A step-by-step treatment method for wastewater containing ruthenium and zinc

Abstract

The present invention discloses a step-by-step treatment method for wastewater containing ruthenium and zinc. In this method, the pH value of the wastewater is first adjusted to acidic to convert ruthenium into a precipitate and remove it; then the pH value of the wastewater is adjusted to alkaline to convert zinc into a precipitate and remove it. The present invention can make the concentrations of ruthenium and zinc in the wastewater both lower than 1.0 mg / L, eliminate the color of the wastewater, and meet the requirements for metal elements in the direct discharge of wastewater; and it can achieve the step-by-step removal of ruthenium and zinc elements, which is beneficial to subsequent recycling and reuse.

Description

Technical Field

[0001] The present invention belongs to the field of wastewater treatment, and particularly relates to a step-by-step treatment method for ruthenium- and zinc-containing wastewater. Background Art

[0002] In recent years, ruthenium has shown unique and stable catalytic properties in industrial catalysis and organic synthesis, thus attracting the attention of many scholars. The research and application of ruthenium-based catalysts in the chemical industries such as the utilization of by-product hydrogen chloride, ammonia synthesis, Fischer-Tropsch synthesis, and selective hydrogenation of benzene have emerged in an endless stream. Since ruthenium-containing groups generally have colors, colored ruthenium-containing wastewater will be generated during the preparation of ruthenium-based catalysts. The ruthenium in the wastewater must be removed to eliminate the color of the wastewater and meet the requirements for direct discharge of the wastewater. At the same time, the wastewater generated during the preparation of the above catalysts often contains not only ruthenium as a metal element, but also other metal elements that must be removed.

[0003] Taking the catalyst for selective hydrogenation of benzene to cyclohexene as an example, the catalyst is a ruthenium-zinc bimetallic catalyst. The alkaline wastewater generated during the catalyst preparation process contains both ruthenium and zinc elements, and the concentrations of ruthenium and zinc in the wastewater are relatively low, ≤50.0 mg / L and ≤500.0 mg / L respectively. Although the ruthenium concentration in the wastewater is relatively low, the wastewater is still significantly colored. As the ruthenium concentration in the wastewater increases, the color of the wastewater changes from light yellow to brownish yellow. The research results show that when the ruthenium concentration ≤2.0 mg / L, the wastewater chromaticity (dilution multiple) ≤50, and it can basically be considered colorless, meeting the requirements of the national standard GB 8978-1996 Comprehensive Wastewater Discharge Standard; when the ruthenium concentration >2.0 mg / L, the wastewater chromaticity (dilution multiple) >50, and the wastewater cannot be directly discharged. Therefore, to meet the requirements for direct discharge of the wastewater, the ruthenium concentration in the treated wastewater needs to be ≤2.0 mg / L. At the same time, according to the requirements of the national standard GB 8978-1996, the zinc concentration in the treated wastewater needs to be ≤2.0 mg / L. In summary, the ruthenium and zinc concentrations in the treated wastewater are both ≤2.0 mg / L to meet the requirements for direct discharge of the wastewater.

[0004] There are many studies on removing zinc from zinc-containing wastewater, but there is no report on the in-depth removal of ruthenium from ruthenium-containing wastewater from the perspective of wastewater treatment, especially when the ruthenium concentration in the treated wastewater is ≤2.0 mg / L. There are many studies on the field of ruthenium recovery and purification, such as recovering ruthenium from ruthenium-containing solutions. The focus of such studies is on the ruthenium recovery rate, and the ruthenium concentration in the treated solution is still relatively high, making the treated solution still colored and unable to achieve direct discharge.

