Method for removing chemical oxygen demand through catalyst prepared from acid mine wastewater

Abstract

The invention provides a method for removing chemical oxygen demand by using a catalyst prepared from acid mine wastewater, which comprises the following steps: recovering valuable elements in the acid mine wastewater, accurately adding sodium hydrosulfide to control conditions, recovering transition metal elements with catalytic activity in the acid mine wastewater by fractional precipitation, directionally preparing a nano-scale metal catalyst, and removing the chemical oxygen demand by using the catalyst prepared from the acid mine wastewater. And the chemical oxygen demand in the wastewater is degraded through the prepared nano-scale metal catalyst, so that the problem of environmental pollution caused by the mine wastewater and the wastewater containing the chemical oxygen demand is solved, and the dual effects of resource recovery and environmental treatment are realized.

Description

Technical Field

[0001] This disclosure relates to the fields of wastewater treatment technology and resource recycling, and more specifically, to a method for removing chemical oxygen demand (COD) using a catalyst prepared from acidic mine wastewater. Background Technology

[0002] Acid mine wastewater (AMD) originates from the exposure of sulfur-containing and sulfide minerals to air and water during natural or mine ore extraction, transportation, beneficiation, and metallurgical processes. Under the catalysis of microorganisms (such as *Thiobacillus ferrooxidans*), these minerals are oxidized to form sulfuric acid and ferric sulfate, dissolving other metal elements in the process. On the one hand, its strong acidity and high concentration of heavy metal ions cause serious pollution to the ecological environment; on the other hand, the transition metals it contains, such as iron, copper, and manganese, have enormous resource recovery potential, but current technologies do not address the rational development and utilization of these transition metals.

[0003] Prior art 1 (Publication No.: CN105439357A, Application Date: 2015.12.28) discloses a method for resource recovery and deep purification of acidic mine wastewater, including the following steps: 1) adjusting the pH of the acidic mine wastewater to 2.2-2.6 using a neutralizing agent, followed by solid-liquid separation to obtain gypsum; 2) adjusting the pH of the mine wastewater to 2.8-3.2 using a neutralizing agent, removing iron ions, and recovering iron slag; 3) adding a sulfiding agent to the solution after iron removal for efficient sulfidation to obtain copper-zinc slag; 4) leaching the copper-zinc slag with acid to separate copper-rich slag and zinc sulfate solution, and recovering the sulfiding agent; 5) subjecting the final effluent to deep treatment. Prior art 1 does not perform deep treatment of copper and zinc elements, nor does it effectively utilize the copper-zinc slag.

[0004] Therefore, there is an urgent need to provide a method that can treat acidic mine wastewater and also make comprehensive use of the treated products. Summary of the Invention

[0005] In view of this, the present disclosure provides a method for removing chemical oxygen demand using a catalyst prepared from acidic mine wastewater, for treating acidic mine wastewater, and for comprehensively utilizing the treated products.

[0006] This disclosure provides a method for removing chemical oxygen demand (COD) using a catalyst prepared from acidic mine wastewater, comprising the following steps:

[0007] Preparation of transition metal sulfide nanocatalysts, including:

[0008] Acidic mine wastewater is collected, wherein the acidic mine wastewater includes manganese ions, copper ions and iron ions, wherein the manganese ion content is greater than 50 mg / L and the copper ion content is greater than 50 mg / L;

[0009] If the iron ion content in the acidic mine wastewater is greater than 100 mg / L, the acidic mine wastewater is pretreated by adding alkaline solution to the acidic mine wastewater to adjust the pH value to 4-5, producing ferric hydroxide and ferrous hydroxide flocculent precipitates. After stirring evenly, the mixture is allowed to stand to allow the flocs to settle. The pretreated mine wastewater is then filtered to obtain the mine wastewater to be treated.

[0010] If the iron ion content in the acidic mine wastewater is less than 100 mg / L, then no pretreatment is required for the acidic mine wastewater to be treated.

