A method for deep purification of thallium-containing metal mine wastewater

Abstract

This invention belongs to the field of mine water treatment in metal mines, and specifically relates to a method for the deep purification treatment of thallium-containing metal mine wastewater. This method employs a combined process of "multi-element synergistic oxidation adsorption + composite sulfide precipitation + staged flocculation precipitation + activated carbon deep adsorption." It utilizes the synergistic effect of potassium permanganate, sodium hypochlorite, and ozone as a ternary oxidant to catalyze oxidation, generating MnO2 colloids with high adsorption capacity. This strongly adsorbs thallium, preventing its reduction rebound and amplifying the subsequent treatment effect through adsorption enrichment. Further treatment with a compound sulfide agent and a core-shell structured composite flocculant allows for multiple rounds of adsorption and precipitation, increasing the removal efficiency of low-concentration thallium to over 96%, and reducing the thallium concentration in the effluent to below 0.1 μg / L.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment in metal mines, and in particular relates to a deep purification treatment method for thallium-containing metal mine wastewater, achieving the removal of ultra-low concentrations of thallium. Background Technology

[0002] Thallium is a highly toxic heavy metal with high bioaccumulation and strong teratogenic and carcinogenic properties, posing a significant threat to the environment and human health. While thallium is present in very low concentrations in the natural environment, it exhibits lithophile and sulfide-affinity properties, and is widely distributed as an associated mineral in various ores. Traditional metal mines (pyrite, gold, copper, etc.) are particularly vulnerable due to the presence of trace amounts of thallium in their mine water, making them a key focus of regulatory oversight.

[0003] The main methods for treating this type of wastewater can be divided into physical, chemical, and biological methods. Among them, there are many successful engineering cases of physical and chemical methods being applied to the deep treatment of thallium-containing mine water and achieving stable compliance, while biological methods are mostly in the laboratory or pilot-scale stage at present.

[0004] Physical methods primarily remove thallium through physical retention or adsorption, commonly including membrane methods, ion exchange, and adsorption. Membrane methods, such as reverse osmosis and nanofiltration, utilize the selective permeability of semi-permeable membranes to retain metallic thallium. They are easy to operate and have good removal effects on low concentrations of thallium, but suffer from membrane fouling, high maintenance costs, and surface scaling. They are suitable for thallium-containing wastewater with low salinity. Ion exchange utilizes ion exchange resins to exchange thallium ions, offering good selectivity, but is more suitable for wastewater with high thallium concentrations. It is less effective for ultra-low concentration wastewater, has high costs, and the resin's exchange capacity and selectivity are easily affected. Adsorption methods utilize porous solid materials such as activated carbon, metal oxides, and slag for physicochemical adsorption of thallium. They require no chemical reagents and are inexpensive, but are significantly affected by coexisting elements (such as calcium, magnesium, and organic matter), and adsorbent regeneration is difficult.

[0005] Chemical methods mainly involve chemical precipitation and electrochemistry. Chemical precipitation typically involves adding chemical agents to the water, such as sulfides (sodium sulfide, sodium hydrosulfide, TMT, etc.) or metal salts (iron salts, aluminum salts, etc.) coagulants, causing thallium ions to precipitate and separate from the water. Alternatively, thallium can be oxidized with an oxidant to produce hydroxide precipitates, which are then further precipitated with a precipitating agent. This method is rapid, effective, and simple to operate, but it requires the addition of chemicals, easily generates a large amount of sludge and secondary pollution, and produces excessively high salinity in the effluent. Electrochemical methods mainly include electrocoagulation and electrooxidation. Electrocoagulation uses an electric current to cause an electrolytic reaction in the anode material to produce a flocculant, which precipitates metallic thallium through adsorption and coagulation. Electrooxidation involves a reaction at the electrode to generate hydroxyl radicals or other oxidizing substances, oxidizing and degrading the heavy metal thallium. Electrochemical methods have advantages such as simple reaction equipment, easy operation, and no need for other reagents, but they consume more electricity and have higher investment costs.

[0006] Besides single treatment methods, multiple methods are often combined to achieve low-concentration discharge requirements, such as multi-stage treatment of "oxidation + sulfidation + coagulation". However, existing technologies have limitations in treating thallium-containing mine water, especially for low-concentration thallium-containing mine water, making it difficult to consistently meet ultra-low concentration discharge requirements, which is an urgent problem to be solved. Technicians have proposed corresponding solutions to this problem. For example, patent CN118388079A discloses a deep purification treatment method for thallium-containing heavy metal wastewater based on electrocoagulation, employing a three-stage combined treatment of oxidation precipitation + electrocoagulation + adsorption, removing thallium content below 0.05 μg / L. However, this method involves electrocoagulation, resulting in high investment costs for large-scale wastewater treatment. Therefore, researching treatment processes for low-concentration thallium-containing metal mine wastewater is of significant practical importance. Summary of the Invention

