A polysulfide heavy metal removing agent, its preparation method and application

Abstract

The application discloses a multi-sulfur-based heavy metal removal agent for steel plant ash washing wastewater, a preparation method thereof and a method for treating ash washing wastewater by using the same, and high-purity potassium chloride is produced by using high-salt solid waste ash generated by a steel enterprise. Meanwhile, based on the characteristics of the high-salt solid waste ash, such as high thallium, ammonia nitrogen and sulfate radical concentration in the water washing wastewater, a deep thallium removal idea based on weak reduction and complexation breaking, same ion effect precipitation and chelation thallium removal is first proposed, the multi-sulfur-based heavy metal removal agent is used to realize deep removal of thallium in the high-salt wastewater, and combined with the characteristics of the sintering flue gas purification and acid wastewater containing a large amount of sulfite ions and low acidity, the multi-sulfur-based heavy metal removal agent is used for removing sulfur, removing ammonia nitrogen and removing thallium in the ash washing wastewater, and the countercurrent evaporation and potassium and sodium separation are used for the synergistic effect, so that the collaborative treatment and resource utilization of the high-salt solid waste ash and the acid wastewater of the steel plant are realized, and the quality of the recovered potassium salt is greatly improved. Meanwhile, the technical scheme provided by the application also has the advantages of simple process conditions, low energy consumption, no wastewater discharge and the like.

Description

Technical Field

[0001] This invention relates to solid waste and wastewater treatment in the steel industry, specifically to a polysulfide-based de-gravity agent for ash washing wastewater in steel plants, its preparation method, and a method for treating ash washing wastewater using the agent, belonging to the technical field of co-resource utilization of solid waste ash and wastewater in the steel industry. Background Technology

[0002] Currently, the solid waste generated by the steel industry is mainly composed of iron. Most of it is processed through the internal circulation of steel production in high-temperature furnaces such as sintering, blast furnaces, and rotary kilns. However, there is still some high-salt solid waste ash (such as ash from the third and fourth electric fields of sintering, and ash from bag filters in blast furnaces), which contains a lot of alkali metal chlorides. If it is directly returned to high-temperature furnaces such as sintering, blast furnaces, and rotary kilns, it will lead to adverse conditions such as equipment corrosion, pipeline blockage, and kiln caking, and may even affect the quality of sintered ore.

[0003] Currently, for high-salt solid waste generated by steel plants, water washing is commonly used to remove alkali metals and chlorine, while simultaneously recovering potassium and sodium salts. For example, Chinese patent CN101234766B, "Method for producing potassium chloride from sintering electrostatic precipitator ash in steel enterprises," reports the use of tap water to leach sintering electrostatic precipitator ash, significantly reducing potassium and chlorine in the ash, and using the ash washing water to prepare potassium chloride and sodium chloride. Chinese patent CN101723410B, "Method for Recovering Potassium from Sintering Ash in Iron and Steel Plants and Preparing Potassium Sulfate," uses industrial water circulation to wash sintering machine head ash to extract potassium salts. Ammonium bicarbonate and activated carbon are added for impurity removal and decolorization. However, this method has several drawbacks: a long process, high cost due to the addition of numerous impurity removal agents, and the introduction of significant ammonia nitrogen, affecting the quality of the evaporated crystallized salt and increasing fugitive ammonia nitrogen emissions. Furthermore, potassium sulfate production easily generates potassium sulfate, affecting product quality and potentially causing blockages in the evaporation system. Additionally, the sintering machine head ash is rich in thallium from the ore, which is not specifically removed during the impurity removal process, affecting the thallium content in the salt and failing to meet environmental protection requirements. Chinese patent CN114044528A, "A Method for Solvent Crystallization Separation and Recovery of Potassium Chloride from Sintering Ash in Iron and Steel Metallurgy," reports a method for recovering KCl from sintering machine head ash using a two-stage countercurrent water washing technique, which can reduce the cost of potassium salt production. CN113862462A, "A Method for Combined Dechlorination of Sintering Machine Head Ash and Blast Furnace Bag Ash," reports a method for leaching sintering machine head ash and blast furnace bag ash with clean water. This method can achieve the co-processing of various solid wastes with different properties and recover KCl salts simultaneously. However, it has drawbacks such as high water consumption and the risk of failing to leach chloride ions due to excessively high chloride ion concentrations. Furthermore, it only recovers KCl salts, while other mixed salts need to be treated as hazardous waste, increasing the overall process cost. Additionally, it does not specifically remove thallium, affecting the thallium content in the KCl salts.

[0004] Because high-salt solid waste ash has a complex composition, the washing water also has a complex composition. Besides a high salt concentration, it contains a significant amount of heavy metals, which not only limits the quality of potassium salt production but also leads to excessive heavy metal levels in the cooling water. Conventional precipitation methods for heavy metal removal are lengthy and use expensive reagents. Furthermore, it contains high levels of thallium (Tl), typically between 20 and 200 mg / L. Tl reacts with Cl in the solution... - The combination forms a very stable [TlCl4] - Thallium complexes are difficult to remove by conventional precipitation methods, which means that existing technologies cannot effectively remove thallium from high-salt wastewater and achieve compliant discharge.

[0005] The main methods for removing thallium from industrial wastewater include sodium sulfide precipitation, oxidative precipitation, and electrochemical precipitation. Sodium sulfide precipitation has relatively low equipment investment, is simple to operate, and has moderate process stability. In high-salinity water, the treatment depth is generally 1-2 mg / L, but the treatment effect is unstable, and it produces a lot of sludge, failing to meet the 5 μg / L standard requirement. Oxidative precipitation has relatively high equipment investment and moderate process stability. In high-salinity water, the treatment depth is generally 2-5 mg / L, but the operation is cumbersome, and the reagent consumption is high. It also produces a lot of sludge and fails to meet the 5 μg / L standard requirement. Electrochemical precipitation is simple and stable, producing less sludge, and can treat ≤10 μg / L in high-salinity water. However, it requires huge equipment investment, and the treatment depth is difficult to consistently meet the 5 μg / L standard requirement. Among these methods, oxidative precipitation is the most commonly used. For example, Chinese patent CN1067229A discloses a method for removing thallium by oxidative precipitation, which uses an oxidant to oxidize Tl(I) to Tl(III), and then adds alkali to form a precipitate to achieve thallium discharge compliance. Chinese patent CN106977013A discloses a purification method for high-chlorine thallium-containing wastewater and its application. The method involves oxidizing Tl(I) with an oxidant, pretreating Tl(III) with an ion exchange resin, and then further removing Tl(III) with sodium sulfide. The methods disclosed above all involve oxidation followed by thallium removal, which has the following drawbacks: ① Adding the oxidant first, then the thallium-removing precipitant, is complex and increases the cost of thallium removal; ② Thorough oxidation of the wastewater is required for thallium removal, but high-salinity wastewater contains large amounts of chlorine and COD, which consumes some of the oxidant, leading to unstable thallium removal efficiency; ③ When using sulfide precipitation, elemental sulfur is formed in the oxidant system, causing waste of reagents or other pollution problems. Furthermore, when applied to high-salinity thallium-containing wastewater, since the wastewater ultimately requires evaporation, salt separation, and crystallization to recover chloride, the added oxidant will enter the final chloride product, reducing the quality of the chloride.

