A method for preparing heavy metal elements by using heavy metal-containing wastewater

Abstract

The application provides a method for preparing heavy metal elements by using heavy metal-containing wastewater, and relates to the technical field of metal wastewater treatment. In the method, aldehyde reducing agent and / or organic solid waste are used as reducing media to perform hydrothermal reduction reaction, and the heavy metals in the heavy metal-containing wastewater are driven to be reduced to heavy metal elements by the reducing media containing unsaturated bonds or capable of generating unsaturated bonds under hydrothermal reduction, so that the reaction barrier is reduced, and the competition of metal ion hydrolysis reaction is broken. The recovery rate of the obtained heavy metal elements is greater than or equal to 99%, the purity is greater than 99%, and the total amount of impurities is less than 50 ppm at the lowest. Moreover, the organic solid waste is used as the reducing media to perform the hydrothermal reduction reaction with the heavy metal-containing wastewater, so that the deep purification of the heavy metal-containing wastewater and the resource utilization of the organic solid waste are simultaneously achieved. In addition, the method provided by the application does not need additional reducing agent, so that the cost is reduced, and the method is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of metal wastewater treatment technology, and specifically to a method for preparing heavy metal elements from wastewater containing heavy metals. Background Technology

[0002] Currently, the main methods for treating precious / heavy metal wastewater (including both precious metal and heavy metal wastewater) include precipitation, liquid-phase chemical reduction, and hydrothermal reduction. Traditional precipitation generates hazardous sludge. While the emerging liquid-phase chemical reduction method can prepare metal powders, it heavily relies on specialized reducing agents such as ascorbic acid and sodium borohydride, and is only applicable to single-metal systems. This is particularly problematic for mixed precious / heavy metal wastewater containing complexing agents (such as electroplating wastewater and PCB industry wastewater), where reducing agent poisoning and low product purity are common issues. Although the existing hydrothermal reduction method overcomes these problems and offers an environmentally friendly reaction medium, the recovery rate of heavy metals from the hydrothermal reduction of precious / heavy metal wastewater is poor. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide a method for preparing heavy metal elements from heavy metal-containing wastewater. The method provided by this invention achieves a heavy metal element recovery rate of ≥99%, which is high.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing heavy metal elements from heavy metal-containing wastewater, comprising the following steps: The wastewater containing heavy metals is mixed with a reducing medium and subjected to a hydrothermal reduction reaction to reduce the heavy metals in the wastewater to obtain elemental heavy metals; the pH value of the wastewater containing heavy metals is <7. The reducing medium includes aldehyde reducing agents and / or organic solid waste; The organic solid waste is organic solid waste that can generate unsaturated bonds under hydrothermal reduction reaction.

[0005] Preferably, the organic solid waste includes one or more of plastics, photovoltaic panels, and waste circuit boards; The particle size of the organic solid waste is 40-60 mesh.

[0006] Preferably, the aldehyde reducing agent includes paraformaldehyde and / or glucose.

[0007] Preferably, the ratio of the mass of the reducing medium to the volume of the heavy metal-containing wastewater is 1~3g:20~45mL.

[0008] Preferably, the heavy metals in the heavy metal-containing wastewater include one or more of gold, silver, indium, copper, nickel, chromium, zinc and iron.

[0009] Preferably, the heavy metal-containing wastewater is one or more of the following: copper-containing wastewater from the electroplating process, copper-containing wastewater from the molecular sieve production process, and nickel-containing wastewater.

[0010] Preferably, the hydrothermal reduction reaction is carried out at a temperature of 100~250℃ for a time of 0.5~9h.

[0011] Preferably, the concentration of heavy metals in the heavy metal-containing wastewater is 1000~60000 mg / mL.

[0012] Preferably, the heating rate to the temperature of the hydrothermal reduction reaction is 5~10℃ / min.

[0013] Preferably, after the hydrothermal reduction reaction is completed, the process further includes cooling the reduced slurry obtained from the hydrothermal raw material reaction and performing solid-liquid separation, and washing and drying the resulting solid.

