A method for improving iron removal efficiency by high-pressure pickling of quartz sand using fluorine-containing waste sulfuric acid

Abstract

The present invention provides a method for improving the iron removal efficiency by high-pressure pickling of quartz sand using fluorine-containing waste sulfuric acid, and relates to the technical field of quartz sand purification. The pickling method comprises the following steps: mixing fluorine-containing waste sulfuric acid, oxalic acid, phosphoric acid, hydrogen peroxide solution, N,N-dimethylformamide, a surfactant and water to obtain a composite high-pressure pickling solution; performing high-pressure pickling on quartz sand using the composite high-pressure pickling solution; and washing the quartz sand with water after the high-pressure pickling is completed to obtain a quartz sand product. The present invention uses fluorine-containing waste sulfuric acid as the main component to prepare the composite high-pressure pickling solution and uses high-pressure pickling equipment to pickle the quartz sand, which not only solves the problem of resource waste and environmental pollution caused by the difficulty in recycling fluorine-containing waste sulfuric acid, but also solves the problem of difficulty in removing impurities inside the quartz sand.

Description

Technical Field

[0001] The invention relates to the technical field of quartz sand purification, in particular to a method for improving iron removal efficiency by high-pressure pickling of quartz sand using fluorine-containing waste sulfuric acid. Background Art

[0002] Quartz sand is an important industrial mineral raw material, mainly made from quartz stone through processes such as crushing and screening. Its main component is silicon dioxide, and it is widely found in igneous rocks, metamorphic rocks, sedimentary rocks, and hydrothermal veins. Quartz sand is widely used in industries such as industry, electronics, metallurgy, and construction. However, there are various impurities in its ore, which have a significant impact on the quality and application of quartz sand. Therefore, before use, it needs to be purified and removed in different ways according to the purity requirements of the application field. The impurities Al and Fe in quartz are the most difficult elements to remove during the quartz sand purification process. Al is often present in quartz in the form of mica and feldspar, and Fe is often present in quartz in the form of hematite, magnetite, limonite, etc. At the same time, both exist in the quartz lattice in an isomorphic manner. When Al and Fe elements exist in minerals such as mica and feldspar, they can be removed through flotation and magnetic separation. However, this process can only remove surface impurities, and deeper impurities cannot be removed. The existing method for removing deep impurities in quartz sand is to calcine the quartz sand at high temperatures to transform its crystal structure. During this process, it expands and deforms, and cracks are generated. The cracks are deepened during the quenching process, exposing the impurities inside the quartz, and then they are efficiently removed during the subsequent pickling process. However, this method requires a relatively high temperature (1500°C) during the calcination process, and a large amount of dye is needed for calcination, resulting in high purification costs and large fossil energy consumption.

[0003] In order to solve the above problems, those skilled in the art are in urgent need of disclosing a high-pressure pickling method that can efficiently remove impurities inside quartz sand without the need for high-temperature roasting. Summary of the Invention

[0004] The object of the present invention is to provide a method for improving the iron removal efficiency by high-pressure pickling of quartz sand using fluorine-containing waste sulfuric acid, so as to solve the problems that fluorine-containing waste sulfuric acid is difficult to treat and easily causes environmental pollution, and that pickling of impurities inside quartz sand is difficult and costly.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for improving iron removal efficiency by high-pressure pickling of quartz sand using fluorine-containing waste sulfuric acid, comprising the following steps:

[0007] 1) mixing fluorine-containing waste sulfuric acid, oxalic acid, phosphoric acid, hydrogen peroxide solution, N,N-dimethylformamide, a surfactant and water to obtain a composite high-pressure pickling solution;

[0008] 2) high-pressure pickling of the quartz sand using the composite high-pressure pickling solution in step 1);

[0009] 3) After the high-pressure pickling is completed, the quartz sand is washed with water to obtain a quartz sand product;

[0010] The iron content in the quartz sand in step 2) is 400-500 ppm.

[0011] Preferably, the mass concentration of sulfuric acid in the fluorine-containing waste sulfuric acid in step 1) is 70-80%, and the mass concentration of fluoride ions is 2-6%;

[0012] The mass concentration of sulfuric acid in the composite high-pressure pickling solution is 20-30%, and the mass concentration of fluoride ions is 1-2%.

