Method for treating electrolytic manganese residues through combination of washing and multiple curing

Abstract

The invention provides a method for treating electrolytic manganese residues by combining water washing with multiple curing, which comprises the following steps: after the manganese residues are washed with water, curing twice and then curing for three times by using quick lime and silicate in sequence, so that the total manganese content is reduced to 0.1 mg / L or below, the ammonia nitrogen content is reduced to 2.1 mg / L or below, and the soluble salt content is reduced to 1.25% or below; the content of organic matters is reduced to 1.7% or below, and mercury, cadmium, chromium, arsenic, lead and nickel are not detected. According to General Industrial Solid Waste Storage and Landfill Pollution Control Standard (GB 18599-2020), the electrolytic manganese residue reaches the standard of entering a first-class landfill site, and innocent treatment is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of harmless treatment of electrolytic manganese slag, and particularly relates to a method for treating electrolytic manganese slag by combining water washing with multiple solidification processes. Background Art

[0002] Manganese processing and production products primarily include electrolytic manganese metal, electrolytic manganese dioxide, manganese-based ferroalloys, and manganese ore. Electrolytic manganese slag, the acid leaching residue produced during the electrolyte preparation process, is a key pollutant in the electrolytic manganese industry. It primarily contains soluble manganese and substances such as ammonia and ammonium sulfate added during the electrolytic manganese production process, as well as organic matter and other pollutants. With the development of science and technology, achieving harmless batch processing of electrolytic manganese slag, reducing pollutant emissions, lowering treatment costs, and achieving controllable pollutant levels have become pressing challenges in industrial production.

[0003] Currently, the main methods for treating electrolytic manganese slag include stockpiling, solidification by mixing with cement and other materials, making unfired bricks, treating with biological bacteria, and using it for plant cultivation, roasting, and firing ceramics. However, these methods still present challenges: high levels of pollutant release from treated manganese slag, prohibitive treatment costs, impracticality for large-scale treatment, and the inability of manganese slag products to enter the market. Meanwhile, the "Technical Specifications for Pollution Control of Manganese Slag" (HJ 1241-2022) (hereinafter referred to as the "Technical Specifications") were issued in March 2022 and officially implemented on October 1, giving manganese industry operators a six-month deadline for rectification and improvement. The Technical Specifications primarily stipulate pollution control technical requirements for manganese slag collection, storage, transportation, pretreatment, utilization, filling, backfilling, and landfilling, as well as monitoring and environmental management requirements. Landfilling of manganese slag reiterates that it must meet the entry requirements of the "Pollution Control Standard for Storage and Landfill of General Industrial Solid Waste" (GB 18599-2020). Pretreatment is required if these requirements are not met. Therefore, further research and development of harmless treatment methods for electrolytic manganese slag are needed to achieve low-cost, scalable and controllable treatment, further reduce the dissolution of pollutants, and reduce the discharge of pollutants to meet entry requirements. Summary of the Invention

[0004] To solve the above problems, the present invention provides a method for treating electrolytic manganese slag by water washing and multiple solidification. After washing the manganese slag, it is solidified twice with quicklime and then silicate respectively, and then solidified three times. In particular, waste glass powder is used as the third solidifying agent. On the basis of the two solidifications, the contents of manganese, ammonia nitrogen and organic matter are further reduced, so that the total manganese content is reduced to below 0.1 mg / L, the ammonia nitrogen content is reduced to below 2.1 mg / L, the organic matter content is reduced to below 1.7%, and the soluble salt content is reduced to below 1.25%. Mercury, cadmium, chromium, arsenic, lead and nickel are not detected, so that the manganese slag meets the first-class solid waste standard and is harmlessly treated.

[0005] The object of the present invention is to provide a method for washing and solidifying electrolytic manganese slag, wherein the electrolytic manganese slag is first washed with water, quicklime is added to the washed manganese slag for primary solidification, silicate is then added for secondary solidification, and finally a third solidifying agent is added for tertiary solidification to obtain treated manganese slag.

[0006] The water washing is to add the electrolytic manganese slag into water and wash it several times. The water used for the water washing is distilled water, deionized water or tap water, preferably tap water.

[0007] After the washing is completed, the washing water is removed and the washed manganese slag is solidified by adding quicklime, wherein the weight of the quicklime accounts for 2-10% of the total weight of the washed manganese slag and quicklime.

[0008] After the primary solidification is completed, a silicate is added to the primary solidified manganese slag for secondary solidification to obtain a secondary solidified manganese slag. The silicate is selected from one or more of aluminum silicate, iron silicate, calcium silicate, magnesium silicate, potassium silicate, and sodium silicate. The mass of the silicate accounts for 1% to 12% of the total mass of the primary solidified manganese slag and the silicate.

[0009] After the secondary curing is completed, a third curing agent is added to the secondary cured manganese slag to perform a third curing to obtain treated manganese slag. The third curing agent is selected from one or more of calcium powder, waste glass powder, cement, and fly ash, preferably waste glass powder and / or fly ash, and more preferably waste glass powder.

[0010] The present invention has the following beneficial effects:

[0011] (1) The filtrate after water washing in the present invention can be used for electrolytic manganese reproduction and recycling, thereby reducing the generation of waste water and saving resources.

[0012] (2) The present invention sequentially solidifies the washed manganese slag using quicklime, silicate and a third solidifying agent, thereby effectively reducing the contents of lead, nickel, manganese, ammonia nitrogen, soluble salts and organic matter in the manganese slag leachate, and making the manganese slag meet the standards of Class I solid waste.

