Method and system for extracting and recovering heavy metals from sludge

Abstract

The present invention discloses a method and system for extracting and recovering heavy metals in sludge, and belongs to the technical field of electroplating sludge treatment. The present invention utilizes biological leaching to dissolve a variety of heavy metals into the leaching solution, first recovers iron by precipitation, and then recovers copper, zinc, lead, and cadmium by combining porous zeolite and multi-stage stripping, which can greatly reduce the influence of various impurities in the leaching solution. Specifically, firstly, copper, zinc, lead, and cadmium are adsorbed by porous zeolite, and then copper, zinc, and cadmium are dissolved from the porous zeolite into the organic phase. At this time, the organic phase is rich in copper, zinc, and cadmium, and the porous zeolite is rich in lead. Then, the cadmium, zinc, and copper in the organic phase are recovered separately by multi-stage stripping, and the porous zeolite is washed with ammonium acetate, and further solid-liquid separation is performed to obtain a lead acetate solution, thereby completing the separation and recovery of iron, copper, zinc, lead, and cadmium heavy metal elements in heavy metal sludge.

Description

Technical Field

[0001] The invention relates to the technical field of electroplating sludge treatment, and in particular to a method and system for extracting and recovering heavy metals in sludge. Background Art

[0002] Electroplating sludge usually contains a wide variety of heavy metal elements, such as iron, copper, zinc, lead, cadmium, etc., which are easy to cause harm to the environment and organisms. It cannot be directly discharged into the environment, and it is also easy to cause waste of resources. Therefore, it is necessary to remove or recover the heavy metal elements in electroplating sludge. In the related field, most heavy metals can be dissolved into the leaching liquid by biological leaching. However, the leaching liquid is not only rich in various heavy metals, but also contains various impurities. How to separate and recover various heavy metals in the biological leaching liquid and improve the recovery purity of heavy metals is a difficult problem. Summary of the invention

[0003] The main purpose of the present invention is to provide a method and system for extracting and recovering heavy metals in sludge, so as to solve the technical problem that it is difficult to separate and recover various types of heavy metals from heavy metal sludge.

[0004] To achieve the above object, the present invention provides a method for extracting and recovering heavy metals in sludge, comprising the following steps:

[0005] S10: leaching the heavy metal sludge by biological leaching to obtain a filter residue and a leaching liquid A, wherein the leaching liquid A is rich in the following heavy metal elements: iron, copper, zinc, lead, and cadmium;

[0006] S20: adding an oxidant to the leaching solution A, adjusting the pH value of the solution to 1.0-1.5, then heating and adding sodium sulfate to obtain a precipitate of sodium ferrocyanide and a leaching solution B, extracting iron from the sodium ferrocyanide, and the leaching solution B is rich in the following heavy metal elements: copper, zinc, lead, and cadmium;

[0007] S30: adding a porous zeolite to the leaching solution B, the porous zeolite adsorbing copper, zinc, lead and cadmium, and then filtering to obtain a leaching solution C and a porous zeolite rich in heavy metal elements copper, zinc, lead and cadmium;

[0008] S40: soaking the porous zeolite rich in heavy metal elements copper, zinc, lead and cadmium in S30 in a mixed solution of 1-(2-hydroxy-5-nonylphenyl) acetone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid to obtain an organic phase rich in heavy metal elements copper, zinc and cadmium, and separating the organic phase rich in heavy metal elements copper, zinc and cadmium and the porous zeolite, wherein the porous zeolite obtained by separation is rich in heavy metal element lead;

[0009] S50: The organic phase of S50 is selectively stripped in multiple stages using sulfuric acid stripping agents of different concentrations in the order of cadmium, zinc, and copper to obtain stripping solutions rich in heavy metal elements cadmium, zinc, and copper, respectively;

[0010] S60: using ammonium acetate to elute the lead in the porous zeolite rich in heavy metal element lead obtained in S40, to obtain a lead acetate washing liquid, and recovering lead from the lead acetate washing liquid.

[0011] In some embodiments of the present invention, the particle size of the porous zeolite ranges from 1.5 mm to 2 mm.

[0012] In some embodiments of the present invention, the pore size of the porous zeolite is 0.5 nm to 1 nm.

[0013] In some embodiments of the present invention, the porosity of the porous zeolite is 70% to 80%.

[0014] In some embodiments of the present invention, in step S20, the oxidant includes at least one of oxygen and hydrogen peroxide.

[0015] In some embodiments of the present invention, in step S20, the reaction temperature is 85°C to 95°C.

[0016] In some embodiments of the present invention, in step S50, the molar ratio of 1-(2-hydroxy-5-nonylphenyl)ethanone oxime to bis(2,4,4-trimethylpentyl)phosphonic acid is 2:1 to 4:1.