[0011] Sodium hydrosulfide solution was added to the mine wastewater to be treated while stirring at a first stirring rate of 250 rpm-300 rpm and at a first drop rate of 0.5 mL / L·s-2 mL / L·s. The mass concentration of the sodium hydrosulfide solution was 20 wt%-30 wt%. The reaction temperature was 20℃-30℃. The addition was stopped after the pH value of the reaction reached 7-8. The reaction formula is as follows:

[0012] Cu 2+ +HS - →CuS↓+H + ;

[0013] Mn 2+ +HS - +H2O→Mn(OH)2↓+H2S↑;

[0014] 2Mn(OH)2 + O2 → 2MnO(OH)2↓;

[0015] Mn 2+ +S 2- →MnS↓;

[0016] The black solid produced after the reaction was collected by centrifugation at a speed of 800 rpm-1000 rpm, and then washed 2-3 times with ethanol and deionized water.

[0017] The washed black solid was vacuum dried to obtain a transition metal sulfide nanocatalyst.

[0018] The transition metal sulfide nanocatalyst removes sulfur from polluted water in a heterogeneous catalytic oxidation system. 2- and reducing substances of organic matter, including:

[0019] Provide polluted water body, wherein the chemical oxygen demand (COD) concentration in the polluted water body is 300 mg / L-500 mg / L, wherein S 2- Concentrations range from 50 mg / L to 200 mg / L;

[0020] Adjust the pH value of the polluted water to 4-9;

[0021] An oxidant and the transition metal sulfide nanocatalyst are added to the polluted water body, wherein the amount of the oxidant added per liter of the polluted water body is 1g-2g, and the amount of the transition metal sulfide nanocatalyst added per liter of the polluted water body is 1g-3g.

[0022] Optionally, an alkaline solution may be added to the acidic mine wastewater, wherein the alkaline solution is either sodium hydroxide or calcium hydroxide.

[0023] Optionally, the oxidant includes potassium persulfate.

[0024] Optionally, the washed black solid is subjected to vacuum drying, wherein the drying temperature is 40℃-45℃ and the drying time is 40h-48h.

[0025] Optionally, the transition metal sulfide nanocatalyst can be recycled more than four times.

[0026] This invention innovatively recovers transition metal elements from acidic mine wastewater through controlled conditions and prepares them into nanocatalysts for heterogeneous catalytic oxidation. This not only enables the treatment of acidic mine wastewater and COD (chemical oxygen demand) wastewater, but also achieves green and sustainable development through resource recovery.

[0027] Compared with existing technologies, the method for removing chemical oxygen demand using a catalyst prepared from acidic mine wastewater provided in this disclosure achieves at least the following beneficial effects:

[0028] 1) Before treating acidic mine wastewater, if the iron ion content in the acidic mine wastewater is greater than 100 mg / L, pretreatment is performed using alkaline solution and Fe... 2+ Fe 3+ The reaction produces flocculent precipitates of ferric hydroxide and ferrous hydroxide. Removing some of the iron ions is beneficial for the subsequent formation of highly catalytically active copper sulfide and manganese sulfide.

[0029] 2) In treating the mine wastewater, this disclosure adds sodium hydrosulfide instead of sodium sulfide. Sodium hydrosulfide solution has a higher effective sulfur content, a slower pH change, and better buffering performance than sodium sulfide. Combined with a specific dropping rate of 0.5 mL / L·s–2 mL / L·s, its addition is more conducive to the formation of smaller metal sulfides, avoiding the formation of hydroxide colloids that cause product agglomeration. Controlling the dropping rate also helps to form a nanoscale catalyst. This disclosure's method for recovering transition metal elements from acidic mine wastewater results in a catalyst with a nanoscale particle size, exhibiting higher catalytic performance compared to micron-sized catalysts under the same conditions.

[0030] 3) This disclosure not only treats acidic mine wastewater by recovering transition metal elements, but also fully utilizes the metal element resources it contains. Furthermore, the prepared nanocatalyst is applied in a heterogeneous catalytic oxidation system to treat COD-containing wastewater, achieving the goal of treating waste with waste. The nanocatalyst prepared by recovering transition metal elements from acidic mine wastewater exhibits excellent COD removal performance in the heterogeneous catalytic oxidation system and can be recycled more than four times, maintaining its COD removal efficiency.

[0031] 4) The process for preparing nanocatalysts by recovering transition metal elements from acidic mine wastewater disclosed in this invention is simple to operate, and the prepared transition metal sulfide catalysts do not have any additional impact on the environment.

