Method for recovering metal from wastewater

Abstract

The invention belongs to the technical field of environmental protection, and aims to effectively enrich precious metals in wastewater, so that the proportion of the precious metals in treated solids is increased, and recycling is easy to implement. The invention specifically provides a method for recovering metals from wastewater, which is used for recovering metals from wastewater containing metals, and is characterized by comprising the following steps: S1, putting zero-valent iron and wastewater containing metal ions to be recovered into a mechanochemical reactor for mechanochemical reaction to form a solid material of the metal to be recovered enriched with simple substances; and S2, molten metal centrifugal separation equipment is adopted, and the elementary substance metal to be recycled is separated from the solid material.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection, relates to a wastewater treatment method, and specifically relates to a method for recovering metals from wastewater. Background Art

[0002] Wastewater generated during the production process of various industries such as metallurgy, machinery manufacturing, chemical industry, and electronics often contains precious metal ions, such as copper, gold, silver, and nickel. The traditional treatment method for this type of wastewater is to use reaction tanks, sedimentation / flocculation tanks, etc. to form solid precipitates from metal ions, and then obtain wastewater that meets the discharge standards after solid-liquid separation. Since the content of metal ions in wastewater is very low, the mass proportion of metal ions in solid precipitates is also very low, and it is basically impossible to recycle them, so they can usually only be disposed of as solid waste.

[0003] There are some technologies for recovering metals from wastewater in the prior art. For example, CN105858779A discloses a method for recovering metals from low-concentration heavy metal ion wastewater, which uses activated carbon as an adsorbent, transfers the adsorbed activated carbon into an electrolytic cell for electrolysis, and obtains different metals by controlling different electrolysis conditions; CN103342423A discloses a process for recovering rare and precious metals from wastewater and a nano-iron reaction device used therein, wherein the heavy metal wastewater enters a regulating tank and is lifted by a lifting pump into the nano-iron reaction device, and is fully contacted with the nano-iron under stirring, and is oxidized, reduced, adsorbed, and co-precipitated, and then enters a coagulation and sedimentation integrated tank after the reaction, where a coagulant is added for catalytic oxidation coupled flocculation reaction, and precipitated and separated, and the sludge containing rare and precious metals is concentrated, and the sludge is dehydrated by a filter press and then recycled.

[0004] Among the above-mentioned methods of the prior art, although easily separable metal elements can be obtained through electrochemical means and selective separation can be achieved, the energy consumption is high and the processing efficiency is low; although the processing efficiency is relatively higher through the nano-iron reaction, the obtained sludge still contains a large amount of iron powder, flocculants, and complexes formed by metals and flocculants, and the content ratio of metal elements in the sludge is low, which makes subsequent recycling difficult to implement. Summary of the invention

[0005] Based on the above problems, in order to effectively enrich the precious metals in the wastewater and thus increase the proportion of precious metals in the solid matter after treatment, so that recycling can be easily implemented, the present invention proposes a method for recovering metals from wastewater, which is used to recover metals from wastewater containing metals, comprising: step S1, putting zero-valent iron and wastewater containing metal ions to be recovered into a mechanochemical reactor for a mechanochemical reaction to form a solid material enriched with the elemental metal to be recovered; and step S2, using a molten metal centrifugal separation device to separate the elemental metal to be recovered from the solid material.

[0006] The method for recovering metals from wastewater provided by the present invention may also have such technical features, wherein the mechanochemical reactor is a high-speed ball milling device, and the mechanochemical enrichment step includes: step S1-1, adding a predetermined amount of zero-valent iron to the mechanochemical reactor; step S1-2, putting a predetermined amount of grinding balls into the mechanochemical reactor; step S1-3, pumping wastewater into the mechanochemical reactor; step S1-4, starting the mechanochemical reactor, controlling the circulation rate of the wastewater in the mechanochemical reactor, sampling from the mechanochemical reactor at predetermined intervals to detect the metal ion concentration, and stopping the reaction after the metal ion concentration drops to a predetermined concentration or reaches a predetermined reaction time; step S1-5, discharging the post-reaction solid-liquid mixture in the mechanochemical reactor, using a magnet device to perform solid-liquid separation, and further drying the separated solid to obtain a solid material.