[0006] Therefore, it is imperative to develop a simple, low-cost, and deep-purification thallium removal agent based on the characteristics of thallium in high-salt wastewater, and to use it to achieve efficient desalination and thallium removal of high-salt solid waste ash washing wastewater. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a polysulfide-based heavy metal removal agent for steel plant ash washing wastewater, its preparation method, and a method for treating the wastewater using this agent. It can utilize wastewater from the sintering process of steel enterprises and high-salt solid waste ash to produce high-purity potassium chloride, while avoiding the corrosion and kiln clogging problems caused by alkali metals and chlorine entering high-temperature furnaces such as sintering, blast furnaces, and rotary kilns. Furthermore, based on the characteristics of high-salt solid waste ash washing wastewater with high concentrations of heavy metals such as thallium, ammonia nitrogen, and sulfate, this invention proposes for the first time a deep thallium removal approach based on weak reduction complexation-complex breaking-common ion effect precipitation-chelation thallium removal. This achieves deep removal of thallium from high-salt wastewater. Combined with the characteristics of steel plant sintering flue gas purification acid production wastewater containing a large amount of sulfite ions and low acidity, this invention utilizes ash washing wastewater for sulfur and ammonia nitrogen removal, and employs countercurrent evaporation for potassium and sodium separation, achieving the synergistic treatment and resource utilization of high-salt solid waste ash and acidic wastewater from steel plants, significantly improving the quality of recovered potassium salts. Meanwhile, the technical solution provided by this invention also has the advantages of simple process conditions, low energy consumption, and no wastewater discharge.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is specifically described as follows:

[0009] According to a first embodiment of the present invention, a polysulfide-based deweighting agent for washing ash wastewater in steel plants is provided.

[0010] A polysulfide-based deweighting agent for washing ash wastewater in steel plants, comprising 10-30% (preferably 15-25%) of Desulfovibrio bacteria metabolites, 3-12% (preferably 5-10%) of sulfides, 3-15% (preferably 5-10%) of sulfur-based heavy metal scavengers, 5-15% (preferably 8-12%) of ferrous salts, 0-5% (preferably 0.5-4%) of alkali, and water.

[0011] Preferably, the Desulfovibrio bacteria metabolite is prepared by culturing Desulfovibrio bacteria (preferably Desulfovibrio desulfuricans) in a culture medium (preferably Postgate medium) for 3-10 days (preferably 5-8 days), then removing it and sterilizing it in an autoclave at 110-140℃ (preferably 115-130℃), and finally performing solid-liquid separation. The resulting filtrate is the Desulfovibrio bacteria metabolite.

[0012] Preferably, the sulfide is selected from one or more of sodium sulfide, calcium sulfide, and potassium sulfide, with sodium sulfide being the most preferred.

[0013] Preferably, the sulfur-based heavy metal scavenger is sodium dimethyl dithiocarbamate (SDD) and / or dithiocarbamate (DTC), with sodium dimethyl dithiocarbamate (SDD) being the most preferred.

[0014] Preferably, the ferrous salt is selected from one or more of ferrous sulfite, ferrous chloride, ferrous sulfate, and ferrous nitrate, and is preferably ferrous sulfite and / or ferrous chloride.

[0015] Preferably, the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide, with sodium hydroxide being the most preferred.

[0016] According to a second embodiment of the present invention, a method for preparing a polysulfide-based de-weighting agent is provided.

[0017] A method for preparing a polysulfide-based heavy metal scavenging agent, or a method for preparing the polysulfide-based heavy metal scavenging agent described in the first embodiment, specifically comprises: dissolving a sulfide, a ferrous salt, and an alkali in water in a certain proportion and mixing them evenly (preferably stirring at room temperature for 0.5-2 hours), wherein the amount of alkali added is such that the pH of the mixture is 8-10 (preferably 8-9). Then, under a nitrogen atmosphere, the mixture is first heated to 40-60°C (preferably 45-55°C), and then the metabolites of *Desulfovibrio* bacteria are added, and the mixture is stirred for 0.5-2 hours (preferably 0.8-1.5 hours). Finally, the mixture is cooled (preferably cooled to room temperature) and a sulfur-based heavy metal scavenging agent is added, and the mixture is stirred for another 0.5-2 hours (preferably 0.8-1.5 hours) to obtain the polysulfide-based heavy metal scavenging agent.

[0018] Preferably, the sulfide is selected from one or more of sodium sulfide, calcium sulfide, and potassium sulfide, with sodium sulfide being the most preferred.

[0019] Preferably, the sulfur-based heavy metal scavenger is sodium dimethyl dithiocarbamate (SDD) and / or dithiocarbamate (DTC), with sodium dimethyl dithiocarbamate (SDD) being the most preferred.

[0020] Preferably, the ferrous salt is selected from one or more of ferrous sulfite, ferrous chloride, ferrous sulfate, and ferrous nitrate, and is preferably ferrous sulfite and / or ferrous chloride.

[0021] Preferably, the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide, with sodium hydroxide being the most preferred.

[0022] Preferably, the mass ratio of the Desulfovibrio bacteria metabolites, sulfides, sulfur-based heavy metal scavengers, ferrous salts, and alkali added is 10-30% (preferably 15-25%): 3-12% (preferably 5-10%): 3-15% (preferably 5-10%): 5-15% (preferably 8-12%): 0-5% (preferably 0.5-4%).

[0023] According to a third embodiment of the present invention, a method for washing, desalinating, and removing thallium from solid waste ash in a steel plant is provided.

[0024] A method for desalination and thallium removal from solid waste ash in a steel plant, comprising the following steps:

[0025] 1) Ash washing treatment: The solid waste ash is washed with water using a three-stage countercurrent water washing process to obtain ash washing wastewater.

[0026] 2) Deep thallium removal: First, add alkali to the ash washing wastewater obtained in step 1), then add the polysulfide-based weight removal agent described in the first embodiment or the polysulfide-based weight removal agent prepared by the method described in the second embodiment to react. After the reaction is completed, perform solid-liquid separation to obtain thallium-removed wastewater.

[0027] 3) Impurity removal treatment: Add hardening agent and flocculant to the thallium removal wastewater obtained in step 2), and obtain high-salt wastewater after solid-liquid separation.

[0028] 4) Countercurrent evaporation to remove sodium chloride: The high-salinity wastewater obtained in step 3) is heated, concentrated, and crystallized. After solid-liquid separation, sodium chloride and filtrate are obtained. The filtrate is cooled and crystallized. After solid-liquid separation, potassium chloride and residual liquid are obtained. The residual liquid is returned to the high-salinity wastewater obtained in step 3) for recycling treatment.

[0029] Preferably, in step 1), the three-stage countercurrent washing specifically involves: first, the solid waste ash undergoes a primary slurry washing, with a slurry washing liquid-to-solid ratio of 2-7:1 (preferably 3-5:1). The primary washing water is the secondary washing clarified liquid. After the primary washing, the ash is dewatered by a primary plate and frame filter press. After solid-liquid separation, a primary clarified liquid and a primary filter cake are obtained. The primary clarified liquid enters a deep thallium removal treatment process, and the primary filter cake undergoes a secondary slurry washing. The secondary washing water is the tertiary washing clarified liquid. After the secondary washing, the ash is dewatered by a secondary plate and frame filter press. After solid-liquid separation, a secondary clarified liquid and a secondary filter cake are obtained. The secondary clarified liquid is discharged into the primary water system for recycling, and the secondary filter cake undergoes a tertiary slurry washing. The tertiary washing water is wastewater from sintering flue gas activated carbon desulfurization and acid production, and / or condensate. After the tertiary washing, the water is dewatered by a tertiary plate and frame filter press to obtain tertiary clear liquid and tertiary filter cake. The tertiary clear liquid is discharged to the secondary washing for recycling, and the tertiary filter cake is returned to the sintering process for batching and disposal.

[0030] Preferably, the solid waste ash is selected from one or more of the following: sintering electric field ash, blast furnace bag ash, rotary kiln surface cooling ash, and waste incineration fly ash.

[0031] Preferably, in step 2), adding alkali to the ash washing wastewater specifically involves adding sodium hydroxide and / or potassium hydroxide to the ash washing wastewater until the pH of the ash washing wastewater is 3-12, preferably 5-11, and more preferably 7-10.

