A method for stepwise recovery of heavy metal ions from arsenic-containing wastewater

Abstract

The application discloses a method for recovering heavy metal ions in arsenic-containing wastewater in stages, and comprises the following steps: the wastewater to be treated is sequentially introduced into at least two treatment containers for precipitation, and carbonate minerals are arranged in the two treatment containers respectively, wherein the solubility product constant of the carbonate mineral in the treatment container at the front is smaller than that of the carbonate mineral in the treatment container at the rear. The application aims at solving the problems in the prior art that the recovery of heavy metals causes the pH of effluent to be too high, the recovered heavy metals are generally mixtures, the heavy metals are not easy to be separated from liquid, and the efficient recovery of metal ions in wastewater cannot be met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wastewater treatment generated by non-ferrous metal sulfide ore smelting, in particular to a method for gradient recovery of heavy metal ions in arsenic-containing wastewater. BACKGROUND

[0002] With the rapid development of China's industry, the demand for non-ferrous metal resources is increasing, among which the exploitation and smelting of non-ferrous metal sulfide ore produces arsenic-containing acidic wastewater with a general pH value of 1-2. The water quality composition is complex and changes greatly, generally containing heavy metal ions such as arsenic, copper, lead, zinc, and cadmium.

[0003] The method commonly used in industry to recover heavy metals in wastewater is mainly chemical precipitation technology using lime. According to the report in the published paper (Mineral Protection and Utilization, 2018(4):93-96), heavy metals can be precipitated by adjusting the pH of the water body to strong alkalinity with lime, but the product is usually a mixture, which cannot effectively recover heavy metals and causes the effluent pH to be too high.

[0004] Chinese patent CN200910067042.6 discloses a method for treating non-ferrous metal wastewater containing nickel, lead, and cadmium by fractional precipitation. The wastewater is raised to a flocculation sedimentation tank for flocculation and sedimentation; lime milk is added to the wastewater in the reaction tank, and the pH value is controlled at 8.0, then the nickel hydroxide is precipitated in the first-stage sedimentation tank; lime milk is added, the pH value is controlled at 11, and FeSO4 and polysilicate ferric sulfate are added, then the metal hydroxide is precipitated in the second-stage sedimentation tank. This method uses acid and alkali to adjust the pH of the wastewater to precipitate heavy metals step by step, but the pH precision requirement is too high, it is difficult to control and filter, and it needs to be compounded with a flocculating agent to make the heavy metals easy to precipitate and filter, which is complex to operate and high in cost. It is difficult to meet the efficient recovery of metal ions in wastewater.

[0005] Therefore, it is urgent to develop a method for gradient recovery of heavy metal ions in arsenic-containing wastewater, which is simple to operate, easy to solid-liquid separation, and has stable effluent pH near neutral after treatment. SUMMARY

[0006] The main purpose of the present application is to provide a method for gradient recovery of heavy metal ions in arsenic-containing wastewater, which aims to solve the problems of existing recovery of heavy metal wastewater, such as high effluent pH value, difficulty in solid-liquid separation, and difficulty in meeting the efficient recovery of metal ions in wastewater.

[0007] To achieve the above-mentioned purpose, the present application provides a method for gradient recovery of heavy metal ions in arsenic-containing wastewater, comprising the following steps:

[0008] The wastewater to be treated is sequentially introduced into at least two treatment containers for precipitation, and the two treatment containers are respectively provided with carbonate minerals, wherein the solubility product constant of the carbonate minerals in the treatment container at the front is less than that of the carbonate minerals in the treatment container at the rear.

[0009] Optionally, the heavy metal ions in the wastewater to be treated include lead ions, cadmium ions, zinc ions and copper ions, and the step of sequentially introducing the wastewater to be treated into at least two treatment containers for precipitation includes:

[0010] S10, introducing the wastewater to be treated into a first treatment container containing carbonate minerals for precipitation to obtain wastewater from which lead has been removed;

[0011] S20, introducing the wastewater from which lead has been removed into a second treatment container containing carbonate minerals for precipitation to obtain wastewater from which cadmium has been removed;

[0012] S30, introducing the wastewater from which cadmium has been removed into a third treatment container containing carbonate minerals for precipitation to obtain wastewater from which zinc has been removed;

[0013] S40, introducing the wastewater from which zinc has been removed into a fourth treatment container containing carbonate minerals for precipitation to obtain wastewater from which copper has been removed;

[0014] The carbonate minerals in the first treatment container include calcium carbonate, the carbonate minerals in the second treatment container include activated calcium carbonate, the carbonate minerals in the third treatment container include magnesium carbonate, and the carbonate minerals in the fourth treatment container include activated magnesium carbonate.

