The dissolution kinetics of sepiolite in hydrochloric acid and nitric acid were studied in a batch reactor. The effects of reaction temperature, acid concentration, particle size and solid-to-liquid ratio on the dissolution process were investigated. Experimental studies were carried out in the ranges of 25–75°C for reaction temperature, 0.25–1.00 mol/L for acid concentration, 0.00755–0.05020 cm for average particle size and 2.5 to 12.5 g of solid/100 mL of acid for solid-to-liquid ratio. It was determined that the dissolution process is controlled by resistance of the diffusion through the product layer. The activation energies of the process were determined to be 40.8 and 38.3 kJ/mol for hydrochloric and nitric acid, respectively. The apparent rate constants were expressed as a function of reaction temperature, acid concentration, particle radius and solid-to-liquid ratio: kαe−4910(1/T)Cr−0.6 (s/l)−1 and kαe−4606(1/T)Cr−0.5 (s/l)−1 for hydrochloric and nitric acid, respectively; k is the apparent rate constant in min−1; T, the reaction temperature (K); C, the acid concentration (mol/L); r, the initial particle radius (cm); s/l, the solid-to-liquid ratio (g of solid/100 mL of acid).

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