[0017] In some embodiments of the present invention, in step S50, the stripping level of copper is 2 to 10; and / or the stripping level of zinc is 4 to 10; and / or the stripping level of cadmium is 4 to 10.

[0018] In some embodiments of the present invention, in step S50, the stripping temperature is 25° C. to 35° C.;

[0019] And / or, in step S60, the mass concentration of the ammonium acetate is 15% to 20%.

[0020] The present invention also provides a heavy metal extraction and recovery system in sludge, which comprises a biological leaching tank, an iron recovery tank, an adsorption tank, a leaching tank, a lead recovery tank, a multi-stage stripping tank, a copper recovery tank, a zinc recovery tank, and a cadmium recovery tank.

[0021] Beneficial effects achieved by the present invention

[0022] The present invention utilizes biological leaching to dissolve a variety of heavy metal elements into the leaching solution, first recovers iron by precipitation, and then combines porous zeolite with multi-stage stripping to recover copper, zinc, lead, and cadmium, which can greatly reduce the impact of various impurities in the leaching solution. Specifically, firstly, copper, zinc, lead, and cadmium are adsorbed by porous zeolite, and then 1-(2-hydroxy-5-nonylphenyl) acetone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid are used to dissolve copper, zinc, and cadmium from porous zeolite into the organic phase, at this time, the organic phase is rich in copper, zinc, and cadmium, and the porous zeolite is rich in lead, and then the cadmium, zinc, and copper in the organic phase are recovered by multi-stage stripping, and the porous zeolite is washed with ammonium acetate, and further solid-liquid separation is performed to obtain a lead-containing washing solution, i.e., a lead acetate solution, and lead is recovered from the lead acetate solution, thereby completing the separation and recovery of iron, copper, zinc, lead, and cadmium in heavy metal sludge.

[0023] The method for extracting and recovering heavy metals in sludge can reduce the influence of various impurities in the leaching liquid on the recovery, and is beneficial to improving the recovery purity and recovery rate of various heavy metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0025] Figure 1 The figure is a schematic diagram of a system for extracting and recovering heavy metals from sludge according to an embodiment of the present invention.

[0026] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0027] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0028] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] In the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0030] The present invention provides a method for extracting and recovering heavy metals in sludge, comprising the following steps:

[0031] S10: leaching the heavy metal sludge by biological leaching to obtain a filter residue and a leaching liquid A, wherein the leaching liquid A is rich in the following heavy metal elements: iron, copper, zinc, lead, and cadmium;

[0032] S20: adding an oxidant to the leaching solution A, adjusting the pH value of the solution to 1.0-1.5, then heating and adding sodium sulfate to obtain a precipitate of sodium ferrocyanide and a leaching solution B, extracting iron from the sodium ferrocyanide, and the leaching solution B is rich in the following heavy metal elements: copper, zinc, lead, and cadmium;

[0033] S30: adding a porous zeolite to the leaching solution B, the porous zeolite adsorbing copper, zinc, lead and cadmium, and then filtering to obtain a leaching solution C and a porous zeolite rich in heavy metal elements copper, zinc, lead and cadmium;

[0034] S40: soaking the porous zeolite rich in heavy metal elements copper, zinc, lead and cadmium in S30 in a mixed solution of 1-(2-hydroxy-5-nonylphenyl) acetone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid to obtain an organic phase rich in heavy metal elements copper, zinc and cadmium, and separating the organic phase rich in heavy metal elements copper, zinc and cadmium and the porous zeolite, wherein the porous zeolite obtained by separation is rich in heavy metal element lead;

[0035] S50: The organic phase of S50 is selectively stripped in multiple stages using sulfuric acid stripping agents of different concentrations in the order of cadmium, zinc, and copper to obtain stripping solutions rich in heavy metal elements cadmium, zinc, and copper, respectively;

[0036] S60: using ammonium acetate to elute the lead in the porous zeolite rich in heavy metal element lead obtained in S40, to obtain a lead acetate washing liquid, and recovering lead from the lead acetate washing liquid.