[0013] (3) When waste glass powder is used as the third curing agent in the present invention, the total manganese content is reduced to below 0.1 mg / L, the ammonia nitrogen content is reduced to below 2.1 mg / L, and the organic matter content is reduced to below 1.7%. This greatly reduces the concentrations of manganese, ammonia nitrogen, and organic matter in the manganese slag leachate, minimizing the release of pollutants. Furthermore, the curing agent is readily available and inexpensive, and the method is easy to implement and control, meeting the operational requirements for batch manganese slag treatment and meeting the standards for entry into a Class I landfill as stipulated in the "General Industrial Solid Waste Storage and Landfill Pollution Control Standard" (GB 18599-2020). BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A comparison of total manganese and ammonia nitrogen concentrations in the leachate of manganese slag obtained by solidification at different sodium hydroxide dosages using sodium hydroxide as a solidifying agent in Example 5 of the present invention is shown;

[0015] Figure 2 The XRD patterns of the electrolytic manganese primary filter press residue (raw manganese slag) in Example 1 of the present invention are shown; the secondary solidified manganese slag (manganese slag after washing and secondary solidification) obtained by solidifying with the addition of 4% quicklime and 2% sodium silicate in Example 7; and the tertiary solidified manganese slag (manganese slag after washing and tertiary solidification) obtained by adding 30% of 200-mesh waste glass powder to the material in Example 7 in Example 9;

[0016] Figure 3 The DSC-TGA curve of the electrolytic manganese primary filter press residue (raw manganese residue) in Example 1 of the present invention is shown;

[0017] Figure 4 The DSC-TGA curve of the secondary solidified manganese slag obtained by solidification by sequentially adding 4% quicklime and 2% sodium silicate in Example 7 of the present invention is shown;

[0018] Figure 5 The DSC-TGA curve of the tertiary solidified manganese slag obtained by adding 30% of 200-mesh waste glass powder to Example 7 according to Example 9 of the present invention is shown;

[0019] Figure 6 (a) Figure 6 (b) Figure 6 (c) shows the electrolytic manganese primary filter press residue (raw manganese residue) in Example 1 of the present invention; Figure 6 (d) Figure 6 (e) Figure 6 (f) shows the secondary solidified manganese slag obtained by adding sodium silicate after solidification for 48 hours in Example 7 of the present invention; Figure 6 (g) Figure 6 (h) Figure 6 (i) shows the tertiary solidified manganese slag obtained by adding 30% of 200-mesh waste glass powder to Example 7 in Example 9 of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be described in detail below through specific embodiments, and the features and advantages of the present invention will become clearer and more distinct with these descriptions.

[0021] The present invention provides a method for treating electrolytic manganese slag by water washing and solidification. The method comprises the following steps: firstly washing the electrolytic manganese slag with water, adding quicklime to the washed manganese slag for primary solidification, then adding silicate for secondary solidification, and finally adding a third solidifying agent for tertiary solidification to obtain treated manganese slag.

[0022] Electrolytic manganese slag, the acid leaching residue produced during the electrolyte preparation process, is a key pollutant in the electrolytic manganese industry. It primarily contains soluble manganese and chemical reagents such as ammonia and ammonium sulfate added during the electrolytic manganese production process. Currently, 8-10 tons of electrolytic manganese slag are produced for every ton of manganese metal produced. The main chemical components of electrolytic manganese slag are CaSO4, SiO2, Al2O3, Fe2O3, MnO2, and SO3, with dihydrate gypsum and silicon dioxide being the primary phases. Electrolytic manganese slag also has a high moisture content (22wt%-28wt%), fine particles (<30μm, with over 70% being present), and a high sulfate content (20-30wt%, calculated as SO3).

[0023] The water washing comprises adding the electrolytic manganese slag to water and washing several times. The water used for the water washing is distilled water, deionized water, or tap water, preferably tap water. The mass ratio of the water to the electrolytic manganese slag is (1-10):1, preferably (1-4):1, and more preferably (2-3):1. The number of washes is preferably 1-10 times, preferably 1-5 times, and more preferably 1-2 times. Each water washing time is 10-80 minutes, preferably 20-70 minutes, and more preferably 30-60 minutes.

[0024] After washing, the washing water is removed, and the washed manganese slag is solidified by adding quicklime. The filtrate of the washed manganese slag must contain no detectable levels of total mercury, alkylmercury, total cadmium, total chromium, hexavalent chromium, total arsenic, or total lead. The total nickel content must be less than 0.1 mg / L, the total manganese content must be less than 200 mg / L, the ammonia nitrogen content must be less than 200 mg / L, the soluble salt mass fraction must be less than 6%, and the organic matter mass fraction must be less than 10%.

[0025] The weight of quicklime accounts for 2%-10% of the total weight of the manganese slag and quicklime after washing, preferably 3%-6%, and more preferably 3.5%-4.5%. Within the above-mentioned quicklime dosage range, the manganese, ammonia nitrogen, and soluble salt contents in the electrolytic manganese slag can be effectively removed. The removal effect improves with increasing quicklime dosage, and tends to be stable above 6%. After adding quicklime, the alkaline environment it provides allows manganese ions to form manganese hydroxide precipitates when exposed to water. This precipitate reacts with oxygen in the air to form manganese oxide precipitates, thereby stabilizing the manganese ions in the form of a precipitate and reducing the soluble manganese and total manganese contents. The ammonium ions in the manganese slag can also react to form volatile ammonia in the alkaline environment provided by quicklime. At the same time, the heat released by the reaction with water promotes the escape of ammonia. As for soluble salts, the main salt component in the manganese slag washing solution is ammonium sulfate. The addition of quicklime causes the ammonium sulfate to react to form gypsum and ammonia, so that the soluble salts can meet Class I standards.

