Cadmium removal method for ammonium sulfate-containing sewage

Abstract

The invention discloses a cadmium removal method for ammonium sulfate-containing sewage, and relates to the technical field of sewage treatment. The method comprises the following steps: adding a composite cadmium removal agent containing porous chitosan and cysteine into pretreated ammonium sulfate-containing sewage, and adjusting process parameters to obtain complexed ammonium sulfate-containing sewage; and adding sulfate into the complexed ammonium sulfate-containing sewage, controlling the process parameters again to hydrolyze the metal ions in the sulfate, carrying out co-precipitation on the metal ions and complexed cadmium ions, standing, carrying out centrifugal separation to obtain precipitates, and remaining supernate, thereby obtaining the cadmium-removed ammonium sulfate-containing sewage. The cadmium removal method for the ammonium sulfate-containing sewage provided by the invention is simple, efficient, high in adaptability, green and environment-friendly.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, and in particular to a method for removing cadmium from wastewater containing ammonium sulfate. Background Technology

[0002] The compliant treatment of cadmium-containing wastewater is a key issue in industrial wastewater treatment and a crucial link in ensuring ecological safety and public health. Currently, the main technologies for removing cadmium ions include chemical precipitation, ion exchange, and adsorption. However, these methods are not highly adaptable to cadmium removal, and their removal efficiency still has significant room for improvement. Furthermore, the presence of ammonium sulfate in the wastewater further affects the removal efficiency of cadmium ions. Therefore, developing a highly adaptable and efficient method for removing cadmium from ammonium sulfate-containing wastewater has become an important requirement in the current water treatment field. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a method for removing cadmium from ammonium sulfate-containing wastewater. The method involves adding a composite cadmium removal agent containing porous chitosan and cysteine ​​to pretreated ammonium sulfate-containing wastewater, and then adjusting process parameters to obtain complexed ammonium sulfate-containing wastewater. Next, sulfate is added to the complexed wastewater, and process parameters are again controlled to cause the metal ions in the sulfate to hydrolyze and co-precipitate with the already complexed cadmium ions. The precipitate is then further separated by settling and centrifugation, and the supernatant is retained to obtain the cadmium-removed ammonium sulfate-containing wastewater. The cadmium removal method for ammonium sulfate-containing wastewater provided in this application is simple, efficient, highly adaptable, and environmentally friendly.

[0004] To achieve the above objectives, this application provides a method for removing cadmium from ammonium sulfate-containing wastewater, comprising the following steps:

[0005] An oxidant was added to the initial ammonium sulfate-containing wastewater, and the mixture was stirred at 200-300 rpm for 10-20 minutes before filtration to obtain pretreated ammonium sulfate-containing wastewater.

[0006] The composite cadmium removal agent was added to the pretreated ammonium sulfate-containing wastewater, and the first set process parameters were executed to obtain the complexed ammonium sulfate-containing wastewater.

[0007] Sulfate is added to the complexed ammonium sulfate-containing wastewater, the second set process parameters are executed, and centrifugation is performed to further separate the wastewater. The supernatant is retained to obtain the cadmium-free ammonium sulfate-containing wastewater.

[0008] The composite cadmium removal agent includes porous chitosan, cysteine, nano-hydroxyapatite, and a crosslinking agent.

[0009] The cadmium removal method provided in this application is simple, efficient, highly adaptable, and environmentally friendly. Firstly, this application pre-treats the initial ammonium sulfate-containing wastewater with an oxidant to oxidize any low-valence impurity ions or organic interferences present, preventing them from reacting with the subsequently added composite cadmium removal agent and ensuring cadmium removal efficiency. In the composite cadmium removal agent, porous chitosan not only adsorbs cadmium ions through its pores, but its surface active groups such as amino and hydroxyl groups can also form stable complexes with cadmium ions. Furthermore, the thiol, carboxyl, and amino groups in cysteine ​​interact with the amino and hydroxyl groups on the porous chitosan surface, improving the efficiency of forming stable complexes with cadmium ions. The addition and filling of nano-hydroxyapatite enhances the mechanical stability of the composite cadmium removal agent and prevents the chitosan and other components from easily dissolving and leaching in aqueous solution, thus limiting the release of cadmium ions in the formed complex and further improving the cadmium removal effect. The cross-linking agent further cross-links and fixes the porous chitosan, cysteine, and nano-hydroxyapatite, making it even more difficult for cadmium ions to be released from the formed complex.

