CN113415936A

CN113415936A - Zero discharge process for electroplating nickel-containing wastewater

Info

Publication number: CN113415936A
Application number: CN202110658259.5A
Authority: CN
Inventors: 曾颖; 周宁娟
Original assignee: Shanghai Canxing Environmental Technology Co ltd
Current assignee: Shanghai Canxing Environmental Technology Co ltd
Priority date: 2021-06-15
Filing date: 2021-06-15
Publication date: 2021-09-21

Abstract

The invention discloses a zero discharge process of electroplating nickel-containing wastewater, which comprises a pretreatment process, a membrane concentration system and an evaporative crystallization system, wherein the evaporative crystallization system comprises a pump, a low-temperature normal-pressure evaporation system and a crystallizer. The invention has the beneficial effects that: continuous and stable operation can be realized; secondary pollution can not be generated; the low-temperature normal-pressure evaporation system has low evaporation temperature, low energy consumption and low operation cost of the whole treatment process; and the zero emission of nickel ions can be realized by matching with a low-temperature normal-pressure evaporation technology.

Description

Zero discharge process for electroplating nickel-containing wastewater

Technical Field

The invention relates to the field of water treatment, in particular to a zero discharge process for electroplating nickel-containing wastewater.

Background

At present, the manufacturing industry has strong capacity, wherein the metal surface treatment industry is widely applied and the influence of waste water pollution of a production line is large. The electroplated nickel is widely applied to electroplating production due to excellent wear resistance, corrosion resistance and weldability, and the processing amount of the electroplated nickel is second to that of galvanizing, and is the second place in the whole electroplating industry. A large amount of nickel-containing wastewater is generated in the nickel plating process, the electroplating nickel-containing wastewater is from the cleaning of a plated part, the filtering of plating solution, the waste plating solution, leakage, ground washing and the like in the electroplating production process, Ni in the wastewater mainly exists in the form of ions, and mainly comprises two ions, namely free ions and complex ions, wherein the complex ions mainly exist in Ni²⁺With organic acid radicals, CN^-、 SCN^-、EDTA substance, ammonium or amine substance. In view of the high toxicity of Ni element, the nickel-containing wastewater must be treated before discharge to reach the wastewater or surface water standard, and the mass concentration of total nickel in the electroplating wastewater discharged into the water body is allowed to be 0.5mg/L at most according to the electroplating pollutant discharge standard (GB 21900-2008). In addition, because the nickel ions belong to valuable metals and have high recovery value, zero discharge of the nickel-containing wastewater is imperative, the environment is protected, the nickel can be recovered to a certain degree, and the resource utilization is realized.

At present, the treatment methods of nickel-containing wastewater are mainly divided into 4 types: (1) a traditional chemical method, (2) a physical method, (3) an electrochemical method, and (4) a biological method;

the traditional chemical method for treating nickel-containing wastewater is a method for adding a certain amount of chemical agents to react to generate harmless or easily separated substances and then removing the substances from the wastewater. At present, the chemical precipitation method and the flocculation method are mainly adopted for treating the nickel-containing wastewater by the chemical method. The disadvantages are that: high treatment cost and easy generation of secondary pollution.

The physical method is to treat the nickel-containing wastewater by means of physical action, no chemical reaction occurs in the treatment process, and the prior physical method for treating the nickel-containing wastewater mainly comprises an adsorption method, an ion exchange method and a membrane separation method. The adsorption method has the defects that nickel cannot be recycled, and the ion exchange method has the defects that the recycling process is complex, the cost of the wastewater treatment process is high, and resin is easy to lose efficacy, so that the large-scale application of the resin in the industry is limited. The simple membrane separation technology has higher cost and complex process, the filter membrane is easy to cause pollution, the enterprise cost is increased, and the method is suitable for treating the low-content nickel wastewater, so the wide implementation in the enterprise is limited to a certain extent.

The electrochemical method utilizes the electrochemical property of metal, and metal nickel is reduced and precipitated at a cathode to remove Ni²⁺The purpose of the method is that common electrochemical methods comprise an electrolytic method, a membrane electrolytic method and an electrodeionization technology. The disadvantages of the method are that: high treatment cost and poor treatment effect on wastewater with complex components.

