A method for efficiently separating and recovering iron, nickel, and chromium metal ions from sulfate solid waste

Abstract

This invention provides a highly efficient method for separating and recovering iron, nickel, and chromium metal ions from sulfate solid waste, relating to the field of solid waste treatment technology. This invention uses column chromatography to separate sulfate solid waste, effectively separating and recovering iron, chromium, and nickel ions, filling a technological gap in the separation of these three metal ions. Compared to traditional chemical separation methods, this invention is not only simpler and faster with significant results, but also does not use or generate any harmful substances. The only solutions used throughout the process are water and anhydrous ethanol, making it environmentally friendly, extremely low-cost, and easily industrialized. Using the separation and recovery method provided by this invention, the recovery rates of iron, chromium, and nickel are high, all exceeding 96%. Furthermore, after processing the collected liquid according to appropriate methods, the resulting chromium hydroxide, nickel hydroxide, and ferrous oxalate have high purity, all exceeding 97%, and can be used in electrode materials for new energy batteries, demonstrating high resource utilization and good economic benefits.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, and in particular to a method for efficiently separating and recovering iron, nickel, and chromium metal ions from sulfate solid waste. Background Technology

[0002] Titanium dioxide, also known as titanium dioxide, is widely used in coatings, inks, plastics, rubber, paper, ceramics, and synthetic fibers due to its stable chemical properties, high refractive index, good hiding power, and tinting strength. The main production processes for titanium dioxide include the sulfuric acid process, the chloride process, and the hydrochloric acid process. Among these, the sulfuric acid solid-phase process is widely used in industry because of its relatively mature technology.

[0003] The sulfuric acid process is the main technology for titanium dioxide production in China, but the "three wastes" (waste gas, wastewater, and solid waste) generated during its production cause significant environmental pollution. The tailings solid waste produced after the sulfuric acid process mainly consists of sulfates such as ferric sulfate, chromium sulfate, and nickel sulfate. Currently, the main focus of industrial waste treatment for titanium dioxide production is on treating the waste acid, with less attention paid to solid waste treatment, and even then, it is limited to the separation and utilization of ferrous sulfate, without including the separation and application of other metals. Summary of the Invention

[0004] The purpose of this invention is to provide a method for efficiently separating and recovering iron, nickel, and chromium metal ions from sulfate solid waste. This invention can effectively separate and recover iron, chromium, and nickel ions from titanium dioxide sulfate solid waste, filling a technological gap in the separation of these three metal ions and improving the application value of sulfate solid waste.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for efficiently separating and recovering iron, nickel, and chromium metal ions from sulfate solid waste, comprising the following steps: mixing sulfate solid waste, water, and anhydrous ethanol to obtain a solution; wherein the sulfate solid waste includes ferrous sulfate, chromium sulfate, and nickel sulfate;

[0007] The solution was added to a silica gel column, where a yellowish-brown band and a light green band were formed. Then, anhydrous ethanol was used for the first elution, and the yellowish-brown liquid was collected. After the yellowish-brown band was completely precipitated, a chromium ion collection solution was obtained.

[0008] The silica gel column was eluted with anhydrous ethanol for a second elution, and the eluent light green liquid was collected. After the light green band was completely precipitated, the nickel ion collection solution was obtained.

[0009] Water was added to the silica gel column for a third elution, forming a dark green band. The dark green liquid that flowed out was collected to obtain the ferrous ion collection solution.

[0010] Preferably, the sulfate solid waste is tailings solid waste generated after the sulfuric acid process for preparing titanium dioxide.

[0011] Preferably, the silica powder filled in the silica column has a particle size of 100-300 mesh.

[0012] Preferably, the diameter of the silicone column is 20-30cm and the height is 85-125cm.

[0013] Preferably, the volume ratio of water to anhydrous ethanol in the solution is 1:1.

[0014] Preferably, before adding the solution to the silica gel column, the process further includes: eluting the silica gel column multiple times with anhydrous ethanol until there are no obvious air bubbles in the silica gel column and the silica gel presents a homogeneous phase system in anhydrous ethanol.

[0015] Preferably, after obtaining the chromium ion collecting solution, the method further includes mixing the chromium ion collecting solution with ammonia water to carry out a precipitation reaction, separating the solid and liquid, and obtaining chromium hydroxide precipitate.

