Heavy metal wastewater treatment method

Abstract

The invention relates to sewage treatment, in particular to a heavy metal wastewater treatment method. The method comprises the following steps: adjusting the pH value of the heavy metal wastewater to 3-6; a substance containing phosphate radicals is added, so that the phosphate radicals are combined with the heavy metal ions, and heavy metal phosphate sol with negative electricity is formed; the method comprises the following steps of: adding a substance containing ferric ions, regulating the pH value to 5-8, hydrolyzing the ferric ions to generate a positively charged iron oxyhydroxide nano reticular floc (Feh nano for short) in situ, and settling the heavy metal phosphate sol under the electrostatic adsorption action of the iron oxyhydroxide nano reticular floc. The method can effectively remove free heavy metal ions or heavy metal complexes in the heavy metal wastewater.

Description

Technical Field

[0001] The invention relates to sewage treatment, and in particular to a method for treating heavy metal wastewater. Background Art

[0002] Heavy metal pollution is characterized by long-term, cumulative, latent and irreversible nature, which may seriously threaten the ecological environment and human health, and has become a major challenge in the field of water resources management. Heavy metal wastewater has complex components and various forms, and the development of economical and efficient technologies for improving standards and reducing emissions faces huge challenges. Although traditional methods such as chemical precipitation and coagulation have performed well in treating high-concentration heavy metals, the chemical composition of wastewater is still complex and there are many types of coexisting matrices, and the quality of treated water is often difficult to meet emission standards. In addition, deep treatment technologies such as ion exchange, adsorption and membrane separation have disadvantages such as high cost and high energy consumption. Therefore, seeking more effective and sustainable deep treatment solutions for heavy metal wastewater has become a research hotspot in the field of water treatment. Summary of the invention

[0003] Based on this, the present invention provides a method for treating heavy metal wastewater, which at least solves one problem in the prior art.

[0004] The present invention provides a method for treating heavy metal wastewater, comprising the following steps:

[0005] Adjust the pH value of heavy metal wastewater to 3-6;

[0006] Adding a phosphate-containing substance to combine the phosphate with the heavy metal ion to form a negatively charged heavy metal phosphate sol;

[0007] A substance containing trivalent iron ions is added, and the pH value is adjusted to 5-8, so that the trivalent iron ions are hydrolyzed and positively charged ferrihydrite nanonet (Feh nanonet) is generated in situ, and the heavy metal phosphate sol is precipitated by the electrostatic adsorption of the ferrihydrite nanonet.

[0008] Due to the adoption of the above technical solution, the embodiments of the present invention have at least the following beneficial effects:

[0009] (1) Both free heavy metals and complexed heavy metals can be removed through substances containing trivalent iron ions;

[0010] (2) Suitable for deep treatment of wastewater containing heavy metals such as Cu, Ni, Cd, Co, Mn, Pb and Cr, and can meet the drinking water standards of the World Health Organization (WHO);

[0011] (3) It can remove organic ligands in water and reduce COD in water; it can also remove phosphate in water and reduce phosphorus content in water;

[0012] (4) The concentrations of residual Fe(III) and phosphate in the water were low, less than 0.02 mg / L and 0.05 mg / L, respectively, meeting the sewage discharge standards;

[0013] (5) Low cost and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The CuSO containing 50 mg / L Cu(II) in Example 1 of the present invention 4 Comparison of the change of residual Cu(Ⅱ) concentration in the solution with pH value after the solution was treated under different conditions.

[0015] Figure 2 The CuSO containing 50 mg / L Cu(II) in Example 1 of the present invention 4 Comparison of the changes in the Zeta potential of the solution with pH value after the solution was treated under different conditions.

[0016] Figure 3 The CuSO4 was treated under different stirring and standing conditions in Example 2 of the present invention. 4 The concentration change of residual Cu(Ⅱ) in the solution.

[0017] Figure 4 The treatment of CuSO under different Cu / P molar ratios in Example 3 of the present invention 4 The concentration change of residual Cu(Ⅱ) in the solution.

