A method for improving nickel removal effect and precipitation performance of stainless steel pickling wastewater

Abstract

The invention discloses a method for improving the nickel removal effect and precipitation performance of stainless steel pickling wastewater, wherein montmorillonite or primary precipitation sludge is added to primary precipitation stainless steel pickling wastewater, the pH is adjusted to alkaline and then reacted at room temperature, and a PAM solution is added after the reaction to continue the reaction at room temperature; the primary precipitation stainless steel pickling wastewater is obtained after the stainless steel pickling wastewater is treated with primary precipitation; the primary precipitation sludge is obtained after the sludge generated after the stainless steel pickling wastewater is treated with primary precipitation and the supernatant is removed after standing. The method of the invention can improve the nickel removal effect and sludge precipitation performance, and reduce the economic cost and time cost of stainless steel pickling wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and more particularly to a method for improving nickel removal effect and precipitation performance of stainless steel pickling wastewater. Background Art

[0002] During stainless steel production, to improve the steel's surface structure or perform surface treatments, the surface must be cleaned with the corrosive action of strong acids to remove rust. However, as the cleaning acid concentration decreases, the pickling effect deteriorates. Maintaining a certain acidity requires replacing the acid solution, which results in the generation of large quantities of stainless steel pickling wastewater containing high concentrations of metal ions. Stainless steel pickling wastewater contains large amounts of nitric acid, hydrofluoric acid, and metal ions such as iron, chromium, and nickel. It is highly toxic, highly acidic, produces large quantities of wastewater, and is difficult to treat. This poses a significant potential threat to the environment and human health, and must meet treatment standards before discharge.

[0003] At present, the treatment of stainless steel pickling wastewater mainly adopts chemical precipitation method, which usually includes two steps of precipitation (such as Figure 1 As shown in the figure), the stainless steel pickling wastewater enters the pickling wastewater collection tank, and after the hexavalent chromium is reduced to trivalent chromium by the reducing agent, it enters the pH regulating tank; carbide slag is added to the pH regulating tank to make the pH = 4.0, so that the F in the pickling wastewater — 、Fe 3+ and a large amount of Cr 3+ The mixed liquid is sent to the primary sedimentation tank for precipitation and separation, and the supernatant is separated and sent to the supernatant clarification tank, and liquid alkali is added to make the remaining Cr 3+ and Ni 2+ Metal hydroxide is formed, and then the waste liquid enters the secondary sedimentation tank. PAM is added to the secondary sedimentation tank to make the sediment settle quickly and achieve mud-water separation. 2+ Sedimentation treatment requires a high pH and a large amount of PAM flocculant, which increases the cost of water post-treatment. Therefore, improvements are needed. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a method for improving the nickel removal effect and precipitation performance of stainless steel pickling wastewater, which can improve the nickel removal effect and sludge precipitation performance and reduce the economic cost and time cost of stainless steel pickling wastewater treatment.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for improving the nickel removal effect and precipitation performance of stainless steel pickling wastewater, comprising adding montmorillonite or primary precipitation sludge to the primary precipitation stainless steel pickling wastewater, adjusting the pH to alkaline, and reacting at room temperature, and then adding a PAM solution to continue the reaction at room temperature;

[0007] The first-level sedimentation stainless steel pickling wastewater is obtained after the stainless steel pickling wastewater is subjected to first-level sedimentation treatment; the first-level sedimentation sludge is obtained after the sludge generated after the stainless steel pickling wastewater is subjected to first-level sedimentation treatment is allowed to stand and the supernatant is removed.

[0008] Furthermore, the primary precipitation stainless steel pickling wastewater contains Cr 3+ 0.2~0.4ppm, containing F — 3~7ppm, containing Ni 2+ 250~400ppm, its pH is 4.2-4.8.

[0009] Furthermore, when the primary sedimentation sludge is added for reaction, the volume ratio of the primary sedimentation stainless steel pickling wastewater to the primary sedimentation sludge is 100:(3~8).

[0010] Furthermore, when the primary sedimentation sludge is added for reaction, the pH of the reaction system is 8-9.5.

[0011] Furthermore, when montmorillonite is added to the reaction, the dosage ratio of the first-stage precipitated stainless steel pickling wastewater to montmorillonite is 100 mL: (50~500) mg.

[0012] Furthermore, when montmorillonite is added for reaction, the pH of the reaction system is 8-9.5.

