Calcium-deficient Hydroxyapatite as a Potential Sorbent for Strontium.

Area of Science:

• Environmental Science
• Materials Science
• Inorganic Chemistry

Background:

• Strontium ion (Sr²⁺) contamination in water poses environmental risks.
• Hydroxyapatite is a potential material for water remediation.
• Understanding cation competition is crucial for effective strontium removal.

Purpose of the Study:

• To investigate the efficacy of calcium (Ca)-deficient hydroxyapatite for strontium (Sr²⁺) removal from water.
• To compare the strontium sorption performance of Ca-deficient hydroxyapatite with stoichiometric hydroxyapatite.
• To evaluate the influence of competing cations (Mg²⁺ and Ca²⁺) on strontium removal.

Main Methods:

• Sorption tests were performed using solutions with varying concentrations of Sr²⁺, Mg²⁺, and Ca²⁺.
• Extended X-ray absorption fine structure (EXAFS) measurements were used to analyze the bonding states of Sr²⁺.
• Sorption ratios were calculated to quantify the removal efficiency.

Main Results:

• Ca-deficient hydroxyapatite demonstrated a high Sr²⁺ sorption ratio (above 80%) even in the presence of Mg²⁺ and Ca²⁺ (0.1–1.0 mmol/L).
• Stoichiometric hydroxyapatite showed significantly lower Sr²⁺ sorption in the presence of competing cations.
• Ca-deficient hydroxyapatite exhibited higher Sr²⁺ sorption across a wide range of Sr²⁺ concentrations (0.01–10 mmol/L).
• EXAFS analysis revealed specific sites in Ca-deficient hydroxyapatite that stably immobilize Sr²⁺.

Conclusions:

• Ca-deficient hydroxyapatite is a highly effective material for removing Sr²⁺ from water, outperforming stoichiometric hydroxyapatite.
• The material's structure facilitates preferential and stable immobilization of Sr²⁺, even under competitive ionic conditions.
• This finding highlights the potential of tailored hydroxyapatite materials for environmental remediation of strontium contamination.