[0018] Figure 5 The treatment of CuSO under different Cu / P molar ratios in Example 3 of the present invention 4 Graph showing changes in Zeta potential of the solution.

[0019] Figure 6 The treatment of CuSO under different Fe(III) concentration conditions in Example 4 of the present invention 4 The concentration change of residual Cu(Ⅱ) in the solution.

[0020] Figure 7 The MnSO containing 50 mg / L Mn(II) in Example 5 of the present invention 4 Comparison of the change of residual Cu(Ⅱ) concentration in the solution with pH value after the solution was treated under different conditions.

[0021] Figure 8 The MnSO containing 50 mg / L Mn(II) in Example 5 of the present invention 4 Comparison of the changes in the Zeta potential of the solution with pH value after the solution was treated under different conditions.

[0022] Fig. 9The residual Mn(II), PO4 and PO6 after treating the manganese sulfate solution under different Fe(III) concentration conditions in Example 6 of the present invention are shown in Table 1. 4 3- and Fe(Ⅲ) concentration changes.

[0023] Fig.10 This is a diagram showing the removal effect of the free heavy metal concentration in deionized water in Example 7 of the present invention.

[0024] Fig.11 This is a diagram showing the removal effect of free heavy metal concentration in tap water in Example 7 of the present invention.

[0025] Fig.12 This is a diagram showing the removal effect of the free heavy metal concentration in the natural water body of Ganjiang River in Example 7 of the present invention.

[0026] Fig.13 Graph showing the concentrations of free copper ions and copper-containing complexes as a function of Fe / Cu molar ratio in Example 8 of the present invention.

[0027] Fig.14 This is a graph showing the concentration of free iron ions and iron-containing complexes as a function of the Fe / Cu molar ratio in Example 8 of the present invention.

[0028] Fig.15 is the Cu / PO in Example 9 of the present invention 4 3- When the molar ratio is 3 / 1, the concentration of free copper and complexed copper in the solution changes with the Fe / Cu molar ratio.

[0029] Fig.16 is the Cu / PO in Example 9 of the present invention 4 3- The concentrations of free copper and complexed copper vary with the Fe / Cu molar ratio when the molar ratio is 3 / 2 and 1, respectively.

[0030] Fig.17 TEM images of flocs formed by 0.1 mM Fe(III) at pH 4.0, 5.0, 6.0, 7.0, 8.0 and 9.0 in Example 11 of the present invention.

[0031] Fig.18 TEM images of flocs formed when the concentration of Fe(III) was 0.1, 0.25, 0.5, 0.75, 1, 1.5, 2.5 and 5 mM respectively under the condition of pH being adjusted to 7.0 in Example 12 of the present invention.

[0032] Fig.19 This is a TEM image of the flocs formed by 0.1 mM Fe(III) at pH 7.0 and 8.0 in Example 12 of the present invention and the copper phosphate sol captured in the water. DETAILED DESCRIPTION

[0033] The following is a clear and complete description of the concept of the present invention and the technical effects produced, so as to fully explain the purpose, scheme and effect of the present invention.

[0034] The present invention provides a method for treating heavy metal wastewater, comprising the following steps:

[0035] S100, adjusting the pH value of heavy metal wastewater to 3-6;

[0036] S200, adding a phosphate-containing substance to combine the phosphate with the heavy metal ion to form a negatively charged heavy metal phosphate sol;

[0037] S300, adding a substance containing trivalent iron ions, and adjusting the pH value to 5-8, so as to hydrolyze the trivalent iron ions and generate positively charged ferrihydrite nanonet flocs (Feh nanonet for short) in situ, and precipitating the heavy metal phosphate sol through the electrostatic adsorption of the ferrihydrite nanonet flocs.

[0038] The method first combines phosphate with free heavy metals to generate negatively charged heavy metal phosphate insoluble sols, thereby increasing the size of heavy metal substances; then, a substance containing trivalent iron ions is added to hydrolyze the trivalent iron ions and generate Feh nanonets in situ; Feh nanonets capture the heavy metal phosphate insoluble sols in wastewater through electrostatic adsorption and net capture, and the ferric oxyhydroxide nano-mesh flocs slowly grow and settle, thereby achieving the removal of heavy metals in wastewater.

