Combined recovery method of waste salt and waste activated carbon

Abstract

The invention relates to a waste salt and waste activated carbon combined recovery method which comprises the following steps: mixing waste activated carbon, waste salt and alkali, and then sequentially crushing and calcining to obtain a calcined product containing sodium sulfide; sequentially performing dissolution and first solid-liquid separation on the calcined product to obtain a solution after dissolution; mixing the dissolved solution with acid for desulfurization reaction to obtain hydrogen sulfide gas and desulfurization mother liquor; carrying out alkali absorption on the hydrogen sulfide gas to obtain an absorption liquid; the absorption liquid is sequentially subjected to first evaporative crystallization and second solid-liquid separation, and a sodium sulfide nonahydrate product is obtained. The method can solve the problems of waste salt recovery and waste activated carbon treatment of the lithium battery, and realizes harmless treatment and resource treatment of solid wastes.

Description

Technical Field

[0001] This invention relates to the field of solid waste recycling technology, specifically to a method for the combined recycling of waste salt and waste activated carbon. Background Technology

[0002] With the continuous expansion of lithium battery production, the amount of lithium salt wastewater generated during lithium carbonate production is also increasing. Lithium salt wastewater mainly contains sulfate ions, chloride ions, and sodium ions. Currently, the main methods for treating lithium salt wastewater are salt separation through cooling crystallization, evaporation crystallization, and recrystallization. However, in this process, impurities in the wastewater are continuously concentrated, leading to a gradual increase in energy consumption, and the added value of the sodium sulfate produced by this process is low. Therefore, considering overall efficiency, the concentrated wastewater can only be produced as waste salt, which needs to be paid to qualified units for treatment. This not only wastes resources and increases environmental pressure but also increases the factory's wastewater treatment costs.

[0003] Waste activated carbon, being a rich source of toxic and hazardous substances, is flammable and toxic, requiring proper disposal to prevent pollution from contacting the environment. Currently, the main methods for treating waste activated carbon include activated carbon regeneration and incineration. Although activated carbon regeneration can restore some of its adsorption capacity to a certain extent, its performance gradually declines with each regeneration cycle, ultimately requiring incineration by a qualified organization. This disposal method also wastes resources and increases treatment costs.

[0004] How to properly handle waste salt and waste activated carbon, reduce the generation of solid waste, and save disposal costs are urgent problems that need to be addressed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the joint recycling of waste salt and waste activated carbon. Compared with the prior art, this invention can solve the problem of waste salt and waste activated carbon disposal in lithium battery recycling, and realize the harmless treatment and resource-based disposal of solid waste.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] This invention provides a method for the joint recovery of waste salt and waste activated carbon, the method comprising the following steps:

[0008] Waste activated carbon, waste salt and alkali are mixed, and then crushed and calcined in sequence to obtain a calcined product containing sodium sulfide.

[0009] The calcined product is sequentially dissolved and subjected to a first solid-liquid separation to obtain a dissolved liquid.

[0010] The dissolved liquid is mixed with acid to carry out a desulfurization reaction, yielding hydrogen sulfide gas and desulfurization mother liquor;

[0011] The hydrogen sulfide gas is subjected to alkaline absorption to obtain an absorbent solution;

[0012] The absorbent was subjected to a first evaporation and crystallization and a second solid-liquid separation to obtain sodium sulfide nonahydrate.

[0013] In this invention, waste activated carbon, waste salt, and alkali are mixed, wherein the waste activated carbon and sodium sulfate in the waste salt react, and the reaction equation is as follows: The waste activated carbon and water in the waste salt react, and the reaction equation is as follows: This invention utilizes the property of hydrogen sulfide to reduce low-value sodium sulfate in waste salt to high-value sodium sulfide, producing gases such as carbon monoxide and hydrogen. By adding alkali and controlling the pH of the calcination system, the decomposition and volatilization of sodium sulfide can be reduced, ensuring that sodium sulfate in the waste salt is transferred to the dissolved solution as much as possible in the form of sodium sulfide. This invention leverages the property of hydrogen sulfide as a diprotic weak acid. Using the principle of strong acid displacing weak acid, a strong acid is added to sulfide ions and hydrosulfide ions, causing them to convert into hydrogen sulfide gas and escape from the solution, thus achieving the separation of sulfide ions. Specifically, hydrogen sulfide gas is produced by adding acid to the dissolved solution to initiate a desulfurization reaction. The reaction equation is as follows: and The obtained hydrogen sulfide gas is then absorbed by an alkaline solution. The reaction equation is as follows: Then, through the first evaporation crystallization and the second solid-liquid separation, a high-purity sodium sulfide nonahydrate product is obtained, realizing the recovery and separation of sulfur elements.

[0014] In this invention, the method of solid-liquid separation is not particularly limited, and any commonly used method in the art can be adopted, such as filtration.

[0015] In this invention, the filter residue obtained after the first solid-liquid separation is returned to the pulverizing process to improve the utilization rate of activated carbon.

[0016] Preferably, the carbon content in the waste activated carbon is 80%-99% by mass, for example, it can be 80%, 82%, 84%, 86%, 88%, 90%, 92%, 95% or 99%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] In this invention, the source of the waste activated carbon is not specifically limited; for example, it can be waste activated carbon generated from liquid phase adsorption or waste gas treatment.

[0018] Preferably, the waste salt contains sodium sulfate and sodium chloride.

[0019] Preferably, the waste salt contains, by mass percentage, 50%-70% sodium sulfate, 20%-45% sodium chloride, and 5%-20% water.

