A low-cost purification process for waste iron phosphate and lithium iron phosphorus slag combined treatment

Abstract

The present invention discloses a low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag, which belongs to the technical field of pretreatment of raw materials for iron phosphate production, and includes the following steps: waste iron phosphate is slurried with water, and then concentrated sulfuric acid is slowly added, and stirred until the waste iron phosphate is completely dissolved to obtain iron phosphorus liquid A; the lithium iron phosphorus slag is leached and filtered through sulfuric acid to obtain iron phosphorus liquid B, alkali is added to the iron phosphorus liquid B, and the endpoint pH value is controlled to be 1-1.8, and then filtered and washed to obtain an amorphous iron phosphate filter cake; the amorphous iron phosphate filter cake is added to the iron phosphorus liquid A, and stirred until the filter cake is completely dissolved to obtain low-acidity iron phosphorus liquid for further synthesis of qualified iron phosphate. The present invention combines waste iron phosphate with lithium iron phosphorus slag to obtain low-acidity and low-impurity iron phosphorus liquid, reduces acid and alkali consumption during raw material pretreatment, reduces pretreatment costs, and provides high-quality raw materials for further synthesis of qualified iron phosphate.

Description

Technical Field

[0001] The invention belongs to the technical field of iron phosphate recovery, and specifically is a low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag. Background Art

[0002] Lithium iron phosphate is an excellent cathode material for lithium batteries, with the advantages of high safety, long cycle life, and environmental friendliness. It is widely used in power batteries, energy storage batteries, and other fields. The main preparation methods for lithium iron phosphate include solid phase method, hydrothermal method, sol-gel method, air oxidation method, controlled crystallization method, etc. Among them, the precipitation method has become the mainstream method because of its simple process, low cost, and easy industrialization.

[0003] The key step in the solid phase method for preparing lithium iron phosphate is the synthesis of iron phosphate, and the quality of iron phosphate directly affects the performance of lithium iron phosphate. At present, there are two main methods for preparing iron phosphate in industry: one is to prepare iron phosphate by reacting purified phosphoric acid (thermal or wet method) with ferrous sulfate, and the other is to prepare iron phosphate by reacting phosphate (such as monoammonium phosphate, diammonium phosphate, etc.) with ferrous sulfate.

[0004] In the process of iron phosphate production, due to process control or production management and other reasons, anhydrous iron phosphate or dihydrate iron phosphate with high metal impurity content or other unsatisfactory properties is sometimes produced (especially in the initial production of enterprises newly entering the industry). The anhydrous iron phosphate or dihydrate iron phosphate requires a higher acidity to dissolve, and the iron phosphate solution with a high acid content obtained by dissolution consumes a large amount of alkali to neutralize the acid contained when used as a raw material for iron phosphate production. The processing cost is very high, so it is necessary to find a low-cost treatment process to treat this kind of waste iron phosphate.

[0005] In addition, the current iron phosphate synthesis methods cannot use the waste iron phosphate after lithium iron phosphate extraction as raw material to produce battery-grade iron phosphate. The main reason is that a large amount of impurity ions such as aluminum, copper, nickel, cobalt, calcium, etc. remain in the waste iron phosphate. The current common methods for removing impurities are: iron sheet reduction, extraction agent extraction, etc. However, both methods have some defects, mainly the following points:

[0006] 1. Waste iron phosphate needs to be dissolved with inorganic acids of higher acidity (such as sulfuric acid, hydrochloric acid, nitric acid, etc.), which consumes a lot of acid, increasing costs and environmental burden;

[0007] 2. When removing impurities or precipitating iron phosphate, the dissolved iron phosphate solution needs to use more alkali (such as sodium hydroxide, ammonia water, sodium bicarbonate, ammonium bicarbonate, etc.) to neutralize the acid in the solution and increase the pH value of the solution, which consumes a large amount of alkali, increasing costs and environmental burdens;

[0008] 3. During the precipitation process of iron phosphate, a large amount of wastewater and waste residue is easily generated, which requires subsequent treatment and disposal, increasing costs and environmental burden;

[0009] 4. During the synthesis process of iron phosphate, it is easily affected by impurities (especially aluminum), which leads to instability in the purity and iron-phosphorus ratio of iron phosphate, affecting the performance of lithium iron phosphate.

[0010] 5. During the impurity removal process, new impurities or additional elements are introduced, and the proportion of recycled raw materials is low, which increases production costs.

