A method for treating industrial heavy metal wastewater by fractional precipitation

Abstract

This invention discloses a method for graded sedimentation treatment of industrial heavy metal wastewater, comprising: pretreating the industrial heavy metal wastewater to obtain pretreated wastewater; performing primary sedimentation treatment on the pretreated wastewater to separate copper precipitates from the pretreated wastewater, obtaining primary treated wastewater; performing secondary sedimentation treatment on the primary treated wastewater to separate lead precipitates from the primary treated wastewater, obtaining secondary treated wastewater; performing tertiary sedimentation treatment on the secondary treated wastewater to separate cadmium and zinc precipitates from the secondary treated wastewater, obtaining tertiary treated wastewater; and performing deep purification treatment on the tertiary treated wastewater to obtain wastewater that meets discharge standards. This invention can achieve graded sedimentation based on the characteristics of different heavy metal ions, thereby efficiently removing multiple heavy metal ions, while reducing the difficulty of sludge disposal and improving the recovery and utilization rate of heavy metal resources.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for graded sedimentation treatment of industrial heavy metal wastewater. Background Technology

[0002] Currently, the main technologies for treating industrial heavy metal wastewater include chemical precipitation, ion exchange, adsorption, membrane separation, and biological treatment. Among these, chemical precipitation is one of the most widely used technologies due to its advantages such as simple operation, relatively low treatment cost, and wide applicability to wastewater concentrations. Traditional chemical precipitation typically involves adding a single type of chemical precipitant to the wastewater. By adjusting the pH value of the wastewater, multiple heavy metal ions in the wastewater undergo a simultaneous precipitation reaction, forming a mixed precipitate, which is then separated into solid and liquid phases to remove the heavy metal ions.

[0003] However, in practical applications, traditional chemical precipitation methods have many insurmountable drawbacks: First, the optimal pH range for the formation of precipitates such as hydroxides, carbonates, or sulfides by different heavy metal ions varies significantly. If a single-stage precipitation treatment is used under a single pH condition, it is often impossible to achieve the ideal precipitation removal effect for all types of heavy metal ions, resulting in some heavy metal ion concentrations in the treated wastewater failing to meet discharge standards. Second, a single addition of precipitant can easily lead to excessively high local concentrations of the reagent, resulting in fine and highly dispersed precipitate particles. This not only makes it difficult to remove the precipitate efficiently through subsequent solid-liquid separation processes such as precipitation and filtration, but also easily causes problems such as sludge caking at the bottom of the sedimentation tank and clogging of filtration equipment, affecting the long-term stable operation of the treatment system. In addition, when the wastewater contains multiple heavy metal ions and other coexisting impurities, such as suspended solids and complexing agents, a single-stage precipitation treatment can easily cause impurities to become intertwined and mixed with the heavy metal precipitates, resulting in low purity of the precipitated sludge. This increases the difficulty and cost of subsequent sludge solidification and landfill disposal, and is also detrimental to the recycling of heavy metal resources, which is inconsistent with the current development concept of green environmental protection and resource recycling. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a graded sedimentation treatment method for industrial heavy metal wastewater. This method can achieve graded sedimentation based on the characteristics of different heavy metal ions, thereby efficiently removing multiple heavy metal ions, reducing the difficulty of sludge disposal, and improving the recycling rate of heavy metal resources.

[0005] To achieve the above objectives, the technical solution adopted by this invention is: a method for graded sedimentation treatment of industrial heavy metal wastewater, comprising: pretreating industrial heavy metal wastewater to obtain pretreated wastewater; performing primary sedimentation treatment on the pretreated wastewater to separate copper precipitates from the pretreated wastewater and obtaining primary treated wastewater; performing secondary sedimentation treatment on the primary treated wastewater to separate lead precipitates from the primary treated wastewater and obtaining secondary treated wastewater; performing tertiary sedimentation treatment on the secondary treated wastewater to separate cadmium and zinc precipitates from the secondary treated wastewater and obtaining tertiary treated wastewater; and performing deep purification treatment on the tertiary treated wastewater to obtain wastewater that meets discharge standards.

