Method for preparing nanoscale iron phosphate and efficiently extracting copper and cobalt from sulfuric-acid residues

Abstract

The invention discloses a method for preparing nanoscale iron phosphate and efficiently extracting copper and cobalt by using sulfuric-acid slag, which comprises the following steps of: performing low-temperature reduction roasting on the sulfuric-acid slag to obtain roasted slag; leaching the roasting slag by using low-concentration sulfuric acid to obtain a first filtrate and a first filter residue containing iron, copper, cobalt and other impurities; adding an oxidizing agent into the first filtrate, then adding a certain amount of phosphorus source, adjusting the pH of the filtrate to precipitate iron ions, and filtering to obtain second filter residues and second filtrate; washing the second filter residue with water to obtain a nanoscale iron phosphate product, and recycling copper and cobalt from the second filtrate. The method is low in production cost, high in product value and high in resource utilization rate, the granularity of the obtained iron phosphate meets the nanoscale requirement, the purity of the obtained iron phosphate meets the battery grade standard, meanwhile, copper and cobalt can be efficiently recycled, the industrial production requirement is met, and efficient value-added utilization of industrial by-products is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy batteries, and specifically relates to a method for preparing nano-scale iron phosphate and efficiently extracting copper and cobalt by using sulfuric acid residue. Background Art

[0002] In modern industry, sulfuric acid residue is a by-product generated during the preparation of sulfuric acid using pyrite. Its main component is iron oxide, and it usually contains valuable metals such as copper and cobalt, as well as heavy metal components such as zinc, lead, and arsenic. Approximately 0.8 - 1.1 tons of sulfuric acid residue are generated per ton of sulfuric acid produced, and the annual new output in China is about 20 million tons. The iron grade in sulfuric acid residue is generally 30% - 60%. Sulfuric acid residue with a high iron grade (>60%) and low impurities can be directly used as an iron-making raw material in the traditional metallurgical field, while relatively low-grade sulfuric acid residue faces many challenges in its development and utilization, especially in high-value utilization due to its complex composition and structure. Therefore, developing a high-efficiency, low-cost, and high-value-added sulfuric acid residue treatment technology has important practical significance.

[0003] Iron phosphate is a key precursor for preparing lithium iron phosphate and has attracted much attention due to its good electrochemical performance, excellent safety performance, etc. Nano-scale iron phosphate has an even higher specific surface area and reaction sites and is favored by fields with extremely high requirements for battery performance, such as electric vehicles, high-end energy storage systems, and drones. However, due to strict requirements for production conditions such as preparation processes and production equipment, the production cost is relatively high. Sulfuric acid residue is a cheap iron resource. If it can be used as the iron source for nano-scale iron phosphate, it can not only reduce the production cost but also achieve high-value utilization of sulfuric acid residue. Previous studies have used sulfuric acid residue as the iron source to directly prepare iron phosphate by phosphoric acid leaching, but the amount of phosphoric acid used is large, the cost is high, and the silicon component in low-iron-grade sulfuric acid residue cannot be dissolved by phosphoric acid and finally remains in the solid product of iron phosphate, reducing its purity. After impurity removal with hydrofluoric acid, the purity meets the battery-grade iron phosphate standard, but the process is complex, and the resulting product is micron-scale.

[0004] Therefore, developing a method for preparing nano-scale iron phosphate at low cost and extracting copper and cobalt is of great significance for environmental protection, resource recycling, and the sustainable development of the chemical and new energy industries in China. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for preparing nano-scale iron phosphate and efficiently extracting copper and cobalt from sulfuric acid slag. By roasting and reducing iron at low temperature and then leaching with low-concentration sulfuric acid, copper and cobalt can be effectively separated while preparing nano-scale iron phosphate from the leaching solution by precipitation method. It is not limited by the iron grade in the sulfuric acid slag, and high-value products can be produced at low cost, realizing the efficient value-added utilization of sulfuric acid slag. This method has low production cost, high product value and high resource utilization rate. The particle size of the obtained iron phosphate meets the nano-scale requirements and the purity meets the battery-grade standard. At the same time, copper and cobalt can be efficiently recovered, meeting the requirements of industrial production.

