Method for treating calcium chloride and sodium chloride mixed brine

Abstract

The invention relates to the technical field of wastewater treatment, and discloses a novel method for treating calcium chloride and sodium chloride mixed saline water, which comprises the following steps: removing water insoluble substances in the calcium chloride and sodium chloride mixed saline water through membrane filtration, adjusting the water temperature and the pH value, intercepting divalent ions and permeating monovalent ions by utilizing the characteristics of a nanofiltration membrane, calcium chloride is intercepted through a multi-stage nanofiltration membrane, sodium chloride is permeated, penetrating fluid mainly containing sodium chloride and concentrated liquid mainly containing calcium chloride are obtained, the penetrating fluid can be returned to the salt chemical industry production process, and all sodium chloride is recycled; the volume of the concentrated liquid is only 20-30% of the volume of the raw brine, and the concentration of calcium chloride is improved by 2-4 times, so that the amount of evaporated water for producing the calcium chloride snow-melting agent is reduced to 20-30% of the total evaporation of the calcium chloride and sodium chloride mixed brine, the energy consumption is greatly reduced, the evaporated condensed water can also be used as production make-up water, and the zero emission of the calcium chloride and sodium chloride mixed brine is realized.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, in particular to a method for treating calcium chloride and sodium chloride mixed brine. Background Art

[0002] Taking the ammonia-soda process as an example, soda ash production uses sodium chloride, ammonia water, lime, and carbon dioxide as raw materials. Its characteristics are that the raw materials are cheap and readily available, ammonia can be recycled with minimal losses, it is suitable for large-scale production, and it is easy to mechanize and automatically control. The reaction process is as follows:

[0003] CaCO3=CaO+CO2↑

[0004] CaO+H2O=Ca(OH)2

[0005] NaCl+NH3+H2O+CO2=NaHCO3↓+NH4Cl

[0006] NaHCO3=Na2CO3+CO2↑+H2O↑

[0007] NH4Cl+Ca(OH)2=Ca Cl2+NH3+H2O

[0008] The main production process includes brine preparation, limestone calcination, ammonia brine preparation and carbonation, separation and calcination of heavy alkali, recovery of ammonia and carbon dioxide, etc. The CO2 and NH3 generated by the reaction can be reused as raw materials.

[0009] However, this method has a low raw material utilization rate, especially the utilization rate of NaCl is not high, and the production process produces a large amount of water and high sodium chloride and calcium chloride content of ammonia waste liquid. This is the most serious environmental problem currently faced by ammonia-soda process companies.

[0010] The composition and characteristics of the ammonia-soda process soda ash wastewater are as follows:

[0011] The ammonia waste liquid is used to recycle ammonia and ensure the alkalinity required for carbonization. Lime is used to convert ammonium chloride into ammonia, which is then returned to the previous process through ammonia distillation. The mother liquor after ammonia distillation contains 60-70g / L of sodium chloride and 100-120g / L of calcium chloride. A device with an annual output of 1 million tons of soda ash from the ammonia-soda process can produce approximately 8 million to 8.8 million cubic meters of ammonia waste liquid annually. Calculated based on 8,000 hours a year, there are 1,000 to 1,100 m3 of ammonia waste liquid per hour. 3 The ammonia vapor waste liquid needs to be treated.

[0012] The current method for treating ammonia waste liquid has the following problems:

[0013] 1. Direct evaporation to produce calcium chloride snow melting agent has problems such as large water volume, low calcium chloride content, large investment in direct evaporation equipment, and high energy consumption;

[0014] 2. The reaction of calcium ions with sulfate ions to form gypsum produces a large amount of calcium chloride, which requires further treatment. The water volume cannot be balanced, and a mixture of calcium chloride and sodium sulfate is generated, which requires further treatment.

[0015] 3. Return to the salt mine to continue dissolving salt to saturation, and circulate the brine to the alkali production process, but this will cause serious scaling of the brine pipeline;

[0016] 4. Reacts with sodium carbonate to produce ultrafine calcium carbonate, but separation is difficult;

[0017] Because of the large amount of ammonia waste liquid, no matter which of the above treatment methods is adopted, soda ash companies need to face and solve the problems of large investment, high energy consumption and high operating costs.