[0006] The above technical solution achieves graded sedimentation treatment of industrial heavy metal wastewater based on the characteristics of different heavy metal ions, realizing efficient removal of multiple heavy metal ions, while reducing the difficulty of sludge disposal and improving the recycling rate of heavy metal resources.

[0007] Furthermore, the industrial heavy metal wastewater is pretreated by adding flocculant to a pretreatment tank containing the industrial heavy metal wastewater, controlling the temperature in the pretreatment tank to be 20-30°C, the stirring speed to be 100-200 r / min, the stirring time to be 15-30 min, and then letting it stand for 20-40 min to remove suspended solids and complexes from the industrial heavy metal wastewater, thereby obtaining pretreated wastewater.

[0008] The above technical solution provides a practical approach for removing suspended solids and complexes from industrial heavy metal wastewater by defining specific pretreatment processes. It creates conditions for subsequent graded sedimentation treatment, facilitates the removal of multiple heavy metal ions based on their characteristics, reduces the difficulty of sludge disposal, and improves the recycling rate of heavy metal resources.

[0009] Furthermore, the flocculant comprises a mixture of polyaluminum chloride and polyacrylamide, wherein the mass ratio of polyaluminum chloride to polyacrylamide is 5~8:1, and the dosage of the flocculant is 0.1%~0.3% of the mass of industrial heavy metal wastewater.

[0010] The above technical solution, by specifying a particular flocculant, provides a practical approach for the efficient removal of suspended solids and complexes from industrial heavy metal wastewater, thereby increasing the formation rate of suspended solids and complexes in industrial heavy metal wastewater and providing conditions for the efficient removal of suspended solids and complexes from industrial heavy metal wastewater.

[0011] Further, the pretreated wastewater undergoes primary sedimentation treatment, including: adding pH adjuster one to the primary sedimentation tank where the pretreated wastewater is stored to adjust the pH value of the pretreated wastewater to 8-10, then adding the first precipitant, controlling the temperature in the primary sedimentation tank to 25-35℃, the stirring speed to 80-150 r / min, the stirring reaction time to 25-45 min, and then allowing it to settle for 30-60 min for solid-liquid separation to separate copper precipitates from the pretreated wastewater and obtain the primary treated wastewater.

[0012] The above technical solution provides a practical approach to removing copper precipitates from industrial heavy metal wastewater by defining a specific primary precipitation process. This approach facilitates the precipitation of copper metal, reduces the difficulty of disposing of copper precipitates, and improves the recycling rate of copper precipitates.

[0013] Furthermore, the pH adjuster includes a sodium hydroxide solution with a mass concentration of 10% to 20%; the first precipitant includes sodium carbonate, and the dosage of the first precipitant is 0.2% to 0.5% of the mass of the pretreated wastewater.

[0014] The above technical solution, by specifying a particular pH adjuster, provides a practical method for removing copper precipitates from industrial heavy metal wastewater. It facilitates the precipitation of copper metal, reduces the difficulty of disposing of copper precipitates, and improves the recycling rate of copper precipitates.

[0015] Further, the primary treated wastewater undergoes secondary sedimentation treatment, including: adding pH adjuster II to the secondary sedimentation tank containing the primary treated wastewater to adjust the pH value of the primary treated wastewater to 9-11, then adding a second precipitant, controlling the temperature in the secondary sedimentation tank to 28-38℃, the stirring speed to 60-120 r / min, the stirring reaction time to 30-50 min, followed by settling for 40-70 min, and solid-liquid separation to separate lead precipitates from the primary treated wastewater and obtain the secondary treated wastewater.

[0016] The above technical solution provides a practical approach to removing lead precipitates from industrial heavy metal wastewater by defining a specific secondary precipitation process. This approach facilitates lead precipitation, reduces the difficulty of disposing of lead precipitates, and improves the recovery rate of lead.

[0017] Furthermore, the second pH adjuster includes a calcium hydroxide solution with a mass concentration of 8% to 15%; the second precipitant includes sodium sulfide, and the dosage of the second precipitant is 0.3% to 0.6% of the mass of the wastewater after primary treatment.

[0018] The above technical solution, by specifying a particular pH adjuster, provides a practical method for removing lead precipitates from industrial heavy metal wastewater. This method facilitates lead precipitation, reduces the difficulty of disposing of lead precipitates, and improves the recovery rate of lead.

