A method for preparing high chloride ion pure ferrous chloride solution in industrial production of titanium dioxide by hydrochloric acid method

Abstract

The invention discloses a method for preparing a high-chloride ion pure ferrous chloride solution in the industrial production of titanium dioxide by a hydrochloric acid method, which solves a series of problems such as difficulty in deep crystallization of ferrous chloride tetrahydrate in a crystallized titanium liquid, high energy consumption, high iron-titanium ratio and poor stability of the clear titanium liquid, low purity of ferrous chloride tetrahydrate crystals and its aqueous solution, difficulty in utilizing low-concentration acid, and generation of low-concentration titanium liquid. The method can prepare a high-chloride ion pure ferrous chloride solution for by-product high-quality ferric oxide powder and efficient acid recovery, so as to realize efficient utilization of iron resources in titanium concentrate and recycling of chloride ions.

Description

Technical Field

[0001] The invention relates to the technical field of titanium dioxide and titanium dioxide production, and in particular to a method for separating, purifying, and dissolving iron ions in hydrochloric acid to prepare a high-purity ferrous chloride solution in an industrialized production process of titanium dioxide using a hydrochloric acid process. Background Art

[0002] During the production of titanium dioxide by the hydrochloric acid method, the titanium and iron in the acid-hydrolyzed titanium solution are both present in the titanium liquid in the form of soluble chloride salts, and cannot be separated directly. They need to be separated by crystallization and hydrolysis. Crystallization is to separate most of the iron ions in the titanium liquid in the form of ferrous chloride tetrahydrate crystals, while hydrolysis is to separate the titanium in the titanium liquid from the hydrochloric acid and ferrous chloride aqueous solution in the form of solid precipitation of hydrated titanium oxide. The crystallization of ferrous chloride tetrahydrate is to cool the acid-hydrolyzed titanium liquid and gradually crystallize it from the titanium liquid. After filtering the ferrous chloride tetrahydrate crystals, the iron-titanium ratio required for the hydrolysis of the titanium liquid is met. The production process of cooling acid-hydrolyzed titanium liquid to crystallize ferrous chloride tetrahydrate is usually divided into two types: one is to use refrigerant for heat exchange to cool the titanium liquid, wherein a large part of the ferrous chloride is crystallized in the form of ferrous chloride tetrahydrate; the other is to cool the titanium liquid (hot filtered or not) clarified by acid hydrolysis, sedimentation and evaporation by vacuum formed by vacuum pump and steam jet pump to remove heat and cool it, so that a large part of the ferrous chloride is crystallized in the form of ferrous chloride tetrahydrate.

[0003] Vacuum evaporation crystallization has no heat exchange interface. It relies on boiling evaporation under high vacuum to take away heat, that is, adiabatic evaporation takes away heat. There is no heat exchange area. Ions collide with each other to form tiny crystal nuclei. After the crystal nuclei are formed, the crystal-forming ions in the solution diffuse to the surface of the crystal nuclei and deposit on the crystal nuclei. The crystal nuclei gradually grow into grains, and the grains further aggregate and arrange in a directional manner to form crystals. Due to boiling vacuum cooling, most grains do not have time to arrange in a directional manner and become non-crystalline grain precipitation; resulting in a large supersaturation of ferrous chloride in the crystallized titanium liquid, resulting in fine ferrous chloride crystals. When separating solids and liquids, whether using a centrifuge or a vacuum turntable filter, the large supersaturation brings about post-crystallization during the filtration process, affecting the dynamic balance of the centrifuge and the clogging of the filter cloth, resulting in low equipment operation efficiency. In addition, because the cooling crystallization adopts an intermittent process, that is, each time the crystallization temperature reaches the end of crystallization, the high vacuum formed by two-stage steam injection requires pressure relief, discharge and re-feeding, which wastes the energy to form a high vacuum. However, when using the freezing crystallization method, the high-temperature heat energy of the titanium liquid is removed in the form of heat exchange with a freezing medium, and is not used for evaporation of the titanium liquid, resulting in poor energy efficiency. Summary of the invention

[0004] The main technical problem solved by the present invention is to provide a method for preparing a high-chloride ion pure ferrous chloride solution which can be used for the spray roasting and absorption steps in the industrial production process of titanium dioxide by the hydrochloric acid method to prepare high-quality ferric oxide and regenerated acid. The method can solve a series of problems such as the difficulty in deep crystallization of ferrous chloride tetrahydrate in the crystalline titanium liquid and high energy consumption, high iron-titanium ratio and poor stability of the clear titanium liquid, low purity of ferrous chloride tetrahydrate crystals and its aqueous solution, difficulty in using low-concentration acid, and generation of low-concentration titanium liquid. The method can realize the efficient utilization of iron resources in titanium concentrate and the recycling of chloride ions.