[0015] Optionally, the heavy metal ions in the wastewater to be treated also include arsenic, and after step S40, the wastewater from which copper has been removed is mixed with a coagulant, and after precipitation, wastewater from which arsenic has been removed is obtained.

[0016] Optionally, the activated calcium carbonate and the activated magnesium carbonate are respectively the calcium carbonate and the magnesium carbonate subjected to mechanical force chemical treatment, and the mechanical force chemical treatment is ball milling, wherein the rotation speed of the ball milling is 200 rpm to 600 rpm, and / or the ball milling time is 10 to 90 min.

[0017] Optionally, the calcium carbonate includes at least one of calcite, aragonite and vaterite.

[0018] Optionally, before step S10, the method further includes detecting the pH value of the wastewater to be treated, and pretreating according to the detected pH value.

[0019] Optionally, the step of pre-treating comprises:

[0020] When the pH value is less than the preset value, adjusting the pH value of the wastewater to the preset value by using lime; wherein, the preset value of the pH value ranges from 3 to 6.

[0021] Optionally, the wastewater to be treated comprises lead, cadmium, zinc and copper, and the carbonate mineral comprises at least one of calcium carbonate, magnesium carbonate, activated calcium carbonate and activated magnesium carbonate, wherein,

[0022] The mass concentration ratio of calcium carbonate to lead in the wastewater to be treated ranges from 1 to 10; and / or,

[0023] The mass concentration ratio of activated calcium carbonate to cadmium in the wastewater to be treated ranges from 1 to 5; and / or,

[0024] The mass concentration ratio of magnesium carbonate to zinc in the wastewater to be treated ranges from 1 to 5; and / or,

[0025] The mass concentration ratio of activated magnesium carbonate to copper in the wastewater to be treated ranges from 1 to 5.

[0026] Optionally, the step of precipitating comprises stirring; wherein, the stirring speed ranges from 100 rpm to 300 rpm; and / or, the stirring time ranges from 30 min to 60 min.

[0027] Optionally, the coagulant comprises calcium carbonate and ferrous salt; wherein, the mass concentration ratio of ferrous salt to arsenic in the wastewater to be treated ranges from 1 to 3; and / or,

[0028] The mass concentration ratio of calcium carbonate to ferrous salt ranges from 1 to 3.

[0029] In the technical solution provided by the application, carbonate minerals with different solubility product constants are added into wastewater containing heavy metal ions in a specific order, and precipitate with the heavy metal ions in the wastewater, so that different kinds of heavy metal ions in the wastewater can be separated step by step. Meanwhile, the hydrolysis of the carbonate ions released slowly produces hydroxyl ions, so that the pH of the wastewater can be adjusted, and the pH of the final effluent is stable in the near-neutral range. Furthermore, the undissolved part of the carbonate mineral can be used as a heavy metal precipitate carrier to accelerate the settlement, so that the sludge after fixing the heavy metal is obviously easy to separate from the liquid, and the different kinds of heavy metal ions in the wastewater are finally recovered efficiently. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings described below only illustrate some of the embodiments of the present application, and the other related drawings can be obtained by those of ordinary skill in the art without any creative effort.

[0031] Figure 1 The flowchart of an embodiment of the method for recovering heavy metal ions in arsenic-containing wastewater proposed in the present application.

[0032] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments.

[0034] It should be noted that the specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not marked with the manufacturer, which are all conventional products that can be purchased on the market. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that a person of ordinary skill in the art can realize it, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor within the scope of protection required by the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0035] With the rapid development of China's industry, the demand for non-ferrous metal resources is increasing, among which the exploitation and smelting of non-ferrous metal sulfide ore produces arsenic-containing acidic wastewater with a general pH value of 1-2. The water quality composition is complex and changes greatly, generally containing heavy metal ions such as arsenic, copper, lead, zinc and cadmium, which causes serious environmental pollution problems and also causes waste of resources.

[0036] For the treatment of such waste liquid, generally, the heavy metals are precipitated by adjusting the pH of the water body to strong alkaline with lime, but the product is usually a mixture, which cannot effectively recover the heavy metals and causes the pH of the effluent to be too high. Or by using acid and alkali to adjust the pH of the wastewater, the heavy metals are precipitated step by step, but the pH precision requirement is too high, it is difficult to control and filter, and a flocculating agent needs to be used to make the heavy metals easy to precipitate and filter, which is complicated to operate and high in cost. It is difficult to meet the efficient recovery of metal ions in wastewater.

