Microwave pyrolysis of typical forestry, manure, algae and kitchen wastes loaded with nickel nitrate: Influence of involvement of organic intermediates on exposure of nickel species

Theoretically, any carbonaceous feedstock could be potentially used as a carrier for preparing metal/char composite material. Nonetheless, organics generated from varied feedstocks in pyrolysis might impact distribution of metals in distinct ways. This was investigated herein by microwave pyrolysis of five typical solid wastes (sawdust, pig manure, spirulina, cabbage, and rice) loaded with nickel nitrate at 400 °C and detailed analysis of Ni/char. The results indicated that pig manure contained abundant inorganics (44.2 %), which together with nickel species induced excessive cracking, rendering 18.2 % of carbon content in resulting char (nearly 70.0 % for rice- or sawdust-derived char) and thus little anchoring sites for fixation of nickel species. The in-situ IR characterization of pyrolysis confirmed intensive cracking of the spirulina with high ash content (11.2 %) and unstable organics, which led to a low anchoring sites of Ni. The volatiles from the cabbage of similar property to spirulina also formed less anchoring sites for nickel. In comparison, carbon/oxygen-rich sawdust or rice provided sufficient anchoring sites for nickel, and the dominance of aromatization in pyrolysis resulted in a much higher dispersion of nickel and also a much superior catalytic activity of Ni/char for hydrogenation of vanillin or furfural.