[0013] Preferably, the mass concentration of oxalic acid in the composite high-pressure pickling solution in step 1) is 1 to 3%;

[0014] The mass concentration of phosphoric acid in the composite high-pressure pickling solution is 1-2%;

[0015] The mass concentration of hydrogen peroxide in the composite high-pressure pickling solution is 0.5-0.8%;

[0016] The mass concentration of N,N-dimethylformamide in the composite high-pressure pickling solution is 0.2-0.5%.

[0017] Preferably, the surfactant in step 1) comprises one or more of triethanolamine, hexadecyltrimethylammonium chloride and dodecyltrimethylammonium chloride;

[0018] The mass concentration of the surfactant in the composite high-pressure pickling solution is 0.2-0.5%.

[0019] Preferably, the pressure of the high-pressure pickling in step 2) is 0.5 to 1 MPa, and the time of the high-pressure pickling is 2 to 5 hours.

[0020] Preferably, the particle size of the quartz sand in step 2) is 20-50 mesh.

[0021] Preferably, the number of water washing in step 3) is 4 to 6 times.

[0022] The present invention has at least the following beneficial effects:

[0023] The present invention adopts industrially produced fluorine-containing waste sulfuric acid as a main component to prepare a composite high-pressure pickling solution for pickling quartz sand, effectively utilizing fluorine ions and sulfuric acid therein. Fluorine ions can react with quartz sand under acidic conditions, and can penetrate into cracks in the quartz sand and expand them in combination with high-pressure pickling, thereby allowing the acid solution to enter the crystal lattice of the quartz sand and remove iron elements present in the crystal lattice of the quartz in an isomorphic manner, thereby improving the whiteness of the quartz sand. High-pressure pickling can increase the rate at which fluorine ions enter the cracks in the quartz sand and shorten the time required for pickling.

[0024] The composite high-pressure pickling solution prepared by the present invention is prepared from fluorine-containing waste sulfuric acid, wherein the sulfuric acid content can reach 80% and the fluorine content is 2-6%. After the sulfuric acid concentration is diluted to an appropriate range, the concentration of fluoride ions is low, and the high-pressure pickling effect of quartz sand directly using the diluted solution is poor. The present invention enhances the activity of hydrofluoric acid in the solution and its erosion effect on quartz sand lattice cracks by adding N,N-dimethylformamide and coordinating with a surfactant, so that the pickling solution can achieve a good pickling effect even at a lower concentration.

[0025] The addition of oxalic acid, phosphoric acid, and hydrogen peroxide solutions can significantly improve pickling efficiency. First, oxalic acid forms a soluble complex with iron ions, making it easier to dissolve and leach iron. Phosphoric acid forms soluble phosphates with various metal ions, which improves the removal efficiency of metal ion impurities. Oxalic acid and phosphoric acid also have a synergistic effect, with the presence of phosphoric acid promoting the complexation of oxalic acid with iron ions. Hydrogen peroxide solution increases the acidity and oxidative activity of the composite high-pressure pickling solution, oxidizing the metal elements in the system into ionic form and accelerating the pickling rate. DETAILED DESCRIPTION

[0026] The present invention provides a method for improving iron removal efficiency by high-pressure pickling of quartz sand using fluorine-containing waste sulfuric acid, comprising the following steps:

[0027] 1) mixing fluorine-containing waste sulfuric acid, oxalic acid, phosphoric acid, hydrogen peroxide solution, N,N-dimethylformamide, a surfactant and water to obtain a composite high-pressure pickling solution;

[0028] 2) high-pressure pickling of the quartz sand using the composite high-pressure pickling solution in step 1);

[0029] 3) After the high-pressure pickling is completed, the quartz sand is washed with water to obtain a quartz sand product.

[0030] In the present invention, the mass concentration of sulfuric acid in the fluorine-containing waste sulfuric acid in step 1) is 70-80%, and the mass concentration of fluoride ions is 2-6%.

[0031] In the present invention, the mass concentration of sulfuric acid in the composite high-pressure pickling solution is 20-30%, preferably 22-28%, more preferably 24-26%, and more preferably 25%; the mass concentration of fluoride ions is 1-2%, preferably 1.2-1.8%, more preferably 1.4-1.6%, and more preferably 1.5%.

