Method for treating heavy metal wastewater using reverse osmosis membrane

Abstract

The invention relates to the technical field of wastewater treatment, and discloses a method for treating heavy metal wastewater using a reverse osmosis membrane. The method comprises: first mixing the heavy metal wastewater with a flocculant, and obtaining a filtrate A after a first solid-liquid separation; treating the filtrate A with a reverse osmosis membrane to obtain fresh water B and concentrated water C; second mixing the concentrated water C with an inorganic acid, and obtaining a precipitate D and a filtrate E after a second solid-liquid separation; third mixing the filtrate E with a composite precipitant, and obtaining a precipitate F and a filtrate G after a third solid-liquid separation. The invention adopts membrane technology combined with a chemical precipitation method to treat heavy metal wastewater, thereby realizing water reuse, rare metal molybdenum resource recovery, and heavy metal resource utilization. The method of the invention effectively improves the recovery rate of rare metal molybdenum and the heavy metal removal rate, and has the characteristics of simple operation and wide application range.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for treating heavy metal wastewater by utilizing a reverse osmosis membrane. Background Art

[0002] Heavy metal wastewater mainly comes from production links such as mining, electroplating, non-ferrous metal smelting, machinery manufacturing, chemical industry, electronics, and instrumentation industries. Heavy metal industrial wastewater has long-term toxicity and can be enriched in large quantities in organisms, endangering humans through the food chain, causing chronic / acute poisoning to the human body, and seriously endangering human health. Therefore, how to effectively control and manage heavy metal pollution is one of the problems that need to be solved urgently.

[0003] At present, the main methods for treating heavy metal wastewater include chemical precipitation, biological treatment, physical adsorption, electrolysis, membrane treatment, etc. Among them, membrane treatment has the advantages of high separation efficiency, no secondary pollution, energy saving and environmental protection, and resource recycling, and is widely used in the field of water treatment.

[0004] CN208471619U discloses a disc-tube reverse osmosis system for heavy metal wastewater, in which the heavy metal wastewater is pretreated and then passed into a secondary disc-tube reverse osmosis system, the clean water produced is reused, and the concentrated water is recovered. This method optimizes the flow channel design of the membrane component of the reverse osmosis system, reduces scaling, pollution and concentration polarization on the membrane surface, but the membrane equipment of the system is complex, no effective treatment plan is proposed for the reverse osmosis concentrated water, and the resource utilization efficiency is low.

[0005] CN105461139B discloses a zero-discharge process for nickel-containing heavy metal wastewater, which removes most of the heavy metals by adding heavy metal capture agents and flocculants to the heavy metal wastewater, and reuses the wastewater after repeated flocculation sedimentation, filtration, and reverse osmosis treatment. The process reduces the input of reagents in the treatment process, and the reflux design reduces the discharge of the final concentrated water, thereby improving the total water recovery rate. However, this method uses a large amount of heavy metal capture agents, treats a relatively single type of heavy metals, and has a high treatment cost.

[0006] CN205616685U discloses a heavy metal wastewater treatment system, which, through multiple reactions and multi-step sedimentation, and filtration through an ultrafiltration membrane filtration device, makes the content of multiple heavy metals in the wastewater, especially rare metals molybdenum and arsenic, meet the standards, and the treated waste residue can be effectively utilized, which can save water and achieve zero emissions. However, this method does not effectively classify and recover rare metal molybdenum and other heavy metal resources, and toxic hydrogen sulfide gas is generated during the treatment process, and the treatment steps are cumbersome.

[0007] Therefore, a method suitable for treating heavy metal wastewater and recovering molybdenum is developed, which has important practical guiding significance in the field of heavy metal wastewater treatment. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention provides a method for treating heavy metal wastewater using a reverse osmosis membrane. The method realizes water reuse, recovery of rare metal molybdenum resources and resource utilization of heavy metals. The method has a high metal molybdenum recovery rate, strong applicability, simple operation, low treatment cost, and is suitable for the treatment of a variety of heavy metal wastewaters.