[0019] Furthermore, the secondary treated wastewater undergoes tertiary sedimentation treatment, including: adding pH adjuster III to the tertiary sedimentation tank containing the secondary treated wastewater to adjust the pH value of the wastewater to 7-9, then adding a third precipitant, controlling the temperature in the tertiary sedimentation tank to 22-32℃, the stirring speed to 50-100 r / min, the stirring reaction time to 20-40 min, followed by settling for 25-50 min, and solid-liquid separation to separate cadmium and zinc precipitates from the secondary treated wastewater, thus obtaining the tertiary treated wastewater.

[0020] The above technical solution provides a practical approach for removing cadmium and zinc precipitates from industrial heavy metal wastewater by defining a specific three-stage sedimentation process. This approach facilitates the precipitation of cadmium and zinc metals, reduces the difficulty of disposing of cadmium and zinc precipitate sludge, and improves the recovery rate of cadmium and zinc metals.

[0021] Furthermore, the third pH adjuster includes a hydrochloric acid solution with a mass concentration of 10% to 18%; the third precipitant includes magnesium hydroxide, and the dosage of the third precipitant is 0.15% to 0.4% of the mass of the secondary treated wastewater.

[0022] The above technical solution, by specifying a particular pH adjuster, provides a practical method for removing cadmium and zinc precipitates from industrial heavy metal wastewater. It facilitates the precipitation of cadmium and zinc metals, reduces the difficulty of disposing of cadmium and zinc precipitate sludge, and improves the recovery and utilization rate of cadmium and zinc metals.

[0023] Furthermore, the wastewater after tertiary treatment undergoes deep purification treatment, including: adding adsorbent to the deep purification tank where the wastewater after tertiary treatment is stored, controlling the temperature in the deep purification tank to be 20~30℃, the stirring speed to be 40~80r / min, the adsorption reaction time to be 15~30min, and then performing solid-liquid separation by filtration to obtain wastewater that meets the discharge standards.

[0024] The above technical solution provides a practical approach for the deep purification of wastewater after tertiary treatment by defining specific deep purification processes, while simultaneously achieving the harmless discharge of wastewater.

[0025] Compared with existing technologies, the beneficial effects achieved by this invention are as follows: This invention pre-treats industrial heavy metal wastewater to obtain pre-treated wastewater; performs primary sedimentation treatment on the pre-treated wastewater to separate copper precipitates, obtaining primary-treated wastewater; performs secondary sedimentation treatment on the primary-treated wastewater to separate lead precipitates, obtaining secondary-treated wastewater; performs tertiary sedimentation treatment on the secondary-treated wastewater to separate cadmium and zinc precipitates, obtaining tertiary-treated wastewater; and performs deep purification treatment on the tertiary-treated wastewater to obtain wastewater that meets discharge standards. This invention enables graded sedimentation based on the characteristics of different heavy metal ions, thereby efficiently removing multiple heavy metal ions, reducing the difficulty of sludge disposal, and improving the recovery rate of heavy metal resources. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the main process of a graded sedimentation treatment method for industrial heavy metal wastewater provided in an embodiment of the present invention;

[0027] Figure 2 This is a comparison of wastewater treatment costs in different embodiments of the present invention;

[0028] Figure 3 This is a comparison of sludge production and heavy metal recovery rate in different embodiments of the present invention. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0030] like Figure 1 As shown, a method for graded sedimentation treatment of industrial heavy metal wastewater includes: pretreating the industrial heavy metal wastewater to obtain pretreated wastewater; performing primary sedimentation treatment on the pretreated wastewater to separate copper precipitates from the pretreated wastewater and obtaining primary treated wastewater; performing secondary sedimentation treatment on the primary treated wastewater to separate lead precipitates from the primary treated wastewater and obtaining secondary treated wastewater; performing tertiary sedimentation treatment on the secondary treated wastewater to separate cadmium and zinc precipitates from the secondary treated wastewater and obtaining tertiary treated wastewater; and performing deep purification treatment on the tertiary treated wastewater to obtain wastewater that meets discharge standards.

[0031] 1. Pre-treatment of industrial heavy metal wastewater to obtain pre-treated wastewater.