[0013] Furthermore, liquid alkali is used to adjust the pH.

[0014] Furthermore, the concentration of the PAM solution is 500-2000 ppm.

[0015] The beneficial effects of the present invention are:

[0016] The present invention uses montmorillonite or the primary sedimentation sludge produced after the primary sedimentation treatment to treat the primary sedimentation stainless steel pickling wastewater, which reduces Ni 2+ The treatment pH and PAM dosage improve the nickel removal effect and sludge sedimentation performance, and can replace the conventional secondary sedimentation method of stainless steel pickling wastewater, reducing the economic and time costs of stainless steel pickling wastewater treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a process flow chart for secondary precipitation treatment of stainless steel pickling wastewater in the prior art;

[0018] Figure 2 This is a comparison chart of nickel removal effects of treating primary sedimentation stainless steel pickling wastewater with different primary sedimentation sludge amounts at pH=8.0;

[0019] Figure 3This is a comparison chart of nickel removal effects with and without adding primary sedimentation sludge at different pH levels;

[0020] Figure 4 This is a comparison chart of nickel removal effects in treating primary precipitation stainless steel pickling wastewater with different montmorillonite addition amounts;

[0021] Figure 5 This is a comparison chart of nickel removal effects when adding equal amounts of montmorillonite to treat primary precipitation stainless steel pickling wastewater at different pH values;

[0022] Figure 6 The figure shows the comparison of nickel removal effect with and without adding montmorillonite at different pH values. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] The overall scheme of the method for improving the nickel removal effect and precipitation performance of stainless steel pickling wastewater of the present invention is: to precipitate stainless steel pickling wastewater (the stainless steel pickling wastewater obtained after the first-level precipitation treatment, containing Cr 3+ 0.2~0.4ppm, containing F — 3~7ppm, containing Ni 2+ The first-stage sedimentation sludge (the sludge produced by the first-stage sedimentation treatment of stainless steel pickling wastewater, which is left to stand and the supernatant is removed) or montmorillonite is added to the reaction mixture (the concentration is 250~400ppm, the pH is 4.2-4.8), the pH is adjusted to alkaline (usually pH 8~9.5) with liquid caustic soda, and the reaction is carried out at room temperature. After the reaction, a PAM solution with a concentration of 500~2000ppm is added to continue the reaction at room temperature.

[0025] When adding primary sedimentation sludge for reaction, the volume ratio of primary sedimentation stainless steel pickling wastewater to primary sedimentation sludge is 100: (3~8); when adding montmorillonite for reaction, the dosage ratio of primary sedimentation stainless steel pickling wastewater to montmorillonite is 100mL: (50~500)mg.

[0026] Specific preferred embodiments are as follows:

[0027] Preparation before the experiment:

[0028] (1) Take the sludge produced by the primary sedimentation treatment of stainless steel pickling wastewater and place it in a container. After standing, pour out the supernatant to obtain the primary sedimentation sludge. 10 mL of the first-stage sedimentation sludge was placed in a watch glass and dried in an oven at 110°C until the difference between the two weights was ≤0.4 mg, yielding 0.899 g of dry sludge (tested to contain 32.415 wt% of F element, 1.3 wt% of Na2O, 0.071 wt% of MgO, 0.98 wt% of Al2O3, 3.082 wt% of SiO2, 0.11 wt% of P2O5, 1.264 wt% of SO3, 0.205 wt% of Cl element, 0.031 wt% of K2O, 21.28 wt% of CaO, 4.025 wt% of Cr2O3, 0.16 wt% of MnO, 31.405 wt% of Fe2O3, 0.157 wt% of Co3O4, 3.257 wt% of NiO, 0.122 wt% of CuO, 0.007 wt% of SrO, and 0.13 wt% of MoO3). The concentration of the first-stage sedimentation sludge was calculated to be 89.9 g / L.

[0029] (2) Prepare the first-level precipitation stainless steel pickling wastewater (containing Cr 3+ 0.262ppm, F — 4.45ppm, Ni 2+ 300ppm, pH=4.2)

[0030] The primary sedimentation sludge and primary sedimentation stainless steel pickling wastewater were both provided by Zhejiang Lishui Songyang Jiayuan Environmental Protection Company and were taken from the primary sedimentation tank after being treated according to the primary sedimentation treatment method for stainless steel pickling wastewater described in the background technology.