[0032] Of course, any product implementing this disclosure does not necessarily need to achieve all of the technical effects described above at the same time.

[0033] Other features and advantages of this disclosure will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0034] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments of the present disclosure and, together with their description, serve to explain the principles of the present disclosure.

[0035] Figure 1 This is a flowchart of a method for removing chemical oxygen demand using a catalyst prepared from acidic mine wastewater, as provided in this disclosure.

[0036] Figure 2 This diagram illustrates the effect of the dosage of the transition metal sulfide nanocatalyst and conventional metal sulfide catalyst prepared in this disclosure on the COD removal efficiency.

[0037] Figure 3 This diagram illustrates the effect of changes in the droplet acceleration rate of sodium hydrosulfide solution on the COD removal efficiency of the prepared metal sulfide catalyst.

[0038] Figure 4 This diagram illustrates the effect of reaction speed on COD removal efficiency as described in this disclosure.

[0039] Figure 5 This is a schematic diagram illustrating the effect of reaction temperature on COD removal efficiency in this disclosure.

[0040] Figure 6 This is a schematic diagram illustrating the effect of pH value on COD removal efficiency as presented in this disclosure.

[0041] Figure 7 The recycling effect of the transition metal sulfide nanocatalyst prepared in this disclosure is shown, where the horizontal axis 1, 2, 3, 4, and 5 represent the 1st, 2nd, 3rd, 4th, and 5th uses, respectively. Detailed Implementation

[0042] Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present disclosure.

[0043] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this disclosure or its application or use.

[0044] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and equipment should be considered part of the specification.

[0045] In all the examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0046] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0047] Combination Figure 1 This disclosure provides a method for removing chemical oxygen demand (COD) using a catalyst prepared from acidic mine wastewater, comprising the following steps:

[0048] S1, Preparation of transition metal sulfide nanocatalysts, including:

[0049] S11, acidic mine wastewater, which contains manganese ions, copper ions and iron ions, wherein the manganese ion content is greater than 50 mg / L and the copper ion content is greater than 50 mg / L;

[0050] S121. If the iron ion content in the acidic mine wastewater is greater than 100 mg / L, the acidic mine wastewater is pretreated by adding alkaline solution to the acidic mine wastewater to adjust the pH value to 4-5, producing flocculent precipitates of ferric hydroxide and ferrous hydroxide. After stirring evenly, the mixture is allowed to stand to allow the flocs to settle. The pretreated mine wastewater is then filtered to obtain the mine wastewater to be treated.

[0051] S122. If the iron ion content in the acidic mine wastewater is less than 100 mg / L, then no pretreatment is required for the acidic mine wastewater to be treated.

[0052] S13. While stirring at a first stirring rate, add sodium hydrosulfide solution to the mine wastewater to be treated at a first drop rate. The first stirring rate is 250 rpm-300 rpm, the first drop rate is 0.5 mL / L·s-2 mL / L·s, the mass concentration of the sodium hydrosulfide solution is 20 wt%-30 wt%, the reaction temperature is 20℃-30℃, and the addition is stopped after the reaction pH reaches 7-8. The reaction formula is as follows:

[0053] Cu 2+ +HS - →CuS↓+H + ;

[0054] Mn 2+ +HS - +H2O→Mn(OH)2↓+H2S↑;

[0055] 2Mn(OH)2 + O2 → 2MnO(OH)2↓;

[0056] Mn 2+ +S 2- →MnS↓;

[0057] S14, the black solid produced after the reaction is collected by centrifugation at a speed of 800 rpm-1000 rpm, and then washed 2-3 times with ethanol and deionized water.

[0058] S15, the washed black solid was vacuum dried to obtain a transition metal sulfide nanocatalyst.

[0059] S2, transition metal sulfide nanocatalysts for the removal of S from polluted water in heterogeneous catalytic oxidation systems 2- and reducing substances of organic matter, including:

[0060] S21 provides polluted water with a chemical oxygen demand (COD) concentration of 300 mg / L-500 mg / L, of which S 2- Concentrations range from 50 mg / L to 200 mg / L;

[0061] S22 adjusts the pH of polluted water to 4-9;

[0062] S23, adding an oxidant and a transition metal sulfide nanocatalyst to the polluted water body, wherein the amount of oxidant added per liter of polluted water body is 1g-2g, and the amount of transition metal sulfide nanocatalyst added per liter of polluted water body is 1g-3g.