[0032] In the present invention, the mass concentration of oxalic acid in the composite high-pressure pickling solution in step 1) is 1-3%, preferably 1.2-2.8%, more preferably 1.5-2.5%, and even more preferably 1.8-2.3%.

[0033] In the present invention, the mass concentration of phosphoric acid in the composite high-pressure pickling solution is 1-2%, preferably 1.3-1.7%, and more preferably 1.5%.

[0034] In the present invention, the mass concentration of hydrogen peroxide in the composite high-pressure pickling solution is 0.5-0.8%, preferably 0.6-0.7%.

[0035] In the present invention, the mass concentration of N,N-dimethylformamide in the composite high-pressure pickling solution is 0.2-0.5%, preferably 0.3-0.4%.

[0036] In the present invention, the surfactant in step 1) includes one or more of triethanolamine, hexadecyltrimethylammonium chloride and dodecyltrimethylammonium chloride.

[0037] In the present invention, the mass concentration of the surfactant in the composite high-pressure pickling solution is 0.2-0.5%, preferably 0.25-0.45%, more preferably 0.3-0.4%, and even more preferably 0.35%.

[0038] In the present invention, the pressure of the high-pressure pickling in step 2) is 0.5-1 MPa, preferably 0.6-0.9 MPa, more preferably 0.7-0.8 MPa; the time of the high-pressure pickling is 2-5 h, preferably 2.5-4.5 h, more preferably 3-4 h, and more preferably 3.5 h.

[0039] In the present invention, the high-pressure pickling method is to place quartz sand in a pickling device, add a composite high-pressure pickling liquid to immerse the quartz sand, introduce nitrogen to increase the pressure inside the pickling device, and the high-pressure pickling liquid flows out through a circulating water pump below the pickling device and then flows into the water inlet above the pickling device for circulating pickling.

[0040] If the pressure of high-pressure pickling is too low, the pickling effect will be poor, and the acid cannot enter the quartz sand lattice, resulting in poor pickling effect; if the pressure of high-pressure pickling is too high, the structure of the quartz sand will be destroyed, resulting in a smaller particle size of the quartz sand, affecting its use.

[0041] In the present invention, the particle size of the quartz sand in step 2) is 20-50 mesh, preferably 25-40 mesh, and more preferably 30-35 mesh.

[0042] In the present invention, the number of water washing in step 3) is 4 to 6 times, specifically, washing until the pH value of the washing liquid is neutral.

[0043] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0044] Example 1

[0045] (1) Fluorine-containing waste sulfuric acid (sulfuric acid concentration of 80%, fluoride ion concentration of 5%) is diluted with water to obtain a dilution solution, and then oxalic acid, phosphoric acid, hydrogen peroxide solution (30wt%), N,N-dimethylformamide and triethanolamine are added to obtain a composite high-pressure pickling solution, wherein the concentration of sulfuric acid in the composite high-pressure pickling solution is 25%, the mass concentration of fluoride ions is 1.6%, the concentration of oxalic acid is 1%, the concentration of phosphoric acid is 2%, the concentration of hydrogen peroxide is 0.5%, the concentration of N,N-dimethylformamide is 0.2%, and the concentration of triethanolamine is 0.3%.

[0046] (2) Quartz sand with a particle size of 25 to 50 mesh is placed in a high-pressure pickling device, and the composite high-pressure pickling liquid prepared in step (1) is injected to immerse the quartz sand. Nitrogen is flushed into the device to make the pressure in the device 0.5 MPa. The circulation device in the high-pressure pickling device is turned on to circulate the high-pressure pickling liquid from the lower part of the pickling device through the water pump to the water inlet at the upper part to perform circulated pickling on the quartz sand. The high-pressure pickling is completed after pickling for 3 hours.

[0047] (3) Wash the quartz sand after high-pressure acid washing with water. After washing 5 times, use pH test paper to detect that the pH value of the washing solution is neutral. Stop washing and dry the quartz sand at 80°C to obtain a quartz sand product.

[0048] The iron content of the quartz sand before and after pickling was tested. The iron content of the quartz sand before pickling was 428ppm, and the iron content of the quartz sand after pickling was 48ppm, with a whiteness of 85.