[0007] This invention aims to overcome the problems of poor thallium removal rates and difficulty in consistently meeting ultra-low concentration emission standards in existing technologies for low-concentration thallium-containing metal mine wastewater. It provides a deep purification method for thallium-containing metal mine wastewater, employing a synergistic catalytic adsorption process using potassium permanganate, sodium hypochlorite, and ozone as ternary oxidants. This is followed by sulfidation precipitation using a compound sulfiding agent and staged flocculation and precipitation using a core-shell composite flocculant, effectively improving the removal efficiency of low-concentration thallium. Furthermore, this method utilizes conventional chemical and physical methods, is easily scalable and widely applicable, and has low economic costs.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for deep purification treatment of thallium-containing metal mine wastewater includes the following steps: (1) Multi-component synergistic oxidation adsorption: First, adjust the pH of the thallium-containing mine wastewater to 6-9, then add potassium permanganate and sodium hypochlorite, introduce ozone, and stir the reaction; (2) Composite sulfide precipitation: Adjust the pH of the wastewater after oxidation treatment to 8-9, add the compound sulfide agent, and stir to react; the compound sulfide agent contains Na2S and FeSO4 or ZnSO4; (3) Graded flocculation and sedimentation: Add a core-shell structured composite flocculant to the wastewater after sulfidation treatment and stir to react; the core of the composite flocculant is a highly positively charged inorganic flocculant and the shell is a long-chain organic polymer.

[0009] First, the multi-element synergistic oxidation adsorption process employs a potassium permanganate-sodium hypochlorite system in conjunction with ozone treatment technology. This achieves efficient removal of low-concentration thallium through the synergistic effect of the three oxidants. The synergistic effect and catalytic cycle among the three oxidants include: ① Interaction between potassium permanganate and sodium hypochlorite: Under neutral conditions, potassium permanganate and sodium hypochlorite can act as oxidants to oxidize pollutants in water, reducing the solubility and mobility of Tl. +Oxidation into Tl, which readily binds to colloids / particulate matter. 3+ On the other hand, potassium permanganate and sodium hypochlorite react to produce nano-sized MnO2 colloids (as shown in Formula 1), which can effectively adsorb microgram-level concentrations of thallium. MnO4 - +ClO - +2H ＋ →MnO2↓+ClO2↓+H2O (Formula 1) ② Interaction between ozone and potassium permanganate: Intermediate manganese oxides (such as MnO2) generated by the reduction of potassium permanganate are highly efficient catalysts for ozone decomposition. They can catalyze the rapid decomposition of ozone molecules in aqueous solution, producing highly oxidizing hydroxyl radicals. The oxidation potential of ·OH is much higher than that of ozone and potassium permanganate, and it can oxidize almost all organic and reducing inorganic substances without selectivity, thus greatly enhancing the oxidation of complexed and encapsulated Tl. + Its complex-breaking and oxidation capabilities solve the problem of insufficient oxidizing power when relying solely on potassium permanganate; ③ Interaction between ozone and sodium hypochlorite: Ozone can oxidize the hypochlorite ions in sodium hypochlorite, generating ClO2 in situ (as shown in Formula 1). ClO2 is a highly efficient and rapid oxidant, with superior oxidizing power compared to sodium hypochlorite, and is less affected by pH. It can more quickly attack Tl. + It reacts with organic pollutants, forming an oxidation gradient with potassium permanganate and ·OH to ensure a more complete oxidation reaction; 2NaClO+O3+H2O→2ClO2+2NaOH (Formula 2) ④ Three-way synergistic catalytic cycle network: Potassium permanganate oxidation of Tl + Generate Tl 3+ With MnO2, advanced treatment is initiated; the newly generated MnO2 acts as a catalyst to decompose O3, producing a large amount of ·OH; on the other hand, the MnO2 colloid can efficiently adsorb thallium in the water, fully exerting its catalytic adsorption effect; the ·OH non-selectively oxidizes the remaining Tl. + The oxidation process is enhanced by the reaction of ozone and organic pollutants. Simultaneously, ozone reacts with sodium hypochlorite to generate ClO2, providing another rapid oxidation pathway. Sodium hypochlorite maintains the alkalinity of the system, ensuring all reactions occur within a highly efficient pH range, while it itself is also catalytically activated. Therefore, an effective and stable ternary synergistic catalytic cycle network is constructed.

[0010] To avoid dissolution and precipitation in strong acid or strong alkaline environments during the synergistic oxidation and adsorption process, and to better leverage the oxidizing effect of the oxidant, the optimal pH range for this process is 6–9. Through the synergistic catalytic oxidation and adsorption of multiple oxidants, the reduction rebound of thallium is prevented, and the subsequent treatment effect is amplified through adsorption and enrichment.

[0011] Secondly, this invention addresses the water quality characteristics of mine water with ultra-low concentrations of thallium by proposing the use of a compound sulfiding agent, including Na₂S, FeSO₄, and ZnSO₄, overcoming the shortcomings of single sulfide precipitation in precipitating low-concentration thallium. The sulfiding agent generates S in the water. 2- Tl 3+ With S 2- The reaction produces Tl2S3 precipitate, thereby transferring thallium from water to the solid phase for separation.