[0032] Industrial heavy metal wastewater is introduced into a pretreatment tank. Flocculant is added to the pretreatment tank containing the wastewater, and the temperature is controlled at 20-30°C, the stirring speed at 100-200 r / min, and the stirring time at 15-30 min. The mixture is then allowed to stand for 20-40 min to remove suspended solids and complexes from the wastewater, resulting in pretreated wastewater. The flocculant comprises a mixture of polyaluminum chloride and polyacrylamide, wherein the mass ratio of polyaluminum chloride to polyacrylamide is 5-8:1, and the flocculant dosage is 0.1%-0.3% of the mass of the industrial heavy metal wastewater.

[0033] Second, the pretreated wastewater is subjected to primary sedimentation treatment to separate copper precipitates from the pretreated wastewater, resulting in primary treated wastewater.

[0034] The pretreated wastewater is introduced into a primary sedimentation tank. First, a pH adjuster is added to the primary sedimentation tank to adjust the pH value of the pretreated wastewater to 8-10. Then, a first precipitant is added. The temperature in the primary sedimentation tank is controlled at 25-35℃, the stirring speed at 80-150 r / min, and the stirring reaction time at 25-45 min. Afterward, the mixture is allowed to settle for 30-60 min for solid-liquid separation to separate copper precipitates from the pretreated wastewater, yielding the primary treated wastewater. The pH adjuster includes a sodium hydroxide solution with a mass concentration of 10%-20%. The first precipitant includes sodium carbonate, and its dosage is 0.2%-0.5% of the mass of the pretreated wastewater. The primary sedimentation sludge mainly consists of copper precipitates and is used for copper resource recovery.

[0035] Third, the wastewater after primary treatment is subjected to secondary sedimentation treatment to separate lead precipitates from the wastewater after primary treatment, and the wastewater after secondary treatment is obtained.

[0036] The primary treated wastewater is introduced into a secondary sedimentation tank. A second pH adjuster is added to the secondary sedimentation tank to adjust the pH value of the primary treated wastewater to 9-11. Then, a second precipitant is added. The temperature in the secondary sedimentation tank is controlled at 28-38℃, the stirring speed at 60-120 r / min, and the stirring reaction time at 30-50 min. Afterward, the mixture is allowed to settle for 40-70 min for solid-liquid separation to separate lead precipitates from the primary treated wastewater, thus obtaining the secondary treated wastewater. The second pH adjuster includes a calcium hydroxide solution with a mass concentration of 8%-15%. The second precipitant includes sodium sulfide, and the dosage of the second precipitant is 0.3%-0.6% of the mass of the primary treated wastewater. The secondary sedimentation sludge mainly consists of lead precipitates and is used for lead resource recovery.

[0037] Fourth, the secondary treated wastewater is subjected to tertiary sedimentation treatment to separate cadmium and zinc precipitates from the secondary treated wastewater, thus obtaining tertiary treated wastewater.

[0038] The secondary-treated wastewater is introduced into a tertiary sedimentation tank. A pH adjuster (type 3) is added to the tertiary sedimentation tank to adjust the pH value of the secondary-treated wastewater to 7-9. Then, a third precipitant is added. The temperature in the tertiary sedimentation tank is controlled at 22-32℃, the stirring speed at 50-100 r / min, and the stirring reaction time at 20-40 min. Afterward, the mixture is allowed to settle for 25-50 min for solid-liquid separation to separate cadmium and zinc precipitates from the secondary-treated wastewater, yielding the tertiary-treated wastewater. The pH adjuster (type 3) comprises a hydrochloric acid solution with a mass concentration of 10%-18%. The third precipitant comprises magnesium hydroxide, and the dosage of the third precipitant is 0.15%-0.4% of the mass of the secondary-treated wastewater. The tertiary sedimentation sludge mainly consists of cadmium and zinc precipitates, which are used for cadmium and zinc resource recovery.

[0039] Fifth, the wastewater after tertiary treatment undergoes further purification to obtain wastewater that meets discharge standards.

