Impurity removal and purification method for leachate

Abstract

The impurity removal and purification method comprises the following steps: (1) removing iron and aluminum step by step: controlling the temperature of the leachate to be 45-50 DEG C, adjusting the pH value to be less than or equal to 3, and taking a saturated calomel electrode as a reference and an oxidation-reduction potential gt; the voltage is 400 mV; (2) extraction and reverse extraction: under the condition that the pH value of the leachate is 3.5-4.0, extracting Mn < 2 + > in the leachate by using an extracting agent P204 with the volume concentration of 20-30% and the saponification rate of 60-70%; (3) membrane separation and deep purification: firstly removing Ca < 2 + > and Mg < 2 + > from the manganese-rich liquid through carboxylic acid type chelating resin, and then filtering SO4 < 2-> by using a nanofiltration membrane; the method is high in heavy metal ion removal rate and low in cost, and avoids the risk of vulcanizing agent residue.

Description

Technical Field

[0001] This invention relates to the field of electrolytic manganese dioxide preparation technology, and specifically to a method for removing impurities and purifying leachate. Background Technology

[0002] Electrolytic manganese dioxide (EMD) is an excellent depolarizer for batteries. Compared with dry batteries produced by natural discharge manganese dioxide, it has the characteristics of large discharge capacity, strong activity, small size and long life. Therefore, electrolytic manganese dioxide has become a particularly important raw material in the battery industry.

[0003] Depending on the raw materials, electrolytic manganese dioxide production methods can be divided into manganese carbonate ore method, manganese oxide reduction roasting method, and "two-ore" method. Currently, the manganese carbonate ore method is mostly used in China. This involves leaching manganese carbonate ore powder with sulfuric acid to obtain manganese sulfate solution, followed by impurity removal, purification, and electrolysis. The impurities in the leaching solution usually include iron ions, aluminum ions, and some heavy metal ions. The current impurity removal and purification methods have problems such as high cost, risk of sulfiding agent residue, and low removal rate of heavy metal ions, which need to be improved. Summary of the Invention

[0004] The purpose of this invention is to provide a method for removing impurities and purifying leachate to solve the problems existing in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for removing impurities from a leachate, comprising the following steps:

[0006] (1) Stepwise removal of iron and aluminum: control the temperature of the leachate at 45-50℃, adjust the pH to ≤3, use a saturated calomel electrode as a reference, ensure the redox potential is >400mV, and introduce 10-20ppm of ozone to remove Fe. 2+ Oxidized to Fe 3+ Then adjust the pH to 3.5-4.0 to precipitate Fe. 3 + After filtration, while maintaining the pH of the filtrate at ≤3, continue to introduce ozone at 5-10 ppm to oxidize the residual Fe. 2+ Then adjust the pH to 5.0-5.5 to precipitate Al. 3+ And filter;

[0007] (2) Extraction and back-extraction: Under the condition of pH 3.5-4.0 of the leachate, extractant P204 with a volume concentration of 20-30% and a saponification rate of 60-70% is used to extract Mn from the leachate. 2+ The extraction time is 15-20 min. The extract is back-extracted with dilute sulfuric acid with a concentration of 0.8 mol / L to obtain a manganese-rich solution. The pH of the raffinate is adjusted to 6.0-6.5, and heavy metal concentration ≤0.5 mg / L is adsorbed by mercapto resin or iminodiacetic acid resin before being discharged.

[0008] (3) Membrane separation for deep purification: The manganese-rich solution is first treated with a carboxylic acid chelating resin to remove Ca. 2+ Mg 2+ Then, SO4 is filtered using a nanofiltration membrane. 2- The nanofiltration membrane is a polyamide composite membrane with a molecular weight cutoff of 200-300 Da and an operating pressure of 1.5-2.0 MPa. The nanofiltration membrane is periodically backwashed using pulses. The manganese-rich solution, after impurity removal by the nanofiltration membrane, is concentrated to Mn. 2+ ≤1.2mol / L, which meets the requirements for electrolyte inlet.

[0009] As a preferred technical solution, the extraction adopts three-stage countercurrent extraction.

[0010] As a preferred technical solution, the carboxylic acid chelating resin is regenerated with 5% hydrochloric acid for 30-60 minutes, and the number of regenerations is ≤20 times / year.

[0011] As a preferred technical solution, the periodic pulse backwash is a 30-second backwash every 2 hours.

[0012] Compared with the prior art, the beneficial effects of the present invention are:

[0013] 1. This invention controls Fe in stages by adjusting the pH value. 3+ And Al 3+ It achieves high separation of oxidation and precipitation, minimal manganese loss, and reduces the amount of adjustment reagent required.

[0014] 2. This invention improves the recovery rate of manganese through extraction, back-extraction, and the use of nanofiltration membranes.

[0015] 3. This invention uses resin adsorption, which has a good effect on heavy metal removal, reduces regeneration costs, and reduces the addition of sulfur in traditional processes. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. 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.

