Titanium dioxide production process

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Brief introduction to the production process principle and the relevant reaction chemical equations: Precursor powder: The purchased ilmenite is crushed using a ball mill into ilmenite powder that meets the process requirements, and then sent to the silo for storing this powder. Acidolysis: Titanium ore is decomposed using sulfuric acid to produce soluble sulfates. The main component of ilmenite is iron titanate (FeTiO3), which is a weak acid-weak base salt that can be decomposed using strong acids. Using an excess of acid can drive the reaction to completion. Since this reaction is exothermic and the maximum temperature can reach 250°C, a high-boiling-point acid—sulfuric acid—must be used to address this issue. During the acid decomposition process, various impurities present in the ore are also decomposed, forming corresponding sulfates which then enter the titanium melt during leaching. To remove iron, metallic iron is used to reduce the ferric iron in the titanium melt to ferrous iron; meanwhile, in order to prevent the ferrous iron from being oxidized again, an excess of metallic iron must also be used to reduce a certain amount of tetragonal titanium to trivalent titanium. The reaction equations are as follows: FeTiO3 + 3H2SO4 === Ti(SO4)2 + 3H2O + FeSO4 + Q (1) FeTiO3 + 2H2SO4 === TiOSO4 + 2H2O + FeSO4 + 24.5 J (2) The reactions of other impurities present in ilmenite with H2SO4 are as follows: FeO + H2SO4 === FeSO4 + H2O + 121.4 J (3) Fe2O3 + 3H2SO4 === Fe2(SO4)3 + 3H2O + 141.5 J (4) Al2O3 + 3H2SO4 === Al2(SO4)3 + 3H2O (5) CaO + H2SO4 === CaSO4 + H2O (6) Elemental iron is used to reduce Fe3+ in the titanium melt to Fe2+: Fe2(SO4)3 + Fe === 3FeSO4 (7) After elemental iron has reduced all the ferric salts, it further reduces some of the Ti4+ ions to Ti3+: 2Ti(SO4)2 + Fe === Ti2(SO4)3 + FeSO4 (8) Silicon oxides and silicates react with sulfuric acid to form colloidal silicate substances. Settling: The system after acid leaching and reduction is a complex one, containing soluble impurities as well as insoluble impurities. Sulfates of metals such as iron, vanadium, chromium, and manganese are soluble impurities that can be removed during crystallization, hydrolysis, or washing. Most of the insoluble impurities, such as partially unreacted ilmenite and sand particles, can be naturally settled and removed by gravity. Another part of the insoluble impurities consists of colloidal compounds of silicon and aluminum, as well as some titanium that has hydrolyzed earlier; although their quantity is not large, they possess high kinetic stability, requiring the addition of additional precipitants to enhance the sedimentation and clarification process. The plant uses a combination of organic flocculants and inorganic coagulants as sedimentation agents for sedimentation. The process principles for sedimentation are briefly described as follows: Sb2O3 + 3H2SO4 === Sb2(SO4)3 + 3H2O (occurs during acidolysis) (9) FeS + H2SO4 === FeSO4 + H2S↑ (10) Sb2(SO4)3 + H2S === Sb2S3 + 3H2SO4 (11) The Sb2S3 sol has a negative charge, and it can undergo electrochemical neutralization with the positively charged silica and aluminum colloids, resulting in coagulation; this enables the silica and aluminum colloids to precipitate together with Sb2S3 and thus be removed. In modified PAM, the tertiary carbon atoms possess high electronegativity; when they adsorb onto the surface of colloids, they neutralize the zeta potential at that surface and cause it to decrease. As a result, the repulsive forces between colloids are reduced. When a large number of colloidal particles are adsorbed, the PAM molecular chains curl up and settle. Inorganic-organic combined flocculant: These two types of flocculants are used together; an organic flocculant is added first to induce specific adsorption, followed by the formation of a network that binds the suspended particles together through polymer links, thereby enabling their sedimentation. The partially settled particles are further aggregated using an inorganic coagulant added later, thus achieving purification and clarification. Experiments have shown good results. Sludge compression: The sludge resulting from purification and sedimentation still contains large amounts of soluble and insoluble titanium. Therefore, to ensure a high yield, it is necessary to recover the soluble titanium using a plate and frame filter press. Vacuum crystallization: In titanium melt, the solubility of FeSO4 is most affected by the temperature of the solution. Therefore, in a titanium melt with a fixed composition, the solubility of FeSO4 decreases as the temperature drops. Based on the principle of adiabatic evaporation of solutions, flash evaporation is used to rapidly remove the water from the titanium melt, thereby absorbing heat from the melt and lowering its temperature. This results in FeSO4 becoming supersaturated, and the supersaturated portion crystallizes out, along with some water. The resulting crystals are then separated and removed using a centrifuge. Titanium hydraulic filter: A plate and frame filter press is used, with charcoal powder as a filtering aid to carry out filtration; the strong adsorption capacity of charcoal is utilized to further remove insoluble impurities from the titanium solution. Concentration: By utilizing the principle that the boiling point of a solution decreases under vacuum, the water content in the titanium melt is evaporated, thereby increasing the concentration of the purified titanium melt to meet the requirements for hydrolysis.