A green synthesis strategy toward calcined calcium-aluminum layered double hydroxide with sludge as aluminum source for efficient removal of phosphate from water

Abstract

Layered double hydroxides promise efficient phosphorus removal from water, yet their preparation process inevitably leads to the consumption of metal minerals and incurs high material costs. The drinking water treatment aluminum sludge with high aluminum content is a suitable source for obtaining metal aluminum. Recognizing the environmental and economic challenges in traditional layered double hydroxides production, this research proposes a novel approach utilizing high-aluminum drinking water treatment aluminum sludge as an alternative aluminum source. Herein, calcium-aluminum layered double oxides with aluminum sludge as aluminum source (Ca/(Al-DWTAS)-LDOs) were prepared by co-precipitation and calcination method. The study meticulously examines the influence of variables such as dosage, initial pH, and the presence of coexisting ions on phosphorus removal efficiency: at the optimal dosage (0.5 g/L), the adsorption efficiencies of Ca/(Al-DWTAS)-LDOs for phosphate in the range of 2.0 < pH < 11.0 and in the environment of common anionic disturbances were maintained at more than 90%. After six adsorption-desorption tests, the phosphate removal efficiency of Ca/(Al-DWTAS)-LDOs only decreased from 98.85% to 74.38%. According to the Sips isotherm model, the maximal adsorption capacity of Ca/(Al-DWTAS)-LDOs at ambient temperature (25 °C) was determined to be 110.14 mg/g. Adsorption mechanism of Ca/(Al-DWTAS)-LDOs were explored through characterization, kinetic and thermodynamic studies, mainly involving electrostatic reactions, ion exchange reaction, surface complexation reaction, and surface precipitation. When 0.5 g/L Ca/(Al-DWTAS)-LDOs was added to the actual swine wastewater with phosphate content of 37.25 mg/L, the phosphate removal efficiency reached 86.19%. This study not only provides an alternative process method for the acquisition of layered double hydroxides, but also has wide applications for environmental protection.