[0037] The present invention utilizes biological leaching to dissolve most of the various heavy metal elements into the leaching solution A, and then separates the iron by precipitation to obtain a leaching solution B rich in copper, zinc, lead, and cadmium. However, in addition to the above target heavy metals copper, zinc, lead, and cadmium, the leaching solution B is also rich in other impurities. Therefore, the present application uses a porous zeolite that has an adsorption effect on heavy metals to adsorb the filtrate B, and then leaches the heavy metals in the porous zeolite to complete the separation of various heavy metals. Specifically, the porous zeolite has a silicon-oxygen lattice, and many channels with uniform pore sizes and large cavities on the inner surface are formed inside, which has a strong adsorption capacity for copper, zinc, lead, and cadmium, thereby separating the above heavy metals from other impurities in the leaching solution. Next, a mixed solution of 1-(2-hydroxy-5-nonylphenyl) acetone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid is used to soak the porous zeolite, and copper, zinc and cadmium in the porous zeolite are dissolved into the organic phase. The copper, zinc and cadmium dissolved into the organic phase are separated in sequence by means of a graded stripping method. The porous zeolite soaked with 1-(2-hydroxy-5-nonylphenyl) acetone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid is also rich in lead. At this time, the lead-rich porous zeolite can be filtered out, and then the lead element in the porous zeolite is eluted with ammonium acetate, and reacted to generate soluble lead acetate. Thus, the separation and recovery of multiple heavy metal elements copper, zinc, lead, cadmium and iron in heavy metal sludge are completed, and the recovery purity and recovery rate of the above heavy metal elements can be greatly improved.

[0038] In step S10, the heavy metal sludge is leached by biological leaching to obtain filter residue and filtrate, and the biological leaching includes the following steps: placing the heavy metal sludge, surfactant and leaching agent in a biological leaching tank for leaching reaction until the pH drops below 2.5, and dissolving the heavy metal into the water phase; the leaching agent includes acidophilic thiobacillus and a substrate, and the substrate includes elemental sulfur powder and ferrous sulfate.

[0039] In the present invention, Acidithiobacillus directly adsorbs on the surface of heavy metal sulfides in sludge through the extracellular polymers (EPS) secreted by it, directly oxidizes the metal sulfides through the unique oxidase system in the cell to generate soluble sulfates, dissolves the heavy metals into the water phase, and then treats the heavy metal elements in the water phase, thereby completing the harmless treatment of heavy metal sludge.

[0040] Electroplating sludge is usually colloidal, which is not conducive to the dispersion of acidophilic thiobacillus, substrate elemental sulfur powder and ferrous sulfate, which will affect the leaching effect, resulting in a low dissolution rate of heavy metals, or causing the leaching time to be too long. In the present embodiment, heavy metal sludge, surfactant and leaching agent are mixed and then leached, which can weaken the colloidal properties of heavy metal sludge, facilitate the dispersion of acidophilic thiobacillus and substrate, increase the suspension and dispersibility of acidophilic thiobacillus and substrate in heavy metal sludge, alleviate elemental sulfur powder and ferrous sulfate as substrates added to heavy metal sludge, prone to sedimentation and agglomeration, not easy to acidophilic thiobacillus oxidation and utilization of sulfur element, improve acidophilic thiobacillus oxidation and utilization of sulfur element, improve the oxidation utilization rate of substrate, strengthen the dissolution of various heavy metal elements in heavy metal sludge.

[0041] In some embodiments, the surfactant includes Tween 80, and the surfactant is used to improve the colloidal properties of heavy metal sludge, enhance the dispersion effect of the leaching agent in the heavy metal sludge, and also enhance the dispersibility of the substrate, increase the suspension and dispersibility of the substrate in the heavy metal sludge, improve the oxidation utilization rate of the substrate by Acidithiobacillus, and promote the dissolution of heavy metals in the sludge.

[0042] In some embodiments, based on the volume of heavy metal sludge, the amount of surfactant added is 5 g / L to 15 g / L.

[0043] In some embodiments, the acidithiobacillus comprises at least one of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans can directly oxidize metal sulfides into soluble sulfates in acidic conditions and filter out heavy metals.

[0044] In the present invention, the substrate is a mixture of elemental sulfur powder and ferrous sulfate, which can increase the acidification rate of heavy metal sludge and accelerate the dissolution of heavy metal elements such as iron, copper, zinc, lead, and cadmium.

[0045] In some embodiments, the added amount of the elemental sulfur powder is (5g-10g) / L.

[0046] In some embodiments, the added amount of ferrous sulfate is (30 g to 50 g) / L.

[0047] In some embodiments, the leaching agent also contains phosphoric acid and hydrogen peroxide. In this embodiment, by adding phosphoric acid and hydrogen peroxide to the leaching agent, the redox potential of the heavy metal sludge can be increased. When the redox potential of the heavy metal sludge increases, it is beneficial to oxidize the metal sulfide into sulfate and dissolve it, further improving the leaching effect and efficiency of the heavy metal, and shortening the leaching reaction time. In addition, phosphoric acid and hydrogen peroxide can also be used to destroy extracellular polymers and microbial cells in the heavy metal sludge, thereby accelerating the dissolution of organically bound heavy metals in the heavy metal sludge.

[0048] In some embodiments, the amount of phosphoric acid added is (5 g to 8 g) / L; and / or the amount of hydrogen peroxide added is (8 ml to 15 ml) / L.