[0017] Example 1: A method for removing impurities from a leachate, comprising the following steps: (1) Stepwise removal of iron and aluminum: controlling the leachate temperature to 50°C, adjusting the pH to 3, using a saturated calomel electrode as a reference, setting the oxidation-reduction potential to 420 mV, and introducing 20 ppm of ozone to remove Fe 2+ Oxidized to Fe 3+ Then adjust the pH to 3.5 to precipitate Fe.3+ After filtration, while maintaining the pH of the filtrate at 3, ozone at 10 ppm was continuously introduced to oxidize the residual Fe. 2+ Then adjust the pH to 5.0 to precipitate Al. 3+ After filtration, the redox potentiometer uses a platinum electrode as the working electrode. After immersing the electrode in the solution, it is allowed to stand for at least 30 minutes before taking a reading to ensure potential stability. pH adjustment is achieved by adding sodium hydroxide. At pH=3, the ozone oxidation efficiency was measured to be 98%, and Fe... 3+ Selective precipitation of Fe at pH 3.5 3+ Precipitation rate 95%, residual Al 3+ 8 mg / L; Al at pH=4.0 3+ Precipitation rate 97%, Al 3+ Separate precipitation at pH 5.5 avoids manganese loss caused by co-precipitation of iron and aluminum. (2) Extraction and back-extraction: Under the condition of pH 3.5 of the leachate, extractant P204 with a volume concentration of 20% and a saponification rate of 70% is used to extract Mn from the leachate. 2+ Extraction time 20 min, three-stage countercurrent extraction, single-stage extraction rate 84%, the extract was back-extracted with 0.8 mol / L dilute sulfuric acid to obtain manganese-rich solution; the raffinate was adjusted to pH 6.0 and then discharged after adsorbing heavy metal concentration ≤0.5 mg / L with mercapto resin; (3) Membrane separation deep purification: the manganese-rich solution was first treated with carboxylic acid chelating resin to remove Ca 2+ Mg 2+ The carboxylic acid chelating resin is regenerated using 5% hydrochloric acid for 60 minutes, with a regeneration frequency of 20 times per year. SO4 is then filtered using a nanofiltration membrane. 2- The nanofiltration membrane is a polyamide composite membrane with a molecular weight cutoff of 300 Da and an operating pressure of 1.5 MPa. The nanofiltration membrane effectively filters SO42-. 2- With a rejection rate of 94%, the nanofiltration membrane is periodically backwashed by pulses. The manganese-rich solution after impurity removal by the nanofiltration membrane is concentrated to Mn. 2+ 1.2 mol / L, which meets the requirements for electrolyte inlet, and periodic pulse backwashing is a 30-second reverse flush every 2 hours.

[0018] Example 2: A method for removing impurities from a leachate, comprising the following steps: (1) Stepwise removal of iron and aluminum: controlling the leachate temperature at 45°C, adjusting the pH to 2, using a saturated calomel electrode as a reference, setting the oxidation-reduction potential to 500 mV, and introducing 10 ppm of ozone to remove Fe 2+ Oxidized to Fe 3+ Then adjust the pH to 4.0 to precipitate Fe. 3+ After filtration, while maintaining the filtrate at pH 2, ozone at 5 ppm was continuously introduced to oxidize the residual Fe. 2+ Then adjust the pH to 5.5 to precipitate Al. 3+And filtered; at pH=2, the ozone oxidation efficiency was measured to be 97%, Fe 3+ Selective precipitation of Fe at pH 3.8 3+ Precipitation rate 96%, residual Al 3+ 9 mg / L; Al³⁺ precipitation rate of 96% at pH=4.0, Al 3+ Separate precipitation at pH 5.8. (2) Extraction and back-extraction: Under the condition of pH 4.0 of the leachate, extractant P204 with a volume concentration of 30% and a saponification rate of 60% was used to extract Mn from the leachate. 2+ The extraction time was 15 min, and a three-stage countercurrent extraction method was used, with a single-stage extraction rate of 89%. The extract was back-extracted with 0.8 mol / L dilute sulfuric acid to obtain a manganese-rich solution. The raffinate was first adjusted to pH ≤ 4, and then subjected to a second extraction with 10% (v / v) extractant P204 to extract residual Mn. 2+ Mn after secondary extraction 2+ <0.01g / L, then the raffinate is adjusted to pH 6.5, and heavy metal concentration ≤0.5mg / L is adsorbed by iminodiacetic acid resin before discharge. (3) Membrane separation deep purification: The manganese-rich solution is first treated with carboxylic acid chelating resin to remove Ca 2+ Mg 2+ The carboxylic acid chelating resin is regenerated using 5% hydrochloric acid for 30 minutes, with a regeneration frequency of 18 times per year. SO4 is then filtered using a nanofiltration membrane. 2- The nanofiltration membrane is a polyamide composite membrane with a molecular weight cutoff of 200 Da and an operating pressure of 2.0 MPa. The nanofiltration membrane effectively filters SO42-. 2- With a rejection rate of 90%, the nanofiltration membrane is periodically backwashed using pulses, i.e., backwashed for 30 seconds every 2 hours. The manganese-rich solution after impurity removal by the nanofiltration membrane is concentrated to Mn. 2+ ≤1.2mol / L, which meets the requirements for electrolyte inlet.

