Method for preparing high-purity ferrous chloride

Abstract

The invention discloses a method for preparing high-purity ferrous chloride, which comprises the following steps of: performing acid leaching on titanium concentrate by hydrochloric acid, filtering to obtain mother liquor I, introducing hydrogen chloride gas into the mother liquor I, stopping introducing the hydrogen chloride gas when the mass concentration of hydrogen chloride in the solution is 26-28% to obtain mother liquor II, cooling the mother liquor II to 10-15 DEG C, and crystallizing the ferrous chloride to obtain the high-purity ferrous chloride. The purity of the obtained ferrous chloride crystal is larger than or equal to 99%, the content of the Mn element is smaller than or equal to 0.01 wt%, and the total content of other impurity elements is smaller than or equal to 0.99 wt%; according to the method, the problem of recycling mother liquor generated after acid leaching and filtering of the titanium concentrate is solved, high-purity ferrous chloride is obtained, and full utilization of ferrotitanium metal resources in the titanium concentrate is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of ferrous chloride preparation, and more specifically, to a method for preparing high-purity ferrous chloride. Background Art

[0002] At present, the mature processes for the industrial production of titanium dioxide are the sulfuric acid method and the chlorination method. The advantages of the chlorination method of titanium dioxide production are short process and high product quality, but it will produce a large amount of waste liquid. The waste liquid also contains some valuable metal substances, such as ferrous ions, manganese ions, aluminum ions, etc. If the waste liquid is discharged directly without treatment, it is easy to cause environmental pollution. Using a treatment agent to treat it before discharging it will increase the treatment cost on the one hand, and cause a waste of resources on the other hand. Therefore, it is of great significance to recycle the waste liquid of titanium dioxide produced by the chlorination method in industry.

[0003] The preparation of titanium dioxide by the hydrochloric acid method is mainly done by acid leaching titanium concentrate or titanium slag with hydrochloric acid. The iron content in titanium concentrate or titanium slag is second only to titanium. Therefore, there are a large number of ferrous ions in the waste liquid after acid leaching. Ferrous chloride is widely used in lithium batteries, pigments, and water treatment fields. If the ferrous ions in the waste liquid are separated to obtain ferrous chloride and then applied to other fields, it will not only make full use of resources but also reduce the processing costs of enterprises.

[0004] There have been some studies on this in the prior art. For example, the invention patent with publication number CN104263016 provides a method for preparing pearlescent pigments from ilmenite hydrochloric acid acid hydrolyzate by a co-extraction method, wherein hydrochloric acid is added to the ilmenite for acid leaching, and then filtered to obtain slag and acid hydrolyzate, and then the acid hydrolyzate is cooled and filtered to obtain ferrous chloride and ferrotitanium acid hydrolyzate, wherein the acid hydrolyzate is directly cooled and crystallized to obtain ferrous chloride, which is used in iron red, but there may be a problem of incomplete precipitation of ferrous chloride.

[0005] For example, the invention patent with publication number CN115974166A provides a method for preparing a high chloride ion pure ferrous chloride solution in the industrial production of titanium dioxide by hydrochloric acid method, which is to introduce HCl gas into the crystallized titanium liquid in the industrial production of titanium dioxide by hydrochloric acid method, and then cool it to 8-12°C to crystallize ferrous chloride tetrahydrate, and then use a filter press to separate the solid and liquid to obtain a ferrous chloride tetrahydrate filter cake, acid wash the filter cake, remove Ti 4+ , prepare high chloride ion pure ferrous chloride solution, in which the crystalline titanium liquid contains titanium dioxide, ferrous ions and chloride ions, and the precipitated ferrous chloride tetrahydrate contains more titanium ions. Summary of the invention

[0006] In view of the above, in order to overcome the deficiency of separating ferrous chloride from acid leaching solution or mother liquor after acid leaching filtration in the prior art, the present invention provides a method for preparing high-purity ferrous chloride, which directly obtains high-purity ferrous chloride from the mother liquor after acid leaching filtration and has a high utilization rate.

