Kinetics of selective chlorination of pre-reduced limonitic nickel laterite using hydrogen chloride

The selective chlorination process of pre-reduced limonitic nickel laterite using hydrogen chloride was investigated in this work. In HCl-O₂-H₂O-N₂ atmosphere, the effects of variations in temperature, the partial pressures of hydrogen chloride, oxygen and water vapor, and total gas flow rate were all studied. It was found that the chlorination of nickel and cobalt could be described by two stages; and it was controlled by gas diffusion through product layer. Four apparent activation energies, including 20.43 kJ/mol and 12.89 kJ/mol for the first and second stage of nickel chlorination, 14.95 kJ/mol and 13.02 kJ/mol for the first and second stage of cobalt chlorination respectively, were obtained in the temperature range of 420-460 °C. And the apparent reaction order of hydrogen chloride was also obtained. During the selective chlorination, the oxidation of pre-reduced ore could take place with the selected conditions; chlorinated iron was mostly rejected as hematite and thus nickel and cobalt were selectively chlorinated by hydrogen chloride.     

Deep surface reconstruction of Co-based cocatalyst on Ti-doped α-Fe2O3 photoanode for highly efficient water oxidation

Transition metal-based cocatalysts play important roles in promoting the surface kinetics of hematite (α-Fe₂O₃) photoanode. However, their performances are restricted by the shallow reconstruction process for generating highly efficient metal oxyhydroxides, where the oxygen evolution reaction (OER) occurs. Therefore, a Brnsted base-regulated strategy is developed to promote the in situ surface reconstruction of cocatalysts on Ti-doped α-Fe₂O₃ (Ti–Fe₂O₃) under photoelectrochemical conditions. After deep surface reconstruction by electrochemical activation, the CoWO₄ cocatalyst decorated Ti–Fe₂O₃ photoanode (a-CoWO₄/Ti–Fe₂O₃) delivers a photocurrent density of 0.88 mA cm^?2 at 1.23 V_RHE, which is about 3.0 times of activated Ti–Fe₂O₃ (a-Ti-Fe₂O₃) and 1.5 times of activated CoO_x/Ti–Fe₂O₃. Tungstate promotes the surface reconstruction of cobalt-based cocatalyst, resulting in a significant increase in bulk charge separation efficiency (η_sep) and surface charge injection efficiency (η_inj). Moreover, the type-II heterojunction between CoWO₄-derived CoOOH and a-Ti-Fe₂O₃ drives the rapid separation and transfer of photogenerated electron-hole pairs, and enhances the performance of Ti–Fe₂O₃ photoanode.