A method for treating semi-coke wastewater by cyanide tailings and persulfate oxidation

Abstract

The invention discloses a method for treating semi-coke wastewater with cyanide tailings and persulfate oxidation. Cyanide tailings and persulfate are added to the semi-coke wastewater, and pyrite in the cyanide tailings can dissolve Fe 2+ Thus activating persulfate to produce highly oxidizing SO4 ‑ · and OH·, oxidize the organic matter and ammonia nitrogen in the semi-coal wastewater into small molecular organic matter or remove them by oxidation. 2+ Fe generated by activated persulfate 3+ Through coagulation and adsorption, a coagulated precipitate is formed, which settles rapidly under the influence of coarse gangue minerals in the cyanide tailings, achieving the coagulation and removal of organic pollutants in the wastewater. Simultaneously, while treating semi-coke wastewater, the present invention also washes and oxidatively decyanates cyanide in the cyanide tailings, achieving harmless treatment of the cyanide tailings. The present invention has a simple process, a short flow, and excellent treatment effects, without introducing new pollutants, resulting in excellent economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the field of semi-coke wastewater treatment, and in particular to a method for treating semi-coke wastewater by using cyanide tailings in conjunction with persulfate oxidation. Background Art

[0002] The quality of semi-coke wastewater varies depending on the composition of the raw coal and the production process. It primarily contains volatile phenols, polycyclic aromatic hydrocarbons, ammonia nitrogen, and polycyclic and heterocyclic compounds such as oxygen, sulfur, and nitrogen. This complex organic wastewater is difficult to degrade, exhibits high toxicity, and exhibits high chroma. Direct discharge or improper treatment poses a serious threat to the ecological environment. Therefore, the development of an economical and efficient semi-coke wastewater treatment technology is crucial for the sustainable development of my country's semi-coke industry.

[0003] CN202210562064.5 introduces a semi-coke wastewater treatment catalyst, its preparation method, and application. Nitric acid is used to pretreat the gasification slag of coal chemical waste; a nitrogen source is then mixed with the pretreated gasification slag and calcined to prepare a crude catalyst; finally, the catalyst is washed with water and dried to produce a catalyst with rich pores and a high nitrogen doping content. Persulfate is then added to the wastewater at a mass ratio of 1:10 to 20 to the wastewater, and 0.3 to 1 g / L of catalyst is added to treat the COD in the semi-coke wastewater. Compared to no catalyst addition, the COD removal rate is increased by approximately 30 times. This method primarily focuses on catalyst preparation. Although it can improve COD removal, it has problems such as a complex catalyst preparation process, large amounts of persulfate, and high costs.

[0004] CN202111507258.7 introduces a method for treating lignite wastewater using pre-oxidation degreasing and dephenolization-electro-Fenton technology. In the pre-oxidation stage, iron powder is added and aeration oxidation is performed. The reduction reaction of zero-valent iron is used to oxidize organic matter that is difficult to be directly oxidized into short-chain small molecule compounds that are easily oxidized; then the pH value is adjusted and iron powder and hydrogen peroxide are added to the wastewater at the same time, and the Fenton system formed by them is used to oxidize and remove organic matter in the lignite wastewater; finally, the pH is adjusted, and flocculants are added for precipitation to complete the treatment of the lignite wastewater. Although this method can effectively treat lignite wastewater, the process is complicated, and Fenton oxidation and flocculation precipitation need to be carried out step by step; and if the amount of iron powder is too large, a large amount of iron ions will be introduced into the lignite wastewater, causing heavy metal ion pollution.

[0005] CN202211676349.8 describes a method for treating semi-coal wastewater. First, an aldehyde-containing solution is added to the semi-coal wastewater to produce a first treated effluent. Then, a reactant containing divalent iron ions and hydrogen peroxide is added to produce a second treated effluent. Finally, the pH value is adjusted and a composite flocculant is added for treatment. This method requires the stepwise addition of various oxidants, activators, pH adjusters, and flocculants, resulting in a complex process.

