The three main constituents of the apatite mineral group are fluorapatite, chlorapatite and hydroxylapatite. Since these minerals are found in low temperature environments, their composition can be affected by the amount of carbon dioxide dissolved in the air, water and soil. This can lead to the substitution of carbonate into their crystal structure resulting in the formation of carbonate apatite. The carbonate ion an substitute for the anion in the channels of the apatite structure resulting in A-type carbonate apatite (CAp), for a phosphate group resulting in B-type CAp or both sites resulting in an AB-type CAp. Hydroxylapatite has been used in permeable reactive barriers (PBR) to remediate groundwater contaminated with Pb²⁺, Zn²⁺, Cd²⁺, As⁵⁺, Se⁴⁺, and U⁶⁺. Apatite is also one of the few minerals created in biological systems. The inorganic component that comprises human bone material is an analogue of hydroxylapatite (HAp) [Ca₁₀(PO₄)₆(OH)₂] which can contain many ions, of which the most abundant is carbonate (~8 wt%). A better understanding of the carbonate environments in carbonate apatite could lead to better remediation PRBs and better artificial bone biocompatibility.

The purpose of our study will be to characterize the carbonate environments and the surface properties of A-type, B-type and AB-type CAp. X-ray diffraction (XRD) will be utilized to characterize the samples. Using synthesized samples enriched with ¹³C the carbonate environments will be analyzed using solid-state nuclear magnetic resonance (NMR) spectroscopic techniques such as ¹³C single-pulse MAS, ¹³C{¹H} CP/MAS, ¹H-³¹P HetCor, and ¹³C- ³¹P REDOR NMR. The surface characteristics will be analyzed using zero point charge (ZPC) measurements to determine surface charge, BET analysis will be performed to measure mean particle size and SEM will be used to determine crystallite morphology. We hope that our results will show a relationship between the surface properties of A-type, B-type and AB-type CAp and the carbonate environment observed.