A method for preparing battery-grade ferrous phosphate solution and copper / graphite recovery by co-leaching of phosphorus iron slag and siderite

Abstract

The application discloses a method for preparing battery-grade ferrous phosphate solution and recovering copper and graphite by co-leaching of phosphorus iron slag and siderite. The method comprises the following steps: reducing leaching of raw materials including phosphorus iron slag, siderite and elemental iron by using phosphoric acid as a leaching agent, and solid-liquid separation to obtain battery-grade ferrous phosphate solution and leaching residue; and graphite flotation separation of the leaching residue after slurry adjustment to obtain copper-rich tailings and graphite concentrate. The method can selectively recover valuable components in the phosphorus iron slag and the siderite, obtain battery-grade ferrous phosphate solution, and efficiently recover graphite and copper components by the synergistic effect of the phosphorus iron slag and the siderite and by using weakly acidic phosphoric acid as a leaching agent, and the method is simple in process, low in cost and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to a method for preparing ferrous dihydrogen phosphate solution and recovering graphite and copper from ferrophosphate slag and copper components from siderite. In particular, it relates to a method for simultaneously leaching ferrophosphate slag and siderite after lithium extraction to produce battery-grade ferrous dihydrogen phosphate solution and recovering graphite and copper components, belonging to the field of new energy battery materials. Background Technology

[0002] Iron phosphate slag is the waste residue generated after dismantling and extracting lithium from spent lithium iron phosphate batteries. Its main components are iron phosphate and graphite, with some copper components. Furthermore, some separators from the batteries can also enter the iron phosphate slag during dismantling, increasing its impurity content and affecting its utilization. Current cathode recycling technologies for lithium iron phosphate batteries mainly involve direct regeneration and hydrometallurgy. Direct regeneration has a short process, but the recycled product contains some impurities; hydrometallurgical recycling produces high-purity products, but requires excessive amounts of acids and alkalis, making the recycling process uneconomical. Lithium iron phosphate does not contain high-value metals such as cobalt and nickel, making recycling unprofitable. Therefore, improving efficient recycling technology for lithium iron phosphate batteries and achieving low-cost, green recycling is crucial for promoting the healthy development of my country's lithium battery industry.

[0003] Siderite is a low-grade iron mineral with a theoretical grade of only 48.27%, and its actual iron content is usually only 20%–40%, making it unsuitable for blast furnace smelting. Its main component is ferrous carbonate, often associated with other carbonates, and it also contains small amounts of valuable metals such as copper. Therefore, beneficiation is difficult, and roasting-magnetic separation or hydroleaching processes are generally used for its separation and utilization. However, siderite has a low iron grade, and roasting temperatures are mostly in the range of 600℃–800℃. Heating a small amount of iron components and a large amount of gangue minerals to such high temperatures consumes a lot of energy, resulting in high costs, large carbon emissions, and the inability to utilize other valuable metals. Hydroleaching processes generally use strong acids to decompose the carbonates in siderite, dissolving the iron components into iron ions, which are then extracted through precipitation. This process is lengthy, costly, and produces iron products with low added value.

[0004] Currently, the recovery of ferrophosphate slag mostly employs strong acid leaching, which leaches iron ions and phosphate ions separately in ionic form. Subsequently, by adjusting the pH value, the iron ions and phosphate ions are precipitated as ferric phosphate. However, because ferrophosphate slag contains a large amount of aluminum and copper components, these impurity ions also enter the solution during the strong acid leaching process, making subsequent impurity removal difficult. Siderite is often processed using a roasting-magnetic separation process, converting FeCO3 into strongly magnetic Fe3O4, followed by magnetic separation to recover iron. However, this process is energy-intensive, costly, and cannot recover valuable by-products such as copper.

[0005] Therefore, developing a simple and efficient method for simultaneously leaching ferrophosphate slag and siderite to produce battery-grade ferrous dihydrogen phosphate solution and recovering graphite and copper components is of great significance to the sustainable development of my country's chemical and new energy industries. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite through co-leaching of ferrophosphate slag and siderite. This method utilizes the synergistic effect of siderite and ferrophosphate slag during the leaching process and employs weakly acidic phosphoric acid as the leaching agent, enabling selective dissolution of phosphorus and iron components from the ferrophosphate slag to obtain a high-purity ferrous dihydrogen phosphate solution, which can be directly used to prepare battery-grade iron phosphate. Simultaneously, the leaching residue is used to recover graphite and copper components through flotation and acid leaching. This method achieves full utilization of the components of both siderite and ferrophosphate slag while reducing production costs. Furthermore, the method of the present invention eliminates the need for subsequent impurity removal, greatly simplifying the process.

[0007] To achieve the above-mentioned technical objectives, this invention provides a method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite by co-leaching of ferrophosphate slag and siderite. The method involves reducing and leaching raw materials, including ferrophosphate slag, siderite, and elemental iron, with phosphoric acid as the leaching agent, followed by solid-liquid separation to obtain battery-grade ferrous dihydrogen phosphate solution and leaching residue. The leaching residue is then subjected to graphite flotation separation after slurry preparation to obtain copper-rich tailings and graphite concentrate.