[0049] In some embodiments, Acidophilic Thiobacillus is obtained by culturing the following method: using the heavy metal sludge with a solid content of less than 6% as a material, adding the substrate, and performing an enrichment culture until the substrate is completely consumed to obtain Acidophilic Thiobacillus, adding the Acidophilic Thiobacillus as a strain to another heavy metal sludge with a solid content of less than 6%, and adding the substrate for a second enrichment culture; the enrichment culture is performed at least three times to obtain a high concentration of Acidophilic Thiobacillus with a pH below 2.5. The method of the present invention obtains a bioleaching culture by culturing and domesticating indigenous heavy metal sludge, without the need to add pure sulfur bacteria or perform complex indigenous sulfur bacteria screening and pure culture, which greatly reduces the processing cost and the difficulty of operation. Moreover, culturing indigenous sulfur bacteria with heavy metal sludge with a solid content of less than 6% is conducive to the dispersion of the substrate and the rapid cultivation of high concentrations of Acidophilic Thiobacillus.

[0050] In some embodiments, the leaching reaction temperature is 25° C. to 35° C. The above leaching reaction temperature conditions are conducive to the dissolution of various heavy metal elements.

[0051] In some embodiments, the leaching reaction time is 1 day to 5 days, which can be 1 day, 2 days, 3 days, 4 days, or 5 days, which is beneficial for dissolving most of the heavy metal elements into the water phase and improving the dissolution rate of heavy metals.

[0052] In the present invention, after the heavy metals are dissolved in the water phase, the water phase can be treated to collect the heavy metals in the water phase.

[0053] In some embodiments, a metal salt coagulant may be added to the aqueous phase to obtain floccules, wherein the metal salt coagulant includes an inorganic polymer coagulant, and the inorganic polymer coagulant includes polyferric sulfate.

[0054] Polyferric sulfate is an inorganic polymer coagulant with superior performance. It is widely used in the purification of drinking water, industrial water, various industrial wastewater, urban sewage, sludge dewatering, etc. However, polyferric sulfate has the disadvantage of being easily hydrolyzed, with poor coagulation-flocculation effect and low flocculation bridging ability. Moreover, it is easily hydrolyzed when it encounters water in sludge and is unstable, which further reduces the flocculation effect of polyferric sulfate.

[0055] In some embodiments, based on the volume of the aqueous phase, the added amount of the metal salt coagulant is (5 mg to 150 mg) / L, which can be 5 mg / L, 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, 30 mg / L, 35 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 100 mg / L, 120 mg / L, 130 mg / L, 140 mg / L, 150 mg / L, etc.

[0056] In some embodiments, during the step of adding a metal salt coagulant, a stabilizer is also added. The stabilizer includes a saponin compound. The saponin compound can solve the problem of instability of polyferric sulfate due to further hydrolysis in water, can greatly improve the flocculation effect of the composite flocculant, and is beneficial to the flocculation and precipitation of heavy metals in the water phase.

[0057] In some embodiments, saponin compounds include saponins.

[0058] In some embodiments, the mass ratio of the metal salt coagulant to the saponin compound is 100:(3-10), and 100:3, 100:5, 100:8, and 100:10 can be tried.

[0059] In step S20, an oxidant is added to the leaching liquid A, and the oxidant oxidizes all the divalent iron ions in the leaching liquid A into trivalent iron ions, and then sodium sulfate is added under the conditions of pH 1.0 to 1.5 to precipitate light yellow sodium iron sail. The present invention extracts the iron element in the leaching liquid A by the precipitation method in step S20, which can not only recover a large amount of iron element, but also is not easy to affect other elements in the leaching liquid A, and can effectively improve the recovery rate and recovery purity of the iron element in the sludge.

[0060] In some embodiments of step S20, sodium sulfate is added at 85° C. to 95° C., which can promote the reaction between sodium sulfate and trivalent iron ions in the solution to form yellow sodium iron sail.

[0061] In some embodiments of step S20, the oxidant includes oxygen. The above oxidant can easily oxidize the divalent iron ions in the leaching solution A into trivalent iron ions, so that the iron element reacts with sodium sulfate to form yellow sodium iron sail. At the same time, it is not easy to affect other heavy metal elements in the leaching solution A, which is beneficial to improve the recovery rate and recovery purity of the iron element in the sludge.

[0062] In the present invention, after the separation and recovery of the iron element in the leaching liquid is completed, the leaching liquid contains many impurities in addition to the target heavy metal element. Therefore, the present invention combines the porous zeolite with the multi-stage stripping method, adsorbs the lead element and the copper, zinc and cadmium that can be separated by the multi-stage stripping method, and separates them from the impurities in the leaching liquid. Then, the copper, zinc and cadmium adsorbed by the porous zeolite are dissolved into the organic phase by using a mixed solution of 1-(2-hydroxy-5-nonylphenyl) acetone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid, and the organic phase and the porous zeolite are separated. Then, the copper, zinc and cadmium are separated by the multi-stage stripping method, and the lead in the porous zeolite is washed out with ammonium acetate to form soluble lead acetate, thereby completing the separation and recovery of the heavy metal elements iron, copper, zinc, lead and cadmium.