[0018] In addition, there are large amounts of calcium chloride waste brine in the wastewater from lime saponification of epichlorohydrin, the water produced after neutralization treatment of pickling waste liquid with lime, and the water produced after neutralization treatment of waste hydrochloric acid with lime. Most companies use the evaporation method to make calcium chloride snow-melting agent, which has the significant characteristics of large water volume, high energy consumption, and large equipment investment. Summary of the Invention

[0019] The purpose of the present invention is to overcome the defects of the existing treatment methods of the above-mentioned calcium chloride and sodium chloride mixed brine, and to provide a new method for treating the calcium chloride and sodium chloride mixed brine. The method is applicable to the salt chemical industry, chlor-alkali chemical industry, soda ash and other industries, and is particularly suitable for the existing production status of ammonia-soda process soda ash enterprises, thereby improving the recycling rate of sodium chloride, reducing treatment costs, achieving zero discharge of ammonia evaporation waste liquid, and fundamentally solving the environmental pollution problem of ammonia evaporation waste liquid.

[0020] In order to achieve the above object, the present invention adopts the following technical solutions:

[0021] A method for treating calcium chloride and sodium chloride mixed brine comprises the following steps:

[0022] S1, separating water-insoluble matter from the calcium chloride and sodium chloride mixed brine A to obtain refined calcium chloride and sodium chloride mixed brine B and calcium chloride and sodium chloride mixed brine C with a higher content of water-insoluble matter;

[0023] S2, dehydrating calcium chloride and sodium chloride mixed with brine C to obtain dry residue D with low moisture content and filtrate E;

[0024] S3, separating the calcium chloride and sodium chloride in the refined calcium chloride and sodium chloride mixed brine B to obtain a permeate with a sodium chloride concentration of 10 to 100 g / L and a concentrated solution with a calcium chloride concentration of 80 to 250 g / L.

[0025] Preferably, in step S1, the calcium chloride and sodium chloride mixed brine A is filtered through a membrane to separate water-insoluble matter from the brine, and the SS in the refined filtered brine B is less than 1 mg / L.

[0026] Preferably, in step S3, the refined calcium chloride and sodium chloride mixed brine B is separated into calcium chloride and sodium chloride by nanofiltration.

[0027] Preferably, the specific steps of step S3 include:

[0028] S301, the refined calcium chloride and sodium chloride mixed brine B is subjected to heat exchange by a heat exchange device to control the temperature of the calcium chloride and sodium chloride mixed brine B at 30-40° C. to obtain calcium chloride and sodium chloride mixed brine F that meets the temperature requirements;

[0029] S302, adjusting the pH of the calcium chloride and sodium chloride mixed brine F to 4-7 according to the pH value of the calcium chloride and sodium chloride mixed brine, to obtain a calcium chloride and sodium chloride mixed brine G that meets the requirements for entering the nanofiltration membrane;

[0030] S303, the refined and temperature- and pH-adjusted calcium chloride and sodium chloride mixed brine G enters the multi-stage nanofiltration system, wherein the permeate of each stage of nanofiltration device serves as the influent of the next stage of nanofiltration device.

[0031] Preferably, the calcium chloride and sodium chloride mixed brine used in step S1 includes the ammonia distillation waste liquid produced by the ammonia-soda process in the soda ash industry, the waste liquid produced by the neutralization of waste hydrochloric acid with lime in the production of good chlorine products, the calcium chloride wastewater produced by the lime saponification of epichlorohydrin, and the calcium chloride wastewater produced in the treatment process of pickling waste liquid in steel and metallurgical enterprises.

[0032] Preferably, in step S301, the temperature of the calcium chloride and sodium chloride mixed brine is adjusted in the form of indirect heat exchange. When the temperature is lower than 30° C., steam or hot water is used as a heat source to heat the calcium chloride and sodium chloride mixed brine; when the temperature is higher than 40° C., circulating water is used as a cold source to cool the calcium chloride and sodium chloride mixed brine, thereby obtaining the calcium chloride and sodium chloride mixed brine F that meets the requirements for entering the nanofiltration membrane.

[0033] Preferably, in step S302, a calcium chloride and sodium chloride mixed brine G with a pH of 4 to 7 is obtained by adding hydrochloric acid or caustic soda;

[0034] in:

[0035] The hydrochloric acid is an aqueous solution of high-purity industrial hydrochloric acid diluted with pure water to a hydrochloric acid concentration of 5-10%;

[0036] The caustic soda is a sodium hydroxide solution produced by ion membrane electrolysis with a sodium hydroxide concentration not exceeding 32%.

