Method for removing copper ions in strong acidic wastewater by ascorbic acid induced sulfidation

Abstract

The application discloses a method for removing copper ions in strong acidic wastewater by ascorbic acid induced sulfuration, and the method comprises the following steps: adding ascorbic acid into the strong acidic wastewater containing copper ions, then adding a sulfuration agent to stir and react, and removing the precipitate to obtain treated wastewater. By adding ascorbic acid, the removal rate of copper ions in the wastewater and the precipitation efficiency are both significantly improved.

Description

A method for removing copper ions from strongly acidic wastewater using ascorbic acid-induced sulfidation. Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for removing copper ions from strongly acidic wastewater by ascorbic acid-induced sulfidation. Background Technology

[0002] In processes such as metal electroplating, mining, and smelting, highly concentrated copper-containing wastewater with large amounts of acidic substances is generated. This wastewater is extremely acidic (pH < 4). Copper most commonly exists in acidic wastewater as Cu(II), and excessive copper intake can lead to serious toxicological problems such as vomiting or convulsions. Therefore, the large amounts of copper in acidic wastewater should be separated and recovered as much as possible. Compared with other commonly used technologies, CuS has a lower solubility product (Ksp = 6.3 × 10⁻⁶). -36 Sulfide precipitation is highly selective for removing copper from aqueous solutions.

[0003] Sulfide precipitation is a method of removing or recovering metals by adding a sulfiding agent to wastewater, causing it to react with the metals in the wastewater to form a precipitate. Commonly used sulfiding agents include H₂S, NaHS, and Na₂S. Besides its rapid reaction and quick sedimentation, the biggest advantage of sulfide precipitation lies in the reuse value of the effluent and the precipitate. The sulfide process does not consume the acidity of the raw water, and the effluent can be reused or used to produce waste acid.

[0004] The reaction rate between Cu(II) and S(-II) in solution is extremely fast, and the addition of a sulfiding agent can quickly form copper sulfide precipitate. However, in existing processes, the amount of sulfiding agent used is always excessive. Excess sulfiding agent can easily form hydrogen sulfide gas under acidic conditions, causing secondary pollution. Furthermore, because copper sulfide particles are relatively small, the solid-liquid separation effect is poor, often requiring additional processes to promote sedimentation, such as ultraviolet irradiation and coagulation. Therefore, it is essential to develop new technologies that can reduce the amount of sulfiding agent used while achieving efficient removal of Cu(II) and efficient sedimentation of CuS. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for removing copper ions from strongly acidic wastewater using ascorbic acid-induced sulfidation. This method requires a small amount of sulfiding agent and achieves a rapid coagulation rate. Ascorbic acid is a widely used environmentally friendly reducing agent in industry and has broad prospects for scientific research and practical applications.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] This invention provides a method for removing copper ions from strongly acidic wastewater using ascorbic acid-induced sulfidation, comprising the following steps:

[0008] Ascorbic acid is added to strongly acidic wastewater containing copper ions, followed by the addition of a sulfiding agent and stirring to react. The precipitate is then removed to obtain the treated wastewater.

[0009] Preferably, the pH of the copper-containing strongly acidic wastewater is 2-4. The coagulation rate is particularly faster at pH 2.

[0010] Preferably, the molar ratio of ascorbic acid to copper ions is (0.5-1.5):1;

[0011] Preferably, the stirring speed when adding ascorbic acid is 50-100 rpm. A lower stirring speed is used to avoid incorporating too much air.

[0012] Preferably, the vulcanizing agent is at least one selected from H2S, NaHS, and Na2S;

[0013] Preferably, the molar ratio of the vulcanizing agent to copper ions is (0.2-0.8):1; especially when the molar ratio is above 0.5, it has a 100% copper ion removal rate and a faster coagulation rate.

[0014] Preferably, the stirring speed when adding the vulcanizing agent is 350-400 rpm. The higher stirring speed allows sodium sulfide to diffuse rapidly in the wastewater.

[0015] Preferably, the stirring reaction rate is 50-100 rpm;

[0016] Preferably, the stirring reaction time is 30-100 min.

[0017] More preferably, the stirring reaction time is 60-90 minutes.

[0018] Preferably, the copper-containing strongly acidic wastewater also includes SO4. 2- The wastewater contains SO4. 2- Not only does it not reduce the removal efficiency of copper ions, but it also increases the coagulation rate. The wastewater treatment method of the present invention has a wider range of applications and can regulate the wastewater composition to improve the wastewater treatment effect.

