A process for the extraction and recovery of heavy metals

Abstract

The application adopts the innovative extractant of main extractant EDTA (ethylene diamine tetraacetic acid), auxiliary extractant sodium persulfate and ammonium chloride, carries out water phase extraction on sewage sludge incineration ash, electronic plant sewage filter residue and municipal waste incineration bottom ash, and the extraction efficiency is higher than the sum of exchangeable part, reducible part and oxidizable part in the standard BCR extraction method, only leaving the heavy metal part extracted by digestion method in the last residue, fully cleaning the solid waste polluted by heavy metals, and providing basic demonstration for further application instead of landfill; the application adopts the innovative method of acidification quick freezing, rapid precipitation of main precipitant EDTA, thawing solid-liquid separation, can separate the chelating agent and heavy metal after chelation very quickly and effectively, and recycle the chelating agent; combined with sequential precipitation and coprecipitation, high-purity heavy metal compounds are separated, which are important industrial raw materials; the amount of consumed acid and alkali and other chemical products is less, the cost is lower, and the application prospect is wide.

Description

Technical Field

[0001] This invention relates to the field of green environmental protection technology, and in particular to a method for the extraction and recovery of heavy metals. Background Technology

[0002] Heavy metals have wide applications in industry, agriculture, aerospace, energy, chemical industry (paints, pesticides, electrodes, etc.). Heavy metals are highly toxic, and heavy metal pollution poses a significant safety hazard, endangering human safety, animal and plant safety, ecosystem safety, and environmental safety. This invention relates to the field of heavy metal extraction and recycling technology. How to effectively extract heavy metals while reducing the use and waste of extractants, smoothly separating heavy metals from extractants, and recycling extractants to reduce the cost of heavy metal treatment and recycling are all important issues in this technical field.

[0003] The main methods for treating solid waste contaminated by heavy metals include physical methods, biological methods and chemical methods. Physical methods use isolation, foam flotation, high-temperature vitrification, heat treatment and water washing to treat solid waste or soil contaminated by heavy metals. Isolation is to separate pollutants with physical barriers. Foam flotation uses water and air bubbles to blow pollutants to the upper foam layer. High-temperature vitrification uses high temperature to melt solids into a whole block to achieve the purpose of solidifying and encapsulating heavy metals, but its disadvantage is that the energy consumption is too high and the solidified waste is difficult to recycle and reuse. Heat treatment method heats the solid waste contaminated by heavy metals to evaporate pollutants to achieve the purpose of purification. Water washing method can only remove very limited heavy metal pollution. Physical methods are fast and low cost, but their efficiency in removing or fixing heavy metals is not high[1].

[0004] Bioremediation uses biological tissues, including algae, plants, animals, bacteria, fungi, and combinations thereof, to treat solid waste or soil contaminated with heavy metals. Phytoremediation uses special plants to absorb or adsorb heavy metal pollutants, and then incinerates the sacrificial harvested plants to collect heavy metals from the ash. Algae-bacterial remediation uses algae to absorb or adsorb heavy metal pollutants. Microalgae and seaweed can be used to degrade, absorb, adsorb, transform, accumulate, and mineralize heavy metals. Finally, the algae are harvested to extract the heavy metals, and biodiesel can also be harvested. Fungal remediation uses fungi (mushrooms) to absorb and adsorb heavy metals. Microbial remediation uses microorganisms (bacteria) to treat heavy metal pollution. Some lower animals, such as earthworms, have significant potential to increase the proportion of stable heavy metals and reduce the proportion of mobile heavy metals. Bioremediation is inexpensive; however, its remediation effect is low to moderate, the remediation time and cycle are long (months to decades), the operation is complex, and the effect is unstable. Due to these disadvantages, bioremediation has only a few application cases [2].

[0005] Chemical remediation methods include chemical immobilization, stabilization, solidification, electrochemical methods, adsorption, chemical cleaning, and cement kiln methods. Chemical immobilization fixes mobile heavy metal ions onto solid particles to prevent them from leaking into the environment. Stabilization primarily utilizes chelating agents to form metal-ligand complexes; however, these chelating agents must firmly adhere to the solid particles, otherwise, negative effects may occur. Solidification encapsulates heavy metal ions within polycrystalline crystals or solidified complexes, making it difficult for the encapsulated ions to escape the physical barrier and migrate into the environment. Electrochemical methods use voltage to move heavy metal ions to the cathode for enrichment; however, they consume a lot of energy and require a long time to remove heavy metals from contaminated solid waste, thus incurring high costs. Adsorption uses adsorbents to enrich heavy metals, but the adsorption process is often slow and inefficient. Chemical cleaning transfers heavy metal ions from the solid phase to the aqueous phase, and then removes the heavy metals from the aqueous phase. The cement kiln method utilizes the high temperatures of the cement production process to react with heavy metals, thereby fixing and encapsulating the heavy metals within the polycrystalline structure of cement particles. However, this sacrifices cement quality and increases the safety risks associated with cement applications. Chemical fixation, stabilization, curing, and cement kiln methods cannot remove heavy metals from contaminants. Chemical cleaning and electrostatic methods can remove heavy metals from contaminants, but they are quite expensive [3-4].