[0016] Preferably, after obtaining the nickel ion collecting solution, the method further includes mixing the nickel ion collecting solution with ammonia water to carry out a precipitation reaction, separating the solid and liquid, and obtaining nickel hydroxide precipitate.

[0017] Preferably, after obtaining the ferrous ion collecting solution, the method further includes mixing the ferrous ion collecting solution with oxalic acid to carry out a precipitation reaction, followed by solid-liquid separation to obtain ferrous oxalate precipitate.

[0018] Preferably, the third elution process further includes a recovery wash of the used silica gel column, which includes: washing the used silica gel column with water until no sulfate ions are present, and then repeatedly washing it with anhydrous ethanol until the silica gel presents a homogeneous phase in anhydrous ethanol.

[0019] This invention provides a method for efficiently separating and recovering iron, nickel, and chromium metal ions from sulfate solid waste, comprising the following steps: mixing sulfate solid waste, water, and anhydrous ethanol to obtain a solution; the sulfate solid waste includes ferrous sulfate, chromium sulfate, and nickel sulfate; adding the solution to a silica gel column, forming a yellowish-brown band and a light green band in the silica gel column, then performing a first elution with anhydrous ethanol, collecting the yellowish-brown liquid, and obtaining a chromium ion collection solution after the yellowish-brown band has completely precipitated; performing a second elution with anhydrous ethanol on the silica gel column, collecting the light green liquid, and obtaining a nickel ion collection solution after the light green band has completely precipitated; adding water to the silica gel column for a third elution, forming a dark green band, collecting the dark green liquid, and obtaining a ferrous ion collection solution.

[0020] This invention uses column chromatography to separate sulfate solid waste, which can effectively separate and recover iron, chromium and nickel ions in titanium dioxide sulfate solid waste, filling the technological gap in the separation of these three metal ions.

[0021] Compared with traditional chemical separation methods, the method provided by this invention is not only simpler and faster with significant results, but also does not use or generate any harmful substances. The only solutions used throughout the process are water and anhydrous ethanol, making it green and environmentally friendly, with extremely low cost and easy to industrialize.

[0022] The separation and recovery method provided by this invention achieves high recovery rates of iron, chromium, and nickel, all exceeding 96%. Furthermore, after processing the collected liquid according to the corresponding methods, the resulting chromium hydroxide, nickel hydroxide, and ferrous oxalate have high purity, all exceeding 97%, and can be used as electrode materials for new energy batteries. This method offers high resource utilization and good economic benefits.

[0023] Furthermore, the eluents used in this invention can all be recycled and reused, the silica gel column can also be reused, and ammonium sulfate byproducts can be obtained, which has good recycling and economic benefits. Attached Figure Description

[0024] Figure 1 The XRD pattern of the chromium hydroxide precipitate obtained in Example 1 is shown below.

[0025] Figure 2 The XRD pattern of ferrous oxalate obtained in Example 1;

[0026] Figure 3 The image shows the XRD pattern of nickel hydroxide obtained in Example 1. Detailed Implementation

[0027] This invention provides a method for efficiently separating and recovering iron, nickel, and chromium metal ions from sulfate solid waste, comprising the following steps: mixing sulfate solid waste, water, and anhydrous ethanol to obtain a solution; wherein the sulfate solid waste includes ferrous sulfate, chromium sulfate, and nickel sulfate;

[0028] The solution was added to a silica gel column, where a yellowish-brown band and a light green band were formed. Then, anhydrous ethanol was used for the first elution, and the yellowish-brown liquid was collected. After the yellowish-brown band was completely precipitated, a chromium ion collection solution was obtained.

[0029] The silica gel column was eluted with anhydrous ethanol for a second elution, and the eluent light green liquid was collected. After the light green band was completely precipitated, the nickel ion collection solution was obtained.

[0030] Water was added to the silica gel column for a third elution, forming a dark green band. The dark green liquid that flowed out was collected to obtain the ferrous ion collection solution.

[0031] Unless otherwise specified, all raw materials used in this invention are commercially available products well known in the art.

[0032] This invention involves mixing sulfate solid waste, water, and anhydrous ethanol to obtain a solution.

[0033] In this invention, the sulfate solid waste preferably includes ferrous sulfate, chromium sulfate, and nickel sulfate. In the embodiments of this invention, the main components of the sulfate solid waste are FeSO4·7H2O, small amounts of hydrated Cr2(SO4)3 and hydrated NiSO4, trace amounts of hydrated MnSO4, and other trace impurities. The sulfate solid waste is preferably tailings solid waste generated after the sulfuric acid process for preparing titanium dioxide. This invention does not impose specific requirements on the exact content of each component in the sulfate solid waste; the content may vary between different batches.