[0049] Example 2

[0050] (1) Fluorine-containing waste sulfuric acid (sulfuric acid concentration of 80%, fluoride ion concentration of 5%) is diluted with water to obtain a dilution solution, and then oxalic acid, phosphoric acid, hydrogen peroxide solution (30wt%), N,N-dimethylformamide and triethanolamine are added to obtain a composite high-pressure pickling solution, wherein the concentration of sulfuric acid in the composite high-pressure pickling solution is 20%, the mass concentration of fluoride ion is 1.25%, the concentration of oxalic acid is 3%, the concentration of phosphoric acid is 1.5%, the concentration of hydrogen peroxide is 0.5%, the concentration of N,N-dimethylformamide is 0.5%, and the concentration of triethanolamine is 0.5%.

[0051] (2) Quartz sand with a particle size of 25 to 50 mesh is placed in a high-pressure pickling device, and the composite high-pressure pickling liquid prepared in step (1) is injected to immerse the quartz sand. Nitrogen is flushed into the device to make the pressure in the device 0.6 MPa. The circulation device in the high-pressure pickling device is turned on to circulate the high-pressure pickling liquid from the lower part of the pickling device through the water pump to the water inlet at the upper part to perform circulated pickling on the quartz sand. The high-pressure pickling is completed after pickling for 2.5 hours.

[0052] (3) Washing the quartz sand after high-pressure acid washing with water. After washing 6 times, using pH test paper to detect that the pH value of the washing solution is neutral, stopping washing, and drying the quartz sand at 80°C to obtain a quartz sand product.

[0053] The iron content of the quartz sand before and after pickling was tested. The iron content of the quartz sand before pickling was 424ppm, and the iron content of the quartz sand after pickling was 43ppm, with a whiteness of 85.

[0054] Example 3

[0055] (1) Fluorine-containing waste sulfuric acid (sulfuric acid concentration of 80%, fluoride ion concentration of 5%) is diluted with water to obtain a dilution solution, and then oxalic acid, phosphoric acid, hydrogen peroxide solution (30wt%), N,N-dimethylformamide and hexadecyltrimethylammonium chloride are added to obtain a composite high-pressure pickling solution, wherein the concentration of sulfuric acid in the composite high-pressure pickling solution is 30%, the mass concentration of fluoride ion is 1.9%, the concentration of oxalic acid is 2.5%, the concentration of phosphoric acid is 1.4%, the concentration of hydrogen peroxide is 0.6%, the concentration of N,N-dimethylformamide is 0.3%, and the concentration of hexadecyltrimethylammonium chloride is 0.5%.

[0056] (2) placing quartz sand with a particle size of 30 to 50 meshes in a high-pressure pickling device, injecting the composite high-pressure pickling solution prepared in step (1) to immerse the quartz sand, flushing nitrogen gas to make the pressure in the device 1 MPa, turning on the circulation device in the high-pressure pickling device, and allowing the high-pressure pickling solution to circulate from the lower part of the pickling device through the water pump to the water inlet at the upper part to perform circulated pickling on the quartz sand. The high-pressure pickling is completed after pickling for 2 hours.

[0057] (3) Wash the quartz sand after high-pressure acid washing with water. After washing 5 times, use pH test paper to detect that the pH value of the washing solution is neutral. Stop washing and dry the quartz sand at 80°C to obtain a quartz sand product.

[0058] The iron content of the quartz sand before and after pickling was tested. The iron content of the quartz sand before pickling was 433ppm, and the iron content of the quartz sand after pickling was 47ppm, with a whiteness of 85.

[0059] Example 4

[0060] (1) Fluorine-containing waste sulfuric acid (sulfuric acid concentration of 80%, fluoride ion concentration of 5%) is diluted with water to obtain a dilution solution, and then oxalic acid, phosphoric acid, hydrogen peroxide solution (30wt%), N,N-dimethylformamide and hexadecyltrimethylammonium chloride are added to obtain a composite high-pressure pickling solution, wherein the concentration of sulfuric acid in the composite high-pressure pickling solution is 28%, the mass concentration of fluoride ion is 1.75%, the concentration of oxalic acid is 1%, the concentration of phosphoric acid is 1%, the concentration of hydrogen peroxide is 0.8%, the concentration of N,N-dimethylformamide is 0.5%, and the concentration of hexadecyltrimethylammonium chloride is 0.3%.

