CN107055713B

CN107055713B - High-hardness salt-containing water concentration method based on monovalent cation selective electrodialysis

Info

Publication number: CN107055713B
Application number: CN201710351071.XA
Authority: CN
Inventors: 袁俊生; 刘杰; 纪志永; 王军; 郭小甫; 赵颖颖; 谢英惠
Original assignee: Hebei University of Technology
Current assignee: Hebei University of Technology
Priority date: 2017-05-18
Filing date: 2017-05-18
Publication date: 2020-05-12
Anticipated expiration: 2037-05-18
Also published as: CN107055713A

Abstract

The invention relates to a method for concentrating high-hardness salt-containing water based on monovalent cation selective electrodialysis, which comprises the following steps: firstly, raw water is subjected to chemical precipitation for hardness removal and pretreatment; secondly, reverse osmosis desalination treatment; thirdly, adjusting the pH value of the reverse osmosis concentrated saline water in the second step to 4-6 by using hydrochloric acid or sulfuric acid to serve as electrodialysis raw water, and then respectively entering a desalting chamber and a concentrating chamber which are formed by a positive membrane and a negative membrane at intervals in an electrodialysis membrane stack; to obtain electrodialysis high salt water and electrodialysis low salt water. The invention does not need additional equipment and devices, and realizes the separation of two ions forming the scaling substances under the condition of not sacrificing the recovery rate, thereby avoiding the scaling phenomenon caused by simultaneous interception or simultaneous permeation.

Description

High-hardness salt-containing water concentration method based on monovalent cation selective electrodialysis

Technical Field

The invention relates to a high-hardness saline water concentration process and system based on monovalent cation selective electrodialysis, and belongs to the field of wastewater treatment and environmental protection.

Background

The rapid development of social economy drives enterprises to develop rapidly, but the accompanying environmental problems, particularly the discharge of waste water, become bottlenecks which restrict the sustainable development of economy, society and environmental coordination. In the industrial enterprises of chemical industry, paper making, printing and dyeing, leather and the like, on one hand, salt can be used as one of raw materials in the process, and on the other hand, the salt content of the wastewater is higher due to the gradual concentration of the salt in the process water, and if the wastewater is not well treated, the ecological environment pollution of water and soil is inevitably brought. Therefore, the economic and efficient concentration treatment of the high-salinity brine becomes a key problem of the economical efficiency and feasibility of the liquid zero-discharge process.

The invention patent CN103342432B 'a near zero discharge process for salt-containing wastewater' discloses a near zero discharge process for salt-containing wastewater, which mainly comprises the steps of pretreatment, electro-adsorption, ultrafiltration, reverse osmosis, electrodialysis and evaporative crystallization. Wherein, the reverse osmosis concentrated water is used as the raw material of the electrodialysis, the electrodialysis water production concentrated brine is subjected to evaporation crystallization treatment, the produced fresh water enters a water supply system, and the comprehensive recovery rate of the water can reach 99.5 percent. The invention patent CN 104016529B discloses a method for treating coal chemical industry salt-containing wastewater based on a multistage countercurrent reverse-electrode electrodialyzer, which comprises ozone catalytic oxidation multi-medium filtration and membrane filtration multistage countercurrent reverse-electrode electrodialyzer, and realizes the deep treatment and desalination recycling of the coal chemical industry salt-containing wastewater. The utility model discloses a CN205011538U "low energy consumption coal chemical industry strong brine divides matter crystallization composite set" it is by removing hard softening, NF separating membrane, high salt reverse osmosis, produce water/concentrated water ED membrane concentration, produce water/concentrated water evaporation crystallization, produce water/concentrated water mother liquor desicator, AOP catalytic oxidation, multiple device combinations such as active carbon filtration form, and then realize the whole recycle of coal chemical industry strong brine. The utility model CN201520882324.2 "treatment system of coal chemical industry high salt waste water" discloses a treatment system of coal chemical industry high salt waste water, and it utilizes and receives the coupling technology of electrodialysis + reverse osmosis that filter, ionic membrane reactor and reverse osmosis filter constitute to handle coal chemical industry high salt waste water system.

