Phosphorus Binding by Lanthanum Modified Pyroaurite-like Clay: Performance and Mechanisms

In situ immobilization of phosphorus (P) by using P binding agents is a facile and effective strategy for eutrophication control. Currently, the most successful commercial agent (Phoslock, a lanthanum modified bentonite, LMB) still suffers low P removal efficiency from natural waters of complex chemistry, largely due to the competitive complexation of the active La species by humic substances (HAs) and bicarbonate. Herein, we describe an attempt to address these issues by intercalating La into Mg/Fe layered double hydroxides, a pyroaurite-like anionic clay, to obtain a hybrid agent (denoted L-CMF-1.0) of phosphate capacity five times higher than that of LMB. More attractively, the binding stability and capacity of L-CMF-1.0 toward P were significantly enhanced in the presence of HAs and bicarbonate, resulting in a high La usage (P/La ratio at ∼1.30). A continuous P immobilization test in the simulated natural waters validates that the addition of L-CMF-1.0 at 0.12 g/L could result in an efficient P removal from 580 μg/L to <100 μg/L within 38 days, outperforming LMB within 10 days only under otherwise identical conditions. Such improvement results from the rational design of the agent structure, i.e., the host, not only contributes to the direct P uptake but also provides a flexible nanoshelter microenvironment to favor the specific La–P interaction under complex solution chemistry. This work is believed to shed new light on the rational design of P binding agent for enhanced eutrophication control.