[0007] Furthermore, the method for recovering metals from wastewater provided by the present invention may also have such a technical feature, wherein in S1-4, the reaction is stopped after the metal ion concentration drops below 1 mg / L.

[0008] The method for recovering metals from wastewater provided by the present invention may also have such a technical feature, wherein the metal to be recovered is gold or silver, and the reaction time in step S1-4 is greater than or equal to 120 minutes.

[0009] In addition, the method for recovering metals from wastewater provided by the present invention may also have such a technical feature, wherein the metal to be recovered is copper, and the reaction time in step S1-4 is no more than 10 minutes.

[0010] In addition, the method for recovering metals from wastewater provided by the present invention may also have such a technical feature, wherein the metal to be recovered is nickel, and the reaction time in step S1-4 is no more than 60 minutes.

[0011] The method for recovering metals from wastewater provided by the present invention may also have the following technical features: the grinding balls are zirconium oxide grinding balls with a diameter of 0.2 mm to 0.6 mm and an input amount of 0.5 kg / L to 1 kg / L.

[0012] The method for recovering metals from wastewater provided by the present invention may also have the following technical features, wherein the particle size of the zero-valent iron is 3 μm to 8 μm, and the input amount is 0.3 g / L to 2 g / L.

[0013] In addition, the method for recovering metals from wastewater provided by the present invention may also have such a technical feature, wherein the rotation speed of the mechanochemical reactor in step S1-4 is set to 2500-3500 rpm.

[0014] According to the method for recovering metals from wastewater provided by the present invention, since the wastewater containing the metal ions to be recovered is subjected to a mechanochemical reaction with zero-valent iron through a mechanochemical reactor, the metal to be recovered in the wastewater can be formed into a single substance and efficiently enriched, and then the enriched metal can be separated by melting and stratified and graded centrifugation. Therefore, the present invention can efficiently realize the recovery of the metal to be recovered. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the principle of the method for recovering metals from wastewater of the present invention.

[0016] Figure 2 The present invention is a flow chart of the method for recovering metals from wastewater.

[0017] Figure 3 It is a schematic structural diagram of the mechanochemical reactor of the present invention.

[0018] Figure 4 This is a graph showing the detection results of the reaction sampling X-ray diffraction spectrum of Example 1 of the present invention.

[0019] Figure 5 1 is a graph showing the results of solid material content detection in Example 1 of the present invention and Comparative Example 1.

[0020] Figure 6 This is a graph showing the detection results of the reaction sampling X-ray diffraction spectrum of Example 2 of the present invention.

[0021] Figure 7 It is a graph showing the results of solid material content detection in Example 2 of the present invention and Comparative Example 2.

[0022] Figure 8 This is a graph showing the detection results of the reaction sampling X-ray diffraction spectrum of Example 3 of the present invention.

[0023] Fig. 9 3 is a graph showing the results of solid material content detection in Example 3 of the present invention and Comparative Example 3.

[0024] Fig.10 This is a graph showing the detection results of the reaction sampling X-ray diffraction spectrum of Example 4 of the present invention.

[0025] Fig.11 4 is a graph showing the results of solid material content detection in Example 4 of the present invention and Comparative Example 4. DETAILED DESCRIPTION

[0026] Figure 1 This is a schematic diagram of the principle of the method for recovering metals from wastewater of the present invention. Figure 2 The present invention is a flow chart of the method for recovering metals from wastewater.

[0027] like Figure 1, Figure 2 As shown, the method for recovering metals from wastewater of the present invention is implemented by using a mechanochemical reactor, comprising the following steps: Step S1, putting zero-valent iron and wastewater containing metal ions to be recovered into a mechanochemical reactor for mechanochemical reaction to form a solid material enriched with elemental metals to be recovered. Specifically comprising: Step S1-1, adding a predetermined amount of zero-valent iron into a mechanochemical reactor.

[0028] Step S1-2, putting a predetermined amount of grinding balls into the mechanochemical reactor.

[0029] Step S1-3, pumping the wastewater into the mechanochemical reactor.

