阅读说明：本技术 一种离子膜烧碱一次精制盐水精制的方法 (Method for refining primary refined brine of ionic membrane caustic soda ) 是由 程雄 程淏奇 于 2020-11-25 设计创作，主要内容包括：本发明涉及一种离子膜烧碱一次精制盐水精制的方法,该方法在饱和盐水中通过加入碳酸钠与钙离子反应形成碳酸钙,加入氢氧化钠与镁离子反应形成氢氧化镁,直接采用平板陶瓷膜过滤得到满足离子膜烧碱二次盐水精制要求的一次精盐水,其中钙镁离子≤1mg/L、悬浮物≤1mg/L。与现有技术相比,本发明去除了常规的预处理工序,一次性得到了质量高且稳定的精制盐水。(The invention relates to a method for refining primary refined brine of ionic membrane caustic soda, which comprises the steps of adding sodium carbonate into saturated brine to react with calcium ions to form calcium carbonate, adding sodium hydroxide to react with magnesium ions to form magnesium hydroxide, and directly filtering by adopting a flat ceramic membrane to obtain the primary refined brine meeting the refining requirement of secondary brine of ionic membrane caustic soda, wherein the calcium and magnesium ions are less than or equal to 1mg/L, and suspended matters are less than or equal to 1 mg/L. Compared with the prior art, the method removes the conventional pretreatment process, and obtains the high-quality and stable refined brine at one time.)

1. A method for refining primary refined brine of ionic membrane caustic soda is characterized in that sodium carbonate is added into saturated brine to react with calcium ions to form calcium carbonate, sodium hydroxide is added to react with magnesium ions to form magnesium hydroxide, and the primary refined brine meeting the requirement of refining the secondary brine of ionic membrane caustic soda is obtained by directly adopting a flat ceramic membrane for filtration, wherein the calcium and magnesium ions are less than or equal to 1mg/L, and suspended matters are less than or equal to 1 mg/L.

2. The method for refining the primary refined brine of the ionic membrane caustic soda as claimed in claim 1, which comprises the following steps:

(1) dissolving solid salt in water to prepare raw material brine A, wherein the raw material brine A is saturated brine, and the concentration of each component is as follows: 305 +/-5 g/L of sodium chloride, 7.4-15 g/L of sodium sulfate and Ca²⁺5～2000mg/L，Mg²⁺5～200mg/L；

(2) Adding a sodium carbonate solution B and a sodium hydroxide solution C serving as refining agents into the raw material saline water A, allowing the raw material saline water A and the sodium hydroxide solution C to enter a reaction tank, and performing reaction to remove calcium and magnesium to obtain crude saline water D;

the concentrations of the individual components of the crude brine D were as follows: 305 +/-5 g/L of sodium chloride, 7.4-15 g/L of sodium sulfate, Ca (OH)₂5～4000mg/L，Mg(OH)₂ 5～500mg/L，SS5～5000mg/L；

(3) And the crude brine D obtained after the calcium and magnesium removal reaction automatically flows into a flat ceramic membrane separation membrane pool, is sucked by a suction pump under negative pressure, water insoluble substances are intercepted on the surface of the flat ceramic membrane, a circulating brine flow formed by scrubbing by gas is carried away from the surface of the flat ceramic membrane, and brine permeates through the flat ceramic membrane to obtain primary refined brine E.

3. The method for refining the primary refined brine of the ionic membrane caustic soda as claimed in claim 2, wherein the solid salt adopted in the step (1) comprises tedded sea salt, lake salt in inland areas, refined salt produced by a vacuum salt making device, or solid salt obtained by other means.

4. The method for refining the primary refined brine of ionic membrane caustic soda as claimed in claim 2, wherein the water distribution in step (1) is to mix the weak brine, condensed water, brine sludge filtrate or other miscellaneous water produced in the ionic membrane caustic soda production together to prepare unsaturated sodium chloride brine for salt saturation.

5. The method for refining primary refined brine from ionic membrane caustic soda as claimed in claim 2, wherein the raw brine a in step (1) is saturated underground brine or saturated sodium chloride brine obtained by other means.

6. The method for refining the primary refined brine of the ionic membrane caustic soda as claimed in claim 2, wherein the raw brine A in the step (1) is prepared in a salt dissolving tank, and the salt dissolving tank adopts a concrete structure or a glass flake anti-corrosion structure.

7. The method for refining the primary refined brine of the ionic membrane caustic soda as claimed in claim 2, wherein the sodium carbonate solution B in the step (2) is prepared from industrial-grade sodium carbonate and industrial water, and the mass concentration of the sodium carbonate solution B is 5-15%;

the sodium hydroxide solution C is a sodium hydroxide solution discharged from an electric tank by using ionic membrane caustic soda, and the mass concentration of the sodium hydroxide solution C is 30-32%.

