(180t) Phosphate Adsorption from Water Using Iron and Magnesium Oxide-Modified Acacia-Derived Biochar

A novel biochar (BC) was produced from pruning waste of Acacia tortilis trees and evaluated for its ability to remove phosphate from water. The biochar was obtained through calcination at 600 °C and further modified with iron oxide and magnesium oxide using a hydrothermal method. The incorporation of iron and magnesium into the BC structure was verified through EDS and XRD analyses. Both unmodified and modified BCs were tested for their phosphate removal capabilities in synthetic aqueous solutions with concentrations ranging from 1 to 500 ppm. The unmodified BC showed minimal phosphate removal, whereas the modified version demonstrated near-complete phosphate removal. This improvement is attributed to the increased surface charge and surface area resulting from doping with metal oxides. Specifically, the average porosity and BET surface area rose by over 20%, from 322 to 394 m²/g, following the modification. Additionally, the point of zero charge (PZC) shifted from pH 3.4 for the unmodified BC to pH 5.3 after doping. The adsorption process was rapid, achieving 82.5% phosphate removal within 30 minutes, and reaching 97.5% after 4 hours, due to the increased surface area and strong interactions between phosphate ions and the modified BC surface. The maximum adsorption capacity reached 98.5 mg/g at a phosphate concentration of 500 ppm and pH 8.5. Furthermore, among four commonly used adsorption isotherm models, the Langmuir model best described the phosphate adsorption behavior onto the modified BC.