[0020] In this invention, the waste salt may contain a small amount of impurities in addition to sodium sulfate, sodium chloride, and water. The content of impurities is <1%, which can be ignored.

[0021] Preferably, the molar ratio of carbon in the waste activated carbon to sulfur in the waste salt is 1:(6-8), for example, it can be 1:6, 1:6.2, 1:6.4, 1:6.6, 1:6.8, 1:7, 1:7.2, 1:7.4, 1:7.6, 1:7.8 or 1:8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0022] In this invention, controlling the molar ratio of carbon in the waste activated carbon to sulfur in the waste salt ensures a moderate excess of carbon source. This allows sulfate ions in the waste salt to fully react with the carbon source in a redox reaction, increasing the conversion rate of sulfate ions to sulfur ions. Insufficient carbon source leads to the production of other products such as sulfite, thus reducing the sulfur yield. Furthermore, waste salt typically contains small amounts of free water and water of crystallization. Adding an excess of carbon source allows water to react with the carbon source, reducing the probability of sodium sulfide hydrolyzing in water vapor to form hydrogen sulfide, further increasing the sulfur yield. However, excessive carbon source causes it to continuously circulate within the system, reducing the system's productivity.

[0023] Preferably, before calcination, the pulverized material and water are soaked in water at a mass ratio of 1:10. The pH value of the soaked material is 9.5-10.5, for example, 9.5, 9.6, 9.7, 9.8, 9.9, 10, 10.1, 10.2, 10.3, 10.4 or 10.5, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] In this invention, controlling the pH range provides an alkaline environment, reducing the likelihood of sodium sulfide hydrolysis in high-temperature steam. It also prevents excessive sodium hydroxide from being added, which could melt and coat the material at high temperatures, leading to incomplete reaction. Furthermore, if the waste activated carbon is acid-washed, adding alkali neutralizes residual hydrogen ions, preventing them from reacting with the generated sodium sulfide to produce hydrogen sulfide, which would then be discharged with the exhaust gas, reducing the sulfur yield.

[0025] Preferably, the alkali used in the mixture of waste activated carbon, waste salt, and alkali includes sodium hydroxide.

[0026] In this invention, the alkali can be sodium hydroxide commonly used in the art, including but not limited to industrial-grade sodium hydroxide.

[0027] Preferably, the waste activated carbon is subjected to acid washing and a third solid-liquid separation before mixing to obtain a post-acid-washed liquid and solid phase.

[0028] Preferably, the pickling agent used in the pickling includes hydrochloric acid.

[0029] In this invention, the pickling agent is generally prepared by hydrochloric acid and water. The water includes, but is not limited to, production water, distilled water, and condensate. For example, distilled water obtained from the second evaporation crystallization and the first evaporation crystallization or condensate generated during drying can be used. The hydrochloric acid includes, but is not limited to, industrial hydrochloric acid.

[0030] Preferably, the mass concentration of hydrochloric acid used for pickling is 15%-30%, for example, it can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29% or 30%, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0031] Preferably, the mass ratio of waste activated carbon to pickling agent in the pickling process is 1:(5-7), for example, it can be 1:5, 1:5.2, 1:5.5, 1:5.8, 1:6, 1:6.2, 1:6.5, 1:6.8 or 1:7, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the pH value of the pickling is 0.5-1.5, for example, it can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] In this invention, by controlling the pH value of the acid washing process, metallic impurities adsorbed in the waste activated carbon can be fully dissolved into the post-acid washing solution, thereby reducing the content of metallic impurities in the waste activated carbon. This reduces the interference of metallic impurities on subsequent redox and desulfurization reactions during calcination, improves the purity of sodium chloride products and the recovery rate of sulfur, and also increases the recovery rate of metallic elements from the waste activated carbon. Furthermore, it avoids excessive acid addition leading to hydrochloric acid waste and sodium hydroxide consumption during subsequent neutralization and precipitation, thus controlling production costs.

[0034] Preferably, the pickling time is 12h-36h, for example, it can be 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h or 36h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the solid phase is dried to obtain pretreated waste activated carbon, which is then mixed with the waste salt and the alkali.

[0036] In this invention, drying removes moisture from spent activated carbon. This avoids excessive moisture from consuming the activated carbon in subsequent reactions and allows for the recovery of condensate, saving water consumption. Furthermore, the condensate generated during drying can be used to prepare pickling agents in the pickling process, achieving water resource recycling.

[0037] Preferably, the drying temperature is 120℃-150℃, for example, it can be 120℃, 122℃, 125℃, 128℃, 130℃, 132℃, 135℃, 138℃, 140℃, 142℃, 145℃, 148℃ or 150℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0038] Preferably, the drying time is 2h-4h, for example, it can be 2h, 2.2h, 2.5h, 2.8h, 3h, 3.2h, 3.5h, 3.8h or 4h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the pickling solution is subjected to neutralization precipitation and a fourth solid-liquid separation in sequence to obtain the precipitated solution.

[0040] Preferably, the precipitant used for neutralization and precipitation includes sodium hydroxide.

[0041] In this invention, the acid-washed liquid is neutralized and precipitated with alkali, and a metal precipitate is obtained through a sixth solid-liquid separation, which can further recover valuable metals mixed in with the waste activated carbon.