[0061] (2) Quartz sand with a particle size of 20 to 40 mesh is placed in a high-pressure pickling device, and the composite high-pressure pickling liquid prepared in step (1) is injected to immerse the quartz sand. Nitrogen is flushed into the device to make the pressure in the device 0.6 MPa. The circulation device in the high-pressure pickling device is turned on to circulate the high-pressure pickling liquid from the lower part of the pickling device through the water pump to the water inlet at the upper part to perform circulated pickling on the quartz sand. The high-pressure pickling is completed after pickling for 3 hours.

[0062] (3) Washing the quartz sand after high-pressure acid washing with water. After washing 6 times, using pH test paper to detect that the pH value of the washing solution is neutral, stopping washing, and drying the quartz sand at 80°C to obtain a quartz sand product.

[0063] The iron content of the quartz sand before and after pickling was tested. The iron content of the quartz sand before pickling was 428ppm, and the iron content of the quartz sand after pickling was 52ppm, with a whiteness of 85.

[0064] Example 5

[0065] (1) Fluorine-containing waste sulfuric acid (sulfuric acid concentration of 80%, fluoride ion concentration of 5%) is diluted with water to obtain a dilution solution, and then oxalic acid, phosphoric acid, hydrogen peroxide solution (30wt%), N,N-dimethylformamide and dodecyltrimethylammonium chloride are added to obtain a composite high-pressure pickling solution, wherein the concentration of sulfuric acid in the composite high-pressure pickling solution is 20%, the mass concentration of fluoride ion is 1.25%, the concentration of oxalic acid is 2.8%, the concentration of phosphoric acid is 1.3%, the concentration of hydrogen peroxide is 1%, the concentration of N,N-dimethylformamide is 0.4%, and the concentration of dodecyltrimethylammonium chloride is 0.3%.

[0066] (2) Quartz sand with a particle size of 25 to 45 mesh is placed in a high-pressure pickling device, and the composite high-pressure pickling liquid prepared in step (1) is injected to immerse the quartz sand. Nitrogen is flushed into the device to make the pressure in the device 0.7 MPa. The circulation device in the high-pressure pickling device is turned on to circulate the high-pressure pickling liquid from the lower part of the pickling device through the water pump to the water inlet at the upper part to perform circulated pickling on the quartz sand. The high-pressure pickling is completed after pickling for 4.5 hours.

[0067] (3) Washing the quartz sand after high-pressure acid washing with water. After washing 6 times, using pH test paper to detect that the pH value of the washing solution is neutral, stopping washing, and drying the quartz sand at 80°C to obtain a quartz sand product.

[0068] The iron content of the quartz sand before and after pickling was tested. The iron content of the quartz sand before pickling was 428ppm, and the iron content of the quartz sand after pickling was 50ppm, with a whiteness of 85.

[0069] Comparative Example 1

[0070] (1) Fluorine-containing waste sulfuric acid (sulfuric acid concentration of 80%, fluoride ion concentration of 5%) is diluted with water to obtain a dilution solution, and then oxalic acid, phosphoric acid, hydrogen peroxide solution (30wt%) and N,N-dimethylformamide are added to obtain a composite high-pressure pickling solution, wherein the concentration of sulfuric acid in the composite high-pressure pickling solution is 25%, the mass concentration of fluoride ions is 1.6%, the concentration of oxalic acid is 1%, the concentration of phosphoric acid is 2%, the concentration of hydrogen peroxide is 0.5%, and the concentration of N,N-dimethylformamide is 0.2%.

[0071] (2) Quartz sand with a particle size of 25 to 50 mesh is placed in a high-pressure pickling device, and the composite high-pressure pickling liquid prepared in step (1) is injected to immerse the quartz sand. Nitrogen is flushed into the device to make the pressure in the device 0.5 MPa. The circulation device in the high-pressure pickling device is turned on to circulate the high-pressure pickling liquid from the lower part of the pickling device through the water pump to the water inlet at the upper part to perform circulated pickling on the quartz sand. The high-pressure pickling is completed after pickling for 3 hours.

[0072] (3) Wash the quartz sand after high-pressure acid washing with water. After washing 5 times, use pH test paper to detect that the pH value of the washing solution is neutral. Stop washing and dry the quartz sand at 80°C to obtain a quartz sand product.

