Phosphate removal performance and mechanism of magnesium–lanthanum-modified coal gasification coarse slag

Herein we present a novel coal gasification coarse slag (CGCS)-loaded magnesium–lanthanum bimetallic phosphate remover. The as-prepared composite (denoted ML2-CGCS) with a magnesium (Mg): lanthanum (La) molar ratio of 1:2 was found to be the best phosphate remover. The modification of CGCS with magnesium instead of lanthanum not only maintains a good phosphate adsorption capacity but also greatly reduces the cost of lanthanum-modified materials; this can save 4601 yuan per ton (in RMB). The maximum phosphate adsorption capacity was 39.22 mg/g, and 35 mg/L phosphate was nearly completely adsorbed within 180 min, exhibiting good phosphate removal capabilities. The effects of humic acid and anions demonstrated that ML2-CGCS has a good selectivity for phosphate removal. A metal leaching study showed that loading Mg–La on CGCS can reduce the lanthanum release problem of Mg–La hydroxides. Saturated ML2-CGCS can be reclaimed at least four times, and can continuously treat more than 1026 bed volumes of actual wastewater. The phosphate removal mechanism involves precipitation, electrostatic attraction, and the inner-sphere complexation. This study revealed that ML2-CGCS exhibits good selectivity, phosphate removal efficiency, and reproducibility, and it can be used to treat actual phosphate wastewater and thereby recover phosphate. This study provides a new method for the development of phosphate adsorbents while recycling CGCS.