[0006] In summary, it is particularly important to propose a method for treating lignite wastewater with simple process and low cost. Summary of the Invention

[0007] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a method for treating semi-coke wastewater by using cyanide tailings in conjunction with persulfate oxidation. The process of the present invention is simple, the flow is short, the cost is low, the treatment effect of semi-coke wastewater is good, and no new pollutants are introduced.

[0008] The technical solution adopted in the present invention is as follows:

[0009] A method for treating semi-coke wastewater by using cyanide tailings in conjunction with persulfate oxidation, comprising the following steps:

[0010] Cyanide tailings and persulfate are added to the semi-coke wastewater to react, so that the cyanide tailings cooperate with the persulfate to oxidize and treat the semi-coke wastewater, wherein the addition amount of the cyanide tailings is 10-40 g / L, and the addition amount of the persulfate is 0.05-0.5 mol / L.

[0011] Preferably, the COD concentration of the semi-coke wastewater ranges from 2000 to 8000 mg / L.

[0012] Preferred:

[0013] Cyanide tailings and persulfate were added to the semi-coke wastewater for reaction. The COD removal rate of the semi-coke wastewater was 76.08%-96.88%, the NH3-N removal rate was 35.82%-85.63%, and the CN in the cyanide tailings was 2.3%. T The removal rate is 65.43%-91.45%.

[0014] Preferably, the cyanide tailings are tailings containing pyrite and silicon dioxide obtained by direct cyanide leaching of gold from flotation gold concentrate.

[0015] Preferably, the persulfate is sodium persulfate or ammonium persulfate.

[0016] Preferably, the reaction temperature of the semi-coke wastewater, cyanide tailings and persulfate is 40°C to 75°C.

[0017] Preferably, during the reaction process of adding cyanide tailings and persulfate to the semi-coke wastewater, stirring is performed at a stirring speed of 200 to 400 r / min.

[0018] Preferably, the reaction time of the semi-coke wastewater, cyanide tailings and persulfate is 60 to 240 minutes.

[0019] Preferably, after the reaction of the semi-coke wastewater, cyanide tailings and persulfate is completed, solid-liquid separation is performed, and the separated wastewater is used in the semi-coke production process.

[0020] The present invention has the following beneficial effects:

[0021] The present invention applies persulfate advanced oxidation technology to the field of blue carbon wastewater treatment, and utilizes the activation ability of iron sulfide minerals in cyanide tailings to persulfate to oxidize and treat organic pollutants, ammonia nitrogen in blue carbon wastewater and cyanide washed out from tailings. At the same time, the Fe generated in the persulfate oxidation system 3+ This method can remove some organic pollutants through coagulation and adsorption, and the gangue minerals in the cyanide tailings act as coarse particles carrying fine particles, facilitating the aggregation and precipitation of fine coagulation products. This process also simultaneously completes the washing and oxidative decyanation of cyanide in both the semi-coke wastewater and the cyanide tailings, achieving harmless treatment of the cyanide tailings and converting them from hazardous solid waste to general solid waste. This method has a simple process, a short flow, requires low amounts of waste residue and chemicals, and offers excellent treatment results without introducing new pollutants. It embodies the principle of "treating waste with waste" and offers excellent economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the XRD pattern of the cyanide tailings used in the embodiment of the present invention;

[0023] Figure 2 This is the GC-MS spectrum of the semi-coal wastewater before treatment in Example 4 of the present invention;

[0024] Figure 3 This is the GC-MS spectrum of the semi-coal wastewater after treatment in Example 4 of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0026] The method of treating blue carbon wastewater by using cyanide tailings in conjunction with persulfate oxidation of the present invention comprises the following steps:

[0027] A certain amount of cyanide tailings and persulfate are directly added to the semi-coke wastewater, and the reaction is stirred at 40°C to 75°C for 60 to 240 minutes at a stirring speed of 200 to 400 r / min. The cyanide tailings can be tailings from direct cyanide leaching of gold from flotation gold concentrate, and the amount of cyanide tailings added is 10 to 40 g / L. The persulfate is used as an oxidant and is added in an amount of 0.05 to 0.5 mol / L. The persulfate can be sodium persulfate or ammonium persulfate.

