Comprehensive utilization of non-water quenched high-titanium blast furnace slag

Panzhihua is the world-famous capital of vanadium and titanium . Its titanium reserves account for 90.54% of the proven reserves in China, 35.17% of the world's proven reserves, and its potential economic value reaches 8 trillion US dollars. However, the conventional steel production process using only vanadium and titanium magnetite 20% by mass of titanium. The titanium dioxide in the iron concentrate is basically smelted into the blast furnace slag after being smelted in the blast furnace, and finally discarded as waste together with the slag. The mass fraction of titanium dioxide in the blast furnace slag of Panzhihua Iron & Steel Co., Ltd. is 20%-23%, and the annual output of blast furnace slag is 3.2 million tons, including TiO _{2 of} about 900,000 tons per year. The direct economic losses amounted to more than 5 billion yuan. Panzhihua Iron and Steel has accumulated more than 50 million tons of titanium-containing blast furnace slag, except for a small part of it used as building materials, most of which are piled up in two slag yards. The current comprehensive utilization rate is less than 15%, and waste of resources. It is serious and pollutes the environment. Therefore, the rational and effective use of Panzhihua Iron and Steel Titanium Blast Furnace Slag has significant economic and social benefits.

Some foreign experts have studied the extraction of titanium from Panzhihua Iron and Steel Co., Ltd., but did not propose an effective solution. In recent years, Chinese scientists and technicians have carried out a lot of research work on this slag, and initially formed the "composite method", "application phase separation method", "high temperature carbonization-low temperature chlorination method", "selective precipitation method of valuable components" ", "Use Titanium-containing blast furnace slag to make TiC1 ₄ " and other methods. Although these methods have their own advantages, they all have some problems. At present, there is no one way to achieve industrialization.

Pangang high-titanium blast furnace slag is divided into water-quenched slag and non-water-quenched slag. The water quenching slag refers to blast furnace slag formed by adding water and cooling from the blast furnace, and the non-water quenching slag refers to blast furnace slag obtained by directly cooling in air. Compared with the water-quenched slag, the non-water-quenched high-titanium blast furnace slag has high crystal order and physicochemical properties, and TiO ₂ is almost insoluble in acid at normal temperature. The characteristics of non-aqueous quenching blast furnace slag, the use of TiO ₂ slag stability to acid, hydrochloric acid solution with an acid soluble impurities to the slag, slag preparing titanium-rich material and recovering Fe, Al and other valuable elements, the nonaqueous Comprehensive utilization of quenched high-titanium blast furnace slag. The research in this aspect has not been reported in the relevant literature at home and abroad.

First, the test part

(1) Test materials and equipment

The non-water quenched high-titanium blast furnace slag is taken from the Baguanhe slag yard of Panzhihua Iron and Steel Group Co., Ltd., Sichuan. After drying, high-energy ball milling and sieving, the particle size is 100-160 mesh. The chemical composition is shown in Table 1. The pure hydrochloric acid, ammonia water and hydrogen are analyzed. Sodium oxide is a product of Chengdu Kelon Chemical Co., Ltd.

Table 1 Chemical composition of non-water quenched high-titanium blast furnace slag

Main equipment for testing: SX2-1700°C box-type resistance furnace of Tianjin Taisite Instrument Co., Ltd.; SYP-II glass thermostatic water bathtub of Nanjing Sangli Electronic Equipment Factory; 202-Electrical constant temperature drying box of Beijing Yongguangming Medical Instrument Factory .

(2) Test methods

1. Preparation of titanium-rich slag

The blast furnace slag of 100-160 mesh is heated to a certain temperature in a water bath, and is acidified with a certain concentration of hydrochloric acid under stirring for a certain time, then cooled, suction filtered, and washed to obtain a titanium-rich residue.

