Method for removing ferric oxide in fluorine-containing sludge

Abstract

The invention belongs to the technical field of solid waste treatment and resource recovery, and particularly relates to a method for removing ferric oxide in fluorine-containing sludge. The method comprises the following steps: (1) screening and grinding fluorine-containing sludge to obtain a uniformly refined raw material; (2) mixing the raw materials refined in the step (1) with a complexing agent solution, and then carrying out complexation reaction under the conditions that the temperature is 80-150 DEG C and the pH value is 6-8; and (3) carrying out solid-liquid separation on the solution after the complexation reaction in the step (2) to obtain a solid phase which is fluorine-containing sludge without Fe2O3 and a liquid phase which is a solution in which an iron complex is dissolved. The method is based on a comprehensive method of complexing dissolution and solid-liquid separation, the efficient, cheap and environment-friendly complexing agent is selected, ferric oxide in the fluorine-containing sludge can be effectively removed, the influence on CaF2 solid-phase components in the fluorine-containing sludge is small, and the method has the advantages of being simple in treatment process, mild in condition, environmentally friendly and low in cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid waste treatment and resource recovery, and particularly relates to a method for removing iron oxide from fluorine-containing sludge. Background Art

[0002] The presence of iron oxide (Fe2O3) in fluorine-containing sludge will affect the purity and performance of the final product (in fluorine chemical production (such as hydrogen fluoride preparation), fluorite (CaF2) raw materials are often associated with iron-containing phases (such as hematite, magnetite), and during high-temperature calcination or acidolysis, iron elements are oxidized to form Fe2O3; in fluorine-containing waste residues in the metallurgical industry, iron-based fluxes (such as Fe2O3, Fe3O4) remain in the sludge. When treating fluorine-containing wastewater, the added lime (CaO) reacts with Fe 3+ in the wastewater to form Fe(OH)3, which is converted into Fe2O3 after dehydration and remains in the fluorine-containing sludge), especially in the preparation of fluorite for building materials and metallurgical-grade calcium fluoride, Fe2O3 will cause the whiteness of the product to decrease and even affect its application in specific industries.

[0003] The existing methods for removing Fe2O3 from sludge mainly include pickling method: using strong acid to dissolve Fe2O3, and then separating the dissolved products. The disadvantages are high corrosiveness of strong acid, high requirements for equipment and high discharge treatment cost. Magnetic separation method: using the magnetism of iron oxide for physical separation. The disadvantage is low separation efficiency for fine-grained Fe2O3 and inability to treat complex mixtures. Reduction method: using a reducing agent to reduce Fe2O3 to a low-valence iron compound that is easy to separate. The disadvantages are complex process, high cost, and easy introduction of new impurities. The existing methods generally have problems of complex operation, low removal efficiency and large environmental impact. Therefore, a new method that is simple, efficient, low-cost and environmentally friendly is needed. Summary of the Invention

[0004] Aiming at the above-mentioned disadvantages and deficiencies of the prior art, the purpose of the present invention is to provide a method for removing iron oxide from fluorine-containing sludge. The method of the present invention is based on a comprehensive method of complexation dissolution and solid-liquid separation. By adding a specific complexing agent, Fe2O3 forms a soluble complex with the complexing agent under mild conditions, and then Fe2O3 is removed by solid-liquid separation.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A method for removing iron oxide from fluorine-containing sludge, comprising the following steps:

[0007] (1) Screening and grinding the fluorine-containing sludge to obtain a uniformly refined raw material;

[0008] (2) Mix the refined raw materials in step (1) with a complexing agent solution, and then carry out a complexation reaction under the conditions of a temperature of 80-150 °C and a pH value of 6-8;

[0009] (3) Separate the solid and liquid from the solution after the complexation reaction in step (2). The obtained solid phase is the fluorine-containing sludge with Fe2O3 removed, and the obtained liquid phase is the solution in which the iron complex is dissolved.

[0010] Furthermore, the mass percentage composition of the fluorine-containing sludge described in step (1) includes 60-80% calcium fluoride (CaF2), 5-18% iron(III) oxide (Fe2O3), 3-8% silicon dioxide (SiO2), and 2-5% calcium carbonate (CaCO3).

[0011] Furthermore, the particle size of the refined raw materials in step (1) is <100 μm.

[0012] Furthermore, the complexing agent solution in step (2) uses an ethylenediaminetetraacetic acid (EDTA) solution with a mass concentration of 3-10% or a citric acid solution with a mass concentration of 5-20%.

[0013] Furthermore, the mass ratio of the refined raw materials to the complexing agent solution mixed in step (2) is 1:5-1:10.

[0014] Furthermore, the time of the complexation reaction in step (2) is 24-48 h.

[0015] Furthermore, the solid-liquid separation in step (3) uses centrifugal separation or filtration separation.

[0016] Furthermore, the obtained solid phase in step (3) is further washed with water and dried to improve the product purity.

[0017] Furthermore, sodium hydroxide is further added to the obtained liquid phase in step (3) until pH > 10 to precipitate and recover Fe(OH)3.