8. The method for refining the primary refined brine of the ionic membrane caustic soda as claimed in claim 2, wherein the addition amount of the sodium carbonate in the step (2) is controlled by the residual amount of the sodium carbonate after the reaction, and the sodium carbonate overbase amount is 0.3-0.6 g/L;

the adding amount of the sodium hydroxide is controlled by the residual amount of the reacted sodium hydroxide, and the excessive alkali amount of the sodium hydroxide is 0.1-0.3 g/L;

the reaction time of the calcium and magnesium removal reaction is determined by the reaction time of sodium carbonate and calcium ions, and the preferable reaction time is more than or equal to 1 hour;

the reactor is a reactor with top dosing and mechanical stirring, the structural form is a tower structure, and liquid in the reactor automatically flows into the membrane pool.

9. The method for refining the brine through the primary refining of the ionic membrane caustic soda as claimed in claim 2, wherein the pore diameter of the flat ceramic membrane in the step (3) is 0.05-0.1 micron, and the material is ball-milled alpha-Al₂O₃Porosity of>20 percent, and the structural form is a flat plate type;

the flat ceramic membrane adopts negative pressure suction and dead-end filtration, and the filtration pressure is 0.01-0.1 Mpa.

10. The method for refining the primary refined brine through the ionic membrane caustic soda as claimed in claim 2, wherein calcium carbonate, magnesium hydroxide and salt slurry carried away by the circulating flow of the brine formed by scrubbing the surface of the flat ceramic membrane by gas are deposited in a mud bucket at the bottom of the membrane pool, and the salt slurry F is periodically discharged to a slag pool; and pumping the salt slurry F into a plate-and-frame filter press through a slurry pump for dehydration to obtain a filtrate G and salt slurry H, and returning the filtrate G after the salt slurry dehydration to the flat-plate ceramic membrane separation membrane pool.

Technical Field

The invention relates to a method for refining brine, in particular to a method for refining brine by one-time refining of ionic membrane caustic soda.

Background

The production of caustic soda by adopting saturated sodium chloride aqueous solution is a mature technology, and since the technology of preparing caustic soda by ion membrane in the middle of eighties in the world is successfully applied to the chlor-alkali industry in China, the chlor-alkali industry in China has the advantages of rapid technology and equipment progress and the productivity is the first in the world. With the continuous progress of the technology, the purposes of obtaining high-quality brine, reducing the cost of sodium chloride raw materials, reducing the brine refining cost, reducing the electrolysis power consumption and prolonging the service life of the ionic membrane also become the targets of various manufacturers in the chlor-alkali industry.

The ionic membrane caustic soda has strict requirements on the primary saline water, such as less than or equal to 1mg/L of calcium and magnesium ions, less than or equal to 1mg/L of suspended matters and the like. The primary brine refining is mainly to remove calcium and magnesium ions and suspended matters, the whole refining process is carried out under alkaline conditions, and the sodium hydroxide excess alkali amount is required: 0.1-0.3 g/L, sodium carbonate and alkali content: 0.3-0.5 g/L, and the existing primary brine refining process comprises clarification, sand filtration and a carbon tube filter (precoating a cellulose, floating clarification tank pretreatment, PTFE membrane filter, coarse filtration, tubular ceramic membrane filter and the like.

Because of the existence of calcium and magnesium impurities and water insoluble substances in raw material salt, membrane filtration brine refining without pretreatment can not be implemented in the chlor-alkali in China all the time, the floating clarifying tank pretreatment and PTFE membrane filtration process which are released at the end of the last century play a good promoting role in improving the quality of the primary brine of the chlor-alkali in China, most chlor-alkali users select the floating clarifying tank pretreatment and PTFE membrane filtration process to carry out the primary brine refining, but as time goes on, the floating clarifying preprocessor restricts the technical progress of the primary brine PTFE membrane filtration refining due to high manufacturing cost, high corrosion prevention difficulty and the like.

In the first application of chlorine alkali ion membrane caustic soda primary brine filtering by using a tubular ceramic membrane, after a refining agent adding reaction and adopting a plate-and-frame filter press as tubular ceramic membrane pretreatment, enterprises gradually develop a primary brine refining process of replacing the plate-and-frame filter press by coarse filtering and then filtering by using the ceramic membrane, but because the inner diameter of the tubular ceramic membrane is small, overhigh SS enters a membrane tube to cause the blockage of the membrane tube, and the solid content of the brine entering the membrane must be reduced, so that the coarse filtering by using the plate-and-frame filter press or other modes is particularly necessary.

The pretreatment is cancelled, and the saturated brine is directly refined by membrane filtration after chemical reaction to become the primary brine refining target of chlor-alkali enterprises, but no enterprise can realize the point so far.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for refining primary refined brine by using ionic membrane caustic soda, which is suitable for the current production situation of chlor-alkali, cancels pretreatment, directly performs membrane separation and improves the quality of brine.

The purpose of the invention can be realized by the following technical scheme: a method for refining primary refined salt water of ionic membrane caustic soda does not adopt any pretreatment equipment, sodium carbonate is added into saturated salt water to react with calcium ions to form calcium carbonate, sodium hydroxide is added to react with magnesium ions to form magnesium hydroxide, and primary refined salt water meeting the requirement of secondary salt water refining of ionic membrane caustic soda is obtained by directly adopting a flat ceramic membrane for filtration, wherein the calcium and magnesium ions are less than or equal to 1mg/L, and suspended matters are less than or equal to 1 mg/L.

