A Developed Spectrophotometric Method for Thorium Determination using Alizarin Red S Dye in Different Types of its Bearing Rocks

The spectrophotometric determination of thorium from its different bearing rock types such as Thorite, Trachyte, and Ring complexes using the well known chromogenic alizarin red S (ARS) dye was proposed in the present work. Optimization of the formed thorium-alizarin red S complex was performed by studying several parameters such as different acid media, suitable buffer pH, dye concentration, duration time of the formed complex, and thorium concentration (calibration curve). The optimized method was applied to different rock types bearing thorium as well as standard phosphate (2). Interference due to major oxides was treated by partial decomposition of rock samples, which minimized their concentrations together with complete leaching of thorium facilitated the accurate determination of thorium in those samples. On the other hand, interference due to high uranium concentrations was overcome by its selective extraction using trioctylamine in xylene. Beers law was obeyed from a concentration of 1 g ml-1 till 80 g ml-1 with a molar absorptivity value of 0.42 x 103 l mol-1 cm-1. The percentage relative standard deviation ( %RSD) for 10 replicate measurements of 10 g ml-1 thorium was 2.23 %.