[0008] The key to this invention lies in the synergistic effect of ferrophosphate slag and siderite. Specifically, this invention first utilizes the high solubility of ferrous ions by adding elemental iron during the leaching process to reduce the ferric iron in the ferrophosphate slag to ferrous iron, making it easier to dissolve into the liquid phase. Simultaneously, siderite itself is a ferrous mineral, providing ferrous ions that can directly react with phosphoric acid to generate ferrous dihydrogen phosphate. However, siderite itself has a low iron grade; using only siderite as the leaching raw material would result in a low iron ion content in the ferrous dihydrogen phosphate solution, affecting subsequent iron phosphate precipitation. Therefore, this invention employs a mixed leaching process using ferrophosphate slag, siderite, and elemental iron, which not only fully utilizes the iron components in these two difficult-to-process iron resources but also yields battery-grade ferrous dihydrogen phosphate solution. On the other hand, siderite reacts with phosphoric acid in the leachate during leaching to produce CO2 gas, which can adjust the pH of the reaction system and prevent local over-acidity. Furthermore, this gas accumulates at the top of the leaching container during leaching, isolating the leachate from the air and preventing the ferrous ions in the leachate from being oxidized to ferric ions by the air. Additionally, by consuming some H₂... + This can optimize the acidity of the system and avoid the reaction between the added elemental iron reducing agent and H+. +The rapid reaction generates H2, which is consumed, preventing the reduction of ferric ions to divalent ions within the system. Based on this principle, the process of this invention can use weakly acidic phosphoric acid as a leaching agent to selectively leach phosphate slag and siderite without adding strong acids such as sulfuric acid, nitric acid, and hydrochloric acid used in traditional processes. This achieves selective dissolution of the desired phosphorus and iron components from the phosphate slag and siderite. After co-leaching, the graphite and copper minerals in the phosphate slag and the gangue components of the siderite form a more easily floatable slag phase. During flotation, the collector can specifically adsorb copper, and the graphite is separated due to differences in surface properties. The graphite and copper components in the leaching slag can be easily recovered and reused through flotation and acid leaching processes. At the same time, the use of phosphoric acid leaching does not introduce new impurity ions into the system, simplifying subsequent impurity removal steps and reducing costs.

[0009] As a preferred embodiment, the mass ratio of the ferrophosphate slag, siderite, elemental iron, and phosphoric acid is 1:(0.4-3):(0.2-1):(3-8). The proportion of siderite used in this invention depends on the amount of ferrophosphate slag and elemental iron. When the proportion of elemental iron is high, the amount of siderite can be increased to increase the amount of CO2 and prevent the oxidation of ferrous ions. When the amount of elemental iron is low, the amount of siderite should be reduced, and the amount of phosphoric acid should also be reduced to increase the ferrous ion content in the leachate. If the amount of phosphoric acid is too low, the pH value of the system is high, which cannot fully dissolve iron ions, resulting in a low leaching rate. If the amount of phosphoric acid is too high, the pH value of the system will be too low, and the elemental iron will react directly with phosphoric acid to generate hydrogen gas, failing to reduce ferric ions. Therefore, within the preferred range of this invention, the amount of CO2 released can be guaranteed to prevent ferrous ions from being oxidized to ferric ions, while simultaneously ensuring a high leaching rate and product purity.

[0010] As a preferred embodiment, the phosphorus-iron slag is phosphorus-iron slag after lithium extraction, and its main components include TFe, P, C, Cu and O, with a total iron content of 21-30%.

[0011] As a preferred embodiment, the siderite mainly comprises TFe, Al2O3 and SiO2, with a total iron content of 35-50%.

[0012] As a preferred embodiment, the reductive leaching conditions are: phosphoric acid concentration of 2–5 mol / L, liquid-to-solid ratio of 6–15 mL / g, temperature of 30–80℃, and time of 4–12 h. During the leaching process, if the phosphoric acid concentration is too low, the iron leaching rate of the ferrophosphate slag and siderite will decrease, and copper ions will be difficult to completely reduce, leading to a decrease in copper recovery rate in subsequent processes. Furthermore, low-concentration phosphoric acid results in a higher pH of the leaching solution, causing some ferric phosphate dihydrate to precipitate, resulting in a higher yield of leaching residue and a lower molar concentration of ferrous dihydrogen phosphate solution.

[0013] As a preferred embodiment, the ferrous ion concentration in the ferrous dihydrogen phosphate solution is 30–60 g / L. The concentration of ferrous ions in the ferrous dihydrogen phosphate solution can be controlled by adjusting the liquid-to-solid ratio and the amount of elemental iron added. In this invention, if the ferrous ion concentration is too low, the purity of the resulting ferrous dihydrogen phosphate solution will decrease; conversely, if the ferrous ion concentration is too high, it will inhibit further dissolution of the ferric phosphate slag through the common ion effect (Fe2+). 2+ With H + (Competitive adsorption on mineral surfaces) reduces the leaching rate. Another reason is that the concentration of ferrous ions is too high, which prevents the obtaining of ferric phosphate products with qualified particle size and composition during subsequent oxidation and precipitation.