[0026] The primary curing temperature is 35-65°C, preferably 40-60°C. The curing time is 8-120 hours, preferably 12-96 hours, and more preferably 40-50 hours. As the curing time increases, the nickel, manganese, ammonia nitrogen, and soluble salts in the manganese slag decrease. After 48 hours, the decrease gradually decreases.

[0027] Dry primary solidified manganese slag is added to water at a mass ratio of 1:10, and the oscillation frequency is 110±10 times / min and the amplitude is 40 mm. After oscillation at room temperature for 8 hours, the oscillation is allowed to stand and filtered to obtain a leachate. The primary solidified manganese slag leachate has a total mercury content of less than 0.05 mg / L, no detectable alkyl mercury, a total cadmium content of less than 0.1 mg / L, a total chromium content of less than 1.5 mg / L, a hexavalent chromium content of less than 0.5 mg / L, a total arsenic content of less than 0.5 mg / L, a total lead content of less than 1.0 mg / L, a total nickel content of less than 0.07 mg / L, a total manganese content of less than 2.0 mg / L, ammonia nitrogen content of less than 10 mg / L, a soluble salt mass fraction of less than 2%, and an organic matter mass fraction of less than 6%.

[0028] After the primary solidification is completed, a silicate is added to the primary solidified manganese slag for secondary solidification to obtain a secondary solidified manganese slag. The silicate is selected from one or more of aluminum silicate, iron silicate, calcium silicate, magnesium silicate, potassium silicate and sodium silicate, preferably potassium silicate and / or sodium silicate, more preferably sodium silicate.

[0029] The mass of the silicate accounts for 1%-12% of the total mass of the primary solidified manganese slag and the silicate, preferably 1%-8%, more preferably 1%-4%.

[0030] The secondary curing temperature is 10-45°C, preferably 15-40°C, more preferably 20-35°C, and the curing time is 12-36h, preferably 16-32h, more preferably 20-28h. As the curing time increases, the nickel, manganese, and soluble salts in the manganese slag decrease.

[0031] Weigh the dry weight of secondary solidified manganese slag, add deionized water at a liquid-to-solid ratio of 10:1, and shake at a frequency of 110±10 times / min and an amplitude of 40 mm. After shaking at room temperature for 8 hours, remove the extraction bottle, let it stand, and filter to obtain a secondary solidified manganese slag leachate. The secondary solidified manganese slag leachate has a total mercury content of less than 0.05 mg / L, no detectable alkyl mercury, a total cadmium content of less than 0.1 mg / L, a total chromium content of less than 1.5 mg / L, a hexavalent chromium content of less than 0.5 mg / L, a total arsenic content of less than 0.5 mg / L, a total lead content of less than 1.0 mg / L, a total nickel content of less than 0.05 mg / L, a total manganese content of less than 1.0 mg / L, an ammonia nitrogen content of less than 5 mg / L, a soluble salt mass fraction of less than 2%, and an organic matter mass fraction of less than 6%.

[0032] After the secondary curing is completed, a third curing agent is added to the secondary cured manganese slag to perform a third curing to obtain treated manganese slag. The third curing agent is selected from one or more of calcium powder (calcium carbonate powder), waste glass powder, cement, and fly ash, preferably waste glass powder and / or fly ash, and more preferably waste glass powder.

[0033] The average particle size of the third curing agent is 20-2000 mesh, preferably 50-1100 mesh, and more preferably 100-200 mesh.

[0034] The mass ratio of the third curing agent to the secondary curing manganese slag is (1-8): (2-9), preferably (2-4): (6-8), and more preferably 3:7. The tertiary curing temperature is 10-45°C, preferably 15-40°C, and more preferably 20-35°C. The curing time is 14-36h, preferably 16-32h, and more preferably 20-28h. After adding the third curing agent, the ammonia nitrogen and organic matter content can be effectively reduced. Compared with calcium powder, cement and fly ash, the use of waste glass powder as the third curing agent can further reduce the content of total manganese, ammonia nitrogen and organic matter. The main components of waste glass powder include silicon dioxide, calcium silicate and sodium silicate, etc., with a certain porosity and surface charge. It has a physical encapsulation and physical adsorption effect on the natural organic matter in the manganese slag, making it difficult for pollutants to be filtered out by water, and the emission concentration is within the range allowed by the environment. It is not easily corroded by chemicals in the water during the addition process, and no secondary pollution will be generated, and it can operate stably for a long time. Relatively speaking, calcium carbonate powder and fly ash have relatively high loss on ignition, making them ineffective in reducing the organic matter index in electrolytic manganese slag. Cement also contains a certain amount of heavy metals, leading to higher levels of some heavy metals compared to secondary curing. Therefore, using waste glass powder as a third curing agent offers better treatment results.

