Synthesis of hydrotalcite-like compounds with drinking water treatment residuals for phosphorus recovery from wastewater

Abstract

Drinking water treatment residuals are the resources containing a large amount of alum and iron. Most of drinking water treatment residuals are directly landfilled without treatment, but it is a promising way to reuse them in the adsorption of pollutants. The composition of drinking water treatment residuals is of Al and/or Fe, thus our hypothesis is whether it is possible to synthesize hydrotalcite-like compounds from drinking water treatment residuals for phosphorus recovery. In this work, Mg–Al–Fe hydrotalcite-like compounds were successfully synthesized from DWTRs with double-drop method. By analyzing the structure of the materials synthesized under different conditions and their adsorption performance, pH = 9, M3+ rate = 0.45, Al: Fe = 1:1 and T = 333 K were selected as the synthesis conditions of materials for subsequent phosphate adsorption. Pseudo second-order model described the kinetic results better, and both Langmuir and Freundlich model fitted well with the experimental isotherm. The maximum adsorption capacity of 51.1 mg/g according to Langmuir model was higher than other similar materials, indicating the Mg–Al–Fe hydrotalcite-like compounds effectively adsorbed the phosphate. Finally, combined with the results of X-ray diffraction, scanning electron microscopy, Fourier transform infra-red and X-ray photoelectron spectroscopy before and after adsorption, the phosphate adsorption mechanism included physical adsorption, surface complexation, ion exchange and surface chemical precipitation. It concluded that Mg–Al–Fe hydrotalcite-like compound fabrication is a potential way to simultaneously achieve the aim of drinking water treatment residuals utilization and phosphorus recovery.