A method for removing and recovering sodium from high-sodium zinc electrolysis wastewater

Abstract

The present invention discloses a method for removing and recovering sodium from high-sodium zinc electrolysis waste liquid. Pure ferrous sulfate and copper sulfate are added to the high-sodium zinc electrolysis waste liquid, stirred and dissolved to adjust the pH to 1.5±0.1, pressurized with oxygen-enriched air, reacted at high temperature for 2-3 hours, depressurized and cooled to 95±5°C, then slowly stirred, reacted for 0.5-1 hour, allowed to stand for more than 2 hours, and filtered to obtain natronaite crystals and a low-sodium zinc sulfate filtrate. The crystallized product is washed with weak alkaline water and dried to obtain a polyferric sulfate water purifier product. The present invention not only removes sodium ions, a harmful impurity in high-sodium zinc electrolysis waste liquid, but also recycles sodium ions to obtain natronaite crystals (polyferric sulfate) water purifier products. At the same time, sulfuric acid, copper, manganese, zinc, etc. in the solution are returned to electrolytic zinc production. Compared with other sodium removal processes, the process has low cost, good economic benefits, and good environmental protection.

Description

Technical Field

[0001] The invention belongs to the field of hydrometallurgy and comprehensive recovery, and particularly relates to a method for removing and recovering sodium from zinc electrolysis waste liquid with a high sodium content. Background Art

[0002] Sodium ions are often present in the solution of hydrometallurgical zinc smelting and are difficult to remove, leading to open circuit accumulation. When concentrations exceed 10g / L, they can impact electrolytic zinc production. When they exceed 50g / L, they can severely impact zinc electrolysis. These impacts primarily increase the resistance of the zinc electrolyte, consuming unnecessary energy and generating heat, increasing the cooling burden of the electrolytic zinc, and causing thermal acid resolubilization of the electrolytic zinc, impacting the surface quality of the zinc flakes and current efficiency. Furthermore, sodium sulfate crystals can easily form on production pipelines and container walls, hindering liquid transport and causing filter press cloth to harden.

[0003] It is well known that simple sodium salts, such as sodium sulfate, sodium chloride, and sodium nitrate, have high solubility in both water and acid solutions, exceeding 100 g / L. Furthermore, they resist hydrolysis and precipitation reactions across the entire pH range and are not easily removed by adsorbents or separated by extractants or ion exchangers. Therefore, their accumulation in zinc sulfate solutions is inevitable. When sodium ion accumulation severely impacts smooth production, companies typically remove a portion of the electrolytic wastewater, neutralize it with alkali or lime to a pH of 7-8, and then hydrolyze zinc hydroxide to precipitate and recover zinc, discharging the sodium sulfate solution. This allows the sodium ions to open the circuit and dilute the sodium content in the zinc sulfate solution. Because zinc electrolytic wastewater contains low zinc and high acid content, open-circuit sodium ion discharge during neutralization and hydrolysis of zinc hydroxide results in significant alkali or lime consumption, leading to both sulfuric acid and mechanical zinc losses. This open-circuit sodium discharge is costly. This conventional treatment method, which involves consuming alkali and sulfuric acid during neutralization, also requires sulfuric acid dissolution to recover zinc from zinc hydroxide, increasing acid consumption.

[0004] The sodium sulfate discharged by the hydrolysis of zinc hydroxide has little value and use, and will only increase the workload of environmental protection management. At present, in the hydrometallurgy of zinc, there is no better method than the hydrolysis of zinc hydroxide to discharge sodium, which is low-cost, high-efficiency, low-pollution, and can comprehensively recover zinc, acid, and sodium. Summary of the Invention

[0005] The object of the present invention is to provide a method for removing and recovering sodium from zinc electrolysis wastewater with a high sodium content. The method removes sodium from the zinc electrolysis wastewater with a high sodium content and uses natronasite crystals (polyferric sulfate) as a water purifier product to achieve low-cost and high-efficiency comprehensive recovery of zinc, sulfuric acid and sodium.