[0014] This invention provides a method for preparing heavy metal elements from heavy metal-containing wastewater, comprising the following steps: mixing heavy metal-containing wastewater with a reducing medium, and carrying out a hydrothermal reduction reaction to reduce the heavy metals in the wastewater to obtain heavy metal elements; the reducing medium includes aldehyde reducing agents and / or organic solid waste; the organic solid waste is organic solid waste capable of generating unsaturated bonds under hydrothermal reduction. Traditional hydrothermal reduction methods for reducing precious metals and / or heavy metals in heavy metal-containing wastewater lack electron transfer media, resulting in excessively high hydrothermal reaction barriers and low heavy metal element recovery rates; moreover, the hydrothermal reduction method relies on supercritical water generated by hydrothermal processes (water is converted into H3O). + and OH - This achieved the reduction of metal ions in the wastewater, while OH... - The reducing properties of certain substances cause the hydrolysis of metal ions, during which the valence state of the metal ions remains unchanged, competing with the hydrothermal reduction reaction and further reducing the recovery rate of heavy metals. This invention, however, uses aldehyde reducing agents and / or organic solid waste as reducing media for the hydrothermal reduction reaction. By using aldehyde reducing agents containing unsaturated bonds and / or organic solid waste that can generate unsaturated bonds under hydrothermal reduction, the heavy metals in the wastewater containing heavy metals are reduced to their elemental form. This lowers the reaction barrier, directing the reaction towards a lower valence state of the heavy metal ions, breaking the competition from the metal ion hydrolysis reaction. The resulting heavy metal recovery rate is ≥99%, purity >99%, and the total impurities can be as low as 50 ppm, demonstrating high recovery rate and purity. Furthermore, this invention uses organic solid waste as a reducing medium in a synergistic hydrothermal reduction reaction with the heavy metal-containing wastewater, simultaneously achieving deep purification of heavy metal-containing wastewater (especially mixed wastewater containing complexing agents containing precious / heavy metals) and resource recovery of organic solid waste. In addition, the method provided by this invention does not require external reducing agents, reducing costs and making it suitable for industrial production. Attached Figure Description

[0015] Figure 1 Photograph of copper elemental powder obtained in Example 1; Figure 2 The X-ray diffraction pattern of the copper elemental powder prepared in Example 1 is shown below. Figure 3 Photograph of copper elemental powder obtained in Example 2; Figure 4 The X-ray diffraction pattern of the copper elemental powder prepared in Example 2; Figure 5 Photograph of copper elemental powder obtained in Example 3; Figure 6 The X-ray diffraction pattern of the copper elemental powder obtained in Example 3 is shown below. Figure 7 Photograph of copper elemental powder prepared in Example 4; Figure 8 The X-ray diffraction pattern of the copper elemental powder obtained in Example 4 is shown below. Figure 9 Photograph of copper elemental powder obtained in Example 5; Figure 10 The X-ray diffraction pattern of the copper elemental powder prepared in Example 5; Figure 11 Photograph of the nickel elemental powder obtained in Example 6; Figure 12 The image shows the X-ray diffraction pattern of the nickel elemental powder prepared in Example 6. Detailed Implementation

[0016] This invention provides a method for preparing heavy metal elements from heavy metal-containing wastewater, comprising the following steps: mixing heavy metal-containing wastewater with a reducing medium and carrying out a hydrothermal reduction reaction to reduce the heavy metals in the heavy metal-containing wastewater to obtain heavy metal elements; the reducing medium includes aldehyde reducing agents and / or organic solid waste; the organic solid waste is organic solid waste that can generate unsaturated bonds under hydrothermal reduction reaction.

[0017] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0018] In this invention, the heavy metals in the heavy metal-containing wastewater may include one or more of gold, silver, indium, copper, nickel, chromium, zinc, and iron; the heavy metal-containing wastewater may specifically be one or more of copper-containing wastewater from electroplating processes, copper-containing wastewater from molecular sieve production processes, and nickel-containing wastewater; the concentration of heavy metals in the heavy metal-containing wastewater may be 1000~60000 mg / mL, specifically 1000 mg / mL, 5000 mg / mL, 8000 mg / mL, 10000 mg / mL, 15000 mg / mL, 30000 mg / mL, or 60000 mg / mL; the pH value of the heavy metal-containing wastewater may be <7, or may be 1~3, specifically 1, 1.5, 2, 3, 4, 5, 6, or 6.5.