2. Extraction of valuable components from acid decomposition liquid

Hydrogenolysis solution is added with hydrogen peroxide to oxidize Fe ^{2 +} to Fe ^{3 +} ; pH is adjusted to 2.8-2.9 with ammonia water (1+1) to completely precipitate Fe(OH) ₃ , filtered, washed and dried to obtain by-product Fe ₂ O ₃ ; continue to add ammonia solution (1+1) in the acid solution to adjust the pH to about 4.8, complete the precipitation of Al(OH) ₃ , filter, wash and dry to obtain A1 ₂ O ₃ ; hydrogenate in the filtrate after separation of Fe and Al The sodium oxide adjusts the pH to 13 to 14, and precipitates impurities such as magnesium and calcium, and then concentrates and freezes and crystallizes to obtain ammonium chloride crystals.

(3) Analytical methods

Determination of titanium-rich slag material mass fraction of TiO2 using ammonium ferric sulfate volumetric method (GB / T 4102.1-1983); total iron content was measured using a weight of chromium potassium volumetric method (GB / T 4102.2-1983); mass fraction of aluminum oxide using The EDTA volumetric method (GB/T4102.8-1983) was determined; the magnesium and calcium mass fractions were determined by the EDTA volumetric method (GB/T 4102.12-1983).

Second, the test results and discussion

(1) Acid solution of high titanium slag

1. Effect of temperature on the mass fraction of TiO ₂ in acid hydrolysis slag

The blast furnace slag with a particle size of 100-160 mesh, 30 g of hydrochloric acid, 7 mol/L hydrochloric acid, and the reaction time of 6 h, the effect of the reaction temperature on the acid hydrolysis effect is shown in Fig. 1.

Fig.1 Effect of temperature on the mass fraction of TiO ₂ in acid hydrolysis slag

It can be seen from Fig. 1 that the mass fraction of TiO _{2 in the} acid-decomposed slag increases as the reaction temperature increases, and tends to be stable at a temperature of 70 °C. Considering that the increase in temperature causes an increase in cost, it is preferable to control the optimum acid hydrolysis temperature to be around 70 °C.

2. Effect of hydrochloric acid concentration on the mass fraction of TiO ₂ in acid hydrolysis slag

The reaction temperature is 90 ° C, the reaction time is 6 h, the mass ratio of acid slag is 1.7:1, and the relationship between the mass fraction of TiO _{2 in the} acid residue and the concentration of hydrochloric acid is shown in Fig. 2 . It can be seen that when the concentration of hydrochloric acid is 7mol/L, the mass fraction of TiO _{2 in the} acid-decomposed slag is the highest; the concentration of hydrochloric acid is more than 7mol/L, and some TiO _{2 is} acid-decomposed into the liquid phase, so that the TO ₂ mass fraction in the acid-decomposed slag decreases. Therefore, the hydrochloric acid concentration is preferably not higher than 7 mol/L.

Fig. 2 Effect of hydrochloric acid concentration on the mass fraction of TiO ₂ in acid hydrolysis slag

3. Effect of reaction time on the mass fraction of TiO ₂ in acid hydrolysis slag

The reaction temperature is 90 ° C, the concentration of hydrochloric acid is 7 mol / L, the mass ratio of acid slag is 1.7:1, and the relationship between the mass fraction of TiO _{2 in the} acid-decomposed slag with the reaction time is shown in Fig. 3. It can be seen that the mass fraction of TiO _{2 in the} acid-decomposed slag increases with the reaction time, and reaches the maximum at 4h, which is 46.65%. After that, the reaction time is prolonged and TiO ₂ is partially dissolved, resulting in TiO in the acid-decomposed slag. _{2 The} quality score is reduced. Therefore, the acid hydrolysis reaction time should be controlled at about 6h.

