Hydrogenation of Various Iron Carbonates and Room-Temperature Pyrophoricity of Reduced Solid Iron in a Fluidized Bed

Thermal decomposition of iron carbonate in the steel industry is one of the major sources of industrial CO2 emissions. Hydrogenation of iron carbonate using renewable-driven green hydrogen (H2) serves a transformative strategy for in situ CO2 utilization by coupling iron production. In this study, we focus on the hydrogenation behavior of various iron carbonates in a fluidized bed using siderite as the raw material, as well as on the room-temperature pyrophoricity of the resulting reduced iron as a fundamental step related to iron-based zero-carbon fuel applications. The effects of siderite type, reaction atmosphere, and hydrogenation temperature during the hydrogenation process on the distribution of resulting gaseous products are systematically investigated using a thermogravimetric analyzer (TGA) and a fluidized bed reactor. Hydrogenation reduced the starting decomposition temperature of siderites by 50–100 °C and increased the decomposition rate. At temperatures below 400 °C, CO was mainly derived from the direct hydrogenation of siderite, and its yield increased with hydrogenation temperature. CH4 was entirely generated from the direct hydrogenation of siderite, with its yield peaked at 400–450 °C. Metallic iron was the primary iron phase after hydrogenation of siderite. At temperatures above 450 °C, metallic iron exhibited catalytic effects on the reverse water-gas shift (RWGS) reaction of CO2. At room temperature, metallic iron was highly reactive and quickly oxidized by O2, leading to pyrophoricity. The peak temperatures during the pyrophoricity process were primarily influenced by the porous structure after hydrogenation and the O2 concentration. Meanwhile, microexplosions were observed during the pyrophoricity process.