Synthesis and application of magnesium amorphous calcium carbonate for removal of high concentration of phosphate

Efforts have been made to fabricate inorganic adsorbents of magnesium amorphous calcium carbonate (Mg-ACC-X, X=0-6) series with specific size, orientation and morphology and extend its environmental applications. The Mg species was introduced into aragonite (CaCO3) with varying the Mg/Ca ratio. The synthesized adsorbents before/after phosphate retention were characterized by powder X-ray diffraction, scanning electron microscopy with energy dispersive X-ray, Fourier-transform infrared spectroscopy, and X-ray Absorption Near-Edge Structure. When Mg/Ca < 0.5, Mg/aragonite material is obtained, the uptake of phosphate is raised up with increasing the surface area of solids, resulting from the introduction of Mg species. If introduced by more magnesium species (Mg/Ca > 0.5), amorphous calcium magnesium carbonate (ACMC) is then synthesized. The monolayer uptake amount of phosphate reaches the maximum at similar to 2.0 mmol/g for ACMC, which is 10 times stronger than that of calcite at 0.19 mmol/g. Further investigation suggested that the formation of various Ca-P and Mg-P phases were detected for all Mg-containing CaCO3 materials. In particular, the introduction of Mg species favor the nucleation growth of Mg-P phases, thus stabilizing the intermediate DCPD/DCP on surface and retarding the transformation from ACP to HAP. This study therefore indicated that ACMC material (Mg/Ca = 4:6) can be used as an ideal and effective adsorbent for removal of high P from wastewater. (C) 2014 Elsevier B.V. All rights reserved.