Enhanced phosphate removal from solution using Al-doped aragonite nanoparticles

Abstract

Attempts have been dealt to stabilize the aragonite (CaCO3) and improve its environmental applications for high concentration of phosphate removal by the introduction of aluminum (Al) species. The nano-pellets of aragonite doped with Al (Al/aragonite) was therefore manufactured in this study. With a combination of XRD, FTIR, zeta potential, SEM-EDX and XPS analysis, the synthesized Al/aragonite materials before/after phosphate sorption were characterized. The incorporation of Al species in aragonite lattice significantly increased the high phosphate scavenging from solution. Compared with the Langmuir monolayer coverage of phosphate on aragonite and calcite, the multi-layer sorption onto Al/aragonite could be described well by Freundlich model. Thus, the phosphate removal of Al/aragonite was 6 time stronger than aragonite, and 15 times than calcite at alkaline pH. The likely reason was that the Al species doped in Al/aragonite nanoparticles increased the surface area and reduced the negative surface charges, especially, provided the more adsorption sites for the formation of irreversible inner-sphere phosphate complexes which induced the vastly unlimited growth of CaHPO4 in the pH range of 5.0–12.0. Overall, the Al/aragonite nanoparticles (Al/Ca molar ratio = 0.205) was found to be the optimal material to efficiently remove the high-level phosphate from wastewater within the wide pH ranges.