[0007] The invention provides a method for preparing high-purity ferrous chloride. Titanium concentrate is acid-leached with hydrochloric acid and filtered to obtain titanium dioxide and mother liquor I. Hydrogen chloride gas is introduced into the mother liquor I. When the mass concentration of hydrogen chloride in the solution is 26-28%, the introduction of hydrogen chloride gas is stopped to obtain mother liquor II. The mother liquor II is then cooled to 10-15 DEG C to crystallize ferrous chloride. Finally, centrifugal filtration is performed to obtain filtrate and ferrous chloride crystals.

[0008] The mass concentration of hydrogen chloride in the mother liquor I is 8-15%.

[0009] The mass concentration of ferrous ions in the mother solution I is 120-170 g / L, the mass concentration of manganese ions is 1-5 g / L, the mass concentration of calcium ions is 1-5 g / L, and the mass concentration of magnesium ions is 5-15 g / L.

[0010] The mass concentration of the residual hydrogen chloride in the mother liquor I is low, and the chloride ions contained in the mother liquor I are less, and cannot be fully combined with the ferrous ions in the mother liquor I to form ferrous chloride, and free ferrous ions may exist; therefore, the present invention introduces hydrogen chloride gas into the mother liquor I, and when the mass concentration of hydrogen chloride in the solution is 26-28%, the introduction of hydrogen chloride gas is stopped, and the mother liquor I has completely absorbed the hydrogen chloride gas at this time, so that not only the ferrous ions in the mother liquor I can be fully combined with hydrogen chloride to form ferrous chloride, thereby improving the utilization rate of ferrous ions, but also the appropriate hydrogen chloride concentration can inhibit the precipitation of other impurities, so that the purity of ferrous chloride crystals is higher; at the same time, as the concentration of hydrogen chloride increases, the hydrogen ions and chloride ions in the solution increase, the binding rate between chloride ions and ferrous ions increases, the crystallization speed is accelerated, a large number of crystal nuclei can be formed and grow in a relatively short time, which is conducive to the formation of ferrous chloride crystals.

[0011] Moreover, as the solution absorbs hydrogen chloride, the content of hydrogen chloride in the solution increases continuously, and hydrogen chloride and ferrous chloride have a common ion effect: first, hydrogen chloride ionizes a large amount of chloride ions in the solution, increases the concentration of chloride ions in the solution, moves the dissolution equilibrium of ferrous chloride toward the crystallization direction, inhibits the ionization degree of ferrous chloride, reduces the solubility of ferrous chloride, promotes the crystallization of ferrous chloride, and precipitates ferrous chloride crystals; second, the increase in hydrogen chloride concentration reduces the activity of water, weakens the solvation effect of each ion, reduces the stability of chloride ions and ferrous ions in the solution, and makes it easier for them to combine with each other to form crystals, thereby promoting the crystallization of ferrous chloride and precipitating ferrous chloride crystals; third, the increase in hydrogen chloride concentration changes the dielectric constant of the solution, affects the electrostatic interaction between ions, enhances the attraction between chloride ions and ferrous ions, and is conducive to their aggregation to form crystal nuclei and further growth; therefore, the introduction of appropriate hydrogen chloride gas can also increase the crystallization amount and grain growth rate of ferrous chloride, and reduce the solubility of ferrous chloride, so that ferrous chloride crystals are precipitated at 10-15°C.

[0012] However, too high a concentration of hydrogen chloride may cause some impurities to precipitate, affecting the purity of ferrous chloride crystals, and excessively inhibiting the ionization of ferrous chloride, leading to other problems such as a decrease in crystal quality. Therefore, it is necessary to reasonably control the concentration of hydrogen chloride, so that its mass concentration is most suitable at 26-28%.

[0013] In addition, in addition to the high calcium and magnesium contents in domestic titanium concentrate, the contents of other impurities are relatively low. After the titanium concentrate is acid-leached and filtered, insoluble substances such as titanium dioxide are separated. The mass concentration of ferrous ions in the mother liquor I is the highest, and the mass concentration of non-ferrous metal chlorides such as manganese ions, calcium ions and magnesium ions is relatively low, but they may still be precipitated together with the crystallization of ferrous chloride. Since hydrogen chloride gas is introduced into the present invention, a large amount of hydrogen chloride is contained in the mother liquor II, which will release a large amount of hydrogen ions and chloride ions. As the concentration of hydrogen chloride in the solution increases, the solubility of ferrous chloride and other non-ferrous metal chlorides in the mother liquor varies with the change of hydrogen chloride concentration. By controlling the concentration of hydrogen chloride, when ferrous chloride reaches supersaturation and crystallizes, other non-ferrous metal chlorides still cannot reach the conditions for precipitation. Therefore, other non-ferrous metal chlorides will not be precipitated together with ferrous chloride. Moreover, a larger hydrogen chloride concentration also prevents the hydrolysis of ferrous chloride, which is beneficial to the precipitation of ferrous chloride, and finally obtains high-purity ferrous chloride.