[0031] Example 1

[0032] Take 5 portions of 100 mL of the first-stage precipitated stainless steel pickling wastewater and add them to 250 mL reaction bottles, respectively. Then add 0 mL, 1 mL, 2 mL, 3 mL, 4 mL, and 5 mL of the first-stage precipitated sludge, respectively. Add liquid alkali to make the system pH = 8.0. Transfer the reaction bottle to a shaker at 25 ° C and 300 rpm to react for 3 hours. After the reaction, the Ni in the wastewater was analyzed using a Shimadzu AA-7000 atomic absorption spectrometer. 2+ Test results are as follows: Figure 2 As shown in the figure, it can be seen that with the increase of the amount of sedimentation sludge, Ni 2+ The concentration of Ni 2+ The removal effect is obvious.

[0033] Example 2

[0034] Take 6 portions of 100 mL of the first-stage precipitation stainless steel pickling wastewater and add them to 250 mL reaction bottles respectively. Then divide them into experimental group and blank control group. Add 5 mL of first-stage precipitation sludge to each experimental group. Add liquid alkali to make the pH value of each solution be pH=8.0, pH=8.5, and pH=9.0 respectively. Then transfer the reaction solution to a shaker at 25 ℃ and 300 rpm for 3 hours. After the reaction, use Shimadzu AA-7000 atomic absorption spectrometer to analyze Ni in the wastewater. 2+ Test results are as follows: Figure 3 As shown in the figure, it can be seen that the nickel content was significantly reduced when the primary sedimentation sludge was added under the experimental pH conditions, and reached the discharge standard (<1ppm) under the treatment condition of pH=9.0.

[0035] Example 3

[0036] The sludge volume index (SVI) value can better reflect the looseness and coagulation and sedimentation performance of activated sludge; a good activated sludge SVI is usually between 50 and 120.

[0037] This example tests the sludge sedimentation performance. Two 200mL portions of primary precipitated stainless steel pickling wastewater were taken and added to reaction bottles, with 5mL of primary precipitated sludge added to one bottle and the other bottle serving as a control group. The pH was then adjusted to 9.0 with liquid caustic soda and the bottles were transferred to a shaker at 25°C and 300rpm for reaction for 3 hours. After the reaction, 1mL of 1000ppm PAM (polyacrylamide) solution was added to each reaction bottle, and the shaker was continued for 5 minutes. After the reaction, the reaction liquids were transferred to 250mL graduated cylinders to obtain 212mL of sludge mixed solution from the experimental group and 208mL of sludge mixed solution from the control group. After standing for 5 minutes, the SVI5 of the sludge was measured and the sludge sedimentation performance was evaluated. The measurement results are shown in Table 1 (in the table, m 湿 is the mass of wet sludge separated by centrifugation after the sludge mixture has been allowed to stand for 5 minutes, m 干 is the mass of wet sludge after drying).

[0038] The sludge volume index (SVI5) is calculated as follows:

[0039]

[0040] Where SV5 is the sludge settling ratio, in mL / L; X TSS is the sludge concentration after reaction, in g / L.

[0041]

[0042]

[0043] Table 1 Sludge sedimentation performance test results

[0044]

[0045] According to the results of sludge sedimentation performance test, after adding the first-stage sedimentation sludge, SVI5 was greatly reduced compared with the blank group, indicating that adding the first-stage sedimentation sludge can promote the sedimentation performance of the sludge and reduce the amount of PAM to a certain extent, which can reduce the economic cost and time cost of the existing stainless steel pickling wastewater treatment process. In addition, after testing, the Cr content in the wastewater of the experimental group after the reaction was 3+ 、F — 、Ni 2+ All meet emission standards.

[0046] Example 4

[0047] Take 6 portions of 100 mL of the first-stage precipitated stainless steel pickling wastewater in 250 mL reaction bottles, add 0 mg, 50 mg, 100 mg, 150 mg, 200 mg, and 250 mg of montmorillonite (sodium montmorillonite, 200 mesh), respectively, add liquid alkali to adjust the pH of the system to 9.1, transfer the reaction bottle to a shaker at 300 rpm and 25 ° C for reaction, and use Japan Shimadzu AA-7000 atomic absorption spectrometer to analyze Ni after 90 minutes of reaction. 2+ The concentration was determined from the results (see Figure 4 ) It can be seen that with the increase of montmorillonite dosage, Ni 2+ The lower the residual concentration, the better the removal effect.