[0037] Preferably, in step S303, the multi-stage nanofiltration system adopts a 4:2:1 arrangement, and the calcium chloride and sodium chloride mixed brine G is pumped into the multi-stage nanofiltration system by a high-pressure pump.

[0038] Preferably, in step S303, in the calcium chloride and sodium chloride mixed brine G, since calcium chloride and sodium chloride are completely ionized into calcium ions, sodium ions and chloride ions in the aqueous solution, the properties of the cationic nanofiltration membrane that intercepts divalent cations and permeates monovalent cations are utilized to intercept calcium ions and permeate sodium ions in the calcium chloride and sodium chloride mixed brine. Under the action of the electric charge, chloride ions of equal charge are partially intercepted and partially permeated, thereby obtaining a permeate H mainly composed of sodium chloride and a concentrated solution I mainly composed of calcium chloride.

[0039] Preferably, the nanofiltration membrane adopts a rolled membrane structure, which is formed by rolling up an organic membrane sheet such as polyamide, a membrane support layer, and a raw liquid separator. The middle part is a water collection pipe. According to the water volume of the calcium chloride and sodium chloride mixed brine G, several membranes are connected in series or associated according to the process requirements and installed in the membrane tube.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The present invention provides a new method for treating calcium chloride and sodium chloride mixed brine, which can be applied to salt chemical industry, chlor-alkali chemical industry, soda ash and other industries, and is particularly suitable for the existing production status of ammonia-soda process soda ash enterprises, improves the recycling rate of sodium chloride, reduces treatment costs, achieves zero discharge of ammonia evaporation waste liquid, and fundamentally solves the environmental pollution problem of ammonia evaporation waste liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic flow chart of a method for treating calcium chloride and sodium chloride mixed brine proposed by the present invention;

[0043] Figure 2 This is a multi-stage nanofiltration principle diagram of a method for treating calcium chloride and sodium chloride mixed brine proposed by the present invention;

[0044] Figure 3 This is the working principle diagram of nanofiltration membrane;

[0045] Figure 4 Schematic diagram of a spiral nanofiltration membrane. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0047] Reference Figure 1-Figure 4 , a method for treating calcium chloride and sodium chloride mixed brine, comprising the following steps:

[0048] A mixed brine A having a sodium chloride concentration of 10 to 100 g / L and a calcium chloride concentration of 20 to 120 g / L is subjected to membrane filtration to separate water-insoluble matter from the brine to obtain a refined calcium chloride and sodium chloride mixed brine B and a calcium chloride and sodium chloride mixed brine C having a higher content of water-insoluble matter. The calcium chloride and sodium chloride mixed brine C is dehydrated by a dehydration device to obtain a dry residue D with a low moisture content and a filtrate E. The filtrate E is returned to the membrane filtration device for cyclic refining filtration, and the refined calcium chloride and sodium chloride mixed brine B is separated by nanofiltration to obtain a permeate with a sodium chloride concentration of 10 to 100 g / L and a concentrated solution with a calcium chloride concentration of 80 to 250 g / L.

[0049] The calcium chloride and sodium chloride brine mainly comes from the ammonia evaporation waste liquid produced by the ammonia-soda process in the soda ash industry, the waste hydrochloric acid generated in the production process of chlorine products after neutralization and conversion, the calcium chloride wastewater produced by the saponification of epichlorohydrin and lime, and the calcium chloride wastewater generated in the treatment process of pickling waste liquid in steel and metallurgical enterprises.

[0050] The membrane filtration can be divided into: microfiltration membrane, ultrafiltration membrane in terms of filtration accuracy; in terms of material composition, it can be divided into: organic membrane: polytetrafluoroethylene, polypropylene, polyvinylidene fluoride, polysulfone, polyethersulfone, etc.; inorganic membrane: Al2O3 ceramic membrane, silicon carbide membrane, stainless steel membrane, etc.; in terms of structural form, it can be divided into: bag membrane, tubular membrane, hollow fiber membrane, flat membrane; ensure that the SS in the brine B after refined filtration is <1mg / L.

