Investigation of Fluorine Distribution on the Surface of Acid-Treated Apatite Single Crystals using Nuclear Resonant Reaction Analysis

The surface of natural fluorine-containing apatite (fluoroapatite) single crystals treated with acidic solutions of pH between 0.05 and 2.5 was investigated by nuclear resonant reaction analysis (NRRA) techniques using the 19F(p,αγ)16O nuclear reaction. The experimental results showed that partial defluoridation takes place due to acid attack characteristically depending on the pH of the solutions. Powder-XRD data indicated that the crystallinity of the apatite surface was etained despite of the etchpits observed by SEM-EDS. Relevant investigations of the surface of acid-treated apophyllite crystals, a typical fluorine-containing mineral, indicated a complete amorphization and besides a total absence of fluorine.