[0030] Step S1-4, start the mechanochemical reactor to carry out a mechanochemical reaction, control the circulation rate of the wastewater in the mechanochemical reactor, take samples from the mechanochemical reactor at predetermined intervals to detect the metal ion concentration, and stop the reaction when the metal ion concentration drops to a predetermined concentration; specifically, take samples for detection every 10-15 minutes, and considering the maximization of the processing efficiency, the reaction can be stopped when the metal ion concentration of the metal to be recovered is lower than 1 mg / L.

[0031] Step S1-5, discharge the solid-liquid mixture after the reaction in the mechanochemical reactor (the grinding balls are still left in the reactor at this time), use a magnetic device to separate the solid and liquid, that is, the metal mixture containing the remaining iron powder and the metal element generated by the reaction is adsorbed and separated by the magnetic device, and the separated solid is further dried to obtain a solid material.

[0032] Step S2, using molten metal centrifugal separation equipment to separate the elemental metal to be recovered from the solid material. Specifically including: Step S2-1, placing the dried solid material in a high-temperature furnace for melting treatment, so that the metal and impurities are completely melted to form a liquid mixture; then the molten metal mixture is transferred to a high-temperature centrifugal separation device, and the centrifugal force generated by high-speed rotation is used to achieve stratified separation of metals of different densities. In this process, the metal with high density is thrown to the periphery of the equipment, while the lighter metal is concentrated in the center, thereby achieving effective separation of the metals.

[0033] Step S2-2, cooling and solidifying the layered metal obtained by centrifugal separation, and collecting metal materials of different layers respectively; further refining the collected metal materials to obtain metal materials with higher purity.

[0034] Step S3, a post-processing step, specifically includes the following operations: Step S3-1, cleaning up the residues in the mechanochemical reactor from which the wastewater after the reaction has been discharged and the materials have been transferred out; Step S3-2, check the wear of the grinding balls in the reactor, and calculate the consumption of zero-valent iron. According to the current wear and consumption, replenish or replace the grinding balls and zero-valent iron, and then proceed to process the next batch of wastewater according to the operation of step S1-1.

[0035] The mechanochemical reactors used in the above method of the present invention are all high-speed ball milling equipment.

[0036] Figure 3 It is a schematic structural diagram of the mechanochemical reactor of the present invention.

[0037] like Figure 3 As shown, the mechanochemical reactor includes a reactor shell 11, a rotor 12 disposed in the reactor shell 11, and a driving mechanism 13 for driving the rotor 12 to rotate. The reactor shell 11 is generally cylindrical, and a cavity as a reaction chamber 11A is formed inside. The reactor shell 11 is also provided with a feed port 11B and a discharge port 11C connected to the reaction chamber, which are used to allow the slurry to enter and flow out of the reaction chamber, respectively.

[0038] The zero-valent iron and grinding balls introduced in step S1-1 and step S1-2 can be directly introduced through the feed port 11B, or an additional feed hopper can be provided to introduce the wastewater through the feed hopper; the wastewater is stored in a liquid storage tank, and a connecting pipeline is provided between the liquid storage tank and the feed port 11B, and a pump is also provided on the pipeline, and the liquid in the liquid storage tank can be pumped into the reaction chamber by the pump. When the reaction of step S1-4 starts, the discharge port 11C is also connected to the liquid storage tank through a pipeline, so that the slurry formed by the mixture of wastewater, zero-valent iron, grinding balls, etc. can circulate between the liquid storage tank and the reaction chamber. In addition, the reactor shell 11 also has an interlayer 11D for circulating cooling water. By passing circulating water of a specific temperature into the interlayer 11D, the reaction chamber can be maintained at a predetermined temperature.

[0039] The present application has found that the metal to be recovered in the wastewater can be enriched by step S1 in the above method, and the enriched metal can be separated by step S2. Moreover, by adjusting the reaction conditions in step S1, metal enrichment can be selectively performed, thereby realizing the recovery of metals with certain specific requirements.

[0040] The following is a detailed description with reference to the embodiments.

[0041] Example 1 This example is the selective recovery of gold.

