Direct Nano-Imaging Reveals the Underestimated Role of Lanthanum Phosphate Formation in Phosphorus Sequestration by Lanthanum Carbonate
Yuhang Li, Wanyi Fu, Yujie Wan, Xing Yan, Bingcai Pan
Abstract
Lanthanum-based materials are recognized as highly effective adsorbents for advanced phosphorus removal, with a prevailing belief that acidic conditions promote phosphorus uptake via enhanced surface complexation. Herein, we demonstrate that lanthanum carbonate exhibits a 1.8-fold higher phosphate adsorption capacity at pH 7 (33.2 mg-P/g) compared to pH 4 (18.5 mg-P/g), attributed to the enhanced formation of LaPO 4 nanocrystals. Leveraging in situ atomic force microscopy (AFM), we resolve real-time phosphorus sequestration dynamics, capturing LaPO 4 nucleation within minutes, contradicting prior reports that LaPO 4 formation is time-intensive. This discrepancy arises because conventional characterization techniques (e.g., X-ray diffraction) overlook transient amorphous LaPO 4 intermediates due to insufficient sensitivity, whereas the nanoscale resolution of AFM directly tracks interfacial transformations. A dissolution-nucleation-growth mechanism was then proposed for the interfacial formation of LaPO 4 . This study revises the mechanistic framework for phosphorus removal and highlights the crucial role of LaPO 4 formation in maximizing the utilization efficiency of lanthanum active sites for enhanced phosphate sequestration by La-based materials.