A zero-emission hardening process using aluminum-based adsorbent materials

Abstract

This invention belongs to the field of water treatment and provides a zero-discharge hardness removal process using aluminum-based adsorbents. The process involves uniformly mixing sodium and aluminum salts in a solution to obtain a mixed solution; performing ion exchange with a cation exchange resin using this mixed solution to obtain an aluminum-based adsorbent; treating water with this aluminum-based adsorbent to adsorb calcium or magnesium ions, forming nano-sized aluminum hydroxide precipitates that adhere to the aluminum-based adsorbent framework, and collecting the effluent; regenerating the aluminum-based adsorbent with carbon dioxide gas to displace calcium or magnesium bicarbonate, collecting the effluent, and allowing it to settle to form calcium carbonate or magnesium carbonate precipitates, thus obtaining the final product. This hardness removal process does not use any chemical agents, only carbon dioxide gas as a regenerator. The regeneration process produces no waste liquid and simultaneously achieves carbon dioxide fixation and hardness ion removal, meeting the requirement of zero discharge.

Description

Technical Field

[0001] This invention belongs to the field of water treatment, specifically a zero-emission hardening removal process using aluminum-based adsorption materials. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Traditional methods for removing water hardness often employ chemical agents, such as lime softening and chemical dosing. While these methods remove hardness, they frequently generate large amounts of wastewater, making true zero discharge difficult. Furthermore, the use of chemical agents may introduce new pollutants, increasing the difficulty and cost of subsequent treatment.

[0004] Some studies have explored the use of aluminum ion-modified resins to remove hardness ions from water, leveraging the resin's hydrolytic polymerization properties to generate hydroxyl or bimetallic oxides, thereby enhancing the ion exchange resin's removal capacity for hardness ions. However, these methods require the introduction of strong acids for resin regeneration, which is complex and environmentally hazardous.

[0005] Therefore, there is an urgent need to develop an environmentally friendly, efficient, and zero-emission water hardness removal process. Summary of the Invention

[0006] To address the aforementioned issues, this invention provides a zero-emission hardening removal process using aluminum-based adsorbent materials. By controlling the aluminum ion concentration and adding a low concentration of dispersant, this invention prepares an aluminum-based adsorbent material. During ion exchange, the aluminum hydroxide precipitate generated by this adsorbent material has a particle size between 5 nm and 70 nm and adheres to the adsorbent material framework. This allows the adsorbent material to be regenerated using a low concentration of carbon dioxide, achieving a regeneration efficiency of over 90% and realizing zero wastewater discharge.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a zero-emission hardening removal process using aluminum-based adsorbent materials, comprising:

[0009] Sodium salt and aluminum salt are mixed evenly in the solution to obtain a mixed solution;

[0010] The aluminum-based adsorbent material is obtained by ion exchange between the mixed solution and a cation exchange resin.

[0011] The aluminum-based adsorbent material is used to treat water, adsorbing calcium or magnesium ions to form nano-sized aluminum hydroxide precipitate that adheres to the aluminum-based adsorbent material framework, and the effluent is collected.

[0012] The aluminum-based adsorbent material is regenerated using carbon dioxide gas to dissolve the nano-sized aluminum hydroxide precipitate, displacing calcium bicarbonate or magnesium bicarbonate. The water is collected, allowed to stand, and calcium carbonate or magnesium carbonate precipitate is formed, thus obtaining the product.

[0013] When the aluminum-based adsorbent material prepared in this invention treats water containing hardness ions (such as calcium and magnesium ions), the hardness ions displace the aluminum ions from the exchange sites, forming nanoscale aluminum hydroxide precipitates that adhere to the adsorbent material framework. Simultaneously, based on the principle of electroneutrality, for every amount of hardness ions removed, an equivalent amount of alkalinity ions (such as hydroxide, bicarbonate, and carbonate ions) are also removed. Taking calcium ions as an example, the specific reaction process is as follows:

[0014] ;

[0015] ;

[0016] ;

[0017] The overall reaction is:

[0018] ;

[0019] Once the aluminum-based adsorbent has completely adsorbed the hardness ions, it no longer has the ability to remove hardness, and therefore needs to be regenerated. The specific regeneration method is as follows.

[0020] (1) When carbon dioxide (CO2) gas is introduced, carbonic acid is produced:

[0021] ;

[0022] (2) Carbonic acid dissociates to form protons:

[0023] ;

[0024] (3) The protons formed can dissolve the aluminum hydroxide precipitated on the adsorbent material framework and release aluminum ions:

[0025] ;

[0026] (4) Low concentrations of aluminum ions utilize the high selectivity of the adsorption material to exchange hardness ions at the sites:

[0027] ;

[0028] (5) The formed calcium bicarbonate solution precipitates calcium carbonate after being removed from the acidic environment of the adsorbent material:

[0029] .

