Spectrophotometric Determination of Ziroconium in Thorium-Zirconium Alloys

In hydrochloric acid solution, zirconium is precipitated by p(p- dimethylaminophenylazo)benzenearsonic acid (pararsonic acid), DPB. When the precipitate is treated with either a basic or an acid fluoride solution, the free DPB is released. Although thorium is also precipitated to a small extent under conditions leading to the formation of the zirconium complex, the coprecipitation is constant and reproducible for a wide range of thorium concentrations when specific precipitation conditions are used. Fluoride interference is prevented by fuming with perchloric acid in the sample preparation. Digestion periods shorter than 45 minutes increase the thorium contaminationp periods from 45 to 120 minutes result in nearly constant absorbance. With increasing concentrations above 1.80 N, zirconium recovery decreases. Between 1.75 and 1.85 N, the resulting absorbance is essentially constant. For the optical measurements, the less sensitive wavelength of 560 m mu is used because the absorbance at the absorption maximum near 500 m mu is generally too high to be measured.