[0051] As a preferred example of the present application, a polyvinylidene fluoride hollow fiber immersed ultrafiltration membrane is used, with negative pressure suction, low filtration pressure, small transmembrane pressure difference, low energy consumption and good water production quality.

[0052] As a preferred example of the present application, the refined calcium chloride and sodium chloride mixed brine B is separated by nanofiltration to obtain a permeate with a sodium chloride concentration of 10 to 100 g / L and a concentrated solution with a calcium chloride concentration of 80 to 250 g / L. This process specifically includes:

[0053] The refined calcium chloride and sodium chloride mixed brine B is subjected to heat exchange by a heat exchange device, and the temperature of the calcium chloride and sodium chloride mixed brine is controlled at 30-40° C. by indirect heat exchange to obtain calcium chloride and sodium chloride mixed brine F that meets the temperature requirements;

[0054] The heat source is steam or hot water, and the cold source is circulating water;

[0055] The indirect heat exchange means that the calcium chloride and sodium chloride mixed brine is not in direct contact with the cold and heat sources, and the heat exchange is carried out through a heat exchange device; the heat exchange device adopts a plate heat exchanger or a shell and tube type made of titanium, 2205 or 904 stainless steel;

[0056] When the temperature of the calcium chloride and sodium chloride mixed brine is less than 30° C., steam or hot water is preferably used as a heat source to heat the calcium chloride and sodium chloride mixed brine to obtain a calcium chloride and sodium chloride mixed brine F that meets the requirements for entering the nanofiltration membrane;

[0057] When the temperature of the calcium chloride and sodium chloride mixed brine is greater than 40° C., circulating water is preferably used as a cold source to cool the calcium chloride and sodium chloride mixed brine to obtain a calcium chloride and sodium chloride mixed brine F that meets the requirements for entering the nanofiltration membrane;

[0058] Adjust the water temperature of the calcium chloride and sodium chloride mixed brine F, and adjust the pH to about 4-7 with hydrochloric acid or sodium hydroxide solution according to the pH of the calcium chloride and sodium chloride mixed brine to obtain the calcium chloride and sodium chloride mixed brine G that meets the requirements of the nanofiltration membrane;

[0059] The hydrochloric acid is an aqueous solution of high-purity industrial hydrochloric acid diluted with pure water to a concentration of 5 to 10%;

[0060] The caustic soda is a sodium hydroxide solution produced by ion membrane electrolysis with a sodium hydroxide concentration not exceeding 32%.

[0061] The refined and temperature- and pH-adjusted calcium chloride and sodium chloride mixed brine G enters the multi-stage nanofiltration system, wherein the permeate of the first-stage nanofiltration device serves as the inlet water of the second-stage nanofiltration device, the concentrated liquid of the first-stage nanofiltration device serves as the concentrated liquid I of the multi-stage nanofiltration, and the permeate of each nanofiltration device serves as the inlet water of the next nanofiltration device, that is, the concentrated liquid of the N+1-stage nanofiltration device and the permeate of the N-1-stage nanofiltration device are mixed and serve as the inlet water of the N-stage nanofiltration device, and so on. The permeate of the last nanofiltration stage serves as the permeate H of the multi-stage nanofiltration.

[0062] Since calcium chloride and sodium chloride are completely ionized into calcium ions, sodium ions, and chloride ions in aqueous solution, the cationic nanofiltration membrane is used to intercept divalent cations and permeate monovalent cations to intercept calcium ions and permeate sodium ions in the calcium chloride and sodium chloride mixed brine. Under the action of the charge, chloride ions of equal charge are partially intercepted and partially permeated, thereby obtaining a permeate H mainly composed of sodium chloride and a concentrated solution I mainly composed of calcium chloride.

[0063] The working principle of nanofiltration membrane is as follows Figure 3 As shown:

[0064] As a preferred example of the present application, the cationic nanofiltration membrane uses commercial nanofiltration membranes produced by Dow, Toray and other companies, and the retention rate of calcium ions is greater than 70%.

[0065] The nanofiltration adopts a 4:2:1 arrangement, and the calcium chloride and sodium chloride mixed brine G is pumped into the nanofiltration membrane device by a high-pressure pump;

[0066] The nanofiltration membrane is a rolled membrane structure, which is made of an organic membrane sheet such as polyamide, a membrane support layer, and a raw liquid separator. The middle part is a water collection pipe. According to the water volume of the calcium chloride and sodium chloride mixed brine G, several membranes are connected in series or in conjunction with each other according to the process requirements and installed in the membrane tube.