[0034] In this invention, the water is preferably deionized water; the volume ratio of water to anhydrous ethanol is preferably 1:1. This invention does not have special requirements regarding the amount of water and anhydrous ethanol used, as long as it is sufficient to dissolve most sulfate solid waste.

[0035] In this invention, the mixing of sulfate solid waste, water, and anhydrous ethanol preferably includes: slurrying the sulfate solid waste with water to dissolve most of the solid material, and then adding anhydrous ethanol to the slurry solution. This invention increases the solubility of sulfate solid waste by adding anhydrous ethanol.

[0036] After obtaining the solution, the present invention adds the solution to a silica gel column.

[0037] The present invention preferably adds a spherical liquid dispenser above the silica gel column for subsequent addition of dissolving solution and various elution solutions.

[0038] In this invention, the particle size of the silica powder filled in the silica column is preferably 100-300 mesh, more preferably 150-250 mesh. In this invention, the diameter of the silica column is preferably 20-30 cm, more preferably 24-28 cm; the height is preferably 85-125 cm, more preferably 100-110 cm.

[0039] The assembly process of the silica gel column in this invention does not have special requirements; a well-known assembly process in the art can be used. In the embodiments of this invention, specifically: white silica gel powder with a particle size of 100-300 mesh is densely packed into a cylindrical acrylic glass container with a diameter of 20-30 cm and a height of 85-125 cm to form the main body of an acidic silica gel column. The lower end is protected by glass fiber filaments or a sand core to prevent silica gel powder from leaking out through the piston; the upper end is flattened with fine sand so that the upper end of the silica gel column is in a relatively flat state. In this invention, the top of the silica gel column is preferably ground, equipped with a spherical liquid dispenser with a volume of at least 1-1.5 L for storing the eluent. This ensures safe operation and facilitates timely addition of the eluent, while the natural gravity of the liquid ensures that the eluent flows out evenly.

[0040] In this invention, before adding the solution to the silica gel column, it is preferable to further include: eluting the silica gel column multiple times with anhydrous ethanol until there are no obvious air bubbles inside the silica gel column, and the silica gel presents a homogeneous phase system in the anhydrous ethanol. The purpose of using anhydrous ethanol to elute the silica gel column multiple times in this invention is to ensure that the silica gel column is completely wetted by ethanol.

[0041] This invention does not have specific requirements regarding the rate at which the dissolving solution is added to the silica gel column, as long as it does not disturb the fine sand above the column. Preferably, the dissolving solution is slowly added along the inner wall of the top of the silica gel column.

[0042] After adding the dissolving solution, a yellowish-brown band and a light green band will form in the silica gel column. The present invention uses anhydrous ethanol for the first elution, collects the yellowish-brown liquid flowing out, and obtains the chromium ion collection solution after the yellowish-brown band has completely precipitated.

[0043] This invention does not have any special requirements for the elution rate of the first elution step. In an embodiment of this invention, the elution rate is 1 L / h.

[0044] In this invention, the pH value of the chromium ion collecting solution is 5-6, and XRD analysis shows that it is an anhydrous ethanol solution of hydrated chromium sulfate Cr2(SO4)3·18H2O.

[0045] After obtaining the chromium ion collecting solution, the present invention preferably further includes mixing the chromium ion collecting solution with ammonia water to carry out a precipitation reaction, separating the solid and liquid to obtain chromium hydroxide precipitate. The present invention does not have special requirements for the solid-liquid separation method; any solid-liquid separation method well-known in the art can be used, such as filtration. After obtaining the chromium hydroxide precipitate, the present invention preferably washes the chromium hydroxide precipitate with deionized water until no sulfate ions and chloride ions (sulfate solid waste contains chloride ions) are present, then washes it with a small amount of anhydrous ethanol, and dries it; the purity can reach over 97%.

[0046] In this invention, the ethanol-containing wastewater obtained through solid-liquid separation is distilled off at atmospheric pressure to remove the ethanol solvent, which can be reused. After further simple negative pressure distillation to remove some water, the water is cooled and crystallized ammonium sulfate (NH4)2SO4 byproduct is precipitated.