[0010] Finally, the sulfate hydrolyzes to generate hydroxide colloids, which adsorb and complex the cadmium-containing complex, producing a coprecipitate. This coprecipitate can then be completely separated by centrifugation, further improving the cadmium removal effect and ensuring that the cadmium-containing ammonium sulfate wastewater after cadmium removal meets the standards and can be used for water treatment.

[0011] In one feasible implementation, the oxidant is hydrogen peroxide; the mass ratio of the hydrogen peroxide to the initial ammonium sulfate-containing wastewater is (0.3-0.8):100; and the concentration of the hydrogen peroxide is 20-30 wt.%.

[0012] This application uses hydrogen peroxide as an oxidant, which can oxidize interfering substances (such as organic impurities, low-valence metal ions, etc.) in the initial ammonium sulfate-containing wastewater, without leaving any pollutants and without affecting the purity of ammonium sulfate.

[0013] In one feasible implementation, the mass ratio of porous chitosan, cysteine, nano-hydroxyapatite and crosslinking agent in the composite cadmium removal agent is (40-60):(15-25):(20-30):(1-5).

[0014] In the composite cadmium removal agent provided in this application, porous chitosan serves as the main adsorbent carrier, thus accounting for the largest proportion. It provides ample adsorption sites, and its surface active groups, such as amino and hydroxyl groups, can form stable complexes with cadmium ions. Cysteine ​​further rapidly complexes cadmium ions, preventing their escape. Nano-hydroxyapatite restricts the release of cadmium ions in the formed complexes, further improving the cadmium removal effect. The crosslinking agent crosslinks other components to form a stable porous structure, further preventing component dissolution and loss while retaining the pore adsorption capacity. Through optimized dosage ratios, a composite cadmium removal agent with strong adaptability, significant cadmium removal effect, and high stability is obtained.

[0015] In one feasible implementation, the crosslinking agent includes either glyoxal or glutaraldehyde.

[0016] In one feasible implementation, the first set process parameters are: pH 5.0-6.0, temperature 25-35℃, stirring speed 200-300rpm, stirring time 30-60min, followed by standing for 10-20min.

[0017] In one feasible implementation, the second set process parameters are: pH 7.5-8.5, temperature 25-35℃, stirring speed 150-200rpm, stirring time 40-80min, followed by standing for 60-90min.

[0018] In one feasible implementation, the parameters for centrifugation are: centrifugation speed 2800-3200 rpm and centrifugation time 10-15 min.

[0019] In one feasible implementation, the mass ratio of the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater is (1-2):100.

[0020] In one feasible implementation, the mass ratio of the sulfate to the complexed ammonium sulfate-containing wastewater is (0.5-1):100.

[0021] In one feasible implementation, the sulfate includes any one of ferric sulfate, aluminum sulfate, and titanium sulfate.

[0022] Beneficial technical effects:

[0023] This application pretreats the initial ammonium sulfate-containing wastewater with an oxidant to oxidize low-valence impurity ions or organic interferences, preventing them from reacting with the subsequently added composite cadmium removal agent and ensuring basic cadmium removal efficiency. In the composite cadmium removal agent used in this application, the porous chitosan component not only adsorbs cadmium ions through its pores, but its surface active groups such as amino and hydroxyl groups can also form stable complexes with cadmium ions. Furthermore, the thiol, carboxyl, and amino groups in the cysteine ​​component interact with the amino and hydroxyl groups on the porous chitosan surface, improving the efficiency of forming stable complexes with cadmium ions. The addition and filling of the nano-hydroxyapatite component, under the action of a crosslinking agent, enhances the mechanical stability of the composite cadmium removal agent from both chemical bonding and physical filling to form a framework. It also prevents the porous chitosan and other components from easily dissolving and leaching in aqueous solution, thereby limiting the release of cadmium ions in the formed complexes and further improving the cadmium removal effect. Furthermore, by hydrolyzing specific sulfate solutions to generate hydroxide colloids, the cadmium-containing complexes are adsorbed and complexed, resulting in co-precipitates. These co-precipitates can then be completely separated by centrifugation, further enhancing the cadmium removal efficiency. The above-mentioned method for removing cadmium from ammonium sulfate-containing wastewater is simple, efficient, highly adaptable, and environmentally friendly, ensuring that the cadmium-removed ammonium sulfate-containing wastewater meets emission standards. Attached Figure Description