[0063] Specifically, in S11, the acidic mine wastewater is rich in manganese ions, copper ions and iron ions. In this embodiment of the present disclosure, the manganese ion content is greater than 50 mg / L and the copper ion content is greater than 50 mg / L.

[0064] In S121, when the iron ion concentration is greater than 100 mg / L, pretreatment is required. The pH is adjusted to 4-5 using an alkaline solution to generate Fe(OH)3 / Fe(OH)2 flocs. Static filtration removes most of the iron ions, preventing iron from interfering with the purity of manganese sulfide / copper sulfide in subsequent sulfidation reactions. When the iron ion concentration is less than 100 mg / L, direct treatment is possible, as low-concentration iron will form FeS during the sulfidation stage, which does not affect the purity of the target product. The filtered flocs (Fe(OH)3 / Fe(OH)2) can be recycled to prepare iron-based catalysts (such as Fe2O3).

[0065] pH 4-5 is Fe 3+ Complete precipitation (Ksp(Fe(OH)3) = 2.79 × 10⁻⁶) -39 ) and avoid Mn 2+ / Cu 2+ The equilibrium point for precipitation (Mn(OH)2 begins to precipitate at pH≈8.1, Cu(OH)2 begins to precipitate at pH≈6.0).

[0066] Optionally, in step S121, an alkaline solution is added to the acidic mine wastewater to adjust the pH value to 4-5. Here, the alkaline solution is either sodium hydroxide or calcium hydroxide.

[0067] The wastewater is highly acidic, but the high solubility and strong alkalinity of NaOH can quickly neutralize the acidity and shorten the reaction time.

[0068] When the wastewater is weakly acidic (pH > 3) or cost is a concern, the low-cost advantage of using Ca(OH)2 is significant. Of course, SO4 in wastewater... 2- At high concentrations, Ca(OH)2 can simultaneously precipitate SO4. 2- (Generates CaSO4·2H2O), reducing the consumption of sulfur resources in subsequent sulfidation stages.

[0069] For the sulfidation conversion stage in step S13: Under stirring at 250-300 rpm, add 20-30 wt% NaHS solution dropwise at a rate of 0.5 mL / L·s-2 mL / L·s, controlling the reaction temperature at 20℃-30℃ and the pH at 7-8. Under these conditions, Mn... 2+ / Cu 2+ With HS - The reaction generates MnS and CuS nanoparticles rapidly, pH control promotes complete sulfide precipitation, and stirring rate ensures uniform mass transfer and H2S gas escape.

[0070] In this disclosure, controlling the droplet acceleration rate is beneficial for forming nanoscale catalysts. Too fast a rate will accelerate the reaction and result in excessively large precipitate particles, while too slow a rate will affect the precipitation efficiency.

[0071] Optionally, the first stirring speed can be 250 rpm, 260 rpm, 270 rpm, 280 rpm, 290 rpm, or 300 rpm, or it can be a range between any two points between 250 rpm and 300 rpm, such as 260 rpm to 290 rpm, without specific limitation here.

[0072] Optionally, the acceleration rate of the first drop can be 0.5 mL / L·s, 1 mL / L·s, 1.5 mL / L·s, 2 mL / L·s, or a range between any two points between 0.5 mL / L·s and 2 mL / L·s, for example, 0.8 mL / L·s to 1.8 mL / L·s.

[0073] Optionally, the mass concentration of the sodium hydrosulfide solution can be 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, or 30wt%, or a range between any two points between 20wt% and 30wt%, for example, 22wt% to 28wt%.

[0074] Optionally, the reaction temperature can be 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, or 30℃. It can also be a range between any two points within the 20℃-30℃ range, such as 22℃-28℃. A temperature of 20℃-30℃ is close to room temperature, thus reducing energy consumption.

[0075] Optionally, in step S13, the addition is stopped after the reaction pH reaches 7-8 to ensure complete precipitation of MnS / CuS (Ksp of MnS = 5 × 10⁻⁶). -15 The Ksp of CuS is 8 × 10⁻⁶. -37 ), while inhibiting FeS (Ksp=6×10 ), -19 The competitive accumulation of ).