[0037] The present application provides a method for recovering heavy metal ions in arsenic-containing wastewater in stages. The wastewater to be treated is sequentially introduced into at least two treatment containers for precipitation, and carbonate minerals are arranged in the two treatment containers, wherein the solubility product constant of the carbonate minerals in the front treatment container is less than that of the carbonate minerals in the rear treatment container.

[0038] In this embodiment, carbonate minerals with different solubility product constants are used, and carbonate minerals with slow-release characteristics are added to wastewater containing heavy metal ions to perform precipitation reactions with heavy metal ions in the wastewater, thereby gradually separating different types of heavy metal ions in the wastewater. In addition, the slow-release carbonate ions hydrolyze to produce hydroxyl ions, thereby adjusting the pH of the wastewater, so that the final effluent pH is stable in the near-neutral range. Furthermore, the undissolved part of the carbonate minerals can act as a heavy metal precipitation carrier and accelerate sedimentation, so that the heavy metal-containing sludge is easy to separate from the liquid, and the efficient recovery of different types of heavy metal ions in the wastewater is achieved.

[0039] Specifically, in some embodiments, to remove heavy metal ions including lead, cadmium, zinc, and copper from wastewater, the following steps are used to treat the wastewater, referring to Figure 1 wherein the step of sequentially introducing the wastewater to be treated into at least two treatment containers for precipitation includes:

[0040] S10, introducing the wastewater to be treated into a first treatment container containing carbonate minerals, and performing a precipitation reaction to obtain wastewater from which lead has been removed; wherein the carbonate minerals in the first treatment container include calcium carbonate.

[0041] It should be noted that the step S10 further includes the following steps before the step S10: detecting the pH value of the wastewater to be treated, and pretreating the wastewater according to the detected pH value.

[0042] The step of pretreatment includes:

[0043] When the pH value is less than a preset value, the pH value of the wastewater is adjusted to the preset value by using lime; wherein the preset value of the pH value is in the range of 3-6. The purpose of this step is that lime is a strong base, which can quickly release alkalinity, and a large amount of precipitate will be generated. Industrial wastewater has a large amount of acidity and a large flowability, and needs to be quickly treated. Lime needs to be added in the early stage to quickly adjust the pH value, so that the efficiency is higher.

[0044] In order to separate and recover lead in the wastewater first, the embodiment adds calcium carbonate to the wastewater to be treated to convert lead ions into precipitates, and obtains wastewater after lead removal. Compared with lime, the calcium carbonate can not only fine-tune the pH value, but also fix precipitated heavy metal ions, so as to achieve the purpose of removing heavy metal ions.

[0045] In some embodiments, the calcium carbonate is derived from at least one of calcite, aragonite, and vaterite; that is, the calcium carbonate can only include calcite, aragonite, or vaterite, or can simultaneously include calcite, aragonite, and vaterite. When simultaneously included, the slow-release range of carbonate is wider, which is more conducive to precipitating heavy metal ions in the wastewater.

[0046] In order to ensure a certain reaction concentration and improve the reaction rate, the mass concentration ratio of the amount of calcium carbonate to lead in the wastewater is controlled to be 1:10, specifically, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1. Within this mass concentration ratio range, the reaction efficiency can be optimal.

[0047] In specific implementation, the wastewater to be treated is introduced into a first treatment container, that is, a precipitation tank 1, and the pH and the content of each heavy metal ion in the wastewater are detected. When the pH of the wastewater to be treated is greater than 3, no pretreatment is required. When the pH is less than 3, the pH of the water body is adjusted to more than 3 by using lime. Then, the calcium carbonate is added to the wastewater treated by lime, and the mass concentration ratio of the amount of calcium carbonate to lead in the wastewater to be treated is controlled to be 1:10. After stirring and precipitation reaction, wastewater after lead removal is obtained.

[0048] S20, the wastewater after lead removal is introduced into a second treatment container containing carbonate minerals, and wastewater after cadmium removal is obtained after precipitation reaction.

[0049] In order to separate and recover cadmium in the wastewater, the embodiment adds activated calcium carbonate to the wastewater after lead removal for stirring and precipitation reaction to obtain wastewater after cadmium removal. The carbonate minerals in the second treatment container include activated calcium carbonate.

