Fe12LaO19 fabricated biochar for removal of phosphorus in water and exploration of its adsorption mechanism

Phosphorus (P) runoff from untreated wastewater and agricultural runoff has become an issue of concern because excessive P is detrimental to the health of water bodies and aquatic organisms such as fishes. Hence, different methods are being developed to salvage this challenge. However, most of the methods are expensive, while some are unsustainable. In this study, a simple method was employed in fabricating an absorbent through the co-precipitation of iron and lanthanum on the matrix of biochar prepared from the spent coffee ground for P uptake. The adsorbent named Fe12LaO19@BC was able to attain equilibrium fast within 60 min when used to adsorb P with 98% P removal within the first 30 min Fe12LaO19@BC also maintained high P adsorption across a pH range of 3–7. In the presence of other anions (SO42−, CO32−, NO3−, Cl−, HCO3−) in the solution, Fe12LaO19@BC enabled 71.5–97.8% uptake of P. 81.58 mg P/g maximum adsorption capacity at was reached at 40 °C. The reusability test reveals that about 60% of P uptake was maintained after five adsorption cycles with almost an undisturbed desorption efficiency. The negative value of ΔG°, as shown by the thermodynamic analysis, indicates a favorable and spontaneous reaction during P removal by Fe12LaO19@BC. The XRD analysis showed a major peak corresponding to Fe12LaO19, which is believed to have facilitated the adsorption of P. The adsorption was controlled by multiple mechanisms. An overview of the study indicates Fe12LaO19@BC as a promising adsorbent for the removal of P in the water.