[0032] Preferably, in step 2), the amount of the polysulfide-based de-gravity agent added is 0.05-5% of the total mass of the ash washing wastewater, preferably 0.1-3%, and more preferably 0.2-2%.

[0033] Preferably, in step 3), the hardening agent is sodium carbonate and / or potassium carbonate, preferably sodium carbonate.

[0034] Preferably, in step 3), the flocculant is polyaluminum chloride (PAC) and / or polyacrylamide (PAM), with polyaluminum chloride (PAC) being the preferred choice.

[0035] Preferably, the amount of the hardening agent added is 0.5-8% of the total mass of the thallium removal wastewater, more preferably 0.8-5%, and even more preferably 1-3%.

[0036] Preferably, the amount of flocculant added is 1 to 5‰ of the total mass of the thallium removal wastewater, and more preferably 1.5 to 3‰.

[0037] Preferably, in step 4), the countercurrent evaporation to remove potassium sodium is carried out using a multi-effect evaporator, wherein the multi-effect evaporator has 2-6 stages (preferably 3-5 stages).

[0038] Preferably, the high-salinity wastewater obtained in heating step 3) is specifically heated to 80-110℃ (preferably 85-100℃). The cooling of the filtrate is specifically achieved by flash evaporation or heat exchange to reduce the temperature to below 60℃ (preferably 25-55℃).

[0039] Preferably, the potassium-to-sodium ratio in the solid waste ash is not less than 2, more preferably not less than 2.5, and even more preferably not less than 3.

[0040] Preferably, the pH of the ash washing wastewater is below 3, preferably 1-3, and more preferably 2-3.

[0041] Preferably, the potassium-to-sodium ratio in the high-salt wastewater is not higher than 1.5, more preferably not higher than 1.3, and even more preferably 1-1.1.

[0042] In existing technologies, to avoid equipment corrosion and kiln clogging caused by alkali metals and chloride elements in high-salt solid waste ash, water washing is commonly used to remove alkali and chloride metals and recover potassium and sodium salts. However, due to the complex composition of high-salt solid waste ash, the washing wastewater also has a complex composition, containing large amounts of metal ions, ammonia nitrogen, and sulfate. To address this, the washing wastewater is often adjusted to alkalinity to remove metal ions and ammonia nitrogen. However, research shows that thallium in high-salt solid waste ash washing wastewater readily forms [TlCl4] under alkaline conditions. - ], due to [TlCl4 - The potassium salt is relatively stable, but once formed, it is difficult to treat using conventional removal processes, resulting in a high level of impurities and relatively low purity in the recovered potassium salt, which affects its utilization. Conventional precipitation methods for heavy metal removal are lengthy, use expensive reagents, and are ineffective at removing heavy metals such as Ti, which form stable chloride complexes. Secondly, for high-salt solid waste ash washing wastewater with a higher potassium content than sodium, existing technologies generally precipitate potassium salt first, followed by sodium salt. Precipitating potassium salt first allows impurities and pollutants to precipitate along with it, reducing the quality of the potassium salt. Furthermore, subsequent sodium salt precipitation requires further heating and concentration, increasing energy consumption. Conversely, if sodium salt is precipitated first, since the potassium content is higher than the sodium, potassium salt will inevitably precipitate first, reducing both the quality and yield of the sodium salt.

[0043] In this invention, since the high-salt solid waste ash from steel plants is high-potassium and low-sodium ash, the potassium-to-sodium ratio in its washing solution is generally not less than 3. Analysis of the potassium-sodium salt phase diagram through variable-temperature evaporation shows that after the high-potassium, low-sodium solution is concentrated through evaporation, potassium salts will inevitably precipitate first. Therefore, the salt separation method for sintered ash washing water is generally co-current evaporation, meaning the solution gradually cools down during evaporation. At the multi-effect outlet, potassium salts are discharged first. This evaporation method causes pollutants to precipitate along with potassium, reducing potassium quality. Furthermore, subsequent sodium salt precipitation requires a second stage of evaporation, increasing investment and energy consumption. Therefore, this invention introduces activated carbon desulfurization and acid production wastewater (containing sodium) from sintered flue gas as washing water for high-salt solid waste ash, thereby achieving a potassium-to-sodium ratio in the washing wastewater close to 1:1. Under these conditions, the evaporation process can be adjusted to counter-current evaporation, meaning the solution gradually heats up during evaporation, and sodium salts are discharged first at the first-effect outlet. Then, the potassium salt is precipitated by cooling. This evaporation method causes residual contaminants to precipitate out along with the sodium, preventing them from entering the potassium salt and thus improving the quality of the potassium. Furthermore, the entire evaporation process utilizes only a single evaporation system, making it adaptable to varying evaporation rates, more versatile for different raw materials, and requiring lower investment.

[0044] In this invention, the wastewater from sintering flue gas activated carbon desulfurization and acid production includes suspended solids, metal ions, ammonia nitrogen, fluorine, chlorine, etc. The metal ions include one or more of sodium, iron, copper, lead, calcium, zinc, cadmium, cobalt, nickel, and aluminum. Based on the characteristics of high-salt solid waste ash washing wastewater containing high levels of heavy metals such as thallium and high concentrations of ammonia nitrogen, and considering the high sulfite content and low acidity of sintering flue gas activated carbon desulfurization and acid production wastewater, this paper proposes using sintering flue gas activated carbon desulfurization and acid production wastewater as the washing water for high-salt solid waste ash, building upon existing high-salt solid waste ash washing and wastewater resource utilization processes. Firstly, this reduces fresh water consumption and the cost of separate wastewater treatment. Secondly, the presence of sodium in the sintering flue gas activated carbon desulfurization and acid production wastewater allows for adjusting the potassium-sodium ratio in the washing wastewater to facilitate countercurrent evaporation and the production of high-quality potassium salts. Thirdly, the sulfite and ferrous ions (with the addition of soluble ferrous salts, such as ferrous chloride, if necessary) in the sintering flue gas activated carbon desulfurization and acid production wastewater can combine with the ammonia nitrogen generated during washing to form ferrous ammonium sulfite precipitate, thus removing ammonia nitrogen. Finally, this approach can suppress thallium at the source of the washing process, as thallium in high-salt wastewater readily forms a relatively stable [TlCl4] under alkaline conditions. - Once formed, [TlCl4] is difficult to treat using conventional removal processes. Because the wastewater from activated carbon desulfurization and acid production in sintering flue gas is highly acidic, using it for ash washing can, on the one hand, reduce the acidity of the washing water, making it acidic and thus preventing the formation of stable [TlCl4]. - On the other hand, since the wastewater from activated carbon desulfurization and acid production in sintering flue gas contains thiosulfate, its addition facilitates the removal of thallium, thus achieving source inhibition of thallium. Studies have shown that the thallium content in the washing water of conventional industrial ash washing is about 30 mg / L. When sintering flue gas activated carbon desulfurization and acid production wastewater is introduced, the thallium content in the washing water can be reduced to about 1 mg / L. That is, this invention uses sintering flue gas activated carbon desulfurization and acid production wastewater to co-treat high-salt solid waste ash, which on the one hand achieves the adjustment of the potassium-sodium ratio to close to 1:1, realizes countercurrent evaporation, and improves the quality of potassium salts; on the other hand, it reduces the dissolution of thallium at the source, further ensuring the purity of potassium salts and increasing their value.