[0011] Therefore, the current iron phosphate synthesis method is not suitable for the treatment of waste iron phosphate, and it is necessary to add a pretreatment step to pretreat the waste iron phosphate to ensure the quality of iron phosphate, reduce the cost of iron phosphate, and reduce the environmental impact of waste iron phosphate. Summary of the invention

[0012] In view of the above problems, the present invention provides a low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag, and utilizes the amorphous iron phosphate filter cake prepared from the iron phosphorus slag leaching solution to reduce the impurities and acidity of the iron phosphorus liquid A, thereby reducing the alkali consumption and reducing the cost. The obtained iron phosphorus liquid with low acidity and low impurities has improved purity and iron-phosphorus ratio for synthesizing qualified iron phosphate, thereby providing high-quality raw materials for further synthesis of qualified lithium iron phosphate.

[0013] To achieve the above object, the technical solution adopted by the present invention is:

[0014] A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag comprises the following steps:

[0015] (1) Adding water to the waste iron phosphate to prepare a slurry, and then slowly adding concentrated sulfuric acid, stirring until the waste iron phosphate is completely dissolved to obtain iron-phosphorus liquid A;

[0016] (2) leaching the lithium iron-phosphorus slag with sulfuric acid and filtering it to obtain iron-phosphorus liquid B;

[0017] (3) adding alkali to the iron-phosphorus solution B to control the end point pH value to 1-1.8, and then filtering and washing to obtain an amorphous iron phosphate filter cake;

[0018] (4) adding the amorphous iron phosphate filter cake obtained in step (3) into the iron-phosphorus liquid A obtained in step (1), stirring until the filter cake is completely dissolved, thereby obtaining an iron-phosphorus liquid with low acidity and low impurities, which is used to further synthesize qualified iron phosphate.

[0019] As a further improvement of the above scheme, the solid-liquid ratio during slurry preparation in step (1) is 1 g: 1-2 mL.

[0020] As a further improvement of the above scheme, the mass concentration of concentrated sulfuric acid in step (1) is 95-98%.

[0021] As a further improvement of the above scheme, in step (1), the weight ratio of waste iron phosphate to concentrated sulfuric acid is 1:1-2.

[0022] As a further improvement of the above scheme, the mass concentration of sulfuric acid in step (2) is 5-20%.

[0023] As a further improvement of the above scheme, the leaching temperature in step (2) is 25-60°C.

[0024] As a further improvement of the above scheme, the alkali in step (3) is one of sodium hydroxide solution, ammonia solution, ammonium bicarbonate solution, sodium bicarbonate solution, and sodium carbonate solution, the concentration of sodium hydroxide solution is 2-32% by mass, the concentration of ammonia solution is 5-25% by mass, the concentration of ammonium bicarbonate solution is 5-28% by mass, the concentration of sodium bicarbonate solution is 5-10% by mass, and the concentration of sodium carbonate solution is 5-22% by mass.

[0025] As a further improvement of the above scheme, the pH value of the low-acidity iron-phosphorus solution in step (4) is 0-0.8.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The present invention utilizes scrapped iron phosphate and iron-phosphorus slag after lithium extraction as raw materials, thereby realizing the recycling of waste iron phosphate, saving resources, reducing the generation and treatment of waste, and simultaneously removing impurities in the raw materials to meet the quality requirements for the production of battery-grade iron phosphate;

[0028] (2) The present invention slowly adds concentrated sulfuric acid to dissolve the waste iron phosphate, and the reaction of concentrated sulfuric acid with water releases a large amount of heat, which increases the dissolution temperature. No additional heating is required, and the temperature is controlled at 70-90° C., saving energy consumption and cost;

[0029] (3) The present invention reduces the acidity of the iron-phosphorus liquid A by adding an amorphous iron phosphate filter cake prepared from an iron-phosphorus slag leaching solution, thereby reducing 83% of the alkali consumption, preparing a qualified iron-phosphorus liquid that can directly synthesize battery-grade iron phosphate, and at the same time improving the purity and iron-phosphorus ratio of the synthesized battery-grade iron phosphate, providing a high-quality raw material for further synthesizing qualified lithium iron phosphate. The principle is: the amorphous iron phosphate prepared from the iron-phosphorus slag after lithium extraction is dissolved in the iron-phosphorus liquid A obtained by dissolving anhydrous waste iron phosphate or dihydrate iron phosphate with concentrated sulfuric acid, so that the residual acid in the iron-phosphorus liquid A can fully play a role, wherein the reaction principle is represented by the following chemical equation:

[0030] 3FePO 4 +3H 2 SO 4 →Fe(H2 PO 4 ) 3 +Fe 2 (SO 4 ) 3 ;

[0031] (4) The process of the present invention is simple, easy to operate, low in energy consumption, and environmentally friendly, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The figure is a flow chart of the processing method of the present invention. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solution, the present invention is described in detail below in conjunction with embodiments. The description in this section is only exemplary and explanatory and should not have any limiting effect on the scope of protection of the present invention.