[0039] In some implementations, before step S200, the following steps are also included:

[0040] S150. Add substances containing trivalent iron ions to liberate heavy metal ions of heavy metal complexes in heavy metal wastewater.

[0041] It should be noted that heavy metal complexes may exist in heavy metal wastewater. If step S200 is directly performed after step S100, it is difficult for phosphate to combine with this part of heavy metal complexes. Adding step S1500 between step S100 and step S200 can release the heavy metal complexes through trivalent iron ions, thereby improving the treatment effect of heavy metal wastewater. For wastewater containing heavy metal complexes, Fe 3+ The complexation constant with organic ligands is usually larger than that of most heavy metals, such as Fe 3+ -EDTA's complex constant (lgK = 25.1) is higher than Ni 2+ -EDTA (lgK = 18.6) and Cu 2+-EDTA (lgK = 18.8) is several orders of magnitude larger; therefore, under slightly acidic conditions, Fe 3+ It will compete with heavy metal ions for organic ligands, causing the heavy metal complex to decomplex and release heavy metal ions; the free heavy metal ions then combine with phosphate to form negatively charged heavy metal phosphate colloids, which are then captured and removed by Feh nanonet formed by the hydrolysis of substances containing trivalent iron ions.

[0042] In some embodiments, the heavy metal wastewater contains at least one heavy metal ion of Cu, Ni, Cd, Co, Mn, Pb, Cr or a complex thereof.

[0043] In some embodiments, the phosphate-containing substance is a soluble phosphate or a solution thereof, and after adding the soluble phosphate or a solution thereof, the concentration of the phosphate is 1 / 3 to 2 times the total charge concentration (Q, mmol / L) of the heavy metals in the heavy metal wastewater. The soluble phosphate includes, but is not limited to, one or more of sodium hydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, and potassium phosphate.

[0044] In some embodiments, the phosphate-containing substance is sodium dihydrogen phosphate.

[0045] In some embodiments, the substance containing trivalent iron ions is a soluble small molecule inorganic iron salt or a solution thereof, and after adding the soluble small molecule inorganic iron salt or a solution thereof, the concentration of trivalent iron ions in the heavy metal wastewater is in the range of 0.05 to 5 mmol / L, preferably 0.1 to 1 mmol / L. The soluble small molecule inorganic iron salt includes, but is not limited to, one or more of ferric sulfate and ferric chloride.

[0046] In some embodiments, the substance containing ferric ions is a ferric chloride solution.

[0047] In some embodiments, step S200 is performed under stirring conditions. Preferably, step S200 is performed under stirring conditions at 500 rpm.

[0048] In some embodiments, step S300 is performed under stirring conditions. Preferably, step S300 is performed under stirring conditions at 100 rpm for 30 minutes.

[0049] In some implementations, after step S300, the following steps are further included:

[0050] S350, let stand for more than 3 hours.

[0051] In some embodiments, the mixture is allowed to stand for 1 to 2 days.

[0052] Some typical embodiments are described below.

[0053] Example 1: Removal of CuSO under different conditions 4 Free copper ions in solution

[0054] Prepare several 1L volumes of CuSO containing 50 mg / L Cu(II) 4 The solution was stirred at 500 rpm and the experiments were carried out according to the following conditions:

[0055] a) Control group: pH was adjusted to 6.0, 6.5, 7.0, 7.5 and 8.0 with NaOH;

[0056] b) Fe(Ⅲ) group: add ferric chloride solution to make CuSO 4 Fe in solution 3+ The concentration reached 0.1mmol / L, and after mixing evenly, the pH was adjusted to 6.0, 6.5, 7.0, 7.5 and 8.0 respectively;