[0028] The semi-coke wastewater treated by the present invention can also be subjected to solid-liquid separation, and the separated wastewater can be used in the semi-coke production process to recycle the wastewater.

[0029] In the above-mentioned scheme of the present invention, the COD concentration in the semi-coke wastewater is preferably in the range of 2000-8000 mg / L. This allows for a high COD removal rate after the addition of cyanide tailings and persulfate. In principle, the amount of cyanide tailings and persulfate added can be adjusted according to the COD content to achieve the same desired treatment effect.

[0030] The present invention uses cyanide tailings to cooperate with persulfate oxidation to treat blue carbon wastewater. The pyrite in the cyanide tailings can dissolve to produce Fe 2+ , Fe 2+ Can activate persulfate to produce SO4 - · and OH· (Formula (1) to Formula (3)). Organic matter (COD) and ammonia nitrogen (NH3-N) in semi-coal wastewater can be converted to S2O8 2- 、SO4 - · and OH· are oxidized to small molecular organic matter or removed by oxidation. 2+ Oxidized to Fe during the activation of persulfate 3+ .Fe 3+ It has a strong tendency of hydrolysis-polymerization-precipitation. 3+ During the hydrolysis process, it will remove some organic matter by coagulation or adsorption (Formula (4) to Formula (6)). The gangue minerals in the cyanide tailings can carry fine particles of coagulant precipitation, promoting the removal of organic matter in the semi-coke wastewater. In addition, the cyanide tailings contain a certain amount of cyanide, and semi-coke wastewater may also contain some cyanide. The stirring during the reaction process also plays a role in washing the cyanide tailings. The cyanide entering the solution can be removed by S2O8 2- 、SO4 - · and OH· are oxidized to CO2 and N2 (Equations (7) to (9)). This technology achieves harmless treatment of cyanide tailings. The method of using cyanide tailings to treat semi-coke wastewater implements the concept of "waste treatment with waste". Compared with traditional treatment technologies, the process is simple, the amount of waste residue and chemicals is low, pH adjustment is not required, no new pollutants are introduced, the cost is low, the treatment effect is good, and it has good application prospects.

[0031] Fe x S y + xS2O8 2- → xFe 2+ + yS 0 + 2xSO4 2- (1)

[0032] S2O8 2- + Fe 2+ → SO4 - + Fe 3+ + SO42- (2)

[0033] SO4 - + H2O → OH + SO4 2- + H + (3)

[0034] [Fe2(H2O)7(OH)3] 3+ + [Fe(H2O)5OH] 2+ → [Fe3(H2O)7(OH)4] 5+ + H2O (4)

[0035] [Fe(H2O)6] 3+ + H2O → [Fe(H2O)5OH] 2+ + H3O + (5)

[0036] [Fe(H2O)5OH] 2+ + H2O → [Fe(H2O)4(OH)2] + + H3O + (6)

[0037] 2CN - + 5S2O8 2- + 8OH - → 10SO4 2- + 2CO2↑ + N2↑ + 4H2O (7)

[0038] 5 SO4 - + CN - +4OH - → 5SO4 2- + CO2↑ + 0.5N2↑ + 2H2O (8)

[0039] 5OH· + CN - + H + → CO2↑ + 0.5N2↑ + 3H2O (9)

[0040] The semi-coal wastewater used in Examples 1-4 and Comparative Examples 1-2 of the present invention was obtained from a semi-coal production enterprise in Yulin, Shaanxi Province. The COD content of the semi-coal wastewater was 2705.76 mg / L and the NH3-N content was 144.83 mg / L. The semi-coal wastewater used in Examples 5-6 was obtained from another semi-coal production enterprise in Yulin, Shaanxi Province. The COD content of the semi-coal wastewater was 7650.54 mg / L and the NH3-N content was 542.17 mg / L.