[0012] This invention employs a Na2S+FeSO4 / ZnSO4 process, utilizing Na2S and thallium ions to rapidly generate nascent microcrystal nuclei for primary precipitation and capture. The treatment effect is then enhanced by a secondary precipitant, FeSO4 or ZnSO4. The synergistic mechanism of the compound vulcanizing agent is as follows: ①The role of FeSO4: FeSO4 is an excellent adsorbent and co-precipitant. It provides Fe... 2+ Can be used with S 2- Further, FeS precipitates, forming a "FeS-Tl2S3" co-precipitation system. This system effectively adsorbs and encapsulates the fine Tl2S3 particles generated from Na2S, preventing their gelation and forming larger, denser flocs, thus greatly improving sedimentation performance. Additionally, Fe... 2+ The hydrolysis of FeS produces a slightly acidic pH, which can buffer the sharp pH rise caused by the hydrolysis of Na2S, stabilizing the pH within a more ideal range (usually maintained at 7-9). Furthermore, FeS has a higher solubility than Tl2S3 but lower solubility than Na2S, thus it can continuously provide sulfur. 2- This also avoids the problem of excessive residual sulfur caused by excessive Na2S addition; ②The role of ZnSO4: The solubility product of ZnS (K sp =2.93×10 -25 ) is much smaller than Tl2S3(K sp ≈5×10 -21 From a thermodynamic point of view, S 2- Preferring to Zn 2+ They combine. However, when both exist together, they readily form mixed crystals or solid solutions in the form of (Tl, Zn)S or Tl2S3·ZnS. This mixed crystal structure is extremely stable, has very low solubility, and can firmly fix thallium. Moreover, the sedimentation performance of ZnS precipitate is usually better than that of fine Tl2S3, and the formation of ZnS continues to "trap" and integrate Tl in the solution. + This allows thallium to enter the crystal lattice, thereby achieving deep purification of thallium.

[0013] The compound sulfide precipitation process needs to be carried out in a weakly alkaline environment with a pH of 8-9 to provide an alkaline environment for subsequent precipitation. However, the pH value should not be too high, as an excessively high pH environment is prone to producing thallium hydroxide colloids, which will affect the effect of sulfide precipitation and sedimentation performance.

[0014] Finally, this invention employs staged flocculation and sedimentation to further treat thallium-containing wastewater, proposing a design concept for a "core-shell" composite flocculant. The core is a highly positively charged inorganic flocculant, while the outer shell is a long-chain organic polymer, achieving efficient thallium precipitation. The mechanism by which this composite flocculant improves flocculation efficiency is as follows: ① High-efficiency charge neutralization and destabilization: The highly positively charged "core" can rapidly diffuse and neutralize the negative charges of Tl2S3, Tl(OH)3, and other colloidal particles after addition, compressing the electric double layer, reducing electrostatic repulsion, and causing the microparticles to destabilize instantly (destabilize). This is the basis for subsequent aggregation; ② Enhanced Adsorption Bridging: After the colloidal particles are destabilized, the long-chain organic polymer in the "shell" can simultaneously adsorb multiple microparticles, forming a "colloid-polymer-colloid" bridge. This bridge pulls countless tiny particles together, creating visible flocs. The long-chain structure greatly expands the radius of action and increases the capture probability. ③ Synergistic net-like capture and sweeping: The inorganic flocculant in the core hydrolyzes to generate a large amount of amorphous hydroxide precipitate, forming a rapidly sinking "filter". During the descent, it can sweep and encapsulate tiny flocs and colloidal particles in the water that have not yet been fully aggregated. The organic polymer in the outer shell makes this "filter" more adhesive, resulting in higher net-like capture efficiency; ④ Functional Synergistic Effect: The "core-shell" structure achieves sequential action and synergistic effect. The core first destabilizes, the shell then bridges, and finally they work together to capture the flocculant. This avoids the re-stabilization phenomenon that may occur when a single flocculant first bridges and then destabilizes, and also avoids the competitive interference that may exist when organic and inorganic flocculants are added alone.

[0015] Therefore, after synergistic oxidation and adsorption with ternary oxidants, compound sulfide precipitation, and graded flocculation precipitation, the thallium removal rate of metal mine wastewater with microgram-level thallium concentration is as high as 96%, effectively solving the problem of treating low-concentration thallium-containing wastewater.

[0016] Preferably, after step (3), deep adsorption with activated carbon is also included. This process serves as the final safeguard of the treatment process, removing the remaining thallium through the adsorption of activated carbon. The effluent thallium content meets the Class II surface water standard (below 0.1 μg / L), and the effluent is stable.

[0017] Further optimization reveals that the deep adsorption process using activated carbon specifically involves: after the fractional flocculation and sedimentation is completed, the supernatant is obtained by filtration, activated carbon is added, the mixture is stirred for adsorption, and then filtered again.

[0018] As a preferred option, a composite flocculant with a core-shell structure is formed by introducing long-chain organic polymers onto the surface of an inorganic flocculant using a physical encapsulation method.

[0019] Further optimization involves the physical encapsulation process as follows: the long-chain organic polymer is stirred in water until completely dissolved to obtain solution A; the inorganic flocculant is stirred in water to obtain solution B; solution A is slowly dripped into solution B under stirring to obtain a core-shell structured composite flocculant.

[0020] More preferably, after solution B has been added dropwise, glutaraldehyde aqueous solution is slowly added to the mixture, and the reaction is continued with stirring for 30 minutes. Adding glutaraldehyde aqueous solution can enhance the stability of the core-shell structure.

[0021] In addition to the physical encapsulation methods mentioned above, chemical grafting can also be used to introduce long-chain molecules onto the surface of inorganic flocculants, forming core-shell structured composite flocculants.

[0022] Preferably, the inorganic flocculant is polyferric sulfate, polyaluminum chloride, or polyferric silicate, and the long-chain organic polymer is cationic polyacrylamide.