[0018] The principle of the present invention is as follows: The complexation reaction of the present invention uses an environmentally friendly complexing agent such as ethylenediaminetetraacetic acid (EDTA) or citric acid. Under specific temperature and pH conditions, Fe in the fluorine-containing sludge 3+ dissolves to form a soluble complex (logK = 25.1) under the action of the complexing agent, such as [Fe(EDTA)] or [Fe(Cit)2]. While the EDTA complexation constant of Ca 2+ is relatively low (logK = 10.7), and CaF2 is almost insoluble at pH 6-8 (Ksp = 3.9×10-11). Heating (80-150 °C) accelerates the complexation dissolution of Fe2O3 and simultaneously inhibits the hydrolysis of CaF2, thereby realizing the effective separation of the Fe2O3 component from the main solid phase component CaF2 in the fluorine-containing sludge.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) The method of the present invention selects an efficient, inexpensive and environmentally friendly complexing agent, such as EDTA or citric acid, which can effectively remove iron oxide from fluorine-containing sludge, and has the advantages of simple treatment process, mild conditions, environmental protection and low cost.

[0021] (2) The present invention further determines the optimal combination of complexing agent concentration, reaction time and temperature to ensure the efficient removal of Fe2O3.

[0022] (3) The solution containing iron complexes obtained by the present invention can recover iron resources by a simple precipitation method, further improving the process economy. Detailed implementation mode

[0023] The present invention will be further described in detail below in conjunction with embodiments, but the implementation modes of the present invention are not limited thereto.

[0024] Embodiment 1

[0025] A method for removing iron oxide from fluorine-containing sludge, comprising the following steps:

[0026] (1) The fluorine-containing sludge (by mass percentage, containing 70% CaF2, 12% Fe2O3, 6% SiO2, 5% CaCO3) is sieved to remove larger particles and impurities, and ground to a particle size <100 μm to obtain a uniformly refined raw material.

[0027] (2) The refined raw material in step (1) is mixed with an 8% mass concentration EDTA solution at a mass ratio of 1:8, and then subjected to a complexation reaction at a temperature of 120 °C and a pH value of 7 for 36 h.

[0028] (3) The solution after the complexation reaction in step (2) is separated by centrifugation to separate the solid and liquid phases. The solid phase is washed with water and dried to obtain fluorine-containing sludge with Fe2O3 removed; the obtained liquid phase is a solution containing iron complexes. NaOH is added to the liquid phase by precipitation method until the pH is 11 to precipitate Fe(OH)3 and recover iron resources.

[0029] After treatment in this embodiment, the removal rate of Fe2O3 in the fluorine-containing sludge is 93.2% (detected by X-ray fluorescence spectroscopy, the same below); the loss rate of CaF2 is 2.1% (the content of CaF2 is determined according to GB / T 5195.1-2017 "Determination of calcium fluoride content in fluorspar - EDTA titration method and distillation - potentiometric titration method", and the loss rate of calcium fluoride is calculated by comparing the calcium fluoride content before and after treatment, the same below), and the Fe recovery rate is 88% (determined by ICP-OES, the same below).

[0030] Example 2

[0031] A method for removing iron(III) oxide from fluorine-containing sludge, comprising the following steps:

[0032] (1) The fluorine-containing sludge (same as in Example 1) is screened to remove larger particles and impurities, and ground to a particle size < 100 μm to obtain a uniformly refined raw material.

[0033] (2) The refined raw material in step (1) is mixed with a citric acid solution with a mass concentration of 15% at a mass ratio of 1:6, and then subjected to a complexation reaction at a temperature of 100 °C and a pH value of 6.5 for 48 h.

[0034] (3) The solution after the complexation reaction in step (2) is separated by centrifugation to obtain solid and liquid phases. The solid phase is washed with water and dried to obtain fluorine-containing sludge with Fe2O3 removed; the obtained liquid phase is a solution in which iron complexes are dissolved. NaOH is added to the liquid phase by a precipitation method to a pH of 11 to precipitate Fe(OH)3 and recover iron resources.

[0035] After treatment in this example, the removal rate of Fe2O3 in the fluorine-containing sludge is 91.5%; the loss rate of CaF2 is 3.8%, and the recovery rate of Fe is 84%.

[0036] Example 3

[0037] A method for removing iron(III) oxide from fluorine-containing sludge, comprising the following steps:

[0038] (1) The fluorine-containing sludge (same as in Example 1) is screened to remove larger particles and impurities, and ground to a particle size < 100 μm to obtain a uniformly refined raw material.

[0039] (2) The refined raw material in step (1) is mixed with a citric acid solution with a mass concentration of 10% at a mass ratio of 1:10, and then subjected to a complexation reaction at a temperature of 80 °C and a pH value of 7.5 for 36 h.