[0005] As disclosed in the patent application CN103380219A, a method for recovering ruthenium or ruthenium compounds discloses a method for recovering ruthenium from a ruthenium compound solution. By adding an inorganic adsorbent to the ruthenium compound solution, then adding an acid to dissolve the inorganic adsorbent, and then adjusting the pH value to above 7 with an alkaline solution to precipitate the inorganic adsorbent, and ruthenium or ruthenium compounds are adsorbed on the inorganic adsorbent. The inorganic adsorbent described is one or a mixture of calcium phosphate compounds, talc compounds, and amorphous aluminosilicates. Examples show that the ruthenium concentration in the solution before treatment is 650 ppm to 810 ppm, and the ruthenium concentration in the solution after treatment is 3.7 ppm to 9.5 ppm.

[0006] As disclosed in the patent application CN111235395A, a method for recovering ruthenium from a ruthenium-containing solution discloses a method for recovering ruthenium from a ruthenium-containing solution. By adding an alkali to adjust the pH value of the prepared ruthenium-containing solution to be alkaline, then adding a sodium hypochlorite solution for reaction, and finally adding a precipitant, filtering, and washing the precipitate until there are no impurity ions, and the filter cake is treated with hydrochloric acid to be converted into a ruthenium chloroacid solution. Examples show that the ruthenium concentration in the solution before treatment is 0.25%, and the ruthenium concentration in the solution after treatment is 5 ppm to 18 ppm.

[0007] The information disclosed in the foregoing background art section is only used to enhance the understanding of the background of the present invention, and it may include information not known to those of ordinary skill in the art. Summary of the Invention

[0008] The object of the present invention is to provide a method for treating wastewater containing ruthenium and zinc, which can treat both the ruthenium concentration and the zinc concentration to below 1.0 mg / L, and can realize the separation of ruthenium-containing precipitate and zinc-containing precipitate, which is beneficial to the recycling and reuse of ruthenium metal.

[0009] The present invention provides a step-by-step treatment method for wastewater containing ruthenium and zinc, including:

[0010] (1) Adjust the pH value of the wastewater containing ruthenium and zinc to acidic to convert ruthenium into a precipitate;

[0011] (2) With or without a flocculant in the wastewater, remove the precipitate;

[0012] (3) Adjust the pH value of the wastewater treated in step (2) to alkaline to convert zinc into a precipitate.

[0013] (4) With or without a flocculant in the wastewater, remove the precipitate;

[0014] The pH value of the wastewater containing ruthenium and zinc > 12, and ruthenium exists in an anionic group.

[0015] According to the treatment method of the present invention, in step (1), the pH value of the wastewater is adjusted to 2 to 4.

[0016] According to the treatment method of the present invention, in step (2), when the wastewater contains a flocculant, it is preferred to firstly allow the wastewater to settle, separate the supernatant, and then separate and remove the precipitate.

[0017] According to the treatment method of the present invention, in step (3), the pH value of the wastewater is adjusted to 10-11.

[0018] According to the treatment method of the present invention, in step (4), when the wastewater contains a flocculant, it is preferred to firstly allow the wastewater to settle, separate the supernatant, and then separate and remove the precipitate.

[0019] According to the treatment method of the present invention, in step (2) and step (4), conventional solid-liquid separation methods can be used to remove the precipitate, such as using one or more of filtration, sedimentation or centrifugal separation to remove the precipitate.

[0020] According to the treatment method of the present invention, the wastewater contains ruthenium in the form of or substantially in the form of [RuCHO 3 ] - 、[RuC 2 H 3 SO 5 ] - 、[RuC 4 H 5 OCl 2 ] - and [RuC 3 H 4 O 4 Cl] - The "substantially" means that, except for [RuCHO 3 ] - 、[RuC 2 H 3 SO 5 ] - 、[RuC 4 H 5 OCl 2 ] - and [RuC 3 H 4 O 4 Cl] - Except for one or several forms of ruthenium present in the wastewater, the total content of other forms of ruthenium in the wastewater is less than 1.0 mg / L.

[0021] According to the treatment method of the present invention, the pH value of the wastewater is greater than 12. In the wastewater, zinc is present in anionic groups (such as ZnO 2 2- ).