[0030] This invention has discovered that during ion exchange, if the particle size of the aluminum hydroxide precipitate is between 5 nm and 70 nm, it can adhere to the framework of the adsorbent material and be regenerated by carbon dioxide. Therefore, in this invention, when aluminum ions are loaded, a dispersant (such as sodium chloride, sodium polyacrylate, sodium hexametaphosphate, etc.) is used to first occupy some of the ion exchange sites on the resin, thus dispersing the distribution of aluminum ions on the resin. In subsequent water treatment, sodium ions exchange with calcium or magnesium ions, but they cannot be regenerated by CO2. Furthermore, because the sodium ion content is low, it has little impact on the overall treatment performance of the resin. Therefore, preferably, the mass concentration of the sodium salt is 0.002%-0.005% to obtain the desired dispersion effect and ensure the water treatment performance of the resin.

[0031] In order to obtain a better dispersion effect, the present invention also studied the types of sodium salts. Preferably, the sodium salt is sodium chloride, sodium polyacrylate or sodium hexametaphosphate.

[0032] The concentration of aluminum salt solution is also an important factor affecting the dispersibility of aluminum ions. Therefore, the present invention has studied the concentration of aluminum salt. Preferably, the mass concentration of the aluminum salt solution is 0.1%-3.0%.

[0033] In order to obtain a better dispersion effect, the present invention also studied the types of aluminum salts, and preferably, the aluminum salt is aluminum chloride.

[0034] To ensure the ion exchange efficiency of sodium ions, aluminum ions and resin, this invention studies the solid-liquid ratio of cation exchange resin and mixed solution. Preferably, the solid-liquid ratio of cation exchange resin to aluminum salt solution is 1:50-60.

[0035] In order to enable sodium ions and aluminum ions to effectively occupy the ion exchange sites of the resin, the present invention studied the contact time between the two. Preferably, the contact time between the mixed solution and the cation exchange resin is 10 min to 15 min.

[0036] Cation exchange resins can exchange ions with sodium and aluminum salts and remove hardness ions. In order to obtain better hardness removal effect, the present invention studies the type of cation exchange resin. Preferably, the cation exchange resin is a strong acid cation exchange resin.

[0037] Unlike traditional methods, the nano-sized aluminum hydroxide precipitate of the present invention can adhere to the framework of the ion exchange resin and can be regenerated by CO2. Therefore, the present invention studies the particle size of the nano-sized aluminum hydroxide precipitate, and preferably, the particle size of the nano-sized aluminum hydroxide precipitate is 2nm-70nm.

[0038] The partial pressure of carbon dioxide affects the regeneration efficiency. Therefore, the present invention optimizes the partial pressure of carbon dioxide. Preferably, the partial pressure of carbon dioxide is 1.5 kg-10 kg.

[0039] In summary, the hardness removal process of this invention does not use any chemical agents, utilizing only carbon dioxide gas. The regeneration process generates no waste liquid; the hardness ions removed from the water are separated in the form of precipitation, truly achieving zero discharge. Throughout the hardness removal process, hardness ions are ultimately separated from the influent as carbonate precipitates, simultaneously achieving both carbon dioxide fixation and hardness ion removal.

[0040] Beneficial effects of the present invention

[0041] (1) The hardness removal process of the present invention does not use any chemical agents, but only carbon dioxide gas as a regenerator. The regeneration process does not produce waste liquid, and the hardness ions are finally separated from the influent in the form of carbonate precipitate. At the same time, carbon dioxide fixation and hardness ion removal are achieved, thus meeting the requirements of zero emission.

[0042] (2) The aluminum-based adsorbent material of the present invention remains structurally stable at 50°C and maintains its hardness removal performance, making it suitable for in-situ hardness removal processes in high-temperature water bodies such as boiler wastewater and circulating cooling water.

[0043] (3) The present invention has a simple process, is easy to operate, has low cost, and is easy to promote and apply. Attached Figure Description

[0044] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0045] Figure 1 This is a schematic diagram of calcium ion exchange with aluminum-based adsorbent materials;

[0046] Figure 2 This is a schematic diagram of the formation of nanoscale aluminum hydroxide precipitate by aluminum ions during ion exchange.

[0047] Figure 3 This is a schematic diagram of the reaction between carbon dioxide and nano-sized aluminum hydroxide precipitate.