[0045] In this invention, addressing the problem of high thallium content in ash washing wastewater, a polysulfide-based heavy metal removal agent is provided, comprising 10-30% (preferably 15-25%) of Desulfovibrio bacteria metabolites, 3-12% (preferably 5-10%) of sulfides, 3-15% (preferably 5-10%) of sulfur-based heavy metal scavengers, 5-15% (preferably 8-12%) of ferrous salts, 0-5% (preferably 0.5-4%) of alkali, with the balance being water. This invention proposes for the first time a deep thallium removal approach based on weak reduction complexation-common ion effect precipitation-chelation, which can achieve deep removal of thallium from ash washing wastewater. Generally, Tl(III) forms a stable [TlCl4] with chlorine in ash washing wastewater.- This complex is relatively stable and difficult to remove completely by precipitation. Therefore, the polysulfide-based heavy removal agent of this invention constructs a micro-reduction zone through ferrous ions and sulfite ions in steel mill ash washing wastewater, thereby destroying [TlCl4]. - The complexed state triggers the dissociation of the complex, converting thallium into free Tl(III) and Tl(I) ions. Simultaneously, since the washing process uses sodium-containing wastewater (sintering flue gas activated carbon desulfurization and acid production wastewater), the acidic wastewater itself reduces thallium dissolution, resulting in a significantly lower thallium concentration in the wastewater. Furthermore, the additional sodium concentration during the washing wastewater treatment, based on the common ion effect, prevents thallium from dissolving, thus disrupting its stability in solution and making it easier to remove.

[0046] In this invention, the polysulfide-based deweighting agent can reduce a small amount of free Tl(III) in wastewater to Tl(I) and destroy [TlCl4]. - The coordination equilibrium of [TlCl4] leads to the [TlCl4] - Internal dissociation promotes the rapid release of the complex center Tl(III) into the aqueous phase. Furthermore, the sulfur-containing groups in the Desulfovibrio bacteria metabolites and the sulfur-based heavy metal scavenger can synergistically form high-stability-constant Tl multivalent, multidentate chelate precipitates with free Tl(III) and Tl(I) ions, occupying all the outermost electrons of Tl(III) and limiting Cl-. - When other anions are re-coordinated, combined with the combined effect of weak reduction complex breaking and common ion effect to thallium precipitation, thallium can be deeply removed from the aqueous system.

[0047] The polysulfide-based heavy metal removal agent of this invention achieves one-step synergistic removal of thallium and heavy metals through a one-step addition method. Through formulation experiments, ferrous salts, Desulfovibrio bacteria metabolites, and sulfur-based heavy metal trapping agents are compounded to form a polysulfide-based thallium removal agent, combining the weak reducing complex-breaking process and the polysulfide chelation of thallium into one process. This rapidly chelates free Tl(III) and Tl(I) ions while breaking the complex. It has the advantages of simple operation and deep removal; moreover, in addition to rapid thallium removal, because the agent also contains a small amount of inorganic sulfides, it can simultaneously precipitate heavy metals such as Cu, Pb, and Zn, achieving one-step removal of multiple heavy metals and shortening the wastewater treatment process. Furthermore, the residual substances in this agent can be removed through subsequent hardening processes and will not enter the final evaporation and salt separation process, ensuring the quality of the recovered chloride salts.

[0048] In this invention, sodium carbonate is added as a subsequent hardening agent and a flocculant during the impurity removal process to remove excess thallium removal agent and other remaining heavy metal ions, preventing excess agent from entering the evaporation and crystallization system and affecting the quality of the salt; the sodium ion concentration is further increased to limit the dissolution of thallium ions and control the thallium content in the salt; excess sodium carbonate can be removed by adjusting the pH value without affecting the quality of the salt.

[0049] In this invention, a three-stage countercurrent water washing technology is used to wash high-salt solid waste ash from steel plants, thereby enhancing the removal of salt from the ash. By circulating the washing water within the washing system, the salt concentration in the water is increased, and the water-to-ash ratio is reduced, saving water consumption and lessening the load on the final evaporation and crystallization system. The three-stage countercurrent water washing source is sintering flue gas activated carbon desulfurization and acid production wastewater and / or condensate from evaporation and crystallization, enabling the co-treatment of high-salt wastewater and high-salt solid waste, further reducing fresh water consumption.

[0050] In this invention, high-salinity wastewater generally needs to undergo homogenization treatment before countercurrent evaporation (to make the potassium-to-sodium ratio close to 1:1, for example, by adding sodium chloride to adjust the potassium-to-sodium ratio) before being fed into a multi-effect evaporator. The multi-effect evaporator employs a countercurrent design, meaning the high-salinity solution sequentially passes through a multi-effect reactor → a second-effect reactor → a first-effect reactor, with the solution temperature rising from room temperature to 80-110℃ (e.g., 95℃). After evaporation, sodium salt precipitates when the sodium salt saturation precipitation point is reached. Sodium salt can be recovered through centrifugation (the recovered sodium salt can be used for homogenization treatment of the high-salinity wastewater), and the mother liquor obtained from centrifugation is returned to the first-effect evaporator for further concentration. After concentration to the potassium salt saturation precipitation point, the solution is cooled to below 60℃ to precipitate potassium salt, which can then be recovered through centrifugation. The mother liquor obtained from centrifugation is returned to the multi-effect evaporator for further concentration. Furthermore, the precipitated potassium chloride solid can be fed into a washing device and washed with a saturated potassium chloride solution to further purify the potassium chloride. After centrifugation, high-purity potassium chloride is obtained. This invention controls the potassium-sodium ratio to approximately 1:1 by adding sodium salt or returning the evaporated sodium salt to the high-salinity wastewater. The evaporation process is adjusted to countercurrent evaporation, meaning the solution gradually heats up during evaporation. Sodium salt is discharged first from the outlet of the first effect. Under this evaporation method, pollutants precipitate out along with the sodium and do not enter the potassium salt, which is beneficial for improving potassium quality. Simultaneously, the entire evaporation process utilizes only one evaporation system, making it adaptable to variations in evaporation rates, more versatile for raw materials, and requiring lower investment.

[0051] In this invention, Desulfovibrio bacteria are desulfovibrio bacteria. All Desulfovibrio bacteria have a common characteristic: their metabolites contain sulfur-containing reducing substances. This invention utilizes the sulfur-containing reducing agent in the metabolites of Desulfovibrio bacteria and the sulfur-based heavy metal scavenger as a polysulfide-based thallium removal agent.

[0052] In this invention, the Desulfovibrio strain is preferably Desulfovibrio desulfuricans, such as desulfuricans subsp. desulfuricans (strain number: CGMCC 1.3469, China General Microbiological Culture Collection Center) or Desulfovibrio desulfuricans subs NCIB8372 (strain number: SHBCCD80484, Shanghai Center for Biotechnology Preservation).

[0053] In this invention, the Desulfovibrio bacteria metabolites are the metabolites produced by Desulfovibrio bacteria during cultivation in the culture medium (this invention mainly utilizes sulfur-containing reducing agents). The culture medium is Postgate medium (e.g., FT-B201955 produced by Shanghai Fantai Biotechnology Co., Ltd., HB8830 produced by Yaji Biotechnology, M2262 produced by Shandong Tuopu Bioengineering Co., Ltd., etc.).

[0054] In this invention, the specific method for obtaining the metabolites of Desulfovibrio bacteria is as follows: Desulfovibrio bacteria are cultured in Postgate medium and enriched under anaerobic and light-protected conditions at 25-30°C for 3 days. The resulting culture solution is centrifuged at 8000G for 15 minutes at 4°C, the bacterial cells are collected, washed three times with sterile phosphate buffer, resuspended, and the OD600 value is adjusted to 0.3 to prepare a bacterial suspension.