[0006] The technical solution of the present invention:

[0007] A method for removing and recovering sodium from zinc electrolysis wastewater with a high sodium content is implemented by the following steps:

[0008] Step 1: Add ferrous sulfate or iron filings to the high sodium zinc electrolysis wastewater to dissolve, mix well, and measure the ferrous ion and sodium ion content in the solution;

[0009] Step 2: Adjust the ratio of ferrous ions and sodium ions and the pH value of the solution in step 1, and then add copper sulfate solution or solid and mix evenly; wherein: iron / sodium = 4-6, pH = 1.5±0.1, the amount of copper ions added is the copper ion mass solution volume ratio of g:L = 0.1-0.5, or the copper sulfate pentahydrate mass solution volume ratio of g:L = 2.56-5.12;

[0010] Step 3: Place the mixed solution from step 2 in a pressure autoclave, pressurize it with oxygen-enriched air with an oxygen content of 30±5%, and heat and stir to react for 2-3 hours;

[0011] Step 4: The reaction solution in step 3 was depressurized and cooled, and then slowly stirred for 0.5-1 hour and then allowed to stand for 2 hours;

[0012] Step 5: Filter the static solution of step 4 to obtain sodium ferroaluminate crystals, wash and dry them to obtain polyferric sulfate water purifier, and the low-sodium zinc electrolysis waste liquid is sent to zinc production for use.

[0013] Furthermore, the high sodium content zinc electrolysis waste liquid in step 1 contains sodium ions ≥10 g / L, pH ≤1.5 or a sulfuric acid content of 100-150 g / L, zinc ions ≤60 g / L, and manganese ions ≤5 g / L.

[0014] Furthermore, the oxygen-enriched air in step 3 contains 30±5% oxygen, is pressurized to 0.3-0.5 MPa or 3-5 kg / m2, is heated to 120-150° C., and is mechanically stirred at a rate of 50-200 r / min.

[0015] Furthermore, in step 4, the pressure is released to normal pressure, the temperature is lowered to 95±5° C., and then stirred with oxygen-enriched air for 0.5-1 hour.

[0016] Furthermore, the washing and drying in step 5 is washing 2-3 times with 40-50° C. hot water or weak alkaline water and then drying.

[0017] Working principle and innovation of the present invention:

[0018] 1. The chemical reaction process of the present invention is

[0019] 3Fe2(SO4)3+12H2O+Na2SO4=Na2Fe6(SO4)4(OH) 12 +6H2SO4 (1)

[0020] 2FeSO4+O2+2H2SO4 Fe2(SO4)3+2H2O (2)

[0021] Fe+2H2SO4+1 / 2O= FeSO4+H2O (3)

[0022] From the reaction formula (1), it can be seen that when Fe2(SO4)3 is directly added to the high sodium content zinc electrolysis wastewater, sodium is eliminated to generate Na2Fe6(SO4)4(OH) 12 The crystallization of natronaite cannot occur smoothly without neutralizing the acid released with alkali or lime. However, according to formula (2) or formula (3), using ferrous ions to react under oxidizing conditions, the oxidation of divalent iron to trivalent iron requires the participation of sulfuric acid. Therefore, it is entirely feasible to use divalent ferrous ions to oxidize and react, remove sodium from the high-sodium zinc electrolysis wastewater, and generate natronaite crystals. The present invention requires that the amount of ferrous ions used must be iron / sodium ≥ 4. In addition to meeting the amount of iron required by the natronaite molecule, the sulfuric acid released by the oxidation of ferrous ions to iron ions must be balanced to ensure that the entire sodium removal and recovery system can proceed smoothly without the additional consumption of alkali or lime. The sulfuric acid in the zinc electrolysis wastewater can also be returned to production for use, thereby reducing the cost of sodium removal. Therefore, the present invention is superior to other sodium removal processes and is innovative.

[0023] 2. The second innovation of this invention is the use of oxygen-enriched air to oxidize ferrous ions to ferric ions under pressure and at high temperature in the presence of copper ions, rather than directly adding strong oxidants such as potassium permanganate or hydrogen peroxide to oxidize ferrous ions to ferric ions. This is because strong oxidants such as potassium permanganate and hydrogen peroxide oxidize rapidly, easily causing an instantaneous accumulation of excess iron ions, resulting in hydrolysis of other iron to form FeOOH (goethite) or Fe(OH)3 precipitates. The hydrolysis pH of the iron ions can begin at pH 1.7. These hydrolysis products waste iron without expelling sodium, and also affect the purity of the natanthal jarosite crystals. Oxidants such as potassium permanganate, hypochlorite, and nitrates introduce other impurities into the system, increasing the difficulty of purification in electrolytic zinc production. Potassium ions also preferentially react with ferric sulfate to form jarosite, rather than expelling sodium. Oxidizing ferrous ions to ferric ions using air is relatively slow and time-consuming, but adding a copper ion catalyst greatly accelerates the oxidation process. Furthermore, the use of pressure and high temperature oxidation is even faster, ensuring the required iron ion content for the natanthal jarosite reaction. Production practice has proved that air oxidation technology is the lowest cost among other oxidant oxidation technologies.

