Method for deep thallium removal in whole process of wet method of steel and iron solid waste treatment plant

Abstract

This invention relates to the field of resource utilization and pollution control technology for steel solid waste, specifically disclosing a method for deep thallium removal at multiple nodes throughout the wet process of a steel solid waste treatment plant. This method incorporates a three-stage deep thallium removal process into the entire recovery process of potassium, sodium, and zinc: in the potassium and sodium recovery line, the first stage of deep thallium removal is performed on the purified potassium and sodium rinsing solution using a Na2S+Na2CO3 co-precipitation method; in the zinc recovery line, the second stage of deep thallium removal is performed on the neutral leachate after iron removal using an ultrasonic-enhanced zinc powder replacement method; and in the deeply purified zinc sulfate solution section, a third stage of guaranteed deep thallium removal is performed using zinc-based composite powder. This invention achieves the graded and efficient removal of trace heavy metal thallium by applying the most suitable thallium removal technology at different process nodes, ensuring the high purity of potassium and sodium salts and nano-zinc oxide products, and preventing the cyclic enrichment of thallium within the system.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical solid waste resource utilization and high-risk heavy metal pollution control, and specifically relates to a method for deep thallium removal through a multi-node wet process in a steel solid waste treatment plant. Background Technology

[0002] Steel dust, a major solid waste generated during the steel industry, is a secondary resource with high recycling value. However, while recovering valuable elements such as Zn, Fe, K, and Na from steel dust, the highly toxic heavy metal thallium (Tl) associated with the dust also enters the process line, highlighting the growing problem of thallium pollution control. Thallium possesses extremely high biotoxicity and is highly cumulative. If not effectively removed during solid waste treatment, it will enter the environment along with byproducts (such as potassium and sodium salts), posing serious environmental and health risks. With increasingly stringent environmental regulations, especially the "Emission Standard of Pollutants from Inorganic Chemical Industry" (GB 31573-2015), which sets clear limits for total thallium emissions in water and air pollutants (0.005 mg / L or 0.05 mg / m³), the situation is becoming increasingly serious. 3 Therefore, achieving efficient and in-depth removal of thallium in the steel solid waste resource utilization process has become a key challenge for the sustainable development of the industry.

[0003] Hydrometallurgical processes, due to their high recovery rate of valuable metals and strong adaptability, are the mainstream technology for treating complex steel dust and sludge. This process typically includes roasting pretreatment, alkaline washing to recover potassium and sodium, acid leaching to recover zinc, and multi-stage deep purification of solutions, ultimately yielding products such as potassium and sodium salts and nano-zinc oxide. However, current hydrometallurgical process designs mainly focus on the recovery efficiency and purity of Zn, K, and Na. For the removal of trace thallium, it is often only addressed in the final wastewater treatment stage, or relies entirely on impurity removal processes (such as iron and heavy metal removal) in the main process as an incidental removal step, lacking specialized and precise control technologies for the deep coupling of thallium removal with the main process. This leads to unstable thallium removal efficiency, making it prone to residues in the final product, posing environmental and product quality risks. Furthermore, although existing technologies exist for thallium removal, determining which specific technology to use at different stages of a particular hydrometallurgical process, and how to coordinate various parameters with each specific stage, remains a technical problem that researchers struggle to solve in detail.

[0004] The doctoral dissertation, "Comprehensive Recovery of Typical Valuable Elements and Whole-Process Disposal of Thallium in Zinc-Containing Dust and Sludge of Iron and Steel," conducted a detailed and comprehensive study on the recovery of valuable elements. However, the dissertation did not provide specific technical solutions for the precise measurement and removal of thallium, including the specific location and setting method.

[0005] Currently, existing technologies for thallium-containing materials generated in the steel production process mainly focus on two aspects: first, the "transfer and enrichment" of thallium-containing pollutants for centralized disposal; and second, the "point-source treatment" of specific wastewater at the end of the process. However, these methods have significant limitations when applied to steel solid waste treatment plants that aim for comprehensive resource recovery.

[0006] Chinese patent application CN117861430A discloses a "process for enriching thallium in sintering machine head flue gas into machine head ash." This technology reuses thallium-containing wastewater from wet desulfurization and wet electrostatic precipitator systems for sintering feed, allowing thallium to circulate within the sintering-dust removal system and ultimately accumulate in the electrostatic precipitator ash at the machine head. While this method innovatively solves the problem of thallium-containing wastewater treatment and achieves thallium enrichment, its core purpose is "enrichment" rather than "removal." It does not completely remove thallium from the system; it merely transfers it from the wastewater phase and concentrates it in the solid phase (machine head ash). The enriched high-thallium machine head ash still needs to be disposed of as hazardous waste, failing to fundamentally eliminate thallium pollution and ensure the purity of valuable element products (zinc, potassium, and sodium salts).

[0007] On the other hand, existing technologies offer various treatment solutions for thallium-containing wastewater, but most are limited to end-of-pipe treatment. Chinese patent application CN117125784A discloses a method for removing thallium and other pollutants from wet desulfurization wastewater in thermal power plants, employing a process of "sodium hypochlorite oxidation + compound thallium removal agent precipitation + lime slurry pH adjustment + flocculation," specifically designed for treating wet desulfurization wastewater from thermal power plants. Chinese utility model patent CN220364441U discloses an oxidation precipitation device for removing thallium from sintering and pelletizing desulfurization wastewater, optimizing oxidation precipitation efficiency by designing oxidation zones, mixing zones, reaction zones, and advection sedimentation zones with pH gradients. Both technologies represent current deep thallium removal solutions for specific end-of-pipe wastewater (such as desulfurization wastewater) and can reduce thallium concentrations to low levels. However, directly applying such end-of-pipe wastewater treatment technologies to the entire process of resource recovery in the steel solid waste wet process has the following shortcomings: 1) Single treatment target and lack of systematicity: The above-mentioned technical solutions mainly treat desulfurization wastewater with relatively specific components. However, the entire process of steel solid waste wet processing involves a variety of process fluids with very different properties, such as high-salt, high-alkalinity potassium and sodium enrichment solutions, near-neutral, high-zinc concentration leachates, and strongly acidic deep-purified solutions. A single end-of-pipe wastewater treatment technology cannot adapt to all these fluids and is difficult to achieve full-process coverage; 2) Weak coupling with the main process and lack of synergy: Existing methods are mostly independent wastewater treatment units and have not been embedded into the main process chain of zinc, potassium, and sodium recovery. Failure to utilize existing reaction and separation equipment and material flow in the main process leads to redundant investment in equipment, increased operating costs, and may interfere with the stability of the main process and the recovery rate of valuable metals; 3) Failure to guarantee the quality of the final product: Treating wastewater only at the end cannot prevent thallium from entering the product phase in the upstream process (such as potassium sodium crystallization, nano zinc oxide preparation), which may lead to excessive thallium content in potassium sodium salt or zinc products, affecting product value and bringing downstream environmental risks.

