Method for removing calcium and magnesium ions in brine by using industrial by-product glaubers salt

Abstract

The present application relates to the field of by-product mirabilite resource utilization, to solve the problem of high cost of two-alkali method for removing calcium and magnesium, and provides a method for removing calcium and magnesium ions in brine by using industrial by-product mirabilite, comprising the following steps: S100, adding lime and part of the by-product mirabilite in the brine, removing the precipitate to obtain a pretreated liquid; S200, adding the remaining by-product mirabilite in the pretreated liquid, removing the precipitate to obtain a final treated liquid; the by-product mirabilite comprises sodium sulfate and sodium carbonate; the brine comprises sodium sulfate, calcium sulfate and magnesium sulfate. The present application uses industrial by-product mirabilite to purify the brine, not only reduces the economic cost of the existing brine purification process, but also solves the problem of by-product treatment in the upstream industry, and has generalizability. In step S100, the magnesium hydroxide floc generated by the reaction of lime is used as a crystal seed to adsorb and co-precipitate fine calcium sulfate crystals separated out due to the common ion effect, realizing the cooperative removal of magnesium and part of calcium, and the precipitation efficiency is higher.

Description

Technical Field

[0001] This invention relates to the field of resource utilization of by-product sodium sulfate, and more specifically, to a method for removing calcium and magnesium ions from brine using industrial by-product sodium sulfate. Background Technology

[0002] Current brine purification technologies primarily rely on primary calcium and magnesium removal from flue gas and the two-alkali method. However, with the continuous development of green and environmentally friendly technologies, the processes that provide flue gas are gradually disappearing. For example, after coal-fired boilers are converted to electricity, the free carbon dioxide source disappears or decreases, making it difficult for flue gas calcium and magnesium removal processes to operate effectively. If the industry's traditional "soda ash-caustic soda method" is used as an alternative, high-value chemical raw materials need to be purchased externally, leading to a sharp increase in production costs and severely weakening the product's market competitiveness.

[0003] Currently, many industries produce sodium sulfate as a byproduct, which contains a large amount of alkali. For example, in the lithium battery industry, sodium sulfate with high alkali content is very difficult to dispose of, and manufacturers have to pay for treatment. Therefore, utilizing byproduct sodium sulfate for brine purification can not only solve the problem of byproduct disposal for manufacturers, but also solve the problem of excessively high brine purification costs. Summary of the Invention

[0004] The purpose of this invention is to provide a method for removing calcium and magnesium ions from brine using sodium sulfate, an industrial by-product. This method not only realizes the resource utilization of sodium sulfate, but also solves the problem of excessively high cost of calcium and magnesium removal using the two-alkali method.

[0005] The embodiments of the present invention are achieved through the following technical solutions:

[0006] A method for removing calcium and magnesium ions from brine using sodium sulfate, an industrial byproduct, includes the following steps:

[0007] S100. After adding lime and some by-product sodium sulfate to the brine, remove the precipitate to obtain the pretreated solution.

[0008] S200. After adding the remaining by-product sodium sulfate to the pretreatment solution, remove the precipitate to obtain the final treatment solution.

[0009] The by-product sodium sulfate includes sodium sulfate and sodium carbonate; the brine includes sodium sulfate, calcium sulfate and magnesium sulfate.

[0010] This invention utilizes the reaction of carbonate ions with calcium ions to remove calcium ions. To avoid or reduce competition and interference between magnesium ions and calcium ions, this invention first uses lime to remove magnesium ions, and then uses sodium carbonate to remove calcium ions. In step S100, during precipitate removal, in addition to the magnesium hydroxide generated by the reaction, calcium sulfate and magnesium sulfate precipitates present in the brine are also removed. The sodium sulfate in the by-product sodium sulfate can increase the sodium sulfate concentration in the brine, while the dissolution of calcium sulfate exhibits a dynamic equilibrium. When the amount of sulfate ions in the system increases, its solubility decreases. That is, when by-product sodium sulfate is added, additional calcium sulfate precipitates will precipitate in the brine. Therefore, when by-product sodium sulfate is added in step S100, the precipitation removal process can remove more calcium sulfate. After the calcium sulfate precipitate is removed, the calcium sulfate originally dissolved in the system precipitates and continues to step S200. Compared to adding all the by-product sodium sulfate in step S200, the amount of calcium sulfate removed is higher.