The method specifically comprises the following steps:

(1) dissolving solid salt in water to prepare raw material brine A, wherein the raw material brine A is saturated brine, and the concentration of each component is as follows: 305 +/-5 g/L of sodium chloride, 7.4-15 g/L of sodium sulfate and Ca²⁺5～2000mg/L，Mg²⁺5～200mg/L；

The solid salt comprises tedded sea salt, lake salt in inland region, refined salt produced by vacuum salt-making device, or solid salt obtained by other methods.

The water distribution is to mix light salt brine, condensed water, salt slurry filtrate or other miscellaneous water produced by the production of the ionic membrane caustic soda together to prepare unsaturated sodium chloride brine for salt saturation.

The feed brine a is a saturated, underground brine, or a saturated sodium chloride brine obtained by other means.

The raw material salt water A is prepared in a salt dissolving pool which adopts a concrete structure or a glass flake anti-corrosion structure.

(2) Adding a sodium carbonate solution B and a sodium hydroxide solution C serving as refining agents into the raw material saline water A, allowing the raw material saline water A and the sodium hydroxide solution C to enter a reaction tank, and performing reaction to remove calcium and magnesium to obtain crude saline water D;

the concentrations of the individual components of the crude brine D were as follows: 305 +/-5 g/L of sodium chloride, 7.4-15 g/L of sodium sulfate, Ca (OH)₂5～4000mg/L，Mg(OH)₂ 5～500mg/L，SS5～5000mg/L；

The sodium carbonate solution B is prepared from industrial-grade sodium carbonate and industrial water, and the mass concentration of the sodium carbonate solution B is 5-15%; the method avoids the reduction of the concentration of sodium chloride caused by low concentration of sodium carbonate and avoids the crystallization of sodium carbonate in the pipeline to block the special pipeline caused by high concentration of sodium carbonate;

the sodium hydroxide solution C is a sodium hydroxide solution discharged from the electric cell by using ionic membrane caustic soda, the mass concentration of the sodium hydroxide solution C is 30-32%, and the sodium chloride concentration of crude brine caused by too low sodium hydroxide concentration is prevented from being reduced.

The adding amount of the sodium carbonate is controlled by the residual amount of the reacted sodium carbonate, and the sodium carbonate alkali content is 0.3-0.6 g/L;

the adding amount of the sodium hydroxide is controlled by the residual amount of the reacted sodium hydroxide, and the excessive alkali amount of the sodium hydroxide is 0.1-0.3 g/L;

the reaction time of the calcium and magnesium removal reaction is determined by the reaction time of sodium carbonate and calcium ions, and the preferable reaction time is more than or equal to 1 hour;

the reactor is a reactor with top dosing and mechanical stirring, the structural form of the reactor is a cylindrical structure, and liquid in the reactor automatically flows into the membrane pool. Preferably, two reactors are adopted, the reactors are connected by a pipeline and enter from bottom to top, crude brine enters from the lower part of the reactor 1, flows out from the upper part and flows into the lower part of the reactor 2 through the pipeline, and then flows out from the upper part of the reactor 2 and flows into a membrane pool through the pipeline, so that the problem of short circuit caused by the fact that calcium ions and sodium carbonate are not reacted after the brine enters the reactor and then flow out of the reactor is solved, mechanical stirring is carried out, and a stirrer is arranged at the top of the reactor.

(3) The crude brine D obtained after the calcium and magnesium removal reaction automatically flows into a flat ceramic membrane separation membrane pool, water insoluble substances such as calcium carbonate, magnesium hydroxide and silt are retained on the surface of the flat ceramic membrane through negative pressure suction of a suction pump, a circulating brine flow formed by scrubbing by gas is carried away from the surface of the flat ceramic membrane, and the brine penetrates through the flat ceramic membrane to obtain primary refined brine E;

the concentrations of the individual components of the primary refined brine E were as follows:

305 +/-5 g/L of sodium chloride, 7.4-15 g/L of sodium sulfate, less than or equal to 1mg/L of calcium and magnesium ions and less than or equal to 1mg/L of suspended matters;

the aperture of the flat ceramic membrane is 0.05-0.1 micron, and the material is ball-milled alpha-Al₂O₃Porosity of>20% of the structure form is flatPlate type;

the flat ceramic membrane adopts negative pressure suction and dead-end filtration, the filtration pressure is 0.01-0.1 Mpa, the air scrubbing and the membrane stack with a special structure can enable the salt water to circularly flow inside and outside the membrane stack to form cross-flow motion on the surface of the membrane, the salt mud is prevented from being accumulated on the surface of the membrane, and the enriched salt mud and partial salt water enter a sludge tank;

(4) calcium carbonate, magnesium hydroxide and salt slurry which are formed by scrubbing with gas and are carried away from the surface of the membrane by the circulating flow of the brine are deposited in a mud bucket at the bottom of the membrane pool, and the salt slurry F is periodically discharged to a slag pool:

the concentrations of the various components of the salt slurry F were as follows: 305 +/-5 g/L of sodium chloride, 7.4-15 g/L of sodium sulfate and less than or equal to 1-5% of SS;