[0019] In this invention, the reducing medium includes aldehyde reducing agents and / or organic solid waste; the aldehyde reducing agents may include paraformaldehyde and / or glucose; the organic solid waste is organic solid waste capable of generating unsaturated bonds under hydrothermal reduction reaction; the organic solid waste may include one or more of plastics, photovoltaic panels, and waste circuit boards; the particle size of the organic solid waste may be 40-60 mesh, specifically 40 mesh, 45 mesh, 50 mesh, 55 mesh, or 60 mesh. This invention may also include crushing or pulverizing organic solid waste with a particle size larger than the above range until the obtained organic solid waste has a particle size of 40-60 mesh. In this invention, the mass ratio of the reducing medium to the volume of heavy metal-containing wastewater may be 1-3 g: 20-45 mL, specifically 1 g: 45 mL, 1 g: 30 mL, 1 g: 25 mL, 1 g: 20 mL, 2 g: 20 mL, 3 g: 20 mL, or 3 g: 45 mL. This invention uses organic solid waste that can generate unsaturated bonds under hydrothermal reduction reaction as a reducing medium. During the hydrothermal reduction reaction, the organic solid waste decomposes and generates unsaturated bonds containing carbonyl, carboxyl, ester and other groups, which serve as reducing groups to drive the hydrothermal reduction reaction.

[0020] Each metal ion has its own redox potential, for example, Ag(I) / Ag = +0.8V; Cu(II) / Cu = +0.337V; Ni(II) / Ni = -0.23V. The lower the redox potential, the higher the reduction barrier, and the higher the required reducing power. This invention uses aldehyde reducing agents and / or organic solid waste as the reducing medium. The aldehyde reducing agents contain unsaturated bonds; the organic solid waste can generate unsaturated bonds under hydrothermal reduction reaction. Through the above-mentioned reducing medium, the heavy metals in the heavy metal-containing wastewater are reduced to heavy metal elements, which lowers the reaction barrier and breaks the competition of metal ion hydrolysis reaction. The recovery rate of the obtained heavy metal elements is ≥99%, the purity is >99%, and the total impurities can be as low as 50ppm, with high recovery rate and purity.

[0021] In this invention, the temperature of the hydrothermal reduction reaction can be 100~250℃, specifically 100℃, 150℃, 160℃, 170℃, 200℃, 220℃, or 250℃; the time of the hydrothermal reduction reaction can be 0.5~9h, specifically 0.5h, 1h, 3h, 5h, 6h, 7h, or 9h; the heating rate to the temperature of the hydrothermal reduction reaction can be 5~10℃ / min, specifically 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min. In this invention, the hydrothermal reduction reaction can be carried out in a closed container, specifically a closed hydrothermal reactor. In this invention, the hydrothermal reduction reaction is carried out in a closed container, where water evaporates to form water vapor during the reaction. No additional pressurization is required; the pressure within the closed container itself promotes the forward progress of the hydrothermal reduction reaction.

[0022] After completing the hydrothermal reduction reaction, the present invention further includes cooling the reduced slurry obtained from the hydrothermal raw material reaction and performing solid-liquid separation, and washing and drying the resulting solid. In the present invention, the cooling can be natural cooling; the washing can include water washing; the number of water washings can be 1 to 3 times, specifically 1, 2 or 3 times; the drying temperature can be 100 to 105℃, specifically 100℃, 101℃, 102℃, 103℃, 104℃ or 105℃; the drying time can be 3 to 5 hours, specifically 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours.

