basic knowledge

Sponge metal titanium produced by metal thermal reduction method. Purity% (mass) is generally 99.1-99.7. The total impurity element% (mass) is 0.3 to 0.9, the impurity element oxygen (mass) is 0.06 to 0.20, and the hardness (HB) is 100 to 157. It is divided into five grades of WHTiO to MHTi4 according to the difference in purity. It is the main raw material for the production of industrial titanium alloys. The production of sponge titanium is the basic link of the titanium industry. It is the raw material of titanium materials, titanium powder and other titanium components. Turn ilmenite into titanium tetrachloride, put it into a sealed stainless steel tank, fill it with argon, and make them react with magnesium metal to obtain "sponge titanium". Such porous "sponge titanium" cannot be used directly, and they must be melted into a liquid in an electric furnace to be cast into titanium ingots.

Discover history

At the end of the eighteenth century, William Gregor, a British pastor and amateur mineralist, and M.H. Klaproth, a German chemist, successively moved from 1791 to 1795. A new element was found in a black magnetite sand (later known as titanomagnetite) and a non-magnetic oxide ore (later it became clear that it was a natural rutile ore). "(The name of the place where the titanomagnetite was found) and" titanite. " A few years later, it was proved that the so-called "Monaquin" and "titanite" found from these two minerals are actually oxides of the same element, and named this new one after the Titans, the great god of Greek mythology. The element is "Titanium".

It took 120 years from the discovery of titanium element to the first time to make the purer metal titanium. It took another 40 years from the first time the laboratory obtained pure titanium to the first industrial production. Many researchers have done a lot of exploration, suffered repeated failures, and finally succeeded in 1948. DuPont produced tons of sponge titanium and porous titanium.

Production Process

Chlorination process

Titanium tetrachloride is mainly used to produce sponge titanium, titanium dioxide and titanium trichloride. There are many preparation methods, including three methods: boiling chlorination, molten salt chlorination and shaft furnace chlorination. Boiling chlorination is the main method of producing titanium tetrachloride (used in China, Japan, and the United States), followed by molten salt chlorination (used in the CIS countries), and shaft furnace chlorination has been eliminated. Boiling chlorination is generally based on high-grade titanium-rich materials with low calcium and magnesium content, while molten salt chlorination can use raw materials containing high calcium and magnesium.

1、Boiling chlorination

Boiling chlorination is a method of preparing titanium tetrachloride by using a fine-grained titanium-rich material and a solid carbonaceous (petroleum) reducing agent under the action of high temperature and chlorine gas flow in a fluidized state. This method has the characteristics of accelerating the mass and heat transfer between gas and solid phases, and strengthening production. The raw materials used for boiling chlorination at home and abroad include high titanium slag, natural rutile, and artificial rutile. The diameters of newly-built boiling chlorination furnaces in Fushun Titanium Plant and Zunyi Titanium Plant in China are Φ1.4 m and Φ2.4 m, respectively. They adopt unique sieveless chlorination technology. Among them, Zunyi Titanium Plant designs crude titanium tetrachloride 70 daily t.

2、Molten salt chlorination

Molten salt chlorination is a method of preparing titanium tetrachloride by suspending ground titanium slag or rutile and petroleum coke in molten salt (mainly composed of KCl, NaCl, MgCl2 and CaCl2) and passing in chlorine gas. . Generally, the waste electrolyte of electrolytic magnesium can also be used, and the chlorine gas is charged under the conditions of 973K ~ 1073K, so the speed of the chlorination reaction is affected by the nature and composition of the melt, the type of the reducing agent, the nature of the raw materials, the chlorination temperature, the chlorine concentration and Influence of factors such as penetration speed, melt height, and carbon content. The optimal molten salt composition in the production of CIS titanium tetrachloride is shown in Table 4.