[0047] After the yellowish-brown band has completely precipitated, the silica gel column is eluted a second time with anhydrous ethanol, and the outflowing light green liquid is collected. After the light green band has completely precipitated, a nickel ion collection solution is obtained.

[0048] In this invention, the pH value of the nickel ion collecting solution is 2-3, and XRD analysis shows that it is an anhydrous ethanol solution of hydrated nickel sulfate NiSO4·6H2O and NiSO4·7H2O.

[0049] After obtaining the nickel ion collecting solution, the present invention preferably further includes mixing the nickel ion collecting solution with ammonia water to carry out a precipitation reaction, separating the solid and liquid to obtain nickel hydroxide precipitate. The present invention does not have special requirements for the solid-liquid separation method; any solid-liquid separation method well-known in the art can be used, such as filtration. After obtaining the nickel hydroxide precipitate, the present invention preferably washes the nickel hydroxide precipitate with deionized water until the pH of the washing water is neutral and free of sulfate and chloride ions, then washes it with a small amount of anhydrous ethanol, and dries it; the purity can reach over 97%.

[0050] In this invention, the ethanol-containing wastewater obtained through solid-liquid separation is distilled off at atmospheric pressure to remove the ethanol solvent, which can be reused. After further simple negative pressure distillation to remove some water, the water is cooled and crystallized ammonium sulfate (NH4)2SO4 byproduct is precipitated.

[0051] After the light green band has completely precipitated, water is added to the silica gel column for a third elution to form a dark green band. The dark green liquid that flows out is collected to obtain a ferrous ion collection solution.

[0052] In this invention, the water is preferably deionized water; the pH value of the ferrous ion collecting solution is 2-3, and XRD analysis shows it to be an aqueous solution of hydrated ferrous sulfate FeSO4·7H2O.

[0053] After obtaining the ferrous ion collecting solution, the present invention preferably further includes mixing the ferrous ion collecting solution with oxalic acid to carry out a precipitation reaction, followed by solid-liquid separation to obtain ferrous oxalate precipitate. The present invention does not have special requirements for the solid-liquid separation method; any solid-liquid separation method well-known in the art can be used, such as filtration. After obtaining the ferrous oxalate precipitate, the present invention preferably washes the ferrous oxalate precipitate with deionized water until the pH value of the washing water is close to neutral and free of sulfate and chloride ions, then washes it with a small amount of anhydrous ethanol and dries it; the purity can reach over 97%.

[0054] In this invention, the ethanol-containing wastewater obtained through solid-liquid separation is distilled off at atmospheric pressure to remove the ethanol solvent, which can be reused. After further simple negative pressure distillation to remove some water, the water is cooled and crystallized ammonium sulfate (NH4)2SO4 byproduct is precipitated.

[0055] After the third elution is completed, a grayish-yellow solid remains between the silica gel and fine sand in the silica gel column. After testing, it was found to be manganese sulfate tetrahydrate. The amount of manganese sulfate present is extremely small and will not affect the separation effect of the silica gel column when it is reused. Therefore, no treatment is required.

[0056] The third elution step preferably includes a recovery wash of the used silica gel column. This recovery wash preferably includes: washing the used silica gel column with water until no sulfate ions are present, followed by repeated washing with anhydrous ethanol until the silica gel presents a homogeneous phase in anhydrous ethanol. Preferably, the present invention uses barium chloride solution for qualitative detection until no sulfate ions are present.

[0057] In this invention, the silica gel column after recovery washing can be recycled and reused. Preferably, the water and anhydrous ethanol waste liquid generated during recovery washing are collected, and the ethanol solvent is distilled off under normal pressure. The resulting anhydrous ethanol can be reused.

[0058] This invention uses column chromatography to separate sulfate solid waste, which can effectively separate and recover iron, chromium and nickel ions in titanium dioxide sulfate solid waste, filling the technological gap in the separation of these three metal ions.

[0059] Compared with traditional chemical separation methods, the method provided by this invention is not only simpler and faster with significant results, but also does not use or generate any harmful substances. The solutions used throughout the process are only water and anhydrous ethanol, making it green and environmentally friendly, with extremely low cost and easy to industrialize.

[0060] The separation and recovery method provided by this invention achieves high recovery rates of iron, chromium, and nickel, all exceeding 96%. Furthermore, after processing the collected liquid according to the corresponding methods, the resulting chromium hydroxide, nickel hydroxide, and ferrous oxalate have high purity, all exceeding 97%, and can be used as electrode materials for new energy batteries. This method offers high resource utilization and good economic benefits.