[0014] As a preferred embodiment, the aluminum ion concentration in the ferrous dihydrogen phosphate solution is controlled below 200 ppm. When the aluminum ion concentration exceeds 200 ppm, the pH of the leachate is adjusted to 1.6–2.2 using a pH adjuster, and then 1–5 times the molar amount of aluminum ions (NaF) is added to reduce the aluminum ion concentration by generating AlF3 precipitate. The pH adjuster is at least one of ammonia and NaOH. Since the prepared ferrous dihydrogen phosphate solution is battery-grade, excessively high aluminum ion concentrations can severely affect the battery's safety and electrochemical performance. Adjusting the pH range of the leachate promotes the ionization of NaF, preventing F ions from forming HF molecules with H ions, which would affect the Al ion precipitation effect.

[0015] As a preferred embodiment, the slurry formed after the leaching residue is sized has a concentration of 30wt% to 50wt%. When the slurry concentration is too high, the slurry viscosity increases, which leads to bubble coalescence and difficulty in the rise of mineralized bubbles. When the slurry concentration is too low, the probability of mineral particles contacting bubbles decreases, and the recovery rate decreases.

[0016] As a preferred embodiment, the graphite flotation separation includes one roughing stage, at least one cleaning stage, and at least one scavenging stage. Further, the graphite flotation separation includes one roughing stage, where the roughing concentrate undergoes 1-4 cleaning stages to obtain the final graphite concentrate. The cleaned tailings are combined and undergo 1-2 scavenging stages, while the middlings are returned to the roughing stage. The final graphite concentrate has a graphite content of 92%-98% and a graphite recovery rate of 93%-95%.

[0017] As a preferred embodiment, a collector, a frother, and an inhibitor are added during the graphite flotation separation process.

[0018] As a preferred embodiment, the collector is at least one of kerosene and diesel oil; the foaming agent is No. 2 oil; and the inhibitor is at least one of phosphoric acid, water glass, lime, sodium carbonate, sodium tripolyphosphate, and sodium hexametaphosphate.

[0019] As a preferred embodiment, the reagent system for the roughing process is as follows: the dosage of collector is 200-350 g / t, the dosage of frother is 40-80 g / t, and the dosage of inhibitor is 500-2000 g / t; the reagent system for the fine selection process is as follows: the dosage of collector is 60-80 g / t; and the reagent system for the scavenging process is as follows: the dosage of collector is 50-100 g / t.

[0020] As a preferred embodiment, the copper-rich tailings are leached with sulfuric acid as the leaching agent to extract copper, and then a precipitant and a pH adjuster are added to precipitate copper.

[0021] As a preferred embodiment, the concentration of the sulfuric acid is 1–5 mol / L, the liquid-to-solid ratio is 3–6 mL / g, the precipitant is sodium thiosulfate, and the pH adjuster is sodium carbonate; the pH range for copper precipitation is 4–7.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] (1) This invention uses ferrophosphate slag as raw material and employs a reduction leaching process to selectively dissolve the ferrophosphate components in the ferrophosphate slag and siderite. Copper from both raw materials enters the leaching residue due to displacement by elemental iron. In addition, taking advantage of the difference in solubility between graphite components and ferrous dihydrogen phosphate, it also enters the residue.

[0024] (2) The product of this invention is a battery-grade ferrous dihydrogen phosphate solution, which is an intermediate product of the iron-based and sodium-based ferric phosphate processes. Compared with the prior art, this invention cleverly utilizes the high solubility of ferrous ions to transform the ferric phosphate phase in the ferric phosphate slag into a soluble ferrous dihydrogen phosphate phase through reduction leaching, and to leach the phosphate component of the iron component in the siderite into a soluble ferrous dihydrogen phosphate phase. At the same time, the released CO2 can isolate the air and prevent the ferrous ions in the leachate from being oxidized by the air. The released CO2 gas can also adjust the pH of the reaction system, avoid local over-acidity, and further promote the oxidation of PO4 in the ferric phosphate slag. 3- The release of valuable components was achieved in one step, enabling the selective leaching of ferrophosphate slag and siderite, and completing the separation of ferrophosphate components from graphite and copper components in ferrophosphate, as well as the separation of iron components from copper components in siderite.

[0025] (3) In the reduction leaching process, this invention can enrich the graphite and copper components in the leaching residue, and reduce reagent consumption and improve the grade and recovery rate of graphite concentrate in the subsequent flotation purification process. In addition, during the flotation purification of graphite, the copper component enters the tailings, which greatly improves the copper grade in the tailings and is beneficial for subsequent acid leaching copper extraction.

[0026] (4) The graphite concentrate obtained by the process of the present invention has a graphite content of 92% to 98%, a graphite recovery rate of 93% to 95%, and a copper recovery rate of 86% to 90%. The graphite separated by the present invention can be directly used for the preparation of negative electrode materials.