[0022] According to the treatment method of the present invention, in step (2) or step (4), a flocculant may or may not be added. Adding a flocculant can accelerate sedimentation, and whether or not a flocculant is added, the object of the present invention can be achieved, meeting the requirements for ruthenium and zinc elements in the direct discharge of wastewater.

[0023] According to the treatment method of the present invention, when a flocculant is added in step (2) and / or step (4), there is no particular limitation on the added flocculant, and those skilled in the art can select it according to the conventional usage requirements of the flocculant. When flocculants are added in both step (2) and step (4), the flocculants may be the same or different, and each independently selected from one or more of organic polymer flocculants and inorganic polymer flocculants. The organic polymer flocculant is preferably a polyacrylamide flocculant. The mass ratio of the polyacrylamide flocculant to the wastewater can be (10 -6 ~10 -5 ) : 1. The polyacrylamide flocculant can be used as an aqueous solution with a mass fraction of 0.01% to 0.5%, preferably as an aqueous solution with a mass fraction of 0.05% to 0.3%. The inorganic polymer flocculant is preferably a polyaluminum chloride flocculant. The mass ratio of the polyaluminum chloride flocculant to the wastewater is (10 -6 ~10 -4 ) : 1. The polyaluminum chloride flocculant can be used as an aqueous solution with a mass fraction of 0.01% to 3.0%, preferably as an aqueous solution with a mass fraction of 0.05% to 0.5%.

[0024] According to the treatment method of the present invention, in the wastewater before treatment, calculated by the mass of ruthenium element, the ruthenium concentration is preferably ≤ 50.0 mg / L, more preferably 5.0 mg / L to 50.0 mg / L.

[0025] According to the treatment method of the present invention, in the wastewater before treatment, calculated by the mass of zinc element, the zinc concentration is preferably ≤ 500.0 mg / L, more preferably 10.0 mg / L to 500.0 mg / L.

[0026] According to the treatment method of the present invention, in the wastewater before treatment, the sodium concentration is generally 800.0 mg / L to 16000.0 mg / L.

[0027] According to the treatment method of the present invention, in the wastewater before treatment, the chloride ion concentration is generally 90.0 mg / L to 6000.0 mg / L.

[0028] According to the treatment method of the present invention, in the wastewater before treatment, the sulfate ion concentration is generally 20.0 mg / L to 1700.0 mg / L.

[0029] According to the treatment method of the present invention, the wastewater is the wastewater generated during the preparation of the benzene selective hydrogenation catalyst. The benzene selective hydrogenation catalyst is a ruthenium-zinc bimetallic catalyst. In this wastewater, the sodium concentration is generally 800.0 mg / L to 16000.0 mg / L; the chloride ion concentration is generally 90.0 mg / L to 6000.0 mg / L; the sulfate ion concentration is generally 20.0 mg / L to 1700.0 mg / L.

[0030] According to the treatment method of the present invention, this method can be carried out at ambient temperature, for example, at 10°C to 35°C.

[0031] According to the treatment method of the present invention, the ruthenium concentration and zinc concentration in the treated wastewater are both < 1.0 mg / L, the color of the wastewater is eliminated, meeting the requirements for the direct discharge of wastewater regarding ruthenium and zinc elements. Moreover, when adopting an embodiment of the present invention (without using a flocculant), not only can the separation of ruthenium-containing precipitate and zinc-containing precipitate be achieved, but also the ruthenium or zinc content in the ruthenium-containing precipitate and zinc-containing precipitate is higher, which is beneficial for the subsequent separate recovery and reuse of ruthenium and zinc.

[0032] According to the treatment method of the present invention, in step (2), while removing the ruthenium element from the wastewater, a ruthenium-containing precipitate is obtained.

[0033] The present invention also provides a method for preparing ruthenium salts, chlororuthenic acid or chlororuthenates, and the raw material of this method is the ruthenium-containing precipitate obtained from step (2) of the aforementioned treatment method.