[0008] Therefore, there is an urgent need to propose a systematic, multi-stage deep thallium removal method that can be implemented from the source to the product and throughout the entire process of wet treatment of steel solid waste, so as to accurately intercept and remove thallium at different process nodes. Summary of the Invention

[0009] To address the aforementioned technical problems, the purpose of this invention is to provide a systematic method that is deeply integrated with existing wet process technologies and employs optimized thallium removal technologies at three key process nodes to achieve precise control of thallium throughout the entire process. Specifically, it provides a systematic method that integrates multi-stage thallium removal technologies, including co-precipitation, zinc powder replacement, and deep purification with composite powder, in the entire process of wet recovery of valuable elements in a steel enterprise's solid waste treatment plant.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: A method for deep thallium removal using a multi-stage wet process in a steel solid waste treatment plant involves three stages of deep thallium removal within a wet process that uses steel dust and sludge as raw materials to prepare nano-zinc oxide and extract potassium chloride and sodium chloride. The specific steps include: S1, Co-precipitation Deep Thallium Removal: In the potassium-sodium preparation process, after obtaining a purified potassium-sodium solution with a thallium content of 1.8~2.5 mg / L, Na2S and Na2CO3 are added sequentially. The amount of Na2S added is such that the concentration of sulfur ions in the solution reaches 43~58 mg / L, and the amount of Na2CO3 added is such that the pH value of the reaction system at the end point is 9.8~10.3. Then, the mixture is stirred continuously for 8~12 minutes at 22~28℃ and a stirring speed of 220~280 r / min. After that, it is allowed to stand for 50~70 minutes for solid-liquid separation to obtain a deeply dethallium-removed potassium-sodium solution with a thallium content of 0.001~0.005 mg / L and a solid thallium-containing precipitate residue.

[0011] S2, Evaporation and Crystallization: The potassium sodium solution obtained in S1 is evaporated and crystallized to obtain high-purity sodium salt with a thallium concentration of 0.005~0.03 mg / kg and potassium salt with a thallium concentration of 0.005~0.05 mg / kg.

[0012] S3, Ultrasonic Enhanced Deep Thallium Removal: In the nano zinc oxide preparation process, after neutral leaching and purification to remove iron, an iron-removed filtrate with a thallium content of 7~9 mg / L is obtained. 3.0~4.5 g of zinc powder is added to each liter of iron-removed filtrate, and then ultrasonic treatment is performed at 50~70℃ and a stirring rate of 180~230 rpm for 25~45 min. Then, solid-liquid separation is performed to obtain a deep thallium-removed iron-removed filtrate with a thallium content of 0.5~0.9 mg / L and a solid thallium-containing precipitate. The deep thallium-removed iron-removed filtrate enters the cadmium removal process.

[0013] S4, Deep thallium removal with zinc-based composite powder: After the cadmium removal process, the oxidation and manganese removal process yields a zinc sulfate composite solution with a thallium content of 0.9~1.3 mg / L. Zinc-based composite powder is added to the zinc sulfate composite solution at a rate of 1.0~3.5 g / L. The mixture is then reacted at a temperature of 50~70℃ and a stirring rate of 190~260 rpm for 50~70 min. Solid-liquid separation is then performed to obtain an ultra-high purity zinc sulfate solution with a thallium content of 0.05~0.10 mg / L and a solid thallium-containing precipitate. The ultra-high purity zinc sulfate solution is then introduced into the nano zinc oxide preparation process. The zinc-based composite powder is a composite powder obtained by mixing zinc powder and P-block group metal powder in a mass ratio of (92~98):(2~8).

[0014] Three thallium removal processes create a "three-level thallium removal barrier": 1. First-level barrier (co-precipitation for thallium removal): For the high-salt, alkaline purification solution generated by the potassium and sodium recovery line, a Na₂S + Na₂CO₃ co-precipitation method is employed. Under gentle stirring and sufficient aging conditions, Na₂S reacts with thallium ions to form a poorly soluble Tl₂S precipitate, while Na₂CO₃ maintains the optimal precipitation pH and synergistically removes residual impurities. This method is particularly suitable for the selective and deep removal of thallium from high-alkalinity, high-salt matrices, ensuring the purity of potassium and sodium salt products.

[0015] 2. Second-stage barrier (Zinc powder replacement for thallium removal): For the near-neutral zinc-rich leachate after iron removal in the zinc recovery line, a zinc powder replacement method is used. Under heating and ultrasonic assistance, utilizing the fact that zinc's standard electrode potential is more negative than thallium's, thallium ions in the solution are replaced and precipitated through a solid-liquid interface reaction. Ultrasonic waves continuously clean the zinc powder surface, maintaining its high activity. This stage aims to efficiently remove most of the thallium after the main process impurity removal and before deep purification, reducing the load on subsequent processes.

[0016] 3. Third-level barrier (deep purification with zinc-based composite powder): For trace impurities in the deeply purified zinc sulfate solution, a special zinc-based composite powder is used for final thallium removal. The active p-block main group metal powder in the composite powder can form a micro-electric field with zinc, inducing negatively charged thallium ions to migrate directionally to the relatively inert metal (positive electrode) surface for reduction. It has a very strong adsorption and alloying capture ability for trace thallium ions, achieving ppb-level deep purification and ensuring the purity of the zinc sulfate solution.

[0017] The three-tiered barrier system targets different liquid phase properties and thallium content levels, progressing from coarse to fine, forming a comprehensive thallium removal network.