[0006] To solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0007] A method for preparing nano-scale iron phosphate and efficiently extracting copper and cobalt from sulfuric acid slag. In this method, the sulfuric acid slag is subjected to roasting and reduction treatment and then leached with sulfuric acid to obtain a first filtrate and a first filter residue. An oxidant and a phosphorus source are added to the first leaching solution and the pH is adjusted for precipitation reaction, and then solid-liquid separation is carried out to obtain a second filtrate and a second filter residue. The second filter residue is washed, dried and calcined to obtain nano-scale iron phosphate. The second filtrate is used for recovering copper and cobalt. The specific steps may be:

[0008] Step 1: Put the sulfuric acid slag into a roasting furnace for low-temperature reduction roasting to obtain reduced roasting slag;

[0009] Step 2: Leach the reduced roasting slag in a low-concentration sulfuric acid solution. After controlling the temperature and stirring, carry out the first solid-liquid separation on the leached slurry to obtain a first filtrate and a first filter residue;

[0010] Step 3: Add a certain amount of oxidant to the first filtrate, then add a certain amount of phosphorus source, and then use sodium hydroxide to adjust the pH of the filtrate to low acid, and carry out the second solid-liquid separation to obtain a second filtrate and a second filter residue;

[0011] Step 4: Wash, dry and calcine the second filter residue to obtain an iron phosphate product;

[0012] Step 5: The second filtrate is used for recovering copper and cobalt.

[0013] In a preferred scheme, in Step 1, the particle size of the sulfuric acid slag is such that the proportion of -200 mesh is 60% to 80%, and the reduction roasting conditions are: temperature is 500 to 700 °C, and time is 10 - 50 min.

[0014] In a preferred scheme, in Step 1, the reducing agent used for reduction roasting is at least one of carbon monoxide, pulverized coal, and hydrogen.

[0015] In a preferred embodiment, in step two, the molar concentration of the sulfuric acid solution used in the leaching process is 1 - 3 mol / L, and the liquid-solid ratio in the leaching process is controlled to be 6 - 12 ml / g; the temperature is 30 - 90 °C, and the time is 3 - 4 h.

[0016] In a preferred embodiment, in step three, the oxidant can be at least one of hydrogen peroxide, air, and oxygen; the phosphorus source includes at least one of phosphoric acid, polyphosphoric acid, and ammonium dihydrogen phosphate; the molar ratio of divalent iron to the oxidant in the first filtrate is 1:1; the molar ratio of iron element in the first filtrate to phosphorus in the phosphorus source is 0.9 - 1.1:1.

[0017] In a preferred embodiment, in step three, the concentration of the sodium hydroxide is 0.1 - 0.5 mol / L, and the pH of the filtrate is adjusted to 1.7 - 2.1.

[0018] In a preferred embodiment, in step four, the calcination temperature of the second filter residue is 500 - 700 °C, and the calcination time is 1 - 2 h.

[0019] In a preferred embodiment, in step five, copper and cobalt are recovered from the second filtrate by fractional precipitation to obtain a copper precipitation residue and a cobalt precipitation residue. First, the second filtrate is mixed with a sodium thiosulfate solution and the pH is adjusted with a sodium carbonate solution for copper precipitation reaction, then solid-liquid separation is carried out to obtain a copper precipitation residue and a cobalt-containing solution. Then, the cobalt-containing solution is further adjusted with a sodium carbonate solution for cobalt precipitation reaction, and solid-liquid separation is carried out to obtain a cobalt precipitation residue.

[0020] In a preferred embodiment, in the copper precipitation reaction, the mass concentration of the sodium thiosulfate solution is 0.2 - 0.4%, and the molar ratio of sodium thiosulfate to copper ions in the solution is 0.7 - 1.1:1. The copper precipitation reaction conditions are: the pH is adjusted to 3.0 - 4.0, the temperature is 70 - 90 °C, and the reaction time is 2 - 4 h.

[0021] In a preferred embodiment, in the cobalt precipitation reaction, the mass fraction of the sodium carbonate solution is 1 - 3%. The cobalt precipitation reaction conditions are: the pH is adjusted to 7.5 - 9.0, and the reaction is stirred at room temperature for 1 - 4 h.