[0042] Preferably, the pH value of the neutralized precipitate is 8-10, for example, it can be 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5, 9.8 or 10, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] Preferably, the mass concentration of the precipitant used for neutralization precipitation is 30%-32%, for example, it can be 30%, 30.5%, 31%, 31.5% or 32%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] Preferably, the neutralization and precipitation time is 1h-3h, for example, it can be 1h, 1.2h, 1.5h, 1.8h, 2h, 2.2h, 2.5h, 2.8h or 3h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] Preferably, the precipitated liquid is subjected to pH adjustment, second evaporation crystallization, and fifth solid-liquid separation in sequence to obtain sodium chloride product.

[0046] In this invention, the distilled water obtained from the second evaporation crystallization and the first evaporation crystallization can be used in the pickling process to prepare pickling agents or in the dissolving process as a solvent, thereby realizing the recycling of water resources.

[0047] Preferably, the precipitated liquid is mixed with the desulfurization mother liquor before pH adjustment.

[0048] In this invention, both the precipitate and the desulfurization mother liquor contain high levels of sodium chloride. After adjusting the pH value and performing a second evaporation crystallization and a fifth solid-liquid separation, a sodium chloride product with high purity can be obtained, ultimately achieving the separation and recovery of sodium sulfide and sodium chloride from waste salt.

[0049] Preferably, the endpoint pH value for pH adjustment is 6-8, for example, it can be 6, 6.2, 6.5, 6.8, 7, 7.2, 7.5, 7.8 or 8, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0050] Preferably, the pH adjuster used for pH adjustment includes sodium hydroxide.

[0051] Preferably, the mass concentration of the pH adjuster used for pH adjustment is 30%-32%, for example, it can be 30%, 30.5%, 31%, 31.5% or 32%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0052] Preferably, the pH value is adjusted and then allowed to stand.

[0053] Preferably, the settling time is 0.5h-1h, for example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h or 1h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0054] In this invention, there are no specific requirements for the operating conditions of the second evaporation crystallization. Conventional evaporation conditions in the art can be used, such as an evaporation crystallization temperature of 60°C-108°C, no requirements for the atmosphere, and the evaporation crystallization method includes, but is not limited to, vacuum evaporation crystallization or atmospheric pressure evaporation crystallization.

[0055] Preferably, the particle size after pulverization is ≤0.1mm, for example, it can be 0.1mm, 0.09mm, 0.08mm, 0.07mm, 0.06mm or 0.05mm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0056] Preferably, the calcination temperature is 850℃-950℃, for example, it can be 850℃, 855℃, 860℃, 865℃, 870℃, 875℃, 880℃, 885℃, 890℃, 895℃, 900℃, 905℃, 910℃, 915℃, 920℃, 925℃, 930℃, 935℃, 940℃, 945℃ or 950℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0057] In this invention, by controlling the calcination temperature, the redox reaction can be promoted, avoiding the redox reaction from being unable to proceed due to excessively low temperature, or the reaction rate being too slow and the reaction being incomplete, while also avoiding the reaction energy consumption from being too high temperature.

[0058] Preferably, the calcination time is 3h-6h, for example, it can be 3h, 3.2h, 3.5h, 3.8h, 4h, 4.2h, 4.5h, 4.8h, 5h, 5.2h, 5.5h, 5.8h or 6h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0059] Preferably, the calcination is carried out under a protective atmosphere.

[0060] Preferably, the protective atmosphere for calcination includes nitrogen.

[0061] In this invention, the calcination also yields exhaust gas containing carbon monoxide and hydrogen. The exhaust gas is incinerated under air conditions to generate carbon dioxide and water before being discharged in compliance with emission standards.

[0062] Preferably, the mass ratio of the calcined product to the solvent in the dissolution process is 1:(4-6), for example, it can be 1:4, 1:4.2, 1:4.5, 1:4.8, 1:5, 1:5.2, 1:5.5, 1:5.8 or 1:6, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0063] Preferably, the solvent includes water.

[0064] In this invention, the water used as the solvent includes, but is not limited to, production water, distilled water, etc., for example, it can be distilled water obtained from the second evaporation crystallization and the first evaporation crystallization.

[0065] Preferably, the dissolution time is 1-3 hours, for example, it can be 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours or 3 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0066] Preferably, the pH value of the desulfurization reaction is 0.5-1, for example, it can be 0.5h, 0.6h, 0.7h, 0.8h, 0.9h or 1h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0067] In this invention, by controlling the pH of the desulfurization reaction, sulfur ions in the solution can fully react with hydrogen ions to generate hydrogen sulfide, thereby improving the sulfur recovery rate, reducing the residual sulfur content in the desulfurization mother liquor, and consequently reducing the impurity sulfur content in the sodium chloride product. Furthermore, it avoids excessive acid addition, which would lead to waste of hydrochloric acid and increased consumption of sodium hydroxide in the subsequent pH adjustment process.

[0068] Preferably, the acid used in the desulfurization reaction includes hydrochloric acid.

[0069] Preferably, the mass concentration of hydrochloric acid used in the desulfurization reaction is 15%-30%, for example, it can be 15%, 16%, 18%, 20%, 22%, 24%, 26%, 28% or 30%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0070] Preferably, the temperature of the desulfurization reaction is 20℃-60℃, for example, it can be 20℃, 25℃, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃ or 60℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0071] Preferably, the desulfurization reaction time is 4h-12h, for example, it can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h or 12h, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0072] Preferably, the pH value of the alkaline solution used for alkaline absorption is ≥13, for example, it can be 13, 13.2, 13.4, 13.6, 13.8 or 14, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0073] Preferably, the alkaline solution used for alkali absorption includes sodium hydroxide.