[0009] In order to achieve the above object, the present invention provides a method for treating heavy metal wastewater using a reverse osmosis membrane, the method comprising:

[0010] (1) performing a first mixing of heavy metal wastewater and a flocculant, and obtaining a filtrate A after a first solid-liquid separation;

[0011] (2) After the filtrate A is treated with a reverse osmosis membrane, fresh water B and concentrated water C are obtained;

[0012] (3) performing a second mixing of the concentrated water C and the inorganic acid, and performing a second solid-liquid separation to obtain a precipitate D and a filtrate E;

[0013] (4) The filtrate E is mixed with the composite precipitant for the third time, and the precipitate F and the filtrate G are obtained through the third solid-liquid separation.

[0014] The present invention adopts membrane technology combined with chemical precipitation method to treat heavy metal wastewater, thereby realizing water reuse, rare metal molybdenum resource recovery and heavy metal resource utilization. The method of the present invention effectively improves the recovery rate of rare metal molybdenum and the heavy metal removal rate, and has the characteristics of simple operation and wide application range. At the same time, the method of the present invention can also reduce the amount of reagents added in the process of molybdenum recovery and heavy metal removal, and reduce the processing cost. In a preferred embodiment of the present invention, the use of a specific flocculant, a specific membrane treatment method and a specific inorganic acid can effectively improve the recovery rate of rare metal molybdenum. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The invention provides a specific implementation method for treating heavy metal wastewater by using a reverse osmosis membrane. DETAILED DESCRIPTION

[0016] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0017] The present invention provides a method for treating heavy metal wastewater using a reverse osmosis membrane, the method comprising:

[0018] (1) performing a first mixing of heavy metal wastewater and a flocculant, and obtaining a filtrate A after a first solid-liquid separation;

[0019] (2) After the filtrate A is treated with a reverse osmosis membrane, fresh water B and concentrated water C are obtained;

[0020] (3) performing a second mixing of the concentrated water C and the inorganic acid, and performing a second solid-liquid separation to obtain a precipitate D and a filtrate E;

[0021] (4) The filtrate E is mixed with the composite precipitant for the third time, and the precipitate F and the filtrate G are obtained through the third solid-liquid separation.

[0022] According to the present invention, the flocculant can be a common flocculant in the art, but in order to improve the recovery rate of metallic molybdenum and the removal rate of heavy metals, preferably, the flocculant includes at least one of aluminum sulfate, polyaluminum sulfate ferric, polyaluminum chloride ferric, polyaluminum chloride, polyacrylamide and sodium carboxymethyl cellulose; More preferably, the flocculant is a combination of polyacrylamide and polyaluminum chloride or polyaluminum chloride ferric, and the flocculant is selected from a combination of polyacrylamide and polyaluminum chloride in a weight ratio of 1-3:1 or a combination of polyacrylamide and polyaluminum chloride ferric in a weight ratio of 1-3:1. For example, the flocculant is composed of polyacrylamide and polyaluminum chloride in a weight ratio of 1:1, or the flocculant is composed of polyacrylamide and polyaluminum chloride ferric in a weight ratio of 2:1.

[0023] According to the present invention, the amount of the flocculant added can be selected within a wide range, preferably, the weight amount of the flocculant is 10-60 mg / L. The amount of the flocculant is relative to each liter of heavy metal wastewater, that is, relative to each liter of heavy metal wastewater, the weight amount of the flocculant is 10-60 mg.

[0024] According to the present invention, in order to improve the operating efficiency of the reverse osmosis membrane and further improve the recovery rate of metal molybdenum and the removal rate of heavy metals, preferably, step (2) further includes subjecting the filtrate A to microfiltration membrane treatment before the reverse osmosis membrane treatment to obtain filtrate H, and then subjecting the filtrate H to reverse osmosis membrane treatment. More preferably, the conditions of the microfiltration membrane treatment include: a temperature of 20-40°C, preferably 20-35°C, and a pressure of 0.1-0.2MPa.