[0040] The tertiary treated wastewater is introduced into a deep purification tank. Adsorbent is added to the deep purification tank containing the tertiary treated wastewater. The temperature in the deep purification tank is controlled at 20-30℃, the stirring speed at 40-80 r / min, and the adsorption reaction time at 15-30 min. Subsequently, solid-liquid separation is performed through a filtration device to obtain wastewater that meets discharge standards. The adsorbent is modified activated carbon, and the dosage of modified activated carbon is 0.2%-0.4% of the mass of the tertiary treated wastewater. Modified activated carbon is obtained by soaking activated carbon in a 5%-10% nitric acid solution, ultrasonically treating it at 60-80℃ for 30-60 min, then filtering, washing until neutral, and drying at 100-120℃ for 2-4 h.

[0041] This invention overcomes the shortcomings of existing industrial heavy metal wastewater treatment methods, such as low treatment efficiency, unstable effluent quality, difficulty in sludge disposal, and low resource recycling rate. It can achieve graded precipitation based on the characteristics of different heavy metal ions, efficiently remove heavy metal ions, reduce the difficulty of sludge disposal, and improve the heavy metal resource recycling rate. It takes into account both sludge reduction and resource recycling, and has important practical significance and broad application prospects.

[0042] Example 1

[0043] Industrial heavy metal wastewater discharged from an electroplating plant was selected as the treatment target. The concentrations of various heavy metal ions in the wastewater were as follows: copper ions (Cu²⁺) 85 mg / L, lead ions (Pb²⁺) 62 mg / L, cadmium ions (Cd²⁺) 18 mg / L, zinc ions (Zn²⁺) 45 mg / L, and suspended solids (SS) 120 mg / L and a small amount of complexing agent (such as EDTA). The pH value of the wastewater was 6.5 and the temperature was 22℃.

[0044] The selected reagents are as follows: industrial-grade polyaluminum chloride (PAC) with an effective content ≥28%, industrial-grade polyacrylamide (PAM) with a molecular weight of 8 million, analytical grade sodium hydroxide (NaOH), industrial-grade sodium carbonate (Na2CO3), industrial-grade calcium hydroxide (Ca(OH)2), industrial-grade sodium sulfide (Na2S), analytical grade hydrochloric acid (HCl) with a mass fraction of 37%, granular activated carbon with a particle size of 0.5~1mm, and analytical grade nitric acid (HNO3) with a mass fraction of 65%.

[0045] The following processing equipment was used: a pretreatment tank with an effective volume of 10 m³ equipped with a stirring device and a temperature control device; a primary sedimentation tank with an effective volume of 8 m³ equipped with an online pH monitor, a stirring device, and a solid-liquid separation device; a secondary sedimentation tank with an effective volume of 8 m³ and configured the same as the primary sedimentation tank; a tertiary sedimentation tank with an effective volume of 6 m³ and configured the same as the primary sedimentation tank; a deep purification tank with an effective volume of 5 m³ equipped with a filtration device; a 500W ultrasonic processor; a forced-air drying oven; and an atomic absorption spectrophotometer for detecting the concentration of heavy metal ions.

[0046] Preparation of modified activated carbon: Take 10 kg of activated carbon, soak it in 8% nitric acid solution with a liquid-to-solid ratio of 5:1, place it in a 70℃ constant temperature water bath, and sonicate it for 45 min using an ultrasonic treatment instrument. Then filter and wash it with deionized water until the pH of the filtrate is 7. Place the washed activated carbon in a 110℃ forced-air drying oven and dry it for 3 h. After cooling, seal it for later use.

[0047] Wastewater pretreatment: 10 m³ of electroplating wastewater to be treated is introduced into the pretreatment tank, with a mass of approximately 10 m³. 4 kg of flocculant was added. The flocculant consisted of polyaluminum chloride and polyacrylamide mixed at a mass ratio of 6:1. The total amount of flocculant added was 0.2% of the wastewater mass, i.e., 20 kg. The temperature in the pretreatment tank was controlled at 25℃, and the stirring speed was 150 r / min. After stirring for 20 min, stirring was stopped, and the mixture was allowed to settle for 30 min. The suspended solids in the sediment were removed by a solid-liquid separation device to obtain the pretreated wastewater. The suspended solids content was measured to be 15 mg / L, and the removal rate of the complexing agent was approximately 35%.