[0050] It should be noted that mechanochemistry is a technology that induces chemical and physical and chemical changes of materials by mechanical energy. Through mechanochemistry, the particle size of the material can be changed, and the crystal phase and crystal structure can also be changed. In the embodiment, the main purpose is to prepare calcium carbonate and magnesium carbonate with different solubility product constants.

[0051] In order to improve the reaction activity of calcium carbonate, the calcium carbonate is distorted and has defects under the mechanical force activation, the reaction activity is improved, and the performance of the calcium carbonate for releasing carbonate is strengthened, and the further dissolution and hydrolysis of the carbonate can control the efficient removal of heavy metal ions by ferrous ions. In the embodiment, the activated calcium carbonate is ball-milled calcium carbonate, the ball-milling speed is 200 rpm to 600 rpm, and specifically, can be 200 rpm, 300 rpm, 400 rpm, 500 rpm or 600 rpm. The greater the activation strength is, the higher the activity of the calcium carbonate is. The ball-milling time is 10 min to 90 min, and specifically, can be 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min or 90 min. The longer the activation time is, the higher the activity of the calcium carbonate is.

[0052] In order to ensure a certain reaction concentration and improve the reaction rate, the ratio of the amount of the activated calcium carbonate to the mass concentration of cadmium in the wastewater to be treated is controlled to be 1 to 5, and specifically, can be 1:1, 2:1, 3:1, 4:1 or 5:1. In this mass concentration ratio range, the reaction efficiency can be optimal.

[0053] In specific implementation, the wastewater after the lead is removed is introduced into the second treatment container, that is, the sedimentation tank 2, and the activated calcium carbonate is further introduced into the second treatment container, the ratio of the amount of the activated calcium carbonate to the mass concentration of cadmium in the wastewater to be treated is controlled to be 1 to 5, and after the stirring and precipitation reaction, the wastewater after the cadmium is removed is obtained.

[0054] S30, the wastewater after the cadmium is removed is introduced into the third treatment container, the third treatment container contains carbonate minerals, and after the precipitation reaction, the wastewater after the zinc is removed is obtained, wherein the carbonate minerals in the second treatment container include magnesium carbonate.

[0055] It should be noted that the ratio of the amount of the magnesium carbonate to the mass concentration of zinc in the mixed solution is controlled to be 1 to 5, and specifically, can be 1:1, 2:1, 3:1, 4:1 or 5:1. In this mass concentration ratio range, the reaction efficiency can be optimal.

[0056] In specific implementation, the wastewater after the cadmium is removed is introduced into the third treatment container, that is, the sedimentation tank 3, and the magnesium carbonate is further introduced into the third treatment container, the ratio of the amount of the magnesium carbonate to the mass concentration of zinc in the wastewater to be treated is controlled to be 1 to 5, and after the stirring and precipitation reaction, the wastewater after the zinc is removed is obtained.

[0057] S40, the wastewater after the zinc is removed is introduced into the fourth treatment container, the fourth treatment container contains carbonate minerals, and after the precipitation reaction, the wastewater after the copper is removed is obtained; wherein the carbonate minerals in the fourth treatment container include activated magnesium carbonate.

[0058] In order to improve the reactivity of magnesium carbonate, activated magnesium carbonate is added to the fourth treatment container, i.e. the precipitation tank 4, and stirred to react, the activated magnesium carbonate is activated by ball milling, the ball milling speed is 200 rpm to 600 rpm, specifically, it can be 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm. The greater the activation intensity, the higher the activity of magnesium carbonate, the ball milling time is 10 to 90 minutes, specifically, it can be 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 70 minutes, 80 minutes, 90 minutes, the longer the activation time, the higher the activity of magnesium carbonate.

[0059] Further, the mass concentration ratio of the activated magnesium carbonate to the copper in the wastewater to be treated is controlled to be 1 to 5, specifically, it can be 1:1, 2:1, 3:1, 4:1, 5:1, within this mass concentration ratio range, the reaction efficiency can be best.

[0060] It should be noted that when the heavy metal ions in the wastewater to be treated also include arsenic, after step S40, the wastewater after copper removal is also mixed with a coagulant, and after precipitation reaction, the wastewater after arsenic removal is obtained. The coagulant includes calcium carbonate and ferrous salt, and the ferrous salt is at least one of ferrous sulfate, ferrous chloride and ferrous carbonate; that is, the ferrous salt can only include ferrous sulfate or ferrous chloride or ferrous carbonate, or can simultaneously include ferrous sulfate, ferrous chloride and ferrous carbonate, and when simultaneously included, the arsenic removal range is wider, which is more conducive to the precipitation of arsenic in the wastewater.

