Phosphorus Speciation and Release in Biochar.

Pyrolysis exerts a significant alteration on the element. Compared to the understanding of carbon and nitrogen, however, less is known about the change of phosphorus speciation during the pyrolytic process. In this study, wood chips, rice husks, and leguminous biomass was pyrolyzed at 300 and 500 ^oC and their elemental alterations were determined. Using chemical fractionation (Hedley sequential extraction) and spectroscopic techniques (solid-state ³¹P NMR and synchrotron-based X-ray absorption spectrometry), we found that phosphorus speciation in raw material was changed into (1) inorganic phosphorus through pyro-mineralization, (2) aromatic carbon ring linked phosphate during pyrolysis. Such change played a significant role in affecting phosphorus release. For biomass with a high carbon-to-phosphorus ratio, converting it into biochar enhanced phosphorus release. In contrast, converting biomass with a low carbon-to-phosphorus ratio into biochar reduced phosphorus release.
THE Studies was support by Ministry of Scicence and Technology, Taiwan.