[0022] Based on the market situation that the price of industrial concentrated phosphoric acid is about 20 times higher than that of industrial concentrated sulfuric acid, the present invention ingeniously utilizes the principle that the solubility of hematite in sulfuric acid is extremely low while the solubility is greatly increased after magnetization reduction. During the reduction roasting process, the hematite in the sulfuric acid residue is reduced to magnetite, and in the sulfuric acid leaching process, the components of iron, copper, and cobalt can be efficiently dissolved with low-concentration sulfuric acid; an oxidant is added to the leaching solution to convert all iron ions into ferric iron ions, and then a phosphorus source is added and the pH is adjusted to cause a selective precipitation reaction of ferric iron ions to form insoluble iron phosphate dihydrate, and the conversion rate is relatively high, while the valuable components of copper and cobalt and other impurities remain in the solution; on the other hand, the reduction roasting also helps the conversion of copper and cobalt in the sulfuric acid residue into components soluble in sulfuric acid, improving the leaching rate of copper and cobalt in the sulfuric acid leaching process. The copper-cobalt-containing filtrate after separating iron phosphate can be directly used for recovering copper and cobalt.

[0023] After adopting the above technical solutions, the present invention has the following beneficial effects compared with the prior art.

[0024] (1) The present invention uses sulfuric acid residue as the iron source and prepares nano-scale iron phosphate products through the processes of reduction roasting - sulfuric acid leaching - oxidation precipitation - roasting dehydration. Compared with the traditional iron phosphate production process, it has the advantages of wide raw material sources, low production costs, and high product value, realizing the efficient value-added utilization of industrial by-products.

[0025] (2) Based on the market situation, sulfuric acid with a market price 20 times lower than that of phosphoric acid is selected during the leaching process. The present invention ingeniously utilizes the phase transformation law of hematite in a reducing atmosphere and the synchronous reduction law of copper and cobalt, and uses low-temperature reduction roasting to convert it into magnetite with extremely high solubility in sulfuric acid. The efficient dissolution of iron elements can be achieved through low-concentration sulfuric acid leaching, greatly reducing the production cost of preparing iron phosphate from sulfuric acid residue.

[0026] (3) By utilizing the solution chemical differences of iron, copper, and cobalt, the present invention can efficiently produce nano-scale iron phosphate products through fractional precipitation, and at the same time, the filtrate can be directly used to separate and recover the precious metal components of copper, cobalt, and rare metals, greatly improving the high-value utilization rate of sulfuric acid residue recovery.

[0027] The following further describes the specific embodiments of the present invention in detail with reference to the accompanying drawings. Description of the Drawings

[0028] As a part of this application, the accompanying drawings are used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the accompanying drawings in the following description are only some embodiments. For those of ordinary skill in the art, other drawings can be obtained based on the provided drawings without creative efforts. In the drawings:

[0029] Figure 1It is a schematic diagram of the technological process of the present invention.

[0030] Figure 2 It is the XRD pattern of the sulfuric acid residue used in Example 1 and the roasted residue obtained after reduction roasting.

[0031] Figure 3 It is the XRD pattern of the iron phosphate prepared in Example 1.

[0032] Figure 4 It is the SEM image of the iron phosphate prepared in Example 1.

[0033] It should be noted that these drawings and textual descriptions are not intended to limit the scope of the concept of the present invention in any way, but to illustrate the concept of the present invention to those skilled in the art by referring to specific embodiments. Detailed Embodiments

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0035] Example 1

[0036] In this embodiment, sulfuric acid residue from a certain sulfuric acid plant is selected, with an iron grade of 56.36%, copper and cobalt grades both of 0.16%, and the remaining main components are shown in Table 1.

[0037] Table 1 Main Chemical Compositions of Sulfuric Acid Residue / %

[0038]

[0039] Process Reference Figure 1 , and using this sulfuric acid residue as the raw material, a gas-based reduction roasting - sulfuric acid leaching experiment is carried out. The roasting reduction temperature is controlled at 500 °C, the roasting time is 50 min, and the proportion of the reducing agent CO in the (CO + N2) mixed gas is 20%, to obtain the reduced roasted residue (XRD pattern shown in Figure 2 ). The reduced roasted residue is subjected to sulfuric acid leaching, with the sulfuric acid concentration controlled at 2 mol / L, the liquid-solid ratio 10 ml / g, the leaching temperature 80 °C, and the leaching time 3 h. After solid-liquid separation, the first filter residue can be used as the raw material for the cementitious material, and the leaching rates of iron, copper, and cobalt in the first filtrate are 97.39%, 76.17%, and 71.64% respectively, and the main chemical compositions are shown in Table 2.