[0027] (5) The preparation process of this invention uses phosphoric acid, which has a relatively weak acidity, as a leaching agent to selectively leach ferrophosphate slag and siderite. Compared with the traditional strong acid leaching of ferrophosphate slag and the fire roasting process of siderite, this process has the advantages of simple process, no need for impurity removal, and low cost, realizing the high added value application of ferrophosphate slag and siderite. At the same time, the use of phosphoric acid leaching will not introduce new impurity ions into the system, simplifying the subsequent impurity removal steps and reducing costs. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1 The process flow diagram is shown for the method of preparing battery-grade ferrous dihydrogen phosphate solution and copper / graphite recovery by co-leaching of ferrophosphate slag and siderite according to the present invention.

[0030] Figure 2 The image shows the XRD diffraction pattern of the phosphorus-iron slag after lithium extraction in Example 1.

[0031] Figure 3 This is a photograph of the ferrous dihydrogen phosphate leachate prepared in Example 1.

[0032] Figure 4 This is a photograph of the sodium fluoride filter residue used to remove aluminum in Example 2.

[0033] Figure 5 This is a photograph of the ferrous dihydrogen phosphate leachate prepared in Comparative Example 1. Detailed Implementation

[0034] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] This embodiment uses lithium-extraction phosphorus-iron slag with a total iron content of 24.06%. The remaining main components are P, C, and Cu, with contents of 13.42%, 32.28%, and 0.63%, respectively. The remaining components are shown in Table 1. Figure 2 (See its XRD pattern). The siderite has a total iron content of 45.33% and a Cu content of 0.173%. Other components are shown in Table 2.

[0037] Table 1. Main chemical components (wt%) of ferrophosphate slag

[0038]

[0039] Table 2. Main chemical components of siderite (wt%)

[0040]

[0041] The leaching test used the aforementioned ferrophosphate slag and siderite. 15g of ferrophosphate slag, 4.0g of reduced iron powder, and 7.5g of siderite were weighed. The mass ratio of ferrophosphate slag, siderite, reduced iron powder, and phosphoric acid was 1:0.5:0.27:4. The leaching agent was 3mol / L phosphoric acid, the liquid-to-solid ratio was 7.70ml / g, the leaching temperature was 30℃, and the stirrer speed was 300r / min. After leaching for 8 hours, the mixture was filtered to obtain ferrous dihydrogen phosphate leachate and leaching residue. Under these conditions, the iron components in the ferrophosphate slag and siderite were almost completely converted into soluble ferrous dihydrogen phosphate. After solid-liquid separation, the initial pH of the leachate was 1.49. 25% ammonia solution was added dropwise until the pH of the leachate reached 2.2. Sodium fluoride was then added, and the sodium fluoride reacted with the Al in the leachate. 3+ The molar ratio was 5:1. After the reaction was complete, the mixture was filtered to obtain ferrous dihydrogen phosphate solution. Figure 3 The product image shows ferrous dihydrogen phosphate solution. The iron leaching rate is 80.01%. The main chemical components of the product are shown in Table 3 (where Fe refers to ferrous ions, the same below). The main components of the leaching residue are graphite, copper, and insoluble gangue minerals from siderite. Their chemical components are shown in Table 4.

[0042] Table 3. Main chemical components (ppm) of ferrous dihydrogen phosphate solution

[0043]

[0044] Table 4. Main chemical components (wt%) of leaching residue

[0045]

[0046] The leaching residue is used to recover graphite and the precious metal copper. Graphite is purified using a "roughing, cleaning, and scavenging" flotation process. The roughing pulp concentration is 35 wt%, with 500 g / t of water glass, 210 g / t of diesel oil, and 40 g / t of No. 2 oil added sequentially at 2-minute intervals and a 3-minute skimming time. In the first cleaning stage, 80 g / t of diesel oil is added. In the second cleaning stage, 60 g / t of diesel oil is added, and in the middlings scavenging stage, 60 g / t of diesel oil is added. The concentrate is graphite with a graphite content of 93.48% and a recovery rate of 94.7%. The scavenging tailings and roughing concentrate are combined for copper recovery.

[0047] Flotation tailings were mixed with 1.5 mol / L sulfuric acid at a solid-liquid mass ratio of 1 g: 3 mL and stirred for 3 hours to obtain copper-containing leachate and leaching residue. Sodium thiosulfate with a mass concentration of 10% was added to the copper-containing leachate, with the amount being twice the amount added for copper ion concentration. Sodium carbonate was used as a pH adjuster to adjust the pH of the leachate to 5. The stirring temperature was 80℃ and the stirring time was 3 hours to finally obtain copper-precipitated residue with a copper recovery rate of 88.57%.

