Ferric acid-base combined leaching and purifying process for crude phosphoric acid

Abstract

The invention discloses an acid-alkali combined leaching purification process for crude ferric phosphate, which belongs to the technical field of waste purification and comprises the following steps: step 1, adding ferric phosphate waste into an inorganic dilute acid solution for leaching, stirring, mixing, slurrying and filtering to obtain an acid leaching solution and acid leaching residues; step 2, adding caustic soda liquid into the iron phosphate waste for leaching, stirring, mixing, slurrying, and filtering to obtain a phosphorus salt solution and iron slag; 3, the iron slag obtained in the step 2 and the acid leaching solution obtained in the step 1 are neutralized, and iron phosphorus slurry or an iron phosphorus solution and neutralized filter residues are obtained through selective filtration; and 4, fully mixing the phosphorus salt solution obtained in the step 2 and the iron-phosphorus slurry or the iron-phosphorus solution obtained in the step 3 for reaction to obtain neutralized slurry, and filtering to obtain neutralized tail liquid and a purified iron phosphate filter cake. According to the method, a unique impurity removal and purification process is adopted, the use amount of acid and alkali is greatly reduced, and low-cost industrial production of purification and recovery of the iron phosphate waste is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste purification, and specifically relates to a purification process for crude iron phosphate by combined acid-base leaching. Background Art

[0002] During the process of recycling lithium carbonate from lithium battery waste, an iron-phosphorus slag mainly composed of iron phosphate is generated. Its impurity components vary greatly due to different lithium carbonate recovery processes, as shown in the following table. This poses relatively high requirements for the purification and impurity removal process, and the impurity removal process is relatively complex. In the prior art, during the wet impurity removal and purification process of iron phosphate waste, usually a relatively large amount of acid and alkali is required, resulting in high production costs.

[0003] Table 1 Composition table of iron-phosphorus slag raw materials for different lithium carbonate recovery processes

[0004]

[0005] In the prior art, the main component of the iron phosphate waste residue formed after wet recycling of lithium from the positive electrode waste of lithium-ion batteries is iron phosphate. To purify it, it is usually necessary to dissolve it into a solution with acid, and the acid in the solution requires an equivalent amount of alkali to be neutralized in subsequent processes; another treatment method for the iron phosphate waste residue is alkali leaching. The iron phosphate waste residue reacts with sodium hydroxide, and most of the metal impurities in the iron phosphate waste residue enter the iron hydroxide slag. If it is necessary to separate and remove the impurity metals and recover iron, it is necessary to dissolve the iron hydroxide slag with acid, so that a relatively large amount of acid and alkali is used. Summary of the Invention

[0006] In view of the above problems, the present invention provides a purification process for crude iron phosphate by combined acid-base leaching. The present invention uses a unique impurity removal and purification process, greatly reducing the amount of acid and alkali used, and realizing the industrial production of low-cost purification and recovery of iron phosphate waste.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A purification process for crude iron phosphate by combined acid-base leaching, comprising the following steps:

[0009] Step 1: Add iron phosphate waste to an inorganic dilute acid solution for leaching, stir and mix to form a slurry, and filter to obtain an acid leaching solution and an acid leaching residue;

[0010] Step 2: Add liquid alkali to the iron phosphate waste for leaching, stir and mix to form a slurry, and filter to obtain a phosphate solution and an iron slag;

[0011] Step 3: Neutralize the iron slag obtained in Step 2 and the acid leaching solution obtained in Step 1, and selectively filter to obtain an iron-phosphorus slurry or an iron-phosphorus solution and a neutralization filter residue;

[0012] Step 4: The phosphate salt solution obtained in step 2 and the iron-phosphorus slurry or iron-phosphorus solution obtained in step 3 are fully mixed and reacted to obtain a neutralized slurry, and the neutralized tail liquid and the purified iron phosphate filter cake are obtained by filtering.