[0034] The lithium iron phosphorus slag used in the following examples is the slag (main component iron phosphate) obtained after lithium extraction from purchased battery positive electrode materials. The main components are shown in the following table:

[0035] Table 1

[0036]

[0037] Embodiment 1:

[0038] A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag comprises the following steps:

[0039] (1) 100 g of waste iron phosphate was slurried with 200 mL of water, and then 150 g of concentrated sulfuric acid was slowly added, the mass concentration of the concentrated sulfuric acid was 98%, and stirred for 1 hour to obtain 550 g of iron-phosphorus liquid A. The composition content of the above waste iron phosphate is shown in Table 2;

[0040] Table 2

[0041]

[0042]

[0043] (2) Weighing 919 g of lithium iron phosphorus slag, adding 2105 g of 20% sulfuric acid for leaching at 25° C., stirring for 3 h, and filtering to obtain 2.54 L of iron phosphorus liquid B and carbon black. The specific composition content of the iron phosphorus liquid B is shown in Table 3;

[0044] Table 3

[0045]

[0046] (3) 512 g of 20% ammonia water (ammonia:sulfur molar ratio = 1.404) was added to the iron-phosphorus liquid B, and the end point pH value was controlled to 1.0, followed by filtration and washing to obtain 1429 g of amorphous iron phosphate filter cake (water content 69%);

[0047] (4) The amorphous iron phosphate filter cake obtained in step (3) is added to the iron-phosphorus liquid A obtained in step (1), and stirred until the filter cake is completely dissolved. 0.4 L of water is added to obtain an iron-phosphorus liquid with low acidity and low impurities, and the pH value is 0.1, which is used to further synthesize qualified iron phosphate. The composition content of the low-acidity iron phosphate solution is shown in Table 4.

[0048] Table 4

[0049]

[0050] Embodiment 2:

[0051] A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag comprises the following steps:

[0052] (1) 100 g of waste iron phosphate was slurried with 200 mL of water, and then 200 g of concentrated sulfuric acid was slowly added and stirred for 1.5 h. The mass concentration of the concentrated sulfuric acid was 97%, and 500 g of iron-phosphorus liquid A was obtained. The composition and content of the waste iron phosphate are shown in Table 5.

[0053] Table 5

[0054]

[0055] (2) 919 g of lithium iron phosphorus slag was added to 4210 g of 10% sulfuric acid for leaching, stirred for 3 h, and filtered to obtain iron phosphorus liquid B.

[0056] The temperature was 60°C, and 4.25 L of iron-phosphorus liquid B and carbon black were obtained; the composition of the iron-phosphorus liquid B is shown in Table 6;

[0057] Table 6

[0058]

[0059]

[0060] (3) Add 754 g of 32% sodium hydroxide to the iron-phosphorus liquid B, control the end point pH value to 1.6, and then filter and wash to obtain 1361 g of amorphous iron phosphate filter cake (water content 65%);

[0061] (4) The amorphous iron phosphate filter cake obtained in step (3) was added to the iron-phosphorus liquid A obtained in step (1), and stirred until the filter cake was completely dissolved. 2 L of water was added to obtain an iron-phosphorus liquid with low acidity and low impurities, and the pH value was 0.22, which was used to further synthesize qualified iron phosphate. The composition content of the iron-phosphorus liquid with low acidity and low impurities is shown in Table 7.

[0062] Table 7

[0063]

[0064] Embodiment 3:

[0065] A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag comprises the following steps:

[0066] (1) 100 g of waste iron phosphate was slurried with 200 mL of water, and then 100 g of concentrated sulfuric acid was slowly added and stirred for 1 h. The mass concentration of the concentrated sulfuric acid was 98%, and 400 g of iron-phosphorus liquid A was obtained. The composition content of the waste iron phosphate is shown in Table 8;

[0067] Table 8

[0068]

[0069] (2) 919 g of lithium iron phosphorus slag was leached with 8420 g of 5% sulfuric acid, stirred for 1.5 h, and filtered to obtain 8.99 L of iron phosphorus liquid B and carbon black, the temperature was 60° C. The composition of the iron phosphorus liquid B is shown in Table 9;

[0070] Table 9

[0071]

[0072] (3) Add 2382 g of 20% ammonium bicarbonate to the iron-phosphorus liquid B, control the end point pH value to 1.8, and then filter and wash to obtain 1192 g of amorphous iron phosphate filter cake (water content 67%);

[0073] (4) adding the amorphous iron phosphate filter cake obtained in step (3) to the iron-phosphorus liquid A obtained in step (1), stirring until the filter cake is completely dissolved, adding 2.4 L of water, and obtaining an iron-phosphorus liquid with low acidity and low impurities, with a pH value of 0.8, for further synthesis of qualified iron phosphate; the composition content of the low-acidity iron phosphate solution is shown in Table 10;

[0074] Table 10

[0075]

[0076] The components of the iron-phosphorus liquid B, the iron-phosphorus liquid A and the iron-phosphorus liquid with low acidity obtained in the above-mentioned Example 1 were tested, and the test results are shown in the following table.

