Kinetics of hydrochloric acid leaching of niobium from TiO2 residues

Production of TiO₂ generates waste containing significant quantities of valuable metals which if recovered, could have a positive impact on the economics of TiO₂ production and waste management. In this investigation, the kinetics of HCl leaching of niobium from TiO₂ residues are studied. The complex mineralisation of niobium in its primary ores makes economic recovery very difficult, often demanding the use of chlorination, carbochlorination or fusion with alkali fluxes for breakdown of its mineral concentrates and upgrading before leaching in acid, usually hydrofluoric acid. The effects of parameters leaching temperature (25–90 °C), HCl concentration (0.5–4 M), stirring speed (100–500 rpm) and solid–liquid ratio were determined in the experiments. A maximum niobium extraction rate > 90% was achieved within 60 min of leaching the residues in 4 M HCl at 70 °C. The kinetics analysis showed that the dissolution of niobium in HCl is governed by pore diffusion of the random pore model, with an activation energy of 16.8 ± 1.2 kJ mol−¹ Nb.