[0061] Further, calcium carbonate and ferrous salt are added to the fifth treatment container, i.e. the precipitation tank 5, and stirred to react,

[0062] The mass concentration ratio of the ferrous salt to the arsenic in the wastewater to be treated is 1 to 3; and / or, the mass concentration ratio of the calcium carbonate to the ferrous salt is 1 to 3. That is, the mass concentration ratio of the ferrous salt to the arsenic in the wastewater to be treated can only be 1:1, 2:1, 3:1, or the mass concentration ratio of the calcium carbonate to the ferrous salt can only be 1:1, 2:1, 3:1, or both can be included, and when both are included, within this mass concentration ratio range, the reaction efficiency can be best.

[0063] In order to improve the reaction rate of the stepwise recovery of heavy metal ions, after uniform stirring in each step, the mixed solution is filtered and introduced into the precipitation tank to obtain a filtrate, the stirring speed is 100 to 300 rpm, specifically, it can be 100 rpm, 200 rpm, 300 rpm, and the stirring time is 30 to 60 minutes, specifically, it can be 30 minutes, 40 minutes, 50 minutes, 60 minutes, within this stirring time and speed range, the reaction efficiency can be best.

[0064] In summary, in the technical solution provided by the present application, the solubility product constant is different under different temperature conditions, and under the same temperature conditions, the solubility product constant of calcium carbonate is 0.99*10 -8 , and the solubility product constant of magnesium carbonate is 3.5*10 -3 , so the performance of magnesium carbonate in releasing carbonate is much higher than that of calcium carbonate, and the crystal phase of calcium carbonate and magnesium carbonate will be distorted and defective under the action of mechanical force, thereby improving the reaction activity and enhancing the performance of calcium carbonate and magnesium carbonate in releasing carbonate, and the further dissolution and hydrolysis of carbonate can control the efficient removal of ferrous ions; and the solubility product constants of lead carbonate, cadmium carbonate, zinc carbonate and copper carbonate are 3.3*10 -14 , 1.0*10 -12 , 1.46*10 -11 , and 1.40*10 -10 , respectively, which have obvious order of magnitude difference, so these four kinds of carbonate substances with different release characteristics are added into the arsenic-containing wastewater according to the mass concentration ratio of heavy metal ion content, so that different kinds of heavy metal ions in the arsenic-containing wastewater can be gradually separated; since calcium carbonate and magnesium carbonate can produce hydroxyl ions by hydrolysis of released carbonate to adjust the pH of the wastewater, the final effluent pH is stable in the near neutral range, and since the undissolved part of calcium carbonate and magnesium carbonate can be used as a heavy metal precipitation carrier to accelerate sedimentation, the heavy metal fixed sediment is obviously easy to separate from the liquid, so that the efficient recovery of different kinds of heavy metal ions in the wastewater is realized.

[0065] The present application has the following advantages and beneficial effects:

[0066] 1. The calcium carbonate, magnesium carbonate and their activated products selected by the present application have obvious differences in the performance of releasing carbonate, and the solubility product of the carbonate products corresponding to different kinds of heavy metal ions has obvious order of magnitude difference, so that different kinds of heavy metal ions can be effectively recovered in stages.

[0067] 2. The calcium carbonate and magnesium carbonate and their activated products used in the present application can produce hydroxyl ions by hydrolysis of released carbonate to adjust the pH of the wastewater, so that the effluent pH can be stabilized to near neutral, and the undissolved part can be used as a heavy metal precipitation carrier to accelerate sedimentation, which is beneficial to solid-liquid separation.

[0068] The technical solution of the present application will be further described in detail in combination with specific examples, and it should be understood that the following examples are only used to explain the present application and do not limit the present application.

[0069] Example 1

[0070] A method for stepwise recovery of heavy metal ions in arsenic-containing wastewater, comprising the following steps: the wastewater to be treated is sequentially introduced into a sedimentation tank 1 and a sedimentation tank 2, and the sedimentation tank 1 is located in the front, the sedimentation tank 1 is provided with barium carbonate, and the sedimentation tank 2 is provided with lithium carbonate, wherein the solubility product coefficient of barium carbonate is less than that of lithium carbonate.

[0071] Example 2

[0072] A method for stepwise recovery of heavy metal ions in arsenic-containing wastewater, comprising the following steps: the wastewater to be treated is sequentially introduced into a sedimentation tank 1 and a sedimentation tank 2, and the sedimentation tank 1 is located in the front, the sedimentation tank 1 is provided with barium carbonate, and the sedimentation tank 2 is provided with lithium carbonate, wherein the solubility product coefficient of barium carbonate is less than that of lithium carbonate.