[0041] The cyanide tailings used in the examples and comparative examples of the present invention were taken from a gold mine in Tongguan, Shaanxi Province. They were cyanide tailings obtained after cyanide extraction of gold from gold concentrate and flotation of lead and copper. The XRD analysis results of the sample are shown in Figure 2. Figure 1 As shown in the figure, the main minerals in the cyanide tailings are quartz and pyrite, with no other minerals present. Chemical element analysis results indicate that the tailings contain high levels of iron and sulfur, at 30.40% and 34.81%, respectively, while the contents of other elements are relatively low.

[0042] The contents of COD and NH3-N in semi-coke wastewater samples were determined by the national standard potassium dichromate method and distillation-neutralization titration method, respectively. The removal rates were calculated as shown in Equations (10) and (11), respectively.

[0043]

[0044]

[0045] Where: [COD]0 and [NH3-N]0 refer to the contents of COD and NH3-N in wastewater, mg / L respectively; [COD] t 、[NH3-N] t They are the contents of COD and NH3-N after treatment, mg / L respectively.

[0046] The leaching toxicity of cyanide in the above cyanide tailings is (CN TL )13.86mg / L, the total cyanide content in the tailings (CN T ) is 1274.55 mg / kg. TL and CN T The determination was carried out by the silver nitrate titration method in the "Determination of Cyanide in Water by Volumetric Method and Spectrophotometry" (HJ484-2009). T The calculation method of the removal rate is shown in Equation 12.

[0047]

[0048] Where: [CN T ]0 and [CN T ] t are the total cyanide content in the cyanide tailings before and after treatment, mg / kg; [CN TL ] t is the cyanide content in the treated wastewater, mg / L; m0 and m t are the masses of cyanide tailings before and after treatment, g; V is the volume of semi-coke wastewater, mL.

[0049] Comparative Example 1:

[0050] 0.1 mol / L sodium persulfate was added to the semi-coke wastewater and stirred at 40°C for 120 minutes. After the reaction, the COD and NH3-N contents in the wastewater were measured. In this comparative example, the COD removal rate was 43.25%, and the NH3-N removal rate was 16.52%.

[0051] Comparative Example 2:

[0052] 10g / L cyanide tailings were added to the semi-coke wastewater and stirred at 40℃ for 120min. After the reaction, the COD and NH3-N contents in the wastewater were measured. In this comparative example, the COD removal rate was 18.67%, the NH3-N removal rate was 6.54%, and the CN T The removal rate is 12.36%.

[0053] Example 1:

[0054] This embodiment uses cyanide tailings in conjunction with persulfate oxidation to treat semi-coke wastewater, and the implementation process includes:

[0055] Add 10 g / L of cyanide tailings and 0.1 mol / L of sodium persulfate to 200 mL of semi-coal wastewater and stir at 40 °C for 120 min at a stirring speed of 300 r / min. After the treatment, the wastewater and tailings were separated, and the removal rates of COD and NH3-N in the semi-coal wastewater were calculated according to formula (10) and formula (11), respectively. The CN3-N in the cyanide tailings was calculated according to formula (12). T removal rate.

[0056] In this embodiment, the COD removal rate is 76.08%, the NH3-N removal rate is 35.82%, and the CN T The removal rate was 65.43%.