[0035] Weigh the dry weight of tertiary solidified manganese slag, add deionized water at a liquid-to-solid ratio of 10:1, and oscillate at a frequency of 110±10 times / min and an amplitude of 40 mm. Oscillate at room temperature for 8 hours, allow to stand, and filter to obtain a tertiary solidified manganese slag leachate. The tertiary solidified manganese slag leachate shall have no detectable total mercury, alkylmercury, total cadmium, total chromium, hexavalent chromium, total arsenic, total lead, and total nickel contents. The total manganese content shall be less than 0.1 mg / L, the ammonia nitrogen content shall be less than 2.1 mg / L, the mass fraction of soluble salts shall be less than 1.25%, and the mass fraction of organic matter shall be less than 1.7%.

[0036] Example

[0037] Example 1

[0038] Three parallel samples of the primary filter press residue to be processed from the electrolytic manganese workshop were taken and named fresh manganese residue #1, fresh manganese residue #2, and fresh manganese residue #3.

[0039] Leach electrolytic manganese slag using the horizontal oscillation method according to HJ5572019, a method for leaching toxicity from solid waste: Weigh 100g of fresh manganese slag #1, fresh manganese slag #2, and fresh manganese slag #3, each with an average particle size of 400 mesh, on a dry basis. Place the slag in a 2L extraction bottle. Add deionized water at a liquid-to-solid ratio of 10:1. Secure the bottle cap tightly and secure it vertically on a horizontal oscillator. Adjust the oscillation frequency to 110±10 times / min and the amplitude to 40mm. Oscillate at room temperature for 8 hours, then remove the slag and let it rest for 16 hours. If gas is generated during the oscillation process, periodically open the slag in a fume hood to release excess pressure. Install a filter membrane on the pressure filter, filter, collect the leachate, and test various indicators.

[0040] The analysis yielded total mercury, alkylmercury, total cadmium, total chromium, hexavalent chromium, total arsenic, total lead, total nickel, total manganese, ammonia nitrogen, soluble salts, organic matter, pH value, and moisture content. The specific results are shown in Table 1.

[0041] Table 1

[0042]

[0043]

[0044] Example 2

[0045] The primary filter press residue from Example 1 was taken and the manganese residue was ground and washed to a particle size of 400 mesh. Tap water was then added. The residue was washed with water at a mass ratio (liquid-to-solid ratio) of 1:1, 2:1, 3:1, and 4:1, respectively. The stirring and washing time was 30 minutes at a temperature of 25°C. After one wash, the manganese residue was filtered out. The contents of various substances in the filtrate were analyzed, and the specific results are shown in Table 2.

[0046] Table 2 Contents of various substances in the filtrate after washing with different solid-liquid ratios

[0047]

[0048] Example 3

[0049] The primary filter press manganese slag from the electrolytic manganese workshop was ground and washed to a 200-mesh average particle size. Tap water was then added. The slag was washed with water at a 2:1 mass ratio of water to manganese slag (liquid-to-solid ratio), with stirring for 15, 45, and 60 minutes, at a temperature of 25°C, and once. After washing, the slag was filtered out, and the filtrate was analyzed for the concentrations of various indicators. The results are shown in Table 3.

[0050] Table 3 Contents of various substances in the filtrate after washing at different washing times

[0051]

[0052] According to the above method, the liquid-to-solid ratio was 2:1, the washing time was 30 min, and the fresh manganese slag was washed twice with fresh tap water. The filtrate after each washing was taken and the concentration of each indicator was analyzed. The specific results are shown in Table 4.

[0053] Table 4 Content of each substance in the filtrate after washing

[0054]

[0055] Example 4

[0056] The filter residue obtained after the secondary washing of Example 3 was added with quicklime as a curing agent according to the mass of quicklime accounting for 3%, 4% and 6% of the total mass of the filter residue. At 50°C, the mixture was mixed and reacted for 48 hours to solidify, thereby obtaining a primary solidified manganese slag. A horizontal oscillation leaching experiment was performed, and the test was carried out in accordance with the standard HJ5572019 "Solid Waste Leaching Toxicity Leaching Method Horizontal Oscillation Method". A primary solidified manganese slag with a dry basis weight of 100g was weighed and placed in a 2L extraction bottle. Deionized water was added at a liquid-solid ratio of 10:1. After the bottle cap was tightly closed, it was fixed vertically on a horizontal oscillation device, and the oscillation frequency was adjusted to 110±10 times / min and the amplitude was 40mm. After oscillating at room temperature for 8 hours, the extraction bottle was removed and allowed to stand for 16 hours. When gas is generated during the oscillation process, the extraction bottle should be opened regularly in a fume hood to release excessive pressure. A filter membrane was installed on the pressure filter, and the leachate was filtered and collected for detection of various indicators. The mass concentrations of total manganese and ammonia nitrogen in the leachate were detected, and the organic matter and soluble salt contents were measured to analyze whether the treated manganese slag met the Class I solid waste standards. The specific test data are shown in Table 5.

[0057] Table 5 Test data of various indicators of manganese slag after solidification with different proportions of quicklime

[0058]

[0059] The data in Table 2 show that a 4% quicklime addition yields the best solidification effect, achieving total manganese, ammonia nitrogen, and soluble salt levels that meet Class I solid waste standards (total manganese ≤ 2 mg / L, ammonia nitrogen ≤ 15 mg / L, and soluble salts < 2 wt%), while organic matter content only meets Class II solid waste standards (organic matter < 5 wt%). Manganese slag was treated with different proportions of solidifying agents, including 3%, 4%, and 6% quicklime. The amount of each solidifying stabilizer was doubled from the 3% to the 6% quicklime group. However, the ammonia nitrogen concentration in the leachate did not change much, while the total manganese concentration changed significantly. However, all results met the Class I standard for comprehensive wastewater discharge.