[0011] In step S100, magnesium hydroxide flocs generated by the lime reaction are used as seed crystals to adsorb and co-precipitate the fine calcium sulfate crystals precipitated due to the common ion effect, thereby achieving the synergistic removal of magnesium and some calcium and resulting in higher precipitation efficiency.

[0012] Preferably, in step S100, the pH value of the system is 10-11 and the temperature is 40-60℃.

[0013] Since the main purpose of step S100 is to remove magnesium ions, and magnesium hydroxide precipitation requires a high pH value, by controlling the pH value, the selective precipitation advantage of hydroxide ions on magnesium ions is utilized to inhibit the formation of magnesium carbonate, while the common ion effect is used to promote the precipitation of calcium sulfate.

[0014] The solubility of calcium sulfate decreases with increasing temperature, showing a significant decrease above 40°C, which is conducive to the coagulation and sedimentation of magnesium hydroxide and reduces the tendency of magnesium carbonate to form.

[0015] Adding pH and temperature not only helps calcium and magnesium ions precipitate, but also accelerates sedimentation and reduces water retention time.

[0016] Preferably, the brine comprises: 200-300 g / L sodium sulfate, 2-4 g / L calcium sulfate, and 0.1-0.3 g / L magnesium sulfate.

[0017] Preferably, under the premise that the residual amount of magnesium ions in the pretreatment solution is ≤ a set threshold, the first relationship curve between the mass ratio of sodium sulfate to sodium carbonate, the amount of sodium sulfate used, and the sedimentation rate in the by-product sodium sulfate in step S100 is obtained.

[0018] Based on the first relationship curve, the range of mass ratios with sedimentation velocity ≥ velocity threshold and the range of sodium sulfate dosage are obtained.

[0019] Although carbonate ions are less competitive for magnesium ions than hydroxide ions, they inevitably affect the precipitation effect of magnesium ions. Therefore, it is necessary to comprehensively consider the removal efficiency of magnesium ions and the removal amount of calcium ions in step S100.

[0020] When obtaining the first relationship curve, this invention does not directly use the amount of calcium ions processed or the processing time as parameters, at least because the sedimentation rate implicitly represents the amount and rate of precipitation.

[0021] Since the composition of sodium sulfate produced as a byproduct of different industries varies, the required mass ratio can be achieved by compounding sodium sulfate from different sources.

[0022] Given a fixed brine composition, system pH, system temperature, and lime dosage, different mass ratios of by-product sodium sulfate were added. The rate at which the precipitate completely separated and the time it took for the precipitate to settle to the bottom were observed to obtain the expected mass ratio range. Based on the existing raw material composition, raw materials within the mass ratio range were selected, or raw materials within the mass ratio range were compounded.

[0023] The threshold can be set as needed, for example, according to factory standards or national standards, using the maximum concentration of magnesium ions that can exist in the final treatment solution as the threshold.

[0024] The velocity threshold can be set as needed and can be characterized by time. It is characterized by the minimum time required for no new precipitate to form in the system, and for the precipitate to settle to the upper surface at a height ≤ a set value or for the rate of change of the upper surface height to be ≤ a set value.

[0025] The amount of lime used can be selected according to the magnesium ion content in the brine. In order to achieve complete removal of magnesium ions, an appropriate amount of lime can be added in excess according to the reaction equation.

[0026] Preferably, the lower and upper surface heights of the sediment are acquired in real time to obtain the shortest time required for the lower surface height to be ≤ a height threshold and the rate of change of the upper surface height to be ≤ a rate threshold; the sedimentation velocity is characterized by the shortest time.

[0027] The sediment aggregate is considered as a whole settling body, and its shape is usually adapted to the shape of the container. The height threshold can be as close as possible to the bottom wall height of the container or directly equal to the bottom wall height of the container.

[0028] After fitting the curve of the upper surface height versus time, the rate of change of the upper surface height can be obtained from the first derivative of the curve function.