[0006] P. Oleszczuk et al. used sequential extraction technology to investigate the changes in the state of nickel and zinc in soil improved by sewer slag or biochar and sewer slag over 18 months. They found that sewer slag promoted the leaching of bioavailable nickel and zinc, while biochar inhibited the leaching of nickel and zinc in soil improved by biochar and sewer slag and converted bioavailable nickel and zinc into insoluble substances [5]. YRGuo et al. recently developed a novel adsorbent - carbon dots / magnesium hydroxide flake composite for adsorbing highly toxic cadmium ions, which are then converted into amazing cadmium hydroxide nanowires after adsorption [6]. This novel adsorbent has great potential for widespread use in the purification of contaminated slag and wastewater treatment.

[0007] Patent CN 105200239A describes a zinc recovery process from electroplating sludge. First, zinc is transferred from the electroplating sludge to the aqueous phase using acid, and then iron and chromium are separated by neutralization with alkali to obtain zinc-containing filtrate. Then, zinc is enriched in the organic phase using organophosphorus extractant and solvent, and then transferred back to the aqueous phase by adding acid to achieve the purpose of leaching, separation and purification. The process has good effect and organophosphorus extractant can be recycled, but it consumes a lot of acid and alkali, and the cost is high[7].

[0008] Chemical cleaning can remove heavy metals from contaminants with satisfactory results and eliminates the risk of heavy metal contamination once and for all, but it is quite expensive [3-4]. One major cost comes from the chemical chelating agents used to remove heavy metals from contaminants, which are expensive, require large quantities, and are difficult to recycle and reuse. The process of this invention provides a feasible solution to the problems of extracting heavy metals from non-combustible solid waste contaminated with heavy metals and separating high-purity heavy metals and high-purity chelating agents from heavy metal chelates for recycling. This significantly reduces the cost of chemical cleaning and hopefully contributes to the basic demonstration of the widespread use of rapid and efficient chemical cleaning methods.

[0009] References

[0010] 1. Ammami, MT; Benamar, A.; Koltalo, F.; Wang, HQ; LeDerf, F.

[0011] 2.Dhal, B.; Thatoi, HN; Das, NN; Pandey, BD, Chemical and microbialremediation of hexavalent chromium from contaminated soil and mining / metallurgical solid waste: A review.J.Hazard.Mater.2013,250,272-291.

[0012] 3.Aldawsari,A.;Khan,M.A.;Hameed,B.H.;Alqadami,A.A.;Siddiqui,M.R.;Alothman,Z.A.;Ahmed,A.,Mercerized mesoporous date pit activated carbon-Anovel adsorbent to sequester potentially toxic divalent heavy metals fromwater.PLoS One 2017,12,(9).

[0013] 4.Masykur,A.;Wibowo,A.H.;Salsabilah;Iop In Preparation of Cu(II)ion-imprinted based on carboxymethyl chitosan and application as adsorbent of Cu(II)ion,13th Annual Joint Conference on Chemistry(JCC),Diponegoro Univ,ChemDept,Semarang,INDONESIA,Sep 07-08,2018;Diponegoro Univ,Chem Dept,Semarang,INDONESIA,2018.

[0014] 5.Bogusz,A.;Oleszczuk,P.,Sequential extraction of nickel and zinc insewage sludge-or biochar / sewage sludge-amended soil.Science of the TotalEnvironment 2018,636,927-935.

[0015] 6. Yin, WM; Wang, Y.; Hou, YC; Sun, Y.; Zhang, JG;

[0016] 7. Tan Xiaotian; A method for separating and recovering zinc from electroplating sludge. CN 105200239A, 2015. Summary of the Invention

[0017] To address the challenges in existing technologies regarding the extraction of heavy metals from non-combustible solid waste contaminated with heavy metals, and the even greater difficulty in separating high-purity heavy metals and high-purity chelating agents from heavy metal chelates for recycling, a method for heavy metal extraction and recovery is provided.