[0025] According to the present invention, preferably, the microfiltration membrane equipment used in the microfiltration membrane treatment is equipped with a backwashing ultrasonic probe, and the power, time and ultrasonic frequency of the ultrasonic treatment can be adjusted according to the equipment and operating conditions, and the backwashing effluent can be returned to step (1); more preferably, the power of the ultrasonic treatment is 20-50W, the ultrasonic treatment time is 10-60s / time, and the ultrasonic frequency is 20-50KHz.

[0026] According to the present invention, preferably, the conditions for the reverse osmosis membrane treatment include: inlet water temperature of 15-40°C, preferably 20-30°C, inlet water pressure of 0.6-2MPa, inlet water pH of 5-6, and inlet water salt concentration of 0.5-1.2wt%.

[0027] According to the present invention, preferably, the reverse osmosis membrane system used in the reverse osmosis membrane treatment is a two-stage or multi-stage reverse osmosis system, and the reverse osmosis treatment stage can be adjusted according to the purpose and requirements of the fresh water B during the treatment process. The fresh water B can be discharged directly or returned to the production process for reuse. In order to reduce production costs, the fresh water B is returned to the microfiltration membrane and reverse osmosis membrane treatment process for reuse.

[0028] According to the present invention, preferably, the amount of the inorganic acid used is such that the pH of the second mixed system is 1-3, preferably 1-1.5.

[0029] According to the present invention, the type of the inorganic acid is not particularly limited. Preferably, the inorganic acid is at least one of sulfuric acid, hydrochloric acid and nitric acid, and more preferably sulfuric acid. The sulfuric acid is secondly mixed with concentrated water C in the form of a solution, the mass percentage of the sulfuric acid solution is 1-10wt%, and the solute in the sulfuric acid solution is water.

[0030] According to the present invention, preferably, the composite precipitant comprises a first component, a second component and a third component, the first component comprises at least one of reduced iron powder, hydrazine hydrate, sulfite and thiosulfate, the second component comprises at least one of alkali metal hydroxide, alkaline earth metal hydroxide, alkali metal oxide and alkaline earth metal oxide, and the third component comprises at least one of insoluble cross-linked starch xanthate, sodium sulfide, thiocarbamate and xanthate. More preferably, the first component comprises at least one of reduced iron powder, sodium sulfite and sodium thiosulfate; more preferably, the second component comprises at least one of sodium hydroxide, potassium hydroxide and calcium hydroxide; more preferably, the third component comprises at least one of sodium dithiodimethylcarbamate, insoluble cross-linked starch xanthate and sodium N,N-piperazine dithiocarbamate.

[0031] According to the present invention, preferably, the weight amount of the first component is 0.005-0.5% of the weight of the filtrate E, preferably 0.05-0.25%.

[0032] According to the present invention, preferably, the second component is used in an amount such that the pH of the filtrate E is 7.5-10, preferably 8-9.

[0033] According to the present invention, preferably, the weight amount of the third component is 0.0005-0.01% of the weight of the filtrate E, preferably 0.001-0.005%.

[0034] According to the present invention, preferably, the first solid-liquid separation, the second solid-liquid separation and the third solid-liquid separation are each independently performed by differential pressure filtration; more preferably, the pressure difference of the differential pressure filtration is 0.1-0.6 MPa; the pore size of the filter medium used in the differential pressure filtration is 0.5-2 μm, and the filter medium can be a filter cloth.

[0035] According to the present invention, preferably, the heavy metal wastewater contains at least one of nickel ions, chromium ions, vanadium ions and iron ions, and molybdenum ions.

[0036] According to the present invention, preferably, the content of molybdenum ions in the heavy metal wastewater is 1000-2000 mg / L.

[0037] According to the present invention, preferably, the content of nickel ions in the heavy metal wastewater is 100-1000 mg / L.

[0038] According to the present invention, preferably, the content of chromium ions in the heavy metal wastewater is 6-1000 mg / L.

[0039] According to the present invention, preferably, the content of vanadium ions in the heavy metal wastewater is 50-200 mg / L.

[0040] According to the present invention, preferably, the content of iron ions in the heavy metal wastewater is 50-200 mg / L.