[0067] Spiral nanofiltration membrane Figure 4 As shown:

[0068] The high-pressure pump is made of titanium or 2205 or 904 stainless steel. A single-stage high-pressure pump or a multi-stage high-pressure pump is selected according to the concentration of calcium chloride. The pump head is generally >200 meters.

[0069] Here, a multi-stage high-pressure pump made of titanium, 2205 or 904 can be used, which has lower energy consumption than a high-pressure pump with the same head. As a preferred example of this application, a multi-stage horizontal high-pressure pump is used.

[0070] The multi-stage nanofiltration is to connect several nanofiltration membrane devices in series, the permeate of the first-stage nanofiltration device is used as the inlet water of the second-stage nanofiltration device, the concentrated liquid of the first-stage nanofiltration device is used as the concentrated liquid I of the multi-stage nanofiltration, and the permeate of each stage nanofiltration device is used as the inlet water of the next stage nanofiltration device, that is, the concentrated liquid of the N+1 stage nanofiltration device and the permeate of the N-1 stage nanofiltration device are mixed and used as the inlet water of the N stage nanofiltration device, and so on. The permeate of the last stage nanofiltration is used as the permeate H of the multi-stage nanofiltration.

[0071] In order to improve the efficiency of the nanofiltration membrane, reduce the amount of concentrated liquid at each stage of the nanofiltration membrane, and increase the concentration of calcium chloride in the concentrated liquid, part of the concentrated liquid at each stage of the nanofiltration membrane can be returned to the inlet of the nanofiltration membrane at that stage to increase the concentration of calcium chloride at the inlet of each stage of the nanofiltration membrane. The specific method is to add a circulation pump after the outlet of each high-pressure pump, and the outlet of the circulation pump is connected to the inlet of the nanofiltration membrane. Part of the concentrated liquid is returned to the pipeline connecting the outlet of the high-pressure pump and the circulation pump, that is, the inlet of the circulation pump, so as to achieve the purpose of increasing the concentration of calcium chloride at the inlet of the nanofiltration membrane, ensuring the membrane surface flow rate of the nanofiltration membrane, reducing the amount of concentrated liquid, and increasing the concentration of calcium chloride in the concentrated liquid.

[0072] The circulation pump adopts a single-stage centrifugal pump. As a preferred example of this application, a horizontal pump or a vertical pump made of titanium, 2205 or 904 is adopted.

[0073] Compared with the prior art, the present invention removes water-insoluble matter in the calcium chloride and sodium chloride mixed brine by membrane filtration, adjusts the water temperature and pH, and then utilizes the characteristics of nanofiltration membranes in intercepting divalent ions and permeating monovalent ions to intercept calcium chloride and permeate sodium chloride through multi-stage nanofiltration membranes to obtain a permeate mainly composed of sodium chloride and a concentrated solution mainly composed of calcium chloride. The permeate can be returned to the salt chemical production process, and all the sodium chloride is reused; the volume of the concentrated solution is only 20-30% of the volume of the brine raw water, and the calcium chloride concentration is increased by 2-4 times, so that the amount of evaporated water in the production of calcium chloride de-icing agent is reduced to 20-30% of the total evaporation of the calcium chloride and sodium chloride mixed brine, the energy consumption is greatly reduced, and the evaporated condensed water can also be used as production supplementary water, thereby achieving zero discharge of the calcium chloride and sodium chloride mixed brine.

[0074] Example 1

[0075] A pilot study on the treatment of ammonia wastewater from an ammonia-soda process soda ash enterprise

[0076] A chemical company uses the ammonia-soda process to produce soda ash, with an annual output of 1 million tons and approximately 10 million tons of ammonia vapor waste liquid generated each year. Currently, a multi-effect evaporation process is used to produce calcium chloride de-icing agent. Although the multi-effect evaporation adopts two-effect rising film, two-effect falling film, and one-effect forced circulation, the large evaporation volume and huge energy consumption result in high processing costs.

[0077] The main components of the company's ammonia vapor waste liquid are: sodium chloride at about 60-70g / L, calcium chloride at about 100-120g / L, and pH at about 9.5-10.