[0060] Compared with the case without adding a curing agent, the total manganese and ammonia nitrogen mass concentrations in the leachate are significantly reduced. This is because quicklime can solidify the soluble manganese ions in the manganese slag. In the alkaline environment provided by quicklime, manganese ions can form manganese hydroxide precipitates when they come into contact with water. This precipitate will react with oxygen in the air to form manganese oxide precipitates, thereby stabilizing the manganese ions in the form of a precipitate and reducing the total manganese content. The ammonium ions in the manganese slag can also react in the alkaline environment provided by quicklime to generate volatile ammonia gas. At the same time, the heat released by the reaction with water promotes the escape of ammonia gas. As for soluble salts, the main salt component in the manganese slag washing solution is ammonium sulfate. The addition of quicklime can cause ammonium sulfate to react to generate gypsum and ammonia gas, so that the soluble salts can meet the first-class standard. In summary, from the perspective of economy and curing effect, the amount of quicklime added is preferably 4%.

[0061] Example 5

[0062] The manganese slag was treated by the method of Example 4, except that 0.5%, 1%, 2% and 3% of the total mass of manganese slag and sodium hydroxide were added as a curing agent. After the curing was completed, a horizontal oscillation leaching experiment was carried out according to the method of Example 4 to detect the concentrations of total manganese, ammonia nitrogen, organic matter and soluble salts in the leachate. The specific results were compared. Figure 1 shown.

[0063] Table 6 Detection data of various indicators in the leachate after solidification of electrolytic manganese slag with different sodium hydroxide dosages

[0064]

[0065]

[0066] from Figure 1 As can be seen from the data in Table 6, the greater the amount of sodium hydroxide added, the lower the total manganese and ammonia nitrogen concentrations in the leachate. From an economic perspective, taking a production line with an annual processing capacity of 400,000 tons of manganese slag as an example, the difference in processing costs per ton of manganese slag between sodium hydroxide and quicklime is nearly 16.67 yuan, and the difference in annual processing costs is 6.67 million yuan. Therefore, quicklime is selected as a curing agent in subsequent embodiments.

[0067] Table 7 Cost calculation of quicklime and sodium hydroxide as curing agents

[0068]

[0069] Example 6

[0070] The primary filter press residue was treated according to the method of Example 4, with the addition amount of quicklime being 4 wt %. The only difference was that the curing times were 12 h, 48 h, 72 h, and 96 h, respectively.

[0071] Weigh 100g of primary solidified manganese slag on a dry basis and place it in a 2L extraction bottle. Add deionized water at a liquid-to-solid ratio of 10:1. After tightening the bottle cap, fix it vertically on a horizontal oscillating device. Adjust the oscillation frequency to 110±10 times / min and the amplitude to 40mm. After oscillating at room temperature for 8 hours, remove the extraction bottle and let it stand for 16 hours. If gas is generated during the oscillation process, the extraction bottle should be opened regularly in a fume hood to release excessive pressure. Install a filter membrane on the pressure filter, filter and collect the leachate, and perform various indices testing. The concentrations of total manganese, ammonia nitrogen, organic matter, and soluble salts in the leachate were tested. The specific results are shown in Table 8.

[0072] Table 8 Various index test data of manganese slag after different quicklime solidification time

[0073]

[0074] As shown in Table 8, the removal rates of total manganese and ammonia nitrogen in manganese slag increase first and then gradually stabilize as the curing time increases. When the curing time increases from 12h to 48h, the concentrations of manganese ions and ammonia nitrogen decrease from 0.91 and 8.95mg / L to 0.598 and 5.157mg / L, respectively. As the curing time continues to be extended, the various indicators in the manganese slag tend to be stable. Therefore, it is considered to add a curing agent to the washed manganese slag so that the pollutants can be stably solidified or removed, and are not leached under extreme conditions. The manganese slag after treatment is landfilled or recycled to minimize the harm to the environment. Meanwhile, an excessively long curing time has little effect on the treatment effect of electrolytic manganese slag. Therefore, a curing time of 48h is preferably used for the harmless treatment of subsequent electrolytic manganese slag.

[0075] Example 7

[0076] Take the manganese slag after quicklime solidification (primary solidified manganese slag) obtained in Example 6 with a solidification time of 48 hours, add sodium silicate, and the mass of the added sodium silicate accounts for 1%, 2%, and 4% of the total mass of the primary solidified manganese slag, respectively. The sodium silicate and the solidified manganese slag are fully mixed, and solidified at 25°C for 24 hours to obtain a secondary solidified manganese slag.

[0077] After solidification, various indicators in the electrolytic manganese slag were tested. Weigh 100g of the secondary solidified manganese slag on a dry basis and place it in a 2L extraction bottle. Add deionized water at a liquid-to-solid ratio of 10:1. After tightening the bottle cap, fix it vertically on a horizontal oscillation device. Adjust the oscillation frequency to 110±10 times / min and the amplitude to 40mm. After oscillating at room temperature for 8 hours, remove the extraction bottle and let it stand for 16 hours. If gas is generated during the oscillation process, the extraction bottle should be opened regularly in a fume hood to release excess pressure. Install a filter membrane on the pressure filter, filter and collect the leachate, and test various indicators.