[0013] In a preferred implementation, the inorganic dilute acid solution in step 1 is selected from any one or more combinations of sulfuric acid, phosphoric acid, nitric acid and hydrochloric acid, and the molar amount of hydrogen ions in the acid used is 0.6-4.0 times the molar amount of iron element in the ferric phosphate waste.

[0014] In a preferred implementation, the inorganic dilute acid solution in step 1 is preferably sulfuric acid, and the molar amount of sulfuric acid is 0.3-2.0 times the molar amount of iron element in the ferric phosphate waste.

[0015] In a preferred implementation, the liquid-to-solid ratio of the slurry in step 1 is 1-3 mL:1 g, the reaction temperature is 25-75° C., and the reaction time is 1.5-8 h.

[0016] In a preferred embodiment, the molar ratio of the amount of liquid caustic soda in step 2 to the amount of acid in step 1 is: - :H + =0.6-0.85:1, the amount of iron phosphate waste is controlled so that the molar ratio of liquid alkali to Na / P in the waste is 3.0-4.0:1; the liquid-solid ratio of the slurry is 2-5mL:1g, the reaction temperature is 50-95°C, and the reaction time is 1-5h.

[0017] In a preferred implementation, the neutralization reaction temperature in step 3 is 25-50° C., and the reaction time is 1-3 h.

[0018] In a preferred implementation, the selective filtration in step 3 is: when the ratio of the corresponding molar amount of hydrogen ions in the acid input for leaching in step 1 to the molar amount of iron element in the ferric phosphate waste is greater than 1.4, the iron-phosphorus solution and the neutralization residue are obtained by filtration; if it is lower than 1.4, the iron-phosphorus slurry is obtained directly without filtration.

[0019] In a preferred embodiment, the reaction temperature in step 4 is 25-50° C. and the reaction time is 1-3 h.

[0020] The reaction principle of the present invention is: the iron phosphate waste residue is subjected to acid leaching and alkali leaching at the same time, and then the iron hydroxide residue obtained by the alkali leaching is used to neutralize the excess acid in the acid leaching solution, the acid leaching solution is neutralized and filtered to obtain an iron phosphate solution, and then reacts with the alkali leaching solution to obtain relatively pure iron phosphate. The above-mentioned reaction equation is:

[0021] Acid leaching reaction: 2FePO 4 +3H 2 SO 4 =Fe 2 (SO 4) 3 +2H 3 PO 4

[0022] Alkali leaching reaction: FePO 4 +3NaOH = Fe(OH) 3 ↓+Na 3 PO 4

[0023] Neutralization reaction: 3H 3 PO 4 +3Fe(OH) 3 +3H 2 SO 4 =Fe(H 2 PO 4 ) 3 +Fe 2 (SO 4 ) 3 +9H 2 O /

[0024] 2Fe(OH) 3 +2Na 3 PO 4 +3H 2 SO 4 =2FePO 4 ↓+3Na 2 SO 4 +6H 2 O;

[0025] The essence of the above reactions is that the liquid alkali originally used to neutralize sulfuric acid in the acid leaching solution is first used for alkali leaching of iron phosphate waste residue, and then the alkali leaching product is used to neutralize the acid leaching solution, so as to obtain the effect of treating more iron phosphate slag with the same amount of acid and alkali, and the acid and alkali consumption cost per unit product is greatly reduced.

[0026] The beneficial effects of the present invention are as follows: by using the iron hydroxide slag generated in the alkali leaching step to neutralize the excessive acid in the acid leaching solution, the present invention realizes the recycling of acid and alkali, avoids the redundant step of separately using alkali to neutralize the acid leaching solution in the traditional process, and the amorphous iron phosphate filter cake produced has higher chemical activity and is suitable for the precursor of the cathode material of lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the process flow chart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] In order to enable those skilled in the art to better understand the technical solution, the present invention will be described in detail below with reference to the embodiments. The description of this part is only exemplary and explanatory, and should not have any restrictive effect on the protection scope of the present invention.