[0061] Furthermore, the eluents used in this invention can all be recycled and reused, and the silica gel column can also be reused, exhibiting good recyclability and economy.

[0062] The following detailed description of the method for efficiently separating and recovering iron, nickel, and chromium metal ions from sulfate solid waste provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0063] Example 1

[0064] The operation uses 10 kg of sulfate solid waste. The solid material composition includes the main component FeSO4·7H2O, small amounts of hydrated Cr2(SO4)3 and hydrated NiSO4, trace amounts of hydrated MnSO4, and other trace impurities.

[0065] (1) Weigh about 10 kg of sulfate solid waste, and slurry it with about 3-5 L of deionized water so that most of the solid material can be dissolved. Then add an equal volume of anhydrous ethanol to the slurry solution. The solution is dark green.

[0066] (2) Pretreatment of silica gel column: Use 100-mesh white silica gel powder to pack into the silica gel column, and wash with anhydrous ethanol several times until there are no obvious bubbles in the silica gel column and the silica gel presents a homogeneous phase system in anhydrous ethanol.

[0067] (3) Slowly add the silica gel column to the top of the silica gel fine sand, and then immediately add anhydrous ethanol eluent at a flow rate of 1L / h. Collect the short yellowish-brown band of anhydrous ethanol eluent for 15 minutes and check the pH of the solution to be 5-6.

[0068] (4) After the yellowish-brown band is completely separated, add anhydrous ethanol as the eluent from the spherical adder and slowly collect the effluent of the light green band. The light green band is relatively long, and the collection time is 51 min. The pH value of the solution is between 2 and 3.

[0069] (5) After the light green band is completely separated, add deionized water as the eluent from the spherical liquid dispenser and slowly collect the effluent of the dark green band. The dark green band is relatively long, and the collection time is 59 min. The pH value of the solution is between 2 and 3.

[0070] (6) Used silica gel columns can be washed with deionized water until no sulfate ions are present (qualitative detection is performed using barium chloride solution), and then repeatedly washed with anhydrous ethanol to form a homogeneous phase. They can then be reused multiple times.

[0071] (7) Adding ammonia solution to the collected yellowish-brown solution produces a greenish-yellow precipitate. Filter out the ethanol and aqueous solution, wash the precipitate with deionized water until no sulfate or chloride ions are present, wash again with a small amount of anhydrous ethanol, dry, and collect the product. XRD analysis shows it to be chromium hydroxide Cr(OH)3 (see...). Figure 1 XRF analysis showed that its purity reached 97.1%.

[0072] (8) Ammonia solution was added to the collected light green solution, producing a green precipitate. The ethanol and aqueous solution were filtered out, and the precipitate was washed with deionized water until the pH of the washing water was neutral and free of sulfate and chloride ions. After washing with a small amount of anhydrous ethanol, the product was dried and the green product was collected. XRD analysis showed that it was nickel hydroxide Ni(OH)2 (see...). Figure 3 XRF analysis showed that its purity reached 97.4%.

[0073] (9) Add oxalic acid aqueous solution to the collected dark green solution to produce a yellow precipitate. Filter out the aqueous solution and wash the FeC2O4 precipitate with deionized water until the pH of the washing water is close to neutral and free of sulfate and chloride ions. Wash with a small amount of anhydrous ethanol, dry, collect, and XRD analysis shows it to be a FeC2O4 microcrystalline product (see...). Figure 2 XRF analysis showed that its purity reached 97.3%.

[0074] (10) The ethanol-containing wastewater collected above is distilled off by simple atmospheric pressure to remove the ethanol solvent, which can be reused; after further simple negative pressure distillation to remove some water, the ammonium sulfate (NH4)2SO4 byproduct is precipitated after cooling. All the wastewater is collected in the wastewater storage tank and can be discharged into the environmental protection pipeline network as wastewater.

[0075] Before separation, the elemental composition was 1.62 g of Fe, 0.096 g of Ni, and 0.256 g of Cr. After separation, the elemental composition was 1.57 g of Fe (96.91% recovery), 0.0923 g of Ni (96.12% recovery), and 0.249 g of Cr (97.52% recovery). Before separation, the elemental composition was obtained by dissolving it in water and anhydrous ethanol and then performing ICP analysis, converting the data into mass values. After separation, the mass of the precipitate was directly weighed, and the composition was calculated based on the molar ratio of each element in the precipitate (the same applies below).