[0042] The wastewater treated in this embodiment is Au(III)-containing wastewater, in which the gold ion concentration is 3000 mg / L, and there are no other metal ions.

[0043] The zero-valent iron used in step S1-1 has a particle size of about 5 μm, a purity greater than 98.5%, and an input amount of 1 g / L (based on the total volume of wastewater, the same below); the grinding ball is a zirconia ball with a diameter of 0.4 mm and a density of 5.89 g / cm 3 The input amount is 0.75 kg / L. The reaction temperature in step S1-4 is controlled to 22°C (i.e., the temperature of the cooling water is controlled to be around 22°C), the rotation speed is set to 3000 rpm, and at the same time, by controlling the speed of the pump, the reaction mixture circulates between the liquid storage tank and the reaction chamber about 15 times per minute.

[0044] In this embodiment, after the reaction of step S1-4 was carried out for about 120 min, the gold ion concentration was measured to drop to 1 mg / L, and the reaction was terminated immediately.

[0045] During the reaction process of step S1-4, samples were taken for X-ray diffraction detection when the reaction time reached 1 min, 10 min, 60 min and 120 min, respectively, to determine the generation of gold during the reaction process.

[0046] Figure 4 This is a graph showing the detection results of the reaction sampling X-ray diffraction spectrum of Example 1 of the present invention.

[0047] like Figure 4 As shown, within 1 minute after the reaction started, Au 0 The diffraction peaks of Au 0 The relative intensity of the gold ions continued to increase, indicating that the reduction and enrichment of gold was very rapid.

[0048] Fe 0 The diffraction peak exists stably, indicating that iron basically maintains its zero-valent state during the entire reaction process.

[0049] from Figure 4 It can also be seen that during the entire reaction, gold appeared in the form of gold alone, indicating that gold alone was always formed, or gold and iron formed an alloy. In addition, the iron / gold molar ratio was the lowest at 120 min.

[0050] Comparative Example 1 This comparative example is a comparative example of Example 1, and the reaction is carried out by a conventional agitator; the wastewater, zero-valent iron, and the input ratio of the two used in this comparative example are exactly the same as those in Example 1. The difference is that in this comparative example, zero-valent iron is directly added to the liquid storage tank where the wastewater is located, and then a paddle-type agitator is placed in the liquid storage tank for stirring, and the stirring speed is 200 rpm.

[0051] In this comparative example, samples were taken from the liquid storage tank every 10-15 minutes for detection. After stirring for about 120 minutes, the gold ion concentration was measured to drop to 1 mg / L, and the reaction was terminated. Then, solid-liquid separation and drying were performed, and XRD detection was performed on the dried solid obtained, and it was known that gold was also formed in the solid.

[0052] The liquid after 120 minutes of reaction in comparative example 1 was sampled, and the liquid after 120 minutes of mechanochemical reaction in step S1-4 of embodiment 1 was sampled at the same time, and the concentrations of gold ions and iron ions in the solutions of the two samples were tested respectively by ICP-OES or ICP-MS, so as to calculate the content of elemental gold and iron in the solid.

[0053] Figure 5 1 is a graph showing the results of solid material content detection in Example 1 of the present invention and Comparative Example 1.

[0054] like Figure 5 As shown, by treating with the conventional method of Example 1, although the gold ion concentration in the wastewater has dropped to a suitable low concentration, the molar ratio of gold to iron in the obtained solid is only about 0.3, and gold accounts for 17.6% of the total amount of the metal mixture, indicating that the enrichment of gold is relatively low under this condition, and at this ratio, it is almost impossible to separate by melting and centrifugation. In contrast, the molar ratio of gold to iron in Example 1 is significantly increased to nearly 2.0, and its enrichment is increased by 6-7 times; and after the mechanochemical treatment process of Example 1, the molar ratio of gold in the metal mixture reaches 68.6% of the total amount, indicating that its enrichment is extremely high and easy to separate by melting centrifugation.

[0055] For gold, since the gold formed by the reaction exists in the form of a single substance during the entire mechanochemical reaction, the time point at which the reaction ends can be selected as the time point when the gold ion content in the wastewater drops to a lower value, such as 120 minutes when it drops to 1 mg / L. In addition, the iron / gold molar ratio is the lowest at 120 minutes, and it can be considered that this time point itself is also the most suitable time point for efficient gold recovery.