From the above, brine concentration by electrodialysis and reverse osmosis, followed by salt separation and crystallization have become important schemes for industrial high-salinity water treatment. The high-salinity wastewater generally has the characteristic of high hardness, and the electrodialysis process in the prior art adopts a reversed-electrode electrodialyzer or nanofiltration pretreatment to reduce the possibility of scaling on the surface of a side membrane of electrodialysis concentrated water, but in the method, the reversed-electrode electrodialyzer needs complicated pipelines and control systems, and simultaneously, the recovery rate of water in an electrodialysis system is reduced; on one hand, new treatment equipment is added by taking nanofiltration as pretreatment, and meanwhile, the nanofiltration membrane still has the scaling problem, so the system recovery rate is low; some of the disclosed technologies treat the electrodialysis fresh water to a lower degree and use the electrodialysis fresh water as process fresh water, so that the electrodialysis treatment cost is increased; the method also adopts the ED desalted water circulation concentration form simply, but increases the concentration risks of COD, hardness and the like.

Disclosure of Invention

Aiming at the problems of the prior high-salt industrial wastewater concentration treatment requirement, complex equipment and low recovery rate in the prior art, the invention provides a high-hardness salt-containing wastewater concentration process and system based on monovalent selective cation electrodialysis, wherein the system takes chemical hardness removal, reverse osmosis and electrodialysis as the core and removes hardness ions in the system by chemical precipitation; desalting and primarily concentrating low-concentration brine by reverse osmosis to produce high-quality desalted water and simultaneously obtain primarily concentrated brine; the preliminary concentration brine is deeply concentrated by electrodialysis to obtain high-concentration brine, and meanwhile, an electrodialysis device consists of a monovalent cation membrane and a common anion membrane, so that the concentration of scaling ions in the concentrated brine can be effectively controlled. Compared with other processes, the method has the advantages of high concentration of concentrated water products, low concentration of scaling cations, simple process, low risk of membrane scaling and the like.

The technical scheme of the invention is as follows:

a method for concentrating high hardness salt-containing water based on monovalent cation selective electrodialysis, comprising the steps of:

first, chemical precipitation for hardness removal and pretreatment of raw water

Pretreating raw water to be treated and chemically removing hardness to obtain SS (suspended solid) in the treated raw water<0.1mg/L，Ca²⁺<40mg/L，SDI ≤3,S&DSI<0；

Second, reverse osmosis desalination

After water produced in the pretreatment procedure is filtered by a cartridge filter, reverse osmosis membrane is adopted for treatment to respectively obtain reverse osmosis desalted water and reverse osmosis strong brine, wherein the reverse osmosis desalted water is extracted, and the reverse osmosis strong brine is used as an electrodialysis raw material for next treatment;

wherein the TDS value of the obtained reverse osmosis concentrated brine is 10000-60000mg/L, and the TDS value of the reverse osmosis desalted water is 0-1000 mg/L;

third step, electrodialysis treatment

Adjusting the pH value of the reverse osmosis concentrated saline water in the second step to 4-6 by using hydrochloric acid or sulfuric acid, taking the reverse osmosis concentrated saline water as electrodialysis raw water, and respectively entering a desalting chamber and a concentrating chamber which are formed by a positive membrane and a negative membrane at intervals in an electrodialysis membrane stack; the electrodialysis raw water entering the desalting chamber returns to the desalting water tank after the action of an electric field, and overflows to obtain electrodialysis low-salt water as a product or as raw water of the next electrodialysis process; meanwhile, electrodialysis raw water entering the concentration chamber returns to the concentration water tank together with ions entering through the positive membrane and the negative membrane after the action of an electric field, and overflows to obtain electrodialysis high-salt water as a product; the electrodialysis treatment is a continuous reaction process;

the electrodialysis membrane stack comprises an anode plate, a desalting chamber, an anode membrane, a concentration chamber, a cathode membrane and a cathode plate; the desalting chambers are connected in parallel, and the concentrating chambers are connected in parallel;

the cation membrane is a monovalent selective cation membrane, and is preferably one of a CIMS ion exchange membrane manufactured by Japan ASTOM corporation or a CSO ion exchange membrane manufactured by Japan AGC corporation;

the negative film is a non-monovalent ion selective negative film.

