Adsorption and immobilization of phosphorus in eutrophic lake water and sediments by a novel red soil based porous aerogel

To effectively mitigate global eutrophication in lakes, regulating sedimentary phosphorus release remains a primary strategy. Enhancing the adsorption and stabilization performance of passivating agents is integral to addressing endogenous phosphorus pollution in aquatic systems. This study presents a novel aerogel with a high specific surface area (663.06 m²/g) and a mean pore size of 2.78 nm, synthesized from cost-effective and abundant red soil. Batch experiments demonstrated that the red soil aerogel (RSA) achieved a maximum phosphorus adsorption capacity of 23.29 mg P/g, surpassing lanthanum-modified bentonite (LMB) by 1.5 times. The RSA exhibited phosphorus removal efficiencies between 82 % and 97 % across a pH range of 4 to 9. Moreover, RSA retained a removal rate exceeding 95 % in the presence of common ions (SO₄^2-, Cl^-, and NO₃^-) at concentrations of 100 mg/L, showing minimal performance reduction even under high HCO₃^2- concentrations. The comprehensive analysis identifies electrostatic attraction, ligand exchange, and Lewis acid-base interactions as the primary mechanisms driving phosphate adsorption onto the RSA surface. RSA exhibited a strong capacity to immobilize phosphorus within sediments, achieving an 83.0 % to 97.5 % reduction in endogenous phosphorus release into the overlying lake water and promoting the conversion of mobile phosphorus into NaOH-P. After 38 days of hypoxic incubation, active phosphorus levels in surface sediments were reduced by over 60 % compared to the control group. The findings highlight RSA's potential as an effective passivating agent for mitigating internal pollution. This study presents a cost-efficient porous silicon-aluminum aerogel with high phosphorus adsorption efficiency, synthesized using the readily available red soil from southern China, offering a viable strategy to address endogenous phosphorus release in eutrophic lake environments.