[0023] The core-shell composite flocculant of the present invention uses a highly positively charged inorganic flocculant, such as polyferric sulfate (PFS) or polyaluminum chloride (PAC), whose hydroxyl complex structure is optimized to increase the positive charge density. It can even use composite inorganic flocculants such as polyferrosilicate (PFSS), which forms larger and denser flocs. The outer shell is chemically grafted or physically wrapped, introducing long-chain, high-functional-group organic polymers onto the surface of the inorganic flocculant particles, preferably cationic polyacrylamide (CPAM).

[0024] Preferably, the reaction time for step (1) is 60-90 min; the reaction time for step (2) is 30-90 min; and the reaction time for step (3) is 20-60 min. The treatment time for each stage can be adjusted according to the actual wastewater to reduce the thallium concentration in the effluent to below 0.1 μg / L. The reaction time for step (1) can be appropriately extended or shortened according to the degree of water pollution. Similarly, the reaction time for step (2) or step (3) can be appropriately extended or shortened according to the precipitation situation.

[0025] Preferably, the thallium content in the treated metal mine wastewater is between 3 and 12 μg / L, and after treatment, the thallium content decreases to below 0.1 μg / L. The deep purification treatment method for thallium wastewater provided by this invention is particularly applicable to wastewater with thallium content at the microgram level, and has significant practical implications for the treatment of metal mine wastewater.

[0026] Preferably, the dosage of potassium permanganate is 0.8~1.15 mg / L; the dosage of sodium hypochlorite, calculated as available chlorine, is 2.0~2.7 mg / L; and the dosage of ozone is 2.0~3.05 mg / L.

[0027] Preferably, the dosage of Na2S is 0.9~1.32 mg / L; the dosage of FeSO4 is 3.27~4.44 mg / L or the dosage of ZnSO4 is 1.68~2.28 mg / L.

[0028] For 1L of wastewater with a thallium content of 3~10μg / L, the multi-element synergistic oxidation and adsorption process uses potassium permanganate at a dosage of 0.8~1.15 mg / L, sodium hypochlorite (available chlorine) at a dosage of 2.0~2.7 mg / L, and ozone at a dosage of 2.0~3.05 mg / L. The mass ratio of potassium permanganate:sodium hypochlorite (available chlorine):ozone is 1:(2.4~2.5):(2.5~2.65). The dosage can be multiplied by a safety factor of 1.2~1.5 according to the water quality. In the compound sulfide precipitation process, the dosage of Na2S is 0.9~1.32 mg / L. If FeSO4 is used in combination, the dosage is 3.27~4.44 mg / L, and the mass ratio of Na2S to FeSO4 is 1:(3.4~3.6). If ZnSO4 is used in combination, the dosage is 1.68~2.28 mg / L, and the mass ratio of Na2S to ZnSO4 is 1:(1.73~1.87).

[0029] Therefore, the present invention has the following beneficial effects: (1) Combining potassium permanganate, sodium hypochlorite and ozone as three oxidants, through the synergistic effect between the three oxidants, on the one hand, the extremely strong ·OH of the oxidant is generated to oxidize thallium, and on the other hand, MnO2 colloid with high adsorption capacity is generated to adsorb pollutants. The multiple measures effectively improve the removal effect of low concentration thallium. (2) The use of sulfide compounding process overcomes the deficiency of single sulfide precipitant in capturing and binding low concentrations of thallium, effectively improving the precipitation effect of trace amounts of thallium, and at the same time solving the problem of excessive sulfur. 2- Secondary pollution problems; (3) A design concept of a "core-shell" structure composite flocculant was proposed, which avoids the re-stabilization phenomenon that may be caused by the bridging and then destabilization of a single flocculant, and also avoids the competition and interference that may exist when organic and inorganic flocculants are added separately. (4) The combined process provided by the present invention is specifically designed for mine water containing low concentration of thallium in metal mines, and the effluent thallium can meet the surface water environmental quality standards. Attached Figure Description

[0030] Figure 1 This is a flow chart of the wastewater treatment process in Embodiment 1 of the present invention. Detailed Implementation

[0031] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0032] The reagents used in this invention can be obtained by purchasing or making them in-house.

[0033] Acid-adjusting solution: Prepare a low-concentration dilute acid solution using commercially available concentrated H2SO4, concentrated HCl, or other acids as raw materials.

[0034] Prepare an alkaline solution: Use commercially available Na2CO3, NaOH, NaHCO3 or other alkalis as raw materials to prepare an alkaline solution of a certain concentration.

[0035] Oxidizing agents: Common commercially available oxidizing agents include KMnO4, NaClO solution and O3.

[0036] Compound vulcanizing agent: Commercially available vulcanizing agent or metal salt, using Na2S and FeSO4 or ZnSO4 compounded.