The electric field is formed under constant current or constant voltage, and the current density is 100-500A/m during the constant current operation in the electrodialysis treatment process²(ii) a When the membrane is operated under constant voltage, the membrane has a voltage of 0.1-0.5V.

The ion mass concentration of the electrodialysis high-salt water flowing out of the concentration chamber is 12-24%; the ion mass concentration of the electrodialysis low-salt water flowing out of the desalting chamber is 0.8-3%; the ion mass mean value is the sum of the masses of all cations and anions in the brine.

The electrode liquid phases of the cathode and the anode in the electrodialysis treatment step are the same or different and are electrodialysis raw water, NaCl solution or NaSO₄One of the solutions, NaCl solution or NaSO₄The mass concentration of the solution is 1-5%.

The TDS value of the raw water in the raw water pretreatment process is 1000-10000 mg/L.

Each stage of the electrodialysis treatment process is composed of 1 electrodialysis assembly or 2-10 electrodialysis assemblies connected in series, and each electrodialysis assembly comprises 10-300 pairs of anion-cation exchange membranes.

And the cation exchange membrane used by the electrodialysis device in the electrodialysis treatment process is a monovalent selective ion exchange membrane, and the anion is a non-monovalent ion selective anion membrane.

The invention has the substantive characteristics that:

in the prior art of high-salinity wastewater treatment, concentration by electrodialysis has been used, and a process of integrating reverse osmosis and electrodialysis has been used. However, for salt solutions with high hardness, the prior patents adopt either nanofiltration or reverse electrodialysis. On one hand, the nano-filtration is adopted as pretreatment, on the other hand, equipment is independently added, the investment cost and the operation cost are increased, meanwhile, the nano-filtration is also a membrane process driven by pressure, a certain interception effect is realized on hardness and scale-causing ions (Ca, SO42 < - >, CO32 < - >), the ions are intercepted on an interception side (a concentrated water side), the scaling risk is caused on the concentrated water side, and meanwhile, the recovery rate of the system is lower; the electrodialysis reversal pipeline and the control system are complex, and simultaneously, part of concentrated water in the electrodialysis reversal process contains high scale-causing ions which cannot be used as products to be wasted. The cation and anion membranes can produce concentration action on any ion in the common electrodialysis, while the cation membrane uses univalent selective cation membrane and the anion membrane uses common anion membrane in the electrodialysis, SO that the univalent cation and all anions can be concentrated, i.e. the concentrated solution contains a large amount of SO₄ ^2-、CO₃ ^2-However, Ca²⁺The concentration is relatively low, the solution does not scale, and Ca trapped in the fresh water side²⁺It can be removed by chemical de-hardening, reverse osmosis can be at lower Ca²⁺The brine is primarily concentrated, so that the electrodialysis is mainly applied to high-concentration, and the respective advantages of the electrodialysis and the reverse osmosis are fully exerted.

The invention has the beneficial effects that:

a monovalent cation selective electrodialysis based high-hardness salt-containing water concentration method uses a monovalent selective cation exchange membrane and a common anion exchange membrane, only the monovalent cation and the anion are concentrated on a concentrated water side, extra equipment and devices are not needed, and the separation of two ions forming a scaling substance is realized under the condition of not sacrificing the recovery rate, so that the scaling phenomenon caused by simultaneous interception or simultaneous permeation is avoided. And reverse osmosis is combined with monovalent selective cation electrodialysis, and the reverse osmosis is at the front section, and as the initial salt content of most industrial wastewater is relatively low, the system has better adaptability, and simultaneously can give full play to the advantages of reverse osmosis in low salinity concentration, high desalination rate and electrodialysis high concentration, thereby realizing the high-efficiency action of the reverse osmosis and the low salinity concentration and producing high-concentration brine. Finally, the hardness removal by chemical precipitation can discharge the hardness in the system in a solid form, and the defect that the hardness in other processes cannot be discharged out of a membrane system to form continuous wrong circulation is overcome.

