Reason analysis of good acid solubility of titanium slag

In the electric furnace smelting at a medium temperature of 1600~1800 °C, in addition to the reduction of iron oxides, a considerable amount of TiO ₂ is reduced to low-valent titanium oxides (only at higher temperatures, TiO ₂ is reduced to produce titanium metal and TiC and dissolved in molten iron).

During the cooling crystallization process after the titanium slag is smelted out, most of the titanium oxides are combined with other more basic metal oxides to form dititanates (such as FeO·2TiO ₂ , MgO·2TiO ₂ , MnO·2TiO _{2 ).} And forming a black titanite solid solution with A1 ₂ O ₃ ·TiO ₂ , Ti ₃ O ₅ or the like. There are also a small amount of metatitadate to form a tower base solid solution, and a small amount of titanium oxide enters the silicate glass body. When the titanium slag melt is cooled in air, some of the low-valent titanium is also oxidized to form free TiO ₂ . When the oxidation occurs at a temperature of >750 ° C, the oxidation product is mainly rutile TiO ₂ . When rutile-type TiO _{2 is formed} , it cannot be dissolved by sulfuric acid. Therefore, it is very important to produce acid-soluble titanium slag in a high-temperature period to keep it in a reducing atmosphere and not to oxidize the air.

Acid dissolution of titanium slag indicates that the titanium oxide of the black iron solid solution is most soluble in sulfuric acid, and the rutile type TiO ₂ is insoluble in sulfuric acid. Therefore, as the acid-soluble titanium slag should meet the following points: 1 should contain appropriate amount of solubilizing impurities (mainly FeO and MgO) and a certain amount of Ti ₂ O ₃ , so that the titanium oxide as much as possible in the black titanium stone solid In the melt; 2 spray water cooling in the process, can prevent high titanium slag from being oxidized by contact with air to form rutile TiO ₂ which is insoluble in sulfuric acid, and can also accelerate the cooling rate. Generally, when the temperature is <750 °C, the oxidation product of titanium is anatase type TiO ₂ instead of rutile type TiO ₂ ; 3 like the former cis, adding waste titanium chips in the late stage of smelting to improve the reduction degree of titanium slag, Avoid high temperatures being oxidized to rutile TiO ₂ .

The analysis of the acid-soluble titanium slag phase of Panzhihua Mine shows that more than 90% of the titanium oxide in the slag enters the black titanite solid solution, 4%~7% enters the silicate phase, and about 1% is rutile TiO. ₂ forms exist.

Fe ²⁺ , Mg ²⁺ , Mn ²⁺ , and Al ³⁺ in the titanium slag provide the necessary divalent and trivalent metal ions for forming the black titanite solid solution, and they have the effect of stabilizing the solid solution. Among them, FeO·2TiO ² and MgO·2TiO ² are most soluble in sulfuric acid, that is, FeO and MgO have the function of promoting dissolution of titanium oxide in titanium slag into sulfuric acid, and are indispensable solubilizing impurities for acid-soluble titanium slag. These two oxides increase the heat of reaction between titanium slag and sulfuric acid, and the reaction formula is as follows:

FeO+H ₂ SO ₄ ===FeSO ₄ +H ₂ O+113.4kJ/mol

MgO+H ₂ SO ₄ === MgSO4+H ₂ O+163.8kJ/mol

It is calculated that the reaction heat of titanium slag and sulfuric acid in Panzhihua Mine is only about 15% lower than that of sand ilmenite (including TiO251%). MgO is an important source of heat for the reaction of titanium slag in Panzhihua Mine with sulfuric acid, which accounts for about 42% of the total heat of reaction. When the titanium slag of Panzhihua Mine is acid-decomposed, when the heating steam pressure is >0.6 MPa, the reaction rate is faster, and the highest reaction temperature can reach about 200 °C. The titanium slag of Panzhihua Mine has good reaction performance and can meet the requirements of titanium dioxide production of sulfuric acid method.

Some research and production units in China have developed acid-soluble titanium slag with a TiO ₂ content of 75% to 78%. When the TiO ₂ content exceeds 80%, the acid solubility is greatly reduced. When using titanium slag with a high grade, it is necessary to use more concentrated sulfuric acid to make it acidolyzed. The use of Liangguang ilmenite and Panzhihua titanium concentrate can refine the acid-soluble titanium slag. Shanghai Dongsheng Titanium Dioxide Factory has completed the preparation of BA-0101 titanium dioxide from the acid-soluble titanium slag produced by the Southern Process on an annual production capacity of 2,000 tons of sulfuric acid titanium dioxide production equipment.