[0073] Example 3

[0074] A method for stepwise recovery of heavy metal ions in arsenic-containing wastewater, comprising the following steps:

[0075] The amount of calcite added to the sedimentation tank 1 is 10:1 compared to the mass concentration of lead ions, and after stirring at 300 rpm for 30 min, the mixed solution is filtered and introduced into the sedimentation tank 2;

[0076] The amount of 600 rpm activated calcite added to the sedimentation tank 2 is 1:1 compared to the mass concentration of cadmium ions, and after stirring at 300 rpm for 30 min, the mixed solution is filtered and introduced into the sedimentation tank 3;

[0077] The amount of magnesium carbonate added to the sedimentation tank 3 is 5:1 compared to the mass concentration of zinc ions, and after stirring at 300 rpm for 30 min, the mixed solution is filtered and introduced into the sedimentation tank 4;

[0078] The amount of 600 rpm activated magnesium carbonate added to the sedimentation tank 4 is 1:1 compared to the mass concentration of copper ions, and after stirring at 300 rpm for 30 min, the mixed solution is filtered and introduced into the sedimentation tank 5;

[0079] A mixture of calcium carbonate and ferrous sulfate is added to the sedimentation tank 5, wherein the mass concentration ratio of calcium carbonate to arsenic concentration is 3:1, and the mass concentration ratio of calcium carbonate to ferrous sulfate is 3:1, and after stirring at 200 rpm for 50 min, the water body after recovery of heavy metals is filtered and discharged.

[0080] Example 4

[0081] A method for stepwise recovery of heavy metal ions in arsenic-containing wastewater, comprising the following steps:

[0082] The amount of calcite added to the sedimentation tank 1 is 8:1 compared to the mass concentration of lead ions, and after stirring at 250 rpm for 40 min, the mixed solution is filtered and introduced into the sedimentation tank 2;

[0083] The amount of 500 rpm activated calcite added to the sedimentation tank 2 is 2:1 with respect to the mass concentration of cadmium ions. After stirring at 250 rpm for 40 min, the mixture is filtered and passed into the sedimentation tank 3;

[0084] The amount of magnesium carbonate added to the sedimentation tank 3 is 4:1 with respect to the mass concentration of zinc ions. After stirring at 250 rpm for 40 min, the mixture is filtered and passed into the sedimentation tank 4;

[0085] The amount of 400 rpm activated magnesium carbonate added to the sedimentation tank 4 is 3:1 with respect to the mass concentration of copper ions. After stirring at 200 rpm for 50 min, the mixture is filtered and passed into the sedimentation tank 5;

[0086] The mixture of calcium carbonate and ferrous sulfate is added to the sedimentation tank 5, in which the mass concentration ratio of calcium carbonate to arsenic concentration is 3:2, and the mass concentration ratio of calcium carbonate to ferrous sulfate is 2:1. After stirring at 200 rpm for 50 min, the water body after recovery of heavy metals is filtered and discharged.

[0087] Example 5

[0088] A method for stepwise recovery of heavy metal ions in arsenic-containing wastewater, comprising the following steps:

[0089] The amount of calcite added to the sedimentation tank 1 is 6:1 with respect to the mass concentration of lead ions. After stirring at 200 rpm for 50 min, the mixture is filtered and passed into the sedimentation tank 2;

[0090] The amount of 400 rpm activated calcite added to the sedimentation tank 2 is 3:1 with respect to the mass concentration of cadmium ions. After stirring at 200 rpm for 50 min, the mixture is filtered and passed into the sedimentation tank 3;

[0091] The amount of magnesium carbonate added to the sedimentation tank 3 is 3:1 with respect to the mass concentration of zinc ions. After stirring at 200 rpm for 50 min, the mixture is filtered and passed into the sedimentation tank 4;

[0092] The amount of 400 rpm activated magnesium carbonate added to the sedimentation tank 4 is 3:1 with respect to the mass concentration of copper ions. After stirring at 200 rpm for 50 min, the mixture is filtered and passed into the sedimentation tank 5;

[0093] The mixture of calcium carbonate and ferrous sulfate is added to the sedimentation tank 5, in which the mass concentration ratio of calcium carbonate to arsenic concentration is 3:1, and the mass concentration ratio of calcium carbonate to ferrous sulfate is 3:1. After stirring at 200 rpm for 50 min, the water body after recovery of heavy metals is filtered and discharged.