[0055] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0056] 1. This invention addresses the unique characteristics of high-salt solid waste ash from steel plants and desulfurization and acid production wastewater from sintering flue gas activated carbon desulfurization. It synergistically treats both waste ash and wastewater for resource recovery. Firstly, by using the desulfurization and acid production wastewater from sintering flue gas activated carbon desulfurization, the leaching of thallium from the high-salt solid waste ash is suppressed, reducing the thallium content in the ash washing wastewater at the source and improving the quality of subsequent potassium salts. Secondly, the sodium contained in the desulfurization and acid production wastewater from sintering flue gas activated carbon desulfurization results in a potassium-to-sodium ratio in the ash washing wastewater close to 1:1, achieving multi-effect countercurrent evaporation and further improving the quality and reuse value of potassium salts.

[0057] 2. This invention proposes for the first time a deep thallium removal approach based on weak reduction complex breaking, common ion effect precipitation, and chelation thallium removal. By compounding ferrous chloride, Desulfovibrio bacteria metabolites, and a sulfur-based heavy metal trapping agent into a polysulfide-based thallium removal agent, the weak reduction complex breaking process and the polysulfide thallium chelation process are combined into one, rapidly chelating free Tl(III) and Tl(I) ions while breaking the complex. Simultaneously, heavy metals such as Cu, Pb, and Zn can be removed using sulfur precipitation, and the micro-charge on the precipitate surface promotes the co-precipitation of polysulfide-based thallium chelates, achieving a one-step synergistic thallium and heavy metal removal process.

[0058] 3. Compared to traditional processes, the present invention improves the evaporation mechanism and process route, avoiding the introduction of other ions during direct impurity removal from wastewater. It also achieves low-cost removal of ammonia nitrogen, thallium, heavy metals, and other pollutants that affect potassium salt recovery, further improving the quality of the recovered potassium salt and preventing contaminants from entering the potassium salt, thereby increasing the value of the potassium chloride product. Furthermore, the present invention has the advantages of low cost and simple operation, requiring no additional equipment or energy consumption, making rational use of system resources, achieving in-system digestion, and significantly reducing pollutant emissions. Attached Figure Description

[0059] Figure 1 This is a process flow diagram of the method for washing, desalinating, and removing thallium from solid waste ash in steel plants according to the present invention. Detailed Implementation

[0060] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments.

[0061] A method for preparing a polysulfide-based heavy metal scavenging agent, specifically comprising: dissolving a sulfide, a ferrous salt, and an alkali in water in a specified ratio and mixing them thoroughly (preferably stirring at room temperature for 0.5-2 hours), wherein the amount of alkali added is such that the pH of the mixture is 8-10 (preferably 8-9). Then, under a nitrogen atmosphere, the mixture is first heated to 40-60°C (preferably 45-55°C), followed by the addition of Desulfovibrio bacteria metabolites and stirring for 0.5-2 hours (preferably 0.8-1.5 hours). Finally, the mixture is cooled (preferably to room temperature) and a sulfur-based heavy metal scavenging agent is added, and stirring is continued for another 0.5-2 hours (preferably 0.8-1.5 hours) to obtain the polysulfide-based heavy metal scavenging agent.

[0062] Preferably, the sulfide is selected from one or more of sodium sulfide, calcium sulfide, and potassium sulfide, with sodium sulfide being the most preferred.

[0063] Preferably, the sulfur-based heavy metal scavenger is sodium dimethyl dithiocarbamate (SDD) and / or dithiocarbamate (DTC), with sodium dimethyl dithiocarbamate (SDD) being the most preferred.

[0064] Preferably, the ferrous salt is selected from one or more of ferrous sulfite, ferrous chloride, ferrous sulfate, and ferrous nitrate, and is preferably ferrous sulfite and / or ferrous chloride.

[0065] Preferably, the alkali is selected from one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide, with sodium hydroxide being the most preferred.

[0066] Preferably, the mass ratio of the Desulfovibrio bacteria metabolites, sulfides, sulfur-based heavy metal scavengers, ferrous salts, and alkali added is 10-30% (preferably 15-25%): 3-12% (preferably 5-10%): 3-15% (preferably 5-10%): 5-15% (preferably 8-12%): 0-5% (preferably 0.5-4%).

[0067] A method for desalination and thallium removal from solid waste ash in a steel plant, comprising the following steps:

[0068] 1) Ash washing treatment: The solid waste ash is washed with water using a three-stage countercurrent water washing process to obtain ash washing wastewater.

[0069] 2) Deep thallium removal: First, add alkali to the ash washing wastewater obtained in step 1), then add the polysulfide-based de-weighting agent as described in any one of claims 1-3 or the polysulfide-based de-weighting agent prepared by the method described in claim 5 to react. After the reaction is completed, perform solid-liquid separation to obtain thallium-removed wastewater.

[0070] 3) Impurity removal treatment: Add hardening agent and flocculant to the thallium removal wastewater obtained in step 2), and obtain high-salt wastewater after solid-liquid separation.

[0071] 4) Countercurrent evaporation to remove sodium chloride: The high-salinity wastewater obtained in step 3) is heated, concentrated, and crystallized. After solid-liquid separation, sodium chloride and filtrate are obtained. The filtrate is cooled and crystallized. After solid-liquid separation, potassium chloride and residual liquid are obtained. The residual liquid is returned to the high-salinity wastewater obtained in step 3) for recycling treatment.

[0072] Preferably, in step 1), the three-stage countercurrent washing specifically involves: first, the solid waste ash undergoes a primary slurry washing, with a slurry washing liquid-to-solid ratio of 2-7:1 (preferably 3-5:1). The primary washing water is the secondary washing clarified liquid. After the primary washing, the ash is dewatered by a primary plate and frame filter press. After solid-liquid separation, a primary clarified liquid and a primary filter cake are obtained. The primary clarified liquid enters a deep thallium removal treatment process, and the primary filter cake undergoes a secondary slurry washing. The secondary washing water is the tertiary washing clarified liquid. After the secondary washing, the ash is dewatered by a secondary plate and frame filter press. After solid-liquid separation, a secondary clarified liquid and a secondary filter cake are obtained. The secondary clarified liquid is discharged into the primary water system for recycling, and the secondary filter cake undergoes a tertiary slurry washing. The water used for the tertiary washing is the sintering flue gas purification acid production wastewater and / or condensate. After the tertiary washing, the water is dewatered by a tertiary plate and frame filter press to obtain tertiary clear liquid and tertiary filter cake. The tertiary clear liquid is discharged to the secondary washing for recycling, and the tertiary filter cake is returned to the sintering process for batching and disposal.

[0073] Preferably, the solid waste ash is selected from one or more of the following: sintering electric field ash, blast furnace bag ash, rotary kiln surface cooling ash, and waste incineration fly ash.

[0074] Preferably, in step 2), adding alkali to the ash washing wastewater specifically involves adding sodium hydroxide and / or potassium hydroxide to the ash washing wastewater until the pH of the ash washing wastewater is 3-12, preferably 5-11, and more preferably 7-10.

[0075] Preferably, in step 2), the amount of the polysulfide-based de-gravity agent added is 0.05-5% of the total mass of the ash washing wastewater, preferably 0.1-3%, and more preferably 0.2-2%.

[0076] Preferably, in step 3), the hardening agent is sodium carbonate and / or potassium carbonate, preferably sodium carbonate.

[0077] Preferably, in step 3), the flocculant is polyaluminum chloride (PAC) and / or polyacrylamide (PAM), with polyaluminum chloride (PAC) being the preferred choice.

[0078] Preferably, the amount of the hardening agent added is 0.5-8% of the total mass of the thallium removal wastewater, more preferably 0.8-5%, and even more preferably 1-3%.

[0079] Preferably, the amount of flocculant added is 1 to 5‰ of the total mass of the thallium removal wastewater, and more preferably 1.5 to 3‰.

[0080] Preferably, in step 4), the countercurrent evaporation to remove potassium sodium is carried out using a multi-effect evaporator, wherein the multi-effect evaporator has 2-6 stages (preferably 3-5 stages).