[0078] First, the pH value of the ammonia evaporation wastewater was adjusted to about 6.5 using 5% hydrochloric acid. The suspended solids in the ammonia evaporation wastewater were removed by filtration using a 0.22-micron mixed fiber membrane. Then, calcium chloride and sodium chloride were concentrated and separated on a membrane filter using a nanofiltration experimental membrane produced by a certain company. The concentrations of calcium chloride and sodium chloride in the permeate and concentrate were tested respectively. The results are shown in the following table:

[0079]

[0080] From the results of the nanofiltration membrane separation experiments of these two samples, it can be seen that this batch of nanofiltration membrane has a significant retention effect on calcium chloride, with the retention rates of the two experiments being 65.23% and 63.30% respectively; and as the concentration of calcium chloride in the concentrate increases, the retention rate of sodium chloride decreases, causing the concentration of sodium chloride in the permeate to slightly increase.

[0081] From the above experimental results, it can be seen that the nanofiltration membrane has an obvious retention effect on calcium chloride, and due to the common ion effect, the sodium chloride concentration in the concentrate decreases slightly with the increase of calcium chloride concentration, while the sodium chloride concentration in the permeate increases slightly. In this way, calcium chloride and sodium chloride in the ammonia vapor waste liquid can be separated.

[0082] Example 2

[0083] A method for increasing the divalent salt concentration of nanofiltration membrane concentrate in a chlor-alkali enterprise

[0084] A certain alkali enterprise uses nanofiltration membrane to separate sodium sulfate and sodium chloride. The mixed brine volume is about 75m3 / h, of which sodium chloride is about 200g / L, sodium sulfate is about 10g / L, and the pH value is about 9-11. The sodium sulfate concentration in the permeate is required to be <2.5g / L and the sodium chloride concentration is >200g / L.

[0085] In order to meet the requirements of nanofiltration membrane entry, the mixed brine needs to be heat exchanged to adjust the temperature to 35-40°C, hydrochloric acid is added to adjust the pH value to 5.5-7.5, and free chlorine in the water needs to be eliminated to ORP < 200mv.

[0086] 45 8-inch nanofiltration membranes are installed in 5-core nanofiltration membrane shells, 2:1 configuration, 30 membranes in 6-piece membrane shells in one section, 15 membranes in 3-piece membrane shells in the second section, equipped with a flow rate of 77m 3 / h, a high-pressure pump with a head of 250 meters. According to the retention rate of sodium sulfate by the nanofiltration membrane, the sodium sulfate in the concentrate can be concentrated to 40g / L. In order to increase the concentration of sodium sulfate in the concentrate, a circulation pump with a flow rate of 84m3 / h and a head of 40 meters is added behind the outlet of the high-pressure pump to circulate part of the concentrate back to the outlet of the high-pressure pump, thereby increasing the amount of brine entering the membrane and the concentration of sodium sulfate. Although the retention rate of sodium sulfate remains unchanged, the concentration of sodium sulfate in the concentrate can be increased to >60g / L.

[0087] Therefore, it can be proved that by using the process of high-pressure pump + circulation pump to circulate part of the concentrated liquid to the inlet of the nanofiltration membrane, the concentration of divalent salts in the concentrated liquid of the nanofiltration membrane can be increased and regulated, the effectiveness of the nanofiltration membrane can be maximized, and the investment and energy consumption of the nanofiltration membrane device can be reduced.

[0088] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for processing calcium chloride and sodium chloride mixed brine, characterized in that: The following steps are involved: S1, separating water-insoluble matter from the calcium chloride and sodium chloride mixed brine A to obtain refined calcium chloride and sodium chloride mixed brine B and calcium chloride and sodium chloride mixed brine C with a higher content of water-insoluble matter; S2, dehydrating calcium chloride and sodium chloride mixed with brine C to obtain dry residue D with low moisture content and filtrate E; S3, separating the calcium chloride and sodium chloride in the refined calcium chloride and sodium chloride mixed brine B to obtain a permeate with a sodium chloride concentration of 10 to 100 g / L and a concentrated solution with a calcium chloride concentration of 80 to 250 g / L.

2. a kind of method of processing calcium chloride and sodium chloride mixed brine according to claim 1, is characterized in that: In step S1, the calcium chloride and sodium chloride mixed brine A is filtered through a membrane to separate water-insoluble matter from the brine, and the SS in the refined filtered brine B is less than 1 mg / L.