[0076] In step S13, the sulfidation reaction will release H2S gas, which can be absorbed by a tail gas absorption device (such as NaOH solution absorption) to avoid environmental pollution.

[0077] Centrifuge at 800-1000 rpm to separate the black solid, and wash with ethanol / deionized water 2-3 times to remove surface-adsorbed impurities (such as unreacted ions, excess HS). - Vacuum drying is used to avoid oxidation, ultimately yielding transition metal sulfide nanocatalysts (such as MnS / CuS composites).

[0078] Optionally, the washed black solid is vacuum dried at a temperature of 40℃-45℃ for 40h-48h.

[0079] The black solid contains easily decomposable metal sulfides (such as MnS and CuS). Drying at 40℃-45℃ can prevent thermal decomposition or structural damage. A drying time of 40-48 hours ensures complete evaporation of moisture from the pores.

[0080] Optionally, staged drying can be performed: Stage 1 (rapid dehydration): vacuum drying at 40℃ for 24 hours to remove surface and macropore moisture. Stage 2 (deep dehydration): drying at 45℃ for 12-24 hours to accelerate the evaporation of micropore moisture.

[0081] For step S21, the COD (chemical oxygen demand) of 300 mg / L-500 mg / L mainly comes from organic matter (such as humic acid, phenols, and hydrocarbons) and some reducing inorganic substances (such as Fe). 2+ S 2- (), needs to be converted into CO2 and H2O through oxidative decomposition. S 2- Concentrations of 50 mg / L-200 mg / L: High concentrations of sulfides are toxic, corrosive, and have a foul odor. They need to be oxidized to elemental sulfur or sulfates to reduce their toxicity.

[0082] For step S22 (pH adjustment): The activity of the oxidant and catalyst is optimized by controlling the pH (4-9), while avoiding extreme pH that could lead to catalyst deactivation or side reactions (such as H2S gas escape). When pH < 4, excessive acidity can cause H2S gas to escape, resulting in secondary pollution. When pH > 9, excessive alkalinity can inhibit the catalytic activity of transition metal sulfides (such as MnS readily forming Mn(OH)2 precipitate in strong alkali).

[0083] In step S23, the oxidant in this disclosure provides free radicals to oxidize pollutants, and the transition metal sulfide nanocatalyst reduces the activation energy of the reaction and promotes the generation and transport of free radicals.

[0084] In step S23, the reaction temperature can be 20℃-30℃. Excessive temperature will accelerate free radical quenching and reduce oxidation efficiency. The stirring speed can be 200rpm-400rpm to ensure thorough mixing of the oxidant, catalyst, and pollutants. The reaction time can be 30min-60min to ensure adequate mixing of COD and S. 2- The shortest time to achieve the removal rate target.

[0085] The dosage of oxidant in each liter of polluted water is 1-2g, and the dosage of transition metal sulfide nanocatalyst is 1-3g per liter of polluted water. To reduce COD (300mg / L-500mg / L), 1g / L-2g / L of oxidant is required, and to reduce S... 2- An additional 0.5g / L-1g / L oxidant is required at concentrations of 50mg / L-200mg / L.

[0086] Optionally, the oxidizing agent includes potassium persulfate.

[0087] Potassium peroxymonosulfate (PMS, chemical formula KHSO5) is a highly efficient oxidant used in the treatment of polluted water to degrade organic matter (reduce COD) and oxidize sulfides.

[0088] Optionally, it also includes the recycling of transition metal sulfide nanocatalysts, with a recycling frequency of more than 4 times.

[0089] The transition metal sulfide nanocatalyst prepared by the method disclosed herein can be recycled, and experiments have shown that it can be recycled more than 4 times. After each cycle, the catalyst is separated (centrifuged or filtered), washed (with deionized water / ethanol), and dried (vacuum dried at 40°C for 48 h) to ensure consistent conditions.

[0090] The nanocatalyst prepared by recovering transition metal elements from acidic mine wastewater exhibits excellent COD removal in heterogeneous catalytic oxidation systems and can be recycled more than four times to maintain the COD removal effect.