[0024] 3. The third feature of the present invention is that after high temperature and pressure are applied to ferrous oxide ions to react with ferric ions to generate sodium ferrosite, the pressure is released, the temperature is lowered, and the reaction is allowed to stand for more than 2 hours before filtering and separating sodium ferrosite and zinc sulfate solution. This is because all crystalline products generated by the reaction have a crystal seed generated, seeded, grown, and aggregated process. In order to make the sodium ferrosite crystals grow smoothly and thicker so as to facilitate filtration and recovery, and at the same time, as the temperature decreases, the solubility decreases and the recovery increases, the reaction is adopted. End Practice has shown that this process is more effective than rapid filtration and separation, with larger crystal particles, less clogging and hardening of the filter cloth, and more complete sodium recovery from the solution. DETAILED DESCRIPTION

[0025] The present invention is further described below by way of examples.

[0026] A method for removing and recovering sodium from zinc electrolysis wastewater with a high sodium content comprises the following steps:

[0027] Step 1: Extract a certain amount of high sodium-zinc electrolytic wastewater and test the ferrous ion, sodium ion, sulfuric acid, zinc ion, manganese ion and other heavy metal components in the solution;

[0028] Step 2: Then add ferrous sulfate or iron filings according to the ratio of iron to sodium = 4-6, heat and dissolve, and after the solids are completely dissolved, test to confirm that the sodium-iron ratio meets the iron / sodium ratio of 4-6, and adjust the solution pH to 1.5±0.1 with sulfuric acid or alkali; add copper ions according to the ratio of copper ions (g, kg) / solution volume (L, m³) = 0.1-0.5, or copper sulfate pentahydrate (g, kg) / solution volume (L, m³) = 2.56-5.12 and mix evenly;

[0029] Step 3: Place the mixed solution from step 2 in a pressure autoclave, pressurize it with oxygen-enriched air with an oxygen content of 30±5% to 0.3-0.5 MPa or 3-5 kg / m2, and heat it to 120-150°C. Stir mechanically while heating at a rate of 50-200 r / min. The reaction time is 2-3 hours.

[0030] Step 4: After the reaction in step 3 is completed, the pressure is released to normal pressure, the temperature is lowered to 95±5°C, and then slowly stirred with oxygen-enriched air for 0.5-1 hour, and then allowed to stand for more than 2 hours; sampling and testing, when the solution contains sodium ions ≥5g / L, ferrous sulfate and copper ions are added and the operation of step 2 or step 3 is repeated until the solution contains sodium ions ≤5g / L;

[0031] Step 5: Filter the solution in step 4 to obtain sodium ferroalloy crystals, wash them with 40-50°C hot water or weak alkaline water for 2-3 times, and dry them to obtain sodium-containing polyferric sulfate water purifier. The zinc sulfate filtrate containing copper and manganese is sent to electrozinc production for use.

[0032] Example 1: The main chemical composition of zinc electrolysis wastewater from a certain enterprise is as follows: 25.3 g / L sodium ion, 45 g / L zinc ion, 5.2 g / L manganese ion, and 127 g / L sulfuric acid. 5 L of this wastewater was taken and the sulfuric acid was neutralized with sodium hydroxide to 72.5 g / L, resulting in a pH of 1.48. The sodium ion content was then measured to be 32.5 g / L. Solid ferrous sulfate was then added at a ratio of 5 iron to sodium, followed by copper sulfate pentahydrate at a ratio of 0.3 g / L copper ion to volume. The mixture was heated to 50-60°C to dissolve and mix thoroughly, then placed in a 10 L pressure vessel. The mixture was pressurized to 0.5 MPa with oxygen-enriched air containing 30% oxygen, and the temperature was raised to 150°C for 2 hours to allow oxidation and sodium removal. After completion, the pressure was released to normal pressure, the temperature was lowered to 100°C, and the mixture was stirred at a rate of 100 r / min for 30 minutes. The temperature was then lowered to 95°C. The mixture was allowed to stand for 2 hours, and the temperature was lowered to 60°C. The liquid was filtered and tested. The filtrate contained 12.3 g / L sodium ions, 0.28 g / L copper ions, 48.6 g / L zinc ions, and 5.8 g / L manganese ions, with a pH of 1.43. The sodium excretion rate was 62.2%.

