Calcium-deficient Hydroxyapatite as a Potential Sorbent for Strontium

Abstract

A calcium (Ca)-deficient hydroxyapatite was investigated for its potential to remove Sr2+ from environmentally relevant water. We conducted sorption tests on solutions containing magnesium ion (Mg2+) and calcium ion (Ca2+) as competing cations at a strontium ion (Sr2+) concentration of 0.05 mmol/L. The Ca-deficient hydroxyapatite maintained a high Sr2+ sorption ratio of above 80% in the presence of Mg2+ and Ca2+ at the concentrations between 0.1 and 1.0 mmol/L, whereas the stoichiometric hydroxyapatite showed a lower ratio even in the presence of small amounts of Mg2+ and Ca2+ (72% for Mg2+ and 51% for Ca2+ at 0.1 mmol/L). For solutions with various Sr2+ concentrations between 0.01 and 10 mmol/L, Ca-deficient hydroxyapatite exhibited a higher Sr2+ sorption ratio than stoichiometric hydroxyapatite. The bonding states of Sr2+ on the Ca-deficient hydroxyapatite were evaluated by extended X-ray absorption fine structure measurements. The results indicated that there are specific sorption sites in Ca-deficient hydroxyapatite where Sr2+ is stably and preferentially immobilized.

(Hydroxy)apatite on cement: insights into a new surface treatment

“…The composition of the control HAp precipitate and powdered surface scrapings from the cement sample after biogenic and abiotic treatments are summarised in Table 1. In the control HAp precipitate, Ca and P are 48.3 wt% and 21.9 wt% respectively, corresponding to a molar Ca/P ratio of 1.70, which is close to the expected value of 1.67-1.68 from stoichiometric HAp 28,29 . Similarly, powdered surface scrapings from the biogenic treatment samples had 37.3 and 16.8 wt% Ca and P respectively, and hence a molar Ca/P ratio of 1.72.…”

“…With the abiotic treatment, however, the surface scrapings had 28.4 and 3.1 wt% Ca and P respectively, which corresponds to a molar Ca/P ratio of 7.13. The latter is more than 4 times higher compared to the control precipitate and other reported values at 1.38 -1.76 for natural, stoichiometric, or carbonated HAp [29][30][31] . HAp does not account for all Ca in the samples and the XRD results show calcite is present in the coated cement samples from both treatments (Figure 2).…”

Preparation and characterization of polyacrylic acid-hydroxyapatite nanocomposite by microwave-assisted synthesis method

“…The groups may be substituted with the OH − group or the group. Thus, calcium-deficient HAp structures are obtained [ 23 ].

Figure 3 SEM image of nano HAp particles.

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“…The CO 3 2À groups may be substituted with the OH À group or the PO 4 3À group. Thus, calcium-deficient HAp structures are obtained [23].…”

From monetite plate to hydroxyapatite nanofibers by monoethanolamine assisted hydrothermal approach

“…Among calcium phosphates, hydroxyapatite (HAp, Ca 10 (PO 4 ) 6 (OH) 2 ) plays an important role thanks to its outstanding properties such as bioactivity, biocompatibility, and osteoconductivity. Due to their high biological activity and specific adsorbability towards various ions and organic molecules, hydroxyapatite-based materials have found application not only as artificial bones or scaffolds for tissue engineering but also as drug delivery carriers 8 , catalysts carriers 9 , and adsorbents 10 , 11 . Another calcium phosphate phase that has recently gained great attention is monetite, or dicalcium phosphate anhydrous (DCPA, CaHPO 4 ).…”