(5) pumping the salt slurry F into a sludge dewatering device through a slurry pump for dewatering to obtain a filtrate G and salt slurry H, and returning the filtrate G after the salt slurry is dewatered to a flat ceramic membrane pool;

the salt sludge slurry in the sludge tank is pumped into sludge dewatering equipment by a slurry pump, the sludge dewatering equipment is a plate and frame filter press, a screw stacking machine, a vacuum filter, a belt filter and the like, and the plate and frame filter press is preferred. The bottom flow of the filter press returns to the membrane pool; most of the salt mud discharged by the plate-and-frame filter press is calcium carbonate and magnesium hydroxide solid;

preferably, the excessive alkali amount of the brine entering the flat ceramic membrane is controlled, the brine entering the membrane pool needs to be kept alkaline, and the sodium hydroxide is 0.1-0.3 g/L; a sodium hydroxide concentration lower than 0.1g/L will not ensure a magnesium ion concentration lower than 1mg/L, and a sodium hydroxide concentration higher than 0.3g/L will increase the running cost and make it uneconomical.

The preferable sodium carbonate is 0.3-0.6 g/L; sodium carbonate below 0.3g/L will not guarantee magnesium ions below 1mg/L, and sodium carbonate above 0.6g/L will increase the operating costs, and is also uneconomical.

The preferred refined brine E enters the refined brine tank of the primary brine refining system.

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

(1) a certain amount of calcium and magnesium impurities exist in sea salt, lake salt, refined salt or brine, the main purpose of brine refining is to remove the calcium and magnesium impurities, calcium carbonate and magnesium hydroxide formed by the calcium and magnesium impurities are water insoluble substances, a tubular ceramic membrane internal filtration mode is adopted, crude brine directly enters a membrane channel, the membrane channel is fine, and the concentration requirement (generally SS <100mg/L) is met for the water insoluble substances entering the membrane channel, so that the tubular ceramic membrane needs to adopt a pretreatment mode of crude filtration to reduce the concentration of the water insoluble substances entering the membrane channel and reduce the probability of membrane channel blockage; although the PTFE membrane in the PTFE organic membrane brine refining process is external filtration, the PTFE membrane has no requirement on water insoluble substances in crude brine, but magnesium hydroxide can be attached to the surface of the organic membrane to form a compact filter cake layer, so that the filtration flux is influenced, the magnesium hydroxide has low density, is difficult to settle and is easy to float, and the floating clarification pretreatment has the functions of both air floatation and settlement, so that the PTFE organic membrane brine refining process needs to adopt the floating clarification pretreatment to reduce the concentration of the magnesium hydroxide entering a membrane filter and improve the filtration flux and stability. The method adopts the flat ceramic membrane and the external filtration mode, but the membrane module adopts gas scrubbing, and salt water inside and outside the flat ceramic membrane module circularly flows to form cross flow due to the gas scrubbing, and the flowing salt water brings magnesium hydroxide on the surface of the membrane out of the membrane module, so that the influence on filtration flux and stability due to the formation of a compact filter cake layer due to the enrichment of magnesium hydroxide on the surface of the membrane is avoided. Therefore, the method does not need floating clarification and other pretreatments, crude salt water which is completely reacted by adding drugs directly enters the flat ceramic membrane for solid-liquid separation, the flow is short, and the equipment, instruments, civil engineering and installation cost are greatly reduced.

(2) The flat ceramic membrane adopts negative pressure suction and dead-end filtration, and has the advantages of negative pressure suction and filtration, small transmembrane pressure difference and low energy consumption. The traditional tubular ceramic membrane adopts positive pressure filtration of conveying salt water by a pump and large-flow circulation, the filtration pressure even reaches 0.5MPa, the membrane pressure difference is also 0.5MPa, and the backwashing pressure also needs 0.5 MPa; the flat ceramic membrane adopts negative pressure suction, the negative pressure of a suction pump is less than-0.1 MPa, the membrane pressure difference is less than the negative pressure of the pump, namely less than 0.1MPa, the flat ceramic membrane belongs to an external filtration mode, and no special requirements are made on the concentration of water insoluble substances such as magnesium hydroxide, calcium carbonate and the like in crude brine entering the membrane filtration assembly, so that no pretreatment is carried out, the filtration flux of the tubular ceramic membrane is sharply reduced and greatly fluctuated, and the flat ceramic membrane can still maintain higher filtration flux and has stable flow.

