Modification of reactivity and strength of formed coke from victorian lignite by leaching of metallic species

Binderless briquetting of lignite at 100-200?C and subsequent carbonization produces formed coke with tensile strength (ST) of 5-40 MPa, while the briquetting often requires mechanical pressure over 100 MPa. High reactivity is another feature of the lignite-derived coke, and this arises from highly dispersed metallic species such as alkali/alkaline-earth metallic species and ferrous/ferric ones that catalyze CO₂ gasification. This work investigated effects of leaching of those metallic species in aqueous solution of hydrochloric acid, acetic acid or oxalic acid on the reactivity and ST of resulting coke from a lignite. The leaching at pH ≤ 1 removed catalytic metallic species near completely, reducing the coke reactivity by a factor of 8-15. The reduced reactivity was similar to the reactivity of coke from a typical coking coal. The leaching at pH ≤?2.2 increased ST from 6 to 13 MPa for briquetting at 200°C and 32 MPa. The performance of leaching with oxalic acid, of that solution had pH of 0.75 at 1 mol/L, was much better than that with acetic acid. This work also examined another type of leaching, oxidation of the lignite in aqueous solution of hydrogen peroxide, which produced organic mono-/di-acids in-situ from the oxidation of aromatic carbons of the lignite. The degree of reduction of the coke reactivity was between that for leaching at pH of 1 and 2. The degradation of macromolecules enhanced plasticizability of the lignite under briquetting and increased ST of the resulting coke to 22 MPa.