[0076] The silica gel used in Example 1 was 100 mesh. As can be seen from the above examples, the column chromatography method for separating the three ions has the advantages of high precipitate concentration and excellent utilization value. On the other hand, the method does not use or generate any waste that is harmful to the environment. It not only achieves the recycling of the eluent, but also obtains the byproduct ammonium sulfate, which has good usability and economy.

[0077] Example 2

[0078] The operation uses 10 kg of sulfate solid waste. The solid material composition includes the main component FeSO4·7H2O, small amounts of hydrated Cr2(SO4)3 and hydrated NiSO4, trace amounts of hydrated MnSO4, and other trace impurities.

[0079] (1) Weigh about 10 kg of sulfate solid waste, and slurry it with about 3-5 L of deionized water so that most of the solid material can be dissolved. Then add an equal volume of anhydrous ethanol to the slurry solution. The solution is dark green.

[0080] (2) Pretreatment of silica gel column: Use 200-mesh white silica gel powder to pack into the silica gel column, and wash with anhydrous ethanol several times until there are no obvious bubbles in the silica gel column and the silica gel presents a homogeneous phase system in anhydrous ethanol.

[0081] (3) Slowly add the silica gel column to the top of the silica gel fine sand, and then immediately add anhydrous ethanol eluent at a flow rate of 1L / h. Collect the short yellowish-brown band of anhydrous ethanol eluent for 7 minutes and check the pH of the solution to be 5-6.

[0082] (4) After the yellowish-brown band is completely separated, add anhydrous ethanol as the eluent from the spherical adder and slowly collect the effluent of the light green band. The light green band is relatively long, and the collection time is 40 minutes. The pH value of the solution is between 2 and 3.

[0083] (5) After the light green band has completely separated, add deionized water as the eluent from the spherical additive container, and slowly collect the effluent of the dark green band. This dark green band is relatively long, and the collection time is 43 minutes. The pH value of the solution is measured to be between 2 and 3.

[0084] (6) Used silica gel columns can be washed with deionized water until no sulfate ions are present (qualitative detection is performed using barium chloride solution), and then repeatedly washed with anhydrous ethanol to form a homogeneous phase. They can then be reused multiple times.

[0085] (7) Add ammonia solution to the collected yellowish-brown solution to produce a greenish-yellow precipitate. The precipitate is identified as Cr(OH)3 by XRD. Filter out the ethanol and aqueous solution, wash the Cr(OH)3 precipitate with deionized water until there are no sulfate ions and chloride ions. Wash it with a small amount of anhydrous ethanol and dry it. XRF test shows that its purity can reach 97.5%.

[0086] (8) Add ammonia solution to the collected light green solution to produce a green precipitate, which is identified as Ni(OH)2 by XRD. Filter out the ethanol and aqueous solution, wash the Ni(OH)2 precipitate with deionized water until the pH of the washing water is neutral and there are no sulfate or chloride ions. Wash with a small amount of anhydrous ethanol, dry, and collect the green nickel hydroxide Ni(OH)2 product. XRF test shows that its purity can reach 97.3%.

[0087] (9) Add oxalic acid aqueous solution to the collected dark green solution to produce a yellow precipitate, which is identified as FeC2O4 by XRD. Filter out the aqueous solution and wash the FeC2O4 precipitate with deionized water until the pH of the washing water is close to neutral and there are no sulfate ions and chloride ions. Then wash with a small amount of anhydrous ethanol, dry, and collect the yellow ferrous oxalate FeC2O4 microcrystal product. XRF test shows that its purity can reach 97.5%.

[0088] (10) The ethanol-containing wastewater collected above is distilled off by simple atmospheric pressure to remove the ethanol solvent, which can be reused; after further simple negative pressure distillation to remove some water, the ammonium sulfate (NH4)2SO4 byproduct is precipitated after cooling. All the wastewater is collected in the wastewater storage tank and can be discharged into the environmental protection pipeline network as wastewater.

[0089] Before separation, the amount of Fe was 1.82 g, Ni was 0.062 g, and Cr was 0.239 g; after separation, the amount of Fe was 1.79 g (recovery rate 98.31%), Ni was 0.06 g (recovery rate 96.78%), and Cr was 0.231 g (recovery rate 96.65%).

