Enhanced reactivity of dicalcium phosphate dihydrate with fluoride ions by coating with apatite nanoparticles

The formation of nanoscale precursors on the surface of dicalcium phosphate dihydrate (DCPD) is an important step in various methods; however, this process requires an unstable solution. Herein, we propose a simple method for the deposition of nanoscale fluorapatite (FAp) particles on the surface of DCPD particles using a weakly acidic, aqueous solution containing only calcium, phosphate, and fluoride ions (C-P-F solution). Repeated immersion in the same solution increases the amount of FAp deposition and almost no delay time is observed. Experimental results indicate that approximately 10 wt.% of FAp on the DCPD surface is optimal to enhance its reactivity with fluoride ions. Our results demonstrate an optimum FAp deposition amount on DCPD particles for improved reactivity with fluoride ions, and we achieved an improved surface of the DCPD particle for fluoride immobilization in wastewater and soil environments.