Recycle of Fe/Ca-rich fly ash in preparation of modified porous ceramsite for selective and efficient phosphate recovery

Abstract

Although wastewater management has systematically developed globally, the removal efficiency of phosphates still posed a serious challenge and attracted worldwide concerns. On the other side, the discharge of fly ash (FA) from sludge incineration also caused serious environmental problems. In this study, Fe/Ca-rich FA was recycled to synthesize a porous ceramsite (modified CFA) through a non-sintered method. It could be an efficient adsorbent for phosphate recovery in virtue of abundant adsorption sites, accompanied by its low-cost and environmental friendliness. The phosphate adsorption capacity was 26.31 mg-P·g^-1 for modified CFA, and its average adsorption rate could reach 1.344 mg-P·(g·day)^-1 in the first 2 days. While it could also efficiently immobilize phosphate for a quite long period in the dynamic system effluent. According to electron microscopic and spectroscopic characterizations, modified CFA was indicated to chemisorb and immobilize phosphates via multiple interface interactions. Phosphates were firstly H-bonded with the surface Fe/Ca-OH of modified CFA and then rapidly coordinate with active Fe sites through a ligand exchange mechanism. When the exposed Fe sites had been saturated-adsorbed, inner-sphere Ca-O-P coordination would be further formed. In summary, this study provides a promising FA-derived adsorbent and realizes the efficient P pollution management with low cost and minimal environmental risks, which would be a potential waste-to-wealth strategy for further applications.