[0090] Compared to Example 1, Example 2 changed the silica gel mesh size to 200 mesh, which reduced the collection time for each ion band while maintaining excellent precipitation concentration. As can be seen from the above examples, column chromatography for separating three ions yields high precipitation concentrations with excellent utilization value. Furthermore, the method does not use or generate any environmentally harmful waste, achieving not only the recycling of the eluent but also the production of the byproduct ammonium sulfate, demonstrating good usability and economy.

[0091] Example 3

[0092] The operation uses 10 kg of sulfate solid waste. The solid material composition includes the main component FeSO4·7H2O, small amounts of hydrated Cr2(SO4)3 and hydrated NiSO4, trace amounts of hydrated MnSO4, and other trace impurities.

[0093] (1) Weigh about 10 kg of sulfate solid waste, and slurry it with about 3-5 L of deionized water so that most of the solid material can be dissolved. Then add an equal volume of anhydrous ethanol to the slurry solution. The solution is dark green.

[0094] (2) Pretreatment of silica gel column: Use 300-mesh white silica gel powder to pack into the silica gel column, and wash with anhydrous ethanol several times until there are no obvious bubbles in the silica gel column and the silica gel presents a homogeneous phase system in anhydrous ethanol.

[0095] (3) Slowly add the silica gel column to the top of the silica gel fine sand, and then immediately add anhydrous ethanol eluent at a flow rate of 1L / h. Collect the short yellowish-brown band of anhydrous ethanol eluent for 4 minutes and check the pH of the solution to be 5-6.

[0096] (4) After the yellowish-brown band is completely separated, add anhydrous ethanol as the eluent from the spherical adder and slowly collect the effluent of the light green band. The light green band is relatively long, and the collection time is 31 min. The pH value of the solution is between 2 and 3.

[0097] (5) After the light green band is completely separated, add deionized water as the eluent from the spherical liquid dispenser and slowly collect the effluent of the dark green band. The dark green band is relatively long, and the collection time is 40 minutes. The pH value of the solution is between 2 and 3.

[0098] (6) Used silica gel columns can be washed with deionized water until no sulfate ions are present (qualitative detection is performed using barium chloride solution), and then repeatedly washed with anhydrous ethanol to form a homogeneous phase. They can then be reused multiple times.

[0099] (7) Add ammonia solution to the collected yellowish-brown solution to produce a greenish-yellow precipitate. The precipitate is identified as Cr(OH)3 by XRD. Filter out the ethanol and aqueous solution, wash the Cr(OH)3 precipitate with deionized water until no sulfate and chloride ions are left, wash with a small amount of anhydrous ethanol, dry, and collect the Cr(OH)3 product. XRF test shows that its purity can reach 97.3%.

[0100] (8) Add ammonia solution to the collected light green solution to produce a green precipitate, which is identified as Ni(OH)2 by XRD. Filter out the ethanol and aqueous solution, wash the Ni(OH)2 precipitate with deionized water until the pH of the washing water is neutral and there are no sulfate ions and chloride ions. Wash with a small amount of anhydrous ethanol, dry, and collect the green nickel hydroxide Ni(OH)2 product. XRF test shows that its purity can reach 97.6%.

[0101] (9) Add oxalic acid aqueous solution to the collected dark green solution to produce a yellow precipitate, which is identified as FeC2O4 by XRD. Filter out the aqueous solution and wash the FeC2O4 precipitate with deionized water until the pH of the washing water is close to neutral and there are no sulfate ions and chloride ions. Then wash with a small amount of anhydrous ethanol, dry, and collect the yellow ferrous oxalate FeC2O4 microcrystal product. XRF test shows that its purity can reach 97.7%.

[0102] (10) The ethanol-containing wastewater collected above is distilled off by simple atmospheric pressure to remove the ethanol solvent, which can be reused; after further simple negative pressure distillation to remove some water, the ammonium sulfate (NH4)2SO4 byproduct is precipitated after cooling. All the wastewater is collected in the wastewater storage tank and can be discharged into the environmental protection pipeline network as wastewater.

[0103] Before separation, the amount of Fe was 2.36 g, Ni was 0.126 g, and Cr was 0.463 g; after separation, the amount of Fe was 2.31 g with a recovery rate of 97.89%, Ni was 0.121 g with a recovery rate of 96.11%, and Cr was 0.451 g with a recovery rate of 97.4%.