[0041] The present invention will be described in detail below by way of examples. In the following examples,

[0042] Calculation method of molybdenum ion recovery rate:

[0043] Calculation method of heavy metal removal rate:

[0044] Among them, C 0,Mo is the concentration of molybdenum in heavy metal wastewater, C 1,Mo is the molybdenum concentration in the filtrate E, C 0,M is the concentration of heavy metals in heavy metal wastewater, C 2,M is the heavy metal concentration in filtrate G.

[0045] Calculation method of fresh water recovery rate:

[0046] Where V B is the volume of fresh water B, and V is the volume of heavy metal wastewater.

[0047] Test method for fresh water conductivity: measured using the Leici DDB-303A portable conductivity meter.

[0048] Ultrafiltration membrane equipment, microfiltration membrane equipment and reverse osmosis membrane equipment all adopt the LNG series of Shanghai Langji Membrane Separation Equipment Co., Ltd.

[0049] Example 1

[0050] Heavy metal wastewater composition: nickel ion 600mg / L, chromium ion 500mg / L, molybdenum ion 1000mg / L.

[0051] (1) Add flocculants to heavy metal wastewater, with the dosage of 30 mg / L polyacrylamide and 30 mg / L polyaluminium chloride, and obtain filtrate A by differential pressure filtration. The pressure difference of the differential pressure filtration is 0.1 MPa, and the pore size of the filter cloth used in the differential pressure filtration is 1.5 μm.

[0052] (2) Filtrate A is passed through a microfiltration membrane device to obtain filtrate H. The operating temperature of the microfiltration membrane device is 25°C, the pressure is 0.1MPa, the power of the backwash ultrasonic probe is 20W, the ultrasonic frequency is 30kHz, and the ultrasonic treatment time is 30s / time. Filtrate H is treated with a two-stage reverse osmosis membrane to obtain fresh water B and concentrated water C. The operating conditions of the reverse osmosis membrane device include: inlet water temperature is 25°C, inlet water pressure is 0.6MPa, inlet water pH is 5, and inlet water salt concentration is 1.2wt%. The reverse osmosis water production rate is 80%, and the conductivity of the fresh water after the two-stage reverse osmosis membrane treatment is 40μs / cm. Fresh water B is returned to the production process for reuse.

[0053] (3) 4 wt % sulfuric acid solution is added to concentrated water C in an amount such that the pH of concentrated water C is 1. The reaction is carried out for 2 h, and a precipitate D (molybdic acid precipitate) and a filtrate E are obtained by pressure differential filtration. The pressure difference of the pressure differential filtration is 0.4 MPa, and the pore size of the filter cloth used in the pressure differential filtration is 1.5 μm.

[0054] (4) 0.25 wt% of sodium sulfite was added to the filtrate E, and then sodium hydroxide was added to make the pH of the filtrate E 8, and then 0.05 wt% of insoluble cross-linked starch xanthate was added to the filtrate E, and the reaction was continued for 1 hour. The precipitate F (containing metal hydroxide) and the filtrate G were obtained by differential pressure filtration. The pressure difference of the differential pressure filtration was 0.4 MPa, and the pore size of the filter cloth used in the differential pressure filtration was 0.5 μm. The filtrate G was discharged after being treated to meet the standards.

[0055] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0056] Example 2

[0057] Heavy metal wastewater composition: nickel ion 600mg / L, vanadium 200mg / L, molybdenum ion 1000mg / L.

[0058] (1) Add flocculants to heavy metal wastewater, with the dosage of 20 mg / L polyacrylamide and 10 mg / L polyaluminium ferric chloride, and obtain filtrate A by differential pressure filtration. The pressure difference of the differential pressure filtration is 0.5 MPa, and the pore size of the filter cloth used in the differential pressure filtration is 1.5 μm.