[0029] The rate threshold can be set according to the actual situation. When the height of the upper surface hardly changes, it indicates that the precipitation reaction and sedimentation process are basically complete.

[0030] Preferably, the system sidewall image is obtained, and the upper surface height and lower surface height are obtained from the sidewall image.

[0031] Existing image recognition technologies can be used to obtain images of the system's sidewalls. During the experiment, the brine can be placed in a transparent container so that the images of the system's sidewalls can show the location of the sediment in the brine.

[0032] When acquiring sidewall images, images of the entire sidewall can be obtained, or images in the four cardinal directions (north, south, east, and west) can be acquired. After the images are converted to grayscale, the grayscale values ​​are used to distinguish between parts belonging to the settlement body and parts outside the settlement body.

[0033] When obtaining the heights of the upper and lower surfaces, the heights may differ at different locations, which can be directly represented by the average. The more data points collected, the more representative the average will be.

[0034] Preferably, an organic flocculant is added in both steps S100 and S200.

[0035] The high salinity of brine promotes flocculation, but the effectiveness of inorganic flocculants may be weakened by the already strong coagulation effect of high ionic strength, and they may also introduce new impurity ions. Therefore, this invention uses organic polymeric flocculants, which mainly connect fine particles and micro-flocs into large, dense flocs through the adsorption and bridging effect of polymer chains. Nonionic polyacrylamide can be selected as the organic flocculant. Its molecular chains are uncharged, and it adsorbs particles through hydrogen bonds via amide groups on the molecular chains. Its effectiveness is less affected by the pH and salinity of the solution, and it has good stability in a wide pH range and high salinity environment, making it more suitable for brine with complex compositions.

[0036] Preferably, the relationship between the amount of organic flocculant added and the settling velocity is obtained to determine the actual amount of organic flocculant added.

[0037] Generally, as the amount of organic flocculant added increases, the settling velocity gradually increases and eventually stabilizes. Therefore, the minimum amount of organic flocculant added that meets the expected settling velocity can be obtained by looking at the relationship curve between the amount of organic flocculant added and the settling velocity.

[0038] Preferably, the composition of the by-product sodium sulfate in step S200 is the same as that in step S100.

[0039] In step S200, the relationship between the amount of by-product sodium sulfate added and the precipitation reaction time is obtained, thereby obtaining the actual amount of sodium sulfate added.

[0040] Under the premise of using the actual amount of sodium sulfate added, the relationship between settling time and flocculant addition amount is obtained, and then the actual amount of flocculant added is obtained.

[0041] Since magnesium ions are almost absent in step S200, magnesium ions have little effect on the sedimentation rate of calcium ions. In this invention, the precipitation reaction time is used as an indicator of the amount of by-product sodium sulfate added in step S200, and the increase in sedimentation rate is mainly due to the action of flocculants.

[0042] Preferably, the final treated liquid contains ≤0.35g / L CaSO4, 1.0-2.0g / L Na2CO3, and ≤0.25g / L NaOH.

[0043] The present invention has at least the following beneficial effects:

[0044] This invention utilizes sodium sulfate, an industrial byproduct, to purify brine, which not only reduces the economic cost of existing brine purification processes but also solves the problem of byproduct disposal in upstream industries, making it scalable.

[0045] To avoid or reduce competition and interference between magnesium and calcium ions, this invention first uses lime to remove magnesium ions, and then uses sodium carbonate to remove calcium ions. In step S100, the removal of precipitates includes not only the magnesium hydroxide generated in the reaction, but also calcium sulfate and magnesium sulfate precipitates present in the brine. The sodium sulfate in the by-product sodium sulfate can increase the concentration of sodium sulfate in the brine, while the dissolution of calcium sulfate exhibits a dynamic equilibrium. When the amount of sulfate ions in the system increases, its solubility decreases. That is, when by-product sodium sulfate is added, additional calcium sulfate precipitates will precipitate in the brine. Therefore, when by-product sodium sulfate is added in step S100, the precipitation removal process can remove more calcium sulfate. After the calcium sulfate precipitate is removed, the calcium sulfate originally dissolved in the system precipitates and continues to step S200. Compared to adding all the by-product sodium sulfate in step S200, the amount of calcium sulfate removed is higher.

