Phosphorus removal by concrete-based layered double hydroxides: The influence of titration mode for continuous flow coprecipitation

Abstract

The global phosphorus (P) crisis and eutrophication promotes the development of dephosphorization technology from wastewater. To seek an effective and sustainable way for phosphorus removal, concrete-based layered double hydroxides (C-LDH) was synthesized from waste concrete by continuous flow coprecipitation method. Results indicated that the dropping mode of the titration had significant effects on the property of C-LDH. The product of single-point titration coprecipitation (C-LDH_S) presented developing flakes morphology, which contained more Ca/Al-LDH and a certain amount of Mg/Al-LDH, while the product of multipoint titration coprecipitation (C-LDH_M) exhibited a good hexagonal morphology and contained more Mg/Al-LDH. C-LDH_M provided more valid adsorption sites and higher adsorption energy for phosphorus, resulting in a larger adsorption capacity. Ca/Al-LDH in C-LDH tended to dissolve when the environmental pH value was lower than its formed pH, but Mg/Al-LDH remained, the difference between the two components brought about different P-uptake efficiency and mechanism between C-LDH_S and C-LDH_M. The dissolution of Ca/Al-LDH from C-LDH_S initiated the dephosphorization way dominated by CaP precipitation, whereas the more reservation of Mg/Al-LDH in C-LDH_M derived more P-uptake by adsorption. The phosphorus held by C-LDH_M presented better recyclability. The overall results indicated that C-LDH_M was an economical and sustainable candidate for phosphorus removal.