(3) In the membrane stack with a special structure, the salt water formed by gas scrubbing flows circularly, the membrane surface is similar to cross-flow filtration, the membrane flux is large, and the working principle is shown in figure 3: dull and stereotyped ceramic membrane pile often adopts six penetrating cuboid frame construction, and the aeration pipe is installed to the frame bottom, leans on the bubble that the aeration produced to carry out the gas to the water insoluble substance that the membrane surface was held back and cleans, and rivers in the membrane pond are in turbulent state, and the efficiency of taking away the water insoluble substance from the membrane surface is lower relatively, and the gas is cleaned the effect unsatisfactory. The membrane stack with a special structure of the invention also adopts a cuboid structure, but other four surfaces except the upper surface and the lower surface are sealed to form a cylinder, when in aeration, the density of the saline water in the cylinder is reduced because of a large amount of bubbles, the saline water outside the cylinder still keeps the original density, thus an internal and external density difference can be formed, the external saline water enters the membrane stack together with the aerated bubbles through the bottom and flows to the upper part, the saline water is discharged out of the frame, the bubbles continuously rise up and flow from the lower part to the lower part along the wall of the outer cylinder, a circulating flow is formed, the gas scrubbing efficiency is obviously improved under the combined action of the bubbles and the water flow, the intercepted water insoluble substances are ensured to be taken away from the surface of the membrane, and the intercepted water insoluble substances are accelerated to sink from the outer wall of the. The average flux of the filtration of the membrane can be stabilized at 0.1m due to the avoidance of the accumulation of water-insoluble substances such as salt mud on the surface of the membrane³/m²H or more.

(4) The invention saves pretreatment equipment and one-time refining, so the process equipment is simple and convenient to control.

(5) In order to ensure that calcium and magnesium are less than or equal to 1mg/L and SS is less than or equal to 1mg/L in refined brine and can be stable for a long time, the tubular ceramic membrane ensures that the membrane tube is easy to break due to high filtering pressure (0.5MPa) and high back flushing pressure (0.5MPa), the ceramic membrane tube is sealed in the membrane shell, once the ceramic membrane tube is not broken, even if the ceramic membrane tube is installed for on-line monitoring, the unqualified brine enters the subsequent working procedures when the unqualified brine index is detected. And the flat ceramic membrane low-pressure filtration (<0.1MPa) low-pressure back washing (<0.1MPa) does not cause the problem of membrane fracture, and can ensure the quality and stability of the brine. And the ion membrane caustic soda is immersed in an open membrane pool, so that the maintenance is very convenient, an online monitoring device is not required to be installed, and the requirements that the ion membrane caustic soda enters a secondary brine refining boundary area are met, namely calcium and magnesium are less than or equal to 1mg/L, and SS is less than or equal to 1 mg/L.

(6) Can reduce power consumption and prolong the service life of the ionic membrane. The power consumption and ionic membrane life of caustic soda production are determined by the quality of brine, the ionic membrane caustic soda technology is used in China in eighty years of the last century, the ionic membrane life is about 2 years, the alternating current power consumption is more than 2300 kwh/ton of soda due to poor quality of brine, and the PTFE membrane is approved by industrial users after being promoted from the beginning of the century, the quality of brine is greatly improved, the ionic membrane life can be prolonged to about 5 years, the alternating current power consumption is reduced to within 2200 kwh/ton of soda, but floating clarification pretreatment becomes a new obstacle restricting the development of the PTFE membrane; the flat ceramic membrane is superior to PTFE membrane and tubular ceramic membrane in quality and stable filtering flux, and has no floating clarification, low power consumption and long service life of ion membrane.

Drawings

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 is a reaction scheme in example 1;

FIG. 3 is a schematic diagram showing the operation of the membrane tank in example 1.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

Example 1

Improved pilot plant for one-time refined brine of chlor-alkali enterprises

The existing ionic membrane caustic soda primary brine refining system adopts the processes of adding sodium hydroxide for magnesium removal in the pre-reaction, floating a clarifying tank for pretreatment of crude brine, adding sodium carbonate for calcium removal in the post-reaction, and filtering by a PTFE organic membrane to remove water insoluble substances formed in the reaction, wherein the calcium and magnesium removal is carried out by adding drugs to control the amount of the sodium hydroxide and the sodium carbonate in the excess alkali, so that the refined brine is alkaline, the pH value is about 10.5-11.5, and the sodium hydroxide is about 0.1-0.3 g/L; the sodium carbonate is about 0.3-0.5 g/L, the pretreatment adopted by the existing process is the requirement of PTFE organic membrane filtration refining, floating clarification pretreatment is not adopted, the filtration flow of the PTFE organic membrane is greatly fluctuated, and the yield of refined brine can not be stably ensured to meet the requirement of subsequent processes.

Because the preprocessor of the enterprise is built in 2008, the internal corrosion protection is serious, the leakage phenomenon of the preprocessor occurs, and in order to avoid the production halt of a primary brine refining system caused by the fact that the preprocessor cannot be used, the enterprise adopts a pilot plant with the improved process, because the flat ceramic membrane adopts an immersed negative pressure suction filtration mode and a membrane stack with a special structural design, water insoluble substances intercepted on the surface of the membrane can be taken away through air scrubbing and brine circulation flow, the filtration flux and the stability of the membrane are ensured, the improved process cancels floating clarification pretreatment, brine after sodium hydroxide reaction is directly led into a post-reaction tank through short circuit, sodium carbonate is added for reaction, and then the brine directly led into a membrane tank and is separated by the flat ceramic membrane. The specific method comprises the following steps:

(1) dissolving solid salt to be treated in water in a salt dissolving pool to prepare raw material brine A, and controlling the concentration of each component of the raw material brine A as follows: 305 +/-5 g/L of sodium chloride, 7.4-15 g/L of sodium sulfate and Ca²⁺5～2000mg/L，Mg²⁺5～200mg/L；

The salt dissolving pool adopts a concrete structure.