[0063] In some embodiments, the particle size of the porous zeolite ranges from 1.5 mm to 2 mm, for example, it can be any value in the range of 1.5 mm to 2 mm, such as 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2 mm, etc. The porous zeolite particle size within the above range is conducive to the adsorption of a large amount of heavy metal elements.

[0064] In some embodiments, the pore size of the porous zeolite is 0.5 nm to 1 nm, and can be any value in the range of 0.5 nm to 1 nm, such as 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, etc. The porous zeolite having the above pore size range has a larger inner surface, which is conducive to promoting the adsorption of heavy metal elements.

[0065] In some embodiments, the porosity of the porous zeolite is 70% to 80%, which can be any value in the range of 70%, 72%, 75%, 76%, 78%, 79%, 80%, etc. Under the above porosity range conditions, the porous zeolite with the above pore size range has a larger inner surface, which is conducive to promoting the adsorption of heavy metal elements. At the same time, because of the larger porosity, it is also conducive to the desorption of heavy metals after adsorption, which is conducive to improving the recovery rate of heavy metals.

[0066] In step S40, after the porous zeolite rich in copper, zinc, lead and cadmium in step S30 is immersed in a mixed solution of 1-(2-hydroxy-5-nonylphenyl)ethanone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid, copper, zinc and cadmium can be dissolved and extracted into an organic phase, and the organic phase and the porous zeolite are separated to obtain an organic phase rich in copper, zinc and cadmium and a porous zeolite rich in lead. The copper, zinc and cadmium in the organic phase are further subjected to multi-stage extraction, and the lead in the porous zeolite is dissolved, so that the extraction of various heavy metals can be completed, and it is not easily affected by other impurities in the leaching liquid.

[0067] In some embodiments of step S40, the molar ratio of 1-(2-hydroxy-5-nonylphenyl)ethanone oxime to bis(2,4,4-trimethylpentyl)phosphonic acid is 2:1 to 4:1, for example, any ratio in the range of 2:1 to 4:1, such as 2:1, 2.5:1, 3:1, 3.5:1, 4:1, etc. Under the above molar ratio conditions, most of the copper, zinc, and cadmium in the porous zeolite are dissolved into the organic phase.

[0068] In step S40, the amount of the mixed solution of 1-(2-hydroxy-5-nonylphenyl)ethanone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid added is preferably sufficient to immerse the porous zeolite, which is beneficial to the dissolution of copper, zinc and cadmium.

[0069] In step S40, the immersion time of the porous zeolite in the mixed solution of 1-(2-hydroxy-5-nonylphenyl)ethanone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid is 1 to 3 days, during which the mixed solution of 1-(2-hydroxy-5-nonylphenyl)ethanone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid can be replaced, and repeated leaching is performed multiple times to collect the organic phase. In some embodiments, the number of repeated leaching is 2 times or more.

[0070] In S40, the organic phase of S40 is selectively stripped in multiple stages with different high-concentration sulfuric acid stripping agents in the order of cadmium, zinc, and copper to obtain stripping solutions rich in cadmium, zinc, and copper, respectively. In some embodiments, the stripping level of copper is 2 to 10; and / or, the stripping level of zinc is 4 to 10; and / or, the stripping level of cadmium is 4 to 10. For example, the stripping level of cadmium can be 4, 5, 6, 7, 8, 9, 10, etc.; and / or, the stripping level of zinc can be 4, 5, 6, 7, 8, 9, 10, etc.; and / or, the stripping level of copper can be 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0071] In some embodiments of S50, the stripping equilibrium pH of cadmium is controlled to be 2.80-3.20, the mass concentration of sulfuric acid stripping agent is 4-8 g / L, and the stripping ratio is controlled to be 1:1-5:1.

[0072] In some embodiments of S50, the stripping equilibrium pH of zinc is controlled to be 1.30-1.60, the mass concentration of sulfuric acid stripping agent is 10-15 g / L, and the stripping phase ratio is controlled to be 1:1-5:1.

[0073] In some embodiments of S50, the stripping equilibrium pH of copper is controlled to be 1.30-1.60, the mass concentration of sulfuric acid stripping agent is 80-160 g / L, and the stripping phase ratio is controlled to be 1:1-15:1.

[0074] In some embodiments, the stripping of copper, cadmium and zinc in step S60 is carried out at a temperature of 25°C to 35°C, which can be any value in the range of 25°C to 35°C, such as 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, etc.