[0023] To further illustrate the present invention, the solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0024] Example 1 Copper-containing wastewater refers to wastewater containing copper from the electroplating process; copper is represented by Cu. 2+ The concentration was 10281 mg / L, and the pH was 1.5. Copper-containing wastewater was mixed with polyethylene plastic granules with a particle size of 2 mm and placed in a closed hydrothermal reactor. The mixture was subjected to hydrothermal reduction at 200℃ for 6 hours. After the hydrothermal reduction reaction was completed, the mixture was allowed to cool naturally to room temperature. The liquid phase was separated, and the solid product was washed with deionized water and dried to obtain elemental copper powder. The mass ratio of the polyethylene plastic granules to the volume of the copper-containing wastewater was 1 g:30 mL, and the heating rate to the hydrothermal reaction temperature was 10℃ / min.

[0025] Figure 1 Photograph of copper elemental powder prepared in Example 1. Figure 2 The X-ray diffraction pattern of the copper elemental powder prepared in Example 1 is shown below. Figure 1 and Figure 2It can be seen that the XRD pattern of the copper elemental powder prepared in Example 1 has sharp diffraction peaks and no other impurity peaks, which matches the standard card of Cu, confirming that the copper elemental powder obtained by the hydrothermal reduction reaction is copper elemental.

[0026] The obtained copper powder was digested using the following steps: 0.1000 g of copper powder was accurately weighed and placed in a clean polytetrafluoroethylene (PTFE) digestion vessel. 5 mL of analytical grade concentrated nitric acid was added, the vessel was capped, and pre-digestion was performed at room temperature. After the vigorous reaction ceased, the digestion vessel was placed in a microwave digestion apparatus, and the microwave digestion program was set as follows: the temperature was raised to 150°C and held for 15 min, then further raised to 190°C and held for 20 min. After the digestion program was completed, the digestion vessel was allowed to cool to room temperature. The digestion solution was completely transferred to a 50 mL volumetric flask. The inner wall of the digestion vessel was rinsed several times with deionized water, and the washings were added to the volumetric flask. Finally, the solution was diluted to the mark with ultrapure water and shaken well to obtain the test solution A. Simultaneously, two reagent blank solutions B were prepared following the same steps to correct for systematic errors and reagent background. Inductively coupled plasma mass spectrometry (ICP-MS) was used to test solution A, and reagent blank solution B was used for calibration. Tests showed that the total amount of impurities in the copper powder prepared in Example 1 was <1000ppm, and the purity of the copper powder was >99%, indicating high purity.

[0027] Cu in the liquid phase after hydrothermal reduction reaction 2+ The concentration of Cu was detected. 2+ With a concentration of 0.2019 mg / L, the removal rate of copper ions was 99.998%, which meets the Class I standard of the "Integrated Wastewater Discharge Standard" (Cu<0.5 mg / L). Calculated based on the fact that no loss of copper elemental powder occurs during the recovery process, the recovery rate of copper elemental is 99.998%, which is a high recovery rate.

[0028] Example 2 Copper-containing wastewater refers to wastewater containing copper from the electroplating process; copper is represented by Cu. 2+ The concentration was 10281 mg / L, and the pH was 1.5. Copper-containing wastewater was mixed with crushed photovoltaic panel particles with a particle size of 1-2 mm and placed in a closed hydrothermal reactor. The mixture was subjected to a hydrothermal reduction reaction at 220℃ for 9 hours. After the hydrothermal reduction reaction was completed, the mixture was allowed to cool naturally to room temperature. The liquid phase was separated, and the solid product was washed with deionized water and dried to obtain elemental copper powder. The mass ratio of the photovoltaic panel particles to the volume of the copper-containing wastewater was 1 g:30 mL, and the heating rate to the hydrothermal reaction temperature was 10℃ / min.

[0029] Figure 3 Photograph of copper elemental powder prepared in Example 2. Figure 4 The X-ray diffraction pattern of the copper elemental powder prepared in Example 2 is shown below. Figure 3 and Figure 4 It can be seen that the XRD pattern of the copper elemental powder prepared in Example 2 has sharp diffraction peaks and no other impurity peaks, which matches the standard card of Cu, confirming that the copper elemental powder obtained by the hydrothermal reduction reaction is copper elemental.

[0030] The copper powder obtained in Example 2 was digested using the same method as in Example 1. Testing showed that the total impurities in the copper powder prepared in Example 2 were <800 ppm, and the purity of the copper powder was >99.9%, indicating high purity.

