[Efficiency of Magnesium Hydroxide Capping and Amendment to Control Phosphorus Release from Sediments].

Eutrophication of freshwater bodies has become a global environmental problem, and phosphorus (P) has been identified as one of the key limiting factors responsible for this eutrophication problem. Reducing internal P release is crucial to the control of the eutrophication of freshwater bodies besides reducing the input of external P. To control sedimentary P release, magnesium hydroxide[Mg(OH) ₂ ] was applied as a capping and amendment material in this study. The adsorption performance of phosphate on Mg(OH) ₂ was investigated in batch mode, and the effect of Mg(OH) ₂ capping and amendment on the mobilization of P in sediments was studied using sediment incubation experiments. Results showed that Mg(OH) ₂ exhibited good adsorption performance toward phosphate. The phosphate removal efficiency of Mg(OH) ₂ increased with increasing adsorbent dosage. The adsorption equilibrium data of phosphate on Mg(OH) ₂ could be better described by the Freundlich and Dubinin-Radushkevich isotherm models compared to the Langmuir isotherm model. Mg(OH) ₂ capping and addition both could effectively control the release of reactive soluble P (SRP) from sediments into the overlying water, resulting in a low concentration of SRP in the overlying water under Mg(OH) ₂ capping and amendment conditions. Mg(OH) ₂ capping and amendment both could reduce pore water SRP in the uppermost sediment (0-10 mm), which played a key role in the control of the release of SRP from sediments into the overlying water. The as-prepared Mg(OH) ₂ possessed a much higher phosphate adsorption ability than commercial Mg(OH) ₂ , and the former also had a higher controlling efficiency of sedimentary P release than the latter. In summary, Mg(OH) ₂ is a promising capping and amendment material for the control of internal phosphorus release in freshwater bodies.