[0024] Figure 1 This is a schematic flowchart of the cadmium removal method for ammonium sulfate-containing wastewater provided in this application for water treatment. Detailed Implementation

[0025] To make the technical problems, solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. However, this should not be construed as limiting the scope of this application to the following embodiments. All other embodiments obtained by those skilled in the art without creative effort, without departing from the above-described methodological spirit, are within the scope of protection of this application.

[0026] In this application, the terminology used is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application.

[0027] The singular forms “for,” “a,” “any one,” and “as described” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0028] Furthermore, the terms "first" and "second" appearing in this application are for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0029] The following will describe in detail the method for removing cadmium from ammonium sulfate-containing wastewater provided in this application, with reference to different embodiments.

[0030] Example 1

[0031] like Figure 1 As shown, a method for removing cadmium from ammonium sulfate-containing wastewater includes the following steps:

[0032] 1. Add 20 wt.% hydrogen peroxide to the initial ammonium sulfate-containing wastewater, stir at 300 rpm for 10 min, and then filter to obtain pretreated ammonium sulfate-containing wastewater;

[0033] The mass ratio of hydrogen peroxide to the initial ammonium sulfate-containing wastewater was 0.3:100.

[0034] 2. Add the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater, stir for 60 minutes at pH 5.0, temperature 25℃ and stirring speed 200 rpm, and then let it stand for 10 minutes to obtain the complexed ammonium sulfate-containing wastewater;

[0035] The mass ratio of the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater is 1:100.

[0036] The composite cadmium removal agent includes porous chitosan, cysteine, nano-hydroxyapatite, and glyoxal; the mass ratio of porous chitosan, cysteine, nano-hydroxyapatite, and glyoxal is 40:25:30:5.

[0037] 3. Add ferric sulfate to the complexed ammonium sulfate-containing wastewater, stir for 80 minutes at pH 7.5, temperature 25℃ and stirring speed 150 rpm, then let stand for 60 minutes, and further centrifuge for 10 minutes at a speed of 2800 rpm. Keep the supernatant to obtain the cadmium-removed ammonium sulfate-containing wastewater.

[0038] The mass ratio of ferric sulfate to the complexed ammonium sulfate-containing wastewater is 0.5:100.

[0039] Example 2

[0040] like Figure 1 As shown, a method for removing cadmium from ammonium sulfate-containing wastewater includes the following steps:

[0041] 1. Add 30 wt.% hydrogen peroxide to the initial ammonium sulfate-containing wastewater, stir at 200 rpm for 20 min, and then filter to obtain pretreated ammonium sulfate-containing wastewater;

[0042] The mass ratio of hydrogen peroxide to the initial ammonium sulfate-containing wastewater was 0.8:100.

[0043] 2. Add the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater, stir for 30 minutes at pH 6.0, temperature 35℃ and stirring speed 300 rpm, and then let it stand for 20 minutes to obtain the complexed ammonium sulfate-containing wastewater;

[0044] The mass ratio of the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater is 2:100.

[0045] The composite cadmium removal agent includes porous chitosan, cysteine, nano-hydroxyapatite, and glutaraldehyde; the mass ratio of porous chitosan, cysteine, nano-hydroxyapatite, and glutaraldehyde is 60:15:20:5.

[0046] 3. Add aluminum sulfate to the complexed ammonium sulfate-containing wastewater, stir for 40 minutes at pH 8.5, temperature 35℃ and stirring speed 200 rpm, then let stand for 90 minutes, and then centrifuge for 15 minutes at a speed of 3200 rpm. Keep the supernatant to obtain the cadmium-free ammonium sulfate-containing wastewater.