[0057] Example 2:

[0058] This embodiment uses cyanide tailings in conjunction with persulfate oxidation to treat semi-coke wastewater, and the implementation process includes:

[0059] Add 20 g / L of cyanide tailings and 0.3 mol / L of ammonium persulfate to 200 mL of semi-coal wastewater and stir at 75 °C for 60 min at a stirring speed of 200 r / min. After the treatment, the wastewater and tailings were separated, and the removal rates of COD and NH3-N in the semi-coal wastewater were calculated according to formula (10) and formula (11), respectively. The CN3-N in the cyanide tailings was calculated according to formula (12). T removal rate.

[0060] In this embodiment, the COD removal rate is 80.53%, the NH3-N removal rate is 36.42%, and the CN T The removal rate was 68.45%.

[0061] Example 3:

[0062] This embodiment uses cyanide tailings in conjunction with persulfate oxidation to treat semi-coke wastewater, and the implementation process includes:

[0063] Add 40 g / L of cyanide tailings and 0.5 mol / L of ammonium persulfate to 200 mL of semi-coal wastewater and stir at 60 °C for 240 min at a stirring speed of 400 r / min. After the treatment, the wastewater and tailings were separated, and the removal rates of COD and NH3-N in the semi-coal wastewater were calculated according to formula (10) and formula (11), respectively. The CN3-N in the cyanide tailings was calculated according to formula (12). T removal rate.

[0064] In this embodiment, the COD removal rate is 84.35%, the NH3-N removal rate is 48.92%, and the CN T The removal rate was 76.53%.

[0065] Example 4:

[0066] This embodiment uses cyanide tailings in conjunction with persulfate oxidation to treat semi-coke wastewater, and the implementation process includes:

[0067] Add 10 g / L of cyanide tailings and 0.05 mol / L of sodium persulfate to 200 mL of semi-coal wastewater and stir at 60 °C for 120 min at a stirring speed of 300 r / min. After the treatment, the wastewater and tailings were separated, and the removal rates of COD and NH3-N in the semi-coal wastewater were calculated according to formula (10) and formula (11), respectively. The CN3-N in the cyanide tailings was calculated according to formula (12). T removal rate.

[0068] In this embodiment, the COD removal rate is 96.88%, the NH3-N removal rate is 85.63%, and the CN T The removal rate was 91.45%.

[0069] Example 5:

[0070] This embodiment uses cyanide tailings in conjunction with persulfate oxidation to treat semi-coke wastewater, and the implementation process includes:

[0071] Add 10 g / L of cyanide tailings and 0.2 mol / L of sodium persulfate to 200 mL of semi-coal wastewater and stir at 60 °C for 120 min at a stirring speed of 300 r / min. After the treatment, the wastewater and tailings were separated, and the removal rates of COD and NH3-N in the semi-coal wastewater were calculated according to formula (10) and formula (11), respectively. The CN3-N in the cyanide tailings was calculated according to formula (12). T removal rate.

[0072] In this embodiment, the COD removal rate is 83.62%; the NH3-N removal rate is 78.59%;T The removal rate is 89.25%.

[0073] Example 6:

[0074] This embodiment uses cyanide tailings in conjunction with persulfate oxidation to treat semi-coke wastewater, and the implementation process includes:

[0075] Add 40 g / L of cyanide tailings and 0.5 mol / L of sodium persulfate to 200 mL of semi-coal wastewater and stir at 75 °C for 240 min at a stirring speed of 400 r / min. After the treatment, the wastewater and tailings were separated, and the removal rates of COD and NH3-N in the semi-coal wastewater were calculated according to formula (10) and formula (11), respectively. The CN3-N in the cyanide tailings was calculated according to formula (12). T removal rate.

[0076] In this embodiment, the COD removal rate is 90.43%; the NH3-N removal rate is 82.17%; T The removal rate is 85.46%.