[0056] Example 2 This embodiment is the selective recovery of silver.

[0057] The wastewater treated in this embodiment is Ag(I)-containing wastewater, in which the silver ion concentration is 3000 mg / L, and there are no other metal ions.

[0058] The zero-valent iron used in step S1-1 has a particle size of about 5 μm, a purity greater than 98.5%, and an input amount of 1 g / L; the grinding balls are zirconium oxide balls with a diameter of 0.4 mm and a density of 5.89 g / cm 3 , the input amount is 0.75 kg / L. In step S1-4, the reaction temperature is controlled to 22°C (i.e., the temperature of the cooling water is controlled to be around 22°C), the rotation speed is set to 3000 rpm, and at the same time, by controlling the speed of the pump, the reaction mixture circulates between the liquid storage tank and the reaction chamber about 15 times per minute.

[0059] In this embodiment, after the reaction of step S1-4 was carried out for about 120 minutes, the silver ion concentration was measured to drop to 1 mg / L, and the reaction was terminated immediately.

[0060] During the reaction process of step S1-4, samples were taken for X-ray diffraction detection when the reaction time reached 1 min, 10 min, 60 min and 120 min, respectively, to determine the generation of silver during the reaction process.

[0061] Figure 6 This is a graph showing the detection results of the reaction sampling X-ray diffraction spectrum of Example 2 of the present invention.

[0062] like Figure 6 As shown, similar to the gold in Example 1, within 1 minute after the reaction started, the Ag in this example 0 The diffraction peak of Fe 0 The diffraction peak exists stably.

[0063] from Figure 6 It can also be seen that during the entire reaction, silver appears in the form of a single substance, indicating that the substance formed is always a single substance of silver, or an alloy of silver and iron. In addition, the iron / silver molar ratio is the lowest at 120 min.

[0064] Comparative Example 2 This comparative example is a comparative example of Example 2, and the reaction is carried out by a conventional agitator; the wastewater, zero-valent iron, and the input ratio of the two used in this comparative example are exactly the same as those in Example 1. The difference is that in this comparative example, zero-valent iron is directly added to the liquid storage tank where the wastewater is located, and then a paddle-type agitator is placed in the liquid storage tank for stirring, and the stirring speed is 200 rpm.

[0065] In this comparative example, samples were taken from the liquid storage tank every 10-15 minutes for detection. After stirring for about 120 minutes, the silver ion concentration was measured to drop to 1 mg / L, and the reaction was terminated immediately. Then, solid-liquid separation and drying were performed, and XRD detection was performed on the dried solid obtained, and it was known that silver elemental substance was also formed in the solid.

[0066] The liquid after 120 minutes of reaction in Comparative Example 2 was sampled, and the liquid after 120 minutes of mechanochemical reaction in step S1-4 of Example 2 was sampled. The concentrations of silver ions and iron ions in the solutions of the two samples were tested by ICP-OES or ICP-MS, respectively, to calculate the content of elemental silver and iron in the solid.

[0067] Figure 7 It is a graph showing the results of solid material content detection in Example 2 of the present invention and Comparative Example 2.

[0068] like Figure 7 As shown, by the conventional method of comparative example 2, although the silver ion concentration in the wastewater has dropped to a suitable low concentration, the molar ratio of silver to iron in the obtained solid is only about 0.15, and silver accounts for 13.5% of the total amount of the metal mixture, indicating that the enrichment degree of silver is relatively low under this condition. In contrast, the molar ratio of silver to iron in Example 2 is significantly increased to nearly 4.0, and its enrichment amount is increased by about 26 times. Moreover, after the mechanochemical treatment of Example 2, silver accounts for 78.9% of the total amount of the metal mixture, which is easy to separate by melt centrifugation.

[0069] For silver, since the silver formed in the entire mechanochemical reaction process exists in a single substance, the time point for the end of the reaction can be selected as the time point when the silver ion content in the wastewater drops to a lower value, such as the time point when it drops to 1 mg / L (i.e. 120 min); in addition, the iron / silver molar ratio is lowest at 120 min, and it can be considered that this time point itself is also the most suitable time point for efficient recovery of silver.