[0031] Cu in the liquid phase after hydrothermal reduction reaction 2+ The concentration of Cu was detected. 2+ With a concentration of 0.3174 mg / L, the removal rate of copper ions was 99.997%, which meets the Class I standard of the "Integrated Wastewater Discharge Standard". Based on the calculation that no loss occurs in the copper element powder during the recovery process, the recovery rate of copper element is 99.997%, which is a high recovery rate.

[0032] Example 3 Copper-containing wastewater refers to wastewater containing copper from the electroplating process; copper is represented by Cu. 2+ The concentration was 10281 mg / L, and the pH was 1.5. Copper-containing wastewater was mixed with pulverized waste circuit board powder (non-metallic powder) with a particle size of 0.5-1 mm, and placed in a closed hydrothermal reactor. The mixture was subjected to a hydrothermal reduction reaction at 250℃ for 7 hours. After the hydrothermal reduction reaction was completed, the mixture was allowed to cool naturally to room temperature. The liquid phase was separated, and the solid product was washed with deionized water and dried to obtain elemental copper powder. The mass ratio of the waste circuit board powder to the volume of the copper-containing wastewater was 1 g: 20 mL, and the heating rate to the hydrothermal reaction temperature was 10℃ / min.

[0033] Figure 5 Photograph of copper elemental powder obtained in Example 3. Figure 6 The X-ray diffraction pattern of the copper elemental powder prepared in Example 3 is shown below. Figure 5 and Figure 6 It can be seen that the XRD pattern of the copper elemental powder prepared in Example 3 has sharp diffraction peaks and no other impurity peaks, which matches the standard card of Cu, confirming that the copper elemental powder obtained by the hydrothermal reduction reaction is copper elemental.

[0034] The obtained elemental copper powder was digested using the same method as in Example 1. Testing showed that the total impurities in the elemental copper powder prepared in Example 3 were <1000 ppm, and the purity of the elemental copper powder was >99%, indicating high purity.

[0035] Cu in the liquid phase after hydrothermal reduction reaction 2+ The concentration of Cu was detected. 2+The concentration was 0.4129 mg / L, and the removal rate of copper ions was 99.996%, which meets the Class I standard of the "Integrated Wastewater Discharge Standard". Based on the calculation that no loss occurs in the copper element powder during the recovery process, the recovery rate of copper element is 99.996%, which is a high recovery rate.

[0036] Example 4 Copper-containing wastewater refers to wastewater containing copper from the electroplating process; copper is represented by Cu. 2+ The concentration was 10281 mg / L, and the pH was 1.5. Copper-containing wastewater was mixed with D-glucose and placed in a closed hydrothermal reactor. The mixture was subjected to hydrothermal reduction at 160℃ for 5 hours. After the hydrothermal reduction reaction, the mixture was allowed to cool naturally to room temperature. The liquid phase was separated, and the solid product was washed with deionized water and dried to obtain copper powder. The D-glucose was of analytical grade; the mass ratio of D-glucose to the volume of copper-containing wastewater was 1 g:20 mL; and the heating rate to the hydrothermal reaction temperature was 10℃ / min.

[0037] Figure 7 Photograph of copper elemental powder prepared in Example 4. Figure 8 The X-ray diffraction pattern of the copper elemental powder prepared in Example 4 is shown below. Figure 7 and Figure 8 It can be seen that the XRD pattern of the copper elemental powder prepared in Example 4 has sharp diffraction peaks and no other impurity peaks, which matches the standard card of Cu, confirming that the copper elemental powder obtained by the hydrothermal reduction reaction is copper elemental.

[0038] The copper powder obtained was digested using the same method as in Example 1. Testing showed that the total impurities in the copper powder prepared in Example 4 were <100 ppm, and the purity of the copper powder was ≥99.99%, indicating extremely high purity.

