Sustainable Green Chemistry: Water-Soluble Ozonized Biochar Molecules To Unlock Phosphorus from Insoluble Phosphate Materials

A dramatic enhancement by a factor of 15 for the production of ozonized biochar molecular products measured as dissolved organic carbon (DOC) was achieved by an innovative biochar ozonization process. The filtrate of the ozonized biochar molecular products contained substantially more carboxyl groups than that of the nonozonized biochar. The ozonized biochar molecules are now identified to be highly potent, even at a ppm DOC concentration level, to “unlock” phosphorus (P) from insoluble phosphate material hydroxyapatite (HA). At a DOC concentration of 600 ppm, the filtrates from the wet-ozonized pine 400 biochar and the dry-ozonized rogue biochar substances were both able to solubilize HA, resulting in a concentration of solubilized phosphorus up to 396.8 ± 28.8 and 339.6 ± 8.5 mg HPO₄^2–/L, respectively. Even at a DOC concentration as low as 10 ppm, the ozonized biochar molecules solubilized up to 8.3 ± 1.1 mg/L of phosphate. At neutralized pH 7, the efficiency in solubilizing phosphate decreased, indicating the importance of the protonic effect. The ozonized biochar organic acids solubilized more phosphate than a hydrochloric acid solution with the same pH, thus showing the applicability of this green chemistry with ozonized biochar molecules to unlock P from insoluble phosphate rock materials. The discovery of ozonized biochar molecules capable of unlocking P is highly relevant to agricultural phosphorus and environmental sustainability on the Earth.