[0005] In order to solve the above technical problems, the technical scheme adopted by the present invention comprises the following steps: crystallizing ferrous chloride tetrahydrate crystals by vacuum crystallization or freezing method from a crystallized titanium liquid, and then separating the solid and liquid of the crystallized titanium liquid, washing the crystallized titanium liquid, and dissolving the ferrous chloride tetrahydrate crystals to prepare a ferrous chloride solution; specifically, a method for preparing a high-chloride ion pure ferrous chloride solution in the industrial production of titanium dioxide by a hydrochloric acid method, characterized in that it comprises: (1) freezing the crystallized titanium liquid after filtering the acid hydrolysis slurry, while introducing HCl gas generated by a hydrochloric acid analysis system to crystallize the crystallized titanium liquid ferrous chloride tetrahydrate; (2) pumping the slurry after the crystallization of ferrous chloride tetrahydrate into a filter press for solid-liquid separation to obtain a clear titanium liquid and a filter cake of ferrous chloride tetrahydrate crystals; after solid-liquid separation, washing the filter cake with a regenerated acid produced by a chloride salt roasting system to prepare an acid hydrolysis acid to obtain an acid-washed filter cake; the Ti entrained in the filter cake is adsorbed and removed; 4+ All of the ferrous chloride is transferred to the acid solution without producing low-concentration titanium liquid; (3) the analytical acid produced after the hydrochloric acid analytical system is analyzed by HCl is pumped into the filter press, and the ferrous chloride tetrahydrate crystals are dissolved in the filter press and circulated to prepare the ferrous chloride solution; (4) the ferrous chloride solution is recirculated and pumped into the filter press to dissolve the remaining ferrous chloride tetrahydrate crystals in the plate frame until the Fe in the ferrous solution is 2+ When the concentration reaches 160g / L, Cl - The concentration can reach 350 g / L, and a high chloride ion pure ferrous chloride solution can be obtained which can be used in the spray roasting and absorption processes to prepare high-quality ferric oxide and regenerated acid.

[0006] According to the characteristics of high iron and low acid in the crystallized titanium liquid and the principle that the solubility of ferrous chloride tetrahydrate solid decreases with decreasing temperature, the freezing crystallization method is used to reduce the solubility of ferrous chloride tetrahydrate in the crystallized titanium liquid, so that a large amount of iron in the crystallized titanium liquid is precipitated in the form of ferrous chloride tetrahydrate crystals, which is beneficial to the control of the iron-titanium ratio in the prepared clear titanium liquid. The crystallized titanium liquid is a crystallized titanium liquid prepared by the acid leaching process with a mineral acid ratio of 1:2-1:2.5. The original Fe 2+ Concentration: 135-165g / L, Cl - Concentration: 375-400g / L, effective acid concentration: 155-195g / L, freezing temperature: 8-12°C, preferably 10°C.

[0007] According to the characteristics of high iron and low acid in the titanium-clearing liquid, HCl gas generated by the hydrochloric acid analysis system is introduced during freezing and crystallization, and the HCl concentration in the analytical acid is 180-220g / L, preferably 200g / L. The common ion effect of the increased chloride ion concentration after the solution absorbs HCl is utilized to increase the crystallization amount and grain growth rate of ferrous chloride tetrahydrate, and increase the effective acid concentration in the titanium-clearing liquid, thereby ensuring the F value and stability of the titanium-clearing liquid, and the ferrous chloride tetrahydrate crystal product is easy to filter and wash. This operation reduces energy consumption by more than 25% compared with the conventional vacuum evaporation crystallization method, and reduces the amount of frozen brine. The solution after washing the filter cake is acid-acidification and flows into the acid-acidification storage tank by gravity, and the residual acid-acidification in the ferrous chloride filter cake is blown into the acid-acidification storage tank by compressed air.

[0008] After the ferrous chloride tetrahydrate crystallization, the slurry is separated into solid and liquid in a chamber filter press to obtain a clear titanium solution that meets the process requirements and a filter cake in the ferrous chloride tetrahydrate crystal frame, and then the filter cake is washed with a regenerated acid produced by a chloride salt roasting system to prepare a titanium concentrate acid solution to obtain an acid-washed filter cake; the HCl concentration in the regenerated acid is 345-350g / L, preferably 349g / L, and the Ti adsorbed and entrained in the filter cake is 4+ All of them are transferred into the acid hydrolysis, and the whole hydrated titanium dioxide preparation process does not produce low-concentration titanium liquid; because high-concentration hydrochloric acid is used to wash the ferrous chloride tetrahydrate filter cake, the dissolution loss of ferrous chloride tetrahydrate crystals can be reduced according to the common ion effect, the pickling efficiency is improved, and the primary recovery rate of iron is improved.