Drawings

The invention is further illustrated with reference to the following figures and examples.

FIG. 1 is a schematic diagram of a method for concentrating high-salinity wastewater by integrating reverse osmosis and electrodialysis.

FIG. 2 is a schematic diagram of an electrodialysis sequence of the present invention;

figure 3 is a schematic diagram of an electrodialysis membrane stack.

Fig. 4 is a schematic diagram of fluid flow and ion migration inside an electrodialysis membrane stack.

Detailed Description

The embodiment shown in fig. 1 shows that the process flow of the method for preparing liquid salt from concentrated seawater comprises the following steps: raw material salt water is firstly subjected to corresponding pretreatment steps, filtered by a cartridge filter with the filtering precision of 1-10 mu m after meeting the requirement of reverse osmosis water inflow, and pressurized by a high-pressure pump to enter a reverse osmosis membrane stack formed by a certain stage, wherein reverse osmosis desalted water is produced as one of products of the process, concentrated water is used as an electrodialysis raw material to adjust the pH value to 4-6, and the raw material is subjected to concentration treatment in an electrodialysis process to be converted into high-concentration electrodialysis high salt water and low-concentration electrodialysis low salt water, wherein the electrodialysis high salt water is produced as one of products of the process, and the electrodialysis low salt water is mixed with the raw water before returning to the raw water pretreatment process.

The reverse osmosis desalination treatment process comprises 1-3 stages and 1-2 stages. The quantity of the reverse osmosis sections is determined by the requirements of reverse osmosis raw water TDS and reverse osmosis concentrated water TDS, wherein 1 section of the concentrated water TDS is concentrated to 2-3 times of raw water, 2 sections are 4-6 times, and 3 sections are 8-9 times; adding 1 section of reverse osmosis concentration; the quantity of reverse osmosis stages is determined by the requirements of raw water TDS and reverse osmosis produced water TDS, and each stage can reduce the produced water TDS to 0.1-5% of the raw water.

The electrodialysis treatment process comprises 1-3 stages. The electrodialysis stage number is determined by the raw water concentration and the low and high brine concentrations, and the relationship can be approximately expressed by the following empirical formula: electroosmosis low salt water concentration ═ raw water concentration × (30-60%)^{Number of stages}。

The electrodialysis treatment process, the circulation flow of desalted water and concentrated water is determined by the logarithm of electrodialysis membranes, and the circulation flow is 0.01-0.5m³H for the membrane.

Example 1

The raw water is mixed water of waste water of a chemical enterprise and return water of each strand, and the water quality is shown in the table

Composition (I)	Concentration of
		Na₂SO₄/mg·L^-1	7 000
Ca²⁺/mg·L^-1	20
		Cl^-/mg·L^-1	36
COD/mg·L^-1	3 000
		SS/mg·L^-1	50
pH	8.2

First, raw water pretreatment process

98.7m of the above raw water³Respectively removing SS value by a mechanical clarification tank, removing COD in water by an anaerobic/aerobic (A/O) biological reaction tank and an aeration biological filter (BAF), ultrafiltering, and producing water of 88m³TDS 7050mg/L, SS 0mg/L, COD 100mg/L, SDI value 3. Wherein the ultrafiltration adopts PVDF hollow fiber membrane, adopts cross-flow filtration form, the recovery rate is 90%, and the operation pressure is 0.1 MPa.

