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Dissolution of mechanically activated Panzhihua ilmenite was conducted in 5–20% sulphuric acid solutions. With high milling intensity the milling atmosphere significantly affected the dissolution with milling under vacuum almost double the dissolution of ilmenite milled in air. This was due to formation of a lot of acid-resistant pseudorutile and lowering level of the lattice strains, especially in the c-axis direction of the ilmenite unit cell, upon milling in air. Under the experimental conditions applied, titanium and iron dissolved at a nearly stoichiometric ratio. Hydrolysis of the dissolved titanium, however, was also in progress simultaneously. The sulphuric acid concentration and reaction temperature remarkably influenced the hydrolysis rate, thus affecting the microstructure of the hydrolysate. In 5 wt.% and 10 wt.% acid solutions, the hydrolyzed product was poorly compacted and dissolution could continue. In contrast, the product in 20 wt.% acid exhibited a compact structure and was strongly adherent preventing further dissolution of the un-reacted ilmenite. In both cases the hydrolysis product appeared to be rutile TiO2. The experimental results showed that significant hydrolysis was inevitable when the acid concentration was ≤ 20 wt.%. Therefore, preparation of synthetic rutile from mechanically activated ilmenite is a better alternative to direct production of pigment TiO2. And the method could directly and fully reuse the spent acid discharged in the sulphate process.

Dissolution of mechanically activated Panzhihua ilmenite was carried out at 100 °C with a 50% sulfuric acid solution. The particle size, specific surface area, crystallite size, lattice strain and mechano-chemical reaction of milled ilmenite were measured. The cleavage induced by energetic milling occurred more preferentially along the a -axis of ilmenite unit cell. It was found that the defects formed in milling process, especially the lattice strain in the c -axis of ilmenite unit cell, greatly enhanced the leaching reaction. At low temperatures, the leaching reaction is likely to start along the direction of the basal plane (0 0 0 1) of milled ilmenite. With the mechanically activated ilmenite, leaching conversion at 100 °C reached 82.1%. However, the leaching kinetic tests revealed that the ball milling only partially activated the ilmenite. The initial rapid dissolution is due to the leaching of both the fine powders and highly reactive crystal faces. In the later stage, the dissolution exhibited essentially the same behavior as non-activated ilmenite.