[0009] The low-concentration analytical acid generated after the hydrochloric acid is analyzed by the hydrochloric acid analysis system is pumped into the chamber filter press, and the ferrous chloride tetrahydrate crystals are dissolved in the filter press and output to prepare the ferrous chloride solution.

[0010] The ferrous chloride solution is recirculated and pumped into the chamber filter press to acid dissolve the remaining ferrous chloride tetrahydrate crystals in the plate frame until Fe 2+ When the concentration reaches 160g / L, Cl - The concentration can reach 350g / L, and a high chloride ion pure ferrous chloride solution can be obtained which can be used for the spray roasting and absorption process to prepare high-quality ferric oxide and regenerated acid, and various acid-insoluble colloids and suspended solids are filtered out.

[0011] In one cycle operation on the same chamber filter press, the filtration of ferrous chloride tetrahydrate crystal liquid, the washing of filter cakes and the preparation of high-chloride ion pure ferrous chloride solution by dissolving ferrous chloride crystals with analytical acid can be realized, which shortens the process flow, reduces the corresponding equipment and facilities and reduces the labor intensity. The low-concentration analytical acid produced by the hydrochloric acid analytical system when analyzing HCl is fully utilized to increase the total ion concentration in the ferrous solution and meet the process requirements of the roasting system, so as to prepare high-quality iron oxide powder and produce high-concentration regeneration acid, realize the efficient utilization of iron resources in titanium concentrate and the recycling of chloride ions, and pump the prepared high-chloride ion pure ferrous chloride solution to the high-chloride ion pure ferrous chloride intermediate storage tank of the regeneration acid spray roasting process for the preparation of high-quality ferric oxide powder and regeneration acid.

[0012] The beneficial effects of the present invention are that a series of problems such as difficulty in deep crystallization and high energy consumption of ferrous chloride tetrahydrate in crystalline titanium liquid, high iron-titanium ratio and poor stability of clear titanium liquid, low purity of ferrous chloride tetrahydrate crystals and its aqueous solution, difficulty in utilizing low-concentration acid, and production of low-concentration titanium liquid are solved, and high-chloride ion pure ferrous chloride solution can be prepared for by-product high-quality ferric oxide powder and efficient acid recovery, so as to realize efficient utilization of iron resources in titanium concentrate and recycling of chloride ions. DETAILED DESCRIPTION

[0013] The preferred embodiments of the present invention are described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0014] Embodiments of the present invention include:

[0015] The invention discloses a method for preparing a high-chloride ion pure ferrous chloride solution in the industrial production of titanium dioxide by hydrochloric acid method, aiming to solve a series of problems in the existing production process of titanium dioxide by hydrochloric acid method, such as the difficulty of deep crystallization of ferrous chloride tetrahydrate of crystallized titanium liquid and high energy consumption, high iron-titanium ratio and poor stability of clear titanium liquid, low purity of ferrous chloride tetrahydrate crystals and its aqueous solution, difficulty in utilizing low-concentration acid, and generation of low-concentration titanium liquid. The method is implemented by freezing the crystallized titanium liquid and introducing HCl gas generated by a hydrochloric acid analysis system to crystallize the ferrous chloride tetrahydrate of the crystallized titanium liquid, washing the filter cake with regenerated acid produced by a chloride salt roasting system to prepare acid hydrolysis acid, and dissolving ferrous chloride tetrahydrate crystals with analytical acid generated after the hydrochloric acid analysis system analyzes HCl to prepare a high-chloride ion pure ferrous chloride solution.

[0016] Example 1

[0017] Open the discharge valve of the intermediate storage tank of the crystal titanium liquid, open the crystal titanium liquid pump, and pump 800L of crystal titanium liquid prepared by the acid leaching process with a mineral acid ratio of 1:2.5 into the closed crystal titanium liquid tank. In the crystal titanium liquid, TiO2: 195.37g / L, Fe 2+:141.20g / L,Cl - : 390g / L, effective acid concentration: 176.35g / L.

[0018] Start stirring at a stirring rate of 50 r / min. Turn on the ice water pump, and ice water will cool the crystalline titanium liquid from the jacket.

[0019] During the cooling process, open the HCl valve and introduce 500 L of HCl gas at a pressure of 0.1 MPa within 1 hour.

[0020] When the crystalline titanium liquid cools to 10°C, turn off the ice water pump.