[0046] In step S100, magnesium hydroxide flocs generated by the lime reaction are used as seed crystals to adsorb and co-precipitate the fine calcium sulfate crystals precipitated due to the common ion effect, thereby achieving the synergistic removal of magnesium and some calcium and resulting in higher precipitation efficiency. Detailed Implementation

[0047] To make the objectives, methods, and advantages of the embodiments of the present invention clearer, the methods in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0048] Example 1: A method for removing calcium and magnesium ions from brine using sodium sulfate, an industrial byproduct, includes the following steps:

[0049] S100: After adding lime, some by-product sodium sulfate, and nonionic polyacrylamide to the brine, the precipitate is removed to obtain the pretreated solution.

[0050] S200. After adding the remaining by-product sodium sulfate and nonionic polyacrylamide to the pretreatment solution, the precipitate is removed to obtain the final treatment solution.

[0051] The by-product sodium sulfate includes sodium sulfate and sodium carbonate; the brine includes sodium sulfate, calcium sulfate and magnesium sulfate.

[0052] In step S100, the pH of the system is 10 and the temperature is 40°C.

[0053] The brine contains: 200g / L sodium sulfate, 2g / L calcium sulfate, and 0.1g / L magnesium sulfate.

[0054] Example 2: A method for removing calcium and magnesium ions from brine using industrial by-product sodium sulfate, comprising the following steps:

[0055] S100: After adding lime, some by-product sodium sulfate, and nonionic polyacrylamide to the brine, the precipitate is removed to obtain the pretreated solution.

[0056] S200. After adding the remaining by-product sodium sulfate and nonionic polyacrylamide to the pretreatment solution, the precipitate is removed to obtain the final treatment solution.

[0057] The by-product sodium sulfate includes sodium sulfate and sodium carbonate; the brine includes sodium sulfate, calcium sulfate and magnesium sulfate.

[0058] In step S100, the pH of the system is 11 and the temperature is 60°C.

[0059] The brine contains: 300g / L sodium sulfate, 4g / L calcium sulfate, and 0.3g / L magnesium sulfate.

[0060] Example 3: A method for removing calcium and magnesium ions from brine using industrial by-product sodium sulfate, comprising the following steps:

[0061] S100: After adding lime, some by-product sodium sulfate, and nonionic polyacrylamide to the brine, the precipitate is removed to obtain the pretreated solution.

[0062] S200. After adding the remaining by-product sodium sulfate and nonionic polyacrylamide to the pretreatment solution, the precipitate is removed to obtain the final treatment solution.

[0063] The by-product sodium sulfate includes sodium sulfate and sodium carbonate; the brine includes sodium sulfate, calcium sulfate and magnesium sulfate.

[0064] In step S100, the pH of the system is 10.5 and the temperature is 50°C.

[0065] The brine contains: 250g / L sodium sulfate, 3g / L calcium sulfate, and 0.2g / L magnesium sulfate.

[0066] Example 4: In order to obtain the raw material parameters in steps S100 and S200, this method is further improved based on Examples 1-3. In this example, the method includes: under the premise that the amount of magnesium ions remaining in the pretreatment liquid is ≤ a set threshold, obtaining the first relationship curve between the mass ratio of sodium sulfate to sodium carbonate, the amount of sodium sulfate used and the sedimentation rate in the by-product sodium sulfate in step S100.

[0067] Based on the first relationship curve, the range of mass ratios with sedimentation velocity ≥ velocity threshold and the range of sodium sulfate dosage are obtained.

[0068] In the specific implementation process, although carbonate ions are less competitive for magnesium ions than hydroxide ions, they inevitably affect the precipitation effect of magnesium ions. Therefore, it is necessary to comprehensively consider the removal efficiency of magnesium ions and the removal amount of calcium ions in step S100.

[0069] When obtaining the first relationship curve, this invention does not directly use the amount of calcium ions processed or the processing time as parameters, at least because the sedimentation rate implicitly represents the amount and rate of precipitation.

[0070] Since the composition of sodium sulfate produced as a byproduct of different industries varies, the required mass ratio can be achieved by compounding sodium sulfate from different sources.

