Reactivity Improvement of Dicalcium Phosphate Dihydrate with Fluoride for Its Removal from Waste and Drinking Water

Abstract

Dicalcium phosphate dihydrate (DCPD) reacts with fluoride ion in an aqueous solution and forms stable fluoroapatite (FAp). This reaction requires a lag time to form nano-sized precursor, hydroxyapatite (HAp)-like calcium phosphate, on DCPD surface. This long lag time prevents DCPD from applying as an effective fluoride removal agent from waste water. The purpose of this study is to improve the reactivity of DCPD with fluoride ion by HAp-coating on the DCPD surface by soaking it in the simulated body fluid (SBF) under various DCPD/SBF ratios and soaking periods. The results showed the HAp-coating on DCPD by soaking in the SBF reduced the lag time to be negligible with increasing in amount of HAp up to 2 % in mass to the DCPD; however, further HAp formation had no affects on improvement of the reactivity.

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

“…In our previous study on the treatment of DCPD using SBF [18], the content of the HAp particles present on the DCPD particle surfaces was an important factor in the improvement of its reactivity with fluoride ions. The effect of the C-P-F solution treatment method on the amount of FAp deposited onto the DCPD particle was investigated to determine if this amount could be controlled.…”

“…The FAp amount on the DCPD particle surfaces was calculated from the Ca/P molar ratio obtained via ICP-OES analysis of the DCPD dissolved in nitric acid. This method was used in our previous study to investigate the amount of HAp present on the DCPD particle surfaces [18]. Figure 12 shows the relationship between the amount of FAp in DCPD and the Ca/P ratio.…”

“…Based on these observations, the optimum amount of FAp hybridized on the DCPD particle surface is limited by the induction period and the amount of fluoride removed during the DCPD reaction. In our previous study, we suggested that the enhancement of the reaction could be evaluated by noting the amount of fluoride ions removed after 1 h of reaction [18]. The amount of fluoride ions removed by the DCPD/FAp hybrid can be determined by the variation in the fluoride ion concentration after 24 h of reaction.…”

“…In our previous reports, the deposition of HAp nanoparticles was achieved by immersing DCPD in simulated body fluid (SBF) [18], which has similar concentrations of inorganic ions to human body plasma and is widely used for the HAp coating of various materials in the field of biomaterials [19]. The concentrations of calcium and phosphate ions in SBF are supersaturated for the HAp coating, meaning that SBF is an unstable solution.…”