[0037] Flocculants and precipitants include common commercially available inorganic and organic flocculants, such as polyferric sulfate (PFS), polyaluminum chloride (PAC), polyferrosilicate (PFSS), polyacrylamide (CPAM), etc.; and the core-shell structured composite flocculant and precipitant used in this invention. The core-shell structured composite flocculant and precipitant is prepared using a physical encapsulation method, the specific process of which is as follows: (1) Pre-dissolution of CPAM: Weigh 5g of CPAM solid and slowly add it to 300mL of deionized water at about 45℃ while stirring. Continue stirring for about 60min until it is completely dissolved, and a clear or translucent viscous solution is obtained. (2) Core preparation and mixing: Weigh about 40g of PAC or PFS solution (containing 20g of dry basis), add an appropriate amount of deionized water to dilute to about 100 mL, and stir continuously at a medium speed (300 rpm) at room temperature; (3) Physical encapsulation composite: The CPAM solution prepared in step 1 is slowly added to the PAC or PFS solution at a rate of 2-3 drops / second under stirring, so that the CPAM molecular chains are uniformly adsorbed on the surface of PAC or PFS particles to obtain a core-shell structured composite flocculant, which is denoted as core-shell PAC-CPAM and core-shell PFS-CPAM, respectively.

[0038] Activated carbon: Commercially available powdered or granular activated carbon. Example 1

[0039] The treatment target was mine water discharged from a gold mine, which contained various heavy metals, including thallium at a concentration of approximately 3.2 μg / L.

[0040] The deep purification process is as follows Figure 1 The details are as follows: (1) Adjust pH: Adjust the pH of the water sample to 7; (2) Multi-component synergistic oxidation adsorption: Add 1.2 mg KMnO4 to 1 L of mine water, then add 0.03 mL NaClO solution (effective chlorine content 8%) and 2.5 mg O3, and stir the reaction for 90 min; (3) Composite sulfide precipitation: After oxidation treatment, the pH of the water sample was adjusted to 8, and 1 mg of compound sulfide agent Na2S and 3.5 mg of FeSO4 were added. The mixture was stirred and reacted for 60 min. (4) Graded flocculation and sedimentation: After sulfidation and sedimentation, 0.5 mL of composite flocculant core-shell PFS-CPAM is added to the water, stirred and reacted for 60 min, and then precipitated and filtered. (5) Deep adsorption of activated carbon: Add 3g of washed activated carbon to the supernatant of the filter, stir slowly for 90min, filter again after the adsorption is completed, and effluent is discharged.

[0041] The thallium content of the treated water sample was determined. In Example 1, the thallium concentration of the effluent sample was reduced to 0.08 μg / L. Example 2

[0042] The wastewater being treated was from a lead-zinc mine, containing trace amounts of thallium, with a thallium content of approximately 6.5 μg / L.

[0043] The specific process of deep purification treatment is as follows: (1) Adjust pH: Adjust the pH of the water sample to 7; (2) Multi-component synergistic oxidation adsorption: Add 1.2 mg KMnO4 to 1 L of mine water, then add 0.03 mL NaClO solution (effective chlorine content 8%) and 2.5 mg O3, and stir the reaction for 90 min; (3) Composite sulfide precipitation: After oxidation treatment, the pH of the water sample was adjusted to 8, and 1 mg of compound sulfide agent Na2S and 2 mg of ZnSO4 were added. The mixture was stirred and reacted for 60 min. (4) Graded flocculation and sedimentation: After sulfidation and sedimentation, 0.5 mL of composite flocculant core-shell PFS-CPAM is added to the water, stirred and reacted for 60 min, and then precipitated and filtered. (5) Deep adsorption of activated carbon: Add 3g of washed activated carbon to the supernatant of the filter, stir slowly for 90min, filter again after the adsorption is completed, and effluent is discharged.

[0044] The thallium content of the treated water sample was determined. In Example 1, the thallium concentration of the effluent sample was reduced to 0.05 μg / L. Example 3

[0045] The wastewater being treated was from an abandoned pyrite mine pit, containing a low concentration of thallium, approximately 10.6 μg / L.

[0046] The specific process of deep purification treatment is as follows: (1) Adjust pH: Adjust the pH of the water sample to 7; (2) Multi-component synergistic oxidation adsorption: Add 1.2 mg KMnO4 to 1 L of mine water, then add 0.03 mL NaClO solution (effective chlorine content 8%) and 2.5 mg O3, and stir the reaction for 90 min; (3) Composite sulfide precipitation: After oxidation treatment, the pH of the water sample was adjusted to 8, and 1 mg of compound sulfide agent Na2S and 3.5 mg of FeSO4 were added. The mixture was stirred and reacted for 60 min. (4) Graded flocculation and sedimentation: After sulfidation and sedimentation, 0.5 mL of composite flocculant core-shell PAC-CPAM is added to the water, stirred and reacted for 60 min, and then precipitated and filtered. (5) Deep adsorption of activated carbon: Add 3g of washed activated carbon to the supernatant of the filter, stir slowly for 90min, filter again after the adsorption is completed, and effluent is discharged.

[0047] The thallium content of the treated water sample was determined. In Example 1, the thallium concentration of the effluent sample was reduced to 0.07 μg / L. Example 4

[0048] The treatment target was mine water discharged from a gold mine, which contained various heavy metals, including thallium at a concentration of approximately 3.2 μg / L.

[0049] The specific process of deep purification treatment is as follows: (1) Adjust pH: Adjust the pH of the water sample to 7; (2) Multi-component synergistic oxidation adsorption: Add 1.2 mg KMnO4 to 1 L of mine water, then add 0.03 mL NaClO solution (effective chlorine content 8%) and 2.5 mg O3, and stir the reaction for 90 min; (3) Composite sulfide precipitation: After oxidation treatment, the pH of the water sample was adjusted to 8, and 1 mg of compound sulfide agent Na2S and 3.5 mg of FeSO4 were added. The mixture was stirred and reacted for 60 min. (4) Graded flocculation and sedimentation: After sulfidation and sedimentation, 0.5 mL of composite flocculant core-shell PFS-CPAM is added to the water, stirred and reacted for 60 min, then precipitated, filtered, and discharged.