[0059] (2) Filtrate A is passed through a microfiltration membrane device to obtain filtrate H. The operating temperature of the microfiltration membrane device is 30°C, the pressure is 0.2MPa, the power of the backwash ultrasonic probe is 30W, the ultrasonic frequency is 40kHz, and the ultrasonic treatment time is 30s / time. Filtrate H is treated with a two-stage reverse osmosis membrane to obtain fresh water B and concentrated water C. The operating conditions of the reverse osmosis membrane device include: inlet water temperature is 20°C, inlet water pressure is 2MPa, inlet water pH is 6, and inlet water salt concentration is 1wt%. The reverse osmosis water production rate is 85%, and the conductivity of the fresh water after the two-stage reverse osmosis membrane treatment is 35μs / cm. Fresh water B is returned to the production process for reuse.

[0060] (3) 4 wt % sulfuric acid solution is added to concentrated water C in an amount such that the pH value of concentrated water C is 1.2. The reaction is carried out for 2 h, and a precipitate D (molybdic acid precipitate) and a filtrate E are obtained by differential pressure filtration. The pressure difference of the differential pressure filtration is 0.3 MPa, and the pore size of the filter cloth used in the differential pressure filtration is 1.5 μm.

[0061] (4) Add 0.05 wt% of reduced iron powder to the filtrate E, then add sodium hydroxide to make the pH of the filtrate E 8.5, then add 0.01 wt% of sodium N,N-piperazine dithiocarbamate to the filtrate E, react for 1 hour, and obtain precipitate F (containing metal hydroxide) and filtrate G by differential pressure filtration. The pressure difference of the differential pressure filtration is 0.5 MPa, and the pore size of the filter cloth used in the differential pressure filtration is 1.0 μm. The filtrate G is discharged after being treated to meet the standards.

[0062] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0063] Example 3

[0064] Heavy metal wastewater composition: nickel ion 1000mg / L, iron ion 100mg / L, molybdenum ion 1500mg / L.

[0065] (1) Add flocculants to heavy metal wastewater, with the dosage of 30 mg / L polyacrylamide and 10 mg / L polyaluminium chloride, and obtain filtrate A by differential pressure filtration. The pressure difference of the differential pressure filtration is 0.3 MPa, and the pore size of the filter cloth used in the differential pressure filtration is 1 μm.

[0066] (2) Filtrate A is passed through a microfiltration membrane device to obtain filtrate H. The operating temperature of the microfiltration membrane device is 35°C, the pressure is 0.2MPa, the power of the backwash ultrasonic probe is 50W, the ultrasonic frequency is 50kHz, and the ultrasonic treatment time is 30s / time. Filtrate H is treated with a three-stage reverse osmosis membrane to obtain fresh water B and concentrated water C. The operating conditions of the reverse osmosis membrane device include a temperature of 30°C, an inlet pressure of 1.5MPa, an inlet pH of 5, and an inlet salt concentration of 0.7wt%. The reverse osmosis water production rate is 85%, and the conductivity of the fresh water after the three-stage reverse osmosis membrane treatment is 25μs / cm. Fresh water B is returned to the production process for reuse.

[0067] (3) 4 wt % sulfuric acid solution is added to concentrated water C in an amount such that the pH of concentrated water C is 1.5. The reaction is carried out for 2 h, and a precipitate D (molybdic acid precipitate) and a filtrate E are obtained by differential pressure filtration. The pressure difference of the differential pressure filtration is 0.5 MPa, and the pore size of the filter cloth used in the differential pressure filtration is 1 μm.

[0068] (4) 0.15 wt% of sodium thiosulfate was added to the filtrate E, and then calcium hydroxide was added to make the pH of the filtrate E 9, and then 0.05 wt% of sodium dithiodimethylcarbamate was added to the filtrate E, and the reaction was continued for 1 hour. The precipitate F (containing metal hydroxide) and the filtrate G were obtained by differential pressure filtration. The pressure difference of the differential pressure filtration was 0.6 MPa, and the pore size of the filter cloth used in the differential pressure filtration was 1 μm. The filtrate G was discharged after being treated to meet the standards.

[0069] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0070] Example 4

[0071] Heavy metal wastewater composition: vanadium ion 100mg / L, chromium ion 1000mg / L, molybdenum ion 2000mg / L.