[0019] Further preferred, SO4 2- The concentration is 30-100mM.

[0020] Preferably, the copper-containing strongly acidic wastewater also includes Fe. 2+ The wastewater contains Fe. 2+ Not only does it not reduce the removal efficiency of copper ions, but it also increases the coagulation rate at low concentrations. The wastewater treatment method of this invention has a wider range of applications and can also control the wastewater composition to improve the wastewater treatment effect.

[0021] Further preferred, Fe 2+ The concentration is 30-100 mg / L.

[0022] Preferably, the precipitate is removed by filtration.

[0023] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0024] The method for removing copper ions from highly acidic wastewater in this invention improves the removal efficiency of copper ions by adding ascorbic acid, reduces the amount of sulfiding agent, and increases the coagulation rate; appropriately increasing the amount of sulfiding agent can improve the copper ion removal rate and coagulation rate; the coagulation rate is even faster at pH 2.

[0025] The method for removing copper ions from strongly acidic wastewater according to this invention is highly adaptable and has low requirements for the wastewater, which can contain other components, such as SO4. 2- Fe 2+ It can also regulate SO4 in wastewater. 2- Fe 2+ The content of [something] increases the coagulation rate. Attached Figure Description

[0026] Figure 1 shows the effects of copper ion wastewater treatment in Example 1, Comparative Example 1, and Comparative Example 2; (a) Kinetics of Cu(II) removal; (b) Image of the suspension after the reaction in the AA-free system of Comparative Example 1; (c) Image of the suspension after the reaction in the AA system of Example 1.

[0027] Figure 2 shows the treatment effect of copper ion wastewater in Examples 2-5; (a) different sulfur-copper ratios, pH, SO4 2- (a) Copper removal rate at Fe(II) concentration; (b) Copper-sulfur compound particle coagulation rate; (c) Copper-sulfur compound particle hydrodynamics; where the green line represents the multiple by which the removal rate and coagulation rate are increased under AA conditions. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0029] The wastewater in the following examples is simulated wastewater obtained by dissolving copper chloride in water and adjusting the pH with hydrochloric acid.

[0030] Example 1

[0031] This embodiment provides a method for removing copper ions from strongly acidic wastewater using ascorbic acid-induced sulfidation, comprising the following steps:

[0032] Step 1: At room temperature, add ascorbic acid to wastewater with a pH of 2 and a copper ion concentration of 100 mg / L, controlling the stirring speed at 100 rpm to avoid introducing excessive air. The molar ratio of copper ions to ascorbic acid in the wastewater should be controlled at 1.6:1.

[0033] Step 2: After increasing the stirring speed to 400 rpm, quickly add sodium sulfide solution (1000 mg / L) to allow the sodium sulfide solution to diffuse rapidly in the wastewater. The molar ratio of copper ions to sodium sulfide in the wastewater should be controlled at 2:1.

[0034] Step 3: After stirring at 400 rpm for 5 minutes, reduce the stirring speed to 100 rpm and continue stirring for 90 minutes. Test the concentration of copper ions in the solution at different time points.

[0035] As shown in Figure 1, after the reaction was completed, the removal rate of copper in the strongly acidic copper-containing wastewater reached 100%; within 0-20 min, the precipitate coagulation rate k = 2.78 nm / s.

[0036] Example 2

[0037] This embodiment provides a method for removing copper ions from strongly acidic wastewater by ascorbic acid-induced sulfidation. The difference from Embodiment 1 is that the S / Cu molar ratio in step 2 is different, being 0.2, 0.3, and 0.4 respectively. The rest is the same as in Embodiment 1.

[0038] As shown in Figure 2, when the S / Cu molar ratios were 0.2, 0.3, and 0.4, the copper removal rates in the copper-containing wastewater after the reaction were 41%, 64%, and 81%, respectively, and the coagulation rates (within 0-20 min) were 1.49, 1.94, and 2.38 nm / s, respectively. Compared with Example 1, the copper removal rates under the conditions of S / Cu molar ratios of 0.2, 0.3, and 0.4 were 0.4, 0.6, and 0.8 times that under the condition of S / Cu molar ratio of 0.5, respectively, and the coagulation rates were 0.5, 0.7, and 0.9 times that under the condition of S / Cu molar ratio of 0.5, respectively. This proves that the S / Cu molar ratio should preferably be 0.5.

[0039] The control group without ascorbic acid was used, and the rest of the process was the same as described above.