[0048] Example 2

[0049] The raw materials for this embodiment are the ferrophosphate slag and siderite from Example 1, with iron grades of 24.06% and 45.33%, respectively. Other main components are shown in Tables 1 and 2. 15g of ferrophosphate slag, 6g of reduced iron powder, and 10.5g of siderite were weighed. The mass ratio of ferrophosphate slag, siderite, reduced iron powder, and phosphoric acid was 1:0.4:0.7:5, the phosphoric acid concentration was 3.5mol / L, the liquid-to-solid ratio was 8.33ml / g, the leaching temperature was 30℃, the leaching time was 6h, and the stirrer speed was 300r / min. The leaching results showed that the iron component in the reaction system was almost completely converted to ferrous dihydrogen phosphate. After solid-liquid separation, the initial pH of the leachate was 1.35. Sodium fluoride was added to precipitate aluminum ions, with a molar mass ratio of sodium fluoride to aluminum ions in the leachate of 4:1. After sufficient reaction, the mixture was filtered to obtain the ferrous dihydrogen phosphate solution product. Figure 4 The iron leaching rate was 79.26% (for the generated AlF3 precipitate), and its main chemical components are shown in Table 5. The main components of the leaching residue are shown in Table 6.

[0050] Table 5. Main components (ppm) of ferrous dihydrogen phosphate solution

[0051]

[0052] Table 6 Chemical composition of reduction leaching residue (wt%)

[0053]

[0054] The leaching residue flotation process is "one roughing, two cleaning, and one scavenging". The roughing pulp concentration is 35 wt%, and water glass 500 g / t, diesel oil 210 g / t, and No. 2 oil 40 g / t are added sequentially, with a 1-minute interval between additions and a 3-minute skimming time. In the first cleaning stage, 80 g / t of diesel oil collector is added; in the second cleaning stage, 60 g / t of diesel oil collector is added; and in the scavenging stage, 50 g / t of diesel oil collector is added. The final concentrate is high-purity graphite with a grade of 92.68% and a recovery rate of 94.23%. The scavenging tailings and roughing tailings are combined for copper recovery.

[0055] The merged tailings were mixed with 1.5 mol / L sulfuric acid at a solid-liquid mass ratio of 1 g: 3 mL and stirred for 3 hours at a stirrer speed of 300 r / min. After filtration, copper-containing leachate and leaching residue were obtained. Sodium thiosulfate with a mass concentration of 10% was added to the copper-containing leachate, and the amount added was twice the amount added for copper ion concentration. Sodium carbonate was used as a pH adjuster to adjust the pH of the leachate to 5. The stirring temperature was 80℃ and the stirring time was 3 hours. Finally, copper precipitate residue was obtained, and the copper recovery rate was 89.59%.

[0056] Example 3

[0057] This embodiment uses lithium-extraction phosphorus slag from a certain field. The iron content of the siderite is 45.33%, and the main components are shown in Table 2. The iron content of the phosphorus slag is 21.89%, and the main components are shown in Table 7.

[0058] Table 7 Chemical composition (wt%) of ferrophosphate slag from a certain farm

[0059]

[0060] 15g of ferrophosphate slag, 6g of reduced iron powder, and 12g of siderite were weighed out. The mass ratio of ferrophosphate slag, siderite, reduced iron powder, and phosphoric acid was 1:0.8:0.4:5. The phosphoric acid concentration was 3.5mol / L, the liquid-to-solid ratio was 6.63ml / g, the leaching temperature was 30℃, the leaching time was 6h, and the stirrer speed was 300r / min. The leaching results showed that the iron component in the reaction system was almost completely converted into ferrous dihydrogen phosphate. The leaching residue mainly consisted of graphite, copper, and insoluble gangue minerals from the siderite, which can be used for subsequent recovery of graphite and precious metals.

[0061] After solid-liquid separation, ferrous dihydrogen phosphate solution was obtained with an iron leaching rate of 79.27%. Its main chemical composition is shown in Table 8, and the chemical composition of the leaching residue is shown in Table 9.

[0062] Table 8 Chemical composition (ppm) of ferrous dihydrogen phosphate solution

[0063]

[0064] Table 9 Chemical composition of reduction leaching residue (wt%)

[0065]

[0066] The leaching residue flotation process is "one roughing, two cleaning, and one scavenging". The roughing pulp concentration is 35 wt%, and water glass 500 g / t, diesel oil 210 g / t, and No. 2 oil 40 g / t are added sequentially, with a 1-minute interval between additions and a 3-minute skimming time. In the first cleaning stage, 80 g / t of diesel oil collector is added; in the second cleaning stage, 60 g / t of diesel oil collector is added; and in the scavenging stage, 50 g / t of diesel oil collector is added. The final concentrate is high-purity graphite with a grade of 93.65% and a recovery rate of 93.61%. The scavenging tailings and roughing tailings are combined for copper recovery.

[0067] The merged tailings were mixed with 1.5 mol / L sulfuric acid at a solid-liquid mass ratio of 1 g: 3 mL and stirred for 3 hours at a stirrer speed of 300 r / min. After filtration, copper-containing leachate and leaching residue were obtained. 10% sodium thiosulfate was added to the copper-containing leachate, with the amount being twice the amount added for copper ion concentration. Sodium carbonate was used as a pH adjuster to adjust the pH of the leachate to 5. The stirring temperature was 80℃ and the stirring time was 3 hours. Finally, copper precipitate residue was obtained, and the copper recovery rate was 86.63%.