[0081] Preferably, the high-salinity wastewater obtained in heating step 3) is specifically heated to 80-110℃ (preferably 85-100℃). The cooling of the filtrate is specifically achieved by flash evaporation or heat exchange to reduce the temperature to below 60℃ (preferably 25-55℃).

[0082] Preferably, the potassium-to-sodium ratio in the solid waste ash is not less than 2, more preferably not less than 2.5, and even more preferably not less than 3.

[0083] Preferably, the pH of the ash washing wastewater is below 3, preferably 1-3, and more preferably 2-3.

[0084] Preferably, the potassium-to-sodium ratio in the high-salt wastewater is not higher than 1.5, more preferably not higher than 1.3, and even more preferably 1-1.1.

[0085] Preparation Example 1

[0086] Desulfovibrio desulfuricans were cultured in Postgate medium for 8 days, then removed and sterilized in an autoclave at 120°C. Finally, solid-liquid separation was performed, and the obtained filtrate was the metabolite of Desulfovibrio desulfuricans.

[0087] Preparation Example 1

[0088] The *Desulfuricans* subsp. *desulfuricans* was cultured in FT-B201955 medium produced by Shanghai Fantai Biotechnology Co., Ltd. The culture was enriched under anaerobic and light-protected conditions at 28℃ for 3 days. The resulting culture was centrifuged at 8000G for 15 min at 4℃, and the bacterial cells were collected. After washing three times with sterile phosphate buffer, the cells were resuspended and the OD600 value was adjusted to 0.3 to prepare a bacterial suspension, labeled as metabolite I.

[0089] Preparation Example 2

[0090] The bacteria *Desulfovibrio desulfuricans* subs NCIB8372 were cultured in HB8830 medium produced by Yaji Biotechnology. Enrichment culture was carried out at 28℃ under anaerobic and light-protected conditions for 3 days. The resulting culture was centrifuged at 8000G for 15 min at 4℃, and the bacterial cells were collected. After washing three times with sterile phosphate buffer, the cells were resuspended, and the OD600 value was adjusted to 0.3 to prepare a bacterial suspension, labeled as metabolite II.

[0091] Preparation Example 3

[0092] The bacteria *Desulfuricans subsp. desulfuricans* were cultured in M2262 medium produced by Shandong Top Biotechnology Co., Ltd. They were enriched under anaerobic and light-protected conditions at 28℃ for 3 days. The resulting culture was centrifuged at 8000G for 15 min at 4℃, and the bacterial cells were collected. After washing three times with sterile phosphate buffer, the cells were resuspended and the OD600 value was adjusted to 0.3 to prepare a bacterial suspension, labeled as metabolite I.

[0093] Example 1

[0094] Dissolve 8 parts sodium sulfide, 10 parts ferrous chloride, and sodium hydroxide in water and stir for 40 minutes at room temperature. The amount of sodium hydroxide added is such that the pH of the mixture is 8. Then, under a nitrogen atmosphere, the mixture is first heated to 48°C, and then 22 parts of metabolite I are added, with stirring continuing for 1 hour. The mixture is then cooled to room temperature, and 7 parts of sodium dimethyl dithiocarbamate (SDD) are added. After stirring for another 1 hour, polysulfide-based weight removal agent I is obtained.

[0095] Example 2

[0096] Eight parts of sodium sulfide, ten parts of ferrous chloride, and sodium hydroxide were dissolved in water and stirred at room temperature for 40 minutes. The amount of sodium hydroxide added was such that the pH of the mixture was 8. Then, under a nitrogen atmosphere, the mixture was heated to 48°C, and then 22 parts of metabolite II were added, with stirring continuing for 1 hour. The mixture was then cooled to room temperature, and seven parts of dithiocarbamate (DTC) were added. After stirring for another hour, polysulfide-based deweighting agent II was obtained.

[0097] Example 3

[0098] Ten parts of sodium sulfide, ten parts of ferrous sulfite, and sodium hydroxide were dissolved in water and stirred at room temperature for 45 minutes. The amount of sodium hydroxide added was such that the pH of the mixture was 9. Then, under a nitrogen atmosphere, the mixture was heated to 50°C, and then 25 parts of metabolite III were added, with stirring continuing for 1 hour. The mixture was then cooled to room temperature, and 8 parts of sodium dimethyl dithiocarbamate (SDD) were added. After stirring for another 1 hour, polysulfide-based weight removal agent III was obtained.

[0099] Application Example 1

[0100] Sintering flue gas was used to purify acid-producing wastewater for a three-stage countercurrent water wash of 100 kg of sintering machine head ash. After pressure filtration, filter cake and approximately 431 L of ash-washing wastewater (with a potassium-to-sodium ratio of approximately 5.0) were obtained. The filter cake was transported off-site for disposal. Sodium hydroxide was added to the ash-washing wastewater to adjust the pH to 3. Then, 4.5% of the total ash-washing wastewater was added to the polysulfide-based heavy weight removal agent I prepared in Example 1, and the mixture was stirred and reacted for 1 hour. Solid-liquid separation yielded thallium-removed wastewater (wherein the thallium content decreased from 31.5 mg / L to 2.8 μg / L). Simultaneously, Zn and Cu levels decreased from 328.3 mg / L and 447.6 mg / L to below 5 μg / L, respectively. Sodium carbonate (1.1% of the total ash washing wastewater) and PAC (1‰ of the total ash washing wastewater) were added to the thallium removal wastewater. After stirring and mixing for 30 minutes, solid-liquid separation was performed to obtain high-salt wastewater. The high-salt wastewater was homogenized to adjust its potassium-to-sodium ratio to approximately 1:1. Then, the homogenized high-salt wastewater was heated to 95°C in a multi-effect countercurrent evaporator for concentration and crystallization. Sodium chloride and filtrate were obtained by centrifugation. The filtrate was cooled to below 60°C to precipitate crystals, and potassium chloride (99.95% purity) was obtained by centrifugation. Sodium chloride and residual liquid were returned to participate in the homogenization of the high-salt wastewater.

[0101] Application Example 2

[0102] 100 kg of sintering machine head ash was subjected to a three-stage countercurrent water washing process using condensate. After pressure filtration, filter cake and approximately 404 L of ash washing wastewater (with a potassium-to-sodium ratio of approximately 5.9) were obtained. The filter cake was transported off-site for disposal. Sodium hydroxide was then added to the ash washing wastewater to adjust the pH to 3. Then, 4.5% of the total ash washing wastewater volume of the polysulfide-based heavy metal removal agent I prepared in Example 1 was added, and the mixture was stirred and reacted for 1 hour. Solid-liquid separation yielded thallium removal wastewater (wherein the thallium content decreased from 38 mg / L to 12.6 μg / L, and Z...). The concentrations of n and Cu decreased from 311.4 mg / L and 409.6 mg / L, respectively, to below 5 μg / L. Sodium carbonate (1.1% of the total thallium removal wastewater) and PAM (1.2‰ of the total thallium washing wastewater) were added to the thallium removal wastewater. After stirring and mixing for 30 min, solid-liquid separation was performed to obtain high-salt wastewater. The high-salt wastewater was homogenized to adjust its potassium-to-sodium ratio to approximately 1:1. Then, the homogenized high-salt wastewater was heated to 95°C in a multi-effect countercurrent evaporator for concentration and crystallization. Sodium chloride and filtrate were obtained by centrifugation. The filtrate was cooled to below 60°C to precipitate crystals, which were then centrifuged to obtain potassium chloride (99.90% purity). Sodium chloride and residual liquid were returned to participate in the homogenization of the high-salt wastewater.