The biological method for treating the electroplating wastewater is mainly completed by artificially culturing complex functional bacteria. The functional bacteria have electrostatic adsorption, enzyme catalytic conversion, complexation, flocculation, occlusion and codeposition, and pH buffering effects. Heavy metal ions such as Ni in the wastewater are adsorbed and complexed by the thalli into clusters, and the wastewater is discharged or recycled after reaching the standard through solid-liquid separation, while the heavy metal ions are precipitated into sludge. The method has the following defects: the requirements for strains are high, and the culture conditions and the cost are strict, so the cost is high. And continuous and stable operation can not be ensured under the condition that the water quality and the water quantity have large fluctuation.

Therefore, there is a strong need in the art for a low-cost and stable-operation treatment process for electroplating nickel-containing wastewater.

Disclosure of Invention

The invention aims to provide a zero discharge process for electroplating nickel-containing wastewater, which aims to solve the current problems in the background technology.

In order to achieve the purpose, the invention provides the following technical scheme:

the zero discharge process of the electroplating nickel-containing wastewater comprises a pretreatment procedure, a membrane concentration system and an evaporation crystallization system, wherein the evaporation crystallization system comprises a pump, a low-temperature normal-pressure evaporation system and a crystallizer.

Through above-mentioned technical scheme, the raw water passes through preliminary treatment process, membrane concentration system, evaporation crystallization system, and ionic state nickel can generate nickel hydroxide sediment under the alkaline environment of coagulating basin, can get rid of the large granule suspended solid and partial ionic state nickel in the waste water, reduces the effluvium of cyanide simultaneously.

Further, the evaporation temperature of the low-temperature normal-pressure evaporation process is 70-85 ℃, the steam use temperature is 120-150 ℃, and the cooling water temperature is 25-35 ℃. The low-temperature evaporation system has low evaporation temperature, low energy consumption and low operation cost of the whole treatment process.

Further, the pretreatment process comprises the following steps:

raw water enters a regulating tank through a pump, the pH value of the raw water is regulated to be in an alkaline environment in the regulating tank, the raw water enters a coagulation tank, PAC is added into the coagulation tank, the raw water enters a flocculation tank after being fully stirred, PAM is added into the flocculation tank and then fully precipitated, precipitated sludge is subjected to filter pressing through a plate-and-frame filter press, solids are treated by units with qualification, filter pressing effluent returns to a raw water tank and is treated again, supernatant of the sedimentation tank enters a balancing tank, and HCL is added to regulate the pH value to be 6-8.

Furthermore, sodium hydroxide is added into the regulating tank to regulate the pH value to be about 11 in an alkaline environment.

Further, the membrane concentration system comprises a cartridge filter, a reducing agent dosing device, a scale inhibitor, a dosing device, a water feeding pump, a high-pressure pump, a membrane group, a chemical cleaning system and a membrane concentrated solution water tank.

Through the technical scheme, the membrane concentration system mainly aims at desalination and comprises a cartridge filter, a reducing agent dosing device, a scale inhibitor, a dosing device, a water feeding pump, a high-pressure pump, a membrane group, a chemical cleaning system and a membrane concentrated solution water tank. In order to prevent secondary pollution in the storage link, the microfiltration is carried out again through the security filter to remove suspended matters with the diameter of more than 1 mu m so as to protect the subsequent RO membrane from being blocked. Meanwhile, sediment generated by the dosing device can be trapped. The inlet and outlet of the cartridge filter are provided with pressure indicating gauges, and the filter element is replaced when the pressure difference is increased to a set value. The effluent of the cartridge filter enters an RO membrane system through a high-pressure pump to remove most of inorganic salts, organic matters, microorganisms and the like.

And further, the evaporation crystallization process comprises a pump, a low-temperature normal-pressure evaporation system and a crystallizer, wherein the membrane concentrated solution enters the low-temperature normal-pressure evaporation system through the pump, the evaporated effluent is recycled or directly discharged, the evaporated concentrated solution enters the crystallizer, the generated crystals are subjected to outside treatment by solid waste generated after separation by a centrifugal machine, and the mother liquor enters the reaction kettle for circular evaporation.

Further, the crystallizer utilizes a single-effect kettle to perform evaporative crystallization treatment.

Furthermore, the main body of the low-temperature normal-pressure evaporation system can be made of PPH and 316L stainless steel, and the partial structure can be made of PVDF and PTFE. The main body of the low-temperature normal-pressure evaporation system can be made of non-metallic materials, so that the investment cost is greatly saved.

