Lanthanum-loaded peanut shell biochar prepared via one-step pyrolysis method for phosphorus removal and immobilization

Phosphorus (P) is a nutrient element triggering eutrophication. Therefore, the removal of excess phosphorus has become an emergent demand. In this study, lanthanum-loaded biochar (La-BC) was prepared via a simple one-step pyrolysis method. Its surface properties and structural characteristics were analyzed by SEM, XRD, FTIR and pH_pzc. The phosphate removal by the La-BC was systematically investigated in batch mode. Results showed that the phosphorus adsorption obeyed the pseudo-second-order model and Langmuir isotherm. The calculated maximum adsorption capacities were 31.94, 33.06 and 33.98 mg/g at 25, 35 and 45°C, respectively. Except for SO₄²⁻ and CO₃²⁻, phosphate adsorption by the La-BC showed strong anti-interference to coexisting ions. For real water samples, the phosphate concentrations in the effluents were below 0.02 mg/L after treatment. The P loaded the La-BC was difficult to be desorbed, suggesting that the La-BC was not only a P-capping agent but also a P-immobilizing agent. More interestingly, a large number of stable LaPO₄ nanofibers were formed on the La-BC surface via the reaction between the dissolved phosphate anions and La(OH)₃ loaded on the adsorbent. Their intertwining facilitated the formation of the floc, which was conducive to the solid–liquid separation. Hence, the developed La-BC can be used as a potential adsorbent for natural waterbody remediation.