[0040] Table 2 Chemical Compositions of the First Filtrate / ppm

[0041]

[0042] (a), (b): Unit is mol / L

[0043] Hydrogen peroxide was added to the first filtrate in a molar ratio of 1:1 with ferrous iron, and stirred at room temperature for 10 min to completely oxidize ferrous iron to ferric iron. Stirring was continued, and phosphoric acid was added in a molar ratio of 1:1 with the total iron element. The pH of the first filtrate was adjusted to 1.85 using a 0.25 mol / L sodium hydroxide solution, followed by solid-liquid separation to obtain a second filtrate and a crude product of iron phosphate dihydrate. The crude product was washed with water to obtain purified iron phosphate dihydrate, which was calcined at 600 °C for 1 h to obtain an iron phosphate product. Figure 3 (Its XRD pattern) shows spheroids with an average particle size of 20-30 nm. Figure 4 (Its SEM image) shows that the comprehensive recovery rate of iron is 90.23%. The chemical composition comparison of the crude product, purified product, and standard battery-grade iron phosphate (HG / T 4701-2021) is shown in Table 3.

[0044] Table 3 Total elemental analysis of iron phosphate / %

[0045]

[0046] The second filtrate was heated to 90 °C in a water bath, and the pH was adjusted to 4.0 using a 1% sodium carbonate solution by mass. Stirring was continued, and a 0.2% sodium thiosulfate solution by mass was slowly added thereto. The amount of sodium thiosulfate used was in a molar ratio of 1:1 with the copper ions in the solution, and the reaction time was 3 h. Copper slag and cobalt-containing solution were obtained by filtration, and the comprehensive recovery rate of copper was 71.73%.

[0047] A 2% sodium carbonate solution by mass was added to the cobalt-containing solution as a precipitant, the pH of the solution was adjusted to 8, and after stirring and reacting at room temperature for 4 h, solid-liquid separation was carried out to obtain cobalt slag, and the comprehensive recovery rate of cobalt was 70.02%.

[0048] Example 2

[0049] In this example, the sulfuric acid slag from a certain sulfuric acid plant in the previous example was still selected, with an iron grade of 56.36%, copper and cobalt grades both of 0.16%, and the remaining main components are shown in Table 1.

[0050] Using this sulfuric acid slag as raw material, a coal-based reduction roasting-sulfuric acid leaching test was carried out. The roasting reduction temperature was controlled at 600 °C, the roasting time was 20 min, and the mass ratio of the reducing agent pulverized coal to the sulfuric acid slag was 6%. The reduced roasted slag was obtained. The reduced roasted slag was subjected to sulfuric acid leaching, with the sulfuric acid concentration controlled at 3 mol / L, the liquid-solid ratio at 8 ml / g, the leaching temperature at 80 °C, and the leaching time at 3 h. After solid-liquid separation, the leaching rates of iron, copper, and cobalt in the first filtrate were 95.36%, 72.37%, and 70.58% respectively.

[0051] Take a certain volume of the first filtrate and stir it in the air at room temperature for 60 min to oxidize all divalent iron to trivalent iron. Keep stirring, add phosphoric acid in a molar ratio of 1:1 to the total iron element, and adjust the pH of the first filtrate to 1.9 with a 0.1 mol / L sodium hydroxide solution. Then perform solid-liquid separation to obtain the second filtrate and the crude product of iron phosphate dihydrate. After washing with water, the purified iron phosphate dihydrate is obtained and calcined at 700 °C for 1 h to obtain the iron phosphate product, and the comprehensive recovery rate of iron is 90.53%. The chemical composition of the purified product is shown in Table 4.

[0052] Table 4 Total element analysis of iron phosphate / %

[0053]

[0054] Heat the second filtrate in a water bath to 90 °C, adjust the pH to 4.0 with a 1% sodium carbonate solution by mass fraction, keep stirring, and slowly add a 0.2% sodium thiosulfate solution by mass concentration. The dosage of sodium thiosulfate is in a molar ratio of 1:1 to the copper ions in the solution, and the reaction time is 3 h. Filter to obtain the copper-precipitated slag and the cobalt-containing solution, and the comprehensive recovery rate of copper is 70.69%.

[0055] Add a 2% sodium carbonate solution by mass fraction to the cobalt-containing solution as a precipitant, adjust the pH of the solution to 8, stir and react at room temperature for 4 h, and then perform solid-liquid separation to obtain the cobalt-precipitated slag, and the comprehensive recovery rate of cobalt is 69.80%.