[0040] As shown in Figure 2, when the S / Cu molar ratios were 0.2, 0.3, and 0.4, the copper removal rates in the copper-containing wastewater after the reaction were 24%, 31%, and 43%, respectively, and the coagulation rates (within 0-20 min) were 0.72, 0.77, and 0.74 nm / s, respectively. In the above AA system, the copper ion removal rate in the copper-containing wastewater with the same S / Cu molar ratio was twice that of the control group, and the coagulation rates of the AA system were 2.1, 2.5, and 3.2 times that of the control group, respectively.

[0041] Example 3

[0042] This embodiment provides a method for removing copper ions from strongly acidic wastewater by ascorbic acid-induced sulfidation. The difference from Embodiment 1 is the pH, which is 3 and 4 respectively. The pH is adjusted in advance with 0.1M HCl / NaOH before step 1. Otherwise, it is the same as Embodiment 1.

[0043] As shown in Figure 2, under pH conditions of 3 and 4, the copper removal rate in the copper-containing wastewater reached 100% after the reaction, and the coagulation rates (within 0-20 min) were 1.65 and 1.52 nm / s, respectively. Compared with Example 1, the copper removal rate in the copper-containing wastewater remained unchanged at 100% under pH conditions of 3 and 4, while the coagulation rates were 0.6 and 0.5 times that under pH condition 2, respectively. This proves that pH condition 2 is preferred.

[0044] The control group without ascorbic acid was used, and the rest of the process was the same as described above.

[0045] As shown in Figure 2, under pH conditions of 3 and 4, the removal rate of copper in copper-containing wastewater was 50% after the reaction, and the coagulation rates (within 0-20 min) were 0.93 and 1.16 nm / s, respectively. In the above AA system, the removal rate of copper ions in copper-containing wastewater with the same pH was twice that of the control group, and the coagulation rates of the AA system were 1.8 and 1.3 times that of the control group, respectively.

[0046] It can be seen that the synergistic effect of ascorbic acid is still significant when the pH of the wastewater solution is 3 and 4.

[0047] Example 4

[0048] This embodiment provides a method for removing copper ions from strongly acidic wastewater using ascorbic acid-induced sulfidation, which differs from Embodiment 1 in that SO4 in the wastewater solution... 2- The concentrations were different, 30, 60, and 100 mmol / L. The corresponding mass of Na2SO4 was added before step 1 and allowed to dissolve completely. Everything else was the same as in Example 1.

[0049] As shown in Figure 2, SO4 2- At concentrations of 30, 60, and 100 mM, the copper removal rate in the copper-containing wastewater was 100% after the reaction, and the coagulation rates (within 0-20 min) were 2.87, 3.27, and 3.52 nm / s, respectively. Compared to Example 1, SO4 2- The removal rate of copper in copper-containing wastewater with concentrations of 30, 60, and 100 mM remained unchanged, while the removal rate of SO4 remained unchanged. 2- The coagulation rates at concentrations of 60 and 100 mM were increased by 1.2 and 1.3 times, respectively, compared to Example 1.

[0050] The control group without ascorbic acid was used, and the rest of the process was the same as described above.

[0051] As shown in Figure 2, SO4 2- At concentrations of 30, 60, and 100 mM, the copper removal rate in the copper-containing wastewater was 50% after the reaction, and the coagulation rates (within 0-20 min) were 0.72, 0.93, and 1.26 nm / s, respectively. The SO4 content in the above AA system was [not specified]. 2- The removal rate of copper ions in copper-containing wastewater with the same concentration was twice that of the control group, and the coagulation rate of the AA system was 4.0, 3.5, and 2.8 times that of the control group, respectively.

[0052] It can be seen that when SO4 is present in the wastewater solution 2- At the same time, the synergistic effect of ascorbic acid is still significant, and the removal effect of copper ions is further improved.

[0053] Example 5

[0054] This embodiment provides a method for removing copper ions from strongly acidic wastewater using ascorbic acid-induced sulfidation, which differs from Embodiment 1 in that Fe in the wastewater solution... 2+ The concentrations were different, 30, 60, and 100 mg / L. The corresponding mass of FeCl2 was added before step 1 and allowed to dissolve completely. Everything else was the same as in Example 1.