Compared with the prior art, the invention has the beneficial effects that:

1. continuous and stable operation is realized;

2. secondary pollution can not be generated;

3. the low-temperature evaporation system has low evaporation temperature, low energy consumption and low operation cost of the whole treatment process;

4. and the zero emission of nickel ions can be realized by matching with a low-temperature normal-pressure evaporation technology.

Drawings

FIG. 1 is a flow chart of an exemplary embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, according to an exemplary embodiment of the present invention, a zero discharge process for nickel-containing electroplating wastewater is provided, which includes a pretreatment process, a membrane concentration system, and an evaporative crystallization system, wherein the evaporative crystallization system includes a pump, a low-temperature normal-pressure evaporation system, and a crystallizer.

Preferably, the evaporation temperature of the low-temperature normal-pressure evaporation process is 70-85 ℃, the steam use temperature is 120-150 ℃, and the cooling water temperature is 25-35 ℃. The low-temperature evaporation system has low evaporation temperature, low energy consumption and low operation cost of the whole treatment process.

Preferably, the pretreatment process comprises the steps of:

Preferably, sodium hydroxide is added into the adjusting tank to adjust the pH value to be about 11 in an alkaline environment.

Preferably, the membrane concentration system comprises a cartridge filter, a reducing agent dosing device, a scale inhibitor, a dosing device, a water feeding pump, a high-pressure pump, a membrane group, a chemical cleaning system and a membrane concentrated solution water tank.

Preferably, the evaporation crystallization process comprises a pump, a low-temperature normal-pressure evaporation system and a crystallizer, wherein concentrated water of the membrane concentration system enters a concentrated water tank and enters the low-temperature normal-pressure evaporation system through the pump, the evaporated effluent is recycled or directly discharged, the evaporated concentrated solution enters the crystallizer, generated crystals are separated by a centrifuge to generate solid waste, the solid waste is subjected to external treatment, and mother liquor enters the reaction kettle for circular evaporation.

Preferably, the crystallizer utilizes a single-effect kettle to perform evaporative crystallization treatment.

Preferably, the main body of the low-temperature normal-pressure evaporation system can be made of PPH and 316L stainless steel, and partial structure can be made of PVDF and PTFE.

Example 1

The method is characterized in that production wastewater is treated on the surface of a workshop of a certain metal processing enterprise Shanghai Jiading, wherein the main pollution is nickel-containing wastewater generated by sealing holes, the water amount is 80t/d, the main chemical components of the sealing holes are nickel acetate, complexing agents and surfactants, and the main pollutants in water are nickel, organic matters and the like. The water quality of the wastewater is shown in the table 1:

index of wastewater quality

Species of	pH	COD mg/L	Nickel mg/L	SS mg/L	Conductivity μ s/cm
						Comprehensive waste water	3-6	60-80	20-50	70-90	About 2000

TABLE 1

1) Pretreatment step

Raw water enters an adjusting tank through a pump, sodium hydroxide is added into the adjusting tank to adjust the pH value to be about 11, the raw water enters a coagulation tank, ionic nickel can generate nickel hydroxide precipitate under an alkaline environment, PAC is added into the coagulation tank, the PAC adding amount is 12mg/L, the coagulation time is 20-30 min, the raw water enters a flocculation tank after being fully stirred, PAM is added into the flocculation tank, the PAM adding amount is 10mg/L, the sedimentation time of the sedimentation tank is 60min, precipitated sludge is subjected to pressure filtration through a plate-and-frame filter press, solids are treated by qualified units, and pressure filtration effluent is returned to the raw water tank for treatment again. The step can remove large-particle suspended matters and partial ionic nickel in the wastewater, and simultaneously reduce the emission of cyanide.

And (4) allowing supernatant in the sedimentation tank to enter an equalizing tank, and adding HCL to adjust the pH to 6-8.

The water quality indexes of the effluent after the pretreatment are shown in a table 2:

species of	pH	COD mg/L	Nickel mg/L	SS mg/L	Conductivity μ s/cm
						Comprehensive waste water	6-9	＜50	＜0.1	＜10	＜2000
Removal rate	-	＞15％	＞99％	＞90％	-

TABLE 2

2. Membrane concentration system:

the membrane concentration system mainly aims at desalination, and the system comprises a security filter, a reducing agent dosing device, a scale inhibitor, a dosing device, a water feeding pump, a high-pressure pump, a membrane group and a chemical cleaning system, wherein 8 RO membranes are arranged in the embodiment.