[0018] The technical solution adopted by this invention to solve its technical problem is as follows: a method for heavy metal extraction and recovery, the process of which is as follows:

[0019] This innovative aqueous extractant solution, consisting of EDTA as the primary extractant and sodium persulfate and ammonium chloride as auxiliary extractants, is used to extract heavy metals from sewage sludge incineration ash, wastewater filter residue from electronics factories, and bottom ash from municipal solid waste incineration. The process involves acidification followed by rapid freeze-thaw to separate the primary extractant EDTA from the chelate between the heavy metals and the extractant. A combination of sequential precipitation and co-precipitation is then used to separate the heavy metals, allowing for their recovery and recycling. The main process includes:

[0020] Step 1: Heavy Metal Extraction

[0021] The extract is added to the solid waste containing heavy metals in a certain proportion, stirred, and reacted at a certain temperature for a period of time, so that most of the heavy metals are extracted into the solution; the effective components of the extract are the extractant and water; the effective concentration of the extractant and the pH value need to be controlled; the main extractant is EDTA (ethylenediaminetetraacetic acid); the auxiliary extractants are sodium persulfate and ammonium chloride;

[0022] Step 2: Solid-liquid separation

[0023] Perform solid-liquid separation on the solid-liquid mixture after extraction; filtration or centrifugation are both acceptable. Continue to step three for the separated solid fraction. Continue to steps one and two for the separated liquid fraction until the effective concentration of the extractant decreases and the extraction effect deteriorates. Add more solid main extractant and perform steps one and two with a new batch of contaminated material until the effective concentration of the extractant decreases and the extraction effect deteriorates, until the total amount of main extractant reaches 13% wt. Continue to step four for the clear liquid.

[0024] Step 3: Cleaning

[0025] Clean the extracted solid waste; water, distilled water, deionized water, or solvent can be used; remove residual heavy metals and extract; solid-liquid separation is required after each cleaning; clean solid waste free of heavy metals is obtained, which can be used for building materials, roadbeds, agriculture, and horticulture;

[0026] Step 4: Acidify the heavy metal extraction solution, quickly freeze and thaw to rapidly precipitate the main precipitant EDTA.

[0027] Extraction solutions saturated with heavy metals exhibit reduced effective extractant concentrations and decreased extraction efficiency. Acidification-induced rapid freeze-thaw cycles are employed to quickly separate the extractant from the heavy metal chelates. Acidification-induced rapid freeze-thaw cycles cause the primary extractant, EDTA, to precipitate, releasing it from the heavy metal-EDTA chelate. After acidification-induced rapid freeze-thaw, only the primary extractant, EDTA, precipitates, while the remaining auxiliary extractants and heavy metals remain in solution; this achieves rapid separation of EDTA and heavy metals.

[0028] Step 5: Solid-liquid separation

[0029] Solid-liquid separation is performed on the extract after precipitation of the main extractant EDTA; filtration or centrifugation are both acceptable methods.

[0030] Step Six: Separation of Heavy Metals by Combining Sequential Precipitation and Co-precipitation

[0031] The extract saturated with heavy metals after separation by the main extractant EDTA contains a large amount of heavy metals. Appropriate sequential precipitation is performed by adding sequential precipitating agents one by one, allowing the heavy metals to precipitate sequentially. Solid-liquid separation is then performed on each precipitate. Some co-precipitation is unavoidable during sequential precipitation and needs to be dissolved and separated. Combining sequential precipitation and co-precipitation yields high-purity single heavy metal compounds with low impurity content, which can be reused as chemical raw materials for resource utilization. A recyclable auxiliary extract after heavy metal separation is also obtained.

[0032] Step 7: Extract Regeneration

[0033] The main extractant EDTA separated in step five is redissolved in the recyclable auxiliary extract after heavy metal separation in step six, and the pH value is adjusted to obtain a recycled extract equivalent to the original extract, which can be recycled and reused in step one.

[0034] The heavy metals mentioned refer to lead, mercury, chromium, cadmium, arsenic, copper, zinc, iron, nickel, manganese, cobalt, molybdenum, vanadium, antimony, bismuth, titanium, silver, aluminum, tin, and mixtures thereof; especially lead, mercury, chromium, cadmium, arsenic, copper, zinc, nickel, manganese, cobalt, antimony, and mixtures thereof. Lead, mercury, chromium, cadmium, and arsenic are the most toxic, while copper, zinc, nickel, manganese, cobalt, antimony, lead, chromium, and mixtures thereof are often found in the largest quantities.