Second, reverse osmosis desalination process

The pretreatment step 88m³The pH value of the produced water is adjusted to 6.5 by 10 percent wt hydrochloric acid, the produced water is filtered by a cartridge filter (the operating pressure is 0.1MPa, the filtering precision is 5 mu m) and then enters a reverse osmosis membrane through a high-pressure pump, the reverse osmosis membrane consists of 1 stage and 2 sections, wherein the first section of reverse osmosis membrane consists of 9 membrane components which are connected in parallel, a single membrane component consists of 6 membrane components which are connected in series, and the inflow of the produced water is 88m³The operation pressure is 1.4MPa, the recovery rate is 50 percent, and the membrane element adopts a U.S. DOW BW30FR400 commercial membrane element; the second stage reverse osmosis is composed of 4 membrane modules connected in parallel, the single membrane module is composed of 6 membrane modules connected in series, and the water inlet flow is 44m³H, the operating pressure is 2.2MPa, and the recovery rate is 50 percent. The membrane element described above was a us DOW SW30XHR400i commercial membrane element. The reverse osmosis produces 22.5m of concentrated water³The TDS of the calcium carbonate is 27890mg/L, the COD is 400mg/L, and the calcium carbonate is Ca²⁺80 mg/L; desalted water amounting to 65.5m³The TDS is 90 mg/L. The reverse osmosis desalted water is produced as one of the products of the process, and the concentrated water is used as the raw material of electrodialysis for the next step of treatment.

Third, electrodialysis treatment step

The electrodialysis is composed of two stages, continuous operation is adopted, each stage is as shown in fig. 2, wherein the first stage is composed of 2 membrane stacks connected in parallel (a single electrodialysis membrane stack diagram is as shown in fig. 3), each membrane stack 240 is arranged at intervals for the positive and negative membranes, the two ends are respectively the positive electrode and the negative electrode, meanwhile, frame-shaped clapboards are distributed at intervals between the positive and negative membranes (the clapboards are used for separating the positive and negative membranes, and the middle gap becomes a desalination chamber or a concentration chamber for containing raw water) to sequentially form a membrane stack structure of 'positive plate-desalination chamber-positive membrane-concentration chamber-negative membrane', meanwhile, all desalination chambers are connected in parallel, and all concentration chambers are connected in parallel; as shown in fig. 4. Concentrated water from a concentrated water tank and desalted water from a desalted water tank respectively enter an electrodialysis lower flow passage, then respectively enter a desalting chamber and a concentrating chamber formed by partition plates between anion and cation membranes, and then are respectively converged and returned to the concentrated water tank and the desalted water tank by an upper flow passage;

under the action of an electric field, raw water entering a desalting chamber is subjected to monovalent cation removal by a positive membrane and monovalent and polyvalent anions removal by a negative membrane to form a solution containing the polyvalent cations and the monovalent anions, the solution is returned to a desalting water tank and overflows to obtain electrodialysis low-salt water as a product or raw water of the next electrodialysis process; meanwhile, raw water entering the concentration chamber, along with monovalent cations permeating the positive membrane and monovalent and polyvalent anions permeating the negative membrane, becomes a high-concentration solution mainly containing monovalent cations and monovalent and polyvalent anions, returns to the concentration water tank, and overflows to obtain electrodialysis high-salt water as a product;

under the action of an electric field, cations in the desalting chamber move to the cathode, and only monovalent cations penetrate through the cation membrane to enter the concentrating chamber because the cation membrane has monovalent selectivity; all anions migrate towards the anode and permeate the cathode membrane into the concentrating compartment (since the anion membrane is a non monovalent ion selective cathode membrane, there is no selectivity for monovalent and multivalent, so monovalent and multivalent permeate together), causing the concentration of ions in the concentrated water to increase and the concentration in the desalination compartment to decrease due to ion migration.

In the film stack, the effective area of a single film is 1.4m²The first stage totals 480 pairs of films, and the total effective area is 672 pairs of m²(i.e. 672m for yin and yang membrane respectively²) (ii) a The second stage consists of 1 membrane stack, likewise a total of 240 pairs of cathodesTotal effective area of the anode film 336 pairs m²。