[0072] (1) A flocculant, polyacrylamide in an amount of 30 mg / L, was added to heavy metal wastewater, and filtrate A was obtained by differential pressure filtration. The pressure difference of the differential pressure filtration was 0.2 MPa, and the pore size of the filter cloth used in the differential pressure filtration was 1.5 μm.

[0073] (2) Filtrate A is passed through a microfiltration membrane device to obtain filtrate H. The operating temperature of the microfiltration membrane device is 40°C, the pressure is 0.2MPa, the power of the backwash ultrasonic probe is 20W, the ultrasonic frequency is 20kHz, and the ultrasonic treatment time is 30s / time. Filtrate H is treated with a three-stage reverse osmosis membrane to obtain fresh water B and concentrated water C. The operating conditions of the reverse osmosis membrane device include a temperature of 40°C, an inlet pressure of 1.5MPa, an inlet pH of 6, and an inlet salt concentration of 1wt%. The reverse osmosis water production rate is 90%, and the conductivity of the fresh water after the three-stage reverse osmosis membrane treatment is 55μs / cm. Fresh water B is returned to the production process for reuse.

[0074] (3) 4 wt % nitric acid solution is added to concentrated water C in an amount such that the pH of concentrated water C is 3. The reaction is carried out for 2 h, and a precipitate D (molybdic acid precipitate) and a filtrate E are obtained by pressure differential filtration. The pressure difference of the pressure differential filtration is 0.3 MPa, and the pore size of the filter cloth used in the pressure differential filtration is 1.5 μm.

[0075] (4) 0.3 wt% of sodium thiosulfate was added to the filtrate E, and then calcium hydroxide was added to make the pH of the filtrate E 10, and then 0.005 wt% of sodium dithiocarbamate was added to the filtrate E, and the reaction was continued for 1 hour. The precipitate F (containing metal hydroxide) and the filtrate G were obtained by differential pressure filtration. The pressure difference of the differential pressure filtration was 0.5 MPa, and the pore size of the filter cloth used in the differential pressure filtration was 1.5 μm. The filtrate G was discharged after being treated to meet the standards.

[0076] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0077] Example 5

[0078] Heavy metal wastewater composition: nickel ion 100 mg / L, chromium ion 100 mg / L, molybdenum ion 1500 mg / L.

[0079] (1) A flocculant, 20 mg / L sodium carboxymethyl cellulose, was added to heavy metal wastewater, and filtrate A was obtained by differential pressure filtration. The pressure difference of the differential pressure filtration was 0.2 MPa, and the pore size of the filter cloth used in the differential pressure filtration was 2 μm.

[0080] (2) Filtrate A is passed through a microfiltration membrane device to obtain filtrate H. The operating temperature of the microfiltration membrane device is 20°C, the pressure is 0.2MPa, the power of the backwash ultrasonic probe is 20W, the ultrasonic frequency is 20kHz, and the ultrasonic treatment time is 30s / time. Filtrate H is treated with a two-stage reverse osmosis membrane to obtain fresh water B and concentrated water C. The operating conditions of the reverse osmosis membrane device include a temperature of 20°C, an inlet pressure of 2MPa, an inlet pH of 5, and an inlet salt concentration of 0.5wt%. The reverse osmosis water production rate is 90%, and the conductivity of the fresh water after the two-stage reverse osmosis membrane treatment is 53μs / cm. Fresh water B is returned to the production process for reuse.

[0081] (3) 4 wt % hydrochloric acid solution is added to concentrated water C in an amount such that the pH of concentrated water C is 2. The reaction is carried out for 2 h, and a precipitate D (molybdic acid precipitate) and a filtrate E are obtained by pressure differential filtration. The pressure difference of the pressure differential filtration is 0.4 MPa, and the pore size of the filter cloth used in the pressure differential filtration is 2 μm.

[0082] (4) Add 0.03 wt% of ferrous sulfate to the filtrate E, then add sodium hydroxide to make the pH of the filtrate E be 7.5, then add 0.01 wt% of sodium xanthate to the filtrate E, react for 1 hour, and obtain precipitate F (containing metal hydroxide) and filtrate G by differential pressure filtration. The pressure difference of the differential pressure filtration is 0.5 MPa, and the pore size of the filter cloth used in the differential pressure filtration is 2 μm. The filtrate G is discharged after being treated to meet the standards.

