First-principles Study of the Removal of Boron by Co-precipitation with Hydroxyapatite Using Dolomite as a Starting Material

Boron is a toxic chemical in drinking water and a major health concern worldwide. One method to reduce boron concentration in water consists of co-precipitating boron with hydrated minerals. Nevertheless, little is known about the chemical mechanisms underlying boron reactions with complex minerals. In this work, we have applied first-principles calculations based on density-functional theory (DFT) to characterize boron-bearing hydroxyapatite (HAp) resulting from co-precipitation with hydrated dolomite. DFT calculations have been performed to interpret X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) experiments and to characterize solid residues after boron removal with a focus on determining the absorption sites of B(OH)$_{3}$ and B(OH)$_{4}$ in the formed minerals. The computed results indicate that the absorption takes place at phosphate (PO$_4$) sites. In addition, changes in the lattice parameters of B-bearing HAp as a function of boron concentration have been calculated and compared with experimental results. Good agreement of the decreasing trend in $a$-direction and the increasing trend in $c$-direction has been observed by our calculations. Raman and infrared (IR) spectra have been studied as well to achieve a better understanding the B-HAp structures.