Selenite sorption by carbonate substituted apatite

Area of Science:

• Environmental Chemistry
• Materials Science
• Geochemistry

Background:

• Selenium contamination poses risks to ecosystems and human health.
• Hydroxylapatite is a potential adsorbent, but its efficacy for selenite removal needs enhancement.
• Carbonate substitution can modify hydroxylapatite properties for improved contaminant sorption.

Purpose of the Study:

• To investigate the sorption of selenite (SeO3^2-) by carbonate-substituted hydroxylapatite.
• To compare the sorption performance of carbonated hydroxylapatite with uncarbonated hydroxylapatite.
• To evaluate the potential of carbonated hydroxylapatite for selenium remediation applications.

Main Methods:

• Synthesis of carbonate-substituted hydroxylapatite via precipitation.
• Characterization using SEM, XRD, FT-IR, TGA, BET, and solubility measurements.
• Batch kinetic and equilibrium experiments to determine selenite sorption.

Main Results:

• Carbonated hydroxylapatite exhibited an order of magnitude higher selenite uptake compared to uncarbonated hydroxylapatite.
• Distribution coefficients (Kd) ranged from approximately 4200 to over 14,000 L/kg.
• Selenite sorption by carbonated hydroxylapatite was 23 times faster than uncarbonated hydroxylapatite, normalized to surface area.

Conclusions:

• Carbonate substitution significantly enhances hydroxylapatite's capacity and kinetics for selenite sorption.
• Carbonated hydroxylapatite is a promising sorbent for pump-and-treat technologies, soil amendments, and permeable reactive barriers.
• This material offers an effective solution for remediating selenium-contaminated sediments and groundwaters.