[0070] Example 3 This embodiment is the selective recovery of copper.

[0071] The wastewater treated in this embodiment is copper-containing wastewater, in which the copper ion concentration is 1000 mg / L, and there are no other metal ions.

[0072] The zero-valent iron used in step S1-1 has a particle size of about 5 μm, a purity greater than 98.5%, and an input amount of 1 g / L; the grinding balls are zirconium oxide balls with a diameter of 0.4 mm and a density of 5.89 g / cm 3 , the input amount is 0.75 kg / L. In step S1-4, the reaction temperature is controlled to 22°C (i.e., the temperature of the cooling water is controlled to be around 22°C), the rotation speed is set to 3000 rpm, and at the same time, by controlling the speed of the pump, the reaction mixture circulates between the liquid storage tank and the reaction chamber about 15 times per minute.

[0073] In this embodiment, after the reaction of step S1-4 was carried out for about 120 minutes, the copper ion concentration was measured to drop to 1 mg / L, and the reaction was terminated immediately.

[0074] During the reaction process of step S1-4, samples were taken for X-ray diffraction detection when the reaction time reached 1 min, 10 min, 60 min and 120 min, respectively, to determine the generation of copper during the reaction process.

[0075] Figure 8 This is a graph showing the detection results of the reaction sampling X-ray diffraction spectrum of Example 3 of the present invention.

[0076] like Figure 8 As shown, within the first minute after the reaction started, Cu 0 The diffraction peaks of Cu2O and CuFeO gradually appeared and significantly enhanced after 60 minutes, and the characteristic peaks of CuFeO2 and Fe4Cu3 appeared at the same time.

[0077] When the reaction was continued for 120 minutes, Cu 0 The diffraction peaks of Cu2O, CuFeO2, and Fe4Cu3 are all enhanced, indicating that copper gradually forms more complex intermetallic compounds and oxides over time.

[0078] That is to say, the reduction and enrichment process of copper is more complicated than that of gold and silver. 0 The formation of Cu2O begins at an early stage, and during the mechanochemical reaction, part of Cu 0 Further alloys (Fe4Cu3) and oxides (CuFeO2) are formed with iron. This reaction process shows that the mechanochemical treatment not only promotes the reduction of copper, but also leads to the formation of new compounds.

[0079] In this embodiment, as the reaction time increases, although a lower molar ratio of iron / copper is formed, indicating that the ratio of the metal copper to be recovered in the solid product is higher, since copper no longer exists as a single substance, it is not conducive to the melting separation in step S2. Therefore, when the metal to be recovered is copper, the mechanochemical reaction time should be controlled within 10 minutes as much as possible.

[0080] Comparative Example 3 This comparative example is a comparative example of Example 3, and the reaction is carried out by a conventional agitator; the wastewater, zero-valent iron, and the input ratio of the two used in this comparative example are exactly the same as those in Example 1. The difference is that in this comparative example, zero-valent iron is directly added to the liquid storage tank where the wastewater is located, and then a paddle-type agitator is placed in the liquid storage tank for stirring, and the stirring speed is 200 rpm.

[0081] In this comparative example, samples were taken from the liquid storage tank every 10-15 minutes for testing. After stirring for about 120 minutes, the copper ion concentration was measured to drop to 1 mg / L, and the reaction was terminated. Then, solid-liquid separation and drying were performed, and the obtained dried solid was subjected to XRD testing. From the results, it can be seen that copper element, alloy (Fe4Cu3) and oxide (CuFeO2) were also formed in the solid, which is similar to Example 3.

[0082] The liquid after 120 minutes of reaction in comparative example 3 was sampled, and the liquid after 120 minutes of mechanochemical reaction in step S1-4 of example 3 was sampled at the same time. The concentrations of copper ions and iron ions in the solutions of the two samples were tested respectively by ICP-OES or ICP-MS, so as to calculate the contents of copper and iron in the solid.

[0083] Fig. 9 3 is a graph showing the results of solid material content detection in Example 3 of the present invention and Comparative Example 3.