[0074] Preferably, the mass concentration of the alkali solution used for alkali absorption is 30%-32%, for example, it can be 30%, 30.5%, 31%, 31.5% or 32%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0075] Preferably, the first evaporation crystallization method includes vacuum evaporation.

[0076] Preferably, the temperature of the first evaporation crystallization is 70℃-80℃, for example, it can be 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0077] In this invention, by controlling the pH of alkali absorption and the temperature of the first evaporation crystallization, the hydrolysis of sodium sulfide into hydrogen sulfide and its volatilization during evaporation can be effectively avoided.

[0078] Preferably, the first evaporation crystallization is carried out under a protective atmosphere.

[0079] Preferably, the protective atmosphere used for the first evaporation crystallization includes nitrogen.

[0080] In this invention, the first evaporation crystallization is controlled to be carried out under nitrogen protection, which can prevent sodium sulfide from being oxidized and deteriorated by oxygen in the air.

[0081] Preferably, the boiling point elevation of the mother liquor in the first evaporation crystallization is ≤15°C, for example, it can be 15°C, 14°C, 13°C or 12°C, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0082] In this invention, when the boiling point of the mother liquor in the first evaporation crystallization process rises to 15°C, evaporation is stopped, and the mother liquor is cooled down and reused in the alkali absorption process.

[0083] In this invention, when the boiling point of the mother liquor rises by 15°C, it is cooled and reused in the alkali absorption process. This is because the boiling point of a saturated pure sodium sulfide solution rises by 4.0°C. During the first evaporation and crystallization process, the mother liquor is a mixed solution of sodium sulfide and sodium hydroxide. As evaporation and crystallization proceed, sodium sulfide nonahydrate is continuously extracted, and the mother liquor becomes increasingly concentrated, leading to a further increase in the concentration of sodium hydroxide. This results in a further increase in the boiling point of the mother liquor, and simultaneously, an increase in sodium hydroxide impurities carried during the precipitation of sodium sulfide nonahydrate. Therefore, to ensure the purity of the sodium sulfide nonahydrate product, the boiling point rise of the mother liquor during evaporation must be controlled to ≤15°C; otherwise, not only will energy consumption increase, but the purity of the sodium sulfide nonahydrate product will also decrease.

[0084] As a preferred embodiment of the present invention, the method includes the following steps:

[0085] Waste activated carbon is acid-washed using hydrochloric acid with a mass concentration of 15%-30% as the acid washing agent. The mass ratio of waste activated carbon to acid washing agent is 1:(5-7). The pH value of acid washing is 0.5-1.5, and the acid washing time is 12h-36h. Then, the mixture is filtered to obtain the acid-washed liquid and solid phase. The solid phase is dried at 120℃-150℃ for 2h-4h to obtain pretreated waste activated carbon.

[0086] Pretreated waste activated carbon, waste salt, and sodium hydroxide are mixed to obtain a mixture. The waste activated carbon contains 80%-99% carbon by mass, and the waste salt contains 50%-70% sodium sulfate, 20%-45% sodium chloride, and 5%-20% water by mass. The molar ratio of carbon in the waste activated carbon to sulfur in the waste salt is 1:(6-8). The mixture is pulverized to a particle size ≤0.1mm, and the pH value of the pulverized material is measured by immersing the pulverized material and water at a mass ratio of 1:10. The pH value of the immersed material is 9.5-10.5. The pulverized material is then calcined at 850℃-950℃ under a nitrogen atmosphere for 3-6 hours to obtain a calcined product containing sodium sulfide and a tail gas containing carbon monoxide and hydrogen. The tail gas is incinerated under air conditions to generate carbon dioxide and water before being discharged in compliance with emission standards.

[0087] The calcined product was dissolved in water at a mass ratio of 1:(4-6) for 1-3 hours, and then filtered to obtain the dissolved liquid.

[0088] The dissolved solution is mixed with hydrochloric acid with a mass concentration of 15%-30%, and the desulfurization reaction is carried out at 20℃-60℃ for 4h-12h. The pH value of the desulfurization reaction is 0.5-1, and hydrogen sulfide gas and desulfurization mother liquor are obtained.

[0089] Hydrogen sulfide gas is absorbed by an alkaline solution with a mass concentration of 30%-32% sodium hydroxide. The pH value of the alkaline solution used for alkaline absorption is ≥13, and an absorption solution is obtained.

[0090] The absorbent is evaporated under reduced pressure at 70°C-80°C in a nitrogen atmosphere until the boiling point increases by 15°C. Then it is filtered to obtain sodium sulfide nonahydrate product and mother liquor. The mother liquor is cooled and reused in the alkali absorption process.

[0091] The pickling solution was neutralized and precipitated using a 30%-32% sodium hydroxide solution as a precipitant. The pH value of the neutralization precipitation was 8-10, and the neutralization precipitation time was 1-3 hours. Then, the solution was filtered to obtain the recovered valuable metal precipitate and the precipitated solution.

[0092] The precipitated liquid and the desulfurization mother liquor were mixed, and the pH value was adjusted to the final pH value of 6-8 using a sodium hydroxide solution with a mass concentration of 30%-32%. The mixture was then allowed to stand for 0.5-1 hour, followed by a second evaporation and crystallization to obtain sodium chloride product.