(2) Adding a sodium carbonate solution B and a sodium hydroxide solution C serving as refining agents into the raw material saline water A, allowing the raw material saline water A to enter a reaction tank, and performing reaction for removing calcium and magnesium for 2 hours to obtain crude saline water D;

the concentrations of the individual components of the crude brine D were as follows: 305 +/-5 g/L of sodium chloride, 7.4-15 g/L of sodium sulfate, Ca (OH)₂5～4000mg/L，Mg(OH)₂ 5～500mg/L，SS5～5000mg/L；

The sodium carbonate solution B is prepared from industrial-grade sodium carbonate and industrial water, and the mass concentration of the sodium carbonate solution B is 5-15%; the method avoids the reduction of the concentration of sodium chloride caused by low concentration of sodium carbonate and avoids the crystallization of sodium carbonate in the pipeline to block the special pipeline caused by high concentration of sodium carbonate;

the sodium hydroxide solution C is a sodium hydroxide solution discharged from the electric cell by using ionic membrane caustic soda, the mass concentration of the sodium hydroxide solution C is 30-32%, and the sodium chloride concentration of crude brine caused by too low sodium hydroxide concentration is prevented from being reduced.

The adding amount of the sodium carbonate is controlled by the residual amount of the reacted sodium carbonate, and the sodium carbonate alkali content is 0.3-0.6 g/L;

the adding amount of the sodium hydroxide is controlled by the residual amount of the reacted sodium hydroxide, and the excessive alkali amount of the sodium hydroxide is 0.1-0.3 g/L;

the reactor is a reactor with top dosing and mechanical stirring, the structure adopts a cylindrical structure, and liquid in the reactor automatically flows into the membrane tank through a pipeline. In the embodiment, two reactors are adopted, the reactors are connected by a pipeline and enter from bottom to top, crude brine enters from the lower part of the reactor 1, flows out from the upper part and flows into the lower part of the reactor 2 through the pipeline, and then flows out from the upper part of the reactor 2 and flows into a membrane pool through the pipeline, so that the problem of short circuit caused by the fact that calcium ions and sodium carbonate do not react before entering the reactor after the brine enters the reactor is solved, mechanical stirring is carried out, and a stirrer is arranged at the top of the reactor to avoid short circuit; see figure 2 for details.

(3) Crude salt water D obtained after the calcium and magnesium removal reaction automatically flows into a flat ceramic membrane separation membrane pool 3, the structure of the membrane pool 3 is shown in figure 3, and the membrane pool comprises a membrane stack with a cuboid structure, a flat ceramic membrane installation cylinder which is sealed by removing the upper surface and the lower surface and is formed into a cylinder is arranged in the membrane stack, a flat ceramic membrane is installed in the installation cylinder, the aperture of the flat ceramic membrane is 0.05-0.1 micron, and the material is ball-milled alpha-Al₂O₃Porosity of>20 percent, and the structural form is a flat plate type; the bottom of the mounting cylinder is provided with an aerator pipe which is connected with a compressed air delivery pipe, the upper part of the mounting cylinder is provided with a refined brine delivery pipe which is connected with a suction pump, negative pressure suction is carried out through the suction pump, the flat ceramic membrane adopts negative pressure suction and dead end filtration, the filtration pressure is 0.05Mpa, during aeration, the density of brine in the cylinder is reduced due to a large amount of bubbles, the brine outside the cylinder still keeps the original density, thus forming an internal and external density difference, the outside brine enters the membrane stack through the bottom and flows upwards together with the aerated bubbles, the brine after exiting from the frame flows along the wall of the outer cylinder to flow downwards to form a circulating flow, the gas scrubbing efficiency is obviously improved under the combined action of the bubbles and the water flow, water insoluble substances such as calcium carbonate, magnesium hydroxide, silt and the like are intercepted on the surface of the flat ceramic membrane, and the circulating brine flow formed by gas scrubbing is carried away from the surface of, and followCirculating brine flow is precipitated in a cone hopper of the membrane tank from the outer wall of the cylinder in an accelerated manner, and the enriched salt slurry and part of brine enter a sludge tank; the salt water permeates a flat ceramic membrane to obtain primary refined salt water E;

the concentrations of the individual components of the primary refined brine E were as follows:

the concentration of each component of the refined brine is as follows: sodium chloride about 305g/L, sodium sulfate 7.4g/L, Ca²⁺+Mg²⁺0.78mg/L and SS 0.45mg/L, the pilot plant achieved the expected target.

(4) Calcium carbonate, magnesium hydroxide and salt slurry which are formed by scrubbing with gas and are carried away from the surface of the membrane by the circulating flow of the brine are deposited in a mud bucket at the bottom of the membrane pool, and the salt slurry F is periodically discharged to a slag pool:

the concentrations of the various components of the salt slurry F were as follows: 305g/L sodium chloride, 7.4g/L sodium sulfate and about 3.5% SS;

(5) and pumping the salt slurry F into a sludge dewatering device through a slurry pump for dewatering to obtain a filtrate G and salt slurry H, and returning the filtrate G after the salt slurry is dewatered to the flat ceramic membrane pool.