[0035] The extractant consists of EDTA as the main extractant and sodium thiosulfate and ammonium chloride as auxiliary extractants. The initial concentration of EDTA is 0.1-9% wt., preferably 0.6-7% wt., and most preferably 4-6% wt. During the extraction process, EDTA can be added in addition, with a maximum concentration of 13% wt. The concentration range of sodium thiosulfate as auxiliary extractant is 0.1-5% wt., preferably 1-3% wt. The concentration range of ammonium chloride as auxiliary extractant is 3-20% wt., preferably 3-10% wt., and most preferably 3-6% wt.

[0036] The pH adjustment control uses inorganic strong acids (sulfuric acid, hydrochloric acid, nitric acid) and strong bases (NaOH, KOH, Ca(OH)2).

[0037] The liquid-to-solid ratio of the extract and solid waste, referred to as the liquid-to-solid ratio, is preferably in the range of 1 / 1 to 200 / 1, more preferably 2 / 1 to 50 / 1, and most preferably 3 / 1 to 15 / 1.

[0038] The stirring mentioned refers to mechanical stirring, magnetic stirring, ultrasonic stirring, pipeline mixers, and liquid circulation; the higher the stirring speed and the greater the stirring intensity, the better the extraction effect; however, the stirring intensity should take into account machine costs, electricity costs, and production safety.

[0039] The reaction temperature range is 0.5-220℃; the higher the reaction temperature, the better the extraction effect; a reaction temperature range of 15-170℃ is better, and 130-170℃ is ideal, but energy consumption costs should also be considered; within the temperature range of 130-170℃, the reaction pressure is 0.3-0.7 MPa; room temperature reaction is energy-saving and can also be used, with a temperature range of 0.5-35℃; if waste heat can be utilized, it can be applied flexibly to achieve a balance between energy saving and reaction time.

[0040] The reaction time range is 0-24 hours; the longer the reaction time, the better the extraction effect; a heating reaction time range of 1-5 hours is better, and 1-3 hours is best; a room temperature reaction time range of 12-24 hours is better, and 18-24 hours is best.

[0041] The effective concentrations of the extractants refer to the effective concentrations of the main extractant and the co-extractant, respectively. The initial concentration range of the main extractant EDTA is 0.1-9% wt., preferably 0.6-7% wt., and most preferably 4-6% wt. Before use, the effective concentration of the main extractant EDTA in the extract is its initial concentration. After use, the effective concentration of the main extractant EDTA decreases and falls below its initial concentration, equal to the initial concentration minus the portion already chelated with heavy metals. The effective concentration of the co-extractant sodium thiosulfate decreases if consumed, equal to its initial concentration minus the consumed concentration. If its effective concentration is less than half of the initial concentration, it can be replenished.

[0042] In step two, if the extraction effect deteriorates, more solid primary extractant EDTA should be added. The amount of added solid primary extractant EDTA should be equivalent to the amount of primary extractant EDTA that has already chelated with heavy metals. After addition, the total amount of primary extractant EDTA should not exceed 13% wt.

[0043] The pH range mentioned in steps one and seven is preferably 3.08-8.0, better 3.1-5.0, and best 3.2-4.0.

[0044] The acidification mentioned in step four should preferably have a pH range of 0.1-3.07, with 0.3-2.0 being better and 0.5-1.0 being ideal.

[0045] The quick-freezing mentioned in step four refers to quick-freezing at a temperature below 0℃, preferably in the range of 0 to -195.8℃, even better in the range of 0 to -50℃, and best in the range of -10 to -30℃.

[0046] The sequential precipitation mentioned in step six refers to the sequential precipitation of individual heavy metal ions, with only one metal ion precipitated at a time.

[0047] The co-precipitation mentioned in step six refers to the precipitation of multiple heavy metal ions at once, with at least two ions.