[0029] In the following examples and comparative examples, the raw materials and the components of the obtained iron phosphate filter cake were determined by the ICP component detection method.

[0030] Example 1:

[0031] The composition of the iron phosphate waste, i.e., iron phosphate slag, in this example is shown in the following table:

[0032] Table 2 Composition Table of Iron Phosphate Slag Raw Materials in Example 1

[0033]

[0034] A crude iron phosphate acid-base combined leaching and purification process includes the following steps:

[0035] Step 1: Prepare 500 g of iron phosphate slag, add 1000 mL of 6% dilute sulfuric acid solution for leaching, stir and mix to form a slurry, react at 25 °C for 3 h, and after the reaction, perform suction filtration to obtain 1184 mL of acid leaching solution and 389 g of acid leaching residue;

[0036] Step 2: Prepare 78 g of iron phosphate slag, add 233 mL of 12.8% dilute liquid alkali solution for leaching, stir and mix to form a slurry, react at 50 °C for 3 h, and perform suction filtration to obtain 225 mL of phosphate solution and 82 g of iron slag;

[0037] Step 3: At 26 °C, after neutralizing and reacting the iron slag obtained in Step 2 and the acid leaching solution obtained in Step 1 for 1 h, an iron phosphate slurry is obtained;

[0038] Step 4: Use a peristaltic pump to control the flow rate and add the phosphate solution obtained in Step 2 to the iron phosphate slurry obtained in Step 3 within 1 h, fully mix and continue to stir for 30 min to obtain a neutralized slurry, and filter to obtain 1150 mL of neutralized tail liquid and 436 g of purified iron phosphate filter cake. The composition of this filter cake is shown in the following table.

[0039] Table 3 Composition Table of Amorphous Iron Phosphate Filter Cake after Purification in Example 1

[0040]

[0041] Example 2:

[0042] The composition of the iron phosphate waste, i.e., iron phosphate slag, in this example is shown in the following table:

[0043] Table 4 Composition Table of Iron Phosphate Slag Raw Materials in Example 2

[0044]

[0045] A crude iron phosphate acid-base combined leaching and purification process includes the following steps:

[0046] Step 1: Prepare 1000 g of iron phosphate slag, add 1000 mL of 23.2% dilute sulfuric acid solution for leaching, stir and mix to form a slurry, react at 75 °C for 2 h, and after the reaction, perform suction filtration to obtain 1682 mL of acid leaching solution and 503 g of acid leaching residue;

[0047] Step 2: Prepare 215 g of iron phosphate slag, add 430 mL of 26.46% dilute liquid alkali solution for leaching, stir and mix to form a slurry, react at 80 °C for 2 h, and perform suction filtration to obtain 385 mL of phosphate solution and 279 g of iron slag;

[0048] Step 3: At 30 °C, after neutralization reaction of the iron slag obtained in Step 2 and the acid leaching solution obtained in Step 1 for 1 h, iron phosphate slurry is obtained;

[0049] Step 4: Use a peristaltic pump to control the flow rate and add the phosphate solution obtained in Step 2 to the iron phosphate slurry obtained in Step 3 within 2 h, fully mix and continue stirring for 30 min to obtain neutralized slurry, and filter to obtain 1086 mL of neutralized tail liquid and 1458 g of purified iron phosphate filter cake. The composition of this filter cake is shown in the following table.

[0050] Table 5 Composition Table of Amorphous Iron Phosphate Filter Cake after Purification in Example 2

[0051]

[0052] Example 3:

[0053] The composition of the iron phosphate waste, i.e., iron phosphate slag, in this example is shown in the following table:

[0054] Table 6 Composition Table of Iron Phosphate Slag Raw Material in Example 3

[0055]

[0056]

[0057] A process for purifying crude iron phosphate by combined acid-base leaching includes the following steps:

[0058] Step 1: Prepare 1000 g of iron phosphate slag, add 3000 mL of 17.38% dilute sulfuric acid solution for leaching, stir and mix to form a slurry, react at 50 °C for 2 h, and after the reaction, perform suction filtration to obtain 3460 mL of acid leaching solution and 406 g of acid leaching residue;