[0039] Cu in the liquid phase after hydrothermal reduction reaction 2+ The concentration of Cu was detected. 2+ With a concentration of 0.3248 mg / L, the removal rate of copper ions is 99.997%, which meets the Class I standard of the "Integrated Wastewater Discharge Standard". Calculated based on the fact that no loss occurs during the recovery of elemental copper powder, the recovery rate of elemental copper is 99.997%, which is a high recovery rate.

[0040] Example 5 The copper-containing wastewater is from the molecular sieve production process, and the copper is Cu. 2+ The concentration was 7492 mg / L, and the pH was 2.3. Copper-containing wastewater was mixed with paraformaldehyde and placed in a sealed hydrothermal reactor. The mixture was subjected to hydrothermal reduction at 170°C for 6 hours. After the hydrothermal reduction reaction was completed, the mixture was allowed to cool naturally to room temperature. The liquid phase was separated, and the solid product was washed with deionized water and dried to obtain elemental copper powder. The paraformaldehyde was of analytical grade; the mass ratio of paraformaldehyde to the volume of copper-containing wastewater was 1 g:20 mL; and the heating rate to the hydrothermal reaction temperature was 10°C / min.

[0041] Figure 9 Photograph of copper elemental powder prepared in Example 5. Figure 10 The X-ray diffraction pattern of the copper elemental powder prepared in Example 5 is shown below. Figure 9 and Figure 10 It can be seen that the XRD pattern of the copper elemental powder prepared in Example 5 has sharp diffraction peaks and no other impurity peaks, which matches the standard card of Cu, confirming that the copper elemental powder obtained by the hydrothermal reduction reaction is copper elemental.

[0042] The copper powder obtained was digested using the same method as in Example 1. Testing showed that the total impurities in the copper powder prepared in Example 5 were <50 ppm, and the purity of the copper powder was >99.995%, indicating extremely high purity.

[0043] Cu in the liquid phase after hydrothermal reduction reaction 2+ The concentration of Cu was detected. 2+ With a concentration of 0.1018 mg / L, the removal rate of copper ions is 99.999%, which meets the Class I standard of the "Integrated Wastewater Discharge Standard". Based on the calculation that no loss occurs in the copper element powder during the recovery process, the recovery rate of copper element is 99.999%, which is extremely high.

[0044] Example 6 Nickel-containing wastewater, where nickel is Ni 2+ The concentration was 5869 mg / L, and the pH was 1.6. Nickel-containing wastewater was mixed with paraformaldehyde and placed in a closed hydrothermal reactor. The mixture was subjected to hydrothermal reduction at 250°C for 9 hours. After the hydrothermal reduction reaction, the mixture was allowed to cool naturally to room temperature. The liquid phase was separated, and the solid product was washed with deionized water and dried to obtain elemental nickel powder. The paraformaldehyde was of analytical grade; the mass ratio of paraformaldehyde to the volume of nickel-containing wastewater was 1 g:20 mL; and the heating rate to the hydrothermal reaction temperature was 10°C / min.

[0045] Figure 11 Photograph of the nickel elemental powder obtained in Example 6. Figure 12 The X-ray diffraction pattern of the nickel elemental powder prepared in Example 6 is shown below. Figure 11 and Figure 12It can be seen that the XRD pattern of the nickel elemental powder prepared in Example 6 has sharp diffraction peaks and no other impurity peaks, which matches the standard card of Ni, confirming that the hydrothermal reduction reaction yields nickel elemental.

[0046] The obtained elemental nickel powder was digested using the same method as in Example 1. Testing showed that the total impurities in the elemental nickel powder prepared in Example 6 were <100 ppm, and the purity of the elemental nickel powder was >99.99%, indicating extremely high purity.

[0047] Ni in the liquid phase after hydrothermal reduction reaction 2+ Concentration was measured for Ni 2+ With a concentration of 0.1921 mg / L, the removal rate of nickel ions is 99.996%, which meets the Class I standard of the "Integrated Wastewater Discharge Standard". Based on the calculation that no loss occurs in the recovery process of nickel elemental powder, the recovery rate of nickel elemental is 99.996%, which is a high recovery rate.