[0034] According to the preparation method of the present invention, first obtain the ruthenium-containing precipitate by using step (2) of the aforementioned treatment method, and then use the ruthenium-containing precipitate as the raw material to prepare ruthenium salts, chlororuthenic acid or chlororuthenates. Those skilled in the art can adopt known methods to manufacture ruthenium salts, chlororuthenic acid or chlororuthenates with the ruthenium-containing precipitate as the raw material.

[0035] The beneficial effects of the present invention are that it can efficiently remove ruthenium and zinc, making the ruthenium and zinc concentrations in the treated wastewater both < 1.0 mg / L, the color of the wastewater is eliminated, meeting the requirements for the direct discharge of wastewater regarding ruthenium and zinc elements, and it can also achieve the separation of ruthenium-containing precipitate and zinc-containing precipitate, thus being beneficial for the subsequent separate recovery and reuse of ruthenium and zinc. Specific Embodiments

[0036] The present invention is described in detail below in combination with specific embodiments. However, it should be noted that the protection scope of the present invention is not limited by these specific embodiments and theoretical explanations, but is determined by the claims.

[0037] In the present invention, except for the contents explicitly described, any matters or items not mentioned are directly applicable to those known in the art without any changes. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas formed thereby are regarded as part of the original disclosure or record of the present invention, and should not be regarded as new contents not disclosed or anticipated herein, unless a person skilled in the art considers that the combination is obviously unreasonable.

[0038] All features disclosed in the present invention may be combined arbitrarily, and these combinations shall be understood as the contents disclosed or recorded in the present invention, unless a person skilled in the art considers that the combination is obviously unreasonable, and shall be deemed to be specifically disclosed and recorded in the present invention. The numerical points disclosed in this specification, unless explicitly stated, include not only the numerical points specifically disclosed in the embodiments, but also the endpoints of each numerical range in the specification, and the range of any combination of these numerical points shall be deemed to be the range disclosed or recorded in the present invention.

[0039] The technical and scientific terms in the present invention shall be based on their definitions if they are defined, and shall be understood according to the general meaning in the art if no definitions are given.

[0040] Unless explicitly stated otherwise, the numerical ranges defined herein include the endpoints of the numerical ranges.

[0041] It should be understood that in the ruthenium- and zinc-containing wastewater described in the present invention, the ruthenium concentration and the zinc concentration are both greater than 2.0 mg / L, calculated based on the mass of the ruthenium element and the mass of the zinc element, respectively.

[0042] In the embodiment, the concentrations of ruthenium and zinc in the wastewater containing ruthenium and zinc are measured by using a Baird PS-4 ICP-AES plasma inductively coupled atomic emission spectrometer according to the standard curve method.

[0043] In the embodiment, the ruthenium-containing groups were detected by ultra-high performance liquid chromatography-quadrupole electrostatic field orbitrap mass spectrometry (UPLC-Orbitrap) analysis of Thermo Fisher Scientific. The analysis conditions were: mobile phase A was water, mobile phase B was methanol, and the PDA detection wavelength was 210-800nm. After testing, the ruthenium-containing groups in the wastewater of the embodiment were [RuCHO 3 ] - , [RuC 2 H 3 SO 5 ] - , [RuC 4 H 5 OCl 2 ] - and [RuC 3 H 4 O 4 Cl]- exist in one or several of the following forms.

[0044] Example 1

[0045] Take 100 g of ruthenium- and zinc-containing wastewater (wastewater generated during the preparation of the benzene selective hydrogenation catalyst. After detection, the wastewater contains 5.2 mg / L of ruthenium, 437.3 mg / L of zinc, the pH value of the wastewater is 13.2, and the color of the wastewater is light yellow). Add sulfuric acid to adjust the pH value to 2.0. Precipitation occurs. Stir for 10 min, filter. After detection, the ruthenium concentration in the filtrate < 1.0 mg / L, the zinc concentration is 437.0 mg / L, and the filtrate is colorless. Add sodium hydroxide solution to the filtrate to adjust the pH value to 10.7. Precipitation occurs. Stir for 10 min, filter. After detection, the ruthenium and zinc concentrations in the filtrate are both < 1.0 mg / L, and the filtrate is colorless.