[0047] The mass ratio of aluminum sulfate to the complexed ammonium sulfate-containing wastewater is 1:100.

[0048] Example 3

[0049] like Figure 1 As shown, a method for removing cadmium from ammonium sulfate-containing wastewater includes the following steps:

[0050] 1. Add 25wt.% hydrogen peroxide to the initial ammonium sulfate-containing wastewater, stir at 250rpm for 15min, and then filter to obtain pretreated ammonium sulfate-containing wastewater;

[0051] The mass ratio of hydrogen peroxide to the initial ammonium sulfate-containing wastewater was 0.5:100.

[0052] 2. Add the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater, stir for 45 minutes at pH 5.5, temperature 30℃ and stirring speed 250 rpm, and then let it stand for 15 minutes to obtain the complexed ammonium sulfate-containing wastewater.

[0053] The mass ratio of the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater is 1.5:100.

[0054] The composite cadmium removal agent includes porous chitosan, cysteine, nano-hydroxyapatite, and glutaraldehyde; the mass ratio of porous chitosan, cysteine, nano-hydroxyapatite, and glutaraldehyde is 50:20:29:1.

[0055] 3. Add titanium sulfate to the complexed ammonium sulfate-containing wastewater, stir for 60 minutes at pH 8.0, temperature 30℃ and stirring speed 175 rpm, then let stand for 75 minutes, and then centrifuge for 12 minutes at a speed of 3000 rpm. Keep the supernatant to obtain the cadmium-free ammonium sulfate-containing wastewater.

[0056] The mass ratio of titanium sulfate to the complexed ammonium sulfate-containing wastewater is 0.7:100.

[0057] Example 4

[0058] like Figure 1 As shown, a method for removing cadmium from ammonium sulfate-containing wastewater includes the following steps:

[0059] 1. Add 20 wt.% hydrogen peroxide to the initial ammonium sulfate-containing wastewater, stir at 250 rpm for 15 min, and then filter to obtain pretreated ammonium sulfate-containing wastewater;

[0060] The mass ratio of hydrogen peroxide to the initial ammonium sulfate-containing wastewater was 0.8:100.

[0061] 2. Add the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater, stir for 30 minutes at pH 5.0, temperature 35℃ and stirring speed 250 rpm, and then let it stand for 20 minutes to obtain the complexed ammonium sulfate-containing wastewater;

[0062] The mass ratio of the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater is 2:100.

[0063] The composite cadmium removal agent includes porous chitosan, cysteine, nano-hydroxyapatite, and glyoxal; the mass ratio of porous chitosan, cysteine, nano-hydroxyapatite, and glyoxal is 55:22:20:3.

[0064] 3. Add ferric sulfate to the complexed ammonium sulfate-containing wastewater, stir for 40 minutes at pH 8.5, temperature 25℃ and stirring speed 200 rpm, then let stand for 90 minutes, and then centrifuge for 15 minutes at a speed of 2900 rpm. Keep the supernatant to obtain the cadmium-removed ammonium sulfate-containing wastewater.

[0065] The mass ratio of ferric sulfate to the complexed ammonium sulfate-containing wastewater is 0.9:100.

[0066] Example 5

[0067] like Figure 1 As shown, a method for removing cadmium from ammonium sulfate-containing wastewater includes the following steps:

[0068] 1. Add 30 wt.% hydrogen peroxide to the initial ammonium sulfate-containing wastewater, stir at 200 rpm for 20 min, and then filter to obtain pretreated ammonium sulfate-containing wastewater;

[0069] The mass ratio of hydrogen peroxide to the initial ammonium sulfate-containing wastewater was 0.3:100.

[0070] 2. Add the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater, stir for 60 minutes at pH 6.0, temperature 25℃ and stirring speed 300 rpm, and then let it stand for 10 minutes to obtain the complexed ammonium sulfate-containing wastewater;

[0071] The mass ratio of the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater is 1:100.