[0014] At the same time, there may be some complexing agents or ions in the solution, which have different complexing abilities with other impurity ions such as iron ions and manganese. When the concentration of hydrogen chloride is controlled to increase, the ion environment in the solution changes. These complexing agents will preferentially complex with iron ions, inhibiting the precipitation of other impurity ions, thereby reducing the precipitation of other impurity ions in ferrous chloride crystals and ensuring the purity of ferrous chloride crystals.

[0015] In the process of mother liquor I absorbing hydrogen chloride gas to obtain mother liquor II, the solution temperature is maintained at 40-60°C. In the process of mother liquor I absorbing hydrogen chloride gas, heat is released and the temperature rises. Hydrochloric acid is a volatile acid. At a higher temperature, the absorption rate of hydrogen chloride gas in the solution slows down and the absorption amount decreases. Therefore, in the process of absorbing hydrogen chloride gas, it is necessary to maintain a suitable temperature to ensure the rapid and sufficient absorption of hydrogen chloride gas. At the same time, temperature control can optimize the crystal size distribution, which is conducive to the growth of ferrous chloride crystals.

[0016] The mass concentration of ferrous ions in the filtrate is 30-60 g / L.

[0017] The purity of the ferrous chloride crystals produced by salting out is ≥99%, the content of Mn element is ≤0.01wt%, and the total content of other impurity elements is ≤0.99wt%.

[0018] The invention introduces hydrogen chloride gas into mother liquor I obtained after acid leaching and filtering titanium concentrate with hydrochloric acid, and then cools and crystallizes to precipitate high-purity ferrous chloride crystals, thereby overcoming the problem of non-ferrous metal ions being precipitated along with ferrous chloride crystals, obtaining high-purity ferrous chloride crystals with a purity of ≥99%, solving the problem of recycling mother liquor generated after acid leaching and filtering titanium concentrate, and improving the utilization rate of ferrous ions, thereby achieving full utilization of titanium-iron metal resources in titanium concentrate; at the same time, chlorine in hydrogen chloride in the mother liquor is discharged from the system in the form of ferrous chloride, and the acid concentration of the system is improved after salting out, and can be directly returned to the acid leaching process for acid leaching, with low processing cost, thereby achieving full utilization of chlorine in the mother liquor obtained after acid leaching and filtering. DETAILED DESCRIPTION

[0019] The embodiments of the present application will be described in more detail below. The application can be implemented in various forms, and should not be construed as being limited to the embodiments set forth herein, but rather these embodiments are provided to provide a more thorough and complete understanding of the present application. It should be understood that the embodiments of the present application are only for exemplary purposes and are not intended to limit the scope of protection of the present application.

[0020] Embodiments of the present invention are as follows:

[0021] Titanium concentrate is acid-leached with hydrochloric acid and filtered to obtain titanium dioxide and mother liquor I, wherein the mass concentration of hydrogen chloride in mother liquor I is 8-15%, hydrogen chloride gas is introduced into mother liquor I, and when the mass concentration of hydrogen chloride in the solution is 26-28%, the introduction of hydrogen chloride gas is stopped to obtain mother liquor II, wherein during the process of mother liquor I absorbing hydrogen chloride gas to obtain mother liquor II, the solution temperature is maintained at 40-60°C, and then mother liquor II is cooled to 10-15°C to crystallize ferrous chloride, and finally centrifugally filtered to obtain filtrate and ferrous chloride crystals, and the filtrate is reused for acid leaching of titanium concentrate.