[0046] Example 2

[0047] Take 100 g of ruthenium- and zinc-containing wastewater (wastewater generated during the preparation of the benzene selective hydrogenation catalyst. After detection, the wastewater contains 5.2 mg / L of ruthenium, 437.3 mg / L of zinc, the pH value of the wastewater is 13.2, and the color of the wastewater is light yellow). Add sulfuric acid to adjust the pH value to 2.0. Precipitation occurs. Stir for 10 min, add 0.2 g of cationic polyacrylamide solution (mass fraction 0.1%). Stir for 10 min, let stand for 2 h, suck out about 70 mL of the supernatant, filter the remaining liquid. Mix the sucked-out supernatant and the filtrate. After detection, the ruthenium concentration in the mixed liquid < 1.0 mg / L, the zinc concentration is 436.1 mg / L, and the mixed liquid is colorless. Add sodium hydroxide solution to the mixed liquid to adjust the pH value to 10.7. Precipitation occurs. Stir for 10 min, add 1.0 g of anionic polyacrylamide solution (mass fraction 0.05%). Stir for 10 min, let stand for 2 h, suck out about 60 mL of the supernatant, filter the remaining liquid. Mix the sucked-out supernatant and the filtrate. After detection, the ruthenium and zinc concentrations in the mixed liquid are both < 1.0 mg / L, and the mixed liquid is colorless.

[0048] Example 3

[0049] Take 100 g of ruthenium- and zinc-containing wastewater (wastewater generated during the preparation of a benzene selective hydrogenation catalyst. After detection, the wastewater contains 9.4 mg / L of ruthenium, 152.2 mg / L of zinc, the pH value of the wastewater is 12.9, and the color of the wastewater is yellow). Add hydrochloric acid to adjust the pH value to 2.5. A precipitate appears. Stir for 10 min, then filter. After detection, the ruthenium concentration in the filtrate is < 1.0 mg / L, the zinc concentration is 152.1 mg / L, and the filtrate is colorless. Add sodium hydroxide solution to the filtrate to adjust the pH value to 10.3. A precipitate appears. Stir for 10 min, add 1.0 g of polyaluminum chloride solution (mass fraction 0.1%), stir for 10 min, let stand for 2 h, suck out about 60 mL of the supernatant, filter the remaining liquid, mix the sucked-out supernatant and the filtrate. After detection, the ruthenium and zinc concentrations in the mixed liquid are both < 1.0 mg / L, and the mixed liquid is colorless.

[0050] Example 4

[0051] Take 100 g of ruthenium- and zinc-containing wastewater (wastewater generated during the preparation of a benzene selective hydrogenation catalyst. After detection, the wastewater contains 9.4 mg / L of ruthenium, 152.2 mg / L of zinc, the pH value of the wastewater is 12.9, and the color of the wastewater is yellow). Add hydrochloric acid to adjust the pH value to 2.5. A precipitate appears. Stir for 10 min, then add 0.4 g of non-ionic polyacrylamide solution (mass fraction 0.2%). Stir for 10 min, let stand for 2 h, suck out about 70 mL of the supernatant, filter the remaining liquid, mix the sucked-out supernatant and the filtrate. After detection, the ruthenium concentration in the mixed liquid is < 1.0 mg / L, the zinc concentration is 151.3 mg / L, and the mixed liquid is colorless. Add sodium hydroxide solution to the mixed liquid to adjust the pH value to 10.3. A precipitate appears. Stir for 10 min, then filter. After detection, the ruthenium and zinc concentrations in the filtrate are both < 1.0 mg / L, and the filtrate is colorless.