[0056] Example 3

[0057] In this example, the sulfuric acid residue from a certain sulfuric acid plant is selected, with an iron grade of 52.47%, copper and cobalt grades of 0.33% and 0.34% respectively, and the main components of the rest are shown in Table 5.

[0058] Table 5 Main chemical components of sulfuric acid residue / %

[0059]

[0060] Using this sulfuric acid residue as the raw material, a gas-based reduction roasting-sulfuric acid leaching experiment is carried out. Control the roasting reduction temperature at 700 °C, the roasting time at 10 min, and the proportion of the reducing agent H2 in the (H2 + N2) mixed gas at 20% to obtain the reduced roasting slag. Perform sulfuric acid leaching on the reduced roasting slag, control the sulfuric acid concentration at 1 mol / L, the liquid-solid ratio at 12 ml / g, the leaching temperature at 90 °C, and the leaching time at 4 h. After solid-liquid separation, the first filter residue can be used as the raw material for the cementitious material, and the leaching rates of iron, copper, and cobalt in the first filtrate are 95.83%, 81.47%, and 65.38% respectively.

[0061] Take a certain volume of the first filtrate, stir at room temperature for 20 min and introduce O₂ into it to oxidize all divalent iron to trivalent iron. Keep stirring, add phosphoric acid in a molar ratio of 1:1 to the total iron element, adjust the pH of the first filtrate to 1.9 with a 0.5 mol / L sodium hydroxide solution, perform solid-liquid separation to obtain the second filtrate and the crude product of iron phosphate dihydrate, wash it with water to get the purified iron phosphate dihydrate, calcine it at 500 °C for 2 h to obtain the iron phosphate product, and the comprehensive recovery rate of iron is 92.36%. The chemical composition of the purified product is shown in Table 6.

[0062] Table 6 Total element analysis of iron phosphate / %

[0063]

[0064] Heat the second filtrate in a water bath to 90 °C, adjust the pH to 4.0 with a 1% sodium carbonate solution by mass, keep stirring, and slowly add a 0.2% sodium thiosulfate solution by mass concentration to it. The dosage of sodium thiosulfate is in a molar ratio of 1:1 to the copper ions in the solution, and the reaction time is 3 h. Filter to obtain the copper-precipitated slag and the cobalt-containing solution, and the comprehensive recovery rate of copper is 78.54%.

[0065] Add a 2% sodium carbonate solution by mass to the cobalt-containing solution as a precipitant, adjust the solution pH to 8, stir and react at room temperature for 4 h, then perform solid-liquid separation to obtain the cobalt-precipitated slag, and the comprehensive recovery rate of cobalt is 65.03%.

[0066] Example 4

[0067] In this example, the sulfuric acid residue in Example 2 is still selected as the raw material to carry out the reduction roasting-sulfuric acid leaching-precipitation test. Control the roasting reduction temperature at 600 °C, the roasting time at 20 min, and the proportion of the reducing agent CO in the (CO + N₂) mixed gas at 20% to obtain the reduction roasted slag. Perform sulfuric acid leaching on the reduction roasted slag, control the sulfuric acid concentration at 2 mol / L, the liquid-solid ratio at 6 ml / g, the leaching temperature at 30 °C, and the leaching time at 4 h, then perform solid-liquid separation. The leaching rates of iron, copper, and cobalt in the first filtrate are 89.45%, 65.58%, and 68.26% respectively.

[0068] Take a certain volume of the first filtrate, add hydrogen peroxide in a molar ratio of 1:1 to the divalent iron in it to oxidize all divalent iron to trivalent iron. Keep stirring, add polyphosphoric acid in an Fe:P element molar ratio of 0.9:1, adjust the pH of the first filtrate to 1.7 with a 0.25 mol / L sodium hydroxide solution, perform solid-liquid separation to obtain the second filtrate and the crude product of iron phosphate dihydrate, wash it with water to get the purified iron phosphate dihydrate, calcine it at 600 °C for 1 h to obtain the iron phosphate product, and the comprehensive recovery rate of iron is 85.41%.

[0069] The second filtrate was heated in a water bath to 90 °C, and the pH was adjusted to 4.0 with a 1% sodium carbonate solution by mass. Stirring was continued, and a 0.2% sodium thiosulfate solution by mass was slowly added thereto. The amount of sodium thiosulfate used was in a molar ratio of 1:1 to the copper ions in the solution, and the reaction time was 3 h. The copper precipitate and the cobalt-containing solution were obtained by filtration, and the comprehensive copper recovery rate was 62.38%.