[0072] The composite cadmium removal agent includes porous chitosan, cysteine, nano-hydroxyapatite, and glyoxal; the mass ratio of porous chitosan, cysteine, nano-hydroxyapatite, and glyoxal is 53:17:26:4.

[0073] 3. Add titanium sulfate to the complexed ammonium sulfate-containing wastewater and stir for 80 minutes at pH 7.5, temperature 35℃ and stirring speed 150 rpm. Then let it stand for 60 minutes and centrifuge for 10 minutes at a speed of 3200 rpm. Keep the supernatant to obtain the cadmium-free ammonium sulfate-containing wastewater.

[0074] The mass ratio of titanium sulfate to the complexed ammonium sulfate-containing wastewater is 0.6:100.

[0075] Example 6

[0076] like Figure 1 As shown, a method for removing cadmium from ammonium sulfate-containing wastewater includes the following steps:

[0077] 1. Add 27wt.% hydrogen peroxide to the initial ammonium sulfate-containing wastewater, stir at 300rpm for 12min, and then filter to obtain pretreated ammonium sulfate-containing wastewater;

[0078] The mass ratio of hydrogen peroxide to the initial ammonium sulfate-containing wastewater was 0.6:100.

[0079] 2. Add the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater, stir for 50 minutes at pH 5.5, temperature 28℃ and stirring speed 250 rpm, and then let it stand for 18 minutes to obtain the complexed ammonium sulfate-containing wastewater.

[0080] The mass ratio of the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater is 1.2:100.

[0081] The composite cadmium removal agent includes porous chitosan, cysteine, nano-hydroxyapatite, and glutaraldehyde; the mass ratio of porous chitosan, cysteine, nano-hydroxyapatite, and glutaraldehyde is 48:23:27:2.

[0082] 3. Add aluminum sulfate to the complexed ammonium sulfate-containing wastewater, stir for 70 minutes at pH 8.5, temperature 28℃ and stirring speed 180 rpm, then let stand for 80 minutes, and then centrifuge for 12 minutes at a speed of 3000 rpm. Keep the supernatant to obtain the cadmium-free ammonium sulfate-containing wastewater.

[0083] The mass ratio of aluminum sulfate to the complexed ammonium sulfate-containing wastewater is 0.8:100.

[0084] Comparative Example 1

[0085] A method for removing cadmium from ammonium sulfate-containing wastewater includes the following steps:

[0086] 1. Add 20 wt.% hydrogen peroxide to the initial ammonium sulfate-containing wastewater, stir at 300 rpm for 10 min, and then filter to obtain pretreated ammonium sulfate-containing wastewater;

[0087] The mass ratio of hydrogen peroxide to the initial ammonium sulfate-containing wastewater was 0.3:100.

[0088] 2. Porous chitosan was added to the pretreated ammonium sulfate-containing wastewater and stirred for 60 minutes at pH 5.0, temperature 25℃ and stirring speed 200 rpm, and then allowed to stand for 10 minutes to obtain the complexed ammonium sulfate-containing wastewater.

[0089] The mass ratio of porous chitosan to pretreated ammonium sulfate-containing wastewater is 1:100.

[0090] 3. Add ferric sulfate to the complexed ammonium sulfate-containing wastewater, stir for 80 minutes at pH 7.5, temperature 25℃ and stirring speed 150 rpm, then let stand for 60 minutes, and further centrifuge for 10 minutes at a speed of 2800 rpm. Keep the supernatant to obtain the cadmium-removed ammonium sulfate-containing wastewater.

[0091] The mass ratio of ferric sulfate to the complexed ammonium sulfate-containing wastewater is 0.5:100.

[0092] Comparative Example 2

[0093] A method for removing cadmium from ammonium sulfate-containing wastewater includes the following steps:

[0094] 1. Add 25wt.% hydrogen peroxide to the initial ammonium sulfate-containing wastewater, stir at 250rpm for 15min, and then filter to obtain pretreated ammonium sulfate-containing wastewater;

[0095] The mass ratio of hydrogen peroxide to the initial ammonium sulfate-containing wastewater was 0.5:100.