[0078] Table 9 Test data of various indicators of adding different proportions of sodium silicate manganese slag

[0079]

[0080] The results showed that the addition of sodium silicate reduced the heavy metal content in the electrolytic manganese slag. Adding 2% sodium silicate reduced the total manganese content to 0.106 mg / L, with total nickel reaching undetectable levels. The soluble salt content was also reduced to 1.31%, further reducing the heavy metal content in the slag. However, the addition of sodium silicate had little effect on the organic matter and ammonia nitrogen content in the slag. Therefore, for economic reasons and curing effectiveness, the sodium silicate content used in subsequent examples was 2%.

[0081] Example 8

[0082] Take the secondary solidified manganese slag obtained in Example 7 (obtained by solidification with 2% sodium silicate), and add calcium powder with an average particle size of 200 mesh, 200 mesh waste glass powder, 200 mesh fly ash, and 200 mesh cement, respectively. The mass ratio of calcium powder, waste glass powder, fly ash, and cement to the secondary solidified manganese slag is 3:10. Stir and mix at room temperature for 24 hours. Weigh 100g of the tertiary solidified manganese slag on a dry basis and place it in a 2L extraction bottle. Add deionized water at a liquid-to-solid ratio of 10:1. After tightening the bottle cap, fix it vertically on a horizontal oscillating device, adjust the oscillation frequency to 110±10 times / min and the amplitude to 40mm. After oscillating at room temperature for 8 hours, remove the extraction bottle and let it stand for 16 hours. If gas is generated during the oscillation process, the extraction bottle should be opened regularly in a fume hood to release excessive pressure. Install a filter membrane on the pressure filter, filter and collect the leachate, and test various indicators. The test results are shown in Table 10.

[0083] Table 10 Detection data of various indicators in harmless manganese slag in the presence of different additives

[0084]

[0085] The data in the table above shows that cement contains a certain amount of heavy metals, making it unsuitable as a treatment agent for harmless electrolytic manganese slag. High concentrations of lead and cadmium in cement hinder its harmlessness. The current standard for determining organic matter in electrolytic manganese slag is the organic matter loss on ignition method (HJ761-2015). Electrolytic manganese slag is primarily composed of gypsum (hydrated calcium sulfate), which contains a large amount of crystalline water. Therefore, the loss on ignition of the additive itself cannot be too high. The additives selected in the table show that incorporating a certain amount of waste glass powder can effectively reduce the loss on ignition of the manganese slag, effectively lowering the organic matter content to ultimately meet the Class I solid waste standard (organic matter <2%). Recycling one ton of waste glass can save 720 kg of quartz sand, 250 kg of soda ash, 60 kg of feldspar powder, 10 tons of coal, and 400 kWh of electricity, representing excellent economic benefits. Furthermore, waste glass powder, primarily composed of silicon dioxide, calcium silicate, and sodium silicate, possesses a certain porosity and surface charge, physically encapsulating and adsorbing the natural organic matter in manganese slag. This prevents pollutants from being removed by water, keeping discharge concentrations within environmentally acceptable limits. Furthermore, during the addition process, waste glass powder is not easily corroded by chemicals in the water, preventing secondary pollution and enabling long-term stable operation. However, calcium carbonate powder and fly ash have high ignition loss and are unable to effectively reduce the organic matter index in electrolytic manganese slag.

[0086] Example 9

[0087] The curing process was carried out using 200-mesh waste glass powder according to the method of Example 8, with the only difference being that the mass ratios of waste glass powder to secondary cured manganese slag were 1:10 (10%), 3:10 (30%), 5:10 (50%), and 10:10 (100%), respectively. After the curing process was completed, the concentrations of various indicators in the leachate of the tertiary cured manganese slag were measured, as shown in Figure 11.

[0088] Table 11 Concentration of various indicators of secondary solidified manganese slag treated with different proportions of waste glass powder

[0089]

[0090]

[0091] Example 10

[0092] Waste glass powder was solidified according to the method described in Example 8, with the only difference being that the average particle sizes of the waste glass powder were 20 mesh and 2000 mesh, respectively. The mass ratio of waste glass powder to secondary solidified manganese slag was 3:10 (30%). After solidification, the concentrations of various indicators in the leachate from the tertiary solidified manganese slag were measured, as shown in Table 12.

[0093] Table 12 Concentration of various indicators of secondary solidified manganese slag treated with waste glass powder of different particle sizes

[0094]

[0095] The leaching tests of heavy metals, ammonia nitrogen, soluble salts and organic matter meet the requirements of Class I general industrial solid waste in the "General Industrial Solid Waste Storage and Landfill Pollution Control Standards" (GB18599-2020), and the electrolytic manganese slag after harmless treatment meets the standards for entering Class I landfill.

[0096] Experimental example

[0097] Experimental Example 1

[0098] X-ray diffraction (XRD) tests were performed on the electrolytic manganese primary filter press residue (raw manganese residue) in Example 1, the secondary solidified manganese residue (water-washed + secondary solidified manganese residue) obtained by solidifying with 2% sodium silicate in Example 7, and the tertiary solidified manganese residue (water-washed + tertiary solidified manganese residue) obtained by adding 30% 200-mesh waste glass powder in Example 9. The test results are shown in the figure below. Figure 2 shown.