[0091] This disclosed method for recovering transition metal elements from acidic mining wastewater effectively converts iron, manganese, and copper elements in the wastewater into nano-metal sulfides, which can be applied to the environmental remediation of water bodies polluted by reducing agents. The preparation process of this transition metal sulfide nanocatalyst is simple and low-cost, and the harmful heavy metal elements it contains can be ignored. The transition metal element catalyst exhibits good performance in heterogeneous catalytic oxidation systems for sulfur... 2- It has a good removal effect on reducing substances and good recycling performance, showing good application prospects.

[0092] In the following examples, the COD concentration in the water sample was determined by the national standard dichromate method (HJ828-2017).

[0093] Example 1:

[0094] The acidic mine wastewater provided in this embodiment contains 2951.144 mg / L of iron ions, 71.61 mg / L of copper ions, and 156.88 mg / L of manganese ions.

[0095] Metal sulfide nanocatalysts were prepared by recovering transition metal elements from acidic mine wastewater. These nanocatalysts exhibit the characteristics of nanoscale catalysts, and the preparation process is as follows:

[0096] (1) Take 500 mL of acidic mine wastewater for pretreatment. Adjust the pH to 4.5 with 10% sodium hydroxide solution. Stir the reaction at 300 rpm. After reacting evenly for 15 min, let it stand to allow the flocs to settle and then filter it.

[0097] (2) While stirring, add 20% sodium hydrosulfide solution to the filtered wastewater at a rate of 0.5 mL / L·s. The reaction speed is 300 rpm and the reaction temperature is 25℃. During the reaction, monitor the pH value and stop adding after it reaches 7.5.

[0098] (3) The black solid produced after the reaction was collected by centrifugation, and after being washed once with ethanol and twice with deionized water, it was dried under vacuum at 40°C for 48 h to obtain a transition metal sulfide nanocatalyst.

[0099] Comparative Example 1:

[0100] Acidic mine wastewater was treated using a sulfide precipitation method based on existing technology. The water sample was the acidic mine wastewater from Example 1, and the preparation was carried out using a direct sodium sulfide precipitation method. 500 mL of acidic mine wastewater was directly added to a 20% sodium sulfide solution at a rate of 0.5 mL / L·s, with a reaction speed of 300 rpm. The addition was stopped once the pH reached 7.5. The remaining steps were the same as in Example 1, yielding conventional metal sulfides.

[0101] Example 2:

[0102] This embodiment provides a method for removing COD from polluted water using the transition metal sulfide nanocatalyst prepared in Example 1.

[0103] The polluted water body is wastewater from a mineral processing plant in southwestern China, with a COD concentration of 488 mg / L and a S concentration of [missing information]. 2- The concentration was 179 mg / L, the initial pH was 11, and it contained organic matter added during the production process that entered the wastewater.

[0104] COD was removed by adding the transition metal sulfide nanocatalyst and oxidant prepared in Example 1 to the wastewater in a heterogeneous catalytic oxidation system. The specific steps of the COD removal method are as follows:

[0105] A 250mL conical flask was used as the reaction vessel. 100mL of wastewater was added, and the pH was adjusted to 6 using sodium hydroxide solution. 3g of transition metal sulfide nanocatalyst and 2g of potassium persulfate were added, and the reaction vessel was placed on a shaker at 300rpm for 30min.

[0106] The COD removal efficiency in the wastewater was measured, and the COD level decreased to 49.3 mg / L after the reaction. The results indicate a COD removal rate of 89.90%, demonstrating the feasibility of recovering transition metal elements from acidic mining wastewater to prepare nanocatalysts for application in heterogeneous catalytic oxidation systems.

[0107] Example 3:

[0108] This embodiment examines the effect of the prepared transition metal sulfide nanocatalyst and the catalyst dosage in existing technologies on COD removal efficiency.

[0109] The polluted water body is still the wastewater in Example 2, and the steps and methods for removing COD are consistent with those in Example 2. The difference is that the nano-catalyst and conventional catalyst from Example 1 and Comparative Example 1 are added respectively, with dosages of 1 g / L, 1.5 g / L, 2.0 g / L, 2.5 g / L, and 3 g / L. Figure 2 The black curve represents the transition metal sulfide nanocatalyst (nanometal sulfide) prepared in this disclosure, while the red curve represents the conventional metal sulfide prepared in Comparative Example 1.

