Synthesis of Al-modified hydrochar from corn stover for efficient phosphate removal

Abstract

The development of a simple and feasible process for preparing adsorbent materials to recover phosphorus resources would have significant environmental and social benefits. In this study, the Al-modified hydrochar was synthesized for phosphate adsorption by hydrothermal carbonization in one pot using corn stover as raw material. The results showed that phosphate adsorption mainly depended on the precipitation reaction between Al element and phosphate, in which the hydrochar carrier played a synergistic role. Al element through the hydrothermal treatment loaded on hydrochar expressed a much higher phosphate adsorption performance than that on pyrochar. When the concentration of AlCl3 solution added in the hydrothermal process was 2 mol·L−1 and the hydrothermal temperature exceeded 180 ℃, Al element could transform from the amorphous state, which was less effective for phosphate adsorption, to Al24O11(OH)44Cl6 crystal with high adsorption performance and could be more stably loaded onto the hydrochar. Although the preparation process was simple, the adsorption performance of hydrochar is good. The phosphate adsorption capacity and removal efficiency by the hydrochar prepared at 260 °C reached to 114.40 mg·g−1 and 76.27%, which could be further increased by adjusting the dosage of adsorbent and pH of water. The pseudo-second-order kinetic model and Langmuir isotherm model could better describe the phosphate adsorption process on Al-loaded hydrochar. Phosphate was rapidly adsorbed on the surface of the hydrochar rich in mesoporous structure and bound to the surface-active sites. This study could transform agricultural waste into a functional hydrochar-based adsorbent and provide a low-cost, simple operation and efficient phosphate removal technology.