[0055] As shown in Figure 2, Fe 2+ For copper-containing wastewater with concentrations of 30, 60, and 100 mg / L, the removal rate of copper ions in the solution was 100% after the reaction, and the coagulation rates (within 0-20 min) were 2.93, 2.89, and 2.76 nm / s, respectively. Compared with Example 1, Fe 2+ The copper removal rate in copper-containing wastewater with concentrations of 30, 60, and 100 mg / L remained constant at 100%, while the coagulation rate, except when Fe... 2+ When the content is 30 mg / L, in addition to increasing by 0.1 times, Fe 2+ The coagulation rate remained essentially unchanged at concentrations of 60 and 100 mg / L. This demonstrates that the addition of 30 mg / L of Fe... 2+ It can improve the removal effect of copper ions to a certain extent.

[0056] The control group without ascorbic acid was used, and the rest of the process was the same as described above.

[0057] As shown in Figure 2, Fe 2+For copper-containing wastewater with concentrations of 30, 60, and 100 mg / L, the removal rate of copper ions in the solution was 50% after the reaction, and the coagulation rates (within 0-20 min) were 0.65, 0.58, and 0.59 nm / s, respectively. The Fe in the above AA system... 2+ The removal rate of copper ions in the copper-containing wastewater with the same content was twice that of the control group. In the above AA system, Fe... 2+ The coagulation rate of the copper-containing wastewater with the same content was 4.5, 5.0, and 4.7 times that of the control group.

[0058] It can be seen that when Fe is present in the wastewater solution 2+ At the same time, the synergistic effect of ascorbic acid is still significant.

[0059] Comparative Example 1

[0060] Compared with Example 1, this comparative example omits step 1 and does not add ascorbic acid, but is otherwise the same as Example 1.

[0061] As shown in Figure 1, after the reaction, the removal rate of copper ions in the wastewater was only 50%, which is twice that of Comparative Example 1. Precipitation also formed during the reaction, but the aggregation rate of the precipitate (within 0-20 min) was 0.66 nm / s, which is 4.2 times that of Comparative Example 1. This demonstrates that the addition of ascorbic acid can double the copper removal rate and increase the aggregation rate by 4.2 times.

[0062] Comparative Example 2

[0063] Compared with Example 1, this comparative example omits step 2 and does not add sodium sulfide, but is otherwise the same as Example 1.

[0064] As shown in Figure 1, no precipitate was formed in the solution after the reaction, and the concentration of copper ions remained unchanged. This proves that ascorbic acid itself has no precipitation effect on copper ions.

[0065] Data Analysis:

[0066] (1) As shown in Figure 1, under the conditions of pH 2 and Cu(II) concentration of 100 ppm, when Na2S was added to Comparative Example 1 at a Cu / S molar ratio of 2:1, the reaction tended to stabilize after about 30 min, and the removal rate of Cu(II) in the solution was 50%. Comparative Example 2, which only added ascorbic acid, had no effect on the removal of copper ions. However, in Example 1, with the Cu / S molar ratio unchanged, AA was added at a Cu / AA molar ratio of 1.6:1. Within 15-30 min, all Cu(II) in the solution would form a precipitate (Figure 1a). Within 0-20 min, the hydraulic radius of the precipitate formed in the AA-added system of Example 1 was about 2250 nm, while the hydraulic radius of the control group of Comparative Example 1 without AA was about 750 nm, and the coagulation rate k control =0.66, k AA =2.78. After 90 minutes of reaction, it can be observed with the naked eye that in the system without added AA, a large number of black particles are still suspended in the solution (Figure 1b), while in the system with added AA, the black precipitate has been deposited at the bottom of the reaction vessel (Figure 1c).

[0067] Therefore, by adding ascorbic acid to copper-containing wastewater beforehand, and then adding the sulfiding agent Na2S, compared with not adding ascorbic acid, the removal rate of Cu(II) in the solution is increased by 2 times and the precipitation rate is increased by 4.2 times. The addition of ascorbic acid can not only improve the utilization rate of divalent sulfur, but also increase the aggregation rate of particles, and the precipitation effect is significantly improved.

[0068] (2) As shown in Figure 2, the coexistence of SO4 in solutions with different S / Cu molar ratios, pH, and other conditions was investigated. 2- Concentration and Fe 2+ Effects of concentration on the effectiveness and rate of copper ion precipitation under the action of AA.