Fig. 3 Effect of acid hydrolysis time on the mass fraction of TiO ₂ in acid hydrolysis slag

4. Effect of mass ratio of acid slag on mass fraction of TiO ₂ in acid hydrolysis slag

The reaction temperature is 90 ° C, the reaction time is 6 h, the hydrochloric acid concentration is 7 mol / L, and the effect of the mass ratio of acid slag on the mass fraction of TiO ₂ in the acid hydrolysis slag is shown in Fig. 4. It can be seen that when the mass ratio of acid slag is 1.7:1, the mass fraction of TiO _{2 in the} acid slag is the highest, being 46.5%; the mass ratio of acid slag is more than 1.7:1, and the mass fraction of TiO ₂ is slightly decreased, because hydrochloric acid and titanium occur. The reaction produces TiOCl ₂ dissolved in the solution, while TiOCl ₂ is not easily hydrolyzed to TiO ₂ , resulting in a decrease in the mass fraction of TiO ₂ in the slag.

Fig. 4 Effect of mass ratio of acid slag on mass fraction of TiO ₂ in acid hydrolysis slag

(II) Orthogonal test of acid hydrolysis process

In order to determine the influence of various factors in the acid hydrolysis process and the optimum process conditions, according to the single factor test results, four factors—hydrochloric acid concentration, temperature, acid slag mass ratio and acid hydrolysis time—are selected for orthogonal test. The test factor levels and results are shown in Tables 2 and 3.

Table 2 Orthogonal test factors and results

Table 3 Analysis results of each indicator

It can be seen from Tables 2 and 3 that the optimum reaction conditions are: hydrochloric acid concentration of 7 mol/L, reaction temperature of 90 ° C, acid slag mass ratio of 1.7:1, reaction time of 7 h. Under this condition, the mass fraction of TiO _{2 in the} titanium-rich slag is 46.22%; among the influencing factors, the order of influence on the mass fraction of TiO ₂ is hydrochloric acid concentration (A), reaction temperature (B), acid slag mass ratio (C) and reaction time (D).

(III) Precipitation separation of iron and aluminum in acid hydrolysis solution

Acid hydrolysis solution containing iron, aluminum, calcium, magnesium and other metal ions and C1 ^-, in which iron, aluminum as a valuable component, C1 ^- if adverse effects on the environment directly discharged. Since Fe ^{3 +} and A1 ^{3 + have} similar radii, the isomorphism phenomenon is likely to occur during the formation of crystals. Therefore, it is necessary to precipitate Fe ^{3 +} first, and then precipitate A1 ^{3 +} , and then add ammonia water to adjust the pH to remove Ca ^{2 +} and Mg ^{2 +} plasma in the solution.

According to the solubility product of the poorly soluble metal hydroxide, the stepwise precipitation of the metal ions can be achieved by adjusting the pH of the solution. As apparent from Table 4 Fe ^{3 +} Theory complete precipitation at pH = 2.81, then ^{A1 3 +, Mg 2 +,} Ca 2 + has not yet begins to precipitate; Al ^{3 +} precipitation is complete when theoretical pH = 4.71, at this time Mg ^{2 +} , Ca ^{2 + has} not started to precipitate, and Fe ^{3 +} has precipitated completely.

Table 4 pH of metal hydroxide precipitation

1. Precipitation of iron in acid solution

It is seen from an iron salt potential: at a pH of about 2.3, the solution rapidly to form an amorphous Fe (OH) _3; pH about 2.8, Fe (OH) _3. A large amount of precipitate formed; and the pH at the start of precipitation of A1 ^{3 + was} about 3.37, so the precipitation test of iron was carried out at a pH of 2.5 to 3.5, and the results are shown in Table 5.

Table 5 Test results of iron precipitation in acid solution

It can be seen from Table 5 that when the precipitation starts to appear, the pH of the solution is about 2.8, the main precipitate is Fe(OH) ₃ , and the impurities are rarely precipitated; when the pH is 2.8-2.9, the iron ions in the solution are substantially precipitated; the pH is greater than After 3.10, the amount of Fe(OH) ₃ precipitated decreased, and A1 ^{3 +} may begin to precipitate. Considering synthetically, the pH of the precipitated iron is preferably 2.8 to 2.9.