[0050] The thallium content of the treated water sample was determined. In Example 1, the thallium concentration of the effluent sample was reduced to 0.13 μg / L.

[0051] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not include a multi-component synergistic oxidation adsorption process.

[0052] The thallium content of the treated water sample was determined, and the thallium concentration of the effluent sample of Comparative Example 1 was reduced to 0.91 μg / L.

[0053] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the multi-component synergistic oxidation adsorption process uses only KMnO4 and O3.

[0054] The thallium content of the treated water sample was determined, and the thallium concentration of the effluent sample of Comparative Example 2 was reduced to 0.37 μg / L.

[0055] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the multi-component synergistic oxidation adsorption process only uses KMnO4 and NaClO.

[0056] The thallium content of the treated water sample was determined, and the thallium concentration of the effluent sample of Comparative Example 3 was reduced to 0.18 μg / L.

[0057] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the multi-component synergistic oxidation adsorption process uses only NaClO and O3.

[0058] The thallium content of the treated water sample was determined, and the thallium concentration of the effluent sample of Comparative Example 4 was reduced to 0.63 μg / L.

[0059] As shown in Examples 1 and Comparative Examples 1-4, the combined process of "multi-element synergistic oxidation adsorption + composite sulfide precipitation + staged flocculation precipitation + activated carbon deep adsorption" in Example 1 reduced the thallium concentration in the effluent of low-concentration thallium-containing mine water to 0.08 μg / L, which is lower than the Class II environmental quality standard for surface water, with a removal rate as high as 97.5%. However, when the multi-element synergistic oxidation adsorption process was absent in Comparative Example 1, the effluent thallium concentration was still 0.91 μg / L, with a removal rate of only 71.6%, clearly failing to meet the effluent requirements. This indicates that the oxidation process is indispensable for treating low-concentration thallium-containing wastewater, as it can both prevent thallium reduction rebound and facilitate adsorption, enrichment, and scale-up for subsequent treatment.

[0060] Comparative Examples 2-4 show that when any two of KMnO4, NaClO, and O3 are used in combination, the thallium content in the treated water is 0.18-0.63 μg / L, which cannot meet the Class II surface water standard. In particular, the treatment effect is significantly reduced when no KMnO4 oxidant is added. The treatment effect of each combination is ranked as follows: the combination of KMnO4 and NaClO is better than the combination of KMnO4 and O3, which is better than the combination of NaClO and O3.

[0061] This indicates that the synergistic catalytic and adsorption effects of the three oxidants in the potassium permanganate-sodium hypochlorite system for ozone treatment confirm the synergistic effect and catalytic cycle among the three oxidants. Specifically, potassium permanganate or sodium hypochlorite oxidizes Tl + Generate Tl 3+ Meanwhile, potassium permanganate and sodium hypochlorite react to produce MnO2 (reaction formula MnO4). - +ClO - +2H ＋ →MnO2↓+ClO2↓+H2O), initiating deep treatment; the newly generated MnO2 acts as a catalyst to catalyze the decomposition of ozone to produce a large amount of ·OH, and the MnO2 colloid can efficiently adsorb thallium in the water, fully exerting its catalytic adsorption effect; the oxidation potential of ·OH (2.8 V) is much higher than that of ozone (2.07 V) and potassium permanganate (1.68 V), and it can almost non-selectively oxidize all organic matter and reducing inorganic matter (including Tl). + This enhances the oxidation process. Simultaneously, ozone reacts with sodium hypochlorite to generate ClO2 (reaction formula 2NaClO+O3+H2O→2ClO2+2NaOH), providing another rapid oxidation pathway. Chlorine dioxide is a highly efficient and rapid oxidant, with superior oxidizing power compared to sodium hypochlorite. It is also less affected by pH, and sodium hypochlorite can maintain the alkalinity of the system, ensuring all reactions occur within a highly efficient pH range, while simultaneously being catalyzed and activated itself.

[0062] Among the three oxidants, potassium permanganate and sodium hypochlorite react to produce nanoscale MnO2 colloids. These colloids have a huge specific surface area and strong adsorption capacity; the adsorption capacity of the colloid alone for thallium can reach 120 mg / g, effectively adsorbing microgram-level concentrations of thallium. Furthermore, the intermediate manganese oxides (such as MnO2) generated by the reduction of potassium permanganate promote ozone decomposition, further producing highly oxidizing ·OH, which is effective for complexed and encapsulated Tl. + It possesses complex-breaking and oxidizing capabilities. Therefore, potassium permanganate is the core oxidant in the ternary oxidant system, playing a crucial role in initiating the oxidation process. The addition of ozone and sodium hypochlorite significantly improves the oxidizing power of potassium permanganate alone, providing multiple oxidation pathways and ensuring a more thorough oxidation reaction.

[0063] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that Comparative Example 5 does not include the complex sulfurization precipitation process.

[0064] The thallium content of the treated water sample was determined, and the thallium concentration of the effluent sample of Comparative Example 5 was reduced to 0.85 μg / L.

[0065] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that only Na2S is used in the composite sulfur precipitation process.