[0059] Step 2: Prepare 453 g of iron phosphate slag, add 1359 mL of 15.48% dilute liquid alkali solution for leaching, stir and mix to form a slurry, react at 95 °C for 3 h, and perform suction filtration to obtain 1110 mL of phosphate solution and 548.4 g of iron slag;

[0060] Step 3: At 50 °C, neutralize the iron slag obtained in Step 2 and the acid leaching solution obtained in Step 1 for 3 h and then filter to obtain 4002 mL of iron phosphate solution and 154.6 g of neutralization filter residue;

[0061] Step 4: Use a peristaltic pump to control the flow rate and add the phosphate solution obtained in Step 2 to the iron phosphate solution obtained in Step 3 within 3 h, mix well and continue stirring for 30 min to obtain neutralized slurry, and filter to obtain 2475 mL of neutralization tail liquid and 3202 g of purified iron phosphate filter cake.

[0062] Table 7 Composition Table of Amorphous Iron Phosphate Filter Cake after Purification in Example 3

[0063]

[0064] Comparative Example 1:

[0065] The composition of the iron phosphate waste, i.e., iron phosphate slag, in this comparative example is shown in the following table:

[0066] Table 8 Composition Table of Iron Phosphate Slag Raw Material in Comparative Example 1

[0067]

[0068] A crude iron phosphate acid-base combined leaching and purification process includes the following steps:

[0069] (1) Primary leaching: Prepare 500 g of the above iron phosphate slag, add 1000 mL of 6% dilute sulfuric acid solution and mix evenly, react at room temperature for three hours, and after the reaction, perform suction filtration to obtain 1152 mL of primary leaching solution and 392 g of primary acid leaching residue.

[0070] (2) Primary synthesis: Weigh 107 g of 32% liquid caustic soda, and then use a peristaltic pump to control the flow rate and add the liquid caustic soda to the primary leaching solution obtained in (1) within 2 h. After the addition, continue stirring for 30 min and then filter to obtain 488 g of primary purified iron phosphate filter cake and 1475 mL of primary neutralization tail liquid. The data of this filter cake is as follows.

[0071] Table 9 Composition Table of Amorphous Iron Phosphate Filter Cake after Purification in Comparative Example 1

[0072]

[0073] Comparative Example 2:

[0074] The composition of the iron phosphate waste, i.e., iron phosphate slag, in this comparative example is shown in the following table:

[0075] Table 10 Composition Table of Iron Phosphate Slag Raw Material in Comparative Example 2

[0076]

[0077] A process for purifying crude iron phosphate by combined acid-base leaching, comprising the following steps:

[0078] (1) Primary leaching: Prepare 1000 g of the above-mentioned iron phosphate slag, add 3000 mL of 17.38% sulfuric acid solution and mix evenly, react at 50 °C for 2 h, and after the reaction, perform suction filtration to obtain 3430 mL of primary leaching solution and 417 g of primary acid leaching residue.

[0079] (2) Primary synthesis: Weigh 657 g of 32% liquid caustic soda, and then use a peristaltic pump to control the flow rate to add the liquid caustic soda into the primary leaching solution obtained in (1) within 3 h. After the addition, continue stirring for 30 min and then filter to obtain 2075 g of primary purified iron phosphate filter cake and 2220 mL of primary neutralization tail liquid. The data of this filter cake is as follows.

[0080] Table 11 Composition table of the amorphous iron phosphate filter cake after purification in Comparative Example 2

[0081]

[0082] Compare the process treatment costs of Examples 1-3 and Comparative Examples 1-2, and the comparison results are shown in the following table.

[0083] Table 12 Comparison table of treatment costs between examples and comparative examples

[0084]

[0085]

[0086] It can be seen from the comparison between Example 1 and Comparative Example 1 that the treatment cost has decreased by 13.49%, while in Example 3 and Comparative Example 2, the treatment cost has decreased by 31.18%.