The reverse osmosis concentrated salt water in the second step is adjusted to pH 6 by using 10% wt hydrochloric acid, and is used as raw water with the pH value of 22.5m³The flow rate of the water enters a first-stage electrodialysis raw water tank, the water enters a first-stage electrodialysis membrane stack desalting chamber through a desalting water circulating pump, the water flows out of the electrodialysis desalting chamber and returns to the desalting water tank, and the water overflows to obtain a water with the concentration of 12.8g/L and the concentration of 21m³The low salt water of the first-stage electrodialysis is used as raw water of the second-stage electrodialysis; the concentration water tank also utilizes 10% wt hydrochloric acid to adjust the raw water with the pH value of 6 as an initial solution (at the beginning, the raw water is filled with the concentration water tank, then in the system operation process, the raw water does not enter the concentration water tank any more, but depends on the electric field effect, water molecules in the desalted water penetrate through an ion exchange membrane to enter the concentration water, so the volume of the concentration water is continuously increased, and then the concentrated water overflows in the concentration water tank to produce a concentrated water product, enters an electrodialysis membrane stack concentration chamber through a concentrated water circulating pump, then returns to the concentration water tank, and overflows to obtain first-stage electrodialysis high-salinity water with the volume of³/h。

The stage adopts constant current operation, and the current density is 250A/m². First-stage electrodialysis of low-salt water 21m³The raw water as the second-stage electrodialysis enters a second-stage electrodialysis raw water tank, enters a second-stage electrodialysis membrane stack desalting chamber through a desalting water circulating pump, flows out of the electrodialysis desalting chamber, returns to the desalting water tank, and overflows to obtain the product with the thickness of 20.1m³H,7.5g/L of second stage electrodialysis low salt water as final electrodialysis low salt water; the concentration water tank uses raw water as initial solution, enters an electrodialysis membrane stack concentration chamber through a concentration water circulating pump, returns to the concentration water tank, and overflows to obtain second-stage electrodialysis high-salt water with the thickness of 0.9m³H, 2.4m after mixing with first stage high salt water³200g/L high salt water product, the second stage is operated by constant current, and the current density is 140A/m²。

The first-stage cathode-anode electrode liquid and the second-stage cathode-anode electrode liquid both adopt Na with the mass concentration of 3%₂SO₄The circulation is carried out, and each stage of circulation flow is 3m³H is used as the reference value. Second electrodialysis 20.1m³And h, returning 7.5g/L of low-salt water to the first raw water pretreatment process, mixing the low-salt water with raw water, and treating the mixed low-salt water as raw water.

Example 2

The raw water of the part is the wastewater of an enterprise, and the water quantity is 360m³The water quality with pH value of 7 is shown in the table.

Index of water quality	Numerical value mg/L
		K	50
Na⁺	1700
		Mg²⁺	100
NO₃ ^-	260
		Cl^-	1100
SO₄ ^2-	3800
		Total hardness	3000
TDS	8300
		COD_Cr	120

First, raw water pretreatment process

From a raw water adjusting tank to 360m³Flow rate and return water of each part enter a regulating tank, and the total water quantity is 400m³Entering an ozone and BAF process, wherein COD in the water is mainly removed in the process, the designed removal rate is 40 percent, the COD in the produced water is 70mg/L, and other indexes are basically unchanged; followed by the addition of Na₂CO₃Coagulant FeCl₃(mg/L) and a coagulant aid PAM (mg/L) enter a high-density clarification tank, the hardness in raw water is mainly removed, the designed removal rate is 95 percent, meanwhile, partial COD can be removed, the total hardness in produced water is 200mg/L, the COD is 60mg/L, and the water quantity is about 360m³H; then the mixture enters a multi-media filter to remove part of suspended matters and then sequentially enters a sodium bed and a weak acid cation bed to remove residual hardness, and the total hardness is the concentration behind the weak acid cation bed<5mg/L, COD about 40mg/L, SS value 0mg/L, TDS 8300mg/L, SDI value 2.