[0096] 2. Cysteine ​​was added to the pretreated ammonium sulfate-containing wastewater and stirred for 45 minutes at pH 5.5, temperature 30℃ and stirring speed 250 rpm, and then allowed to stand for 15 minutes to obtain the complexed ammonium sulfate-containing wastewater.

[0097] The mass ratio of cysteine ​​to pretreated ammonium sulfate-containing wastewater was 1.5:100.

[0098] 3. Add titanium sulfate to the complexed ammonium sulfate-containing wastewater, stir for 60 minutes at pH 8.0, temperature 30℃ and stirring speed 175 rpm, then let stand for 75 minutes, and then centrifuge for 12 minutes at a speed of 3000 rpm. Keep the supernatant to obtain the cadmium-free ammonium sulfate-containing wastewater.

[0099] The mass ratio of titanium sulfate to the complexed ammonium sulfate-containing wastewater is 0.7:100.

[0100] Comparative Example 3

[0101] A method for removing cadmium from ammonium sulfate-containing wastewater includes the following steps:

[0102] 1. Add 27wt.% hydrogen peroxide to the initial ammonium sulfate-containing wastewater, stir at 300rpm for 12min, and then filter to obtain pretreated ammonium sulfate-containing wastewater;

[0103] The mass ratio of hydrogen peroxide to the initial ammonium sulfate-containing wastewater was 0.6:100.

[0104] 2. Add the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater, stir for 50 minutes at pH 5.5, temperature 28℃ and stirring speed 250 rpm, and then let it stand for 18 minutes to obtain the complexed ammonium sulfate-containing wastewater.

[0105] The mass ratio of the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater is 1.2:100.

[0106] The composite cadmium removal agent includes porous chitosan, cysteine, nano-hydroxyapatite, and glutaraldehyde; the mass ratio of porous chitosan, cysteine, nano-hydroxyapatite, and glutaraldehyde is 48:23:27:2.

[0107] 3. Then, stir for 70 minutes at pH 8.5, temperature 28℃, and stirring speed 180 rpm, then let stand for 80 minutes, and then centrifuge for 12 minutes at a speed of 3000 rpm. Keep the supernatant, which is the ammonium sulfate-containing wastewater after cadmium removal.

[0108] Table 1. Test results of cadmium removal methods for ammonium sulfate-containing wastewater in Examples 1-6 and Comparative Examples 1-3.

[0109]

[0110] As shown in Table 1, the Cd in Examples 1-6 2+ The removal efficiency was superior to that of comparative examples 1-3.

[0111] This is because, by pretreating the initial ammonium sulfate-containing wastewater with an oxidant, the low-valence impurity ions or organic interferences present are oxidized, preventing them from reacting with the subsequently added composite cadmium removal agent and ensuring basic cadmium removal efficiency. In the composite cadmium removal agent used in this application, the porous chitosan component not only adsorbs cadmium ions through its pores, but its surface active groups such as amino and hydroxyl groups can also form stable complexes with cadmium ions. Furthermore, the thiol, carboxyl, and amino groups in the cysteine ​​component work together with the amino and hydroxyl groups on the porous chitosan surface, improving the efficiency of forming stable complexes with cadmium ions. The addition and filling of the nano-hydroxyapatite component, under the action of a crosslinking agent, enhances the mechanical stability of the composite cadmium removal agent from both chemical bonding and physical filling to form a framework. It also prevents the porous chitosan and other components from easily dissolving and leaching in aqueous solution, thereby limiting the release of cadmium ions in the formed complexes and further improving the cadmium removal effect. Furthermore, by hydrolyzing specific sulfate solutions to generate hydroxide colloids, the cadmium-containing complexes are adsorbed and complexed, resulting in co-precipitates. These co-precipitates can then be completely separated by centrifugation, further enhancing the cadmium removal efficiency. The above-mentioned method for removing cadmium from ammonium sulfate-containing wastewater is simple, efficient, highly adaptable, and environmentally friendly, ensuring that the cadmium-removed ammonium sulfate-containing wastewater meets emission standards.