[0075] In step S60, the lead element in the porous zeolite can be eluted with ammonium acetate and reacted to generate a lead acetate solution. The lead acetate solution and the porous zeolite are separated by filtration, and lead is recovered from the lead acetate solution.

[0076] In some embodiments, the mass concentration of ammonium acetate is any value in the range of 15% to 20%, such as 15%, 16%, 17%, 18%, 19%, 20%, etc., thereby promoting the elution of lead elements in the porous zeolite.

[0077] The present invention also provides a heavy metal extraction and recovery system in sludge, which recovery system at least includes a biological leaching tank, an iron recovery tank, an adsorption tank, a leaching tank, a lead recovery tank, a multi-stage stripping tank, a copper recovery tank, a zinc recovery tank, and a cadmium recovery tank.

[0078] In the recovery system of the present invention, the biological leaching tank leaches the heavy metal sludge, dissolving most of the heavy metals into the leaching liquid A, and the leaching liquid A is rich in heavy metal elements such as iron, copper, zinc, lead and cadmium.

[0079] The leachate A is collected in an iron recovery pool, and treated by a precipitation method to obtain a yellow sodium iron sail precipitate. The iron element is collected in the iron recovery pool and filtered to obtain a leachate B rich in copper, zinc, lead and cadmium. The leachate B is rich in copper, zinc, lead and cadmium.

[0080] The leaching liquid B is introduced into an adsorption tank containing porous zeolite, and the porous zeolite is used to adsorb copper, zinc, lead and cadmium in the leaching liquid B. Then, the porous zeolite rich in copper, zinc, lead and cadmium is collected by solid-liquid separation, and most of the impurities in the leaching liquid are filtered out.

[0081] The porous zeolite is placed in a leaching tank, and a mixed solution of 1-(2-hydroxy-5-nonylphenyl) acetone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid is added to leach copper, zinc and cadmium in the porous zeolite to obtain an organic phase rich in copper, zinc and cadmium. The organic phase is separated from the porous zeolite, and the separated porous zeolite is rich in lead. In the leaching tank, the separation of copper, zinc, cadmium and lead is completed.

[0082] The organic phase is collected in a multi-stage stripping tank, and copper, zinc and cadmium in the organic phase are separated by a graded stripping method.

[0083] The lead-rich porous zeolite can be separated and then the lead in the porous zeolite can be dissolved by ammonium acetate in the lead recovery tank to form a lead acetate solution, which can then be filtered and collected to recover the lead. Thus, the separation and recovery of heavy metals iron, copper, zinc, lead and cadmium in the sludge are completed.

[0084] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to explain the present invention, and are not used to limit the present invention.

[0085] The present invention collects 5 electroplating sludges from the electroplating plant of Huizhou Jinmaoyuan Environmental Protection Technology Co., Ltd. as samples, and separates and recovers the heavy metal elements iron, copper, zinc, lead, and cadmium in the 5 groups of electroplating sludges by the recovery methods of Examples 1 to 5, respectively.

[0086] The porous zeolite used in the following Examples 1 to 5 has a particle size range of 1.5 mm to 2 mm, a pore size range of 0.5 nm to 1 nm, and a porosity of 70% to 80%.

[0087] Example 1

[0088] In this embodiment, the iron, copper, zinc, lead and cadmium in the electroplating sludge sample are separated and recovered, and the steps are as follows:

[0089] S10: In a biological leaching tank, the electroplating sludge is leached by biological leaching to obtain a residue and a leaching liquid A. The leaching steps include:

[0090] S11: taking electroplating sludge as material, adding elemental sulfur powder and ferrous sulfate as substrates, performing an enrichment culture once, until the substrate is completely consumed to obtain Acidithiobacillus ferrooxidans, adding Acidithiobacillus ferrooxidans as a strain to another electroplating sludge, and continuing to add the above substrates to perform a second enrichment culture; repeating the enrichment culture three times in this way to obtain a high-concentration Acidithiobacillus ferrooxidans inoculum with a pH below 2.5;

[0091] S12: The electroplating sludge to be treated and the acidthiobacillus inoculum in S11 are mixed and placed in a biological leaching tank, and 5g of elemental sulfur powder, 30g of ferrous sulfate, 5g-15g of Tween 80, 5g-8g of phosphoric acid and 8ml-15ml of hydrogen peroxide are added per liter of electroplating sludge, and the mixture is evenly mixed. The biological leaching is carried out at 25°C-35°C until the pH value is reduced to below 2.5. The leaching is continued for 3 to 5 days to dissolve the heavy metals in the heavy metal sludge into the aqueous phase, and the aqueous phase is the leaching liquid A.

