Formation of organic carbon compounds from metal carbonates

Abstract

Natural metal carbonates, in particular the abundant alkaline-earth metal carbonates MgCO3 (magnesite), MgCa(CO3)2 (dolomite) and CaCO3 (calcite), are formed by various carbonatization processes with atmospheric carbon dioxide. They represent not only an important buffer system within the ecological carbon cycle, but also the most important feedstocks for the production of MgO (magnesia), CaO (calcia) and related chemicals. The thermal decomposition of these naturally occurring carbonates is well documented: in vacuum, inert or oxidizing atmosphere the main gaseous product is carbon dioxide, and as solid products the pure or mixed metal oxides are formed. Here we report the results of an investigation of the thermal reactivity of pure alkaline-earth metal carbonates and mixed alkaline-earth metal transition metal carbonates in a hydrogen atmosphere. We found that, compared with the analogous degradations in inert or oxidizing atmospheres, the reaction temperatures are lowered by at least 150 K. Depending on the transition metal present in the initial mixed carbonates, CO or CH4 is formed as the main gaseous carbon compound.