[0103] Application Example 3

[0104] 100 kg of sintering machine head ash was subjected to a three-stage countercurrent water washing process using sintering flue gas purification acid production wastewater. After pressure filtration, filter cake and approximately 435 L of ash washing wastewater (with a potassium-to-sodium ratio of approximately 5.2) were obtained. The filter cake was transported off-site for disposal. Then, sodium hydroxide was added to the ash washing wastewater to adjust the pH to 3, followed by the addition of sodium sulfide (4.5% of the total wastewater volume). The mixture was stirred and reacted for 1 hour. Solid-liquid separation yielded thallium-removed wastewater (with a thallium content of 34.9%). The concentration of sodium chloride was reduced to 6.5 mg / L. Sodium carbonate (1.1% of the total thallium removal wastewater) and PAC (1‰ of the total thallium washing wastewater) were added to the thallium removal wastewater. After stirring and mixing for 30 minutes, solid-liquid separation was performed to obtain high-salt wastewater. The high-salt wastewater was homogenized to adjust its potassium-to-sodium ratio to approximately 1:1. Then, the homogenized high-salt wastewater was heated to 95°C in a multi-effect countercurrent evaporator for concentration and crystallization. Sodium chloride and filtrate were obtained by centrifugation. The filtrate was cooled to below 60°C to precipitate crystals, and potassium chloride (purity only 91.27%) was obtained by centrifugation. Sodium chloride and residual liquid were returned to participate in the homogenization of the high-salt wastewater.

[0105] Application Example 4

[0106] Sintering flue gas was used to purify acid-producing wastewater for a three-stage countercurrent water wash of 100 kg of sintering machine head ash. After pressure filtration, filter cake and approximately 430 L of ash-washing wastewater (with a potassium-to-sodium ratio of approximately 5.0) were obtained. The filter cake was transported off-site for disposal. Sodium hydroxide was added to the ash-washing wastewater to adjust the pH to 3. Then, 4.5% of the total ash-washing wastewater was added to the polysulfide-based heavy weight removal agent I prepared in Example 1, and the mixture was stirred and reacted for 1 hour. Solid-liquid separation yielded thallium-removed wastewater (wherein the thallium content decreased from 32.3 mg / L to 2.1 μg / L, and Zn...). The concentrations of potassium and copper were reduced from 331 mg / L and 442.8 mg / L to below 5 μg / L, respectively. Sodium carbonate (1.1% of the total thallium removal wastewater) and PAC (1‰ of the total thallium washing wastewater) were added to the thallium removal wastewater. After stirring and mixing for 30 minutes, solid-liquid separation was performed to obtain high-salt wastewater. The high-salt wastewater was homogenized to adjust its potassium-to-sodium ratio to approximately 1:1. The homogenized high-salt wastewater was treated by co-current evaporation to first crystallize potassium chloride (purity only 86.88%). Then, further evaporation, concentration, and crystallization were performed to obtain sodium chloride.

[0107] Application Example 5

[0108] 100 kg of sintering machine head ash was subjected to a three-stage countercurrent water washing process using sintering flue gas purification acid production wastewater. After pressure filtration, filter cake and approximately 418 L of ash washing wastewater (with a potassium-to-sodium ratio of approximately 5.2) were obtained. The filter cake was transported off-site for disposal. Sodium hydroxide was added to the ash washing wastewater to adjust the pH to 3. Then, 4.5% of the total ash washing wastewater volume of the polysulfide-based heavy metal removal agent II prepared in Example 2 was added, and the mixture was stirred and reacted for 1 hour. Solid-liquid separation yielded thallium removal wastewater (wherein the thallium content decreased from 34.3 mg / L to 8.7 μg / L). Simultaneously, Zn and Cu concentrations decreased from 321.3 mg / L and 434.2 mg / L to below 5 μg / L, respectively. Sodium carbonate (1.1% of the total ash washing wastewater volume) and PAC (1‰ of the total ash washing wastewater volume) were added to the thallium removal wastewater. After stirring and mixing for 30 minutes, solid-liquid separation was performed to obtain high-salt wastewater. The high-salt wastewater was homogenized to adjust its potassium-to-sodium ratio to approximately 1:1. Then, the homogenized high-salt wastewater was heated to 95°C in a multi-effect countercurrent evaporator for concentration and crystallization. Sodium chloride and filtrate were obtained by centrifugation. The filtrate was cooled to below 60°C to precipitate crystals, and potassium chloride (99.91% purity) was obtained by centrifugation. Sodium chloride and residual liquid were returned to participate in the homogenization of the high-salt wastewater.

[0109] Application Example 6

[0110] 100 kg of sintering machine head ash was subjected to a three-stage countercurrent water washing process using sintering flue gas purification acid production wastewater. After pressure filtration, filter cake and approximately 424 L of ash washing wastewater (with a potassium-to-sodium ratio of approximately 5.5) were obtained. The filter cake was transported off-site for disposal. Then, sodium hydroxide was added to the ash washing wastewater to adjust the pH to 3. Next, 4.5% of the total ash washing wastewater volume of the polysulfide-based heavy metal removal agent III prepared in Example 3 was added, and the mixture was stirred and reacted for 1 hour. Solid-liquid separation yielded thallium removal wastewater (wherein the thallium content decreased from 32.7 mg / L to 3.1 μg / L). L, while Zn and Cu decreased from 317.5 mg / L and 421.2 mg / L to below 5 μg / L, respectively; 1.1% sodium carbonate and 1‰ PAC of the total ash washing wastewater were added to the thallium removal wastewater, and after stirring and mixing for 30 min, solid-liquid separation was performed to obtain high-salt wastewater; the high-salt wastewater was homogenized to adjust its potassium-sodium ratio to approximately 1:1; then, the homogenized high-salt wastewater was heated to 95°C in a multi-effect countercurrent evaporator for concentration and crystallization, followed by centrifugation to obtain sodium chloride and filtrate. The filtrate was cooled to below 60°C to precipitate crystals, and centrifugation was performed to obtain potassium chloride (purity 99.94%). Sodium chloride and residual liquid were returned to participate in the homogenization of the high-salt wastewater.

Claims

1. A multi-sulphur-based heavy-removal agent for use in steel plant ashing wastewater, characterized by: This polysulfide-based heavy metal scavenging agent comprises 10-30% Desulfovibrio bacteria metabolites, 3-12% sulfides, 3-15% sulfur-based heavy metal scavengers, 5-15% ferrous salts, 0-5% alkali, and water. The Desulfovibrio bacteria metabolites are obtained by culturing Desulfovibrio bacteria in a culture medium for 3-10 days, then sterilizing them in an autoclave at 110-140℃, and finally separating the solid and liquid components. The resulting filtrate is the Desulfovibrio bacteria metabolite. The steel plant ash washing wastewater is obtained by washing high-salt solid waste ash from steel plants using sintered flue gas activated carbon desulfurization and acid production wastewater.

2. The polysulfide-based heavy particle removing agent according to claim 1, characterized by: This polysulfide-based heavy metal scavenging agent comprises 15-25% Desulfovibrio bacteria metabolites, 5-10% sulfides, 5-10% sulfur-based heavy metal scavengers, 8-12% ferrous salts, 0.5-4% alkali, and water.

3. The polysulfide-based heavy agent according to claim 1 or 2, characterized in that: The Desulfovibrio bacteria metabolites are obtained by culturing Desulfovibrio desulfuricans on Postgate medium for 5-8 days, then sterilizing them in an autoclave at 115-130℃, and finally separating the solid and liquid components. The resulting filtrate is the Desulfovibrio bacteria metabolite.

