High-gravity-assisted controlled synthesis of lanthanum carbonate for highly-efficient adsorption of phosphate

Algal bloom caused by excessive phosphate is toxic to the ecosystem and human health, and lanthanum carbonate (LC) as an adsorbent is efficient for phosphate removal. Herein, we propose an efficient high-gravity-assisted precipitation method to synthesize LC with polymorphs and various morphologies including amorphous LC (ALC), flower, layer, and rod in a rotating packed bed (RPB) by adjusting reaction temperature, time, and solvent. Compared to traditional stirred tank reactor, the RPB can prepare smaller LC particles with narrower size distribution in a shorter reaction time. Remarkably, the 35 nm ALC with the highest BET surface area (106 m 2 /g) can remain steady among 6 months of storage and exhibits superior adsorption performances with a high adsorption rate (reaching equilibrium within 1 h) and adsorption capacity (162 mg P/g). Especially, its adsorption capacity per unit time is currently at the leading level reported in the literature. The possible adsorption mechanism reveals that the amorphous state, nanonization and high BET surface area of LC accelerate the dissolution procedure to allow more complete exposure of the intrinsic active sites for ligand exchange and maximize La utilization, resulting in the remarkable improvement of adsorption performance. These findings suggest that amorphous nanoparticles serve as a novel state-of-art candidate toward greatly improved efficiency of ions removal in wastewater.