Process optimization and kinetic modeling of phosphate ore dissolution in hydrochloric (HCl)-perchloric (HClO₄) media

This study investigates the leaching of phosphate ore in a mixed hydrochloric (HCl)-perchloric (HClO₄) system to optimize and determine the kinetics of the reaction. The raw, calcined, and leached samples were analyzed using X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM) to determine the chemical composition, mineral phases, and surface morphology. A Box–Behnken design under Response Surface Methodology (RSM) was applied to evaluate the effects of temperature (°C), acid concentration (M), and reaction time (min) on phosphate leaching efficiency, and shrinking models were tested to study the kinetics of the reaction. The XRF results showed that CaO (61.966%) and P₂O₅ (16.929 %) in the calcined phosphate ore reduced drastically to 7.51 % and 1.28 % after leaching, while Fe₂O₃ and SiO₂ increased to 47.31 % and 26.97 %, confirming selective phosphate leaching. XRD analysis revealed the disappearance of apatite peaks and the emergence of quartz and hematite phases, while SEM showed porous, corroded surfaces in the leached residue. Within the selected RSM design space, the optimum condition was identified as 50 °C, 0.5 M HCl-HClO₄, and 60 min. At this condition, the highest experimental response in the Box–Behnken design matrix was 97.0%, the model-predicted dissolution efficiency was 96.25%, and the independent validation experiment gave 95.5%. Kinetic analysis showed that the dissolution process was best described by the surface chemical reaction control model among the shrinking-core models evaluated, with an apparent reaction order of 0.478 with respect to acid concentration. The apparent activation energy was estimated as 16.11 kJ mol⁻¹.