[0093] Compared with the prior art, the present invention has the following beneficial effects:

[0094] (1) The method provided by the present invention is to mix and calcine waste activated carbon and waste salt, and then use a desulfurization reaction process of strong acid to weak acid and an alkali absorption process to convert waste salt into sodium sulfide nonahydrate with high added value and high purity. Under optimal conditions, the sulfur recovery rate reaches more than 95.1%, and the content of sodium sulfide nonahydrate in the sodium sulfide nonahydrate product reaches more than 98.5%. It can be sold as a product, realizing the resource utilization of waste salt and waste activated carbon and reducing the disposal cost of solid waste.

[0095] (2) The method provided by the present invention obtains the precipitated liquid through processes such as acid washing and neutralization precipitation, mixes it with the desulfurization mother liquor obtained by the desulfurization reaction process, and obtains sodium chloride with high added value and high purity through processes such as pH adjustment and second evaporation crystallization. Under better conditions, the sodium chloride content in the sodium chloride product reaches more than 95.5%, which meets the standard of first-grade industrial wet salt in "Industrial Sodium Chloride" (GB / T 5462-2015). It can be sold as a product, realizing the resource utilization of waste salt and waste activated carbon, and reducing the disposal cost of solid waste.

[0096] (3) The method provided by the present invention can wash out the valuable metal ions contained in the waste activated carbon and obtain metal oxide precipitates through processes such as acid washing, neutralization and precipitation, so as to further realize the recycling of resources. Attached Figure Description

[0097] Figure 1 This is a flowchart of the method described in Embodiment 1 of the present invention. Detailed Implementation

[0098] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0099] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0100] Example 1

[0101] This embodiment provides a method for the combined recovery of waste salt and waste activated carbon, such as... Figure 1 As shown, the method includes the following steps:

[0102] Waste activated carbon was pickled using 30% hydrochloric acid (prepared with water and industrial hydrochloric acid) with stirring. The mass ratio of waste activated carbon to pickling agent was 1:6, the pH value of the pickling was 0.6, and the pickling time was 22 hours. Then, it was filtered through a plate and frame filter press to obtain the pickled liquid and solid phase. The solid phase was sent to a drying oven and dried at 135°C for 3 hours to obtain pretreated waste activated carbon. The condensate generated during drying was returned to the pickling process for the preparation of pickling agent.

[0103] Pretreated waste activated carbon, waste salt, and sodium hydroxide are mixed to obtain a mixture. The waste activated carbon contains 85% carbon by mass, and the waste salt contains 70% sodium sulfate, 20% sodium chloride, and the remainder is mainly water by mass. The molar ratio of carbon in the waste activated carbon to sulfur in the waste salt is 1:7. The mixture is pulverized to a particle size of <0.1mm, and the pH value of the pulverized material is measured by immersing the pulverized material and water at a mass ratio of 1:10. The pH value of the immersed material is 10. The pulverized material is then fed into a kiln and calcined at 900℃ under a nitrogen atmosphere for 4 hours to obtain a calcined product containing sodium sulfide and a tail gas containing carbon monoxide and hydrogen. The tail gas is incinerated under air conditions to generate carbon dioxide and water before being discharged in compliance with emission standards.

[0104] The calcined product was dissolved in water at a mass ratio of 1:5 for 1.5 hours. The solution was then filtered through a plate and frame filter press to obtain the dissolved liquid. The filter residue was returned to the crushing process.

[0105] The dissolved solution was mixed with 30% hydrochloric acid and subjected to a desulfurization reaction at 50°C for 7 hours. The pH value of the desulfurization reaction was 0.6, yielding hydrogen sulfide gas and desulfurization mother liquor.

[0106] Hydrogen sulfide gas was absorbed by an alkaline solution of 30% sodium hydroxide (prepared from water and industrial sodium hydroxide). The pH value of the sodium hydroxide solution used in the alkaline absorption process was ≥13. When the pH value was <13, the sodium hydroxide solution was replaced and absorption continued to obtain the absorption solution.

[0107] The absorbent is subjected to a first evaporation crystallization at 70°C under a nitrogen atmosphere, i.e., reduced pressure evaporation until the boiling point increases by 15°C. The distilled water produced by evaporation crystallization is reused in the preparation of the pickling agent. Then, the solution is filtered to obtain sodium sulfide nonahydrate product and evaporation mother liquor. The evaporation mother liquor is cooled and reused in the alkali absorption process.

[0108] The pickling solution was neutralized and precipitated using a 30% sodium hydroxide solution as a precipitant. The pH value of the neutralization precipitation was 9.5, and the neutralization precipitation time was 2 hours. Then, it was filtered through a plate and frame filter press to obtain the recovered valuable metal precipitate and the precipitated solution.

[0109] The precipitated liquid and the desulfurization mother liquor were mixed, and the pH value was adjusted to the final pH value of 7 using a 30% sodium hydroxide solution. After standing for 0.5 hours, a second evaporation and crystallization were carried out to obtain sodium chloride product.

[0110] Example 2

[0111] This embodiment provides a method for the combined recovery of waste salt and waste activated carbon, the method comprising the following steps:

[0112] Waste activated carbon was pickled using 20% ​​hydrochloric acid (prepared with water and industrial hydrochloric acid) with stirring. The mass ratio of waste activated carbon to pickling agent was 1:5, the pH value of the pickling was 0.5, and the pickling time was 12 hours. Then, it was filtered through a plate and frame filter press to obtain the pickled liquid and solid phase. The solid phase was sent to a drying oven and dried at 150°C for 2 hours to obtain pretreated waste activated carbon. The condensate generated during drying was returned to the pickling process for the preparation of pickling agent.