[0094] Example 6

[0095] A method for stepwise recovery of heavy metal ions in arsenic-containing wastewater, comprising the following steps:

[0096] The amount of calcite added to the sedimentation tank 1 was 4:1 with respect to the mass concentration of lead ions, and after stirring at 150 rpm for 60 min, the mixture was filtered into the sedimentation tank 2;

[0097] The amount of activated calcite added to the sedimentation tank 2 was 4:1 with respect to the mass concentration of cadmium ions, and after stirring at 150 rpm for 60 min, the mixture was filtered into the sedimentation tank 3;

[0098] The amount of magnesium carbonate added to the sedimentation tank 3 was 2:1 with respect to the mass concentration of zinc ions, and after stirring at 150 rpm for 60 min, the mixture was filtered into the sedimentation tank 4;

[0099] The amount of activated magnesium carbonate added to the sedimentation tank 4 was 4:1 with respect to the mass concentration of copper ions, and after stirring at 150 rpm for 60 min, the mixture was filtered into the sedimentation tank 5;

[0100] A mixture of calcium carbonate and ferrous sulfate was added to the sedimentation tank 5, in which the mass concentration ratio of calcium carbonate to arsenic concentration was 2:1, and the mass concentration ratio of calcium carbonate to ferrous sulfate was 5:1, and after stirring at 150 rpm for 60 min, the water body after recovery of heavy metals was filtered and discharged.

[0101] Example 7

[0102] A method for stepwise recovery of heavy metal ions in arsenic-containing wastewater, comprising the following steps:

[0103] The amount of calcite added to the sedimentation tank 1 was 1:1 with respect to the mass concentration of lead ions, and after stirring at 100 rpm for 60 min, the mixture was filtered into the sedimentation tank 2;

[0104] The amount of activated calcite added to the sedimentation tank 2 was 5:1 with respect to the mass concentration of cadmium ions, and after stirring at 100 rpm for 60 min, the mixture was filtered into the sedimentation tank 3;

[0105] The amount of magnesium carbonate added to the sedimentation tank 3 was 1:1 with respect to the mass concentration of zinc ions, and after stirring at 100 rpm for 60 min, the mixture was filtered into the sedimentation tank 4;

[0106] The amount of activated magnesium carbonate added to the sedimentation tank 4 was 5:1 with respect to the mass concentration of copper ions, and after stirring at 100 rpm for 60 min, the mixture was filtered into the sedimentation tank 5;

[0107] A mixture of calcium carbonate and ferrous sulfate was added to the sedimentation tank 5, in which the mass concentration ratio of calcium carbonate to arsenic concentration was 1:1, and the mass concentration ratio of calcium carbonate to ferrous sulfate was 1:1, and after stirring at 100 rpm for 60 min, the water body after recovery of heavy metals was filtered and discharged.

[0108] Comparative Example 1

[0109] Only lime precipitant is added to the wastewater to be treated.

[0110] Comparative Example 2

[0111] Only calcium carbonate precipitant is added to the wastewater to be treated.

[0112] Comparative Example 3

[0113] Only activated calcium carbonate precipitant is added to the wastewater to be treated.

[0114] Stepwise recovery of heavy metals test

[0115] The precipitating methods used in Examples 1-5 and the lime precipitating method of Comparative Example 1, the calcium carbonate precipitating method of Comparative Example 2, and the activated calcium carbonate of Comparative Example 3 were used to treat 1L of mixed pollution water containing 500mg / L of lead, cadmium, zinc, copper, and arsenic, respectively. After the reaction was completed, the pH of the water and the heavy metal content of each precipitate were measured. The results are shown in Table 1:

[0116] Table 1: Changes in the pH of the water and the content of each metal

[0117]

[0118] As can be seen from Table 1, in the mixed heavy metal water treated by the precipitating methods of Examples 3-7, the five heavy metals of lead, cadmium, zinc, copper, and arsenic were enriched and precipitated, respectively, and the solution pH remained near neutral, while in Comparative Example 1, the precipitate was a mixture and the solution pH was as high as 12.10, which needed to be further neutralized with acid to meet the discharge standard. In Comparative Examples 2 and 3, the pH of the effluent was also near neutral because they were also treated with carbonate minerals, so the effluent pH was not much different. However, because Comparative Examples 2 and 3 did not follow the gradient classification method of the present application, the obtained precipitates were mixtures and could not achieve the purpose of separating and recovering heavy metals. The above is only a preferred embodiment of the present application and does not limit the patent scope of the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the patent protection scope of the present application.

