Ion exchange capacity of Sr ²⁺ onto calcined biological hydroxyapatite and implications for use in permeable reactive barriers

With the recent Fukushima incident, there is an urgent need to find cost effective and workable permeable reactive barrier (PRBs) for the remediation/retardation of problematic radionuclides. Catfish bones were calcined at various temperatures (4001100° C) to remove the organic matter (87.1 mgg ¹) and to change the structural properties of the hydroxyapatite (HAP). Increasing temperatures increased the HAP crystallinity as indicated by a decrease in lattice strain (0.0098 to 0.00135) and an increase in crystallite sizes (5.0 × 10 ⁸ to 7.7 × 10 ⁸ m). There was also an observed decrease in specific surface areas (98.9 to 0.99m ²g ¹) and increase in particle sizes (50 to 1000 nm). The sorption densities of Sr2+ decreased with increasing calcination temperatures, from 0.34 to 0.05 mmolg ^1. However, once normalized for surface area, the sorption densities increased from 1.8 to 5.9 mmolm ². Overall, this research has important implications for the design of hydroxyapatite PRBs with higher calcination temperatures producing a more reactive material with larger particle sizes for increased permeability. Lower calcination temperatures produced amorphous HAP material, which released more aqueous PO4 ^/3 3 and resulted in the precipitation of strontium phosphates, ultimately reducing the permeability of PRBs.