| Hydroxyapatite(HA) is an effective adsorbent with high stability for removing heavy metal ions in soil and water. It has been reported that dentifrice containing HA can dispel the oral smell, whiten teeth, remove plaque, promote early enamel lesion remineralization, and prevent caries and periodontal disease. We have found in our previous study that the potential value of dentifrice containing HA in relieving dentin hypersensitivity and removing chromium ions in aqueous solution. With the development of economy, the discharge from mining, metallurgy and curriery is getting increasing, which caused the water on and underground the surface polluted. However, there are not yet any studies about capacity of dentifrice containing HA in adsorption of other common heavy metals in aqueous solution.ObjectiveIn this study, the adsorption of heavy metals were divided into two parts, including adsorption of single heavy metal and adsorption of mixed heavy metal so as to explore and compare the capacity of dentifrice containing HA with different particle sizes and doses in heavy metals aqueous sorption, as well as the stability of the sorption capacity and adsorption mechanism. MethodsFifty mL of heavy metal solution was divided into four groups (dentifrice containing80nm HA, dentifrice containing300nm HA, dentifrice containing600nm HA, blank dentifrice) and added to1mL of dentifrice solution with different concentration, respectively then been kept still for1day. The residual heavy metal ion concentration of the supernatant was measured by ICP and the removal rate of was calculated. The precipitate of the solution was dried and the elements constitute was detected by EDS. The procedure was repeated and kept the mixed solution placed at room temperature for14d,28d, then the residual heavy metal ion concentration and calculated the removal rate were remeasured.Results<1>Dentifrice mixed HA showed good capacity in adsorption of single ion and with the increase of concentration of dentifrice suspension, the residual ions concentration of Pb2+, Cu2+, Cd2+, Zn2+in the reaction system presented a gradual downward tendency. Specifically, the best capacity in Pb2+adsorption is the dentifrice containing300nm HA group, which is up to92.65mg/g, with the adsorption rate more than99.5%, and Cd2+adsorption up to11.73mg/g with the adsorption rate more than89.8%. There was no significant difference in the adsorption rate of Cu2+, but significantly higher than the blank group, and the best capacity to Cu2+adsorption is up to305mg/g, with adsorption rate is more than75%. Furthermore,at low concentration the adsorption was unstable and appeared to be desorptive, and otherwise at high concentration. Finally, the best capacity in Zn2+adsorption is up to11.65mg/g appeared in the dentifrice containing300nm HA group, with the adsorption rate of52.92%and stable adsorption.<2>Heavy metal ions could be detected in the precipitate by EDS after reaction of HA dentifrice with ion solution. And these ions could be adsorbed by HA dentifrice were further confirmed.<3>In the mixed ion solution, dentifrice with HA also demonstrated good adsorption of mixed ions, especially the dentifrice containing300nm HA. The adsorption differences to heavy metal ions were as follows:Pb2+>Cu2+> Cd2+> Zn2+. It was also found that the adsorption rate of the dentifrice with HA to mixed ions was lower than to single ion, for there exsisted competitive inhibition phenomenon between ions.ConclusionsDentifrice containing HA have good adsorptions of aqueous Cd2+, Zn2+, Pb2+, Cu2+. In this study hydroxyapatite with different particle sizes have different adsorption effects. Dentifrice containing300nm HA has the best adsorption capacity not only in the low concentration of single heavy metal but also in the high concentration of mixed ion. |
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