Recovery of phosphate and removal of Cr(VI) from water by calcium-modified panda manure biochar: Synergistic effect of adsorption and reduction

Abstract

Background

Although phosphate and hexavalent chromium (Cr (VI)) are common pollutants in wastewater, there is still a lack of effective recovery and removal methods. The nutrient and pollution elements represented by phosphate and Cr(VI) in the water bodies of rivers and lakes exceed the standard and need to be treated urgently.

Methods

This study explores a novel nanocomposite of calcium-modified panda manure compost biochar used to remove Cr(VI) and phosphate from water. Surface characterization methods, including thermogravimetric analyzer (TGA), X-ray diffractometer (XRD), Electron scanning microscope coupled with an X-ray spectrometer (SEM-EDS), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) were conducted to clarify the degradation mechanism. Furthermore, the interfacial adsorption of phosphate and Cr(VI) on the surface of the material was studied by molecular dynamics simulation.

Significant findings

Recovery of phosphate and removal of Cr(VI) was examined under various experimentations. The results show that biochar pyrolysis at 300 °C exhibits excellent performance, and in the presence of both pollutants, the phosphate recovery efficiency of calcium-modified panda manure compost biochar can reach 90% and the removal efficiency of Cr(VI) can reach 75%. And adsorption process was in accord with the pseudo-second-order kinetics and Temkin adsorption model. Characterization results suggested that the removal of phosphate is mainly dependent on the chemisorption of Ca²⁺ in calcium-modified panda manure compost biochar, and the π-π interaction and -OH redox are the main adsorption mechanisms of Cr(VI). We also found that when the concentration of phosphate was 40 mg/L and Cr(VI) was 5 mg/L, with the increase of time, the recovery rate of phosphate could reach 93.46% and the removal efficiency of Cr(VI) could reach 97.54%. The findings suggest that the further application of calcium-modified panda manure compost biochar in environmental contexts can be optimized by adjusting the initial concentration ratio of phosphate and Cr(VI) ions. This research demonstrates that the assessed material is highly effective for the efficient recovery and removal of phosphate and Cr(VI) from water, thereby enhancing the recycling strategies for panda manure.