[0066] The thallium content of the treated water sample was determined, and the thallium concentration of the effluent sample of Comparative Example 6 was reduced to 0.17 μg / L.

[0067] As shown in Examples 1, 2, and Comparative Examples 5 and 6, the combined process of Example 1 for treating low-concentration thallium-containing mine water reduced the effluent thallium concentration to 0.08 μg / L, achieving a removal rate of 97.5%. The combined process of Example 2 for treating low-concentration thallium-containing lead-zinc mine wastewater reduced the effluent thallium concentration to 0.05 μg / L, achieving a removal rate of 99.2%. However, when Comparative Example 5 did not undergo the combined sulfidation precipitation treatment process, the effluent thallium content of the thallium-containing wastewater was as high as 0.85 μg / L, with a removal rate of only 73.4%. Comparative Example 6, using only Na₂S as a sulfiding agent to treat the thallium-containing wastewater, reduced the effluent thallium concentration to 0.17 μg / L, achieving a removal rate of 94.7%. Although Comparative Example 6 showed a significant improvement in treatment effect, it could not achieve the same results as Example 1 using a combination of Na₂S and FeSO₄ as a sulfiding agent, or Example 2 using a combination of Na₂S and ZnSO₄ as a sulfiding agent. This indicates that the composite sulfidation precipitation process plays a crucial role in the removal of low-concentration thallium, and this process is indispensable; moreover, the effect of the composite sulfiding agent is superior to that of using Na2S alone, and it can solve the problem of excessive S caused by high dosage of a single sulfiding agent. 2- The problem of secondary pollution.

[0068] This is mainly because the secondary precipitant FeSO4 or ZnSO4 enhances the Na2S treatment effect. Specifically, the synergistic mechanism involves the use of Na2S + FeSO4, where FeSO4 provides Fe... 2+ Can be used with S 2- Further, FeS precipitates, forming a "FeS-Tl2S3" co-precipitation system. This system effectively adsorbs and encapsulates the fine Tl2S3 particles generated from Na2S, preventing their gelation and forming larger, denser flocs, thus greatly improving sedimentation performance. Furthermore, Fe... 2+ The hydrolysis of FeS produces a slightly acidic solution, which can buffer the sharp pH rise caused by the hydrolysis of Na2S, stabilizing the pH within a more ideal range. Furthermore, FeS has a higher solubility than Tl2S3 but lower solubility than Na2S, thus it can continuously provide sulfur. 2- This avoids the problem of excessive residual sulfur caused by excessive Na2S addition. When using Na2S + ZnSO4, it readily forms mixed crystals or solid solutions in the form of (Tl, Zn)S or Tl2S3·ZnS, which can firmly fix thallium. Furthermore, the settling performance of ZnS precipitate is generally better than that of fine Tl2S3, and the formation of ZnS continues to "trap" and integrate Tl in the solution. + This allows thallium to enter the crystal lattice, thereby achieving deep purification of thallium.

[0069] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the flocculants CPAM and PFS were added separately during the staged flocculation and sedimentation process.

[0070] The treatment target was mine water discharged from a gold mine, which contained various heavy metals, including thallium at a concentration of approximately 3.2 μg / L.

[0071] The specific processing technology is as follows: (1) Adjust pH: Adjust the pH of the water sample to 7; (2) Multi-component synergistic oxidation adsorption: Add 1.2 mg KMnO4 to 1 L of mine water, then add 0.03 mL NaClO solution (effective chlorine content 8%) and 2.5 mg O3, and stir the reaction for 90 min; (3) Composite sulfide precipitation: After oxidation treatment, the pH of the water sample was adjusted to 8, and 1 mg of compound sulfide agent Na2S and 3.5 mg of FeSO4 were added. The mixture was stirred and reacted for 60 min. (4) Graded flocculation and sedimentation: After sulfidation and precipitation, 6.25 mg CPAM and 50 mg PFS solution (containing 25 mg dry basis) were added to water successively, and the mixture was stirred and reacted for 60 min before precipitation and filtration. (5) Deep adsorption of activated carbon: Add 3g of washed activated carbon to the supernatant of the filter, stir slowly for 90min, filter again after the adsorption is completed, and effluent is discharged.

[0072] The thallium content of the treated water sample was determined, and the thallium concentration of the effluent sample of Comparative Example 7 was reduced to 0.19 μg / L.

[0073] The above embodiments and comparative examples, treatment processes, and effluent conditions are shown in Table 1: Table 1. Treatment process and effluent conditions of the examples and comparative examples Combined with Examples 1, 3, and Comparative Example 7, it can be seen that the core-shell structured composite flocculants (such as core-shell PFS-CPAM and core-shell PAC-CPAM) used in this invention can achieve better thallium removal effects. For example, Example 1 achieved a removal rate of up to 97.5% for thallium-containing mine water (thallium content 3.2 μg / L), and Example 3 achieved a removal rate of up to 99.3% for thallium-containing mine wastewater (thallium content 10.6 μg / L), with both effluents below 0.1 μg / L. In contrast, Comparative Example 7, with only two flocculants added, showed a decrease in thallium removal rate to only 94.1%, with effluent above 0.1 μg / L, failing to meet the Class II surface water standard. This indicates that the core-shell structured composite flocculant proposed in this invention has a highly efficient sedimentation effect. The "core-shell" structure achieves sequential action and synergistic effect, avoiding the re-stabilization phenomenon that may occur when a single flocculant first bridges and then breaks down, and also avoiding the competitive interference that may exist when organic and inorganic flocculants are added alone.

