Summary Detailed investigations of CuCl2 hydrolysis step of Cu–Cl thermochemical cycle were carried out on various aspects: (a) characterization and thermal properties of reactants/products using X‐ray diffraction (XRD), thermogravimetry–mass spectrometry (TG‐MS), scanning electron microscopy (SEM), temperature‐programmed desorption (TPD), and extended X‐ray absorption fine structure (EXAFS); (b) performance evaluation of fixed bed hydrolysis; (c) parametric optimization with respect to S/Cu, flow rate (gas hourly space velocity, GHSV), reaction duration, temperature, and particle size; and (d) monitored hydrolysis using isothermal TG experiments at 360°C, 370°C, 380°C, 390°C, and 400°C to derive kinetic parameters rate constant (k) and activation energy (Ea) on the basis of the shrinking‐core model. 97% conversion to Cu2OCl2 at 17 630 h−1 of GHSV, 400°C was achieved using ball‐milled CuCl2 (BM6), as compared with that of 55% over commercial un–ball‐milled reactant, CuCl2 (UBM). Correspondingly, higher k value of 2.84 h−1 over BM6 as compared with 0.97 h−1 over UBM reactant at 400°C was achieved. Ea for hydrolysis of BM6 was 93 kJ/mol, while it was 106 kJ/mol for UBM as derived from the Arrhenius plot. A probable pathway for CuCl2 hydrolysis is proposed here. It was found to be diffusion controlled, and the particle size of reactant molecules affects the packing and diffusion length. Based on our investigations, it is very unlikely to get >99% phase pure product (Cu2OCl2). Cu2OCl2 is labile in nature and tends to transform into structurally similar and stable compounds CuO and CuCl2.

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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.