[0071] Given a fixed brine composition, system pH, system temperature, and lime dosage, different mass ratios of by-product sodium sulfate were added. The rate at which the precipitate completely separated and the time it took for the precipitate to settle to the bottom were observed to obtain the expected mass ratio range. Based on the existing raw material composition, raw materials within the mass ratio range were selected, or raw materials within the mass ratio range were compounded.

[0072] The threshold can be set as needed, for example, according to factory standards or national standards, using the maximum concentration of magnesium ions that can exist in the final treatment solution as the threshold.

[0073] The velocity threshold can be set as needed and can be characterized by time. It is characterized by the minimum time required for no new precipitate to form in the system, and for the precipitate to settle to the upper surface at a height ≤ a set value or for the rate of change of the upper surface height to be ≤ a set value.

[0074] The amount of lime used can be selected according to the magnesium ion content in the brine. In order to achieve complete removal of magnesium ions, an appropriate amount of lime can be added in excess according to the reaction equation.

[0075] Example 5: In order to make the settling velocity better characterize the rate of precipitation reaction, an improvement was made based on Example 4. In this example, the method includes: real-time acquisition of the lower surface height and upper surface height of the settling body, and obtaining the shortest time used when the lower surface height is ≤ a height threshold and the rate of change of the upper surface height is ≤ a rate threshold; the settling velocity is characterized by the shortest time.

[0076] In practice, the sediment aggregate is regarded as a whole sedimentation body. Its shape is usually adapted to the shape of the container, and the height threshold can be as close as possible to the bottom wall height of the container or directly equal to the bottom wall height of the container.

[0077] After fitting the curve of the upper surface height versus time, the rate of change of the upper surface height can be obtained from the first derivative of the curve function.

[0078] The rate threshold can be set according to the actual situation. When the height of the upper surface hardly changes, it indicates that the precipitation reaction and sedimentation process are basically complete.

[0079] Example 6: Obtain the sidewall image of the system, and obtain the upper surface height and lower surface height based on the sidewall image.

[0080] In the specific implementation process, existing image recognition technology can be used to obtain images of the system's sidewalls. During the experiment, the brine can be placed in a transparent container so that the images of the system's sidewalls can show the location of the sediment in the brine.

[0081] When acquiring sidewall images, images of the entire sidewall can be obtained, or images in the four cardinal directions (north, south, east, and west) can be acquired. After the images are converted to grayscale, the grayscale values ​​are used to distinguish between parts belonging to the settlement body and parts outside the settlement body.

[0082] When obtaining the heights of the upper and lower surfaces, the heights may differ at different locations, which can be directly represented by the average. The more data points collected, the more representative the average will be.

[0083] Example 7: In order to accelerate sedimentation and reduce hydraulic residence time, an improvement was made based on Example 4. In this example, organic flocculants were added in both steps S100 and S200.

[0084] In practice, the high salinity of brine promotes flocculation, while the effectiveness of inorganic flocculants may be weakened by the already strong coagulation effect of high ionic strength, and may introduce new impurity ions. Therefore, this invention uses organic polymeric flocculants, which mainly connect fine particles and micro-flocs into large, dense flocs through the adsorption and bridging effect of polymer chains. Nonionic polyacrylamide can be selected as the organic flocculant. Its molecular chains are uncharged, and it adsorbs particles through hydrogen bonds via amide groups on the molecular chains. Its effectiveness is less affected by solution pH and salinity, and it has good stability in a wide pH range and high salinity environment, making it more suitable for brine with complex composition.

[0085] Example 8: In order to minimize the amount of organic flocculant added, an improvement was made based on Example 7. In this example, the relationship between the amount of organic flocculant added and the settling velocity was obtained to obtain the actual amount of organic flocculant added.

[0086] In practice, the settling velocity usually increases with the increase of the amount of organic flocculant added, and then tends to stabilize. Therefore, the minimum amount of organic flocculant added that meets the expected settling velocity can be obtained by looking at the relationship curve between the amount of organic flocculant added and the settling velocity.

[0087] Example 9: In order to reduce the difficulty of the process, an improvement was made based on Examples 1-8. In this example, the composition of the by-product sodium sulfate in step S200 is the same as that in step S100.