[0019] Example 3: A method for removing impurities from a leachate, comprising the following steps: (1) Stepwise removal of iron and aluminum: controlling the leachate temperature at 48°C, adjusting the pH to 2.5, using a saturated calomel electrode as a reference, setting the redox potential to 450 mV, and introducing 16 ppm of ozone to remove Fe 2+ Oxidized to Fe 3+ Then adjust the pH to 3.8 to precipitate Fe. 3+ After filtration, while maintaining the filtrate at pH 2.5, ozone at 8 ppm was continuously introduced to oxidize the residual Fe. 2+ Then adjust the pH to 5.2 to precipitate Al. 3+ And filtered; at pH=2.5, the ozone oxidation efficiency was measured to be 96%, Fe 3+ Selective precipitation of Fe at pH 3.6 3+ Precipitation rate 98%, residual Al3+ Al at 6 mg / L; pH=5.2 3+ Precipitation rate 97%, Al 3+ Separate precipitation at pH 5.5. (2) Extraction and back-extraction: Under the condition of pH 3.8 of the leachate, extractant P204 with a volume concentration of 25% and a saponification rate of 65% was used to extract Mn from the leachate. 2+ The extraction time was 17 min, and the extraction was carried out by three-stage countercurrent extraction with a single-stage extraction rate of ≥85%. The extract was back-extracted with dilute sulfuric acid with a concentration of 0.8 mol / L to obtain a manganese-rich solution; the raffinate was adjusted to pH 6.4 and then discharged after adsorption of heavy metal concentration ≤0.5 mg / L by mercapto resin; (3) Membrane separation for deep purification: the manganese-rich solution was first treated with carboxylic acid chelating resin to remove Ca 2+ Mg 2+ The carboxylic acid chelating resin is regenerated using 5% hydrochloric acid for 50 minutes, with a regeneration frequency of 16 times per year. SO4 is then filtered using a nanofiltration membrane. 2- The nanofiltration membrane is a polyamide composite membrane with a molecular weight cutoff of 250 Da and an operating pressure of 1.8 MPa. The nanofiltration membrane effectively filters SO42-. 2- With a rejection rate of 92%, the nanofiltration membrane is periodically backwashed by pulses, i.e., backwashed for 30 seconds every 2 hours. The manganese-rich solution after impurity removal by the nanofiltration membrane is concentrated to Mn. 2+ ≤1.2mol / L, which meets the requirements for electrolyte inlet.

[0020] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for removing impurities and purifying a leachate, characterized in that, Includes the following steps: (1) Stepwise removal of iron and aluminum: control the temperature of the leachate at 45-50℃, adjust the pH to ≤3, use a saturated calomel electrode as a reference, ensure the redox potential is >400mV, and introduce 10-20ppm of ozone to remove Fe. 2+ Oxidized to Fe 3+ Then adjust the pH to 3.5-4.0 to precipitate Fe. 3+ After filtration, while maintaining the pH of the filtrate at ≤3, continue to introduce ozone at 5-10 ppm to oxidize the residual Fe. 2+ Then adjust the pH to 5.0-5.5 to precipitate Al. 3+ And filter; (2) Extraction and back-extraction: Under the condition of pH 3.5-4.0 of the leachate, extractant P204 with a volume concentration of 20-30% and a saponification rate of 60-70% is used to extract Mn from the leachate. 2+ The extraction time is 15-20 min. The extract is back-extracted with dilute sulfuric acid with a concentration of 0.8 mol / L to obtain a manganese-rich solution. The pH of the raffinate is adjusted to 6.0-6.5, and heavy metal concentration ≤0.5 mg / L is adsorbed by mercapto resin or iminodiacetic acid resin before being discharged. (3) Membrane separation for deep purification: The manganese-rich solution is first treated with a carboxylic acid chelating resin to remove Ca. 2+ Mg 2+ Then, SO4 is filtered using a nanofiltration membrane. 2- The nanofiltration membrane is a polyamide composite membrane with a molecular weight cutoff of 200-300 Da and an operating pressure of 1.5-2.0 MPa. The nanofiltration membrane is periodically backwashed using pulses. The manganese-rich solution, after impurity removal by the nanofiltration membrane, is concentrated to Mn. 2+ ≤1.2mol / L, which meets the requirements for electrolyte inlet.

2. The method according to claim 1, characterized in that: The extraction process employed a three-stage countercurrent extraction method.

3. The method according to claim 1, characterized in that: The carboxylic acid chelating resin is regenerated using 5% hydrochloric acid for 30-60 minutes, with a regeneration frequency of ≤20 times per year.

4. The method according to claim 1, characterized in that: The periodic pulse backwash is a 30-second backwash every 2 hours.