[0099] The main mineral phases in raw manganese slag are silicon dioxide (SiO2) and gypsum (CaSO4·2H2O). Silica is a common mineral component widely found in rocks and soils, while gypsum is a hydrated calcium sulfate mineral typically formed during the smelting process. After washing and solidification, the raw gypsum in the manganese slag is mostly converted into gypsum sinter (CaSO4·0.5H2O) and a small amount of anhydrite (CaSO4). This change is due to the heat generated by the reaction of the added quicklime and cement with water during the solidification process. When the temperature rises to 128°C, the raw gypsum begins to lose some of its crystallization water and transforms into gypsum sinter. If the temperature continues to rise to above 175°C, the gypsum sinter will further dehydrate, eventually forming anhydrous anhydrite. The purpose of harmless treatment is to convert harmful mineral phases into more stable and less harmful forms. In this process, the conversion of raw gypsum not only reduces its potential harm to the environment but also helps stabilize the overall structure of the manganese slag. The XRD spectrum shows that the added solidification stabilizer has little effect on the mineral composition of the manganese slag, which means that the solidifying agent mainly plays a stabilizing role without significantly changing the mineral composition of the manganese slag. This may be because the role of the solidifying agent is mainly to fix heavy metals and other harmful substances by physical and chemical means, reducing their migration and release, rather than changing the basic mineral composition of the manganese slag. During the entire water washing and solidification process, the mineral phase of silica did not change significantly, indicating that silica has a high chemical stability under these conditions. After the second water washing and solidification treatment, the gypsum continued to dehydrate and further converted into anhydrite. This step may further improve the stability of the manganese slag and reduce its potential impact on the environment.

[0100] Experimental Example 2

[0101] DSC-TGA analysis was performed on the electrolytic manganese primary filter press residue (raw manganese residue) in Example 1, the secondary solidified manganese residue obtained by solidifying with 2% sodium silicate in Example 7, and the tertiary solidified manganese residue obtained by adding 30% 200 mesh waste glass powder in Example 9. The DSC-TGA (differential scanning calorimetry - thermogravimetric) curves are shown as follows: Figure 3 、 Figure 4 and Figure 5 shown.

[0102] Based on the thermogravimetric (DSC-TGA) curve data, general thermal analysis knowledge, and common characteristics of manganese slag, possible causes of weight loss can be hypothesized. Manganese slag is a byproduct of the electrolytic manganese metal production process and typically contains the following components: manganese compounds such as manganese dioxide (MnO2) and manganese oxide (Mn2O3), and ammonium salts such as ammonium sulfate ((NH4)2SO4) or ammonium chloride (NH4Cl). These components may be additives to the electrolyte, physically adsorbed or chemically bound water, organic additives from the electrolyte, and other impurities such as metallic impurities or other inorganic salts. Weight loss in the DSC-TGA curve may be caused by several processes. First, at lower temperatures, the sample weight loss may be due to the evaporation of physically adsorbed or chemically bound water. Manganese compounds or ammonium salts may decompose during heating, releasing gases such as oxygen, nitrogen, and ammonia, resulting in weight loss. Manganese compounds may undergo redox reactions at high temperatures, forming gases or more stable compounds. If the manganese slag contains organic matter, these will pyrolyze and volatilize during heating. X-ray diffraction (XRD) was used to compare the mineralogical phases of the raw manganese slag and the washed and solidified manganese slag. Based on the XRD analysis and thermogravimetric (TGA) curves, the weight loss components were determined. The weight loss between room temperature and 133°C is primarily due to the evaporation of adsorbed water. This weight loss is not due to a change in the sample's chemical composition, but rather to the removal of physically adsorbed water by heating. The weight loss between 133°C and 917°C is primarily due to the removal of water of crystallization by dihydrate gypsum (CaSO₄·2H₂O). During the solidification process, raw gypsum (CaSO₄·2H₂O) begins to lose some of its water of crystallization, transforming into plaster of Paris (CaSO₄·0.5H₂O). If the temperature is raised above 175°C, the plaster of Paris further dehydrates, eventually forming anhydrous anhydrite (CaSO₄). Thermal decomposition of sulfates and ammoniacal double salts: At higher temperatures, thermal decomposition of sulfates and ammoniacal double salts may occur, leading to further weight loss. These reactions likely involve sulfate minerals and ammonia-containing compounds, such as ammonium sulfate, in the manganese slag, which decompose upon heating to release gases such as SO₂ and NH₃. Silicate mineral phase: XRD patterns show that the silica (SiO₂) mineral phase does not undergo significant changes during the water washing and solidification processes, demonstrating the high chemical stability of silica under these conditions.

[0103] Experimental Example 3

[0104] Scanning electron microscopy (SEM) analysis was performed on the electrolytic manganese primary filter press residue (raw manganese residue) in Example 1, the secondary solidified manganese residue obtained by solidifying with 2% sodium silicate in Example 7, and the tertiary solidified manganese residue obtained by adding 30% 200-mesh waste glass powder in Example 9. Figure 6 As shown, Figure 6(ac) Morphological characteristics of raw manganese slag, Figure 6 (df) Morphological changes of the secondary cured manganese slag obtained after curing with 2% sodium silicate in Example 7, Figure 6 (gi) Changes in the morphology of manganese slag after three solidification with 30% 200-mesh waste glass powder added in Example 9.