[0057] c)PO 4 3- Group: sodium dihydrogen phosphate was added according to the Cu / P molar ratio of 3 / 2, and the pH was adjusted to 6.0, 6.5, 7.0, 7.5 and 8.0 respectively;

[0058] d)PO 4 3- +Fe(Ⅲ) group: first add sodium dihydrogen phosphate according to the Cu / P molar ratio of 3 / 2, and then add ferric chloride solution to make Fe 3+ The concentration reached 0.1mmol / L, and the pH was adjusted to 6.0, 6.5, 7.0, 7.5, and 8.0;

[0059] After adjusting the pH of the above solutions, the solutions were stirred at 100 rpm for 30 min, and then the solutions were allowed to stand for more than 1 day. The supernatant was taken and the Cu(Ⅱ) concentration (C Cu(Ⅱ) ) and Zeta potential value.

[0060] like Figure 1 As shown in the figure, in each group of experiments, the concentration of Cu(Ⅱ) decreased with the increase of pH value. 4 3- Compared with the PO group 4 3- Under the conditions of the +Fe(Ⅲ) group, the solution has a lower Cu(Ⅱ) concentration.

[0061] like Figure 2 As shown in PO 4 3- +Fe(Ⅲ) group, the Zeta potential of the solution is closer to 0. Example 2: Removal of CuSO under different stirring and standing times4 Free copper ions in solution

[0062] At a stirring speed of 500 rpm, a 1 L volume of CuSO containing a Cu(Ⅱ) concentration of 50 mg / L was first stirred. 4 In the solution, 49 mg / L PO was added according to the Cu / P molar ratio of 3 / 2. 4 3- , then add ferric chloride solution to make CuSO 4 Fe in solution 3+ The concentration was 0.1mmol / L; then the solution was slowly stirred at 100rpm for 60min and then allowed to stand for 2d; samples were taken at 0, 10, 20, 30, 40, 50, 60min after the start of slow stirring and at 3h, 1d, and 2d after the start of standing, and the residual Cu(Ⅱ) concentration (C Cu(Ⅱ) ).

[0063] The change of Cu(Ⅱ) concentration with stirring time and standing time is as follows Figure 3 As shown in the figure, when the slow stirring time is 30 minutes, the concentration of Cu(Ⅱ) in the solution is lower. Moreover, the longer the standing time, the lower the concentration of Cu(Ⅱ) in the solution; when the standing time exceeds 1 day, the concentration of Cu(Ⅱ) basically reaches stability.

[0064] Example 3: Removal of CuSO under different Cu / P molar ratios 4 Free copper ions in solution

[0065] Prepare several 1L volumes of CuSO containing 50 mg / L Cu(II) 4 The solution was stirred at 500 rpm and the experiments were carried out according to the following conditions:

[0066] a)PO 4 3- Group: sodium dihydrogen phosphate was added according to the Cu / P molar ratio of 3 / 1, 3 / 2, 3 / 3, 3 / 4 and 3 / 5, and the pH was adjusted to 7.0;

[0067] b)PO 4 3- +Fe(Ⅲ) group: PO was added at a Cu / P molar ratio of 3 / 1, 3 / 2, 3 / 3, 3 / 4 and 3 / 5 respectively 4 3- Then add ferric chloride solution to make Fe 3+ The concentration was 0.1mmol / L and the pH was adjusted to 7.0;

[0068] After adjusting the pH of the above solutions, the stirring was continued at 100 rpm for 30 min, and then the solutions were allowed to stand for more than 1 day, and the supernatant was taken to measure the Cu(II) concentration and Zeta potential value.

[0069] like Figure 4 and Figure 5 As shown in Figure 2, the concentration of Cu(Ⅱ) decreases with the decrease of Cu / P ratio, and the Zeta potential value of the solution also decreases gradually; moreover, the concentration of Cu(Ⅱ) increases with the decrease of PO 4 3- +Fe(Ⅲ) group than PO 4 3- The decrease in the concentration of Cu(Ⅱ) group was greater, indicating that the presence of Fe(Ⅲ) can reduce the concentration of Cu(Ⅱ) to a lower level. Figure 4 It also shows that in PO 4 3- Under the conditions of the +Fe(Ⅲ) group, when the Cu / P ratio was less than 3 / 2, the Cu(Ⅱ) concentration was lower than 1 mg / L.