4. The polysulfide-based heavy agent according to claim 1 or 2, characterized in that: The sulfide is selected from one or more of sodium sulfide, calcium sulfide, and potassium sulfide; and / or The sulfur-based heavy metal scavenger is sodium dimethyl dithiocarbamate (SDD) and / or dithiocarbamate (DTC); and / or The ferrous salt is selected from one or more of ferrous sulfite, ferrous chloride, ferrous sulfate, and ferrous nitrate; and / or The alkali is selected from one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

5. The polysulfide-based heavy particle removing agent according to claim 4, characterized by: The sulfide is sodium sulfide; and / or The sulfur-based heavy metal scavenger is sodium dimethyl dithiocarbamate (SDD); and / or The ferrous salt is ferrous sulfite and / or ferrous chloride; and / or The alkali is sodium hydroxide.

6. A method of preparing the heavy element removing reagent of any one of claims 1 to 5, characterized by: The method is as follows: sulfides, ferrous salts, and alkali are dissolved in water in a certain proportion and mixed evenly, wherein the amount of alkali added is such that the pH of the mixture is 8-10; then, under a nitrogen atmosphere, the mixture is first heated to 40-60℃, and then the metabolites of Desulfovibrio bacteria are added and stirred for 0.5-2 hours; finally, the mixture is cooled and a sulfur-based heavy metal scavenger is added, and stirring is continued for 0.5-2 hours to obtain a polysulfide-based heavy metal removal agent.

7. The method of claim 6, wherein: The sulfide, ferrous salt, and alkali are dissolved in water in a specific ratio and stirred at room temperature for 0.5-2 hours. The amount of alkali added is such that the pH of the mixture is 8-9. Then, under a nitrogen atmosphere, the mixture is heated to 45-55°C, and then the metabolites of Desulfovibrio bacteria are added and stirred for 0.8-1.5 hours. Finally, the mixture is cooled to room temperature and a sulfur-based heavy metal scavenger is added. After stirring for another 0.8-1.5 hours, a polysulfide-based heavy metal removal agent is obtained.

8. A method for washing and desalting and removing thallium from steel plant solid waste ash, characterized by: The method includes the following steps: 1) Ash washing treatment: The solid waste ash is washed with water using a three-stage countercurrent water washing process to obtain ash washing wastewater; 2) Deep thallium removal: First, add alkali to the ash washing wastewater obtained in step 1), then add the polysulfide-based de-weighting agent as described in any one of claims 1-5 or the polysulfide-based de-weighting agent prepared by the method described in claim 6 or 7 to react. After the reaction is completed, perform solid-liquid separation to obtain thallium-removed wastewater. 3) Impurity removal treatment: Add hardening agent and flocculant to the thallium removal wastewater obtained in step 2), and obtain high-salt wastewater after solid-liquid separation; 4) Countercurrent evaporation to remove sodium chloride: Heat the high-salt wastewater obtained in step 3), concentrate and crystallize it, and obtain sodium chloride and filtrate after solid-liquid separation; cool the filtrate to crystallize it, and obtain potassium chloride and residual liquid after solid-liquid separation. The residual liquid is returned to the high-salt wastewater obtained in step 3) for recycling treatment.

9. The method of claim 8, wherein: In step 1), the three-stage countercurrent water washing specifically involves: firstly, the solid waste ash undergoes a first-stage pulping water washing with a pulping water washing liquid-solid ratio of 2-7:

1. The water used for the first-stage water washing is the second-stage water washing clear liquid. After the first-stage water washing, the ash is dewatered by a first-stage plate and frame filter press. After solid-liquid separation, a first-stage clear liquid and a first-stage filter cake are obtained. The first-stage clear liquid enters the deep thallium removal treatment process, and the first-stage filter cake undergoes a second-stage pulping water washing. The secondary washing water is the tertiary washing liquid. After the secondary washing, the filter is dewatered by a secondary plate and frame filter press. After solid-liquid separation, a secondary clear liquid and a secondary filter cake are obtained. The secondary clear liquid is discharged to the primary water system for recycling. The secondary filter cake is then subjected to tertiary pulping and washing. The water used for the tertiary washing is the wastewater from the desulfurization and acid production of activated carbon in the sintering flue gas and / or condensate. After the tertiary washing, the water is dewatered by a tertiary plate and frame filter press to obtain a tertiary clear liquid and a tertiary filter cake. The tertiary clear liquid is discharged to the secondary washing for recycling, and the tertiary filter cake is returned to the sintering process for batching and disposal.

10. The method of claim 9, wherein: The solid waste ash is selected from one or more of the following: sintering electric field ash, blast furnace bag ash, rotary kiln surface cooling ash, and waste incineration fly ash.

11. The method according to any one of claims 8-10, characterized by: In step 2), adding alkali to the ash washing wastewater specifically involves adding sodium hydroxide and / or potassium hydroxide to the ash washing wastewater until the pH of the wastewater is 3-12; and / or In step 2), the amount of the polysulfide-based de-gravity agent added is 0.05-5% of the total mass of the ash washing wastewater.

12. The method of claim 11, wherein: In step 2), adding alkali to the ash washing wastewater specifically involves adding sodium hydroxide and / or potassium hydroxide to the ash washing wastewater until the pH of the wastewater is 5-11; and / or In step 2), the amount of the polysulfide-based de-gravity agent added is 0.1-3% of the total mass of the ash washing wastewater.

13. The method of claim 12, wherein: In step 2), adding alkali to the ash washing wastewater specifically involves adding sodium hydroxide and / or potassium hydroxide to the ash washing wastewater until the pH of the wastewater is 7-10; and / or In step 2), the amount of the polysulfide-based de-gravity agent added is 0.2-2% of the total mass of the ash washing wastewater.

14. The method of any one of claims 8-10, wherein: In step 3), the hardening agent is sodium carbonate and / or potassium carbonate; and / or In step 3), the flocculant is polyaluminum chloride (PAC) and / or polyacrylamide (PAM).

15. The method of claim 14, wherein: In step 3), the hardening agent is sodium carbonate; and / or In step 3), the flocculant is polyaluminum chloride (PAC).

16. The method of claim 14, wherein: The amount of the hardening agent added is 0.5-8% of the total mass of the thallium removal wastewater; and / or The amount of flocculant added is 1-5‰ of the total mass of the thallium removal wastewater.

17. The method of claim 16, wherein: The amount of the hardening agent added is 0.8-5% of the total mass of the thallium removal wastewater; and / or The amount of flocculant added is 1.5 to 3‰ of the total mass of the thallium removal wastewater.

18. The method of claim 17, wherein: The amount of the hardening agent added is 1-3% of the total mass of the thallium removal wastewater.

19. The method of any one of claims 8-10, wherein: In step 4), the countercurrent evaporation to remove potassium and sodium is carried out using a multi-effect evaporator, wherein the multi-effect evaporator has 2-6 stages; The high-salt wastewater obtained in heating step 3) is specifically heated to 80-110℃; the filtrate is specifically cooled to below 60℃ by flash evaporation or heat exchange.

20. The method of claim 19, wherein: In step 4), the multi-effect evaporator has 3-5 stages; heating the high-salt wastewater obtained in step 3) specifically involves heating the high-salt wastewater to 85-100℃; cooling the filtrate specifically involves cooling it to 25-55℃ using flash evaporation or heat exchange.

21. The method of any one of claims 8-10, wherein: The potassium-to-sodium ratio in the solid waste ash is not less than 2; and / or The pH of the ash washing wastewater is below 3; and / or The potassium-to-sodium ratio in the high-salt wastewater is not higher than 1.

5.

22. The method of claim 21, wherein: The potassium-to-sodium ratio in the solid waste ash is not less than 2.5; and / or The pH of the ash washing wastewater is 1-3; and / or The potassium-to-sodium ratio in the high-salt wastewater is not higher than 1.

3.

23. The method of claim 22, wherein: The potassium-to-sodium ratio in the solid waste ash is not less than 3; and / or The pH of the ash washing wastewater is 2-3; and / or The potassium-to-sodium ratio in the high-salt wastewater is 1-1.1.

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