[0048] Primary sedimentation treatment: The pretreated wastewater is introduced into the primary sedimentation tank. First, a 15% sodium hydroxide solution is added dropwise using a pH adjustment device to adjust the pH of the wastewater to 9. Then, sodium carbonate, the first precipitant, is added at a rate of 0.35% of the pretreated wastewater mass, i.e., 35 kg. The temperature in the primary sedimentation tank is controlled at 30℃, and the stirring speed is 120 r / min. After stirring for 35 min, stirring is stopped, and the mixture is allowed to settle for 45 min. The primary sedimentation sludge and the primary treated wastewater are separated by a solid-liquid separation device. The wet weight of the primary sedimentation sludge is approximately 85 kg. The primary treated wastewater is tested, and the copper ion concentration is reduced to 0.8 mg / L, with a removal rate of 99.1%. The concentrations of lead, cadmium, and zinc ions show no significant changes.

[0049] Secondary sedimentation treatment: The primary treated wastewater is introduced into the secondary sedimentation tank, and a 12% calcium hydroxide solution is added dropwise to adjust the pH of the wastewater to 10. Sodium sulfide, a second precipitant, is added at a rate of 0.45% of the primary treated wastewater mass, i.e., 45 kg. The temperature in the secondary sedimentation tank is controlled at 33℃, and the stirring speed is 90 r / min. After stirring for 40 min, stirring is stopped, and the mixture is allowed to settle for 55 min. Solid-liquid separation yields secondary sedimentation sludge and secondary treated wastewater. The wet weight of the secondary sedimentation sludge is approximately 72 kg. Testing of the secondary treated wastewater shows that the lead ion concentration has decreased to 0.5 mg / L (removal rate 99.2%), the cadmium ion concentration is 12 mg / L, and the zinc ion concentration is 30 mg / L.

[0050] Tertiary sedimentation treatment: The secondary treated wastewater is introduced into a tertiary sedimentation tank, and a 15% hydrochloric acid solution is added dropwise to adjust the pH of the wastewater to 8. Magnesium hydroxide, the third precipitant, is added at a rate of 0.25% of the secondary treated wastewater mass, i.e., 25 kg. The temperature in the tertiary sedimentation tank is controlled at 27℃, and the stirring speed is 75 r / min. After stirring for 30 minutes, stirring is stopped, and the mixture is allowed to settle for 35 minutes. Solid-liquid separation yields tertiary sedimentation sludge and tertiary treated wastewater. The wet weight of the tertiary sedimentation sludge is approximately 60 kg. Testing of the tertiary treated wastewater shows that the cadmium ion concentration has decreased to 0.05 mg / L (removal rate 99.7%), and the zinc ion concentration has decreased to 0.3 mg / L (removal rate 99.3%).

[0051] Deep purification treatment: The wastewater after tertiary treatment is introduced into a deep purification tank, and the prepared modified activated carbon is added at a rate of 0.3% of the mass of the wastewater after tertiary treatment, i.e., 30 kg. The temperature in the deep purification tank is controlled at 25℃, the stirring speed is 60 r / min, and the adsorption reaction is carried out for 22 min. Then, the wastewater is filtered through a filter device with a filter membrane pore size of 0.22 μm. The concentrations of various heavy metal ions in the filtered wastewater are as follows: copper ions 0.08 mg / L, lead ions 0.04 mg / L, cadmium ions 0.005 mg / L, and zinc ions 0.03 mg / L, all of which meet the requirements of the "Electroplating Pollutant Discharge Standard" (GB 21900-2008).

[0052] Sludge recycling: The copper precipitate from the primary sedimentation sludge is sent to a professional recycling workshop, where it is acid-washed and purified to obtain copper powder with a purity of ≥98% and a recovery rate of approximately 85%. The lead precipitate from the secondary sedimentation sludge is roasted and reduced to obtain crude lead with a purity of ≥95% and a recovery rate of approximately 82%. The cadmium and zinc precipitates from the tertiary sedimentation sludge are separated by solvent extraction to obtain elemental cadmium and elemental zinc, respectively. The purity of elemental cadmium is ≥97%, and the purity of elemental zinc is ≥99%, with recovery rates of 78% and 88%, respectively.