[0110] COD removal results as follows Figure 2 As shown in the results, after 30 minutes of reaction, the COD removal efficiency increased with the increase of the amount of nano-catalyst. The removal efficiency was essentially the same at 2.5 g / L and 3 g / L, with a removal rate of approximately 90%. In contrast, the conventional catalyst obtained in Comparative Example 1 showed lower COD removal efficiency at dosages between 1 g / L and 3 g / L, with a maximum removal rate of only 68.7%. Therefore, this indicates that the transition metal sulfide nano-catalyst prepared in this invention has a superior COD removal effect.

[0111] Example 4:

[0112] This example is an embodiment for examining the effect of the change in the drop acceleration rate of sodium hydrosulfide solution on the COD removal effect of transition metal sulfide nanocatalyst.

[0113] The polluted water body was still the wastewater from Example 2, and the steps and methods for COD removal were consistent with those in Example 2. The difference lay in the different droplet acceleration rates of the sodium hydrosulfide solution during the preparation of the metal sulfide catalyst: 0.1 mL / L·s, 0.5 mL / L·s, 1.0 mL / L·s, 1.5 mL / L·s, 2.0 mL / L·s, and 3.0 mL / L·s, respectively. Other reaction parameters were: temperature 30℃, reaction speed 300 rpm, catalyst dosage 3 g / L, and potassium persulfate dosage 2 g / L. The results are as follows: Figure 3 As shown in the figure. After 30 min of reaction, the COD removal effect showed that the drop rate was between 0.5 mL / L·s and 2.0 mL / L·s. The prepared transition metal sulfide nanocatalyst had a better effect on catalytic oxidation and COD removal, which indicates that controlling the drop rate is beneficial to forming a catalyst with better catalytic effect.

[0114] Example 5:

[0115] This example is to examine the effect of reaction temperature on COD removal efficiency.

[0116] The polluted water body was still the wastewater from Example 2, and the steps and methods for removing COD were consistent with those described in Example 2, the difference being the reaction temperature in the COD removal step, which was 20℃, 25℃, and 30℃ respectively. Other reaction parameters were: reaction speed 300 rpm, catalyst dosage 3 g / L, and potassium persulfate dosage 2 g / L. The results are as follows: Figure 4 As shown in the figure, after 30 minutes of reaction, the COD removal rate was above 90% at temperatures ranging from 20℃ to 30℃, with good results. The best effect was observed at 25℃.

[0117] Example 6:

[0118] This embodiment is to examine the effect of reaction speed on COD removal efficiency.

[0119] The polluted water body was still the wastewater from Example 2, and the steps and methods for removing COD were consistent with those described in Example 2, except that the reaction speeds in the COD removal steps were different, at 250 rpm, 275 rpm, and 300 rpm respectively. Other reaction parameters were: temperature 30℃, catalyst dosage 3 g / L, and potassium persulfate dosage 2 g / L. The results are as follows: Figure 5 As shown in the figure, after a reaction time of 30 minutes, the COD removal rate remained above 90% within a rotation speed range of 250 rpm to 300 rpm, indicating good performance.

[0120] Example 7:

[0121] This embodiment verifies the effect of pH on COD removal efficiency.

[0122] The polluted water body was still the wastewater from Example 2, and the steps and methods for removing COD were consistent with those described in Example 2. The difference was that the pH was adjusted to 4-9 before the COD removal reaction, specifically 4, 5, 6, 7, 8, and 9. The results were as follows. Figure 6 As shown in the figure. The results showed that after 30 min of reaction, the COD removal efficiency exceeded 85%, with the best effect observed at pH=4. This indicates that the transition metal sulfide nanocatalyst prepared from the recovery of transition metal elements from acidic mine wastewater exhibits good performance across a wide pH range.

[0123] Example 8:

[0124] This embodiment verifies the recycling effect of transition metal sulfide nanocatalysts.

[0125] The polluted water body is still the wastewater from Example 2, and the steps and methods for removing COD described in Example 2 are consistent with those in Example 2. The difference is that the transition metal sulfide nanocatalyst after the reaction is recovered and recycled five times, and the results are as follows. Figure 7 As shown in the figure, the COD removal efficiency of the transition metal sulfide nanocatalyst gradually decreased with the increase of the number of cycles. The removal efficiency exceeded 80% in the first three cycles, and still exceeded 65% in the fifth cycle, demonstrating a strong recycling effect.