[0070] Example 4: Removal of CuSO under different Fe(III) concentration conditions 4 Free copper ions in solution

[0071] At a stirring speed of 500 rpm, add several portions of 1 L of CuSO containing 50 mg / L Cu(II) 4 PO was added to the solution at a Cu / P molar ratio of 3 / 2. 4 3- Then, ferric chloride solution was added to make Fe 3+ The concentrations were 0.01, 0.05, 0.1, 0.2, 0.3, 0.4 and 0.5 mmol / L, respectively, and the pH was adjusted to 7.0; stirring continued at 100 rpm for 30 min, and then the solution was allowed to stand for more than 1 day, and the supernatant was taken and the Cu(Ⅱ) concentration was determined.

[0072] like Figure 6 As shown in the figure, when the Fe(Ⅲ) concentration exceeds 0.1mmol / L, the Cu(Ⅱ) concentration can be reduced to 0.1mg / L; further increasing the addition of Fe(Ⅲ), the Cu(Ⅱ) concentration will increase slightly.

[0073] Example 5: Removal of free manganese ions from high concentration manganese sulfate solution

[0074] This example is basically the same as Example 1, except that the copper sulfate solution with a Cu(II) concentration of 50 mg / L is replaced with a manganese sulfate solution with a Mn(II) concentration of 50 mg / L; sodium dihydrogen phosphate is added at a Mn / P molar ratio of 3 / 2; and the Mn(II) concentration (C Mn(Ⅱ) ) and Zeta potential value.

[0075] like Figure 7 and Figure 8 As shown, compared with the Control group, Fe(Ⅲ) group and PO 4 3- Compared with the PO group 4 3- +Fe(Ⅲ) group, the solution has a lower Mn(Ⅱ) concentration; 4 3- Under these conditions, the Zeta potential in the solution is lower.

[0076] Example 6: Removal of free manganese ions from low concentration manganese sulfate solution

[0077] Under rapid stirring at 500 rpm, 20.15 mg / L PO4 was added to a 1 L manganese sulfate solution with a Mn(II) concentration of 10 mg / L according to a Mn / P molar ratio of 3 / 4. 4 3- , then add ferric chloride solution to make Fe 3+ The concentrations were 0.1, 0.5, 1, 1.5 and 2.5 mmol / L, respectively, and the pH was adjusted to 8.0; then the stirring was continued at 100 rpm for 30 min, and the solution was allowed to stand for more than 1 day. The supernatant was taken and the residual Mn(Ⅱ), Fe(Ⅲ) and PO were determined respectively. 4 3- concentration.

[0078] like Fig. 9 As shown, the manganese sulfate solution was PO 4 3- +Fe(Ⅲ) treatment can reduce the Mn(Ⅱ) concentration from 10mg / L to below 0.3mg / L, and the residual Fe(Ⅲ) concentration in the solution is less than 0.2mg / L. 4 3- The concentration is lower than 0.30mg / L.

[0079] Example 7: Removal of multiple heavy metal ions from water

[0080] Mixed heavy metal solutions (Pb(Ⅱ), Cr(Ⅲ), Cd(Ⅱ), Cu(Ⅱ), Mn(Ⅱ) and Hg(Ⅱ)) were prepared with deionized water, tap water and Ganjiang River water, respectively. The concentration of each heavy metal (M) was 10 mg / L. 总 Add sodium dihydrogen phosphate with a molar ratio of 6 / 7, and stir rapidly for 3-5 minutes; then add 0.5 mM Fe(Ⅲ), and stir rapidly for 3-5 minutes; then adjust to pH 8, and stir slowly for 15-30 minutes; after standing for 30 minutes, take the supernatant and test the concentration of each heavy metal.