[0048] The sequential precipitation process involves the following steps: After removal by the main precipitant EDTA, iron ions can be adjusted to pH 3.0 with sufficient phosphate ions to produce FePO4 precipitate, which is obtained through solid-liquid separation. Adding an appropriate amount of sodium sulfate produces lead sulfate or barium sulfate precipitate, which is obtained through solid-liquid separation. Adding an appropriate amount of potassium iodide and sodium thiosulfate, and further adjusting the pH to 4.2, produces cuprous iodide precipitate, which is obtained through solid-liquid separation. Adding an appropriate amount of dimethylglyoxime, and further adjusting the pH to 4.6, produces nickel dimethylglyoxime precipitate, which is obtained through solid-liquid separation. Further adjusting the pH to 7.5, produces Al(OH)3 precipitate or titanium dioxide precipitate, which is obtained through solid-liquid separation. Further adjusting the pH to 9.5, produces Zn(OH)2 precipitate, which is obtained through solid-liquid separation.

[0049] The co-precipitation process involves adding an appropriate amount of phosphate and adjusting the pH to 3.0 after the primary precipitant EDTA is removed, resulting in FePO4 precipitate. Solid-liquid separation yields FePO4. Adjusting the pH to 13-14 causes most heavy metals to precipitate. With sufficient phosphate, the precipitates are zinc phosphate, lead phosphate, lead chromate, nickel phosphate, copper phosphate, iron phosphate, etc., which are then separated into a mixed precipitate. Adding concentrated KOH or NaOH and heating causes zinc phosphate to dissolve and lead chromate to precipitate as potassium chromate and Pb(OH)2. The other metals are also converted to Cu(OH)2, Ni(OH)2, and Fe(OH)3. Solid-liquid separation is then performed. The solution contains potassium phosphate / sodium and zinc hydroxide / sodium. With potassium / sodium chromate, the pH is adjusted to 5.0, producing Zn(OH)2 precipitate. Solid-liquid separation separates zinc and chromium. The mixed solid contains Cu(OH)2, Ni(OH)2, Fe(OH)3, and Pb(OH)2 precipitate. Adding an appropriate amount of low-concentration nitric acid dissolves Cu(OH)2, Ni(OH)2, and Pb(OH)2, but Fe(OH)3 does not dissolve. Solid-liquid separation yields a mixed solution of copper, nickel, and lead ions. Adding an appropriate amount of sodium thiosulfate and sodium thiocyanate yields CuSCN precipitate. Solid-liquid separation yields a mixed solution of nickel and lead ions. Adding an appropriate amount of sodium sulfate yields lead sulfate precipitate. Solid-liquid separation yields a nickel ion solution. Adjusting the pH to 9.5 yields Ni(OH)2 precipitate.

[0050] The combination of sequential precipitation and co-precipitation is used in the sequential precipitation process of the extract from sewage sludge incineration ash. If unavoidable co-precipitation occurs, it can be separated in subsequent steps. The extract from sewage sludge incineration ash contains phosphate, iron, aluminum, silicon, zinc, copper, and small amounts of chromium and lead. After acidification, quick-freeze-thaw, and centrifugation to remove EDTA, the supernatant is adjusted to a pH of 0.5-1.0. The pH is then raised to 3.2, producing a small amount of slightly yellowish precipitate (ferric phosphate), followed by solid-liquid separation. The pH of the supernatant is further adjusted to 6.0, producing a large amount of light blue precipitate, followed by solid-liquid separation. This light blue precipitate contains aluminum hydroxide, nickel hydroxide, copper hydroxide, and zinc hydroxide, requiring further separation. The pH of the supernatant is further adjusted to 9.8, producing a small amount of yellowish precipitate (lead chromate), followed by solid-liquid separation. The pH of the supernatant is further adjusted to 12.5, producing a very small amount of reddish-brown precipitate (hydrogen hydroxide). Iron oxide), solid-liquid separation; the recovered EDTA is dissolved in its supernatant (recyclable co-extraction solution), and the pH is adjusted to 3.2-4.0, which is a recyclable extraction solution; the light blue precipitate contains aluminum hydroxide, nickel hydroxide, copper hydroxide and zinc hydroxide, which need to be further separated; zinc hydroxide can be dissolved in an aqueous solution with pH 11-12, and solid-liquid separation is achieved; the pH of the liquid is adjusted to 9-10 to produce zinc hydroxide precipitate; the separated aluminum hydroxide, nickel hydroxide and copper hydroxide are dissolved in dilute acid; an appropriate amount of potassium iodide and sodium thiosulfate are added, and the pH is further adjusted to 4.2 to produce cuprous iodide precipitate, and solid-liquid separation yields CuI; an appropriate amount of dimethylglyoxime is added to the supernatant, and the pH is further adjusted to 4.6 to produce nickel dimethylglyoxime precipitate, and solid-liquid separation yields nickel dimethylglyoxime; the pH of the supernatant is further adjusted to 7.5 to produce Al(OH)3 precipitate; in this way, the four compounds in the light blue co-precipitate are separated sequentially.