[0048] Example 5

[0049] Take 5 portions of 100 mL of the first-stage precipitated stainless steel pickling wastewater and add them to 250 mL reaction bottles, add 150 mg of montmorillonite, and add liquid alkali to adjust the solution pH to 8.5, pH to 8.75, pH to 9.0, pH to 9.25 and pH to 9.5 respectively. Transfer the reaction bottle to a shaker at 300 rpm and 25 ° C for reaction. After the reaction, use Shimadzu AA-7000 atomic absorption spectrometer to analyze the Ni 2+ The concentration was determined from the results (see Figure 5 ) It can be seen that when pH=8~9, as the pH increases, Ni 2+ The concentration continued to decrease, and when pH=9.25, Ni 2+ < 1ppm, meeting emission standards.

[0050] Example 6

[0051] Take 8 portions of 100 mL of primary precipitation stainless steel pickling wastewater and add them to 250 mL reaction bottles, and divide them into experimental group and control group. 150 mg of montmorillonite is added to each experimental group. Liquid alkali is added to adjust the pH of each solution to 8.0, pH=8.5, pH=9.0, and pH=9.25 respectively. Then transfer the reaction bottle to a shaker at 300 rpm and 25 ° C for reaction. After the reaction, the Ni 2+ The concentration was determined from the results (see Figure 6 ) It can be seen that when pH=8~9, with the increase of pH, Ni 2+ The concentration of Ni 2+ It is always smaller than the control group. When pH=9.25, Ni 2+ < 1ppm, meeting emission standards.

[0052] Example 7

[0053] This example tests sludge sedimentation performance. Two 200mL portions of primary stainless steel pickling wastewater were added to reaction flasks, one of which contained 300mg of montmorillonite, while the other served as a blank control. The pH of each flask was then adjusted to 9.25 with caustic soda. The flasks were then shaken at 25°C and 300rpm for reaction. After the reaction, 1mL of a 1000ppm PAM solution was added to the flasks, and the shaker was shaken for 5 minutes. After the reaction, the two reaction solutions were transferred to 250mL graduated cylinders, yielding 208mL of experimental and 202mL of control sludge mixtures. The SVI5 values ​​of the sludges were measured, and the sludge sedimentation performance was evaluated. The results are shown in Table 2.

[0054] Table 2 Results of sludge performance test

[0055]

[0056] According to the results of sludge sedimentation performance test, after adding montmorillonite, SVI5 was greatly reduced compared with the blank group, indicating that adding montmorillonite can promote the sedimentation performance of sludge and reduce the amount of PAM to a certain extent, thus reducing the economic cost and time cost of stainless steel pickling wastewater treatment process. In addition, after testing, the Cr 3+ 、F — 、Ni 2+ All meet emission standards.

[0057] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving the nickel removal effect and precipitation performance of stainless steel pickling wastewater, characterized in that: Add montmorillonite or primary precipitation sludge to the primary precipitation stainless steel pickling wastewater, adjust the pH to alkaline and react at room temperature, add PAM solution after the reaction and continue the reaction at room temperature; When adding primary precipitated sludge to react, the pH of the reaction system is 9, and the dosage ratio of primary precipitated stainless steel pickling wastewater to primary precipitated sludge and PAM is 200mL:5mL:1mg; when adding montmorillonite to react, the pH of the reaction system is 9.25, and the dosage ratio of primary precipitated stainless steel pickling wastewater to montmorillonite and PAM is 200mL:300mg:1mg; The primary precipitated stainless steel pickling wastewater is obtained after the stainless steel pickling wastewater is treated with primary precipitation; the primary precipitated sludge is obtained after the sludge generated after the stainless steel pickling wastewater is treated with primary precipitation is allowed to stand and the supernatant is removed.

2. A method for improving the nickel removal effect and precipitation performance of stainless steel pickling wastewater according to claim 1, characterized in that: Cr in primary precipitation stainless steel pickling wastewater 3+ 0.2~0.4ppm, containing F — 3~7ppm, containing Ni 2+ 250~400ppm, its pH is 4.2-4.

8.

3. A method for improving the nickel removal effect and precipitation performance of stainless steel pickling wastewater according to claim 1, characterized in that: Liquid alkali was used to adjust the pH.

4. A method for improving the nickel removal effect and precipitation performance of stainless steel pickling wastewater according to claim 1, characterized in that: The concentration of PAM solution is 500~2000ppm.

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