[0069] It can be seen that without the addition of AA, Cu(II) in the solution precipitates with sulfur at a 1:1 ratio, meaning that when S / Cu (mol / mol) = 0.2, the removal rate of Cu(II) in the solution is 20%. However, after adding AA, under different S / Cu molar ratios, pH values, and coexistence of SO4 in the solution, the removal rate of Cu(II) was significantly reduced. 2- Under both the AA concentration and Fe(II) concentration conditions, the removal rate of Cu(II) in the solution was twice that of the system without AA (Figure 2a).

[0070] The SO42-coexisting solution under different S / Cu molar ratios, pH, and other conditions was detected by dynamic light scattering particle size analyzer within 20 minutes. 2- Changes in the hydrodynamic radius of copper-sulfur compound precipitation in solution under different concentrations of Fe(II) and S / Cu. 2-Both the AA concentration and Fe(II) concentration experimental groups showed that the hydrodynamic radius increased more significantly after the addition of AA (Figure 2c).

[0071] At pH 2, the hydrodynamic radius of copper-sulfur compound precipitation increased significantly compared to the system without added AA, but the difference decreased at pH 3 and 4. The negative charge on the surface of the copper-sulfur compound particles is due to the adsorption of negatively charged substances. In the AA system, the deprotonation reaction of dehydroascorbic acid (DHA) in aqueous solution affects the surface charge of copper-sulfur compound particles. The pKa value of DHA is approximately 8, and the concentration of anions generated by DHA ionization in solution increases with increasing pH, leading to an increase in the stability of copper-sulfur compound particles with increasing surface negative charge. In a solution at pH 2, H... + At high concentrations, the negative charge neutralizes, thus reducing the absolute value of the particle zeta potential and decreasing stability. Therefore, compared to systems at pH 3 and 4, copper-sulfur compound particles exhibit a higher aggregation rate and larger particle size in the AA system at pH 2.

[0072] The coagulation rate of copper-sulfur compound precipitation within 20 minutes can be calculated from the measured hydraulic radius. When the S / Cu (mol / mol) ratio is in the range of 0.2-0.5 mol / mol, the growth factor of the coagulation rate first increases and then decreases with increasing ratio. When the pH is in the range of 2-4, the coagulation rate decreases with increasing pH. When SO42-... 2- When the concentration is in the range of 30-100 mM, the coagulation rate increases with the concentration of SO42-. 2- The concentration increases and the concentration decreases. When the Fe(II) concentration is in the range of 30-100 mg / L, the coagulation rate remains basically unchanged as the Fe(II) concentration increases (Figure 2b).

[0073] The above embodiments are merely preferred embodiments of the present invention and are only used to explain the present invention, not to limit the present invention. Any changes, substitutions, modifications, etc., made by those skilled in the art without departing from the spirit and essence of the present invention should be within the protection scope of the present invention.

Claims

1. A method for removing copper ions from strongly acidic wastewater using ascorbic acid-induced sulfidation, characterized in that, Includes the following steps: Ascorbic acid is added to strongly acidic wastewater containing copper ions, followed by the addition of a sulfiding agent and stirring to remove precipitate, resulting in treated wastewater. The pH of the strongly acidic wastewater containing copper ions is 2-4; the concentration of copper ions in the wastewater is 50-300 mg / L; the molar ratio of ascorbic acid to copper ions is (0.5-1.5):1; the stirring rate when adding ascorbic acid is 50-100 rpm; the sulfiding agent is at least one of H2S, NaHS, and Na2S; the molar ratio of the sulfiding agent to copper ions is (0.2-0.8):1; the stirring rate when adding the sulfiding agent is 350-400 rpm; the stirring reaction rate is 50-100 rpm; and the stirring reaction time is 30-100 min.

2. The method for removing copper ions from strongly acidic wastewater by ascorbic acid-induced sulfidation according to claim 1, characterized in that, The copper-containing, strongly acidic wastewater also contains SO4. 2- .

3. The method for removing copper ions from strongly acidic wastewater by ascorbic acid-induced sulfidation according to claim 1, characterized in that, SO4 2- The concentration is 30-100 mM.

4. The method for removing copper ions from strongly acidic wastewater by ascorbic acid-induced sulfidation according to claim 1, characterized in that, The strongly acidic wastewater containing copper ions also includes Fe. 2+ .

5. The method for removing copper ions from strongly acidic wastewater by ascorbic acid-induced sulfidation according to claim 4, characterized in that, Fe 2+ The concentration is 30-100 mg / L.

6. The method for removing copper ions from strongly acidic wastewater by ascorbic acid-induced sulfidation according to claim 1, characterized in that, Sediment is removed by filtration.

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