[0073] The iron content of the quartz sand before and after pickling was tested. The iron content of the quartz sand before pickling was 428 ppm, and the iron content of the quartz sand after pickling was 94 ppm. The whiteness was 77. Compared with Example 1, no surfactant was added in this comparative example, and the activation effect of hydrofluoric acid was poor. The lattice of the prepared quartz sand product also contained more iron elements.

[0074] Comparative Example 2

[0075] (1) Fluorine-containing waste sulfuric acid (sulfuric acid concentration of 80%, fluoride ion concentration of 5%) is diluted with water to obtain a dilution solution, and then oxalic acid, phosphoric acid, hydrogen peroxide solution (30wt%) and triethanolamine are added to obtain a composite high-pressure pickling solution, wherein the concentration of sulfuric acid in the composite high-pressure pickling solution is 25%, the mass concentration of fluoride ions is 1.6%, the concentration of oxalic acid is 1%, the concentration of phosphoric acid is 2%, the concentration of hydrogen peroxide is 0.5%, and the concentration of triethanolamine is 0.3%.

[0076] (2) Quartz sand with a particle size of 25 to 50 mesh is placed in a high-pressure pickling device, and the composite high-pressure pickling liquid prepared in step (1) is injected to immerse the quartz sand. Nitrogen is flushed into the device to make the pressure in the device 0.5 MPa. The circulation device in the high-pressure pickling device is turned on to circulate the high-pressure pickling liquid from the lower part of the pickling device through the water pump to the water inlet at the upper part to perform circulated pickling on the quartz sand. The high-pressure pickling is completed after pickling for 3 hours.

[0077] (3) Wash the quartz sand after high-pressure acid washing with water. After washing 5 times, use pH test paper to detect that the pH value of the washing solution is neutral. Stop washing and dry the quartz sand at 80°C to obtain a quartz sand product.

[0078] The iron content of the quartz sand before and after pickling was tested. The iron content of the quartz sand before pickling was 428 ppm, and the iron content of the quartz sand after pickling was 127 ppm, with a whiteness of 79. Compared with Example 1, this comparative example did not add N,N-dimethylformamide. N,N-dimethylformamide has a certain improvement in the permeability of hydrofluoric acid. Directly using a pickling solution with a low hydrofluoric acid concentration without adding N,N-dimethylformamide cannot achieve the purpose of removing iron impurities in the quartz sand lattice.

[0079] Comparative Example 3

[0080] (1) Fluorine-containing waste sulfuric acid (sulfuric acid concentration of 80%, fluoride ion concentration of 5%) is diluted with water to obtain a dilution solution, and then a hydrogen peroxide solution (30wt%), N,N-dimethylformamide and triethanolamine are added to obtain a composite high-pressure pickling solution, wherein the concentration of sulfuric acid in the composite high-pressure pickling solution is 25%, the mass concentration of fluoride ions is 1.6%, the concentration of hydrogen peroxide is 0.5%, the concentration of N,N-dimethylformamide is 0.2%, and the concentration of triethanolamine is 0.3%.

[0081] (2) Quartz sand with a particle size of 25 to 50 mesh is placed in a high-pressure pickling device, and the composite high-pressure pickling liquid prepared in step (1) is injected to immerse the quartz sand. Nitrogen is flushed into the device to make the pressure in the device 0.5 MPa. The circulation device in the high-pressure pickling device is turned on to circulate the high-pressure pickling liquid from the lower part of the pickling device through the water pump to the water inlet at the upper part to perform circulated pickling on the quartz sand. The high-pressure pickling is completed after pickling for 3 hours.

[0082] (3) Wash the quartz sand after high-pressure acid washing with water. After washing 5 times, use pH test paper to detect that the pH value of the washing solution is neutral. Stop washing and dry the quartz sand at 80°C to obtain a quartz sand product.

[0083] The iron content of the quartz sand before and after pickling was tested. The iron content of the quartz sand before pickling was 428 ppm, and the iron content of the quartz sand after pickling was 103 ppm, with a whiteness of 80. Compared with Example 1, this comparative example did not add additional phosphoric acid and oxalic acid. Although the iron content in the quartz sand after pickling was significantly reduced, the removal effect was poor. This is because phosphoric acid and oxalic acid can make iron more easily leached and form soluble complexes or salts with iron ions, thereby improving the iron removal effect.