[0077] Table 11

[0078]

[0079] Comparative Example 1:

[0080] A method for pre-treating waste iron phosphate, comprising the following steps:

[0081] (1) Add water to the reworked or scrapped anhydrous ferric phosphate to prepare a slurry with a solid-liquid ratio of 1:2, then slowly add concentrated sulfuric acid with a concentration of 98% and a weight ratio of anhydrous ferric phosphate to concentrated sulfuric acid of 1:1.5, and stir until the anhydrous ferric phosphate is dissolved to obtain an iron-phosphorus liquid;

[0082] (2) Ammonia water is added to the iron-phosphorus solution to adjust the pH value to 1.8, and all the iron phosphate in the iron-phosphorus solution is precipitated.

[0083] The alkali consumption in the above Example 1 and Comparative Example 1 was calculated, and the calculation results are shown in the following table.

[0084] Table 12

[0085]

[0086] The low-acidity iron-phosphorus liquid obtained after treatment in Example 1-3 is further synthesized into qualified iron phosphate (its indicators are shown in Table 13), and then the iron phosphate is mixed with lithium carbonate and glucose in a stoichiometric ratio, the molar ratio of iron phosphate to lithium carbonate is 2:1, and the amount of glucose added accounts for 6% of the mass of the raw material mixture. The mixture is evenly mixed, and lithium iron phosphate is obtained by wet grinding, drying, high-temperature sintering and grinding. The drying temperature is 105°C and the time is 3h. The high-temperature sintering temperature is 750°C and the time is 9h. The performance experimental test results are shown in Table 14 below.

[0087] Table 13

[0088]

[0089] Table 14

[0090]

[0091] It should be noted that, in this article, the terms: include, contain and any other variants are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. Specific examples are used in this article to illustrate the principle and implementation of the technical solution of the present invention. The above examples are only used to help understand the method of the present invention and its core idea. The above is only a preferred implementation of the present invention. It should be pointed out that due to the limitations of textual expression and the objective existence of infinite specific structures, for ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements, modifications or changes can be made, and the above technical features can also be combined in an appropriate manner; these improvements, modifications, changes or combinations, or the direct application of the concept and technical solution of the present invention to other occasions without improvement, should be regarded as the protection scope of the present invention.

Claims

1. A low-cost purification process for waste iron phosphate and lithium iron phosphorus slag, characterized in that: The following steps are involved: (1) Adding water to the waste iron phosphate to prepare a slurry, and then slowly adding concentrated sulfuric acid, stirring until the waste iron phosphate is completely dissolved to obtain iron-phosphorus liquid A; (2) leaching the lithium iron-phosphorus slag with sulfuric acid and filtering it to obtain iron-phosphorus liquid B; (3) adding alkali to the iron-phosphorus solution B to control the end point pH value to 1-1.8, and then filtering and washing to obtain an amorphous iron phosphate filter cake; (4) adding the amorphous iron phosphate filter cake obtained in step (3) into the iron-phosphorus liquid A obtained in step (1), stirring until the filter cake is completely dissolved, thereby obtaining an iron-phosphorus liquid with low acidity and low impurities, which is used to further synthesize qualified iron phosphate.

2. A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag according to claim 1, characterized in that: The solid-liquid ratio during slurry preparation in step (1) is 1 g: 1-2 mL.

3. A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag according to claim 1, characterized in that: The mass concentration of concentrated sulfuric acid in step (1) is 95-98%.

4. A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag according to claim 1, characterized in that: In the step (1), the mass ratio of waste iron phosphate to concentrated sulfuric acid is 1:1-2.

5. A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag according to claim 1, characterized in that: The mass concentration of sulfuric acid in step (2) is 5-20%.

6. A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag according to claim 1, characterized in that: The leaching temperature in step (2) is 25-60°C.

7. A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag according to claim 1, characterized in that: In the step (3), the alkali is any one of sodium hydroxide solution, ammonia solution, ammonium bicarbonate solution, sodium bicarbonate solution and sodium carbonate solution. The concentration of sodium hydroxide solution is 2-32% by mass, the concentration of ammonia solution is 5-25% by mass, the concentration of ammonium bicarbonate solution is 5-28% by mass, the concentration of sodium bicarbonate solution is 5-10% by mass, and the concentration of sodium carbonate solution is 5-22% by mass.

8. A low-cost purification process for the combined treatment of waste iron phosphate and lithium iron phosphorus slag according to claim 1, characterized in that: The pH value of the low-acid iron-phosphorus solution in step (4) is 0-0.8.

Images