[0077] In Example 4, cyanide tailings were used to treat blue carbon wastewater in combination with persulfate. Under the conditions of persulfate dosage of 0.05 mol / L, cyanide tailings addition amount of 10 g / L, reaction temperature of 60 ° C, reaction time of 120 min, and stirring speed of 300 r / min, the COD removal rate was 96.88%, the NH3-N removal rate was 85.32%, and the CN T The removal rate is 91.45%. The COD content of the treated wastewater is 84.42 mg / L, NH3-N content is 21.26 mg / L, CN T The content is 0.12mg / L, and the treated semi-coke wastewater meets the "Pollutant Emission Standards for Coking Chemical Industry." The leaching toxicity of cyanide tailings is 0.3mg / L, meeting the emission standards specified in the "Technical Specifications for Cyanide Slag Pollution Control in the Gold Industry."

[0078] GC-MS was used to analyze the composition of organic matter in the semi-carbon wastewater before and after treatment. The results are as follows: Figure 2 and Figure 3 The composition and relative content of the main organic pollutants in the wastewater before and after treatment are shown in Table 1.

[0079] Table 1

[0080]

[0081]

[0082] Depend on Figure 2 and Figure 3It can be seen that compared with the original semi-coal wastewater, the intensity of organic matter in the treated wastewater is greatly reduced, indicating that a large amount of organic matter in the wastewater is oxidized into small molecular organic matter or oxidized and removed. Figure 2 、 Figure 3 As shown in Table 1, 150 organic compounds were detected in the raw semi-coke wastewater, with phenols and alkanes accounting for 25.80% and 60.34%, respectively. Other compounds included smaller amounts of alcohols and acids. A total of 105 organic compounds were detected in the treated semi-coke wastewater, with phenols and alkanes accounting for 6.44% and 86.23%, respectively. This indicates that phenols in semi-coke wastewater can be degraded into hydrocarbons in the cyanide tailings plus persulfate system.

Claims

1. A method for treating semi-coke wastewater by using cyanide tailings in conjunction with persulfate oxidation, characterized in that: The process includes the following: Adding cyanide tailings and persulfate to the semi-coke wastewater to react, so that the cyanide tailings cooperate with the persulfate to oxidize the semi-coke wastewater, wherein the amount of the cyanide tailings added is 10-40 g / L, and the amount of the persulfate added is 0.05-0.5 mol / L; Cyanide tailings are tailings containing pyrite and silica after direct cyanide leaching of gold from flotation gold concentrate. The persulfate is sodium persulfate or ammonium persulfate.

2. The method for treating blue carbon wastewater by using cyanide tailings in collaboration with persulfate oxidation according to claim 1, wherein: The COD concentration of semi-coke wastewater ranges from 2000 to 8000 mg / L.

3. The method for treating blue carbon wastewater by using cyanide tailings in collaboration with persulfate oxidation according to claim 2, wherein: Cyanide tailings and persulfate were added to the semi-coke wastewater to react. The COD removal rate of the semi-coke wastewater was 76.08%-96.88%, the NH3-N removal rate was 35.82%-85.63%, and the CN in the cyanide tailings was 2.3%. T The removal rate is 65.43%-91.45%.

4. The method for treating blue carbon wastewater by using cyanide tailings in collaboration with persulfate oxidation according to claim 1, wherein: The reaction temperature of semi-coke wastewater, cyanide tailings and persulfate is 40°C to 75°C.

5. The method for treating blue carbon wastewater by using cyanide tailings in collaboration with persulfate oxidation according to claim 1, characterized in that: During the reaction process of adding cyanide tailings and persulfate into the semi-coke wastewater, stirring operation is performed at a stirring speed of 200 to 400 r / min.

6. The method for treating blue carbon wastewater by using cyanide tailings in collaboration with persulfate oxidation according to claim 5, characterized in that: The reaction time of semi-coke wastewater, cyanide tailings and persulfate is 60 to 240 minutes.

7. The method for treating blue carbon wastewater by using cyanide tailings in collaboration with persulfate oxidation according to claim 1, characterized in that: After the reaction of semi-coke wastewater, cyanide tailings and persulfate is completed, solid-liquid separation is carried out and the separated wastewater is used in the semi-coke production process.

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