[0052] Example 5

[0053] Take 100 g of ruthenium- and zinc-containing wastewater (wastewater generated during the preparation of a benzene selective hydrogenation catalyst. After detection, the wastewater contains 32.1 mg / L of ruthenium, 25.0 mg / L of zinc, the pH value of the wastewater is 12.2, and the color of the wastewater is yellow). Add hydrochloric acid to adjust the pH value to 3.4. A precipitate appears. Stir for 10 min, then filter. After detection, the ruthenium concentration in the filtrate is < 1.0 mg / L, the zinc concentration is 25.0 mg / L, and the filtrate is colorless. Add sodium hydroxide solution to the filtrate to adjust the pH value to 10.8. A precipitate appears. Stir for 10 min, then filter. After detection, the ruthenium and zinc concentrations in the filtrate are both < 1.0 mg / L, and the filtrate is colorless.

[0054] Example 6

[0055] Take 100 g of ruthenium- and zinc-containing wastewater (wastewater generated during the preparation of a benzene selective hydrogenation catalyst. After detection, the wastewater contains 32.1 mg / L of ruthenium, 25.0 mg / L of zinc, the pH value of the wastewater is 12.2, and the color of the wastewater is yellow). Adjust the pH value to 3.4 with hydrochloric acid. Precipitation occurs. Stir for 10 min. Add 0.1 g of cationic polyacrylamide solution (mass fraction is 0.1%). Stir for 10 min. Let stand for 2 h. Suck out about 70 mL of the supernatant. Filter the remaining liquid. Mix the sucked-out supernatant and the filtrate. After detection, the ruthenium concentration in the mixed liquid < 1.0 mg / L, the zinc concentration is 24.8 mg / L, and the mixed liquid is colorless. Add sodium hydroxide solution to the mixed liquid. Adjust the pH value to 10.8. Precipitation occurs. Stir for 10 min. Add 1.0 g of polyaluminum chloride solution (mass fraction is 0.3%). Stir for 10 min. Let stand for 2 h. Suck out about 60 mL of the supernatant. Filter the remaining liquid. Mix the sucked-out supernatant and the filtrate. After detection, the ruthenium and zinc concentrations in the mixed liquid are both < 1.0 mg / L, and the mixed liquid is colorless.

[0056] Example 7

[0057] Take 100 g of ruthenium- and zinc-containing wastewater (wastewater generated during the preparation of a benzene selective hydrogenation catalyst. After detection, the wastewater contains 47.8 mg / L of ruthenium, 470.7 mg / L of zinc, the pH value of the wastewater is 13.5, and the color of the wastewater is brownish-yellow). Adjust the pH value to 4.0 with hydrochloric acid. Precipitation occurs. Stir for 10 min. Filter. After detection, the ruthenium concentration in the filtrate < 1.0 mg / L, the zinc concentration is 470.5 mg / L, and the filtrate is colorless. Add sodium hydroxide solution to the filtrate. Adjust the pH value to 10.5. Precipitation occurs. Stir for 10 min. Filter. After detection, the ruthenium and zinc concentrations in the filtrate are both < 1.0 mg / L, and the filtrate is colorless.

[0058] Example 8

[0059] Take 100 g of ruthenium- and zinc-containing wastewater (wastewater generated during the preparation of a benzene selective hydrogenation catalyst. After detection, the wastewater contains 47.8 mg / L of ruthenium, 470.7 mg / L of zinc, the pH value of the wastewater is 13.5, and the color of the wastewater is brownish yellow). Add hydrochloric acid to adjust the pH value to 4.0. Precipitation occurs. Stir for 10 min. Add 8.0 g of a non-ionic polyacrylamide solution (mass fraction 0.2%). Stir for 10 min. Let stand for 2 h. Suck out about 70 mL of the supernatant. Filter the remaining liquid. Mix the sucked-out supernatant and the filtrate. After detection, the ruthenium concentration in the mixed liquid < 1.0 mg / L and the zinc concentration is 468.8 mg / L. The mixed liquid is colorless. Add potassium hydroxide solution to the mixed liquid to adjust the pH value to 10.5. Precipitation occurs. Stir for 10 min. Add 1.0 g of a polyaluminum chloride solution (mass fraction 0.5%). Stir for 10 min. Let stand for 2 h. Suck out about 60 mL of the supernatant. Filter the remaining liquid. Mix the sucked-out supernatant and the filtrate. After detection, the ruthenium and zinc concentrations in the mixed liquid are both < 1.0 mg / L. The mixed liquid is colorless.

