The thermochemical reactivity of silicate minerals in hydrogen and methane

The thermochemical reduction of transition metal silicates, i.e. garnierite (Ni,Mg)₆[(OH)₈(Si₂O₇)], chrysocolla (Cu,Al)₂H₂Si₂O₅(OH₄)·nH₂O, dioptase CuSiO₃·H₂O, willemite Zn₂SiO₄, and hemimorphite Zn₄Si₂O₇(OH)₂·H₂O has been studied. By means of combined thermogravimetric/mass spectrometric measurements, X-ray diffraction and analytical scanning electron microscopy it is shown that in a 5% H₂/95% N₂ or in a methane atmosphere the transition metals are selectively reduced at temperatures qualitatively corresponding to their electrochemical potential. Mixtures of elemental transition metals and quartz, SiO₂, are obtained as solid products. Depending on the nature of the parent mineral, different mixtures of volatile products are obtained. Principal volatile product, however, is water vapour. The reduction in methane leads to the formation of syngas.The authors acknowledge the financial support of the Schweizerisches Bundesamt für Energiewirtschaft as well as the Fonds der Chemischen Industrie.