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 pHpzc. 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.