[0126] In summary, the proposed procedure for preparing nanocatalysts by recovering transition metal elements from acidic mine wastewater is simple to operate. When applied to heterogeneous catalytic oxidation systems, it exhibits good COD removal efficiency and maintains good performance across a wide pH range. Cyclic experiments show that it is highly effective for repeated use. It not only recovers metal resources to treat acidic mine wastewater but can also be applied to treat COD-containing wastewater, realizing the concept of treating waste with waste and achieving the dual benefits of resource recovery and environmental remediation.

[0127] While specific embodiments of this disclosure have been described in detail by way of example, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of this disclosure. The scope of this disclosure is defined by the appended claims.

Claims

1. A method for removing chemical oxygen demand (COD) using a catalyst prepared from acidic mine wastewater, characterized in that, Including the following steps: Preparation of transition metal sulfide nanocatalysts, including: Acidic mine wastewater is collected, wherein the acidic mine wastewater includes manganese ions, copper ions and iron ions, wherein the manganese ion content is greater than 50 mg / L and the copper ion content is greater than 50 mg / L; If the iron ion content in the acidic mine wastewater is greater than 100 mg / L, the acidic mine wastewater is pretreated by adding alkaline solution to the acidic mine wastewater to adjust the pH value to 4-5, producing ferric hydroxide and ferrous hydroxide flocculent precipitates. After stirring evenly, the mixture is allowed to stand to allow the flocs to settle. The pretreated mine wastewater is then filtered to obtain the mine wastewater to be treated. If the iron ion content in the acidic mine wastewater is less than 100 mg / L, then no pretreatment is required for the acidic mine wastewater to be treated. Sodium hydrosulfide solution was added to the mine wastewater to be treated while stirring at a first stirring rate of 250 rpm-300 rpm and at a first drop rate of 0.5 mL / L·s-2 mL / L·s. The mass concentration of the sodium hydrosulfide solution was 20 wt%-30 wt%. The reaction temperature was 20℃-30℃. The addition was stopped after the pH value of the reaction reached 7-8. The reaction formula is as follows: With 2+ +HS - →CuS↓+H + ; Mn 2+ +HS - +H2O→Mn(OH)2↓+H2S↑; 2Mn(OH)2 + O2 → 2MnO(OH)2↓; Mn 2+ +S 2- →MnS↓; The black solid produced after the reaction was collected by centrifugation at a speed of 800 rpm-1000 rpm, and then washed 2-3 times with ethanol and deionized water. The washed black solid was vacuum dried to obtain a transition metal sulfide nanocatalyst. The transition metal sulfide nanocatalyst removes sulfur from polluted water in a heterogeneous catalytic oxidation system. 2- and reducing substances of organic matter, including: Provide polluted water body, wherein the chemical oxygen demand (COD) concentration in the polluted water body is 300 mg / L - 500 mg / L, wherein S 2- Concentrations range from 50 mg / L to 200 mg / L; Adjust the pH value of the polluted water to 4-9; An oxidant and the transition metal sulfide nanocatalyst are added to the polluted water body, wherein the amount of the oxidant added per liter of the polluted water body is 1g-2g, and the amount of the transition metal sulfide nanocatalyst added per liter of the polluted water body is 1g-3g.

2. The method for removing chemical oxygen demand using a catalyst prepared from acidic mine wastewater according to claim 1, characterized in that, An alkaline solution is added to the acidic mine wastewater, wherein the alkaline solution is either sodium hydroxide or calcium hydroxide.

3. The method for removing chemical oxygen demand using a catalyst prepared from acidic mine wastewater according to claim 1, characterized in that, The oxidant includes potassium persulfate.

4. The method for removing chemical oxygen demand using a catalyst prepared from acidic mine wastewater according to claim 1, characterized in that, The washed black solid is then subjected to vacuum drying at a temperature of 40℃-45℃ for 40h-48h.

5. The method for removing chemical oxygen demand using a catalyst prepared from acidic mine wastewater according to claim 1, characterized in that, It also includes the recycling of the transition metal sulfide nanocatalyst, with a recycling frequency of more than 4 times.

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