Investigation of the Thermal Properties of Alkali Metal Thorium Phosphates and Their Application for the Sorption of Uranyl Ion from Acidic Medium

Herein, we report the investigation on thermal stability and measurements of thermo physical properties of quaternary alkali metal (K/Rb/Cs) thorium phosphates. Among them, potassium thorium phosphates are most efficient for chemisorption of uranyl ions from aqueous medium.

Abstract

Thermo physical properties of potassium, rubidium and cesium thorium phosphate compounds were investigated. All compounds were synthesized by conventional solid state method. Formation of orthorhombic AMThP₃O₁₀, tetragonal AM₂Th(PO₄)₂ and monoclinic AMTh₂(PO₄)₃; [AM=K, Rb and Cs] was confirmed using Powder X-ray diffraction (XRD) technique. Structural study of CsThP₃O₁₀ was carried out for the first time from Rietveld refinement of XRD data. Thermal stability of all compounds was established using Thermogravimetric analysis (TGA) technique. When heated at 1673 K for 30 h in air, all the compounds decompose to ThO₂. High temperature X-ray diffraction (HT-XRD) data of the compounds, synthesized during present study, were collected in an inert atmosphere from ambient to 973 K and their thermal expansion coefficients were calculated. These compounds show positive thermal expansion up to 973 K. Molar heat capacities for all phosphates were measured between 300–863 K using Differential Scanning Calorimeter. Alkali metal thorium phosphates, AMThP₃O₁₀ and AMTh₂(PO₄)₃, showed efficient uptake of uranyl ion from aqueous acidic medium predominantly following Langmuir isotherm and Webber Morris intra particle diffusion kinetics.

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