[0092] S20: collecting the leaching liquid A in step S10 into an iron recovery pool, introducing oxygen as an oxidant into the iron recovery pool, adjusting the pH value of the solution to 1.0-1.5, then heating to 85° C.-95° C., adding sodium sulfate, stirring and reacting sufficiently to obtain yellow sodium ferroalloy precipitate and leaching liquid B, separating the leaching liquid B and yellow sodium ferroalloy, and the leaching liquid B is rich in copper, zinc, lead and cadmium.

[0093] S30: collecting the leaching liquid B into an adsorption pool with porous zeolite, wherein the leaching liquid B completely immerses the porous zeolite and exceeds more than half of the height of the porous zeolite, and soaking for 3 to 5 days, turning the porous zeolite 1 to 3 times in the middle, and then filtering to obtain the porous zeolite and leaching liquid C adsorbed with copper, zinc, lead and cadmium.

[0094] S40: The porous zeolite S30 rich in copper, zinc, lead and cadmium is placed in a leaching tank, and a mixed solution is prepared according to a molar ratio of 2:1 between 1-(2-hydroxy-5-nonylphenyl)ethanone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid, and the mixed solution is added to the leaching tank. The mixed solution completely immerses the porous zeolite and exceeds more than one-half of the height of the porous zeolite. The mixture is soaked for 24 hours, stirred once in the middle, to obtain an organic phase rich in copper, zinc and cadmium and a porous zeolite rich in lead, and the organic phase and the porous zeolite are separated.

[0095] S50: Collect the organic phase of S40 into a multi-stage stripping tank, and use sulfuric acid stripping agents of different concentrations to selectively strip the organic phase of S40 in the order of cadmium, zinc, and copper to obtain stripping solutions rich in cadmium, zinc, and copper, respectively.

[0096] Among them, the stripping steps for cadmium are as follows: the organic phase and the sulfuric acid stripping agent are mixed in the cadmium recovery tank, and stirred at a constant temperature of 30°C. After the extraction reaction reaches equilibrium, the two-phase mixture is allowed to stand for phase separation. The stripping conditions are as follows: the phase ratio (O / A) is 5:1, the stripping equilibrium pH is 4.00, the mass concentration of the sulfuric acid stripping agent is 2 g / L, the mixing reaction time is 30 min, the stirring rate is 500 rpm, and the standing phase separation time is 10 min.

[0097] The stripping steps for zinc are as follows: the organic phase after cadmium stripping and the sulfuric acid stripping agent are mixed in the zinc recovery tank, stirred at a constant temperature of 30°C, and after the extraction reaction reaches equilibrium, the two-phase mixture is allowed to stand for phase separation. The stripping conditions are as follows: the phase ratio (O / A) is 1:1, the concentration of the sulfuric acid stripping agent is 15g / L, the stripping equilibrium pH is 1.50, the mixing reaction time is 30min, the stirring rate is 500rpm, and the standing phase separation time is 10min.

[0098] The stripping steps for copper are as follows: the organic phase after the stripping of cadmium and zinc is mixed with the sulfuric acid stripping agent in the copper recovery tank, and stirred at a constant temperature of 30°C. After the extraction reaction reaches equilibrium, the two-phase mixture is allowed to stand for phase separation. The stripping conditions are as follows: the phase ratio (O / A) is 10:1, the concentration of the sulfuric acid stripping agent is 180g / L, the mixing reaction time is 30min, the stirring rate is 400rpm, and the standing time for phase separation is 10min.

[0099] S60: Collect the porous zeolite of S50 into a lead recovery pool, add ammonium acetate with a mass concentration of 15%, and immerse the porous zeolite in the ammonium acetate, react at 25°C to 30°C for 10 hours, stir 3 to 5 times in the middle, use ammonium acetate to elute the lead in the porous zeolite to obtain lead acetate washing liquid, filter and collect the lead acetate washing liquid, and recover lead therefrom.

[0100] Example 2

[0101] Example 2 refers to Example 1 to separate and recover the heavy metal elements iron, copper, zinc, lead and cadmium in the electroplating sludge, except that in step S40 of Example 2, the molar ratio of 1-(2-hydroxy-5-nonylphenyl)ethanone oxime to bis(2,4,4-trimethylpentyl)phosphonic acid is 4:1.

[0102] Example 3

[0103] Example 3 refers to Example 1 to separate and recover the heavy metal elements iron, copper, zinc, lead and cadmium in the electroplating sludge, except that in step S40 of Example 3, the molar ratio of 1-(2-hydroxy-5-nonylphenyl)ethanone oxime to bis(2,4,4-trimethylpentyl)phosphonic acid is 3:1.