[0018] Preferably, the wet process for preparing nano-zinc oxide and extracting potassium chloride and sodium chloride from steel dust and sludge includes the following steps: (1) The thallium-containing steel dust and sludge are mixed with reducing agent and binder and granulated; then reduced roasting is carried out to obtain roasting residue and roasted flue gas. The roasted flue gas is then dusted to obtain zinc-rich dust containing thallium and dust-removed flue gas.

[0019] (2) The zinc-rich dust containing thallium is washed and then solid-liquid separation is performed to obtain the washing filtrate and the washing residue. The washing filtrate enters the potassium-sodium preparation process, and the washing residue enters the nano zinc oxide preparation process.

[0020] (3) The rinsing filtrate obtained in step (2) is subjected to weight removal treatment to obtain weight removal filter residue and weight removal filtrate.

[0021] (4) The filtrate is treated to remove calcium, magnesium and silicon to obtain a purified potassium and sodium solution with a thallium content of 1.8~2.5 mg / L. Then, the co-precipitation deep thallium removal and evaporation crystallization in steps S1 and S2 are carried out to obtain high-purity sodium salt and potassium salt products.

[0022] (5) The rinsing residue obtained in step (2) is leached with an acidic solution, and then solid-liquid separation is performed to obtain neutral leaching residue and neutral leaching solution.

[0023] (6) The obtained neutral leachate is subjected to iron removal treatment to obtain iron removal filtrate and iron removal residue. The iron removal residue is returned to step (1) and mixed with steel dust and sludge for reduction roasting. The iron removal filtrate is subjected to ultrasonic enhanced deep dethallium removal treatment in step S3 to obtain deep dethallium removal iron removal filtrate.

[0024] (7) The cadmium-removed filter liquid after deep thallium and iron removal is subjected to cadmium removal treatment to obtain cadmium-removed filter residue and cadmium-removed filter liquid.

[0025] (8) The obtained cadmium-removed filtrate is subjected to oxidation and manganese removal treatment to obtain manganese-removed filter residue and zinc sulfate composite solution. The manganese-removed filter residue is returned to step (1) and mixed with steel dust and sludge for reduction roasting. The zinc sulfate composite solution is subjected to zinc-based composite powder deep dethallium removal treatment in step S4 to obtain ultra-high purity zinc sulfate solution.

[0026] (9) Nano zinc oxide was prepared by processing ultra-high purity zinc sulfate solution to obtain nano zinc oxide powder.

[0027] Preferably, in step S1, the amount of Na2S added is 0.18~0.28g of Na2S powder per liter of purified potassium-sodium solution, and the amount of Na2CO3 added is 2.9~3.6g of Na2CO3 powder per liter of purified potassium-sodium solution.

[0028] Preferably, in step S1, Na2S is added by first adding 55-65% of the total amount of Na2S, stirring continuously at a stirring speed of 60-120 r / min for 1-2 min, then adding the remaining amount of Na2S and Na2CO3 while stirring, then stirring continuously at 22-28℃ and a stirring speed of 220-280 r / min for 8-12 minutes, then increasing the stirring speed to 350-360 r / min for 0.8-1.5 min; then allowing it to stand and age for 50-70 min to perform solid-liquid separation.

[0029] Preferably, in step S3, while performing ultrasonic treatment, 10-20 mg / L of thiol-functionalized microbubbles with a diameter of 10-50 μm are added to the iron removal filtrate. After ultrasonic treatment at a stirring rate of 180-230 rpm for 15-35 min, the stirring rate is reduced to 80-100 rpm and stirring is continued for 8-12 min. Taking advantage of the floating property of microbubbles, the microbubbles adsorbing thallium ions and the partially replaced thallium-containing precipitate float to the liquid surface. The floating matter on the liquid surface is first filtered out by filtration before solid-liquid separation is performed. (The thiol-functionalized microbubbles described here are a type of micron-sized bubble carrier with surface-modified thiol (-SH) functional groups. They are mainly based on polystyrene (PS) microspheres or silica (SiO2) microspheres, which are introduced to their surface through oxidation or silanization treatment to introduce reactive active sites. Then, thiol (-SH) covalently modifies the surface of the microspheres through a coupling reaction, and further forms a microbubble structure with a functionalized shell. Afterwards, unreacted reagents and byproducts are removed by centrifugation, dialysis and other methods, and stabilizers are added to prevent microbubble aggregation and thiol oxidation.)

[0030] More preferably, the separated floating matter is mixed with a dilute acid, preferably an HNO3 solution with a concentration of 0.3~0.6 mol / L, and stirred at 25~40℃ for 1~2 h, followed by centrifugation or filtration to achieve solid-liquid separation, obtaining microbubbles and an eluent containing thallium ions. After neutralization and surface reactivation, the microbubbles can be regenerated into thiol-functionalized microbubbles, and the adsorption capacity of the regenerated microbubbles can reach more than 85% of the initial adsorption capacity. The eluent containing thallium ions can be further processed into a precipitation process and used as a raw material for preparing high-purity TlCl or metallic thallium, thereby realizing the resource recovery and reuse of thallium.

[0031] Preferably, the ultrasonic power in step S3 is 90~110W.

[0032] Preferably, in step S4, the P-block group metal powder is one or more of antimony, tin, or lead.

[0033] Preferably, the thallium-containing precipitates obtained after solid-liquid separation in steps S1, S3 and S4 are collected separately, combined and then safely landfilled or used as raw materials for thallium extraction.

[0034] Preferably, the thallium-containing steel dust in step (1) includes sintering machine head ash and blast furnace bag ash; and the thallium content of the thallium-containing steel dust is 10~150mg / kg; the reducing agent includes coke powder or coal powder; and the binder includes water.

[0035] Preferably, the nano zinc oxide powder product obtained in step (9) has a grain size of 30.03~35.28nm, a thallium content of less than 0.08mg / kg, and a purity of more than 97.59wt.%.

[0036] As a preferred embodiment, the heavy metal removal process in step (3) is specifically as follows: the rinsing filtrate obtained in step (2) is introduced into the heavy metal removal unit, a precipitant is added to the rinsing filtrate and the pH of the system is adjusted to be alkaline so that the heavy metal ions in the rinsing filtrate form a precipitate; after stirring and reacting, solid-liquid separation is performed to obtain the heavy metal removal filtrate and the heavy metal removal residue, and the heavy metal removal filtrate enters step (4) for subsequent purification treatment.