3. a kind of method of processing calcium chloride and sodium chloride mixed brine according to claim 1, is characterized in that: In step S3, the refined calcium chloride and sodium chloride mixed brine B is separated into calcium chloride and sodium chloride by nanofiltration.

4. a kind of method of processing calcium chloride and sodium chloride mixed brine according to claim 3, is characterized in that: The specific steps of step S3 include: S301, the refined calcium chloride and sodium chloride mixed brine B is subjected to heat exchange by a heat exchange device to control the temperature of the calcium chloride and sodium chloride mixed brine B at 30-40° C. to obtain calcium chloride and sodium chloride mixed brine F that meets the temperature requirements; S302, adjusting the pH of the calcium chloride and sodium chloride mixed brine F to 4-7 according to the pH value of the calcium chloride and sodium chloride mixed brine, to obtain a calcium chloride and sodium chloride mixed brine G that meets the requirements for entering the nanofiltration membrane; S303, the refined and temperature- and pH-adjusted calcium chloride and sodium chloride mixed brine G enters the multi-stage nanofiltration system, wherein the permeate of each stage of nanofiltration device serves as the influent of the next stage of nanofiltration device.

5. a kind of method of processing calcium chloride and sodium chloride mixed brine according to claim 1, is characterized in that: The calcium chloride and sodium chloride mixed brine used in step S1 includes ammonia distillation waste liquid produced by the ammonia-soda process in the soda ash industry, waste liquid produced by neutralization of waste hydrochloric acid with lime in the production of chlorine products, calcium chloride wastewater produced by lime saponification of epichlorohydrin, and calcium chloride wastewater produced in the treatment process of pickling waste liquid in steel and metallurgical enterprises.

6. a kind of method of processing calcium chloride and sodium chloride mixed brine according to claim 4, is characterized in that: In step S301, the temperature of the calcium chloride and sodium chloride mixed brine is adjusted by indirect heat exchange. When the temperature is lower than 30° C., steam or hot water is used as a heat source to heat the calcium chloride and sodium chloride mixed brine. When the temperature is higher than 40° C., circulating water is used as a cold source to cool the calcium chloride and sodium chloride mixed brine, thereby obtaining a calcium chloride and sodium chloride mixed brine F that meets the requirements for entering the nanofiltration membrane.

7. a kind of method of processing calcium chloride and sodium chloride mixed brine according to claim 2, is characterized in that: In step S302, a calcium chloride and sodium chloride mixed brine G with a pH of 4 to 7 is obtained by adding hydrochloric acid or caustic soda; in: The hydrochloric acid is an aqueous solution of high-purity industrial hydrochloric acid diluted with pure water to a hydrochloric acid concentration of 5-10%; The caustic soda is a sodium hydroxide solution produced by ion membrane electrolysis with a sodium hydroxide concentration not exceeding 32%.

8. a method for processing calcium chloride and sodium chloride mixed brine according to claim 4, is characterized in that: In step S303, the multi-stage nanofiltration system adopts a 4:2:1 arrangement, and the calcium chloride and sodium chloride mixed brine G is pumped into the multi-stage nanofiltration system by a high-pressure pump.

9. a kind of method of processing calcium chloride and sodium chloride mixed brine according to claim 8, is characterized in that: In step S303, in the calcium chloride and sodium chloride mixed brine G, since calcium chloride and sodium chloride are completely ionized into calcium ions, sodium ions, and chloride ions in the aqueous solution, the cationic nanofiltration membrane utilizes the characteristics of intercepting divalent cations and permeating monovalent cations to intercept calcium ions and permeate sodium ions in the calcium chloride and sodium chloride mixed brine. Under the action of the electric charge, chloride ions of equal charge are partially intercepted and partially permeated, thereby obtaining a permeate H mainly composed of sodium chloride and a concentrated solution I mainly composed of calcium chloride.

10. A method for processing calcium chloride and sodium chloride mixed brine according to claim 9, characterized in that: The nanofiltration membrane adopts a rolled membrane structure, which is made of an organic membrane sheet such as polyamide, a membrane support layer, and a raw material liquid separator. The middle part is a water collection pipe. According to the water volume of the calcium chloride and sodium chloride mixed brine G, several membranes are connected in series or associated according to the process requirements and installed in the membrane tube.

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