Molten salt chlorination

The molten salt chlorination method was successfully developed in the former Soviet Union in the 1960s to produce titanium tetrachloride. This method is not only applicable to the characteristics of the raw materials of the former Soviet Union (the titanium slag contains CaO + MgO about 6%), and its furnace capacity Up to 20 t / m2 ~ 25 t / m2 titanium tetrachloride, the cross-sectional area of the molten salt section is 6 m2. The large-scale molten salt chlorination furnace has a daily output of titanium tetrachloride of 120 t ~ 150 t. It was originally a rectangular furnace and is now a circular furnace. The size of the circular molten salt chlorination furnace is Φ 5.0 m × 8.5 m. It is 2.76 m and the rectangle is 4.5 m × 3.5 m × 8.5 m. There is no dead angle in the round furnace, the strength of the furnace body is increased, and it is overhauled once every 3 years, which is nearly double the service life of the rectangular furnace. Molten salt chlorination can use a variety of titanium-rich materials. In addition to calcium and magnesium-containing titanium slag, titanium slag (TiO2 87% ~ 91%) smelted from ilmenite (Fe2O3 3TiO2) is now widely used, and rutile can also be used. .

Ukraine has used molten salt chlorination for more than 40 years. It is not only suitable for the country's high content of MgO and CaO, but also has the following advantages: 1) The unit productivity of the chlorination unit is high, up to 20 t / m2 · D ~ 25t / m2 · d TiCl4; 2) Low chlorination temperature is 800 ° C, many impurities will not enter TiCl4 due to chlorination; 3) From furnace charge to industrial titanium tetrachloride, the recovery rate of titanium is high, and Up to 95%; the molten salt itself has the effect of purifying TiCl4, and the content of impurities obtained by TiCl4 is low, and the total content of impurities such as vanadium, chlorine, silicon, carbon and the like is ≤2%; the product of TiCl4 is over 98%, which can make AlCl3, FeCl3, CaO Impurities such as MgO and SiO2 remain in the molten salt medium and are then discharged; 4) The particle size composition of the raw material is not high, and fine-sized titanium slag can be used; 5) The reaction process does not produce COCl2, and the exhaust gas has no explosion danger. The content of Cl2 and HCl in the exhaust gas is very small, and it does not cause much environmental pollution.

3、Shaft furnace chlorination

Shaft furnace chlorination is to grind the chlorinated titanium slag (or rutile) with petroleum coke, add a binder to mix and make agglomerates, and coke, and stack the produced agglomerates in a vertical chlorination furnace. The method of preparing titanium tetrachloride by reacting with chlorine gas in the state of a solid layer, also known as fixed layer chlorination or pellet chlorination, has basically been eliminated.

Mg reduction method

The essence of magnesium reduction is that in a argon atmosphere at 880 ° C ~ 950 ° C, titanium tetrachloride is reacted with magnesium metal to obtain sponge-like metal titanium and magnesium chloride. The magnesium chloride and excess magnesium in sponge titanium are removed by vacuum distillation. Magnesium, to obtain pure titanium, the distillation condensate can be recovered by melting the metal magnesium, and magnesium chloride can be recovered by molten salt electrolysis to recover magnesium and chlorine. Metal titanium is prepared from refined titanium tetrachloride, and is divided into two steps: reduction and distillation. Over a long period of time, reduction and distillation are carried out step by step, but they have tended to be united and large.

The main reaction of magnesium reduction is：

TiCl4+2Mg=Ti+2MgCl2

During the reduction process, trace impurities in TiCl4, such as AlCl3, FeCl3, SiCl4, and VOCl3, are reduced by magnesium to generate corresponding metals, all of which are mixed in sponge titanium. Potassium, calcium, sodium and other impurities mixed in magnesium are also reducing agents. They reduce TiCl4 and generate corresponding impurity chlorides. The magnesium reduction process includes: gasification of TiCl4 liquid → external diffusion of gas TiCl4 and liquid Mg → adsorption of TiCl4 and Mg molecules on the active center → chemical reaction on the active center → crystal nucleation → titanium grain growth → MgCl2 desorption → MgCl2 diffuses outside. The key step in this process is crystal nucleation, which is accompanied by heterogeneous nucleation as the chemical reaction proceeds.

After the MgCl2 is discharged, the magnesium reduction product contains 55% ~ 60% of titanium, 25% ~ 30% of magnesium, 210% ~ 15% of MgCl, and a small amount of TiCl3 and TiCl2. The magnesium and MgCl2 in sponge titanium are separated by distillation.

The reduced product sponge titanium is subjected to long-term high-temperature sintering in the vacuum distillation process, gradually densifies, the pores gradually shrink, the dendritic structure disappears, and finally it becomes a lumpy monolith, commonly known as titanium rhenium.