[0081] like Figure 10-12As shown, PO 4 3- +Fe(Ⅲ) can remove mixed heavy metal ions in different water bodies. Except for Hg(Ⅱ), the residual concentrations of other heavy metals are lower than the concentrations specified by the World Health Organization's drinking water (WHO) standards.

[0082] Example 8: Promoting the Freedom of Copper Ions in Copper-Containing Complexes by Using Trivalent Iron Ions

[0083] Ferric chloride was added to a Cu-EDTA solution containing a Cu(Ⅱ) concentration of 10 mg / L and a Cu / EDTA molar ratio of 3 / 2 at Fe / Cu molar ratios of 1 / 1, 3 / 2, 2 / 1, 3 / 1 and 4 / 1, and the solution was stirred rapidly for 3-5 minutes; the pH was then adjusted to 8 and stirred slowly for 15-30 minutes; after standing for 30 minutes, the supernatant was taken and the concentrations of various heavy metals were tested.

[0084] like Fig.13 and Fig.14 As shown in Figure 2, with the increase of Fe / Cu molar ratio, the concentration of free Cu(Ⅱ) and complexed Fe(Ⅲ) in the solution gradually increased ( Fig.13 ), while the concentrations of complexed Cu(Ⅱ) and free Fe(Ⅲ) gradually decreased ( Fig.14 ), indicating that Fe(Ⅲ) can break the Cu-EDTA complex and convert the complexed Cu(Ⅱ) into free Cu(Ⅱ).

[0085] Example 9: Removal of free copper ions and copper-containing complexes in water

[0086] Ferric chloride was added to a Cu-EDTA solution containing 10 mg / L Cu(Ⅱ) and a Cu / EDTA molar ratio of 3 / 2 at Fe / Cu molar ratios of 1 / 1, 3 / 2, 2 / 1, 3 / 1 and 4 / 1, and stirred rapidly for 3-5 min. 4 3- PO was added at molar ratios of 3 / 1, 3 / 2 and 1 4 3- ; Then adjust the pH to 8 and stir slowly for 15-30 minutes; after standing for 30 minutes, take the supernatant and test the concentration of various heavy metals.

[0087] like Fig.15 and Fig.16 As shown in the figure, when phosphate is added, both the complexed copper and the free copper in the solution increase with the Cu / PO 4 3- The molar ratio of Cu / PO 4 3-When the molar ratio is 3 / 1 and the Fe / Cu molar ratio is 4 / 1, the total copper concentration (complexed + free) can be reduced to less than 1 mg / L ( Fig.15 ). This result shows that PO 4 3- +Fe(Ⅲ) combination can remove complex heavy metals in water.

[0088] Example 10: Removal of heavy metal ions from electroplating wastewater

[0089] Electroplating wastewater from an industrial park in Wan'an City, Ji'an City, Jiangxi Province, was first added and then 2mg / LPO 4 3- , then add 0.5mmol / L Fe(Ⅲ), adjust the pH to 7.0, and settle for 30min. The indicators of various pollutants before and after water treatment are shown in Table 1.

[0090] Table 1 Pollutant indicators before and after electroplating wastewater treatment

[0091]

[0092] The results show that the method of the present invention can reduce the concentrations of Ni and Cr in electroplating wastewater from about 1 mg / L to 0.0375 and 0.0227 mg / L respectively. At the same time, it has a good removal effect on COD, total phosphorus and total nitrogen in water samples.

[0093] Example 11: Formation of Feh nanonet under different pH conditions

[0094] At a stirring speed of 500 rpm, 1 mol / L NaOH was added dropwise to 6 portions of 1 L ferric sulfate solution with a Fe(III) concentration of 0.1 mmol / L, and the pH values ​​were adjusted to 4.0, 5.0, 6.0, 7.0, 8.0 and 9.0, respectively; then, the stirring speed was reduced to 100 rpm, and the stirring was continued for about 30 min and then allowed to stand; after the sedimentation was completed, the flocs in the water were taken for transmission electron microscopy (TEM) morphology analysis.

