Blocking endogenous phosphorus release in sediments by a hydrotalcite mixture synthesized with natural sepiolite and discarded cans

Abstract

Pure hydrotalcite (LDH) materials prepared from chemical reagents have been investigated as solid-phase phosphorus (P) inactivation materials (SPIM) to manage endogenous P loading in sediments. However, the efficacy and mechanism of LDH mixtures prepared by natural minerals and solid wastes in controlling sediment P release are unclear. Therefore, a Ca/Mg-Al-LDH (CMA-LDH) material was synthesized using sepiolite and cans, and its efficacy, mechanism, and ecological impact in controlling sediment P release were investigated. CMA-LDH-p was prepared as a control material using pure chemical reagents. The CMA-LDH and CMA-LDH-p were both composed of hydrotalcite and hydrocalumite. The maximum P adsorption capacity of CMA-LDH was 123.01 mg/g, comparable to that of CMA-LDH-p. The adsorbed P by CMA-LDH was mostly in the stable P form, accounting for 87.2 % of the total P. The adsorption capacity and immobilization ability of CMA-LDH for P were superior to other reported LDH-based SPIM. Both the CMA-LDH addition and capping successfully blocked sediment P release under anaerobic conditions. Passivation of mobile P in the sediment and DGT-labile P in the interstitial water was critical to preventing sediment P release by the CMA-LDH addition. The CMA-LDH capping inhibited sediment P release through the effective adsorption of CMA-LDH on DGT-labile P at the sediment/overlying water interface. The CMA-LDH addition and capping affected the abundance of microbial communities associated with iron and sulfur cycling, which might affect the stability of endogenous P. These results confirmed that CMA-LDH addition and capping treatments were effective methods for managing sediment P loading.