[0112] In Comparative Example 1, only porous chitosan was added to the pretreated ammonium sulfate-containing wastewater. The thiol, carboxyl, and amino groups in the cysteine ​​component did not interact with the amino and hydroxyl groups on the surface of the porous chitosan, nor did the nano-hydroxyapatite component enhance its mechanical stability. As a result, the release of cadmium ions in the formed complex could not be restricted, and the cadmium removal efficiency was significantly reduced.

[0113] In Comparative Example 2, only cysteine ​​was added to the pretreated ammonium sulfate-containing wastewater. There was no porous structure for adsorbing cadmium ions, and cysteine ​​alone could not combine with the active groups such as amino and hydroxyl groups on the surface of porous chitosan. Similarly, there was no nano-hydroxyapatite component to limit the release of cadmium ions in the formed complex. Therefore, the final cadmium removal efficiency was lower than that of Comparative Example 1.

[0114] In Comparative Example 3, no sulfate was added, so it could not be hydrolyzed to generate hydroxide colloids, which adsorbed and complexed the cadmium-containing complex, resulting in co-precipitation. The cadmium removal effect was somewhat reduced compared to the examples.

[0115] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0116] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for removing cadmium from ammonium sulfate-containing wastewater, characterized in that, Includes the following steps: The oxidant was added to the initial ammonium sulfate-containing wastewater, stirred at 200-300 rpm for 10-20 min, and then filtered to obtain the pretreated ammonium sulfate-containing wastewater. The composite cadmium removal agent was added to the pretreated ammonium sulfate-containing wastewater, and the first set process parameters were executed to obtain the complexed ammonium sulfate-containing wastewater. Sulfate is added to the complexed ammonium sulfate-containing wastewater, the second set process parameters are executed, and centrifugation is performed to further separate the wastewater. The supernatant is retained to obtain the cadmium-free ammonium sulfate-containing wastewater. The composite cadmium removal agent includes porous chitosan, cysteine, nano-hydroxyapatite, and a crosslinking agent.

2. The method for removing cadmium from ammonium sulfate-containing wastewater according to claim 1, characterized in that, The oxidant is hydrogen peroxide; the mass ratio of hydrogen peroxide to the initial ammonium sulfate-containing wastewater is (0.3-0.8):100; the concentration of hydrogen peroxide is 20-30 wt.%.

3. The method for removing cadmium from ammonium sulfate-containing wastewater according to claim 1, characterized in that, In the composite cadmium removal agent, the mass ratio of porous chitosan, cysteine, nano hydroxyapatite and crosslinking agent is (40-60):(15-25):(20-30):(1-5).

4. The method for removing cadmium from ammonium sulfate-containing wastewater according to claim 1, characterized in that, The crosslinking agent includes either glyoxal or glutaraldehyde.

5. The method for removing cadmium from ammonium sulfate-containing wastewater according to claim 1, characterized in that, The first set process parameters are: pH 5.0-6.0, temperature 25-35℃, stirring speed 200-300rpm, stirring time 30-60min, followed by standing for 10-20min.

6. The method for removing cadmium from ammonium sulfate-containing wastewater according to claim 1, characterized in that, The second set process parameters are: pH 7.5-8.5, temperature 25-35℃, stirring speed 150-200rpm, stirring time 40-80min, followed by standing for 60-90min.

7. The method for removing cadmium from ammonium sulfate-containing wastewater according to claim 1, characterized in that, The parameters for centrifugation are: centrifugation speed 2800-3200 rpm, centrifugation time 10-15 min.

8. The method for removing cadmium from ammonium sulfate-containing wastewater according to claim 1, characterized in that, The mass ratio of the composite cadmium removal agent to the pretreated ammonium sulfate-containing wastewater is (1-2):

100.

9. The method for removing cadmium from ammonium sulfate-containing wastewater according to claim 1, characterized in that, The mass ratio of the sulfate to the complexed ammonium sulfate-containing wastewater is (0.5-1):

100.

10. The method for removing cadmium from ammonium sulfate-containing wastewater according to claim 8, characterized in that, The sulfate includes any one of ferric sulfate, aluminum sulfate, and titanium sulfate.

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