[0068] Comparative Example 1

[0069] This comparative example uses the raw materials from Example 1 for phosphoric acid reduction leaching experiments. 15g of ferrophosphate slag, 1g of reduced iron powder, and 7.5g of siderite were weighed. The mass ratio of ferrophosphate slag, siderite, reduced iron powder, and phosphoric acid was 1:0.5:0.06:4. The phosphoric acid concentration was 3.0mol / L, the liquid-to-solid ratio was 8.68ml / g, the leaching time was 8h, the leaching temperature was 30℃, and the stirrer speed was 300r / min.

[0070] The theoretical ratio of iron content in ferrophosphate slag to iron powder mass is 2:1, and the theoretical mass of reduced iron powder is 2.7g. The amount of iron powder added in the experiment was lower than the theoretical amount, resulting in incomplete reduction of ferric ions in the ferrophosphate slag. Since ferric ions have lower solubility than ferrous ions, the iron leaching rate is reduced. In addition, insufficient reduced iron powder results in a large amount of copper elements existing in the leachate in ionic form, affecting the quality of ferrous dihydrogen phosphate product and reducing the yield of copper slag in the subsequent flotation process.

[0071] After solid-liquid separation, the initial pH of the leachate was 1.49. 25% ammonia was added to adjust the pH to 2.2, followed by the addition of sodium fluoride to further remove aluminum ions. The sodium fluoride reacts with the Al in the leachate. 3+ The molar ratio was 5:1. After the reaction was complete, the mixture was filtered to obtain ferrous dihydrogen phosphate solution. Figure 5 (See product image). The iron leaching rate was 70.90%, and its main chemical components are shown in Table 10. The leaching residue mainly consisted of graphite, copper, and refractory gangue minerals from siderite, and its main components are shown in Table 11.

[0072] Table 10 Chemical composition (ppm) of ferrous dihydrogen phosphate solution

[0073]

[0074] Table 11 Main chemical components (wt%) of leaching residue

[0075]

[0076] The leaching residue flotation process is "one roughing, two cleaning, and one scavenging". The roughing pulp concentration is 35 wt%, and water glass 500 g / t, diesel oil 210 g / t, and No. 2 oil 40 g / t are added sequentially, with a 1-minute interval between additions and a 3-minute skimming time. In the first cleaning stage, 80 g / t of diesel oil collector is added; in the second cleaning stage, 60 g / t of diesel oil collector is added; and in the scavenging stage, 50 g / t of diesel oil collector is added. The final concentrate is high-purity graphite with a grade of 91.26% and a recovery rate of 92.71%. The scavenging tailings and roughing tailings are combined for copper recovery.

[0077] The merged tailings were mixed with 1.5 mol / L sulfuric acid at a solid-liquid mass ratio of 1 g: 3 mL and stirred for 3 hours at a stirrer speed of 300 r / min. After filtration, copper-containing leachate and leaching residue were obtained. 10% sodium thiosulfate was added to the copper-containing leachate, with the amount being twice the amount added for copper ion concentration. Sodium carbonate was used as a pH adjuster to adjust the pH of the leachate to 5. The stirring temperature was 80℃ and the stirring time was 3 hours. Finally, copper precipitate residue was obtained, and the copper recovery rate was 54.27%.

[0078] Comparative Example 2

[0079] The elemental contents of the phosphite slag in this comparative example are the same as those in Example 1. The leaching agent is equimolar concentration sulfuric acid, and the mass ratio of phosphite slag, siderite, reduced iron powder, and sulfuric acid is maintained at 1:0.5:0.27:4, the same as in Example 1. 15g of phosphite slag, 4g of reduced iron powder, and 7.5g of siderite were weighed. The sulfuric acid concentration of the leaching agent was 3. mol / L, the liquid-to-solid ratio was 7.70 mg / L, the leaching time was 8 hours, the leaching temperature was 30℃, and the stirrer speed was 300 r / min.

[0080] After solid-liquid separation, ferrous dihydrogen phosphate leachate was obtained, with an iron leaching rate of 69.95%. Its chemical composition is shown in Table 12, and the content of each element in the leaching residue is shown in Table 13.

[0081] Table 12 Chemical composition (ppm) of ferrous dihydrogen phosphate solution

[0082]

[0083] Table 13 Elemental content (wt%) of leaching residue

[0084]