[0087] It should be noted that in this article, the terms: including, containing and any other variants are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to this process, method, article or device. Specific examples are used in this article to elaborate on the principle and implementation mode of the technical solution of the present invention. The description of the above examples is only used to help understand the method and its core idea of the present invention. The above is only the preferred implementation mode of the present invention. It should be pointed out that due to the limited nature of language expression, and objectively there are infinite specific structures. For those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements, retouches or changes can be made, or the above technical features can be combined in an appropriate manner; these improvements, retouches, changes or combinations, or directly applying the concept and technical solution of the present invention to other occasions without improvement, should all be regarded as the protection scope of the present invention.

Claims

1. A crude ferric phosphate acid-base combined leaching and purification process, characterized in that: The following steps are involved: Step 1: adding the iron phosphate waste to an inorganic dilute acid solution for leaching, stirring and mixing to form a slurry, and filtering to obtain an acid leaching solution and an acid leaching residue; Step 2: adding liquid alkali to the iron phosphate waste to leach it, stirring and mixing it into a slurry, and filtering it to obtain a phosphate solution and iron slag; Step 3: neutralizing the iron slag obtained in step 2 and the acid leaching solution obtained in step 1, and selectively filtering to obtain an iron-phosphorus slurry or an iron-phosphorus solution and a neutralized filter residue; Step 4: The phosphate salt solution obtained in step 2 and the iron-phosphorus slurry or iron-phosphorus solution obtained in step 3 are fully mixed and reacted to obtain a neutralized slurry, and the neutralized tail liquid and the purified iron phosphate filter cake are obtained by filtering.

2. A crude ferric phosphate acid-base combined leaching and purification process according to claim 1, characterized in that: The inorganic dilute acid solution in step 1 is selected from any one or more combinations of sulfuric acid, phosphoric acid, nitric acid and hydrochloric acid, and the molar amount of hydrogen ions in the acid used is 0.6-4.0 times the molar amount of iron element in the ferric phosphate waste.

3. A crude ferric phosphate acid-base combined leaching and purification process according to claim 1, characterized in that: The inorganic dilute acid solution in step 1 is preferably sulfuric acid, and the molar amount of sulfuric acid is 0.3-2.0 times the molar amount of iron element in the ferric phosphate waste.

4. A crude ferric phosphate acid-base combined leaching and purification process according to claim 1, characterized in that: The liquid-to-solid ratio of the slurry in step 1 is 1-3 mL: 1 g, the reaction temperature is 25-75° C., and the reaction time is 1.5-8 h.

5. A crude ferric phosphate acid-base combined leaching and purification process according to claim 1, characterized in that: The molar ratio of the amount of liquid alkali in step 2 to the amount of acid in step 1 is: - :H + =0.6-0.85:1, the amount of iron phosphate waste is controlled so that the molar ratio of liquid alkali to Na / P in the waste is 3.0-4.0:1; the liquid-solid ratio of the slurry is 2-5mL:1g, the reaction temperature is 50-95°C, and the reaction time is 1-5h.

6. A crude ferric phosphate acid-base combined leaching and purification process according to claim 1, characterized in that: In step 3, the neutralization reaction temperature is 25-50° C., and the reaction time is 1-3 h.

7. A crude ferric phosphate acid-base combined leaching and purification process according to claim 1, characterized in that: The selective filtration in step 3 is: when the ratio of the corresponding molar amount of hydrogen ions in the acid put into the leaching in step 1 to the molar amount of iron element in the iron phosphate waste is greater than 1.4, the iron-phosphorus solution and the neutralization filter residue are obtained by filtration; if it is less than 1.4, the iron-phosphorus slurry is directly obtained without filtering.

8. A crude ferric phosphate acid-base combined leaching and purification process according to claim 1, characterized in that: In step 4, the reaction temperature is 25-50° C. and the reaction time is 1-3 h.

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