[0088] In step S200, the relationship between the amount of by-product sodium sulfate added and the precipitation reaction time is obtained, thereby obtaining the actual amount of sodium sulfate added.

[0089] Under the premise of using the actual amount of sodium sulfate added, the relationship between settling time and flocculant addition amount is obtained, and then the actual amount of flocculant added is obtained.

[0090] In the specific implementation process, the by-product sodium sulfate is used in the same proportion in steps S100 and S200, which simplifies the process. Since there are almost no magnesium ions in step S200, the effect of magnesium ions on the sedimentation rate of calcium ions is small. This invention uses the precipitation reaction time as an indicator of the amount of by-product sodium sulfate added in step S200, and the increase in sedimentation rate is mainly due to the effect of flocculants.

[0091] As an example, images of the system's sidewalls are continuously acquired, converted to grayscale, and then the grayscale values ​​are used to obtain the area of ​​color patches representing precipitates or sediments. The time it takes for the color patch area to stop increasing represents the precipitation reaction time. As an example, the definition of "no longer increasing" can be determined based on actual conditions; for example, when the rate of increase in color patch area is ≤ a set threshold, it is determined that the color patch area has stopped increasing.

[0092] Example 10: The final treated solution contains ≤0.35g / L CaSO4, 1.0-2.0g / L Na2CO3, and ≤0.25g / L NaOH.

[0093] In the specific implementation process, the composition ratio of the final treatment liquid in this embodiment can be used as the treatment target to obtain the amount of by-product sodium sulfate.

[0094] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for removing calcium and magnesium ions from brine using sodium sulfate, an industrial byproduct, characterized in that, Includes the following steps: S100. After adding lime and some by-product sodium sulfate to the brine, remove the precipitate to obtain the pretreated solution. S200. After adding the remaining by-product sodium sulfate to the pretreatment solution, remove the precipitate to obtain the final treatment solution. The by-product sodium sulfate includes sodium sulfate and sodium carbonate; the brine includes sodium sulfate, calcium sulfate and magnesium sulfate.

2. The method according to claim 1, characterized in that, In step S100, the pH of the system is 10-11 and the temperature is 40-60℃.

3. The method according to claim 1, characterized in that, The brine includes: 200-300 g / L sodium sulfate, 2-4 g / L calcium sulfate, 0.1-0.3 g / L magnesium sulfate.

4. The method according to claim 3, characterized in that, Under the premise that the residual amount of magnesium ions in the pretreatment solution is less than or equal to the set threshold, the first relationship curve between the mass ratio of sodium sulfate to sodium carbonate, the amount of sodium sulfate used and the sedimentation rate in the by-product sodium sulfate in step S100 is obtained. Based on the first relationship curve, the range of mass ratios with sedimentation velocity ≥ velocity threshold and the range of sodium sulfate dosage are obtained.

5. The method according to claim 4, characterized in that, The lower and upper surface heights of the sediment are acquired in real time, and the shortest time required for the lower surface height to be less than or equal to a height threshold and the rate of change of the upper surface height to be less than or equal to a rate threshold is obtained; the sedimentation velocity is characterized by the shortest time.

6. The method according to claim 5, characterized in that, Obtain images of the system's sidewalls, and determine the height of the upper and lower surfaces based on these images.

7. The method according to claim 4, characterized in that, Organic flocculants are added in both steps S100 and S200.

8. The method according to claim 7, characterized in that, The relationship between the amount of organic flocculant added and the settling velocity was obtained to determine the actual amount of organic flocculant added.

9. The method according to any one of claims 1-8, characterized in that, The composition of the by-product sodium sulfate in step S200 is the same as that in step S100. In step S200, the relationship between the amount of by-product sodium sulfate added, the amount of flocculant added, and the sedimentation reaction time is obtained, thereby obtaining the actual amount of by-product sodium sulfate added and the actual amount of flocculant added.

10. The method according to claim 9, characterized in that, The final treated solution contains ≤0.35g / L CaSO4, 1.0-2.0g / L Na2CO3, and ≤0.25g / L NaOH.