[0084] like Fig. 9 As shown, by treating with the conventional method of comparative example 3, although the copper ion concentration in the wastewater has dropped to a suitable low concentration, the molar ratio of copper to iron in the obtained solid is only about 0.3, and copper accounts for 17.9% of the total amount of the metal mixture, indicating that the enrichment of copper is relatively low under this condition. In contrast, the molar ratio of copper to iron in Example 3 is significantly increased to about 3.0, and its enrichment is increased by about 10 times. Moreover, after the mechanochemical treatment of Example 3, copper accounts for 73.5% of the total amount of the metal mixture, and its enrichment is greatly improved.

[0085] In addition, although a long mechanochemical reaction will cause copper to form oxides, as long as the reaction time is controlled within 10 minutes, copper can be allowed to exist in the form of a single substance or an alloy as much as possible. Therefore, when the reaction time of step S1-4 is within 10 minutes, the solid material obtained in step S1-5 can still be separated by melt centrifugation to obtain the copper to be recovered.

[0086] Example 4 This embodiment is the selective recovery of nickel.

[0087] The wastewater treated in this embodiment is nickel-containing wastewater, in which the nickel ion concentration is 500 mg / L, and there are no other metal ions.

[0088] The zero-valent iron used in step S1-1 has a particle size of about 5 μm, a purity greater than 98.5%, and an input amount of 1 g / L; the grinding balls are zirconium oxide balls with a diameter of 0.4 mm and a density of 5.89 g / cm 3, the input amount is 0.75 kg / L. In step S1-4, the reaction temperature is controlled to 22°C (i.e., the temperature of the cooling water is controlled to be around 22°C), the rotation speed is set to 3000 rpm, and at the same time, by controlling the speed of the pump, the reaction mixture circulates between the liquid storage tank and the reaction chamber about 15 times per minute.

[0089] In this embodiment, after the reaction of step S1-4 was carried out for about 120 min, the nickel ion concentration was measured to drop to 1 mg / L, and the reaction was terminated immediately.

[0090] During the reaction of step S1-4, samples were taken for X-ray diffraction detection when the reaction time reached 1 min, 10 min, 60 min and 120 min, respectively, to determine the generation of nickel during the reaction.

[0091] Fig.10 This is a graph showing the detection results of the reaction sampling X-ray diffraction spectrum of Example 4 of the present invention.

[0092] like Fig.10 As shown in the figure, the characteristic peak of Ni is not obvious at the 1st and 10th minutes after the reaction starts; but after 60 and 120 minutes, the peak of NiFe2O4 gradually appears and increases in intensity with time. 0 The diffraction peaks are relatively stable.

[0093] It can be seen that the reduction rate of nickel is slow, and no significant metallic nickel (Ni 0 ) or its compound. However, as the reaction time increases, Ni and Fe 0 Reactions occur between the two metals to form NiFe2O4. This phenomenon indicates that mechanochemical reactions promote the gradual enrichment and fixation of nickel. However, as the reaction time increases, although the molar ratio of iron to nickel becomes lower (indicating that the ratio of metallic nickel to be recovered in the solid is higher), the existence form of nickel will gradually change to mainly oxides (since the initial enrichment of nickel is not as high as that of the previous metals, no peak of elemental nickel is detected, but nickel mainly exists in elemental form at the beginning of the reaction), and oxides are not conducive to melting separation. Therefore, the reaction time should be controlled within 60 minutes as much as possible.

[0094] Comparative Example 4 This comparative example is a comparative example of Example 4, and the reaction is carried out by a conventional agitator; the wastewater, zero-valent iron, and the input ratio of the two used in this comparative example are exactly the same as those in Example 1. The difference is that in this comparative example, zero-valent iron is directly added to the liquid storage tank where the wastewater is located, and then a paddle-type agitator is placed in the liquid storage tank for stirring, and the stirring speed is 200 rpm.

[0095] In this comparative example, samples were taken from the liquid storage tank every 10-15 minutes for testing. After stirring for about 120 minutes, the nickel ion concentration was measured to drop to 1 mg / L, and the reaction was terminated. Then, solid-liquid separation and drying were performed, and XRD detection was performed on the dried solid, which showed that a large amount of oxide NiFe2O4 was also present in the solid.