Second, reverse osmosis desalination process

The pretreatment step 360m³The pH value of the produced water is adjusted to 6 by 10 percent wt hydrochloric acid, the produced water is filtered by a cartridge filter (the operating pressure is 0.1MPa, the filtering precision is 10 mu m) and then enters a reverse osmosis membrane through a high-pressure pump, the reverse osmosis membrane consists of 1 stage and 2 sections, wherein the first section of reverse osmosis membrane consists of 38 membrane components which are connected in parallel, a single membrane component consists of 6 membrane components which are connected in series, and the inflow rate is 360m³H, operating pressure 2.3MPa, water production 210m³H, COD 5mg/L, TDS 100 mg/L; 150m of concentrated water³The TDS19800 mg/L enters the second stage of reverse osmosis and is formed by connecting 18 membrane modules in parallel, wherein a single membrane module is formed by connecting 6 membrane modules in series, the operating pressure is 5.7MPa, and the concentrated water produced by reverse osmosis is about 70m³Perh, its TDS is about 50000mg/L, COD 10 mg/L; desalted water 80m³And/h, TDS is 200 mg/L. The membrane element used was a commercial membrane element made of Nitto electrician hydranautics SWC 58 inches. The reverse osmosis desalted water is produced as one of the products of the process, and the concentrated water is used as the raw material of electrodialysis for the next step of treatment.

Third, electrodialysis treatment step

Electrodialysis consists of four stages, with continuous operation, each stage flow as shown in figure 2 (a single electrodialysis membrane stack diagram is shown in figure 3), wherein each stage 1 and 2 consists of 6 membrane stacks, each stage 3 and 4 consists of 3 membrane stacks, each membrane stack 240 is arranged at intervals for a cathode and an anode, the two ends are respectively an anode and a cathode, meanwhile, frame-shaped clapboards (the function of the clapboards separates the negative and positive membranes, and the middle gap becomes a desalting chamber or a concentrating chamber for containing raw water) are distributed at intervals between the negative and positive membranes to form a membrane stack structure of ' anode plate-desalting chamber-positive membrane-concentrating chamber-negative membrane '. The desalting chamber-positive membrane-concentrating chamber-negative membrane ', and simultaneously, all the desalting chambers are connected in parallel, and all the concentrating chambers are connected in parallel; as shown in fig. 4. Concentrated water from a concentrated water tank and desalted water from a desalted water tank respectively enter an electrodialysis lower flow passage, then respectively enter a desalting chamber and a concentrating chamber formed by partition plates between anion and cation membranes, and then are respectively converged and returned to the concentrated water tank and the desalted water tank by an upper flow passage;

under the action of an electric field, cations in the desalting chamber move to the cathode, and only monovalent cations penetrate through the cation membrane to enter the concentrating chamber because the cation membrane has monovalent selectivity; all anions move to the anode and penetrate through the cathode membrane to enter the concentration chamber, so that the ion concentration in the concentrated water is increased, and the concentration in the desalting chamber is lowered due to ion migration.

In the film stack, the effective area of a single film is 1.4m²The first and second stages are 1440 pairs of films with 2016 pairs of m effective areas²(i.e. 2016m each of the yin and yang membranes)²) (ii) a The third and fourth stages are 720 pairs of yin and yang membranes, and the effective areas are 1008 pairs of m²。

Adjusting the pH value of the reverse osmosis concentrated salt water in the second step to 5 by using 10% wt hydrochloric acid, and taking the reverse osmosis concentrated salt water as raw water to be 70m³The flow rate of the water enters a first-stage electrodialysis raw water tank, the water enters a first-stage electrodialysis membrane stack desalting chamber through a desalting water circulating pump, the water flows out of the electrodialysis desalting chamber and returns to the desalting water tank, and the overflowing first-stage electrodialysis low-salt water is used as raw water of second-stage electrodialysis, and the like; the concentration water tank also utilizes 10% wt hydrochloric acid to adjust the raw water with the pH value of 5 as an initial solution (at the beginning, the raw water is filled with the concentration water tank, then in the system operation process, the raw water does not enter the concentration water tank any more, but depends on the electric field effect, the hydrone in the desalted water penetrates through the ion exchange membrane and enters the concentration water, therefore, the volume of the concentration water is continuously increased, and then the concentrated water overflows in the concentration water tank to produce a concentrated water product, the concentrated water enters the electrodialysis membrane stack concentration chamber through the concentrated water circulating pump, then returns to the concentration water tank, and the overflow is mixed with the first-stage concentrated.