[0113] Pretreated waste activated carbon, waste salt, and sodium hydroxide are mixed to obtain a mixture. The waste activated carbon contains 90% carbon by mass, and the waste salt contains 60% sodium sulfate, 33% sodium chloride, and the remainder is mainly water by mass. The molar ratio of carbon in the waste activated carbon to sulfur in the waste salt is 1:8. The mixture is pulverized to a particle size of <0.1mm, and the pH value of the pulverized material is measured by immersing the pulverized material and water at a mass ratio of 1:10. The pH value of the immersed material is 9.5. The pulverized material is then fed into a kiln and calcined at 950℃ under a nitrogen atmosphere for 3 hours to obtain a calcined product containing sodium sulfide and a tail gas containing carbon monoxide and hydrogen. The tail gas is incinerated under air conditions to generate carbon dioxide and water before being discharged in compliance with emission standards.

[0114] The calcined product was dissolved in water at a mass ratio of 1:6 for 3 hours. The solution was then filtered through a plate and frame filter press to obtain the dissolved liquid. The filter residue was returned to the crushing process.

[0115] The dissolved solution was mixed with 20% hydrochloric acid and subjected to a desulfurization reaction at 60°C for 4 hours. The pH value of the desulfurization reaction was 1, yielding hydrogen sulfide gas and desulfurization mother liquor.

[0116] Hydrogen sulfide gas was absorbed by an alkaline solution of 30% sodium hydroxide (prepared from water and industrial sodium hydroxide). The pH value of the sodium hydroxide solution used in the alkaline absorption process was ≥13. When the pH value was <13, the sodium hydroxide solution was replaced and absorption continued to obtain the absorption solution.

[0117] The absorbent is subjected to a first evaporation crystallization at 75°C under a nitrogen atmosphere, i.e., reduced pressure evaporation until the boiling point increases by 15°C. The distilled water produced by evaporation crystallization is reused in the preparation of the pickling agent. Then, the solution is filtered to obtain sodium sulfide nonahydrate product and evaporation mother liquor. The evaporation mother liquor is cooled and reused in the alkali absorption process.

[0118] The pickling solution was neutralized and precipitated using a 30% sodium hydroxide solution as a precipitant. The pH value of the neutralization precipitation was 10, and the neutralization precipitation time was 1 hour. Then, it was filtered through a plate and frame filter press to obtain the recovered valuable metal precipitate and the precipitated solution.

[0119] The precipitated liquid and the desulfurization mother liquor were mixed, and the pH value was adjusted to the final pH value of 8 using a 30% sodium hydroxide solution. After standing for 1 hour, a second evaporation and crystallization were carried out to obtain sodium chloride product.

[0120] Example 3

[0121] This embodiment provides a method for the combined recovery of waste salt and waste activated carbon, the method comprising the following steps:

[0122] Waste activated carbon was pickled using 15% hydrochloric acid (prepared with water and industrial hydrochloric acid) with stirring. The mass ratio of waste activated carbon to pickling agent was 1:7, the pH value of the pickling was 1.5, and the pickling time was 36 hours. Then, it was filtered through a plate and frame filter press to obtain the pickled liquid and solid phase. The solid phase was sent to a drying oven and dried at 120°C for 4 hours to obtain pretreated waste activated carbon. The condensate generated during drying was returned to the pickling process for the preparation of pickling agent.

[0123] Pretreated waste activated carbon, waste salt, and sodium hydroxide are mixed to obtain a mixture. The waste activated carbon contains 99% carbon by mass, and the waste salt contains 50% sodium sulfate, 45% sodium chloride, and the remainder is mainly water by mass percentage. The molar ratio of carbon in the waste activated carbon to sulfur in the waste salt is 1:6. The mixture is pulverized to a particle size of <0.1mm, and the pH value of the pulverized material is measured by immersing the pulverized material and water at a mass ratio of 1:10. The pH value of the immersed material is 10.5. The pulverized material is then fed into a kiln and calcined at 850℃ under a nitrogen atmosphere for 6 hours to obtain a calcined product containing sodium sulfide and a tail gas containing carbon monoxide and hydrogen. The tail gas is incinerated under air conditions to generate carbon dioxide and water before being discharged in compliance with emission standards.

[0124] The calcined product was dissolved in water at a mass ratio of 1:4 for 1 hour, and then filtered through a plate and frame filter press to obtain the dissolved liquid. The filter residue was returned to the crushing process.

[0125] The dissolved solution was mixed with 15% hydrochloric acid and subjected to a desulfurization reaction at 20°C for 12 hours. The pH value of the desulfurization reaction was 0.5, yielding hydrogen sulfide gas and desulfurization mother liquor.

[0126] Hydrogen sulfide gas was absorbed by an alkaline solution of 30% sodium hydroxide (prepared from water and industrial sodium hydroxide). The pH value of the sodium hydroxide solution used in the alkaline absorption process was ≥13. When the pH value was <13, the sodium hydroxide solution was replaced and absorption continued to obtain the absorption solution.

[0127] The absorbent is subjected to a first evaporation crystallization at 70°C under a nitrogen atmosphere, i.e., reduced pressure evaporation until the boiling point increases by 15°C. The distilled water produced by evaporation crystallization is reused in the preparation of the pickling agent. Then, the solution is filtered to obtain sodium sulfide nonahydrate product and evaporation mother liquor. The evaporation mother liquor is cooled and reused in the alkali absorption process.

[0128] The pickling solution was neutralized and precipitated using a 30% sodium hydroxide solution as a precipitant. The pH value of the neutralization precipitation was 8, and the neutralization precipitation time was 3 hours. Then, it was filtered by a plate and frame filter press to obtain the recovered valuable metal precipitate and the precipitated solution.