[0104] The XRF data of the Cr(OH)3 product, Ni(OH)2 product and FeC2O4 microcrystalline product obtained in Example 3 are shown in Tables 1-3.

[0105] Table 1. XRF data of Cr(OH)3 products obtained in Example 3

[0106] compound Quality percentage (%) element Quality percentage (%) <![CDATA[Cr2O3]]> 97.28 Cr 66.63 MgO 1.22 Mg 0.74 CaO 0.585 Ca 0.4188 <![CDATA[SO3]]> 0.188 <![CDATA[S x ]]> 0.0753

[0107] Table 2. XRF data of Ni(OH)2 obtained in Example 3

[0108] compound Quality percentage (%) element Quality percentage (%) NiO 97.61 Ni 76.79 <![CDATA[Al2O3]]> 1.40 Al 0.741 <![CDATA[SiO2]]> 0.11 Si 0.051 MnO 0.07 Mn 0.086

[0109] Table 3. XRF data of FeC2O4 obtained in Example 3

[0110] compound Quality percentage (%) element Quality percentage (%) <![CDATA[Fe2O3]]> 97.74 Fe 68.36 MnO 1.40 Mn 1.085 ZnO 0.158 Zn 0.233 CaO 0.099 Ca 0.068

[0111] As can be seen from Tables 1-3, the column chromatography method for separating the three ions has several advantages. First, it achieves an ideal ion recovery rate and yields high precipitate concentrations, all ≥97%, which have excellent utilization value. Second, the method does not use or generate any environmentally harmful waste, achieving not only the recycling of the eluent but also the production of ammonium sulfate as a byproduct, demonstrating good usability and economic efficiency.

[0112] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for efficiently separating and recovering iron, nickel, and chromium metal ions from sulfate solid waste, comprising the steps of: Mixing sulfate solid waste, water and anhydrous ethanol to obtain a dissolving solution; the sulfate solid waste comprises ferrous sulfate, chromium sulfate and nickel sulfate; Adding the dissolving solution into a silica gel column, forming a yellowish brown band and a light green band in the silica gel column, then performing first elution with anhydrous ethanol, collecting the yellowish brown liquid flowing out, and obtaining a chromium ion collection solution after the yellowish brown band is completely precipitated; Performing second elution on the silica gel column with anhydrous ethanol, collecting the light green liquid flowing out, and obtaining a nickel ion collection solution after the light green band is completely precipitated; Adding water into the silica gel column to perform third elution, forming a dark green band, collecting the dark green liquid flowing out, and obtaining a ferrous ion collection solution.

2. The method of claim 1, wherein, The sulfate solid waste is tailing solid waste generated after preparing titanium dioxide by a sulfuric acid method.

3. The method of claim 1, wherein, The particle size of the silica gel powder filled in the silica gel column is 100-300 mesh.

4. The method according to claim 2 or 3, characterized in that, The diameter of the silica gel column is 20-30 cm, and the height is 85-125 cm.

5. The method of claim 1, wherein, The volume ratio of water to anhydrous ethanol in the dissolving solution is 1:

1.

6. The method of claim 1, wherein, Before adding the dissolving solution into the silica gel column, further comprising: performing multiple elutions on the silica gel column with anhydrous ethanol until there is no obvious bubble in the silica gel column, and the silica gel presents a uniform phase system in anhydrous ethanol.

7. The method of claim 1, wherein, After obtaining the chromium ion collection solution, further comprising: mixing the chromium ion collection solution with ammonia water to perform a precipitation reaction, and performing solid-liquid separation to obtain a chromium hydroxide precipitate.

8. The method of claim 1, wherein, After obtaining the nickel ion collection solution, further comprising: mixing the nickel ion collection solution with ammonia water to perform a precipitation reaction, and performing solid-liquid separation to obtain a nickel hydroxide precipitate.

9. The method of claim 1, wherein, After obtaining the ferrous ion collection solution, further comprising: mixing the ferrous ion collection solution with oxalic acid to perform a precipitation reaction, and performing solid-liquid separation to obtain a ferrous oxalate precipitate.

10. The method of claim 1, wherein, After the third elution, further comprising: performing recovery washing on the used silica gel column, wherein the recovery washing comprises: washing the used silica gel column with water until there is no sulfate ion, and repeatedly washing with anhydrous ethanol until the silica gel presents a uniform phase in anhydrous ethanol.

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