Claims

1. A method for the stepwise recovery of heavy metal ions from arsenic containing wastewater, characterized by the steps of The application relates to a method for treating wastewater containing heavy metals. The wastewater to be treated is sequentially introduced into at least two treatment containers for precipitation, wherein the two treatment containers are respectively provided with carbonate minerals, the solubility product constant of the carbonate mineral in the front treatment container is less than that of the carbonate mineral in the rear treatment container, and the heavy metals in the wastewater to be treated include lead ions, cadmium ions, zinc ions and copper ions. The step of sequentially introducing the wastewater to be treated into at least two treatment containers for precipitation comprises the following steps: S10, introducing the wastewater to be treated into a first treatment container containing carbonate minerals to carry out a precipitation reaction, thereby obtaining wastewater from which lead has been removed; S20, introducing the wastewater from which lead has been removed into a second treatment container containing carbonate minerals to carry out a precipitation reaction, thereby obtaining wastewater from which cadmium has been removed; S30, introducing the wastewater from which cadmium has been removed into a third treatment container containing carbonate minerals to carry out a precipitation reaction, thereby obtaining wastewater from which zinc has been removed; S40, introducing the wastewater from which zinc has been removed into a fourth treatment container containing carbonate minerals to carry out a precipitation reaction, thereby obtaining wastewater from which copper has been removed; The carbonate mineral in the first treatment container includes calcium carbonate, the carbonate mineral in the second treatment container includes activated calcium carbonate, the carbonate mineral in the third treatment container includes magnesium carbonate, and the carbonate mineral in the fourth treatment container includes activated magnesium carbonate.

2. The method for recovering heavy metal ions from the arsenic-containing wastewater in stages according to claim 1, characterized in that, The heavy metal ions in the wastewater to be treated also include arsenic, and the method further comprises the following steps after step S40: mixing the wastewater from which copper has been removed with a coagulant, carrying out a precipitation reaction, and obtaining wastewater from which arsenic has been removed.

3. The method for recovering heavy metal ions from arsenic-containing wastewater in steps as claimed in claim 1, characterized in that, The activated calcium carbonate and the activated magnesium carbonate are respectively subjected to mechanical force chemical treatment, and the mechanical force chemical treatment is ball milling. The rotating speed of the ball mill is 200 rpm to 600 rpm, and / or the ball milling time is 10 min to 90 min.

4. The method for recovering heavy metal ions from arsenic-containing wastewater in steps as claimed in claim 1, wherein, The calcium carbonate includes at least one of calcite, aragonite and vaterite.

5. The method for recovering heavy metal ions from arsenic-containing wastewater in steps as claimed in claim 1, wherein, The method further comprises the following step before step S10: detecting the pH value of the wastewater to be treated and carrying out pretreatment according to the detected pH value.

6. The method for recovering heavy metal ions from arsenic-containing wastewater in steps as claimed in claim 5, wherein, The pretreatment step comprises the following steps: When the pH value is less than a preset value, the pH value of the wastewater is adjusted to the preset value by using lime to obtain the wastewater to be treated, and the preset value of the pH value is 3 to 6.

7. The method for recovering heavy metal ions from arsenic-containing wastewater in steps as claimed in claim 1, wherein, The wastewater to be treated contains lead, cadmium, zinc and copper, and the carbonate mineral includes at least one of calcium carbonate, magnesium carbonate, activated calcium carbonate and activated magnesium carbonate. The mass concentration ratio of the calcium carbonate to the lead in the wastewater to be treated is 1 to 10, and / or the mass concentration ratio of the activated calcium carbonate to the cadmium in the wastewater to be treated is 1 to 5. The mass concentration ratio of the magnesium carbonate to the zinc in the wastewater to be treated is 1 to 5, and / or the mass concentration ratio of the activated magnesium carbonate to the copper in the wastewater to be treated is 1 to 5. The precipitation reaction step comprises stirring. The stirring speed is 100 rpm to 300 rpm, and / or the stirring time is 30 min to 60 min.

8. The method for recovering heavy metal ions from the arsenic-containing wastewater in stages according to claim 1 or 2, characterized by, The coagulant includes calcium carbonate and ferrous salt. ​ 9. The method for recovering heavy metal ions from arsenic-containing wastewater in steps as claimed in claim 2, wherein, ​ The mass concentration ratio of the ferrous salt to arsenic in the wastewater to be treated is 1-3; and / or, The mass concentration ratio of the calcium carbonate to the ferrous salt is 1-3.

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