In order to prevent secondary pollution in the storage link, microfiltration is carried out once again through a cartridge filter to remove suspended matters with the diameter of more than 1 mu m so as to protect the subsequent RO membrane from being blocked. Meanwhile, sediment generated by the dosing system can be trapped. The inlet and outlet of the cartridge filter are provided with pressure indicating gauges, and the filter element is replaced when the pressure difference is increased to a set value.

The effluent of the cartridge filter enters an RO membrane system through a high-pressure pump to remove most of inorganic salts, organic matters, microorganisms and the like. The high-pressure pump is the main power equipment of the RO membrane system, and the front and the back of the pump are respectively provided with a low switch and a high switch. And when the pressure of the outlet of the high-pressure pump is higher than the set value, the high-pressure pump stops to protect the membrane system. This example uses an 8 inch reverse osmosis membrane installed in a glass reinforced plastic pressure vessel.

In the operation process, when the pressure difference is obviously increased and the water yield is obviously reduced, chemical cleaning is carried out, the multi-medium filter is backwashed once for 24 hours, the UF30min is backwashed once, and the RO system is flushed once for 2 hours.

The effluent quality of the membrane concentration system is shown in table 3:

index (I)

Amount of water

pH

COD

Nickel (II)

SS

Electrical conductivity of

Unit of

t/d

mg/L

ppb

mg/L

μs/cm

Numerical value

6～9

＜50

＜40

＜5

＜200

Removal rate

-

＞60％

＞50％

＞90％

TABLE 3

3. Evaporative crystallization procedure

The inlet water of evaporation is the concentrated water of the front-end membrane concentration unit and the tank liquor produced by production, and the water quality indexes of the membrane concentration concentrated water unit and the tank liquor inlet water are shown in the table 4:

the water inlet index of the membrane concentrated solution is as follows:

index (I)

Amount of water

pH

COD

Nickel (II)

SS

Electrical conductivity of

Unit of

t/d

mg/L

μs/cm

Numerical value

15

6～9

＜300

＜0.6

＜100

＜12000

TABLE 4

The tank liquor water inlet index is shown in Table 5:

index (I)

Amount of water

pH

COD

Nickel (II)

SS

Electrical conductivity of

Unit of

t/d

mg/L

μs/cm

Numerical value

＜1

5.5～9

＜1500

＜0.5

＜30

＜10000

TABLE 5

And (3) after evaporation by an evaporation system (the evaporation temperature is 70-85 ℃, the steam use temperature is 120-150 ℃, and the cooling water temperature is 25-35 ℃), recycling or directly discharging the effluent, carrying out evaporative crystallization treatment on the evaporated concentrated solution by using a single-effect kettle, carrying out external treatment on solid waste generated after separation of the generated crystals by a centrifugal machine, and allowing the mother solution to enter a reaction kettle for circular evaporation.

Because the salt content of the membrane concentrated water and the tank liquor is relatively low, the continuous operation time of the evaporation concentration unit is long, namely the concentration discharge period is long, when the membrane concentrated water of cleaning water is treated, the concentration discharge period is 6-7 days, when the tank liquor is treated, the concentration discharge period is about 4 days, and the energy consumption for treating water per ton is 0.4-0.45 ton of steam.

In view of the characteristics of this type of waste water, PPH and 316L stainless steel are selected for use to evaporimeter main part material, and partial structure selects for use PVDF, PTFE etc. very big investment cost has been saved.

The water quality indexes of the evaporated and condensed water are shown in a table 6:

TABLE 6

The electroplating nickel-containing wastewater treated by the embodiment of the invention completely reaches the discharge standard of electroplating pollutants (GB 21900-2008), and meanwhile, the process stably runs, realizes zero discharge of the wastewater and saves the running cost.