[0095] like Fig.17 As shown in the figure, when the pH of Fe(Ⅲ) solution is adjusted to 5.0, Feh nanonet can be generated in the solution; and as the pH increases, the mesh of Feh nanonet gradually shrinks and aggregates. That is, Fe(Ⅲ) can generate Feh nanonet in the pH range of 5 to 8.

[0096] Example 12: Formation of Feh nanonet under different Fe(III) concentration conditions

[0097] At a stirring speed of 500 rpm, 1 M NaOH was added dropwise to 6 portions of 1 L ferric sulfate solutions with Fe(III) concentrations of 0.1, 0.25, 0.5, 0.75, 1.0, 1.5, 2.5 and 5 mmol / L, respectively, to adjust the pH of the solution to 7.0; then, the stirring speed was reduced to 100 rpm, and stirring was continued for about 30 min and then allowed to stand; after sedimentation was completed, the flocs in the water were taken for transmission electron microscopy (TEM) morphology analysis.

[0098] like Fig.18 As shown in Figure 2, with the increase of Fe(Ⅲ) concentration, the Fe(OH) 3 The skeleton gradually increases in size and aggregates.

[0099] like Fig.19 As shown, Feh nanonet can capture heavy metal phosphate sol from water. Figure 17-Figure 19 The TEM results show that under the conditions of pH range of 5-8 and relatively low Fe(Ⅲ) concentration of 0.01-2mM, the formed Feh nanonet can capture negatively charged electrosols in water, such as heavy metal phosphates and organic colloids.

[0100] The above is only a preferred embodiment of the present invention. The present invention is not limited to the above implementation. As long as the technical effect of the present invention is achieved by the same or equivalent means, it should belong to the protection scope of the present invention. Within the protection scope of the present invention, its technical scheme and / or implementation method can have various modifications and changes.

Claims

1. A method for treating heavy metal wastewater, It is characterized in that The following steps are involved: S100, adjusting the pH value of heavy metal wastewater to 3-6; S200, adding a phosphate-containing substance to combine the phosphate with the heavy metal ion to form a negatively charged heavy metal phosphate sol; S300, adding a substance containing trivalent iron ions, and adjusting the pH value to 5-8, so as to hydrolyze the trivalent iron ions and generate positively charged ferric hydroxide nano-mesh flocs in situ, and precipitating the heavy metal phosphate sol through the electrostatic adsorption of the ferric hydroxide nano-mesh flocs.

2. The method according to claim 1, It is characterized in that Before step S200, the method further includes the following steps: S150. Add substances containing trivalent iron ions to liberate heavy metal ions of heavy metal complexes in heavy metal wastewater.

3. The method according to claim 1 or 2, It is characterized in that Heavy metal wastewater contains at least one heavy metal ion or its complex among Cu, Ni, Cd, Co, Mn, Pb and Cr.

4. The method according to claim 1 or 2, It is characterized in that The phosphate-containing substance is a soluble phosphate or a solution thereof. After the soluble phosphate or a solution thereof is added, the concentration of the phosphate is made to be 1 / 3 to 2 times of the total charge concentration of the heavy metals in the heavy metal wastewater.

5. The method according to claim 4, It is characterized in that The substance containing phosphate is sodium dihydrogen phosphate.

6. The method according to claim 1 or 2, It is characterized in that The substance containing trivalent iron ions is a soluble small molecule inorganic iron salt or its solution. After adding the soluble small molecule inorganic iron salt or its solution, the concentration of trivalent iron ions in the heavy metal wastewater is adjusted to a range of 0.05 to 5 mmol / L.

7. The method according to claim 6, It is characterized in that The substance containing trivalent iron ions is ferric chloride solution.

8. The method according to claim 1 or 2, It is characterized in that Step S200 is performed under stirring conditions.

9. The method according to claim 1 or 2, It is characterized in that Step S300 is performed under stirring conditions.

10. The method according to claim 1 or 2, It is characterized in that After step S300, the following steps are also included: S350, let stand for more than 3 hours.

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