[0053] Example 2

[0054] The difference between this embodiment and Embodiment 1 is that:

[0055] Pretreatment stage: The mass ratio of polyaluminum chloride to polyacrylamide in the flocculant is 5:1, the dosage is 0.15%, the temperature is 22℃, the stirring speed is 120r / min, the stirring time is 15min, and the standing time is 25min.

[0056] Primary precipitation: pH adjusted to 8.5, sodium carbonate dosage 0.25%, temperature 28℃, stirring speed 100r / min, reaction time 30min, standing for 40min;

[0057] Secondary precipitation: pH adjusted to 9.5, sodium sulfide dosage 0.35%, temperature 30℃, stirring speed 80r / min, reaction time 35min, standing for 50min;

[0058] Tertiary precipitation: pH adjusted to 7.5, magnesium hydroxide dosage 0.2%, temperature 25℃, stirring speed 60r / min, reaction time 25min, standing for 30min;

[0059] Deep purification: Modified activated carbon dosage 0.25%, temperature 23℃, stirring speed 50r / min, adsorption time 18min.

[0060] The test results of the treated wastewater were as follows: copper ions 0.12 mg / L, lead ions 0.06 mg / L, cadmium ions 0.008 mg / L, and zinc ions 0.05 mg / L, all of which met the discharge standards; the heavy metal recovery rates were: copper 83%, lead 80%, cadmium 76%, and zinc 86%.

[0061] Comparative Example 1

[0062] The same wastewater was treated using a traditional one-time chemical precipitation method: a 15% sodium hydroxide solution was directly added to 10 m³ of wastewater to adjust the pH to 9.5. A mixed precipitant of 0.5% sodium carbonate and 0.6% sodium sulfide was then added in one step. The mixture was stirred at 120 r / min for 40 min, followed by 60 min of settling. After filtration, the wastewater was tested and found to contain copper ions of 5.2 mg / L, lead ions of 3.8 mg / L, cadmium ions of 2.5 mg / L, and zinc ions of 6.3 mg / L, all of which failed to meet the requirements of the "Electroplating Pollutant Discharge Standard" (GB 21900-2008). The precipitated sludge was a mixed sludge with a wet weight of approximately 210 kg. Due to its complex composition, it could not be separated and recycled, requiring solidification and landfill disposal, which increased the treatment cost by approximately 40 yuan per ton of wastewater. The treatment effects of Example 1, Example 2, and Comparative Example 1 are compared, and the results are shown in Table 1.

[0063] Table 1: Comparison of processing results between Example 1, Example 2 and Comparative Example 1

[0064]

[0065] As shown in Table 1, the staged sedimentation treatment method of the present invention can significantly improve the removal rate of heavy metal ions, and the effluent quality is far superior to that of the traditional one-time sedimentation method. It also achieves efficient recovery of copper, lead, cadmium and zinc, reduces sludge disposal costs, and meets the requirements of green environmental protection and resource recycling.

[0066] from Figure 2 It can be seen that Embodiments 1 and 2 of this application are more cost-effective compared with Comparative Example 1 of the prior art.

[0067] from Figure 3 It can be seen that Embodiments 1 and 2 of this application have a high overall recovery rate and better recovery effect.

[0068] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for graded sedimentation treatment of industrial heavy metal wastewater, characterized in that, include: Pre-treated wastewater is obtained by pre-treating industrial heavy metal wastewater. The pretreated wastewater is subjected to primary sedimentation treatment to separate copper precipitates from the pretreated wastewater, and the primary treated wastewater is obtained. The primary treated wastewater is subjected to secondary sedimentation treatment to separate lead precipitates from the primary treated wastewater, thus obtaining the secondary treated wastewater. The secondary treated wastewater was subjected to tertiary sedimentation treatment to separate cadmium and zinc precipitates from the secondary treated wastewater, thus obtaining the tertiary treated wastewater. The wastewater after tertiary treatment undergoes further purification to obtain wastewater that meets discharge standards.