[0037] Preferably, the calcium, magnesium and silicon removal process in step (4) is as follows: the heavy filtrate obtained in step (3) is introduced into the calcium and magnesium removal unit, calcium removal agent and magnesium removal agent are added, and the reaction conditions are adjusted so that the calcium, magnesium and silicon impurities in the heavy filtrate form precipitates; after stirring, aging and solid-liquid separation, calcium and magnesium filtrate and calcium and magnesium filter residue are obtained, wherein the calcium and magnesium filtrate is purified potassium sodium solution, and enters step S1 and step S2.

[0038] Preferably, the iron removal process in step (6) is as follows: the neutral leachate obtained in step (5) is introduced into the iron removal unit, an oxidant is added and the pH value is adjusted to be alkaline, so that the iron ions in the neutral leachate form a precipitate; after stirring, aging and solid-liquid separation, iron removal filtrate and iron removal filter residue are obtained, and the iron removal filtrate enters step S3 for ultrasonic-enhanced deep thallium removal treatment.

[0039] As a preferred option, the roasting residue obtained in step (1) is ball-milled to reduce the particle size, and then subjected to strong magnetic separation and weak magnetic separation in sequence to recover iron powder; the tailings of the magnetic separation are used to prepare ceramsite products.

[0040] Preferably, the heavy filter residue obtained in step (3) is returned to the pyrometallurgical enrichment unit in step (1) to replace an equal amount of steel dust (or replace 0.8 to 1.0 times the weight of steel dust) for reduction roasting and reuse.

[0041] Preferably, the neutral leaching residue obtained in step (5) is subjected to high acid leaching treatment to extract indium, tin and bismuth.

[0042] Preferably, the cadmium-removed filter residue obtained in step (7) is fed into the replacement process to recover metallic cadmium.

[0043] The technical advantages of this invention are as follows: 1. This invention systematically embeds a deep thallium removal process into the entire wet treatment process of steel solid waste. Specific targeted thallium removal units are set up at three key nodes in the potassium-sodium recovery line and zinc recovery line (after potassium-sodium solution impurity removal, after neutral zinc solution iron removal, and after deep purification). Existing technologies often employ a single end-of-pipe treatment mode, which struggles to handle the diverse properties of process fluids throughout the entire process (high alkali and high salt, near-neutral zinc-rich, and strongly acidic), leading to incomplete thallium removal or interference with the main process. This invention, through a "divide and conquer" strategy, employs the most suitable thallium removal technology (co-precipitation, displacement, and composite adsorption) at different nodes, constructing a "three-barrier" covering the thallium migration path. This achieves precise interception of trace thallium from source to product throughout the entire process, fundamentally eliminating thallium circulation within the system and its residue in the final product.

[0044] (2) This invention significantly improves the efficiency and selectivity of thallium removal by creatively selecting specific thallium removal nodes and optimizing specific process parameters and reagent combinations at each node. In the first stage, the "Na2S+Na2CO3 co-precipitation method" is used for the high-salt-alkalinity potassium-sodium purification solution of this invention, and is carried out under specific temperature, stirring and aging conditions. These conditions preferentially promote the formation of extremely insoluble Tl2S precipitate of thallium, while reducing the entrainment of other valence ions, thus ensuring the purity of potassium-sodium salts. In the second stage, the "ultrasound-assisted zinc powder replacement method" is used for the zinc-rich neutral leachate after iron removal. Taking advantage of the more negative standard electrode potential of zinc, thallium is efficiently replaced under the condition of continuous activation of the zinc powder surface in an ultrasonic field. This design avoids the introduction of new impurities while efficiently removing thallium, creating favorable conditions for subsequent deep purification of zinc. In the third stage, the deeply purified zinc sulfate solution undergoes "deep thallium removal using zinc-based composite powder." This utilizes the synergistic effect of the micro-electric field formed by the P-block group metal powder in the composite powder and zinc to achieve maximal removal of trace thallium at the ppb level. The three stages of thallium removal are not independent but rather work synergistically. The second and third stages are particularly crucial; the specific thallium removal steps employed in the second stage ensure the effective execution of the third stage. In other words, the technologies of these three stages are interconnected, with each stage reducing the burden on the next and each subsequent stage supporting the previous one, forming a highly efficient and synergistic thallium removal chain.

[0045] (3) Through the above-mentioned full-process, multi-node, and differentiated deep thallium removal system, this invention ultimately achieves efficient integration of resource recovery and pollution control. After processing by this process, the thallium content in potassium and sodium crystalline salt products can be reduced to below 0.1 mg / kg, meeting the stringent requirements for high-quality industrial salt or agricultural fertilizers; the thallium concentration in the final zinc sulfate solution can be stably reduced to below 0.005 g / L, and the thallium content in nano zinc oxide products can be reduced to below 0.1 mg / kg, ensuring the high purity (97.59%) of the zinc products. At the same time, this solution makes full use of the existing wet treatment main process plant, equipment, and material flow, only requiring adaptive modifications to the dosing and filtration systems, achieving deep coupling and synergistic optimization of the thallium removal process and the main resource recovery process. With extremely low incremental investment and operating costs, it simultaneously improves the added value of valuable products and the environmental benefits of the entire solid waste treatment system.

[0046] (4) In a preferred embodiment, an ultrasonic-assisted selective adsorption microbubble flotation method is creatively introduced during the ultrasonic-enhanced deep thallium removal process. Under ultrasonic action, the high density of -SH groups on the surface of thiol-functionalized microbubbles affects Tl. + A strong selective adsorption effect was formed; ultrasound not only promoted the surface activation of zinc powder, but also drove the movement of microbubbles in the liquid phase, thereby enhancing the mass transfer process and increasing Tl. + The enrichment efficiency on the microbubble surface. Through the above synergistic effect, the concentration of coexisting metal ions (such as Cd) can be reduced. 2+ Pb 2+ This method reduces interference with thallium removal and decreases zinc powder consumption. Furthermore, by reducing the stirring rate in the later stages of ultrasonic treatment, the microbubble's floating characteristic allows it to rise to the liquid surface, carrying some of the thallium-containing precipitate generated by the displacement reaction, thus forming a stable scum layer. This scum layer effectively separates the scum phase, liquid phase, and precipitate phase, shortening subsequent separation time and improving thallium recovery efficiency, while providing more stable system conditions for subsequent thallium removal. This pre-separation also facilitates the recovery and reuse of thallium-functionalized microbubbles. The separated scum can be eluted with dilute acid to remove thallium adsorbed on the microbubble surface and recover the thallium-functionalized microbubbles. The recovered microbubbles can be reused at least 3-4 times after regeneration. The thallium in the eluent is enriched and can be further used as a raw material for preparing high-purity thallium salts or metallic thallium, thereby achieving high-value recovery and utilization of thallium resources.