[0021] Open the crystalline titanium liquid pump and pump the frozen crystalline titanium liquid into the chamber filter press. When the pressure in the filter press reaches 0.3MP, stop feeding.

[0022] Open the compressed air valve and use compressed air to blow away the residual liquid in the ferrous chloride filter cake. The filtrate obtained is the titanium-clearing liquid. The test indicators are: volume: 668L, TiO2: 223.74g / L, Fe 2+ :44.60 / L,Cl - : 310.43g / L, effective acid concentration: 213.78g / L.

[0023] Open the regeneration acid washing valve and pump 80L of roasted regeneration acid (HCl: 348.97g / L) from the regeneration acid intermediate storage tank into the chamber press to wash the ferrous chloride filter cake. The solution after washing the filter cake is the acid lysis acid which flows into the acid lysis acid storage tank by gravity. Use compressed air to blow the residual acid lysis acid in the ferrous chloride filter cake into the acid lysis acid storage tank.

[0024] Open the valve of the intermediate storage tank of analytical acid (also used as the intermediate storage tank of high chloride ion pure ferrous chloride solution), pump 400L of analytical acid (HCl: 200g / L) after pre-stored hydrochloric acid analysis into the box press, and the outflowing ferrous solution returns to the intermediate storage tank of analytical acid, and then is circulated and pumped into the box press. After complete dissolution, a high chloride ion pure ferrous chloride solution (volume: 519L, Fe 2+ :161.30g / L, HCl: 202.24g / L Cl - :408.71g / L, P:27.42ppm).

[0025] The prepared high chloride ion pure ferrous chloride solution is pumped to the high chloride ion pure ferrous chloride intermediate storage tank of the regeneration acid spray roasting process to prepare high-quality ferric oxide powder and regeneration acid.

[0026] After multiple batches of high chloride ion pure ferrous chloride solution are prepared, the box filter press is opened and unloaded to remove various acid-insoluble colloids, suspended matter, etc.

[0027] Example 2

[0028] Open the discharge valve of the intermediate storage tank of the crystal titanium liquid, open the crystal titanium liquid pump, and pump 800L of crystal titanium liquid prepared by the acid leaching process with a mineral acid ratio of 1:2.0 into the closed crystal titanium liquid tank. In the crystal titanium liquid, the crystal titanium liquid tank, the crystal titanium liquid, TiO2: 242.74g / L, Fe 2+ :163.20g / L,Cl - : 398g / L. Effective acidity: 155.75g / L.

[0029] Start stirring at a stirring rate of 50 r / min. Turn on the ice water pump, and ice water will cool the crystalline titanium liquid from the jacket.

[0030] During the cooling process, open the HCl valve and introduce 500 L of HCl gas at a pressure of 0.1 MPa within 1 hour.

[0031] When the crystalline titanium liquid cools to 10°C, turn off the ice water pump.

[0032] Open the crystalline titanium liquid pump and pump the frozen crystalline titanium liquid into the chamber filter press. When the pressure in the filter press reaches 0.3MP, stop feeding.

[0033] Open the compressed air valve and use compressed air to blow away the residual liquid in the ferrous chloride filter cake. The filtrate obtained is the titanium clearing liquid. The detection indicators are: volume: 642L, TiO2: 277.46g / L, Fe 2+ :56.30 / L,Cl - : 332.57g / L, effective acid: 221.28g / L.

[0034] Open the regeneration acid washing valve and pump 80L of roasting regeneration acid (HCl: 348.97g / L) from the regeneration acid intermediate storage tank into the box press to wash the ferrous chloride filter cake. Use compressed air to blow away the residual liquid in the ferrous chloride filter cake. The solution after washing the filter cake is acid hydrolysis.

[0035] Open the valve of the analytical acid intermediate storage tank (also used as the intermediate storage tank for high chloride ion pure ferrous chloride solution), pump 470L of pre-stored analytical acid (HCl: 200g / L) into the box press, and the ferrous solution flowing out returns to the analytical acid intermediate storage tank, and then is pumped into the box press through the circulation pump. After complete dissolution, a ferrous chloride solution (volume: 590L, Fe 2+ :160.80g / L, HCl: 203.57g / LCl - :409.36g / L, P:33.46ppm).

[0036] The prepared high chloride ion pure ferrous chloride solution is pumped to the high chloride ion pure ferrous chloride intermediate storage tank of the regeneration acid spray roasting process to prepare high-quality ferric oxide powder and regeneration acid.

[0037] After multiple batches of high chloride ion pure ferrous chloride solution are prepared, the box filter press is opened and unloaded to remove various acid-insoluble colloids, suspended matter, etc.