[0022] Comparative Example: No hydrogen chloride gas was introduced and no filtrate was recycled:

[0023] Titanium concentrate is acid-leached with hydrochloric acid and filtered to obtain titanium dioxide and mother liquor I, in which the mass concentration of hydrogen chloride is 12%. Mother liquor I is then cooled to 10°C to crystallize ferrous chloride, and finally centrifuged to obtain a filtrate and ferrous chloride crystals.

[0024] Table 1 shows the specific implementation conditions of Examples 1 to 3, and Table 2 shows the test results of the Examples and Comparative Examples, wherein the overall utilization rate of ferrous ions is the utilization rate of iron in the titanium concentrate obtained after the filtrate is recycled for the same number of times in the acid leaching process.

[0025] As shown in the test results of Table 2, when the concentration of hydrogen chloride in the mother solution II of the present invention is 26-28%, the purity of the ferrous chloride crystals is greater than 99%. The purity of the ferrous chloride crystals obtained without the introduction of hydrogen chloride gas is lower, and contains more impurity elements, particularly the content of manganese element increases sharply. This is because as the temperature decreases, the material solubility decreases, and the ferrous chloride crystals are precipitated. At the same time, because manganese and other impurity elements are similar to iron in nature, particularly manganese and iron have the most similar properties, and hydrogen chloride gas is not introduced to improve the ionic environment in the solution, so that properties such as the solubility of manganese and other impurity elements and iron are changed, and the precipitation condition gap between iron and manganese and other impurity elements is increased. Therefore, when hydrogen chloride gas is not introduced, when the ferrous chloride crystals are precipitated, manganese chloride and other chlorides can be precipitated together with iron, resulting in impure ferrous chloride crystals. It has also been proved that the present invention can significantly improve the purity of ferrous chloride crystals.

[0026] In addition, when the concentration of hydrogen chloride in the mother liquor II of the present invention is 26-28%, the primary utilization rate of ferrous ions is higher than that when no hydrogen chloride gas is introduced. It can be seen that the introduction of hydrogen chloride of an appropriate concentration can increase the precipitation rate of ferrous chloride crystals, so that the ferrous ions in the mother liquor I are more fully utilized, and the utilization rate of iron in the titanium concentrate is improved; and when the filtrate obtained after the precipitation of ferrous chloride crystals is recycled and reused in the acid leaching process, the utilization rate of iron in the titanium concentrate can be greater than 92%, so that the iron in the titanium concentrate is fully utilized and the filtrate is fully utilized.

[0027] Table 1 Specific implementation conditions of Examples 1 to 3

[0028]

[0029] Table 2 Test results of embodiments and comparative examples

[0030]

[0031] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in this application, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing high-purity ferrous chloride, characterized in that: Titanium concentrate is leached with hydrochloric acid and filtered to obtain titanium dioxide and mother liquor I. Hydrogen chloride gas is introduced into mother liquor I. When the mass concentration of hydrogen chloride in the solution is 26-28%, the introduction of hydrogen chloride gas is stopped to obtain mother liquor II. Mother liquor II is then cooled to 10-15°C to crystallize ferrous chloride. Finally, centrifugal filtration is performed to obtain filtrate and ferrous chloride crystals.

2. A method for preparing high-purity ferrous chloride according to claim 1, characterized in that: The mass concentration of hydrogen chloride in the mother liquor I is 8-15%.

3. A method for preparing high-purity ferrous chloride according to claim 1, characterized in that: The mass concentration of ferrous ions in the mother solution I is 120-170 g / L, the mass concentration of manganese ions is 1-5 g / L, the mass concentration of calcium ions is 1-5 g / L, and the mass concentration of magnesium ions is 5-15 g / L.

4. A method for preparing high-purity ferrous chloride according to claim 1, characterized in that: During the process in which mother liquor I absorbs hydrogen chloride gas to obtain mother liquor II, the solution temperature is maintained at 40-60°C.

5. A method for preparing high-purity ferrous chloride according to claim 1, characterized in that: The mass concentration of ferrous ions in the filtrate is 30-60 g / L.

6. A method for preparing high-purity ferrous chloride according to claim 1, characterized in that: The purity of the ferrous chloride crystals is ≥99%, the content of Mn element is ≤0.01wt%, and the total content of other impurity elements is ≤0.99wt%.

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