2. Precipitation of aluminum in acid hydrolysis solution

The hydrolysis process of A1 ^{3 +} is complicated. Since Al ^{3 +} tends to hydrolyze completely in a short time, it is more meaningful to discuss the hydrolysis equilibrium than to discuss the reaction rate. In general, the hydrolysis equilibrium of Al3+ is mainly determined by the concentration of A1 ^{3 +} in the solution and the pH of the solution. From the potential analysis, it was found that Al3+ was hydrolyzed and formed into a large amount of amorphous Al(OH) _{3 at a} pH of 4.1, and a large amount of Al(OH) ₃ precipitate was formed at pH=4.6. Taken together, in the test for precipitation of Al ^{3 +} , the pH should be controlled between 3.7 and 5.0.

The acid hydrolyzate after taking iron was concentrated by heating to [A1 ^{3 +} ] = 0. 140 mol / L and [A1 ^{3 +} ] = 0.187 mol / L. Each test was taken at 200 mL, and the test results are shown in Table 6.

Table 6 Results of precipitation test of aluminum in acid solution

It can be seen from Table 6 that when the pH of the solution is 3.7-4.8, the precipitation and recovery of Al(OH) ₃ increase gradually with the increase of pH, and reach the maximum at pH=4.8. At this time, Al(OH) in the precipitate ₃ ) The mass fraction is 98.29%, and the recovery rate is 86.80%. When the pH is increased to 5, the mass fraction and recovery rate of Al(OH) ₃ are slightly decreased. The reason may be that Al(OH) ₃ partially dissolves and forms AI. (OH) ₄ ^- . The Al ^{3 +} concentration increases, and although the degree of hydrolysis of aluminum decreases, the total amount of hydrolyzed aluminum increases, and therefore, the mass fraction of Al(OH) ₃ and the recovery of aluminum increase. Considering synthetically, the optimum pH for precipitating Al ^{3 +} is preferably 4.8.

(4) Recovery of NH ₄ Cl in acid hydrolysis solution

The mother liquor after precipitating iron and aluminum in a stepwise manner contains a large amount of NH ₄ Cl, which is necessary to be recovered. In order to minimize impurities, before the ammonium salt is recovered, the ammonia and sodium hydroxide are continuously added to the filtrate to increase the pH of the solution to 13 to 14, so that Ca ^{2 +} , Mg ^{2 +} and the like are precipitated, and after filtration, the low temperature is used. The NH ₄ Cl in the solution was recovered by multiple evaporation and cold crystallization.

Table 7 Solubility of ammonium chloride in aqueous solution at different temperatures

As seen from Table 7, the solubility of ammonium chloride in the solution increased with increasing temperature. In view of the volatility of NH ₄ C1, the heating temperature is preferably not more than 80 °C. It is heated by water bath, and after the crystal film appears on the concentrated liquid surface, it is cooled to 4-6 ° C with cold water for 5 h. The primary recovery rate of ammonium chloride is 33% to 39%, the secondary recovery rate is 80% to 90%, and the recovery is three times. The rate is above 95% and the purity is 98%.

Third, the conclusion

(1) Acid-decomposing non-aqueous quenched titanium-containing blast furnace slag can realize separation of titanium, silicon and most soluble impurities, and obtain titanium-rich slag, wherein w(TiO ₂ ) ≥ 45% can be used for producing titanium. The optimum conditions for acid hydrolysis were: hydrochloric acid concentration of 7 mol/L, temperature of 90 ° C, acid slag mass ratio of 1.7:1, and reaction time of 7 h.

(2) Adjusting the acid solution pH to 2.8-2.9, precipitating Fe(OH) ₃ , iron precipitation rate ≥76%; adjusting pH ≈4.8, precipitating A1(OH) ₃ , aluminum precipitation rate ≥86%; The NH ₄ Cl in the waste liquid is recovered by low-temperature multiple evaporation and cold crystallization, and the purity of NH ₄ Cl is over 98%, and the recovery rate is above 75%.

(3) The process is simple and easy to operate, and has positive significance for the rational development and utilization of titanium-containing blast furnace slag which is accumulated in Panzhihua Iron and Steel Co., Ltd. The applicability of the process remains to be further studied.

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