[0083] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0084] Example 6

[0085] The heavy metal wastewater was treated according to the method of Example 1, except that the amount of polyacrylamide used was 55 mg / L and the amount of polyaluminium chloride used was 5 mg / L.

[0086] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0087] Example 7

[0088] The heavy metal wastewater was treated according to the method of Example 1, except that the amount of polyacrylamide used was 10 mg / L and the amount of polyaluminium chloride used was 50 mg / L.

[0089] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0090] Example 8

[0091] The heavy metal wastewater was treated according to the method of Example 1, except that insoluble cross-linked starch xanthate was not added in step (4).

[0092] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0093] Example 9

[0094] The heavy metal wastewater was treated according to the method of Example 1, except that no sodium hydroxide was added in step (4).

[0095] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0096] Example 10

[0097] The heavy metal wastewater was treated according to the method of Example 1, except that sodium sulfite was not added in step (4).

[0098] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0099] Embodiment 11

[0100] The heavy metal wastewater was treated according to the method of Example 1, except that the weight of the sodium sulfite added in step (4) was 0.003% of the weight of the filtrate E, and the weight of the insoluble cross-linked starch xanthate added was 0.25% of the weight of the filtrate E.

[0101] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0102] Comparative Example 1

[0103] The heavy metal wastewater was treated according to the method of Example 1, except that the microfiltration membrane treatment and reverse osmosis membrane treatment process in step (2) were not included.

[0104] The recovery rate of molybdenum ions in step (3) and the removal rate of heavy metals in step (4) are shown in Table 1.

[0105] Comparative Example 2

[0106] The heavy metal wastewater was treated according to the method of Example 1, except that polyferric chloride and polyacrylamide were not added in step (1).

[0107] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0108] Comparative Example 3

[0109] Heavy metal wastewater was treated according to the method of Example 1, except that the reverse osmosis membrane in step (2) was replaced by an ultrafiltration membrane. The operating temperature of the ultrafiltration membrane equipment was 25° C., the water yield of the ultrafiltration membrane was 90%, and the conductivity of the fresh water after the two-stage reverse osmosis membrane treatment was 3180 μs / cm.

[0110] The fresh water conductivity and fresh water recovery rate in step (2), the molybdenum ion recovery rate in step (3), and the heavy metal removal rate in step (4) are shown in Table 1.

[0111] Table 1

[0112]

[0113] It can be seen from the results of Table 1 that the treatment of heavy metal wastewater using the method of the present invention can effectively improve the recovery rate of platinum ions, heavy metal removal rate and fresh water recovery rate, while reducing the fresh water conductivity. Comparing Example 1 with Example 6 and Example 7, it can be found that when the flocculant used is not within the preferred range of the present invention, the platinum ion recovery rate and fresh water recovery rate are significantly reduced, and the fresh water conductivity is significantly improved. Comparing Example 1 with Examples 8-11, it can be found that when the composite precipitant used is not within the preferred range of the present invention, the heavy metal removal rate is significantly reduced.

[0114] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for treating heavy metal wastewater using a reverse osmosis membrane, characterized in that: The method includes: (1) performing a first mixing of heavy metal wastewater and a flocculant, and obtaining a filtrate A after a first solid-liquid separation; (2) After the filtrate A is treated with a reverse osmosis membrane, fresh water B and concentrated water C are obtained; (3) performing a second mixing of the concentrated water C and the inorganic acid, and performing a second solid-liquid separation to obtain a precipitate D and a filtrate E; wherein the precipitate D is molybdic acid; (4) mixing the filtrate E with the composite precipitant for the third time, and performing a third solid-liquid separation to obtain a precipitate F and a filtrate G; wherein the precipitate F contains metal hydroxide; The composite precipitant includes a first component, a second component and a third component, wherein the first component includes at least one of reduced iron powder, sodium sulfite and sodium thiosulfate, the second component includes at least one of alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal oxides and alkaline earth metal oxides, and the third component includes at least one of sodium dithiodimethylcarbamate, insoluble cross-linked starch xanthate and sodium N,N-piperazine dithiocarbamate; the weight amount of the first component is 0.005-0.5% of the weight of the filtrate E; the weight amount of the third component is 0.005-0.1% of the weight of the filtrate E.