Example 2

In a certain chemical plant, a nanofiltration membrane salt separation, reverse osmosis membrane concentration and evaporation salt extraction process is adopted in the zero discharge treatment of high-salt inorganic wastewater, wherein the concentration of sodium chloride and Ca in the wastewater is 10g/L²⁺About 500Mg/L, Mg²⁺About 100mg/L, sulfate is about 5000 mg/L. In order to avoid the influence of calcium sulfate scaling on the nanofiltration membrane, the reverse osmosis membrane and evaporation equipment caused by concentration and enrichment of calcium and magnesium ions and sulfate radicals, the experiment of adopting a dosing reaction and membrane separation magnesium hydroxide and calcium carbonate as pretreatment of the nanofiltration membrane is determined.

In the experiment, sodium hydroxide and sodium carbonate are added to react at normal temperature to react calcium and magnesium ions into magnesium hydroxide and calcium carbonate solids, and the raw water meeting the membrane inlet requirement of the nanofiltration membrane is obtained through solid-liquid separation of a flat ceramic membrane. The specific method comprises the following steps:

(1) the concentrations of the individual components of the raw water a were as follows: 10g/L of sodium chloride, 5000mg/L of sodium sulfate and Ca²⁺500mg/L，Mg²⁺100mg/L；

(2) Adding a sodium carbonate solution B and a sodium hydroxide solution C serving as refining agents into raw material water A, feeding the raw material water A into a reactor, wherein the raw material water A is in a cylindrical structure, the top of the reactor is provided with a stirrer, two reactors are connected in series, the reactors are connected by a pipeline, the raw material water enters from the lower part of the reactor 1, flows out from the upper part of the reactor 1, flows into the lower part of the reactor 2 through the pipeline, flows out from the upper part of the reactor 2, and automatically flows into a membrane pool through the pipeline, so that the problem of short circuit caused by the fact that calcium ions and sodium carbonate do not react after saline water enters the reactor and then flow out of the reactor is solved, the raw material water A is mechanically stirred, the stirrer is arranged at the top of the reactor;

the concentrations of the individual components of the raw water D were as follows: sodium chloride 10g/L, sodium sulfate 5000mg/L, Ca (OH)₂998mg/L，Mg(OH)₂ 230mg/L，SS1310mg/L；

The sodium carbonate solution B is prepared from industrial-grade sodium carbonate and industrial water, and the mass concentration of the sodium carbonate solution B is 12.5%;

the sodium hydroxide solution C is sodium hydroxide solution discharged from an electric tank by ionic membrane caustic soda, the mass concentration of the sodium hydroxide solution C is 32%, the adding amount of sodium carbonate is controlled by the residual amount of the sodium carbonate after reaction, and the sodium carbonate overbasic amount is 0.47 g/L;

the adding amount of the sodium hydroxide is controlled by the residual amount of the reacted sodium hydroxide, and the excessive alkali amount of the sodium hydroxide is 0.26 g/L;

(3) raw water D obtained after calcium and magnesium removal reaction automatically flows into a flat ceramic membrane separation membrane pool, water insoluble substances such as calcium carbonate, magnesium hydroxide and silt are retained on the surface of the flat ceramic membrane through negative pressure suction of a suction pump, circulating saline water flow formed by scrubbing by gas is carried away from the surface of the flat ceramic membrane, and saline water penetrates through the flat ceramic membrane to obtain produced water E;

the concentrations of the individual components of the produced water E were as follows: sodium chloride about 10g/L, sodium sulfate 5000mg/L, Ca²⁺+Mg²⁺0.75mg/L and SS 0.46mg/L, the pilot plant achieved the expected target.

The aperture of the flat ceramic membrane is 0.05-0.1 micron, and the material is ball-milled alpha-Al₂O₃Porosity of>20 percent, and the structural form is a flat plate type;

the flat ceramic membrane adopts negative pressure suction and dead-end filtration, the filtration pressure is 0.048Mpa, the air scrubbing and the membrane stack with a special structure can enable the saline water to circularly flow inside and outside the membrane stack to form cross-flow motion on the surface of the membrane, the salt mud is prevented from being accumulated on the surface of the membrane, and the enriched salt mud and partial saline water enter a sludge tank;

(4) calcium carbonate, magnesium hydroxide and salt slurry which are carried away from the surface of the membrane by the water circulation flow formed by scrubbing are deposited in a mud bucket at the bottom of the membrane pool, and the salt slurry F is periodically discharged to a slag pool:

the concentrations of the various components of the salt slurry F were as follows: 10g/L of sodium chloride, 5g/L of sodium sulfate and less than or equal to 3.2 percent of SS;

(5) and pumping the salt slurry F into a sludge dewatering device through a slurry pump for dewatering to obtain a filtrate G and salt slurry H, and returning the filtrate G after the salt slurry is dewatered to the flat ceramic membrane pool.