[0047] (5) In a preferred embodiment, during the co-precipitation process for thallium removal, a portion of Na2S is added first and maintained under stirring conditions for 1-2 minutes, so that a portion of Tl is removed. +Tl₂S micronuclei were generated; subsequently, the remaining Na₂S and Na₂CO₃ were added (uniformly) while continuing stirring, causing the pH of the system to slowly rise to 9.8–10.3. Under these alkaline conditions, further growth of Tl₂S was favored, while S was inhibited. 2- Excessive release induces colloidal dispersion, thereby mitigating amorphous precipitation caused by localized supersaturation, increasing the density of precipitated particles, and reducing the risk of re-dissolution. Furthermore, after stirring and before settling, the stirring speed is increased and maintained for 0.8–1.5 min to create a pulsed shear field. This pulsed shear field can break up fine flocs and promote re-flocculation, thereby optimizing the structure of the precipitated particles and facilitating solid-liquid separation during the settling stage. Attached Figure Description

[0048] Figure 1 This is a schematic flowchart of a deep thallium removal method according to one embodiment of the present invention.

[0049] Figure 2 This is an XRD analysis diagram of a nano zinc oxide powder product according to one embodiment of the present invention. Detailed Implementation

[0050] The process technology solution of the present invention will be further described below with reference to embodiments and accompanying drawings. Unless otherwise specified, each feature is merely one example of a series of equivalent or similar features. These embodiments are merely for the purpose of aiding understanding the present invention and should not be considered as specific limitations thereof. Example 1

[0051] This embodiment illustrates an implementation method for treating a mixture of sintering machine head ash and blast furnace bag ash containing approximately 45 mg / kg of thallium (the two are mixed in unlimited quantities).

[0052] (1) Raw material pretreatment and roasting: After batching (mixed dust and sludge with water and coke powder) and granulation, the mixed dust and sludge is sent to a rotary hearth furnace for reduction roasting at 1180℃ for 60 minutes (the reduction roasting temperature range is set to 1150~1200℃, and the roasting time is 45~80min). After the flue gas is processed by a waste heat boiler and bag filter, dust-removed flue gas and zinc-thallium-rich dust (Zn 42%, Tl~75mg / kg) are obtained.

[0053] (2) The zinc-rich dust containing thallium was washed in three stages of countercurrent washing with hot water at 60°C. After washing, it was filtered to obtain rinsing filtrate (thallium concentration = 0.18 mg / L) and rinsing residue. The rinsing filtrate was used in the potassium-sodium preparation process, and the rinsing residue was used in the nano zinc oxide preparation process.

[0054] (3) The rinsing filtrate obtained in step (2) is introduced into the heavy metal removal unit, a precipitant is added and the pH value of the system is adjusted to alkaline (for example, pH is adjusted to 8.5) so that the heavy metal ions in the rinsing filtrate form a precipitate; after stirring and reacting, solid-liquid separation is carried out to obtain heavy metal removal filtrate and heavy metal removal residue.

[0055] (4) Add Na2CO3 to the filtrate after heavy removal (the amount of Na2CO3 added is 2.9~3.6g of Na2CO3 powder per liter of purified potassium sodium solution) to remove calcium, magnesium and silicon, and obtain purified potassium sodium solution with thallium content of 1.98mg / L. Then carry out co-precipitation deep thallium removal and evaporation crystallization in steps S1 and S2 to obtain high-purity sodium salt and potassium salt products.

[0056] S1, First-stage co-precipitation method for deep thallium removal: At 25°C, in a stirred tank with a stirring speed of 150 r / min, Na2S solution is first added to the purified potassium-sodium solution (so that S 2- The concentration was increased to 50 mg / L, and then the pH was slowly adjusted to 10 with Na2CO3 solution. The reaction was continued for 10 minutes. Stirring was stopped, and the mixture was allowed to stand for 60 minutes. Subsequently, the solution was filtered using a plate and frame filter press (solid-liquid separation) to obtain a deeply de-thallium potassium sodium solution. Sampling and testing showed that the thallium concentration had decreased to 0.0045 g / L.

[0057] S2, Evaporation and Crystallization: The deep dethallium-depleted potassium-sodium solution obtained in S1 is evaporated and crystallized by MVR to obtain high-purity sodium salt with a thallium concentration of 0.02 mg / kg and potassium salt with a thallium concentration of 0.03 mg / kg.

[0058] (5) The rinsed filter residue obtained in step (2) is leached with an acidic solution (dilute sulfuric acid) to a final pH of 5.2, and then filtered by a plate and frame filter press (solid-liquid separation) to obtain neutral leaching residue and neutral leaching solution (zinc concentration 151155 mg / L, thallium concentration 10 mg / L).

[0059] (6) The obtained neutral leachate is subjected to iron removal treatment (oxidation method), and after filtration, iron removal filtrate and iron removal residue are obtained. The iron removal residue is returned to step (1) and mixed with steel dust and sludge for reduction roasting. The iron removal filtrate is subjected to ultrasonic-enhanced deep dethallium removal treatment in step S3.

[0060] S3, Ultrasonic Enhanced Deep Thallium Removal: An iron-removed filtrate with a thallium content of 8.31 mg / L was obtained. The filtrate was heated to 60°C and transferred to a stirred reactor equipped with an ultrasonic device. Under stirring speed of 200 rpm and ultrasonic power of 100 W, 4.2 g / L of zinc powder with a particle size of 150 mesh and a purity of 99.5% was added. After reacting for 40 minutes, the mixture was filtered using a plate and frame filter press (solid-liquid separation). A deep thallium-removed and iron-removed filtrate with a thallium content of 0.7 mg / L and a solid thallium-containing precipitate were obtained. The deep thallium-removed and iron-removed filtrate then proceeded to the cadmium removal process.