[0096] The liquid after 120 minutes of reaction in comparative example 4 was sampled, and the liquid after 120 minutes of mechanochemical reaction in step S1-4 of example 4 was sampled at the same time. The concentrations of nickel ions and iron ions in the solutions of the two samples were tested respectively by ICP-OES or ICP-MS, so as to calculate the nickel and iron contents in the solid.

[0097] Fig.11 4 is a graph showing the results of solid material content detection in Example 4 of the present invention and Comparative Example 4.

[0098] like Fig.11 As shown, by the conventional method of comparative example 4, although the nickel ion concentration in the wastewater has dropped to a suitable low concentration, the molar ratio of nickel to iron in the obtained solid is only about 0.02, and nickel accounts for 4.7% of the total amount of the metal mixture, indicating that the enrichment of nickel is relatively low under this condition. In contrast, the molar ratio of nickel to iron in Example 4 is significantly increased to about 0.35, and its enrichment is increased by about 18 times. Moreover, after the mechanochemical treatment of Example 4, nickel accounts for 27.5% of the total amount of the metal mixture.

[0099] In addition, although a long period of mechanochemical reaction may cause nickel to form oxides, as long as the reaction time is controlled within 60 minutes, nickel can be kept in a single substance as much as possible. Therefore, when the reaction time of step S1-4 is within 60 minutes, the solid material obtained in step S1-5 can still be separated by melt centrifugation to obtain the nickel to be recovered.

Claims

1. A method for recovering metals from wastewater, for recovering the metals from wastewater containing metals, characterized in that: include: Step S1, putting the zero-valent iron and the wastewater containing the metal ions to be recovered into a mechanochemical reactor for a mechanochemical reaction to form a solid material enriched with the metal ions to be recovered; as well as Step S2, using molten metal centrifugal separation equipment to separate the elemental metal to be recovered from the solid material.

2. The method for recovering metals from waste water according to claim 1, Features: Wherein, the mechanochemical reactor is a high-speed ball milling device, The step S1 comprises: Step S1-1, adding a predetermined amount of zero-valent iron into the mechanochemical reactor; Step S1-2, putting a predetermined amount of grinding balls into the mechanochemical reactor; Step S1-3, pumping the wastewater into the mechanochemical reactor; Step S1-4, starting the mechanochemical reactor, controlling the circulation rate of the wastewater in the mechanochemical reactor, sampling from the mechanochemical reactor at predetermined intervals to detect the metal ion concentration, and stopping the reaction when the metal ion concentration drops to a predetermined concentration or reaches a predetermined reaction time; and Step S1-5, discharging the solid-liquid mixture after the reaction in the mechanochemical reactor, and using a magnetic device to perform solid-liquid separation and solid drying to obtain the solid material.

3. The method for recovering metals from wastewater according to claim 2, characterized in that: in, In S1-4, the reaction is stopped after the metal ion concentration drops below 1 mg / L.

4. The method for recovering metals from wastewater according to claim 2, characterized in that: in, The grinding balls are zirconium oxide grinding balls with a diameter of 0.2 mm to 0.6 mm and an input amount of 0.5 kg / L to 1 kg / L.

5. The method for recovering metals from wastewater according to claim 2, characterized in that: in, The zero-valent iron particle size is 3 μm to 8 μm, and the input amount is 0.3 g / L to 2 g / L.

6. The method for recovering metals from wastewater according to claim 2, characterized in that: in, The rotation speed of the mechanochemical reactor in step S1-4 is set to 2500-3500 rpm.

7. The method for recovering metals from wastewater according to claim 1, characterized in that: in, The metal to be recovered is gold or silver, The reaction time in step S1-4 is greater than or equal to 120 min.

8. The method for recovering metals from wastewater according to claim 1, characterized in that: in, The metal to be recovered is copper, The reaction time in step S1-4 is no more than 10 min.

9. The method for recovering metals from wastewater according to claim 1, characterized in that: in, The metal to be recovered is nickel, The reaction time in step S1-4 is no more than 60 min.

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