[0048] Comparative Example 1 20 mL of 0.1 mol / L copper nitrate, silver nitrate, or nickel nitrate solutions were mixed with 0.5 mL of nitric acid and subjected to hydrothermal reduction reactions at 100℃, 120℃, 140℃, 160℃, 180℃, 200℃, 220℃, or 250℃ for 1 h, 3 h, 5 h, 7 h, or 9 h, respectively. No heavy metals were precipitated. Inductively coupled plasma mass spectrometry (ICP-MS) analysis of the solutions before and after the hydrothermal reduction reaction showed that the heavy metal ions in the solutions remained unchanged, and no metal ions were reduced.

[0049] Comparative Example 2 20 mL of a 0.1 mol / L copper nitrate solution, 0.5 mL of nitric acid, and 1 g of paraformaldehyde or glucose were mixed and subjected to a hydrothermal reduction reaction at 180 °C for 7 h to obtain elemental copper powder. The obtained elemental copper powder was digested using the same method as in Example 1. Testing confirmed that the obtained powder was pure copper.

[0050] Comparative Example 3 20 mL of a 0.1 mol / L nickel nitrate solution, 0.5 mL of nitric acid, and 1 g of paraformaldehyde or glucose were mixed and subjected to a hydrothermal reduction reaction at 2200 °C for 7 h to obtain elemental nickel powder. The obtained elemental nickel powder was digested using the same method as in Example 1. Testing confirmed that the obtained powder was pure nickel powder.

[0051] Comparative Example 4 20 mL of a 0.1 mol / L silver nitrate solution, 0.5 mL of nitric acid, and 1 g of paraformaldehyde or glucose were mixed and subjected to a hydrothermal reduction reaction at 2200 °C for 7 h to obtain elemental silver powder. The obtained elemental silver powder was digested using the same method as in Example 1. Testing confirmed that the obtained powder was pure silver.

[0052] As can be seen from Comparative Examples 1 to 4, in the preparation method provided by the present invention, paraformaldehyde or glucose can be used as a reducing agent to perform hydrothermal reduction of heavy metal ions in the solution, and the pressure generated by water vapor will promote the hydrothermal reduction reaction.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing heavy metal elements from heavy metal-containing wastewater, characterized in that, Includes the following steps: The wastewater containing heavy metals is mixed with a reducing medium and subjected to a hydrothermal reduction reaction to reduce the heavy metals in the wastewater to obtain elemental heavy metals; the pH value of the wastewater containing heavy metals is <7. The reducing medium includes aldehyde reducing agents and / or organic solid waste; The organic solid waste is organic solid waste that can generate unsaturated bonds under hydrothermal reduction reaction.

2. The method according to claim 1, characterized in that, The organic solid waste includes one or more of plastics, photovoltaic panels, and waste circuit boards; The particle size of the organic solid waste is 40-60 mesh.

3. The method according to claim 1, characterized in that, The aldehyde reducing agents include paraformaldehyde and / or glucose.

4. The method according to any one of claims 1 to 3, characterized in that, The ratio of the mass of the reducing medium to the volume of the heavy metal-containing wastewater is 1~3g:20~45mL.

5. The method according to claim 1, characterized in that, The heavy metals in the wastewater containing heavy metals include one or more of gold, silver, indium, copper, nickel, chromium, zinc, and iron.

6. The method according to claim 1, 2, 3 or 5, characterized in that, The hydrothermal reduction reaction is carried out at a temperature of 100~250℃ for a time of 0.5~9h.

7. The method according to claim 1 or 5, characterized in that, The heavy metal-containing wastewater is one or more of the following: copper-containing wastewater from the electroplating process, copper-containing wastewater from the molecular sieve production process, and nickel-containing wastewater.

8. The method according to claim 7, characterized in that, The concentration of heavy metals in the wastewater containing heavy metals is 1000~60000 mg / mL.

9. The method according to claim 6, characterized in that, The heating rate to the temperature of the hydrothermal reduction reaction is 5~10℃ / min.

10. The method according to claim 1, characterized in that, After the hydrothermal reduction reaction is completed, the process further includes cooling the reduced slurry obtained from the hydrothermal raw material reaction and performing solid-liquid separation, and washing and drying the resulting solid.

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