Example 2:

ultrathin metal sheet fine processing and mechanical element manufacturing are produced by a certain photoelectric technology limited company in Jiangsu, a large amount of nickel-containing cleaning wastewater is generated in the mask production process, the wastewater contains nickel sulfate and ferrous sulfate, and the generation amount of the wastewater is 2 t/d. Adding sodium hydroxide into wastewater to adjust the pH value to be about 10-11, enabling the wastewater to enter a coagulation tank, enabling ionic nickel to generate nickel hydroxide precipitate in an alkaline environment, adding PAC into the coagulation tank, fully stirring, then enabling the mixture to enter a flocculation tank, adding PAM into the flocculation tank, enabling precipitated sludge to enter a sludge concentration tank after a certain time, performing filter pressing on the precipitated sludge through a plate and frame filter press, treating the solid by a qualified unit, and returning filter-pressed effluent to a raw water tank for treatment again. And (3) enabling the effluent of the sedimentation tank to enter a membrane concentration system for further desalination, enabling the effluent of the membrane system to be recycled or directly discharged, and enabling the membrane concentrated solution to enter an evaporation crystallization process for further removing nickel, organic matters and salt. Zero emission of nickel ions is achieved in this step. The evaporated water is recycled or discharged, and the crystallized solid is sent to a qualified unit for treatment.

The water inflow index is shown in Table 7:

species of	pH	COD mg/L	Nickel mg/L	SS mg/L	Conductivity μ s/cm
						Comprehensive waste water	2～3	80-120	90-120	100-130	15000

TABLE 7

The effluent indexes are shown in Table 8:

TABLE 8

In the embodiment, the removal rate of COD is up to 60%, the removal rate of nickel is up to more than 99%, the removal rate of SS is up to 92%, and the removal rate of conductivity is up to more than 95%. The wastewater treated by the method completely meets the industrial discharge standard, and the zero discharge of nickel ions is realized.

In conclusion, in the system for treating the electroplating nickel-containing wastewater by utilizing the pretreatment, membrane concentration and evaporative crystallization processes, the removal efficiency of target pollutants in each process is extremely high, the effect is very obvious, the quality of the wastewater discharged after treatment completely meets the recycling standard, and the zero discharge of the wastewater is realized.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. The zero-emission treatment process of the electroplating nickel-containing wastewater is characterized by comprising a pretreatment process, a membrane concentration system and an evaporative crystallization system, wherein the evaporative crystallization system comprises a pump, a low-temperature normal-pressure evaporation system and a crystallizer.

2. The electroplating nickel-containing wastewater treatment process according to claim 1, wherein the low-temperature normal-pressure evaporation process has an evaporation temperature of 70-85 ℃, a steam use temperature of 120-150 ℃ and a cooling water temperature of 25-35 ℃.

3. The nickel-containing electroplating wastewater treatment process according to claim 1 or 2, wherein the pretreatment process comprises the following steps:

raw water enters an adjusting tank through a pump, the adjusting tank adjusts the PH value to be in an alkaline environment and enters a coagulation tank, PAC is added into the coagulation tank, the raw water enters a flocculation tank after being fully stirred, PAM is added into the flocculation tank and then fully precipitated, precipitated sludge is subjected to filter pressing through a plate-and-frame filter press, solids are treated by units with qualification, filter-pressing effluent returns to a raw water tank and is treated again, supernatant of the sedimentation tank enters a balancing tank, and HCL is added to adjust the PH value to be 6-8.

4. The nickel-containing electroplating wastewater treatment process as claimed in claim 3, wherein sodium hydroxide is added into the regulating tank to regulate the alkaline environment with the pH value of about 11.

5. The electroplating nickel-containing wastewater treatment process according to claim 1 or 2, wherein the membrane concentration system comprises a cartridge filter, a reducing agent dosing device, a scale inhibitor, a dosing device, a water feeding pump, a high-pressure pump, a membrane group, a chemical cleaning system and a membrane concentrate water tank.

6. The nickel-containing electroplating wastewater treatment process according to claim 1 or 2, wherein the evaporation and crystallization process comprises a pump, a low-temperature normal-pressure evaporation system and a crystallizer, wherein concentrated water of a membrane concentration system enters a concentrated water tank and enters the low-temperature normal-pressure evaporation system through the pump, evaporated effluent is recycled or directly discharged, evaporated concentrated liquid enters the crystallizer, generated crystals are separated by a centrifuge to generate solid waste, and the mother liquid enters a reaction kettle for circular evaporation.

7. The electroplating nickel-containing wastewater treatment process according to claim 6, wherein the crystallizer utilizes a single-effect kettle to perform evaporative crystallization treatment.

8. The nickel-containing electroplating wastewater treatment process according to claim 1 or 2, wherein the main body of the low-temperature normal-pressure evaporation system is made of PPH and 316L stainless steel, and the parts of pipe fittings, valves, pump linings, instrument diaphragms and the like are made of PVDF and PTFE.