[0060] Comparative Example 1

[0061] Take 100 g of ruthenium- and zinc-containing wastewater (wastewater generated during the preparation of a benzene selective hydrogenation catalyst. After detection, the wastewater contains 5.2 mg / L of ruthenium, 437.3 mg / L of zinc, the pH value of the wastewater is 13.2, and the color of the wastewater is light yellow). Add sulfuric acid to adjust the pH value to 1.5. Stir for 10 min. No precipitation occurs. The wastewater remains light yellow. Add sodium hydroxide solution to the wastewater to adjust the pH value to 10.7. Precipitation occurs. Stir for 10 min. Filter. After detection, the ruthenium concentration in the filtrate is 5.2 mg / L and the zinc concentration < 1.0 mg / L. The filtrate is light yellow.

[0062] Comparative Example 2

[0063] Take 100 g of ruthenium- and zinc-containing wastewater (wastewater generated during the preparation of a benzene selective hydrogenation catalyst. After detection, the wastewater contains 5.2 mg / L of ruthenium, 437.3 mg / L of zinc, the pH value of the wastewater is 13.2, and the color of the wastewater is light yellow). Add sulfuric acid to adjust the pH value to 4.8. Stir for 10 min. No precipitation occurs. The wastewater remains light yellow. Add sodium hydroxide solution to the wastewater to adjust the pH value to 10.7. Precipitation occurs. Stir for 10 min. Filter. The ruthenium concentration in the filtrate is 5.2 mg / L and the zinc concentration < 1.0 mg / L. The filtrate is light yellow.

Claims

1. A step-by-step treatment method for ruthenium- and zinc-containing wastewater, comprising: (1) Adjusting the pH value of the ruthenium- and zinc-containing wastewater to 2-4 to convert ruthenium into a precipitate; (2) Removing the precipitate with or without a flocculant in the wastewater; (3) Adjusting the pH value of the wastewater treated in step (2) to alkaline to convert zinc into a precipitate; (4) Removing the precipitate with or without a flocculant in the wastewater; The pH value of the ruthenium- and zinc-containing wastewater is > 12, and ruthenium exists in anionic groups in the form of [RuCHO 3 - , [RuC 2 H 3 SO 5 - , [RuC 4 H 5 OCl 2 - and [RuC 3 H 4 O 4 Cl] - or several of these forms; the wastewater is the wastewater generated during the preparation of a benzene selective hydrogenation catalyst.​​​ 2. The step-by-step wastewater treatment method according to claim 1, characterized in that in step (3), the pH value of the wastewater is adjusted to 10-11.

3. The step-by-step wastewater treatment method according to claim 1, characterized in that before treatment, the ruthenium concentration in the wastewater is 5.0 mg / L - 50.0 mg / L.

4. The step-by-step wastewater treatment method according to claim 1, characterized in that before treatment, the zinc concentration in the wastewater is 10.0 mg / L - 500.0 mg / L.

5. The step-by-step wastewater treatment method according to claim 1, characterized in that in steps (2) and (4), the flocculants are the same or different.

6. The step-by-step wastewater treatment method according to claim 1, characterized in that in step (2) or step (4), the flocculant is a polyacrylamide flocculant or a polyaluminum chloride flocculant.

7. The step-by-step wastewater treatment method according to any one of claims 1-6, characterized in that using the ruthenium-containing precipitate obtained in step (2) as a raw material to prepare ruthenium salts, chlororuthenic acid or chlororuthenates.