Through experiments, high-salt inorganic wastewater is taken, sodium hydroxide and sodium carbonate are added, and the sodium hydroxide is controlled to be about 0.26 g/L; sodium carbonate of about 0.47g/L, the original sulfate radical concentration is kept unchanged, and Ca in the filtrate is filtered by a flat ceramic membrane²⁺+Mg²⁺The concentration of the sodium chloride in the sodium chloride solution is 0.75mg/L, the scaling hidden danger of a nanofiltration membrane and a reverse osmosis membrane can be avoided under the condition, and meanwhile, calcium sulfate scaling of an evaporator can be avoided only by periodically discharging old brine to a wastewater adjusting tank in evaporation, so that zero emission stable operation is realized.

Example 3

The prior refining process of sodium chlorate produced brine by adopting a Dalmati clarifying barrel, a sand filter and a carbon tube for filtration has the characteristics of long flow, large investment and land occupation, high labor intensity, difficult management and poor brine quality, and the refined brine is generally Ca²⁺+Mg²⁺Are all about 10mg/L, SS>5mg/L。

The prior sodium chlorate brine is filtered and refined, and the treatment capacity is 45m³The raw material brine contains 100g/L of sodium chloride, 530g/L of sodium chlorate and Ca²⁺+Mg²⁺100mg/L, containing a small amount of scrap iron, etc. Adopts the processes of adding sodium hydroxide to remove magnesium, removing calcium by sodium carbonate and filtering and refining by flat ceramic membrane to produce Ca in the refined clear liquid²⁺+Mg²⁺Not more than 1mg/L, and the content of water-insoluble substances (SS) not more than 1 mg/L. The specific method comprises the following steps:

(1) the concentration of the individual components of the sodium chlorate brine A is as followsThe following: 100g/L of sodium chloride, 530g/L of sodium chlorate and Ca²⁺+Mg²⁺100mg/L, a small amount of scrap iron and the like;

(2) adding a sodium carbonate solution B and a sodium hydroxide solution C serving as refining agents into a sodium chlorate brine A, feeding the sodium chlorate solution A and the sodium hydroxide solution C into a reactor, wherein the reactor is of a cylindrical structure, the top of the reactor is provided with a stirrer, two reactors are connected in series, the reactors are connected by a pipeline, and the sodium chlorate solution B and the sodium hydroxide solution C are fed in and out from the lower part of the reactor 1;

the concentrations of the individual components of the sodium chlorate brine D are as follows: 100g/L sodium chloride, 530g/L sodium chlorate, Ca (OH)₂195mg/L，Mg(OH)₂ 45mg/L，SS250mg/L；

The sodium carbonate solution B is prepared from industrial-grade sodium carbonate and industrial water, and the mass concentration of the sodium carbonate solution B is 12.5%;

the sodium hydroxide solution C adopts industrial sodium hydroxide solution with the mass concentration of 32 percent,

the adding amount of the sodium carbonate is controlled by the residual amount of the sodium carbonate after reaction, and the sodium carbonate overbased amount is 0.5 g/L;

the adding amount of the sodium hydroxide is controlled by the residual amount of the reacted sodium hydroxide, and the excessive alkali amount of the sodium hydroxide is 0.2 g/L;

(3) the sodium chlorate brine D obtained after the calcium and magnesium removal reaction automatically flows into a flat ceramic membrane separation membrane pool, water-insoluble substances such as calcium carbonate, magnesium hydroxide and scrap iron are retained on the surface of the flat ceramic membrane through negative pressure suction of a suction pump, a circulating brine flow formed by scrubbing with gas is carried away from the surface of the flat ceramic membrane, and the brine penetrates through the flat ceramic membrane to obtain refined sodium chlorate brine E;

the concentrations of the individual components of the purified sodium chlorate brine E were as follows:

the concentrations of the individual components of the purified sodium chlorate brine are as follows: sodium chloride about 100g/L, sodium chlorate 530g/L, Ca²⁺+Mg²⁺0.82mg/L and SS 0.45mg/L, the expected target was achieved.

The aperture of the flat ceramic membrane is 0.05-0.1 micron, and the material is ball-milled alpha-Al₂O₃Porosity of>20 percent, and the structural form is a flat plate type;

the flat ceramic membrane adopts negative pressure suction and dead-end filtration, the filtration pressure is 0.048Mpa, the air scrubbing and the membrane stack with a special structure can enable the saline water to circularly flow inside and outside the membrane stack to form cross-flow motion on the surface of the membrane, the salt mud is prevented from being accumulated on the surface of the membrane, and the enriched salt mud and partial saline water enter a sludge tank;

(4) calcium carbonate, magnesium hydroxide and scrap iron which are removed from the surface of the membrane by the circulating flow of the brine formed by gas scrubbing are deposited in a mud bucket at the bottom of the membrane pool, and the brine sludge F is periodically discharged to a slag pool:

the concentrations of the various components of the salt slurry F were as follows: 100g/L of sodium chloride, 530g/L of sodium chlorate and less than or equal to 3.8 percent of SS;

(5) and pumping the salt slurry F into a sludge dewatering device through a slurry pump for dewatering to obtain a filtrate G and salt slurry H, and returning the filtrate G after the salt slurry is dewatered to the flat ceramic membrane pool.