[0070] A 2% sodium carbonate solution by mass was added to the cobalt-containing solution as a precipitant, the pH of the solution was adjusted to 8, and after stirring and reacting at room temperature for 4 h, solid-liquid separation was carried out to obtain the cobalt precipitate, and the comprehensive cobalt recovery rate was 63.16%.

[0071] Example 5

[0072] In this example, a certain volume of the first filtrate in Example 4 was taken, and hydrogen peroxide was added in a molar ratio of 1:1 to the divalent iron therein to oxidize all the divalent iron to trivalent iron. Stirring was continued, and sodium dihydrogen phosphate was added in a molar ratio of Fe:P element of 1:1.1. The pH of the first filtrate was adjusted to 2.1 with a 0.25 mol / L sodium hydroxide solution, and solid-liquid separation was carried out to obtain the second filtrate and the crude product of iron dihydrate phosphate. After washing with water, the purified iron dihydrate phosphate was obtained, and it was calcined at 600 °C for 1 h to obtain the iron phosphate product, and the comprehensive iron recovery rate was 87.32%.

[0073] The second filtrate was heated in a water bath to 90 °C, and the pH was adjusted to 4.0 with a 1% sodium carbonate solution by mass. Stirring was continued, and a 0.2% sodium thiosulfate solution by mass was slowly added thereto. The amount of sodium thiosulfate used was in a molar ratio of 1:1 to the copper ions in the solution, and the reaction time was 3 h. The copper precipitate and the cobalt-containing solution were obtained by filtration, and the comprehensive copper recovery rate was 61.59%.

[0074] A 2% sodium carbonate solution by mass was added to the cobalt-containing solution as a precipitant, the pH of the solution was adjusted to 8, and after stirring and reacting at room temperature for 4 h, solid-liquid separation was carried out to obtain the cobalt precipitate, and the comprehensive cobalt recovery rate was 65.18%.

[0075] Comparative Example 1

[0076] In this comparative example, the sulfuric acid residue in Example 1 was used as the raw material for the sulfuric acid leaching test. There was no reduction roasting, and the sulfuric acid residue was subjected to sulfuric acid leaching. The sulfuric acid concentration was controlled at 5 mol / L, the liquid-solid ratio was 10 ml / g, the leaching temperature was 90 °C, and the leaching time was 4 h. After solid-liquid separation, the leaching rates of iron, copper, and cobalt in the first filtrate were 55.32%, 40.75%, and 51.36% respectively.

[0077] Phosphoric acid was added in a ratio of 1:1 in terms of molar ratio to total iron elements. The pH of the first filtrate was adjusted to 1.9 using a sodium hydroxide solution with a concentration of 0.25 mol / L, followed by solid-liquid separation to obtain a second filtrate and a crude product of iron phosphate dihydrate. The comprehensive recovery rate of iron was only 50.31%.

[0078] Comparative Example 2

[0079] In this comparative example, the sulfuric acid residue in Example 1 was selected as the raw material for phosphoric acid leaching test. The phosphoric acid concentration was controlled at 3 mol / L, the liquid-solid ratio was 10 ml / g, the leaching temperature was 110 °C, and the leaching time was 4 h. After solid-liquid separation, the solid product was iron phosphate, with an iron grade of 29.34%, a phosphorus grade of 16.26%, and an iron-phosphorus molar ratio of 1:1. The comprehensive recovery rate of iron was 93.44%. The chemical composition of the iron phosphate product is shown in Table 7. It can be seen that although the iron and phosphorus contents and the Fe / P ratio of the iron phosphate product meet the battery-grade standards, most of the impurity elements exceed the standards. In addition, the average particle size of the obtained product was 2 - 10 μm, and the amount of phosphoric acid consumed was approximately 3 times that used in Example 1 as calculated.

[0080] Table 7 Total element analysis of iron phosphate / %

[0081]

[0082] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art of this patent, without departing from the scope of the technical solution of the present invention, may make some changes or modifications using the technical content prompted above as equivalent embodiments of equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the scope of the present invention's solution.