[0038] The crystalline titanium liquid in Example 1 and Example 2 is prepared under different process conditions of mineral acid ratio in the acid leaching process. The mineral acid ratio used in Example 1 is 1:2.5, and the mineral acid ratio used in Example 2 is 1:2.0.

[0039] The compositions of the crystalline titanium liquid in Example 1 and Example 2 are different. Composition of the crystalline titanium liquid in Example 1: TiO2: 195.37 g / L, Fe 2+ :141.20g / L,Cl - : 390g / L, effective acid concentration: 176.35g / L. ; Example 2 Crystallized titanium liquid composition: TiO2: 242.74g / L, Fe 2+ :163.20g / L,Cl - : 398g / L. Effective acidity: 155.75g / L.

[0040] The composition of 519L high chloride ion pure ferrous chloride solution prepared in Example 1 is: Fe 2+ :161.30g / L, HCl: 202.24g / L Cl - : 408.71 g / L, P: 27.42 ppm; The composition of the 590 L high chloride ion pure ferrous chloride solution prepared in Example 1 is: Fe 2+ :160.80g / L, HCl: 203.57g / L Cl - : 409.36 g / L, P: 33.46 ppm. The compositions of the solutions in the two embodiments are roughly the same, but the crystallized titanium solution in Embodiment 2 comes from the leaching condition of the acid leaching process with a mineral acid ratio of 1:2.0. Under the same crystallization, filtration, washing and dissolution conditions, the high chloride ion pure ferrous chloride solution produces 71 L more than that in Embodiment 1, which is equivalent to improving the production efficiency by 13.7%, or reducing the energy consumption per unit volume of high chloride ion pure ferrous chloride solution by 13.7%.

[0041] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent process changes made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing high chloride ion pure ferrous chloride solution in the industrial production of titanium dioxide by hydrochloric acid method, Its characteristics are In, including: While freezing the crystalline titanium liquid after filtering the acid-lyzed slurry, HCl gas generated by the hydrochloric acid analysis system is introduced to perform crystallization treatment of ferrous chloride tetrahydrate in the crystalline titanium liquid; the crystalline titanium liquid is a crystalline titanium liquid prepared by the acid leaching process with a mineral acid ratio of 1:2-1:2.5, wherein the Fe2+ concentration is 135-165g / L, the Cl- concentration is 375-400g / L, and the effective acid concentration is 155-195g / L; The slurry after the crystallization of ferrous chloride tetrahydrate is pumped into a filter press for solid-liquid separation to obtain a clear titanium liquid and a ferrous chloride tetrahydrate crystal filter cake; after the solid-liquid separation, the filter cake is immediately washed with a regenerated acid produced by a chloride salt roasting system to prepare an acid solution to obtain an acid-washed filter cake; all the Ti4+ adsorbed and entrained in the filter cake is transferred into the acid solution, and no low-concentration titanium liquid is produced; the HCl concentration in the regenerated acid is 345-350g / L, and the solution after washing the filter cake is the acid solution, which flows into the acid solution storage tank by gravity, and the residual acid solution in the ferrous chloride filter cake is blown into the acid solution storage tank by compressed air; The analytical acid generated after the hydrochloric acid analytical system is analyzed by HCl is pumped into the filter press, and the ferrous chloride tetrahydrate crystals are dissolved in the filter press and circulated to prepare the ferrous chloride solution; the HCl concentration in the analytical acid is 180-200g / L; (4) The ferrous chloride solution is recycled and pumped into the filter press to dissolve the remaining ferrous chloride tetrahydrate crystals in the plate frame until the Fe2+ concentration in the ferrous solution reaches 160 g / L, at which time the Cl- concentration can reach 350 g / L, thereby obtaining a high-chloride ion pure ferrous chloride solution that can be used for the spray roasting and absorption process to prepare high-quality ferric oxide and regenerated acid. The prepared high-chloride ion pure ferrous chloride solution is pumped to the high-chloride ion pure ferrous chloride intermediate storage tank of the regenerated acid spray roasting process for preparing high-quality ferric oxide powder and regenerated acid.

2. The method according to claim 1, wherein the filter press is a chamber filter press, and a circulation operation is performed on the same chamber filter press to realize filtration, filter cake washing and analytical acid dissolution of ferrous chloride crystals to prepare high chloride ion pure ferrous chloride solution of tetrahydrate ferrous chloride crystal solution.

3. The method according to claim 1, wherein the freezing temperature in step (1) is 8-12°C.

4. The method according to claim 1, wherein the freezing temperature in step (1) is 10°C.