Production of synthetic rutile from tin ore beneficiation byproduct through preoxidation and reductive leaching in hydrochloric acid

Abstract

This paper examines the effectiveness of the method for producing synthetic rutile from ilmenite through pre-oxidation and reductive leaching of pre-oxidized ilmenite in hydrochloric acid. Thermodynamic simulation of the pre-oxidation of ilmenite concentrate was performed to evaluate the phases formed during the process as a function of temperature. The pre-oxidation experiments were performed at different temperatures between 700 and 1000 °C in a muffle furnace for 6 h. The optimum temperature of pre-oxidation was revealed to be at 700 °C where ilmenite transformed into hematite and rutile, which is in accordance with the result of the thermodynamic simulation. Series of the leaching experiments were carried out under variations of HCl concentration (5-8 M), leaching temperature (70-100 °C), solid/liquid ratio (1/5-1/20 g/mL), ilmenite ore particle size distribution, and duration of leaching (6-12 h). Taguchi method utilizing L16 orthogonal array was adopted in the leaching step to design and reduce the required number of experiments. Analysis of variance (ANOVA) indicated that the temperature and solid/liquid (S/L) ratio were the most influential leaching parameters for the dissolution of iron and titanium. The optimum conditions for maximising the dissolution of iron, while minimizing the dissolution of titanium were at a temperature of 80 °C, HCl of 6 M, S/L ratio of 1/20 g/mL, ore particle size distribution of 44-77 µm (-200 + 325 mesh), and leaching duration of 6 h. The leaching experiment conducted under these conditions resulted in iron extraction of 98.07% with co-extraction of titanium of 11.35%. The leach-residue contains 92.6% rutile, 2.9% hematite, and 2.5% cassiterite which can be classified as synthetic grade rutile.