[0040] (3) The solution after the complexation reaction in step (2) is separated by centrifugation to obtain solid and liquid phases. The solid phase is washed with water and dried to obtain fluorine-containing sludge with Fe2O3 removed; the obtained liquid phase is a solution in which iron complexes are dissolved. NaOH is added to the liquid phase by a precipitation method to a pH of 11 to precipitate Fe(OH)3 and recover iron resources.

[0041] After treatment in this example, the removal rate of Fe2O3 in the fluorine-containing sludge is 86.7%; the loss rate of CaF2 is 1.9%, and the recovery rate of Fe is 82%.

[0042] Example 4

[0043] A method for removing iron(III) oxide from fluorine-containing sludge, comprising the following steps:

[0044] (1) The fluorine-containing sludge (same as in Example 1) is screened to remove larger particles and impurities, and ground to a particle size < 100 μm to obtain a uniformly refined raw material.

[0045] (2) The refined raw material in step (1) is mixed with an EDTA solution with a mass concentration of 5% at a mass ratio of 1:5, and then subjected to a complexation reaction at a temperature of 100 °C and a pH value of 7 for 36 h.

[0046] (3) The solution after the complexation reaction in step (2) is subjected to centrifugal solid-liquid separation, and the solid phase is taken, washed with water and dried to obtain fluorine-containing sludge with Fe2O3 removed; the obtained liquid phase is a solution in which iron complexes are dissolved. NaOH is added to the liquid phase to pH 11 by the precipitation method to precipitate Fe(OH)3 and recover iron resources.

[0047] After being treated by this example, the removal rate of Fe2O3 in the fluorine-containing sludge is 90.3%; the loss rate of CaF2 is 2.7%, and the recovery rate of Fe is 85%.

[0048] Example 5

[0049] A method for removing iron(III) oxide from fluorine-containing sludge, comprising the following steps:

[0050] (1) The fluorine-containing sludge (CaF2 65%, Fe2O3 18%, SiO2 8%, CaCO3 4%) is screened to remove larger particles and impurities, and ground to a particle size < 100 μm to obtain a uniformly refined raw material.

[0051] (2) The refined raw material in step (1) is mixed with a citric acid solution with a mass concentration of 12% at a mass ratio of 1:7, and then subjected to a complexation reaction at a temperature of 150 °C and a pH value of 7 for 24 h.

[0052] (3) The solution after the complexation reaction in step (2) is subjected to centrifugal solid-liquid separation, and the solid phase is taken, washed with water and dried to obtain fluorine-containing sludge with Fe2O3 removed; the obtained liquid phase is a solution in which iron complexes are dissolved. NaOH is added to the liquid phase to pH 11 by the precipitation method to precipitate Fe(OH)3 and recover iron resources.

[0053] After being treated by this example, the removal rate of Fe2O3 in the fluorine-containing sludge is 94.5%; the loss rate of CaF2 is 4.2%, and the recovery rate of Fe is 89%.

[0054] The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for removing ferric oxide from fluoride-containing sludge, characterized in that: The steps include: (1) Screening and grinding the fluorine-containing sludge to obtain a uniformly refined raw material; (2) mixing the raw material refined in step (1) with a complexing agent solution, and then performing a complexing reaction at a temperature of 80 to 150° C. and a pH of 6 to 8; (3) The solution after the complexation reaction in step (2) is subjected to solid-liquid separation, and the obtained solid phase is the fluorine-containing sludge from which Fe2O3 has been removed, and the obtained liquid phase is a solution containing dissolved iron complexes.

2. A method for removing ferric oxide from fluorine-containing sludge according to claim 1, characterized in that: The mass percentage composition of the fluorine-containing sludge in step (1) includes 60-80% calcium fluoride, 5-18% ferric oxide, 3-8% silicon dioxide and 2-5% calcium carbonate.

3. The method for removing ferric oxide from fluorine-containing sludge according to claim 1, characterized in that: The particle size of the refined raw material in step (1) is less than 100 μm.

4. The method for removing ferric oxide from fluorine-containing sludge according to claim 1, characterized in that: The complexing agent solution in step (2) is an ethylenediaminetetraacetic acid solution with a mass concentration of 3-10% or a citric acid solution with a mass concentration of 5-20%.

5. The method for removing ferric oxide from fluorine-containing sludge according to claim 1, characterized in that: The mass ratio of the refined raw material and the complexing agent solution mixed in step (2) is 1:5 to 1:

10.

6. The method for removing ferric oxide from fluorine-containing sludge according to claim 1, characterized in that: The time of the complexation reaction in step (2) is 24 to 48 hours.

7. The method for removing ferric oxide from fluorine-containing sludge according to claim 1, characterized in that: The solid-liquid separation in step (3) is carried out by centrifugal separation or filtration separation.

8. The method for removing ferric oxide from fluorine-containing sludge according to claim 1, characterized in that: The solid phase obtained in step (3) is further washed with water and dried to improve the purity of the product.

9. The method for removing ferric oxide from fluorine-containing sludge according to claim 1, characterized in that: The liquid phase obtained in step (3) is further treated with sodium hydroxide until the pH is > 10 to precipitate and recover Fe(OH)3.