[0105] SEM analysis reveals that the raw manganese slag sample has a loose and porous structure, likely due to rapid cooling or gas escape during its formation. Fresh manganese slag exhibits regular columnar structures composed of CaSO₄·2H₂O (calcium sulfate dihydrate), which are randomly interlaced with irregular particles, forming the basic microstructure of the raw manganese slag. The sample also contains numerous pores, which may provide pathways for the migration of contaminants.

[0106] The columnar structure in the manganese slag structure after water washing and solidification disappears, which may be due to the dissolution effect during the water washing process, resulting in the destruction of the calcium sulfate dihydrate structure. In addition, the number of irregular flaky particles (CaSO4·0.5H2O) increased during this process, indicating that a new calcium sulfate hemihydrate structure was formed after water washing. It is worth noting that short rod-like structures were observed around the flaky particles, which may be substances such as calcium aluminate or calcium zeolite, which may be formed during the water washing and solidification process. At the same time, a small number of small spherical particles can be observed sticking together, which may be due to OH - With Mn 2+ The reaction produced MnOOH and MnO2 precipitates, indicating that manganese compounds began to form.

[0107] After secondary curing, the slag exhibited an increase in flaky structures: irregular flaky structures increased further and became larger, potentially contributing to improved structural stability. Simultaneously, the number of short rod-like structures surrounding the flaky structures decreased significantly, potentially suggesting that the addition of the curing agent altered the formation conditions of these structures or promoted their aggregation. Furthermore, the number of small, clumping particles decreased significantly, suggesting that the addition of the secondary curing agent helped disperse these particles and reduce adhesion. The crystal structure of the slag after water washing and secondary curing became more compact, contributing to improved mechanical strength and durability. Significant gelation and adsorption occurred in the slag, potentially helping to immobilize contaminants within it and reduce their migration risk. In summary, analysis of the SEM images reveals significant changes in the microstructure of the slag after the combined water washing and curing treatments, changes that contribute to improved slag stability and reduced contaminant migration risk.

[0108] The present invention has been described in detail above with reference to specific embodiments and / or exemplary examples and the accompanying drawings. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for treating electrolytic manganese slag by washing and solidification, wherein the electrolytic manganese slag is first washed with water, quicklime is added to the washed manganese slag for primary solidification, silicate is added for secondary solidification, and finally a third solidifying agent is added for tertiary solidification to obtain treated manganese slag. The third curing agent is selected from one or more of calcium powder, waste glass powder, cement and fly ash.

2. The method according to claim 1, characterized in that The water washing is to add the electrolytic manganese slag into water and wash it several times. The washing water is distilled water, deionized water or tap water, preferably tap water. The mass ratio of the water to the electrolytic manganese slag is (1-10):1, preferably (1-4):1, and more preferably (2-3):

1.

3. The method according to claim 1, characterized in that The mass of the quicklime accounts for 2-10% of the total mass of the washed manganese slag and quicklime, preferably 3%-6%, more preferably 3.5%-4.5%. The primary curing temperature is 35-65° C., preferably 40-60° C., and the curing time is 8-120 h, preferably 12-96 h, and more preferably 40-50 h.

4. The method according to claim 1, wherein In the leachate of the primary solidified manganese slag, the total nickel content is less than 0.07 mg / L, the total manganese content is less than 2.0 mg / L, the ammonia nitrogen content is less than 10 mg / L, the mass fraction of soluble salt is less than 5%, and the mass fraction of organic matter is less than 8%.

5. The method according to claim 1, characterized in that After the primary solidification is completed, silicate is added to the primary solidified manganese slag for secondary solidification to obtain secondary solidified manganese slag, wherein the silicate is selected from one or more of aluminum silicate, iron silicate, calcium silicate, magnesium silicate, potassium silicate and sodium silicate. The mass of the silicate accounts for 1%-12% of the total mass of the primary solidified manganese slag and the silicate, preferably 1%-8%, more preferably 1%-4%. The secondary solidification temperature is 10-45° C., and the solidification time is 12-36 hours.

6. The method according to claim 1, characterized in that In the leachate of the secondary solidified manganese slag, the total nickel content is less than 0.05 mg / L, the total manganese content is less than 1.0 mg / L, the ammonia nitrogen content is less than 5 mg / L, the mass fraction of soluble salt is less than 2%, and the mass fraction of organic matter is less than 6%.

7. The method according to claim 1, characterized in that The third curing agent is waste glass powder and / or fly ash, preferably waste glass powder. The mass ratio of the third curing agent to the secondary curing manganese slag is (1-8):(2-9), preferably (2-4):(6-8); the tertiary curing temperature is 10-45° C., and the curing time is 14-36 hours.

8. The method according to claim 1, characterized in that The third curing agent is waste glass powder.

9. The method according to claim 1, characterized in that The average particle size of the third curing agent is 20-2000 mesh, preferably 50-1100 mesh, and more preferably 100-200 mesh.

10. The method according to claim 9, characterized in that In the tertiary solidification manganese slag leachate, the total mercury content, alkyl mercury content, total cadmium content, total chromium content, hexavalent chromium content, total arsenic content, total lead content, and total nickel content shall not be detected; the total manganese content shall be less than 0.1 mg / L, the ammonia nitrogen content shall be less than 2.1 mg / L, the mass fraction of soluble salts shall be less than 1.25%, and the mass fraction of organic matter shall be less than 1.7%.

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