Cloud Point Extraction and Spectrophotometric Determination of Thorium(IV) Ions and their Application in Silicate Rock Samples

Article history: Received 20 August 2019 Accepted 15 October 2019 The phase-separation phenomenon of non-ionic surfactants occurring in aqueous solution was used for the extraction and concentration of thorium ions. The method is based on the complexation reaction of thorium(IV) with 2-(5-bromo-2pyridylazo)-5-diethylaminophenol (5-Br-PADAP) at pH (3.4). The formed complex was quantitatively extracted to the phase rich in octylphenoxypolyethoxyethanol (Triton X-114) after centrifugation. The enriched analyte in the surfactant-rich phase was extracted, dissolved and determined spectrophotometrically at 531 nm. The optimal extraction and reaction conditions (e.g. pH, surfactant concentration, reagent concentration, temperature, effect of time) were evaluated and the analytical characteristics of the method (e.g. limit of detection, linear range and preconcentration factor) were obtained. Linearity was obeyed in the range of 0.125-2.5μg/ml of Th(IV). The interference effect of some foreign ions was also tested. The proposed method was successfully applied for the preconcentration and determination of trace thorium ions in certified reference sample and silicate geological samples.