[0048] Figure 4 This is a schematic diagram of a carbon dioxide regenerated aluminum-based adsorbent material;

[0049] Figure 5 This is a graph showing the change in calcium ion concentration during the treatment process using aluminum-based adsorbent materials in Example 1;

[0050] Figure 6This is a graph showing the change in calcium ion concentration during the second water production experiment of the aluminum-based adsorbent material in Example 1;

[0051] Figure 7 This is a graph showing the change in calcium ion concentration during the treatment process using aluminum-based adsorbent materials in Example 2;

[0052] Figure 8 This is a graph showing the change in calcium ion concentration during the second water production experiment of the aluminum-based adsorbent material in Example 2;

[0053] Figure 9 This is a graph showing the change in calcium ion concentration during the treatment process using aluminum-based adsorbent materials in Example 3. Detailed Implementation

[0054] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0055] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0056] Example 1

[0057] In response to the requirement for mining wastewater to meet discharge standards, the actual wastewater from a mine in Shandong was treated, and the water quality was as follows:

[0058] Table 1 Wastewater Indicators of a Mine in Shandong

[0059]

[0060] Examples of hardness removal in this water quality according to the present invention are as follows:

[0061] The preparation of aluminum-based adsorbent materials includes:

[0062] (1) Sodium chloride and aluminum chloride are added to water in sequence and mixed evenly to obtain a mixed solution, wherein the mass concentration of sodium chloride is 0.002% and the mass concentration of aluminum chloride is 1%.

[0063] (2) Aluminum salt modification: The cation exchange resin and the mixed solution prepared in step (1) are mixed at a solid-liquid ratio of 1:50 and adsorbed under stirring for 10 minutes to obtain aluminum-based adsorbent material.

[0064] (3) Water treatment: Take 50 mL of the aluminum-based adsorbent material prepared in step (2) and fill it into an plexiglass column with an inner diameter of 15 mm to form a resin column. Pass the mining wastewater through the plexiglass column from top to bottom at a flow rate of 5 mL / min. Collect the treated water sample at the lower outlet of the plexiglass column and test its hardness. Record the changes in calcium ion concentration with the number of operating bed sections as follows: Figure 5 As shown.

[0065] from Figure 5 As can be seen, in the first 60 beds of the aluminum-based adsorbent material, the calcium ion concentration in the treated water remained at zero. It was not until the 70th bed that the material began to penetrate, and the calcium ion concentration in the effluent rose to about 10 mg / L. Subsequently, when the 100th bed was reached, the aluminum-based adsorbent material had basically penetrated.

[0066] (4) Regeneration: Regeneration was performed using carbon dioxide gas. The carbon dioxide cylinder was connected to the resin column, and the carbon dioxide pressure was adjusted to 2 kg. After regeneration continued for 60 minutes, the carbon dioxide was depressurized, and the water in the column was drained. After the discharged liquid was left to stand for 20 minutes, a white calcium carbonate precipitate formed. The test results showed that the calcium ion concentration in the discharged liquid was 500 mg / L. The separated calcium carbonate solid was dried and weighed to be 10.75 g. Based on this, the regeneration efficiency was approximately 95%.

[0067] A second permeate test was conducted after regeneration to verify the regeneration effect and the hardness removal effect after regeneration. Under the condition of keeping operating parameters and influent water quality constant, the effect of the second permeate test was as follows: Figure 6 As shown.

[0068] from Figure 6 As can be seen, the calcium ion concentration in the first ten beds of the second permeate was approximately 30 mg / L, subsequently decreasing to 0 mg / L. Therefore, to achieve complete hardness removal, this process requires flushing 5-10 beds after regeneration to remove residual solution from the reactor.

[0069] Example 2:

[0070] The influent was taken from wastewater from a coal mine in Shandong Province. Compared with Example 1, the calcium ion concentration of the coal mine wastewater was lower, at approximately 300 mg / L.

[0071] The preparation of aluminum-based adsorbent materials includes:

[0072] (1) Add sodium chloride and aluminum chloride to water in sequence, mix well to obtain a mixed solution, wherein the mass concentration of sodium chloride is 0.005% and the mass concentration of aluminum chloride is 3%.

[0073] (2) Aluminum salt modification: The cation exchange resin and the mixed solution prepared in step (1) are mixed at a solid-liquid ratio of 1:60 and adsorbed under stirring for 15 minutes to obtain aluminum-based adsorbent material.

[0074] (3) Water treatment: Take 20 mL of the aluminum-based adsorbent material prepared in step (1) and fill it into an organic glass column with an inner diameter of 7 mm to form a resin column. During operation, the influent flow rate of the actual wastewater sample is 10 mL / min, and 5 mL of effluent water sample is taken from every 20 beds for the detection of calcium ion concentration.

