Phosphorus removal by porous aggregate from aerated concrete waste residues：Simulating porous structure, performance optimisation, adsorption mechanisms

Abstract

In order to reveal the action mechanism of porous structure of aerated concrete waste residues as aggregate on its working performance and phosphorus removal performance, the porous aggregate is prepared by adjusting the of hydrogen peroxide (H2O2) content to simulate the pore structure of aerated concrete. The results show that with the increase of H2O2 content, the porosity and pore diameter of porous aggregate increases, which causes that the loose bulk density, cylinder compressive strength and softening coefficient decrease and the water absorption through time increases. The correlation coefficients between the four performances and total porosity exceeds 0.95. With the increase of H2O2 content, the pH value decreases and TP removal rate increases. The better fitting of the pseudo-second-order model and Elovich model confirms the key existence of chemical adsorption. In the fitting curve of Intraparticle diffusion model the second stage of rapid absorption becomes the main control step due to calcium and aluminum ions from capillary pores and gel pores and the hydration of unreacted particles. The Ca/Si and Al/Si decreases by 57.7% and 46.6% in EDS maps after phosphorus removal, and CaO/SiO2 and Al2O3/SiO2 in XRF results decrease. The hydration of unreacted C4A3Š and dissolution of Ca2+ and Al3+ during phosphorus removal promote the chemical absorption of porous aggregate. P/Si increases by 631.9% and P2O5/SiO2 increases from 0.01 to 0.11. The fluffy substances appears on the smooth inner wall of the porous aggregate in SEM morphology is phosphate mineral.