Iron-based biochar materials for phosphorus recovery from agricultural runoff: Mechanism and potential application as a slow-release fertilizer

Agricultural runoff is an important pathway leading to the loss of phosphorus (P) resources. In this study, three amorphous FeOOH biochar (AF-BC) composites with good P adsorption properties were prepared. Batch experiments showed that both the Elovich model and the Langmuir-Friedrich model were effective in describing the P adsorption by AF-BC, suggesting that the P adsorption by these three materials is a multi-mechanism adsorption process dominated by chemical process. Among them, S-AF exhibited the best adsorption performance with an expected maximum adsorption capacity of 276.40 mg/g. This superior performance can be attributed to S-AF having a larger surface area and a higher concentration of basic groups. Plant culture tests have shown this composite to be effective in promoting seed germination and growth, so it can be used to sequester P lost from agricultural runoff and as a slow-release P fertilizer to improve the soil.