[0085] Compared to Example 1, the iron content of the ferrous dihydrogen phosphate solution in this comparative example decreased by 12.60%. This is because the ferrophosphate slag contains a small amount of calcium oxide. Under acidic conditions, calcium ions readily react with sulfate ions to form slightly soluble calcium sulfate. Furthermore, the siderite and ferrophosphate slag, having undergone crushing, have numerous lattice defects on their solid particle surfaces. Sulfate ions, under the influence of van der Waals forces and electrostatic attraction, adsorb onto the surfaces of the siderite and ferrophosphate slag, preventing them from reacting with the leaching solution, thus reducing the leaching rate and the iron content of the product. On the other hand, the use of sulfuric acid (a strong acid) for reduction leaching, due to the high electronegativity of its central atom, more easily releases H+. + It reacts directly with elemental iron to produce hydrogen gas and ferrous ions, but reacts with ferric iron, reducing iron powder and resulting in incomplete reduction of ferric ions. Compared to ferrous ions, ferric ions are more easily hydrolyzed to form precipitates, thus having lower solubility and reducing iron leaching rate. Furthermore, sulfuric acid (a strong acid) more readily dissolves Al compounds in the phosphorus-iron slag. Excessive Al can affect the structural stability of LiFePO4 olivine in subsequent processes, causing thermal runaway and Li... + Diffusion obstruction and other phenomena increase the cost of impurity removal. In addition, the use of sulfuric acid as a leaching agent results in insufficient phosphorus content in the leaching system and an excessively high iron-to-phosphorus ratio, which reduces the quality of ferrous dihydrogen phosphate solution and wastes iron in the subsequent iron phosphate production process. If strong industrial acids such as nitric acid are used, they can also react with elemental copper at room temperature, ultimately reducing copper production.

[0086] The leaching residue flotation process is "one roughing, two cleaning, and one scavenging". The roughing pulp concentration is 35 wt%, and water glass 500 g / t, diesel oil 210 g / t, and No. 2 oil 40 g / t are added sequentially, with a 1-minute interval between additions and a 3-minute skimming time. In the first cleaning stage, 80 g / t of diesel oil collector is added; in the second cleaning stage, 60 g / t of diesel oil collector is added; and in the scavenging stage, 50 g / t of diesel oil collector is added. The final concentrate is high-purity graphite with a grade of 90.97% and a recovery rate of 89.92%. The scavenging tailings and roughing tailings are combined for copper recovery.

[0087] The merged tailings were mixed with 1.5 mol / L sulfuric acid at a solid-liquid mass ratio of 1 g: 3 mL and stirred for 3 hours at a stirrer speed of 300 r / min. After filtration, copper-containing leachate and leaching residue were obtained. Sodium thiosulfate with a mass concentration of 10% was added to the copper-containing leachate, and the amount added was twice the amount added for copper ion concentration. Sodium carbonate was used as a pH adjuster to adjust the pH of the leachate to 5. The stirring temperature was 80℃ and the stirring time was 3 hours. Finally, copper precipitate residue was obtained, and the copper recovery rate was 80.72%.

[0088] Comparative Example 3

[0089] This comparative example uses the ferrophosphorus slag from Example 1, with a total iron content of 24.06%, and phosphoric acid solution as the leaching agent. The iron content and the mass ratio of ferrophosphorus slag to iron powder in the leaching system are kept the same as in Example 1. The mass ratio of ferrophosphorus slag, reduced iron powder, and phosphoric acid is 1:0.27:4. 23.20 g of ferrophosphorus slag and 6.26 g of reduced iron powder are weighed. The concentration of phosphoric acid as the leaching agent is 3 mol / L, the liquid-to-solid ratio is 10.71 ml / g, the leaching time is 8 h, the leaching temperature is 30 °C, and the stirrer speed is 300 r / min.

[0090] After solid-liquid separation, the chemical composition of the ferrous dihydrogen phosphate solution is shown in Table 14, with an iron leaching rate of 68.51%. The chemical composition of the leaching residue is shown in Table 15.

[0091] Table 14 Chemical composition of ferrous dihydrogen phosphate solution

[0092]

[0093] Table 15 Chemical composition of leaching residue (wt%)

[0094]

[0095] Compared to Example 1, the iron content in the ferrous dihydrogen phosphate solution of this comparative example was significantly reduced. The main iron phase in siderite is ferrous carbonate. Under acidic conditions, carbon dioxide is generated in the upper layer of the container, preventing the oxidation of ferrous ions. The absence of siderite in the leaching system led to severe oxidation of ferrous ions, while the solubility product of ferric ions was small, resulting in a lower iron leaching rate. On the other hand, carbonate ions in siderite can combine with hydrogen ions, promoting the forward ionization reaction of phosphoric acid molecules and releasing a large number of phosphoric acid molecules, which is beneficial for the formation of ferrous dihydrogen phosphate. Simultaneously, it promotes the dissolution of phosphorus in the ferrophosphate slag. The lack of siderite resulted in a decrease in the leaching rates of phosphorus and iron in the ferrophosphate slag. Furthermore, the process of carbonate ions combining with hydrogen ions can optimize the acidity of the system. The absence of siderite led to the reaction of phosphoric acid with iron powder to generate hydrogen gas, resulting in incomplete reduction of ferric ions and incomplete replacement of copper ions, thus reducing the iron leaching rate and the yield of copper slag.