[0061] (7) The deep thallium and iron removal filtrate is introduced into the cadmium removal unit, a displacement agent is added and the reaction conditions are adjusted so that the cadmium ions in the deep thallium and iron removal filtrate form a precipitate; after stirring reaction and solid-liquid separation, cadmium removal filtrate and cadmium removal filter residue are obtained, and the cadmium removal filtrate enters step (8).

[0062] (8) The obtained cadmium-removed filtrate is introduced into the oxidation and manganese removal unit, an oxidant is added and the reaction conditions are adjusted so that the manganese ions in the cadmium-removed filtrate form a precipitate; after stirring, aging and solid-liquid separation, manganese-removed filter residue and zinc sulfate composite solution are obtained. The manganese-removed filter residue is returned to step (1) and mixed with steel dust and sludge for reduction roasting. The zinc sulfate composite solution is subjected to the zinc-based composite powder deep dethallium removal treatment in step S4.

[0063] S4, Deep Dethallium Removal of Zinc-Based Composite Powder: A zinc sulfate composite solution with a thallium content of 0.97 mg / L was obtained and heated to 60°C. Zinc-based composite powder was then added to the zinc sulfate composite solution at a concentration of 2 g / L. The mixture was stirred at 250 rpm for 60 minutes. After the reaction, the solution was filtered through a precision filter (solid-liquid separation) to obtain an ultra-high purity zinc sulfate solution with a thallium content of 0.09 mg / L and a solid thallium-containing precipitate. The ultra-high purity zinc sulfate solution was then used in the nano-zinc oxide preparation process. The zinc-based composite powder was obtained by mixing zinc powder and lead powder at a mass ratio of 95:5.

[0064] (9) The ultra-high purity zinc sulfate solution was sent to the zinc recovery workshop for synthesis and roasting (i.e., nano-zinc oxide preparation process) to obtain high-purity nano-zinc oxide powder. The nano-zinc oxide powder product was tested and found to contain 0.07 mg / kg of thallium. The XRD analysis results of the product are shown below. Figure 2 As shown, the product prepared by the method of the present invention is a nano zinc oxide powder with high purity and good crystallinity. Example 2

[0065] This embodiment illustrates an example of adding thiol-functionalized microbubbles in step S3. Other settings in this embodiment are the same as in Embodiment 1, except that step S3 is replaced with: S3, Ultrasonic Enhanced Deep Thallium Removal: Iron-removed filtrate with a thallium content of 8.31 mg / L was obtained. The iron-removed filtrate was heated to 60°C and transferred to a stirred reactor equipped with an ultrasonic device. Under the conditions of stirring speed of 200 rpm and ultrasonic power of 100 W, 4.2 g / L of zinc powder with a particle size of 150 mesh and a purity of 99.5% was added. After the zinc powder was added, 15 mg / L (where "L" is the total volume of the liquid, i.e., the total volume of the iron removal filtrate) of commercially available thiol-functionalized microbubbles with a diameter of 10~50 μm were further added to the iron removal filtrate. The mixture was then ultrasonically treated at a stirring speed of 200 rpm for 23 min. The stirring speed was then reduced to 90 rpm and stirred for another 10 min. Taking advantage of the floating property of the microbubbles, the microbubbles that adsorbed thallium ions and the partially replaced thallium-containing precipitate floated to the surface of the liquid. The floating matter on the surface of the liquid was first removed by filtration (the scum layer was removed by filtration) and then filtered by a plate and frame filter press (solid-liquid separation). The deep thallium removal and iron removal filtrate with a thallium content of 0.7 mg / L and solid thallium-containing precipitate residue were obtained; the deep thallium removal and iron removal filtrate entered the cadmium removal process.

[0066] Furthermore, this embodiment also includes subsequent treatment of the filtered scum layer. The floating matter from the filtered scum layer is mixed with a 0.5 mol / L HNO3 solution and stirred at 35°C for 1.3 hours. Then, centrifugation and filtration are performed to achieve solid-liquid separation, yielding microbubbles and an eluent containing thallium ions. The microbubbles are neutralized and their surfaces reactivated to obtain regenerated thiol-functionalized microbubbles (with an adsorption capacity of over 85%). The eluent containing thallium ions is used as a raw material for preparing high-purity TlCl or metallic thallium through a subsequent precipitation process, thus achieving resource recycling and reuse.

[0067] The nano-zinc oxide powder product obtained in this embodiment was tested and found to contain 0.02 mg / kg of thallium. Compared to Example 1, the degree of thallium removal was further enhanced, thus proving that the overall thallium removal effect can be improved by strengthening the treatment in step S3.

[0068] Comparative Example 1 This comparative example is used to illustrate a comparative test using only one stage of thallium removal. Specifically, the same raw materials and main process as in Example 1 are used, but the thallium removal process is changed to: a third-stage zinc-based composite powder thallium removal method is used only at the end of the zinc process line (i.e., at step S4) instead of steps S1 and S3.

[0069] Testing of the obtained potassium-sodium crystalline salt product revealed that the thallium content exceeded the standard (2.1 mg / kg). The excessively high total thallium content entering the zinc recovery line led to a 50% increase in the consumption of composite powder in the third stage. Furthermore, based on this increased consumption, the final thallium concentration in the zinc sulfate solution fluctuated significantly (the thallium concentration obtained from multiple experiments ranged from 0.05 mg / L to 2 mg / L), affecting the stability of the nano-zinc oxide product's quality.

[0070] This invention utilizes a three-stage tandem thallium removal process—co-precipitation, zinc powder replacement, and composite powder capture—to achieve targeted removal of thallium from liquid phases with different properties. Examples demonstrate that this method can reduce the thallium content in potassium sodium salt and zinc sulfate solutions to extremely low levels, resulting in superior product quality and systematically solving the problem of thallium pollution control in the wet treatment of steel solid waste.

