal ions, reducing the relative content of Fe³⁺, while ESR analysis confirms a further indicates decrease in free radical content, thereby suppressing chain reactions during low-temperature oxidation. FTIR analysis results provided support at the molecular structural level, revealing that the active functional groups (aliphatic hydrocarbons, C=O) in the treated coal sample decreased, while the relative content of oxygen-containing groups such as —OH and —COOH increased. Physically, BET and SEM analyses demonstrate that citric acid treatment alters coal pore structures and surface morphology, resulting in an approximately 20% reduction in specific surface area and restricting oxygen adsorption and transport. The combined effects of metal-ion chelation, radical suppression, and pore blockage account for the significantly reduced spontaneous-combustion tendency, with an optimal inhibitory performance observed at a citric acid mass fraction of 5%.