[0033] Example 2: 5 L of the zinc electrolysis waste liquid from Example 1 was taken, and iron filings were added at an iron / sodium ratio of 6. The mixture was heated and dissolved. After completion, the iron / sodium ratio was determined to be 6.53, and the sulfuric acid was 102.5 g / L. Copper sulfate was added at a copper / volume ratio of 0.5 g / L. After dissolution, the mixture was placed in a 10 L autoclave, pressurized to 0.3 MPa using the oxygen-enriched air from Example 1, heated to 130°C, and subjected to an oxidative sodium removal reaction for 2.5 hours. After completion, the pressure was released and the mixture was cooled to 90°C. The mixture was then stirred at 50 rpm for 40 minutes, cooled to 70°C, and sampled for analysis. The solution contained 8.2 g / L of sodium. After standing for 1 hour, the sample was tested and the sodium ion content was 6.5 g / L. After standing for 2 hours, the solution contained 5.3 g / L of sodium. After standing for 3 hours, the solution temperature dropped to 40°C, the sodium ion content was 4.8 g / L, and the total sodium removal rate was 81.03%.

[0034] Example 3: After five years of recycling, a company's zinc electrolysis wastewater had accumulated sodium ions, reaching 48.5 g / L, impacting the smooth production of electrolytic zinc. This wastewater contained an average of 45 g / L zinc, 130 g / L sulfuric acid, and 5.5 g / L manganese ions. 50 L of this wastewater was acidified according to the conditions of Example 1, with the addition of ferrous sulfate and copper sulfate. The solution was then placed in a 100 L pressure vessel and subjected to the sodium oxidation reaction described in Example 1. After completion, a sample was collected for analysis, revealing a sodium content of 18.5 g / L and a sodium elimination rate of 61.85%. After cooling to 40°C, the sodium content of the solution dropped to 12.3 g / L, with a total sodium elimination rate of 74.64%. Over 30 kg of natronaite crystals were produced. After washing and analysis, the impurities revealed 0.0012% zinc, 0.0001% manganese, and trace amounts of other heavy metal impurities. The water content (including water of crystallization) was 20-25%, making it suitable for use in the production of domestic water purifiers.

[0035] The present invention not only removes sodium ions, a harmful impurity, from zinc electrolysis waste liquid with a high sodium content, but also recycles and utilizes the sodium ions to obtain a crystalline natronasite (polyferric sulfate) water purifier product; at the same time, sulfuric acid, copper, manganese, zinc, etc. in the solution are returned to electrolytic zinc production. Compared with other sodium removal processes, the process has low cost, good economic benefits, and good environmental protection.

[0036] The above examples are only provided to further illustrate the present invention, and the present invention is not limited thereto.

Claims

1. A method for removing and recovering sodium from zinc electrolysis wastewater containing high sodium content, characterized in that: Follow these steps to implement: Step 1: Add ferrous sulfate or iron filings to the high sodium zinc electrolysis wastewater to dissolve, mix well, and measure the ferrous ion and sodium ion content in the solution; Step 2: Adjust the ratio of ferrous ions and sodium ions and the pH value of the solution in step 1, then add copper sulfate solution or solid and mix evenly; wherein: iron / sodium = 4-6, pH = 1.5±0.1, the amount of copper ions added is the copper ion mass solution volume ratio of g:L = 0.1-0.5; Step 3: Place the mixed solution from step 2 in a pressure autoclave, pressurize it with oxygen-enriched air with an oxygen content of 30±5%, and heat and stir to react for 2-3 hours; Step 4: The reaction solution in step 3 was depressurized and cooled, and then slowly stirred for 0.5-1 hour and then allowed to stand for 2 hours; Step 5: Filter the standing solution from step 4 to obtain sodium ferroalloy crystals, wash and dry them to obtain polyferric sulfate water purifier, and send the low-sodium zinc electrolysis waste liquid to zinc production for use; Step 1: The high sodium content zinc electrolysis waste liquid contains sodium ions ≥10 g / L, pH ≤1.5 or sulfuric acid content of 100-150 g / L, zinc ions ≤60 g / L, and manganese ions ≤5 g / L; The oxygen-enriched air in step 3 has an oxygen content of 30±5%, is pressurized to 0.3-0.5 MPa or 3-5 kg / m2, is heated to 120-150°C, and is mechanically stirred at a rate of 50-200 r / min; In step 4, the pressure is released to normal pressure, the temperature is lowered to 95±5°C, and then stirred with oxygen-enriched air for 0.5-1 hour.

2. A method for removing and recovering sodium from high sodium zinc electrolysis wastewater according to claim 1, characterized in that: Step 5: washing and drying: washing with 40-50℃ hot water or weak alkaline water 2-3 times and then drying.