2. The method according to claim 1, wherein: The flocculant comprises at least one of aluminum sulfate, calcium oxide, polyaluminum sulfate ferric, polyaluminum chloride ferric, polyaluminum chloride, polyacrylamide and sodium carboxymethyl cellulose; And / or, the weight dosage of the flocculant is 10-60 mg / L.

3. The method according to claim 1, wherein: The flocculant is selected from a combination of polyacrylamide and polyaluminium chloride in a weight ratio of 1-3:1 or a combination of polyacrylamide and polyaluminium ferric chloride in a weight ratio of 1-3:

1.

4. The method according to claim 1, wherein: Step (2) further comprises treating the filtrate A with a microfiltration membrane before the reverse osmosis membrane treatment to obtain a filtrate H, and then treating the filtrate H with a reverse osmosis membrane; And / or, the conditions of the reverse osmosis membrane treatment include: inlet water temperature of 15-40° C., inlet water pressure of 0.6-2 MPa, inlet water pH of 5-6, and inlet water salt concentration of 0.5-1.2 wt %.

5. The method according to claim 1, wherein: The conditions of the reverse osmosis membrane treatment include: inlet water temperature of 20-30° C., inlet water pressure of 0.6-2 MPa, inlet water pH of 5-6, and inlet water salt concentration of 0.5-1.2 wt %.

6. The method according to claim 4, wherein: The conditions of the microfiltration membrane treatment include: a temperature of 20-40° C. and a pressure of 0.1-0.2 MPa.

7. The method according to claim 4, wherein: The conditions of the microfiltration membrane treatment include: a temperature of 20-35° C. and a pressure of 0.1-0.2 MPa.

8. The method according to claim 1, wherein: The amount of the inorganic acid is such that the pH of the second mixed system is 1-3; And / or, the inorganic acid is at least one of sulfuric acid, hydrochloric acid and nitric acid.

9. The method according to claim 1, wherein: The amount of the inorganic acid used is such that the pH of the second mixed system is 1-1.

5.

10. The method according to claim 1, wherein: The second component includes at least one of sodium hydroxide, potassium hydroxide and calcium hydroxide.

11. The method according to claim 1, wherein: The weight amount of the first component is 0.05-0.25% of the weight of the filtrate E; and / or, the amount of the second component is such that the pH of the filtrate E is 7.5-10; And / or, the weight amount of the third component is 0.01-0.05% of the weight of the filtrate E.

12. The method according to claim 1, wherein: The second component is used in an amount such that the pH of the filtrate E is 8-9.

13. The method according to claim 1, wherein: The first solid-liquid separation, the second solid-liquid separation and the third solid-liquid separation are each independently performed by differential pressure filtration.

14. The method according to claim 13, wherein: The pressure difference of the differential pressure filtration is 0.1-0.6 MPa.

15. The method according to claim 13, wherein: The pore size of the filter medium used in the differential pressure filtration is 0.5-2 μm.

16. The method according to claim 1, wherein: The heavy metal wastewater contains at least one of nickel ions, chromium ions, vanadium ions and iron ions and molybdenum ions.

17. The method according to claim 16, wherein: The content of molybdenum ions in the heavy metal wastewater is 1000-2000 mg / L.

18. The method according to claim 16, wherein: The content of nickel ions in the heavy metal wastewater is 100-1000 mg / L.

19. The method according to claim 16, wherein: The content of chromium ions in the heavy metal wastewater is 6-1000 mg / L.

20. The method according to claim 16, wherein: The content of vanadium ions in the heavy metal wastewater is 50-200 mg / L.

21. The method according to claim 16, wherein: The content of iron ions in the heavy metal wastewater is 50-200 mg / L.

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