[0129] The precipitated liquid and the desulfurization mother liquor were mixed, and the pH value was adjusted to the final pH value of 6 using a 30% sodium hydroxide solution. After standing for 0.5 hours, a second evaporation crystallization was carried out to obtain sodium chloride product.

[0130] Example 4

[0131] This embodiment provides a method for the joint recovery of waste salt and waste activated carbon. The only difference from Embodiment 1 is that the molar ratio of carbon in the waste activated carbon to sulfur in the waste salt is 1:4.

[0132] Example 5

[0133] This embodiment provides a method for the combined recovery of waste salt and waste activated carbon. The only difference from Embodiment 1 is that the crushed material is soaked in water at a mass ratio of 1:10, and the pH value of the resulting material is 8.

[0134] Example 6

[0135] This embodiment provides a method for the combined recovery of waste salt and waste activated carbon. The only difference from Embodiment 1 is that the crushed material is soaked in water at a mass ratio of 1:10, and the pH value of the resulting material is 12.

[0136] Example 7

[0137] This embodiment provides a method for the joint recovery of waste salt and waste activated carbon. The only difference from Embodiment 1 is that the waste activated carbon is not acid-washed.

[0138] Example 8

[0139] This embodiment provides a method for the combined recovery of waste salt and waste activated carbon. The only difference from Embodiment 1 is that the calcination temperature is 800℃.

[0140] Example 9

[0141] This embodiment provides a method for the combined recovery of waste salt and waste activated carbon. The only difference from Embodiment 1 is that the pH value of the desulfurization reaction is 2.

[0142] Example 10

[0143] This embodiment provides a method for the combined recovery of waste salt and waste activated carbon. The only difference from Embodiment 1 is that evaporation is stopped when the boiling point of the mother liquor in the first evaporation crystallization increases by 20°C.

[0144] The recovery rate of sulfur in the above embodiments was calculated as follows: sulfur recovery rate = mass of sulfur in sodium sulfide nonahydrate product / mass of sulfur in waste salt × 100%.

[0145] The sodium sulfide content of the sodium sulfide product nonahydrate in the above examples was detected using the detection method of sodium sulfide in "Industrial Sodium Sulfide" (GB 10500-2009), and then the content of sodium sulfide nonahydrate was calculated. The results are shown in Table 1.

[0146] The sodium chloride content in the sodium chloride products in the above examples was detected using the sodium chloride detection method in "Industrial Sodium Chloride" (GB / T 5462-2015), and the results are shown in Table 1.

[0147] Table 1

[0148]

[0149] As can be seen from Table 1:

[0150] (1) As can be seen from the data in Examples 1-3, the method provided by the present invention can, under better conditions, achieve a sodium sulfide nonahydrate content of more than 98.5%, a sulfur recovery rate of more than 95.1%, and a sodium chloride content of more than 95.5% in the sodium chloride product.

[0151] (2) A comparison of Examples 1 and 4 shows that the present invention, by optimally controlling the molar ratio of carbon in waste activated carbon to sulfur in waste salt, can further ensure the full progress of the redox reaction during calcination. In Example 4, due to insufficient carbon source supply, the reaction was incomplete, and sodium sulfate could not be fully converted into hydrogen sulfide, resulting in a reduced sulfur recovery rate. Furthermore, under incomplete redox conditions, some products were sodium sulfite. Sodium sulfite has a small amount of volatility under acidic conditions and is easily introduced into hydrogen sulfide, which is subsequently absorbed by alkali, leading to a decrease in the purity of the sodium sulfide nonahydrate product. In addition, unconverted sulfur remained in the desulfurization mother liquor, thus affecting the purity of the sodium chloride product.

[0152] (3) A comparison of Examples 1 and 5-6 shows that the present invention, by optimally controlling the pH value of the materials obtained from the crushing of waste activated carbon, waste salt, and sodium hydroxide after water immersion, can further improve the sulfur recovery rate and the purity of the sodium chloride product. In Example 5, the pH value after water immersion was too low, causing the generated sodium sulfide to undergo a hydrolysis reaction with high-temperature steam, and the generated hydrogen sulfide was lost in the tail gas, thereby reducing the sulfur recovery rate. In Example 6, the pH value after water immersion was too high, causing the sodium hydroxide to melt at high temperature, encapsulating the material and hindering the reaction from proceeding fully, thus reducing the sulfur recovery rate and the purity of the sodium chloride product.

[0153] (4) A comparison of Examples 1 and 7 shows that, by optimizing the acid washing of waste activated carbon, the present invention can further improve the sulfur recovery rate and the purity of sodium chloride products. In Example 7, because acid washing was not performed, the metal elements in the waste activated carbon reacted with the sodium sulfide generated during the redox reaction in the calcination process, forming sulfides that are insoluble in acid, thus reducing the sulfur recovery rate. At the same time, some metal elements entered the desulfurization mother liquor and eventually entered the sodium chloride product, thereby reducing the purity of the sodium chloride product.

[0154] (5) As can be seen from the comparison between Example 1 and Example 8, by controlling the calcination temperature in this invention, the oxidation-reduction reaction during calcination can be fully promoted. In Example 8, the calcination temperature was too low, resulting in insufficient oxidation-reduction reaction, which not only reduced the recovery rate of sulfur, but also left unconverted sulfur in the desulfurization mother liquor, thereby reducing the purity of the sodium chloride product.

