Abstract: This paper describes a novel, facile chemical pathway for preparing synthetic rutile from ilmenite. The pathway consists of two primary units, i.e., selectively sulfating ilmenite, which was realized via roasting ilmenite with (NH₄)₂SO₄ followed by selective thermal decomposition of the sulfated ilmenite, and targeted leaching of the impurities. The effects of the process parameters were systematically investigated. The results showed that the optimum sulfation conditions were a mass ratio of (NH₄)₂SO₄ to ilmenite of 14, temperature of 360℃, and time of 120 min with a sulfation ratio of~95%. The optimum thermal decomposition conditions were 480℃ in N₂ atmosphere, and nearly all TiOSO₄ were decomposed with co-decomposition of FeSO₄ of 23%. For acid leaching, the optimum conditions were 2.5 wt% HCl, 98℃ and 120 min. Under those conditions, 94.2% iron was removed with a TiO₂ dissolution loss <1%. For alkali leaching, 67% SiO₂ was removed in 5 wt% NaOH at 102℃ for 1 h. A synthetic rutile with a TiO₂ content >92 wt% and total MgO + CaO <1.5 wt% was obtained. Based on these results, a schematic flowsheet was proposed. Additionally, it was found that the decomposition of FeSO₄ mixed with TiOSO₄ under N₂ was inhibited due to its oxidation to a higher thermal stability Fe₂(SO₄)₃ by oxygen emitted from the decomposition of TiOSO₄. At the same time, TiOSO₄ decomposition was promoted due to the immediate in situ consumption of oxygen by FeSO₄. The synergetic effect might be responsible for the enhanced selectivity of sulfated ilmenite thermal decomposition.

Key words: Synthetic rutile, Ilmenite, Titania, Ammonium sulfate, Thermal decomposition

摘要： This paper describes a novel, facile chemical pathway for preparing synthetic rutile from ilmenite. The pathway consists of two primary units, i.e., selectively sulfating ilmenite, which was realized via roasting ilmenite with (NH₄)₂SO₄ followed by selective thermal decomposition of the sulfated ilmenite, and targeted leaching of the impurities. The effects of the process parameters were systematically investigated. The results showed that the optimum sulfation conditions were a mass ratio of (NH₄)₂SO₄ to ilmenite of 14, temperature of 360℃, and time of 120 min with a sulfation ratio of~95%. The optimum thermal decomposition conditions were 480℃ in N₂ atmosphere, and nearly all TiOSO₄ were decomposed with co-decomposition of FeSO₄ of 23%. For acid leaching, the optimum conditions were 2.5 wt% HCl, 98℃ and 120 min. Under those conditions, 94.2% iron was removed with a TiO₂ dissolution loss <1%. For alkali leaching, 67% SiO₂ was removed in 5 wt% NaOH at 102℃ for 1 h. A synthetic rutile with a TiO₂ content >92 wt% and total MgO + CaO <1.5 wt% was obtained. Based on these results, a schematic flowsheet was proposed. Additionally, it was found that the decomposition of FeSO₄ mixed with TiOSO₄ under N₂ was inhibited due to its oxidation to a higher thermal stability Fe₂(SO₄)₃ by oxygen emitted from the decomposition of TiOSO₄. At the same time, TiOSO₄ decomposition was promoted due to the immediate in situ consumption of oxygen by FeSO₄. The synergetic effect might be responsible for the enhanced selectivity of sulfated ilmenite thermal decomposition.

关键词: Synthetic rutile, Ilmenite, Titania, Ammonium sulfate, Thermal decomposition