UV-Visible spectroscopy can be utilized in an on-line fashion to directly measure the concentration and speciation of special nuclear materials, such as uranium and plutonium, thus allowing real-time process control and tracking for the solvent extraction processes. Attributing UV-Visible data to process conditions is complex due to uranyl nitrate speciation, thus efforts focus on characterizing the system encompassing 0.01-1.26M U and 0.01-8M HNO3. Results suggest dominant speciation changes from low (0.01M) to high (6M) HNO3, and peak shifts in the high (1M) uranyl system imply an ingrowth of species not present at lower uranyl concentrations.