Claims

1. A method for preparing nano-sized iron phosphate and efficiently extracting copper and cobalt using sulfuric acid slag, characterized in that: The following steps are involved: Step 1, placing sulfuric acid slag into a roasting furnace for low-temperature reduction roasting to obtain reduction roasting slag; Step 2: leaching the reduced roasted slag in a low-concentration sulfuric acid solution, and after temperature-controlled stirring, performing a first solid-liquid separation on the leached slurry to obtain a first filtrate and a first filter residue; Step 3, after adding a certain amount of oxidant to the first filtrate, a certain amount of phosphorus source is added, and then sodium hydroxide is used to adjust the pH of the filtrate to low acid, and a second solid-liquid separation is performed to obtain a second filtrate and a second filter residue; Step 4: washing, drying and calcining the second filter residue to obtain an iron phosphate product; Step 5: The second filtrate is used to recover copper and cobalt.

2. The method for preparing nano-sized ferric phosphate and efficiently extracting copper and cobalt by using sulfuric acid slag according to claim 1, characterized in that: In step 1, the particle size of the sulfuric acid slag is -200 mesh, accounting for 60% to 80%, and the reduction roasting conditions are: temperature of 500 to 700° C. and time of 10 to 50 min.

3. The method for preparing nano-sized ferric phosphate and efficiently extracting copper and cobalt by using sulfuric acid slag according to claim 1, characterized in that: In step 1, the reducing agent used for reduction roasting is at least one of carbon monoxide, coal powder and hydrogen.

4. The method for preparing nano-sized ferric phosphate and efficiently extracting copper and cobalt by using sulfuric acid slag according to claim 1, characterized in that: In step 2, the molar concentration of the sulfuric acid solution used in the leaching process is 1-3 mol / L, the liquid-solid ratio is 6-12 ml / g; the temperature is 30-90° C., and the time is 3-4 hours.

5. The method for preparing nano-sized ferric phosphate and efficiently extracting copper and cobalt by using sulfuric acid slag according to claim 1, characterized in that: In step three, the oxidant may be at least one of hydrogen peroxide, air, and oxygen; the phosphorus source includes at least one of phosphoric acid, polyphosphoric acid, and ammonium dihydrogen phosphate; the molar ratio of divalent iron in the first filtrate to the oxidant is 1:1; the molar ratio of iron in the first filtrate to phosphorus in the phosphorus source is 0.9 to 1.1:

1.

6. The method for preparing nano-sized ferric phosphate and efficiently extracting copper and cobalt by using sulfuric acid slag according to claim 1, characterized in that: In step 3, the concentration of sodium hydroxide is 0.1-0.5 mol / L, and the pH of the filtrate is adjusted to 1.7-2.

1.

7. The method for preparing nano-sized ferric phosphate and efficiently extracting copper and cobalt by using sulfuric acid slag according to claim 1, characterized in that: In step 4, the second filter residue is calcined at a temperature of 500 to 700° C. and for a time of 1 to 2 hours.

8. The method for preparing nano-sized ferric phosphate and efficiently extracting copper and cobalt by using sulfuric acid slag according to claim 1, characterized in that: In step five, the second filtrate is used to recover copper and cobalt by a step-by-step precipitation method to obtain copper precipitate slag and cobalt precipitate slag: the second filtrate is first mixed with a sodium thiosulfate solution and the pH is adjusted with a sodium carbonate solution to perform a copper precipitation reaction, and then the solid-liquid separation is performed to obtain a copper precipitate slag and a cobalt-containing solution, and then the cobalt-containing solution is further subjected to a sodium carbonate solution to adjust the pH to perform a cobalt precipitation reaction, and the solid-liquid separation is performed to obtain a cobalt precipitate slag.

9. The method for preparing nano-sized ferric phosphate and efficiently extracting copper and cobalt by using sulfuric acid slag according to claim 8, characterized in that: In the copper precipitation reaction, the mass concentration of the sodium thiosulfate solution is 0.2-0.4%, and the molar ratio of sodium thiosulfate to copper ions in the solution is 0.7-1.1:1, and the mass fraction of the sodium carbonate solution is 1-3%; the copper precipitation reaction conditions are: pH is adjusted to 3.0-4.0, the temperature is 70-90°C, and the reaction time is 2-4h.

10. The method for preparing nano-sized ferric phosphate and efficiently extracting copper and cobalt by using sulfuric acid slag according to claim 8, characterized in that: In the cobalt precipitation reaction, the mass fraction of the sodium carbonate solution is 1-3%; the cobalt precipitation reaction conditions are: pH is adjusted to 7.5-9.0, and the reaction is stirred at room temperature for 1-4 hours.

Images