Preparation and steam gasification of Fe-Ion exchanged lignite prepared with iron metal, water, and pressurized CO₂

This paper proposes an environment-friendly method to load ferrous ion (Fe²⁺) to lignite with water, iron metal and carbon dioxide (CO₂) but without mineral acids or iron salts containing potentially harmful components. Iron metal was dissolved into 25°C water that had been saturated with CO₂ at its gaseous pressure of 4.0 MPa. The solubility of ferrous iron was 1 070 mg-Fe/L-water. This solubility was much higher than that predicted from the solubility product (K_sp) of FeCO₃ with an assumption that Fe²⁺ represented the dissolved ferrous iron. Rather, another assumption of coexistence of Fe²⁺, FeHCO₃⁺, and Fe(HCO₃)₂ reasonably explained the measured solubility of ferrous iron. The dissolved ferrous iron was loaded to a Victorian lignite by ion exchange. The iron-loaded lignites with different iron concentrations (0.3-6.7 wt %-dry-lignite) were subjected to a sequence of pyrolysis and steam gasification to produce synthesis gas in a thermogravimetric analyzer. The gasification was catalyzed by the loaded iron regardless of its concentration, while the quickest at 1.0 wt % where dispersion of iron-derived catalytic species in the char matrix was maintained until its complete gasification with steam.