[0075] like Figure 7 As shown, the experimental results revealed that the calcium ion concentration in the effluent was 0 mg / L in the first 140 beds. Penetration began from the 160th bed and was almost complete by the 240th bed.

[0076] (4) Regeneration: The permeated aluminum-based adsorbent was regenerated with carbon dioxide. The resin column was connected to a carbon dioxide cylinder, and the carbon dioxide pressure was adjusted to 5 kg and maintained at this pressure for 60 minutes. After regeneration, the liquid in the plexiglass column was drained. After standing for 20 minutes, a large amount of white calcium carbonate precipitate was produced. The white precipitate was separated, dried, weighed, and the concentration of calcium ions in the liquid phase was tested. The test results showed that the concentration of calcium ions in the liquid phase was 450 mg / L, and the weight of the obtained white precipitate was 2.7 g. Therefore, the regeneration efficiency was approximately 98%.

[0077] After regeneration, keeping the operating parameters and influent water quality unchanged, a second product water experiment was conducted to verify the regeneration effect of the process. Specific experimental data are as follows: Figure 8 As shown.

[0078] Experimental results show that the regeneration treatment effect is only slightly lower than that of the first treatment. The calcium ion concentration in the effluent when treating 140 beds is about 5 mg / L, and the adsorbent material is completely penetrated when operating 240 beds, which can meet the specific discharge and reuse requirements.

[0079] Example 3

[0080] A solution for removing hardness from boiler circulating water at 50°C was proposed. The aluminum-based adsorbent prepared in Example 2 was used to achieve in-situ hardness removal directly inside the boiler system piping. The hardness of the circulating water was 300 mg / L. The method used 15 mL of the aluminum-based adsorbent, packed into a 7 mm inner diameter plexiglass column to form a resin column. Boiler circulating water at 50°C was passed through at a flow rate of 5 mL / min to verify the stability of the aluminum-based adsorbent at high temperatures and its hardness removal efficiency.

[0081] Removal effect as Figure 9As shown, when the influent temperature is 50℃, the aluminum-based adsorbent material still maintains the stability of its structure and the hardness removal effect at room temperature. After running 140 beds, the hardness of the effluent is still close to 0mg / L.

[0082] Carbon dioxide regeneration and a second water production experiment were conducted using the same method as in Example 2. The results showed that the treatment effect of the regenerated aluminum-based adsorbent material was consistent with that of the original aluminum-based adsorbent material.

[0083] This experiment demonstrates that aluminum-based adsorbent materials can be used for hot water treatment at 50°C.

[0084] The above description is merely a preferred embodiment of the present invention and is 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. An aluminum-based adsorbent material zero discharge softening process characterized by, The application relates to an aluminum-based adsorption material and a preparation method thereof. Sodium salt and aluminum salt are mixed in a solution to obtain a mixed solution; Ion exchange is carried out between the mixed solution and a cation exchange resin to obtain the aluminum-based adsorption material; The aluminum-based adsorption material is used to treat water bodies, adsorb calcium ions or magnesium ions, form nanoscale aluminum hydroxide precipitates and attach the nanoscale aluminum hydroxide precipitates to the skeleton of the aluminum-based adsorption material, and then the water is collected; Carbon dioxide gas is used to regenerate the aluminum-based adsorption material, dissolve the nanoscale aluminum hydroxide precipitates, replace calcium bicarbonate or magnesium bicarbonate, collect the water, and then the water is left to stand to form calcium carbonate or magnesium carbonate precipitates, which are obtained; The mass concentration of the sodium salt in the mixed solution is 0.002%-0.005%; The particle size of the nanoscale aluminum hydroxide precipitates is 2nm-70nm; The aluminum-based adsorption material is stable in structure at 50 DEG C, maintains hardness removal performance, and is suitable for in-situ hardness removal process of boiler wastewater and circulating cooling water; The mass concentration of the aluminum salt in the mixed solution is 0.1%-3.0%; The partial pressure of the carbon dioxide is 1.5Kg-10Kg.

2. The aluminum-based adsorbent material zero discharge softening process of claim 1, wherein, The sodium salt is sodium chloride.

3. The aluminum-based adsorbent material zero discharge softening process of claim 1, wherein, The aluminum salt is aluminum chloride.

4. The aluminum-based adsorbent material zero discharge softening process of claim 1, wherein, The contact time of the mixed solution and the cation exchange resin is 10min-15min.

5. The aluminum-based adsorbent material zero discharge softening process of claim 1, wherein, The solid-liquid ratio of the cation exchange resin and the mixed solution is 1:50-60.

6. The zero discharge hardness removal process of the aluminum-based adsorbent material of claim 1, wherein, The cation exchange resin is a strong acid cation exchange resin.

Images