The stage adopts constant current operation, and the current density of each stage is 270A/m²，220A/m²，170A/m²，150A/m². Wherein the overflow yields 49.7m³H,7.5g/L fourth electrodialysis weak brine as final electrodialysis weak brine; the concentration water tank uses raw water as initial solution, enters an electrodialysis membrane stack concentration chamber through a concentration water circulating pump, returns to the concentration water tank, and overflows to obtain 20.3m³200g/L of high-salt water product.

All levels of cathode and anode electrode liquid are circularly carried out by adopting NaCl with the mass concentration of 3 percent, and the circulating flow of each level is 3m³H is used as the reference value. Fourth electrodialysis 49.7m³H,8.3g/L low-salt water is returned to the first step raw water pretreatment procedure to be mixed with raw waterThe raw water is treated.

The invention is not the best known technology.

Claims

1. A method for concentrating high hardness salt-containing water based on monovalent cation selective electrodialysis, characterized in that the method comprises the steps of:

Pretreating raw water to be treated and chemically removing hardness to obtain SS (suspended solid) in the treated raw water<0.1mg/L，Ca²⁺<40mg/L，SDI≤3,S&DSI<0；

Second, reverse osmosis desalination

third step, electrodialysis treatment

Adjusting the pH value of the reverse osmosis concentrated brine in the second step to 4-6 by using hydrochloric acid or sulfuric acid, and then taking the reverse osmosis concentrated brine as electrodialysis raw water to enter a desalting water tank and a concentration water tank respectively; then respectively enters a desalting chamber and a concentrating chamber which are formed by the anode membrane and the cathode membrane at intervals in the electrodialysis membrane stack; the electrodialysis raw water entering the desalting chamber returns to the desalting water tank after the action of an electric field, and overflows to obtain electrodialysis low-salt water as a product or as raw water of the next electrodialysis process; meanwhile, electrodialysis raw water entering the concentration chamber returns to the concentration water tank together with ions entering through the positive membrane and the negative membrane after the action of an electric field, and overflows to obtain electrodialysis high-salt water as a product; the electrodialysis treatment is a continuous reaction process;

the positive membrane is a monovalent selective positive membrane, and the negative membrane is a non-monovalent ion selective negative membrane;

the electric field is formed under constant current or constant voltage, and the current density is 100-500A/m during the constant current operation in the electrodialysis treatment process²(ii) a When the membrane operates at constant voltage, the membrane has a voltage of 0.1-0.5V;

the electrodialysis membrane stack comprises an anode plate, a desalting chamber, an anode membrane, a concentration chamber, a cathode membrane and a cathode plate; the desalting chambers are connected in parallel, and the concentrating chambers are connected in parallel.

2. The method for concentrating a high-hardness salt-containing water by monovalent cation selective electrodialysis according to claim 1, wherein the cation membrane is one of a CIMS ion exchange membrane manufactured by ASTOM corporation of japan or a CSO ion exchange membrane manufactured by AGC corporation of japan.

3. A method for concentrating brine having high hardness based on monovalent cation selective electrodialysis as claimed in claim 1, wherein the overflow resulting electrodialysis brine has an ionic mass concentration of 12% -24%; the ion mass concentration of the electrodialysis low-salt water flowing out of the desalting chamber is 0.8-3%; the ion mass is the sum of the masses of all cations and anions in the brine.

4. The method for concentrating high-hardness salt-containing water by monovalent cation selective electrodialysis as claimed in claim 1, wherein the electrode liquid phases of the cathode and the anode in the electrodialysis treatment step are the same or different and are electrodialysis raw water, NaCl solution or Na₂SO₄One of the solutions, NaCl solution or Na₂SO₄The mass concentration of the solution is 1-5%.

5. The method for concentrating high hardness salt-containing water based on monovalent cation selective electrodialysis as claimed in claim 1, wherein the TDS value of raw water in the raw water pretreatment process is 1000-10000 mg/L.