[0074] Specifically, the composite flocculant prepared by the physical encapsulation method has a core of highly positively charged inorganic flocculant (PFS, PAC, etc.). After addition, it can rapidly diffuse and neutralize the negative charge of Tl2S3, Tl(OH)3, and other colloidal particles, compressing the electric double layer, reducing electrostatic repulsion, and causing the microparticles to break down instantly. The outer shell is an organic polymer with a long-chain structure (such as CPAM). After the colloidal particles break down, its molecular chains can simultaneously adsorb multiple microparticles, forming a "colloid-polymer-colloid" bridge that pulls and aggregates countless tiny particles together. The long-chain structure can also expand the radius of action and increase the capture probability. When the core hydrolyzes to generate a large number of amorphous Fe(OH)3 or Al(OH)3 precipitates, forming a rapidly sinking "filter," it sweeps and encapsulates the tiny flocs and colloidal particles in the water that have not yet been fully aggregated. Furthermore, because the outer shell is an organic polymer, this "filter" is more viscous, resulting in higher capture efficiency. Therefore, a highly efficient flocculation and sedimentation effect is achieved by first breaking down the core, then bridging the outer shell, and finally capturing the sediment together.

[0075] Furthermore, comparing Examples 1 and 4, it can be seen that when Example 4 does not include the final activated carbon deep adsorption process, the removal rate is 96%, but the thallium concentration in the effluent is 0.13 μg / L, slightly higher than the Class II surface water standard, and the treatment effect is slightly inferior to Example 1. This indicates that the adsorption effect of activated carbon can further remove the remaining thallium, ensuring that the effluent thallium concentration meets the Class II surface water standard (below 0.1 μg / L), and maintaining a stable effluent effect. It can serve as a final-stage guarantee for the treatment of low-concentration thallium-containing wastewater.

[0076] As demonstrated in Examples 1-3, the combined deep purification process proposed in this invention is suitable for treating low-concentration thallium-containing wastewater from metal mines (3-12 μg / L), achieving a thallium removal rate of over 97%, and producing effluent that meets the Class II surface water standard. This has significant practical implications for the treatment of metal mine wastewater. Furthermore, the combined process provided by this invention has a relatively short treatment time, allowing for reasonable adjustment of the treatment time at each stage based on the initial wastewater conditions, which is beneficial for large-scale application.

Claims

1. A method for deep purification treatment of thallium-containing metal mine wastewater, characterized in that, Includes the following steps: (1) Multi-component synergistic oxidation adsorption: First, adjust the pH of the thallium-containing mine wastewater to 6-9, then add potassium permanganate and sodium hypochlorite, introduce ozone, and stir the reaction; (2) Composite sulfide precipitation: Adjust the pH of the wastewater after oxidation treatment to 8-9, add the compound sulfide agent, and stir to react; the compound sulfide agent contains Na2S and FeSO4 or ZnSO4; (3) Graded flocculation and sedimentation: Add a core-shell structured composite flocculant to the wastewater after sulfidation treatment and stir to react; the core of the composite flocculant is a highly positively charged inorganic flocculant and the shell is a long-chain organic polymer.

2. The deep purification treatment method according to claim 1, characterized by, After step (3) is completed, deep adsorption with activated carbon is also included.

3. The deep purification process of claim 2, wherein, The activated carbon deep adsorption process is as follows: after the fractional flocculation and sedimentation is completed, the supernatant is obtained by filtration, activated carbon is added, the mixture is stirred for adsorption, and then filtered again.

4. The deep purification treatment method according to claim 1, characterized by, A composite flocculant with a core-shell structure was formed by introducing long-chain organic polymers onto the surface of an inorganic flocculant using a physical encapsulation method.

5. The deep purification process of claim 4, wherein, The physical encapsulation process is as follows: the long-chain organic polymer is stirred in water until completely dissolved to obtain solution A; the inorganic flocculant is stirred in water to obtain solution B; solution A is slowly dripped into solution B under stirring to obtain a core-shell structured composite flocculant.

6. The deep purification treatment method according to claim 1 or 4 or 5, characterized by, The inorganic flocculant is polyferric sulfate, polyaluminum chloride, or polyferric silicate, and the long-chain organic polymer is cationic polyacrylamide.

7. The deep purification treatment method according to claim 1, characterized by, The reaction time for step (1) is 60-90 min; the reaction time for step (2) is 30-90 min; and the reaction time for step (3) is 20-60 min.

8. The deep decontamination process of claim 1, wherein, The thallium content in the treated metal mine wastewater ranged from 3 to 12 μg / L, but after treatment, the thallium content decreased to below 0.1 μg / L.

9. The deep purification process of claim 1, wherein, The dosage of potassium permanganate is 0.8~1.15 mg / L; the dosage of sodium hypochlorite, calculated as available chlorine, is 2.0~2.7 mg / L; and the dosage of ozone is 2.0~3.05 mg / L.

10. The deep purification treatment method according to claim 1, characterized in that, The dosage of Na2S is 0.9~1.32 mg / L; the dosage of FeSO4 is 3.27~4.44 mg / L or the dosage of ZnSO4 is 1.68~2.28 mg / L.

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