Abstract: Composite particles are disclosed comprising magnesium oxide, iron oxide, and biochar; and methods of making and using the composite particles. The composite particles may be used to recover solutes including phosphate, nitrate, ammonium, and organic compounds from aqueous solution, and the resulting solute-loaded particles may be used as a fertilizer to enhance plant growth. The composites be used to remove pollutants from agricultural runoff, wastewater, and surface water. The particles possess magnetic properties that enhance their recovery following solute adsorption.