[0084] Comparative Example 4

[0085] (1) Fluorine-containing waste sulfuric acid (sulfuric acid concentration of 80%, fluoride ion concentration of 5%) is diluted with water to obtain a dilution solution, and then oxalic acid, phosphoric acid, hydrogen peroxide solution (30wt%), N,N-dimethylformamide and triethanolamine are added to obtain a composite high-pressure pickling solution, wherein the concentration of sulfuric acid in the composite high-pressure pickling solution is 25%, the mass concentration of fluoride ions is 1.6%, the concentration of oxalic acid is 1%, the concentration of phosphoric acid is 2%, the concentration of hydrogen peroxide is 0.5%, the concentration of N,N-dimethylformamide is 0.2%, and the concentration of triethanolamine is 0.3%.

[0086] (2) placing quartz sand with a particle size of 25 to 50 meshes in a high-pressure pickling device, injecting the composite high-pressure pickling solution prepared in step (1) to immerse the quartz sand, turning on the circulation device in the high-pressure pickling device, and allowing the high-pressure pickling solution to circulate from the lower part of the pickling device through the water pump to the water inlet at the upper part to perform circulated pickling on the quartz sand, and completing the high-pressure pickling after pickling for 3 hours.

[0087] (3) Wash the acid-washed quartz sand with water. After washing five times, use pH test paper to detect that the pH value of the washing solution is neutral. Stop washing and dry the quartz sand at 80°C to obtain a quartz sand product.

[0088] The iron content of the quartz sand before and after pickling was tested. The iron content of the quartz sand before pickling was 428 ppm, and the iron content of the quartz sand after pickling was 122 ppm, with a whiteness of 79. In this comparative example, the pickling equipment was not flushed with nitrogen and pressurized during the pickling process. The ability of fluoride ions to penetrate the quartz sand crystal lattice was poor, and the iron removal efficiency was low.

[0089] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for improving iron removal efficiency by high-pressure pickling of quartz sand using fluorine-containing waste sulfuric acid, characterized in that: The following steps are involved: 1) mixing fluorine-containing waste sulfuric acid, oxalic acid, phosphoric acid, hydrogen peroxide solution, N,N-dimethylformamide, a surfactant and water to obtain a composite high-pressure pickling solution; 2) high-pressure pickling of the quartz sand using the composite high-pressure pickling solution in step 1); 3) After the high-pressure pickling is completed, the quartz sand is washed with water to obtain a quartz sand product; The iron content in the quartz sand in step 2) is 400-500 ppm; The mass concentration of sulfuric acid in the fluorine-containing waste sulfuric acid in step 1) is 70-80%, and the mass concentration of fluoride ions is 2-6%; The mass concentration of sulfuric acid in the composite high-pressure pickling solution is 20-30%, and the mass concentration of fluoride ions is 1-2%; The mass concentration of oxalic acid in the composite high-pressure pickling solution in step 1) is 1-3%; The mass concentration of phosphoric acid in the composite high-pressure pickling solution is 1-2%; The mass concentration of hydrogen peroxide in the composite high-pressure pickling solution is 0.5-0.8%; The mass concentration of N,N-dimethylformamide in the composite high-pressure pickling solution is 0.2-0.5%; The pressure of the high-pressure pickling in step 2) is 0.5-1 MPa, and the time of the high-pressure pickling is 2-5 hours.

2. The method for improving iron removal efficiency by high-pressure pickling of quartz sand using fluorine-containing waste sulfuric acid according to claim 1, characterized in that: The surfactant in step 1) includes one or more of triethanolamine, hexadecyltrimethylammonium chloride and dodecyltrimethylammonium chloride; The mass concentration of the surfactant in the composite high-pressure pickling solution is 0.2-0.5%.

3. The method for improving iron removal efficiency by high-pressure pickling of quartz sand using fluorine-containing waste sulfuric acid according to claim 1, characterized in that: The particle size of the quartz sand in step 2) is 20 to 50 meshes.

4. The method for improving iron removal efficiency by high-pressure pickling of quartz sand using fluorine-containing waste sulfuric acid according to claim 3, characterized in that: The number of times of washing with water in step 3) is 4 to 6 times.