REACTION OF Ca-DEFICIENT HYDROXYAPATITE WITH HEAVY METAL IONS ALONG WITH METAL SUBSTITUTION

Abstract

Reaction of Ca-deficient hydroxyapatite, HAP-400, with heavy metals, Pb (II), Fe (III), Fe (II), Cu (II), Cd (II), Cr (II), Co (II), Ni (II), and Zn (II) was investigated at 25˚C for 4 h in water, compared with stoichiometric hydroxyapatite HAP-300. From heavy metal consumption and [Ca]/[Metal], which is defined by molar ratio of eluted Ca and consumed heavy metal, the reactions of HAP-400 with the heavy metals except for Pb (II) and Fe (III) proceed via metal-adsorptive substitution mechanism. In the reactions of HAP-400 with Pb (II) and Fe (III), the metals were completely consumed with equivalent elution of Ca, but these reactions proceeded by no simple substitution mechanism to afford Pb (II)-and Fe (III)-bearing HAP-400 with specific structures, namely HAP-400-Pb and HAP-400-Fe.By XRD and FT-IR microspectroscopy, it was found that HAP-400-Pb is constituted of both newly formed lead apatite crystal and the original apatite crystal, and that HAP-400-Fe is constituted of much amorphous FePO 4 phase around the original apatic phase. Therefore, it was concluded that the reactions of HAP-400 with Pb (II) and Fe (III) proceed by the following mechanism: erosion of the apatic structure and formation of a brand-new structure containing metal. This mechanism can be named apatite-erosive substitution mechanism.

HETEROGENEOUS PHOTO-FENTON REACTION OF A HERBICIDE ATRAZINE BY USING Fe(III)-TREATED HYDROXYAPATITES

“…Chlorine element was not detected in the all treated apatites. IR spectra and X-ray diffraction patterns of the treated apatites were in good accordance with the previous reports, 1,18,24,25 indicating amorphic phases. 24,25 2.3.…”

“…IR spectra and X-ray diffraction patterns of the treated apatites were in good accordance with the previous reports, 1,18,24,25 indicating amorphic phases. 24,25 2.3. Photo-Fenton reaction Referred to the previous paper, 18 photo-Fenton reaction was investigated as follows.…”

Hydroxyapatite for removal of heavy metals from wastewater

“…Some of these mechanisms include: surface complexation, ion exchange, dissolution followed by the precipitation of metal phosphates, and the substitution of Ca 2+ present in the HAP structure by other divalent heavy metals during co-precipitation [16,18,28,34]. Literature presents very little information on the specific contribution of these processes, leading researchers to believe that they are all employed at the same time [16,34] (in aqueous solutions containing multiple competing heavy metal ions [33]).…”

“…Other studies have tried to combine the reactivity of hydroxyapatite as an adsorbent with a magnetic separation process for an increased adsorption of heavy metal ions, synthesizing magnetic HAP particles [22] or magnetic core-shell nanocomposites [5]. Ca deficient HAP has also been reported to exhibit different ion substitution ability to stoichiometric HAP [18], due to its large number of Ca-deficient sites. While the main focus of some research groups is to enhance the properties of HAP by using its composites with various polymers, such as chitosan, others choose to focus on cost effectiveness, by synthesizing hydroxyapatite, using environmental friendly methods.…”

Recovery and Enrichment of Aqueous Phosphate From the Slag Released by a Chemical Factory

“…5,6 However the removal behavior of Fe 3+ in the presence of Ca 2+ and PO 4 3-remains unclear. Therefore the effect of the presence of Ca 2+ (0.110 mmol) and PO 4 3-(0.400 mmol) on the removal of Fe 3+ (0.720 mmol) from the solution (100 ml) using CaHAp was examined in the present study.…”