[0104] Example 4

[0105] Example 4 refers to Example 1 to separate and recover the heavy metal elements iron, copper, zinc, lead and cadmium in the electroplating sludge, except that in step S60 of Example 4, the mass concentration of ammonium acetate is 18%.

[0106] Example 5

[0107] Example 5 refers to Example 1 to separate and recover the heavy metal elements iron, copper, zinc, lead and cadmium in the electroplating sludge, except that in step S60 of Example 5, the mass concentration of ammonium acetate is 20%.

[0108] Performance Testing

[0109] The recoveries of iron, copper, zinc, lead and cadmium were measured in Example 1 to Example 5. The results are shown in Table 1.

[0110] Table 1

[0111] Experimental Group Example 1 Example 2 Example 3 Example 4 Example 5 iron 90.2％ 91.1％ 91.5％ 90.8％ 91.4％ copper 91.6％ 91.5％ 90.4％ 91.1％ 91.7％ Zinc 86.4％ 84.5％ 83.7％ 87.4％ 84.9％ lead 85.2％ 88.7％ 87.1％ 87.7％ 88.5％ cadmium 87.6％ 86.5％ 87.6％ 85.7％ 87.9％

[0112] It can be seen from Examples 1 to 5 and Table 1 that the heavy metals iron, copper, zinc, lead and cadmium in sludge can be recovered and separated by the extraction recovery method of the present invention, and the recovery rate is relatively high.

[0113] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for extracting and recovering heavy metals from sludge, characterized in that: The following steps are involved: S10: leaching the heavy metal sludge by biological leaching to obtain a filter residue and a leaching liquid A, wherein the leaching liquid A is rich in the following heavy metal elements: iron, copper, zinc, lead, and cadmium; S20: adding an oxidant to the leaching solution A, adjusting the pH value of the solution to 1.0-1.5, then heating and adding sodium sulfate to obtain a precipitate of sodium ferrocyanide and a leaching solution B, extracting iron from the sodium ferrocyanide, and the leaching solution B is rich in the following heavy metal elements: copper, zinc, lead, and cadmium; S30: adding a porous zeolite to the leaching solution B, the porous zeolite adsorbing copper, zinc, lead and cadmium, and then filtering to obtain a leaching solution C and a porous zeolite rich in heavy metal elements copper, zinc, lead and cadmium; S40: soaking the porous zeolite rich in heavy metal elements copper, zinc, lead and cadmium in S30 in a mixed solution of 1-(2-hydroxy-5-nonylphenyl) acetone oxime and bis(2,4,4-trimethylpentyl)phosphonic acid to obtain an organic phase rich in heavy metal elements copper, zinc and cadmium, and separating the organic phase rich in heavy metal elements copper, zinc and cadmium and the porous zeolite, wherein the separated porous zeolite is rich in heavy metal element lead; S50: The organic phase of S50 is selectively stripped in multiple stages using sulfuric acid stripping agents of different concentrations in the order of cadmium, zinc, and copper to obtain stripping solutions rich in heavy metal elements cadmium, zinc, and copper, respectively; S60: using ammonium acetate to elute the lead in the porous zeolite rich in heavy metal element lead separated in S40 to obtain a lead acetate washing liquid, and recovering lead from the lead acetate washing liquid; The step S10 comprises the following steps: placing heavy metal sludge, Tween 80 and a leaching agent in a biological leaching tank for leaching reaction until the pH drops below 2.5, dissolving the heavy metal into the water phase, the leaching agent comprising acidophilic thiobacillus and a substrate, and the substrate comprising elemental sulfur powder and ferrous sulfate; The mass concentration of the ammonium acetate is 15% to 20%; The particle size of the porous zeolite ranges from 1.5 mm to 2 mm; The pore size of the porous zeolite is 0.5 nm to 1 nm; The porosity of the porous zeolite is 70% to 80%.

2. The method for extracting and recovering heavy metals from sludge according to claim 1, characterized in that: In step S20, the oxidant includes at least one of oxygen and hydrogen peroxide.

3. The method for extracting and recovering heavy metals from sludge according to claim 1, characterized in that: In step S20, the heating temperature is 85°C to 95°C.

4. The method for extracting and recovering heavy metals from sludge according to claim 1, characterized in that: In step S50, the molar ratio of 1-(2-hydroxy-5-nonylphenyl)ethanone oxime to bis(2,4,4-trimethylpentyl)phosphonic acid is 2:1 to 4:

1.

5. The method for extracting and recovering heavy metals from sludge according to claim 1, characterized in that: In step S50, the stripping level of copper is 2 to 10; and / or the stripping level of zinc is 4 to 10; and / or the stripping level of cadmium is 4 to 10.

6. The method for extracting and recovering heavy metals from sludge according to claim 1, characterized in that: In step S50, the stripping temperature is 25°C to 35°C.

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