[0096] The leaching residue flotation process is "one roughing, two cleaning, and one scavenging". The roughing pulp concentration is 35 wt%, and water glass 500 g / t, diesel oil 210 g / t, and No. 2 oil 40 g / t are added sequentially, with a 1-minute interval between additions and a 3-minute skimming time. In the first cleaning stage, 80 g / t of diesel oil collector is added; in the second cleaning stage, 80 g / t of diesel oil collector is added; and in the scavenging stage, 50 g / t of diesel oil collector is added. The final concentrate is high-purity graphite with a grade of 90.94% and a recovery rate of 91.44%. The scavenging tailings and roughing tailings are combined for copper recovery.

[0097] The merged tailings were mixed with 1.5 mol / L sulfuric acid at a solid-liquid mass ratio of 1 g: 3 mL and stirred for 3 hours at a stirrer speed of 300 r / min. After filtration, copper-containing leachate and leaching residue were obtained. Sodium thiosulfate with a mass concentration of 10% was added to the copper-containing leachate, and the amount added was twice the amount added for copper ion concentration. Sodium carbonate was used as a pH adjuster to adjust the pH of the leachate to 5. The stirring temperature was 80℃ and the stirring time was 3 hours. Finally, copper precipitate residue was obtained, and the copper recovery rate was 77.27%.

Claims

1. A method for preparing battery-grade ferrous dihydrogen phosphate solution by co-leaching of ferrophosphate slag and siderite, and for copper / graphite recovery, characterized in that: Raw materials, including ferrophosphate slag, siderite, and elemental iron, are reduced and leached with phosphoric acid as the leaching agent. Solid-liquid separation is performed to obtain battery-grade ferrous dihydrogen phosphate solution and leaching residue. The leaching residue is then subjected to graphite flotation separation after slurry preparation to obtain copper-rich tailings and graphite concentrate. The mass ratio of the phosphate slag, siderite, elemental iron and phosphoric acid is 1:(0.4~3):(0.2~1):(3~8).

2. The method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite by co-leaching of ferrophosphate slag and siderite according to claim 1, characterized in that: The phosphorus-iron slag is phosphorus-iron slag after lithium extraction, and its main components include TFe, P, C, Cu and O, with a total iron content of 21%~30%. The siderite mainly consists of TFe, Al2O3 and SiO2, with a total iron content of 35% to 50%.

3. The method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite by co-leaching of ferrophosphate slag and siderite according to claim 2, characterized in that: The conditions for the reduction leaching are: phosphoric acid concentration of 2-5 mol / L, liquid-to-solid ratio of 6-15 mL / g, temperature of 30-80℃, and time of 4-12 h.

4. The method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite by co-leaching of ferrophosphate slag and siderite according to claim 3, characterized in that: The ferrous ion concentration in the ferrous dihydrogen phosphate solution is 30~60 g / L.

5. The method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite by co-leaching of ferrophosphate slag and siderite according to claim 1, characterized in that: The aluminum ion concentration in the ferrous dihydrogen phosphate solution is controlled below 200 ppm; when the aluminum ion concentration is greater than 200 ppm, the pH value of the leachate is adjusted to 1.6~2.2 using a pH adjuster, and then 1~5 times the molar amount of aluminum ions of NaF is added to reduce the aluminum ion concentration by generating AlF3 precipitate. The pH adjuster is at least one of ammonia and NaOH.

6. A method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite by co-leaching of ferrophosphate slag and siderite according to any one of claims 1 to 5, characterized in that: The slurry formed after the leaching residue is prepared has a slurry concentration of 30wt%~50wt%. The graphite flotation separation includes one roughing, at least one cleaning, and at least one scavenging.

7. The method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite by co-leaching of ferrophosphate slag and siderite according to claim 6, characterized in that: Collector, frother and inhibitor are added during the graphite flotation separation process; The collector is at least one of kerosene and diesel oil; the foaming agent is No. 2 oil; and the inhibitor is at least one of phosphoric acid, water glass, lime, sodium carbonate, sodium tripolyphosphate, and sodium hexametaphosphate.

8. The method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite by co-leaching of ferrophosphate slag and siderite according to claim 6, characterized in that: The reagent system for the roughing process is as follows: the amount of collector relative to the leaching residue is 200~350g / t, the amount of frother relative to the leaching residue is 40~80g / t, and the amount of inhibitor relative to the leaching residue is 500~2000g / t. The selected reagent system is as follows: the amount of collector relative to the leaching residue is 60~80g / t; The reagent system for the scavenging process is as follows: the amount of collector relative to the leaching residue is 50~100 g / t.

9. The method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite by co-leaching of ferrophosphate slag and siderite according to claim 1, characterized in that: The copper-rich tailings are leached with sulfuric acid as the leaching agent to extract copper, and then a precipitant and a pH adjuster are added to precipitate copper.

10. The method for preparing battery-grade ferrous dihydrogen phosphate solution and recovering copper / graphite by co-leaching of ferrophosphate slag and siderite according to claim 9, characterized in that: The concentration of sulfuric acid is 1~5 mol / L, the liquid-solid ratio in the copper leaching process of copper-rich tailings using sulfuric acid as the leaching agent is 3~6 mL / g, the precipitant is sodium thiosulfate, and the pH adjuster is sodium carbonate; the pH range of the copper precipitation is 4~7.

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