[0071] Comparative Example 2 This comparative example illustrates a comparative experiment using other thallium removal processes during co-precipitation depth removal. The other settings in this comparative example are the same as in Example 1, except that step S1 is replaced with the following: Na2S is first added to the purified potassium-sodium solution at a rate of 0.2 g of Na2S powder per liter of purified potassium-sodium solution, followed by 3 g / L of modified activated carbon loaded with hydrated manganese oxide and mercapto groups. The mixture is stirred continuously for 10 min, then allowed to stand for 60 min for solid-liquid separation, yielding a thallium-containing precipitate and a dethallium-removed potassium-sodium solution. The thallium concentration in the dethallium-removed potassium-sodium solution was measured to be approximately 0.0068 g / L. Although modified activated carbon was added to Comparative Example 2 to enhance adsorption, the thallium concentration in the dethallium potassium-sodium solution was still slightly higher than that in Example 1, even with all other parameters being the same as in Example 1 (generally speaking, the addition of modified activated carbon should enhance the dethallium removal effect by at least 2-3 orders of magnitude, but the result was not so enhanced). This is because, in this invention, although the potassium-sodium solution was highly alkaline and high in salt, no Na2CO3 was added, resulting in a relatively low pH. In contrast, the method in Example 1, with the addition of Na2CO3, promoted the adsorption of Tl2O3 and Pb. 2+ Zn 2+ Co-precipitation of heavy metals, while simultaneously causing Ca 2+ Mg 2+ The formation of carbonate precipitation serves both to soften water and assist in impurity removal. (Fe) 3+ Al 3+The thallium is easily hydrolyzed and precipitated, preventing it from entering the liquid phase and interfering with subsequent salt separation processes. Therefore, Example 1 achieves a low thallium concentration of 0.0045 g / L in potassium-sodium solutions without the addition of adsorption aids (such as activated carbon). In other words, by comparing Example 1 with Comparative Example 2, it can be demonstrated that the "Na2S+Na2CO3 co-precipitation method" designed for the specific process of this invention, with its specific parameter settings, can reduce the thallium concentration in potassium-sodium solutions to the required concentration without the addition of adsorption aids, and is beneficial to the subsequent preparation of potassium and sodium salts. This specific method has the effect of a simpler system and is more suitable for the specific process of this invention, while Comparative Example 2 cannot achieve this effect. This proves that the specific thallium removal settings of this invention are suitable for the specific process of this invention and have high inventiveness.

[0072] The technical principles of the present invention have been described above with reference to specific embodiments. These descriptions are merely for explaining the principles of the invention and should not be construed as limiting the scope of protection of the invention in any way. Based on this explanation, those skilled in the art can readily conceive of other specific embodiments of the invention without inventive effort, and these embodiments will all fall within the scope of protection of the present invention.

Claims

1. A method for deep thallium removal in a full-process multi-node wet process of a steel and iron solid waste treatment plant, characterized by, A three-stage deep thallium removal process is carried out in the wet process of extracting potassium chloride and sodium chloride from steel dust and sludge and preparing nano-zinc oxide. The specific steps include: S1, Co-precipitation Deep Thallium Removal: In the potassium-sodium preparation process, after obtaining a purified potassium-sodium solution with a thallium content of 1.8~2.5 mg / L, Na2S and Na2CO3 are added sequentially. The amount of Na2S added is such that the sulfur ion concentration in the solution reaches 43~58 mg / L, and the amount of Na2CO3 added is such that the final pH value of the reaction system is 9.8~10.

3. Then, the mixture is stirred continuously for 8~12 minutes at 22~28℃ and a stirring speed of 220~280 r / min. After that, it is allowed to stand for 50~70 minutes for solid-liquid separation to obtain a deeply dethallium-removed potassium-sodium solution with a thallium content of 0.001~0.005 mg / L and a solid thallium-containing precipitate. S2, Evaporation and Crystallization: The deeply dethallium-free potassium-sodium solution obtained in S1 is evaporated and crystallized to obtain high-purity sodium salt with a thallium concentration of 0.005~0.03 mg / kg and potassium salt with a thallium concentration of 0.005~0.05 mg / kg. S3, Ultrasonic Enhanced Deep Thallium Removal: In the nano-zinc oxide preparation process, after neutral leaching and purification to remove iron, an iron-removed filtrate with a thallium content of 7~9 mg / L is obtained. 3.0~4.5 g of zinc powder is added to each liter of the iron-removed filtrate. Then, ultrasonic treatment is performed at 50~70℃ and a stirring rate of 180~230 rpm for 25~45 min, followed by solid-liquid separation to obtain a deep thallium-removed and iron-removed filtrate with a thallium content of 0.5~0.9 mg / L and a solid thallium-containing precipitate. The deep thallium-removed and iron-removed filtrate then proceeds to the cadmium removal process. S4, Deep thallium removal with zinc-based composite powder: After the cadmium removal process, the oxidation and manganese removal process yields a zinc sulfate composite solution with a thallium content of 0.9~1.3 mg / L. Zinc-based composite powder is added to the zinc sulfate composite solution at a rate of 1.0~3.5 g / L. The mixture is then reacted at 50~70℃ and 190~260 rpm for 50~70 min. Solid-liquid separation is then performed to obtain an ultra-high purity zinc sulfate solution with a thallium content of 0.05~0.10 mg / L and a solid thallium-containing precipitate. The ultra-high purity zinc sulfate solution is then introduced into the nano zinc oxide preparation process. The zinc-based composite powder is a composite powder obtained by mixing zinc powder and P-block group metal powder in a mass ratio of (92~98):(2~8).