2. The method for graded sedimentation treatment of industrial heavy metal wastewater according to claim 1, characterized in that, Pretreatment of industrial heavy metal wastewater includes: Flocculant is added to a pretreatment tank containing industrial heavy metal wastewater, and the temperature in the pretreatment tank is controlled at 20~30℃, the stirring speed is 100~200r / min, the stirring time is 15~30min, and then it is allowed to stand for 20~40min to remove suspended solids and complexes from the industrial heavy metal wastewater to obtain pretreated wastewater.

3. The method for graded sedimentation treatment of industrial heavy metal wastewater according to claim 2, characterized in that, The flocculant comprises a mixture of polyaluminum chloride and polyacrylamide, wherein the mass ratio of polyaluminum chloride to polyacrylamide is 5~8:1, and the dosage of the flocculant is 0.1%~0.3% of the mass of industrial heavy metal wastewater.

4. The method for graded sedimentation treatment of industrial heavy metal wastewater according to claim 1, characterized in that, Primary sedimentation treatment of pretreated wastewater includes: Add pH adjuster one to the primary sedimentation tank where the pretreated wastewater is stored to adjust the pH value of the pretreated wastewater to 8-10. Then add the first precipitant. Control the temperature in the primary sedimentation tank to 25-35℃, the stirring speed to 80-150 r / min, and the stirring reaction time to 25-45 min. Then let it stand for sedimentation for 30-60 min to perform solid-liquid separation, which is used to separate copper precipitates from the pretreated wastewater and obtain the primary treated wastewater.

5. The method for graded sedimentation treatment of industrial heavy metal wastewater according to claim 4, characterized in that, The pH adjuster includes a sodium hydroxide solution with a mass concentration of 10% to 20%; the first precipitant includes sodium carbonate, and the dosage of the first precipitant is 0.2% to 0.5% of the mass of the pretreated wastewater.

6. The method for graded sedimentation treatment of industrial heavy metal wastewater according to claim 1, characterized in that, Secondary sedimentation treatment is performed on the primary treated wastewater, including: Add pH adjuster II to the secondary sedimentation tank containing the primary treated wastewater to adjust the pH value of the primary treated wastewater to 9-11. Then add the second precipitant. Control the temperature in the secondary sedimentation tank to 28-38℃, the stirring speed to 60-120 r / min, and the stirring reaction time to 30-50 min. Then let it stand for sedimentation for 40-70 min to perform solid-liquid separation. This is used to separate lead precipitates from the primary treated wastewater and obtain the secondary treated wastewater.

7. The method for graded sedimentation treatment of industrial heavy metal wastewater according to claim 6, characterized in that, The second pH adjuster includes a calcium hydroxide solution with a mass concentration of 8% to 15%; the second precipitant includes sodium sulfide, and the dosage of the second precipitant is 0.3% to 0.6% of the mass of the wastewater after primary treatment.

8. The method for graded sedimentation treatment of industrial heavy metal wastewater according to claim 1, characterized in that, The secondary treated wastewater undergoes tertiary sedimentation treatment, including: Add pH adjuster 3 to the tertiary sedimentation tank containing the secondary treated wastewater to adjust the pH value of the wastewater to 7-9. Then add precipitant 3. Control the temperature in the tertiary sedimentation tank to 22-32℃, the stirring speed to 50-100 r / min, and the stirring reaction time to 20-40 min. Then let it stand for sedimentation for 25-50 min to perform solid-liquid separation. This is used to separate cadmium and zinc precipitates from the secondary treated wastewater and obtain the tertiary treated wastewater.

9. The method for graded sedimentation treatment of industrial heavy metal wastewater according to claim 8, characterized in that, The third pH adjuster includes a hydrochloric acid solution with a mass concentration of 10% to 18%; the third precipitant includes magnesium hydroxide, and the dosage of the third precipitant is 0.15% to 0.4% of the mass of the wastewater after secondary treatment.

10. The method for graded sedimentation treatment of industrial heavy metal wastewater according to claim 1, characterized in that, The wastewater after tertiary treatment is subjected to deep purification treatment, including: adding adsorbent to the deep purification tank where the wastewater after tertiary treatment is stored, controlling the temperature in the deep purification tank at 20~30℃, the stirring speed at 40~80r / min, the adsorption reaction time at 15~30min, and then separating solid and liquid through filtration to obtain wastewater that meets the discharge standards.

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