An Investigation On The Liquid Phase Digestion Of Ilmenite For Sulfate Process TiO₂ Pigment Production

The digestion of ilmenite by sulfuric acid is a key process in the production of titanium dioxide. The digestion in the solid phase digestion produce a large amount of spent acid and flue gas emissions. However, lowering the digestion sulfuric acid concentration can greatly reduce such kinds of emissions in sulfate process TiO2 pigment production, which is greatly beneficial to the environmental protection.In this paper, the reaction activity of the liquid phase digestion has been systematically investigated under the condition of lower concentration and the temperature range of 130～170℃. According to the isothermal experimental data of high liquid-solid ratio digestion, the reaction kinetics model was regressed. The kinetics experiments show that reaction rate is influenced by surface chemical reaction over un-reacted core and the diffusion through solid product layer, under a given condition, liquid-solid ratio 500:60 and H2SO4 concentration 75% and stirring rate 520 rpm. The kinetics equation of the reaction donated by both surface reaction and diffusion was obtained:According to the characteristics of the digestion reaction, a liquid-phase digestion operation was realized by continuously adding dilute acid or water to ensure the reaction in the liquid phase. Mechanic agitation was employed to enhance the mass transfer. The micro-analysis was used, for the un-reacted orefrom both the liquid digestion and the solid one. The SEM and EDS characteristics shows that the product layer over the un-reacted core in liquid phase digestion is thinner than that in solid phase digestion, and the mass transfer is enhanced.The experimental optimization for the liquid digestion process showed that with an industrial acid/ore ratio of 1.4 and an acid concentration of 65-75%, digestion degrees higher than 85% can be obtained at 150~160癈 within 120 minutes. Titaniferous solutions with a TiO2 content of 116g/L and a F value of 2.0 was obtained, which was suitable for the pigment production.The main impurity FeSO4 in the sulphuric acid did not affect significantly on the digestion below the quantity of 7.5 (wt%). A conceptional process of continuous liquid phase digestion of ilmenite was simulated by masss and heat balance calculation.