Pyrolysis of agroforestry bio-wastes with Calcium/Magnesium oxides or carbonates – Focusing on biochar as soil conditioner

This work comparatively studied the pyrolysis of agroforestry bio-wastes in the presence of alkaline-earth-metal (AEM) oxides or carbonates (i.e., CaO, CaCO3, MgO and MgCO3). Particularly, the Ca- and Mg-enriched biochars were evaluated for the retention capacity improvement of soil water and nutrient (i.e., K+, PO43−). In general, the Ca-enriched biochars exhibited higher retention capacity of soil water than the Mg-enriched biochars. However, the Mg-enriched biochars showed a much higher adsorption capacity of K+ and PO43−. The MgO-enriched biochar with small specific surface area had a relatively high adsorption capacity on both K+ and PO43−, since the adsorption of nutrient towards biochar was mainly controlled by the chemisorption process. The rapid releasing of PO43− adsorbed in the MgO-enriched biochar indicated its low PO43− retention capacity. In summary, MgCO3 would be an appropriate candidate for production of biochar composite as a good soil conditioner during the pyrolysis valorization of lignocellulosic biomass.