[0155] (6) As can be seen from the comparison between Example 1 and Example 9, the present invention can promote the full progress of the desulfurization reaction by preferentially controlling the pH value of the desulfurization reaction. In Example 9, the pH value of the desulfurization reaction was too high, resulting in incomplete desulfurization reaction, which led to a decrease in the recovery rate of sulfur element and some sulfur element remaining in the desulfurization mother liquor, thereby reducing the purity of sodium chloride product.

[0156] (7) As can be seen from the comparison between Example 1 and Example 10, the purity of sodium chloride product can be further improved by optimally controlling the boiling point rise of the mother liquor during the first evaporation crystallization process. In Example 10, the boiling point rise was controlled too high during the first evaporation crystallization, resulting in a high concentration of sodium hydroxide in the mother liquor. This not only increased the evaporation energy consumption but also increased the amount of sodium hydroxide carried out when the sodium sulfide nonahydrate product precipitated, thus reducing the purity of the sodium sulfide nonahydrate product.

[0157] In summary, this invention can solve the problems of waste salt and waste activated carbon disposal in lithium battery recycling, and realize the harmless treatment and resource-based disposal of solid waste.

[0158] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for the combined recovery of waste salt and waste activated carbon, characterized in that, The method includes the following steps: Waste activated carbon, waste salt and alkali are mixed, and then crushed and calcined in sequence to obtain a calcined product containing sodium sulfide. The calcined product is sequentially dissolved and subjected to a first solid-liquid separation to obtain a dissolved liquid. The dissolved liquid is mixed with acid to carry out a desulfurization reaction, yielding hydrogen sulfide gas and desulfurization mother liquor; The hydrogen sulfide gas is subjected to alkaline absorption to obtain an absorbent solution; The absorbent was subjected to a first evaporation and crystallization and a second solid-liquid separation to obtain sodium sulfide nonahydrate.

2. The method according to claim 1, characterized in that, The carbon content in the waste activated carbon is 80%-99% by mass. Preferably, the waste salt contains sodium sulfate and sodium chloride; Preferably, the waste salt comprises, by mass percentage, 50%-70% sodium sulfate, 20%-45% sodium chloride, and 5%-20% water; Preferably, the molar ratio of carbon in the waste activated carbon to sulfur in the waste salt is 1:(6-8); Preferably, before calcination, the pulverized material and water are soaked in water at a mass ratio of 1:10, and the pH value of the soaked material is 9.5-10.

5. Preferably, the alkali used in the mixture of waste activated carbon, waste salt, and alkali includes sodium hydroxide.

3. The method according to claim 1 or 2, characterized in that, Before the mixing process, the waste activated carbon is sequentially acid-washed and undergoes a third solid-liquid separation to obtain an acid-washed liquid and a solid phase. Preferably, the pickling agent used in the pickling includes hydrochloric acid; Preferably, the pH value of the pickling is 0.5-1.5; Preferably, the pickling time is 12h-36h; Preferably, the solid phase is dried to obtain pretreated waste activated carbon, and the pretreated waste activated carbon is mixed with the waste salt and the alkali; Preferably, the drying temperature is 120℃-150℃; Preferably, the drying time is 2-4 hours.

4. The method according to claim 3, characterized in that, The pickling solution is subjected to neutralization precipitation and a fourth solid-liquid separation in sequence to obtain the precipitated solution; Preferably, the precipitant used for neutralization and precipitation includes sodium hydroxide; Preferably, the pH value of the neutralized precipitate is 8-10; Preferably, the neutralization and precipitation time is 1-3 hours.

5. The method according to claim 4, characterized in that, The precipitated liquid is subjected to pH adjustment, second evaporation crystallization, and fifth solid-liquid separation in sequence to obtain sodium chloride product; Preferably, the precipitated liquid is mixed with the desulfurization mother liquor before pH adjustment; Preferably, the endpoint pH value of the pH adjustment is 6-8; Preferably, the pH adjuster used for pH adjustment includes sodium hydroxide.

6. The method according to any one of claims 1-5, characterized in that, The particle size after pulverization is ≤0.1mm; Preferably, the calcination temperature is 850℃-950℃; Preferably, the calcination time is 3-6 hours; Preferably, the calcination is carried out under a protective atmosphere; Preferably, the protective atmosphere for calcination includes nitrogen.

7. The method according to any one of claims 1-6, characterized in that, The mass ratio of the calcined product to the solvent in the dissolution process is 1:(4-6); Preferably, the solvent includes water; Preferably, the dissolution time is 1-3 hours.

8. The method according to any one of claims 1-7, characterized in that, The pH value of the desulfurization reaction is 0.5-1; Preferably, the acid used in the desulfurization reaction includes hydrochloric acid; Preferably, the temperature of the desulfurization reaction is 20℃-60℃; Preferably, the desulfurization reaction takes 4-12 hours.

9. The method according to any one of claims 1-8, characterized in that, The pH value of the alkaline solution used for alkaline absorption is ≥13; Preferably, the alkaline solution used for alkali absorption includes sodium hydroxide.

10. The method according to any one of claims 1-9, characterized in that, The first evaporation crystallization method includes vacuum evaporation; Preferably, the temperature of the first evaporation crystallization is 70℃-80℃; Preferably, the first evaporation crystallization is carried out under a protective atmosphere; Preferably, the protective atmosphere used for the first evaporation crystallization includes nitrogen; Preferably, the boiling point of the mother liquor in the first evaporation crystallization process is increased by ≤15°C.

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