2. The method for multi-node deep de-thallium of the whole process of wet method of the steel and solid waste treatment plant of the iron and steel according to claim 1, characterized in that, The wet process for extracting potassium chloride and sodium chloride from steel dust and sludge and preparing nano-zinc oxide includes the following steps: (1) The thallium-containing steel dust and sludge are mixed with reducing agent and binder and granulated; then reduced roasting is carried out to obtain roasting residue and roasted flue gas. The roasted flue gas is then dusted to obtain zinc-rich dust containing thallium and dust-removed flue gas. (2) The zinc-rich dust containing thallium is washed, and solid-liquid separation is performed after washing to obtain rinsing filtrate and rinsing residue; the rinsing filtrate enters the potassium-sodium preparation process, and the rinsing residue enters the nano zinc oxide preparation process. (3) The rinsing filtrate obtained in step (2) is subjected to gravimetric treatment to obtain gravimetric filter residue and gravimetric filter liquid; (4) The filtrate after heavy removal is treated to remove calcium, magnesium and silicon to obtain a purified potassium-sodium solution with a thallium content of 1.8~2.5 mg / L. Then, the co-precipitation deep thallium removal and evaporation crystallization in steps S1 and S2 are carried out to obtain high-purity sodium salt and potassium salt products. (5) The rinsing residue obtained in step (2) is leached with an acidic solution, and then solid-liquid separation is performed to obtain neutral leaching residue and neutral leaching solution; (6) The obtained neutral leachate is subjected to iron removal treatment to obtain iron removal filtrate and iron removal residue. The iron removal residue is returned to step (1) and mixed with steel dust and sludge for reduction roasting. The iron removal filtrate is subjected to ultrasonic enhanced deep dethallium removal treatment in step S3 to obtain deep dethallium removal iron removal filtrate. (7) The cadmium-removed filter liquid after deep thallium and iron removal is subjected to cadmium removal treatment to obtain cadmium-removed filter residue and cadmium-removed filter liquid; (8) The obtained cadmium-removed filtrate is subjected to oxidation and manganese removal treatment to obtain manganese-removed filter residue and zinc sulfate composite solution. The manganese-removed filter residue is returned to step (1) and mixed with steel dust and sludge for reduction roasting. The zinc sulfate composite solution is subjected to zinc-based composite powder deep dethallium removal treatment in step S4 to obtain ultra-high purity zinc sulfate solution. (9) Nano zinc oxide was prepared by processing ultra-high purity zinc sulfate solution to obtain nano zinc oxide powder.

3. The method for multi-node deep de-thallium of the whole-process of wet-type of the steel and solid waste treatment plant of claim 1 or 2, characterized in that, In step S1, the amount of Na2S added is 0.18~0.28g of Na2S powder per liter of purified potassium-sodium solution, and the amount of Na2CO3 added is 2.9~3.6g of Na2CO3 powder per liter of purified potassium-sodium solution. In step S1, Na2S is added by first adding 55-65% of the total amount of Na2S and stirring continuously for 1-2 minutes. Then, the remaining amount of Na2S and Na2CO3 is added while stirring. The mixture is then stirred continuously at 22-28℃ and 220-280 r / min for 8-12 minutes. The stirring speed is then increased to 350-360 r / min and held for 0.8-1.5 minutes. The mixture is then allowed to stand for 50-70 minutes for solid-liquid separation.

4. The method for multi-node deep de-thallium of the whole-process of wet-type of the steel and solid waste treatment plant of claim 1 or 2, characterized in that, In step S3, while performing ultrasonic treatment, 10-20 mg / L of thiol-functionalized microbubbles with a diameter of 10-50 μm are added to the iron removal filtrate. After ultrasonic treatment at a stirring rate of 180-230 rpm for 15-35 min, the stirring rate is reduced to 80-100 rpm and stirring is continued for 8-12 min. Taking advantage of the floating property of microbubbles, the microbubbles adsorbing thallium ions and the partially replaced thallium-containing precipitate float to the liquid surface. The floating matter on the liquid surface is first filtered out by filtration before solid-liquid separation is performed.

5. The method of claim 1, wherein the method is characterized by, In step S3, the ultrasonic treatment has an ultrasonic power of 90-110W; in step S4, the P-block group metal powder is one or more of antimony, tin, or lead.

6. The method for multi-node deep de-thallium of the whole-process of wet-type of the steel and solid waste treatment plant of the iron according to claim 1 or 2, characterized in that, The thallium-containing precipitates obtained after solid-liquid separation in steps S1, S3 and S4 are collected separately, combined and then safely landfilled or used as raw materials for thallium extraction.

7. The method of claim 2, wherein the method is characterized by, The thallium-containing steel dust in step (1) includes sintering machine head ash and blast furnace bag ash; and the thallium content of the thallium-containing steel dust is 10~150mg / kg; the reducing agent includes coke powder or coal powder; and the binder includes water.

8. The method for multi-node deep de-thallium of the entire process of the wet method of the steel and solid waste treatment plant according to claim 2, characterized in that, The nano zinc oxide powder product obtained in step (9) has a grain size of 30.03~35.28nm, a thallium content of less than 0.08mg / kg, and a purity of more than 97.59wt.%.

9. The method for deep thallium removal via a multi-node wet process in a steel solid waste treatment plant according to claim 2, characterized in that, The heavy metal removal process in step (3) is as follows: the rinsing filtrate is introduced into the heavy metal removal unit, and a precipitant is added and the pH is adjusted to be alkaline so that the heavy metal ions in the rinsing filtrate form a precipitate. After solid-liquid separation, heavy metal removal filtrate and heavy metal removal residue are obtained. The heavy metal removal filtrate enters step (4). The calcium, magnesium and silicon removal process described in step (4) is as follows: the heavy filtrate is introduced into the calcium and magnesium removal unit, and calcium and magnesium removal agents are added and the reaction conditions are adjusted to cause the calcium, magnesium and silicon impurities in the heavy filtrate to form precipitates. After solid-liquid separation, calcium and magnesium filtrate and calcium and magnesium filter residue are obtained. The calcium and magnesium filtrate is a purified potassium-sodium solution with a thallium content of 1.8~2.5 mg / L. The iron removal process described in step (6) is as follows: the neutral leachate is introduced into the iron removal unit, and an oxidant is added to cause the iron ions in the neutral leachate to precipitate. After solid-liquid separation, iron removal filtrate and iron removal filter residue are obtained.

10. The method of claim 2, wherein the method is characterized by, The roasting residue obtained in step (1) is ball-milled to reduce the particle size, and then subjected to strong magnetic separation and weak magnetic separation to recover the iron powder. The magnetic separation tailings obtained after recovering the iron powder are used to prepare ceramsite products. The heavy filter residue obtained in step (3) is returned to step (1) to replace an equal amount of steel dust and sludge for reduction roasting, so as to realize the reuse of the heavy filter residue. The neutral leaching residue obtained in step (5) is subjected to high acid leaching treatment to extract the In, Sn and Bi metals. The residue after extraction is used as cement raw material. The cadmium-removed filter residue obtained in step (7) is recycled through a replacement process to recover the cadmium metal.

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