[0051] The combination of sequential precipitation and co-precipitation is used in the sequential precipitation process of the extract from the sludge filter residue of the electronics factory. If unavoidable co-precipitation occurs, it can be separated in subsequent steps. The EDTA extract from the sludge filter residue of the electronics factory is blue, with a pH of 6.21, and contains 3350 ppm Cu, 466.7 ppm Ni, 167.8 ppm Zn, and Fe. The total concentration of heavy metals (chromium, cobalt, lead, manganese, vanadium, and tin) was 103.3 ppm, and the total concentration of other heavy metals (chromium, cobalt, lead, manganese, vanadium, and tin) was 11.8 ppm, which can be ignored. After acidification, quick-freezing, and thawing, the supernatant from which EDTA was removed was pH 0.84. The pH was adjusted to increase to precipitate the heavy metals. First, the pH was increased to 5.24, producing a large amount of blue copper hydroxide precipitate, which was then separated from the solid. The pH of the supernatant was further increased to 8.65, producing a moderate amount of brownish-green precipitate, which was then centrifuged. The brownish-green precipitate mainly contained iron hydroxide, zinc hydroxide, and nickel hydroxide, requiring further separation. The pH of the supernatant was further increased to 11.34, producing a moderate amount of blue nickel hydroxide precipitate, which was then centrifuged. The pH of the supernatant was further increased to 12.38, producing a very small amount of blue copper hydroxide precipitate, which was then centrifuged. The recovered EDTA was dissolved in the supernatant (a recyclable auxiliary extractant), and the pH was adjusted to 3.2-4.0, which became a recyclable extractant. The brownish-blue precipitate mainly contains ferric hydroxide, zinc hydroxide, and nickel hydroxide, which require further separation. Zinc hydroxide can be dissolved in an aqueous solution with a pH of 11-12, thus separating the solid and liquid. Adjusting the pH of the liquid to 9-10 will produce zinc hydroxide precipitate. The separated ferric hydroxide and nickel hydroxide are dissolved in dilute acid. Adjusting the pH to 4.0 will produce a brown ferric hydroxide precipitate, thus separating the solid and liquid. Further increasing the pH of the solution to 8-9 will produce a blue nickel hydroxide precipitate, thus separating the solid and liquid.

[0052] The pH adjustment mentioned in step seven can be achieved using strong inorganic acids (sulfuric acid, hydrochloric acid, nitric acid) or inorganic aluminum salts. When using inorganic aluminum salts, the pH is first adjusted to 5.0-7.0 to produce aluminum hydroxide precipitate. After solid-liquid separation, the pH is further adjusted to the aforementioned range using strong inorganic acids. The advantage of using inorganic aluminum salts is that it utilizes the unwanted hydroxide ions to be removed to produce aluminum hydroxide precipitate, which can be further heat-treated to produce alumina. Alumina has high added value and a wide range of applications.

[0053] The beneficial effects of this invention are: compared with the prior art, the method for heavy metal extraction and recovery of this invention consumes less acid and alkali, has lower cost, and has a higher extraction efficiency than the sum of the exchangeable, reducible, and oxidizable components in the standard BCR extraction method, and has broad application prospects. Attached image description:

[0054] Figure 1A flowchart illustrating the process of using EDTA as the primary extractant to extract heavy metals from solid waste and recycle them into various single compounds in an environmentally friendly and pollution-free manner.

[0055] Figure 2 The normalized metal content calculated after sequential BCR extraction of sewage sludge incineration ash samples. The mobile fraction equals the sum of the ion-exchangeable fraction and the reducible fraction.

[0056] Figure 3 The normalized metal content calculated after sequential BCR extraction of filter residue samples from electronics factory wastewater. The mobile fraction equals the sum of the ion-exchangeable fraction and the reducible fraction.

[0057] Figure 4 The normalized metal content calculated after sequential BCR extraction of municipal solid waste incineration residue samples. The mobile fraction equals the sum of the ion-exchangeable fraction and the reducible fraction.

[0058] Figure 5 (Example 23) The pH of the EDTA extract of sewage sludge incineration ash was adjusted from 3.2 to 2.28, 1.65, 0.94, 0.76 and 0.70.

[0059] Figure 6 (Example 24) The EDTA extract of sewage sludge incineration ash was adjusted to pH 3.2 to 1.12 and 0.94 and then placed in a quick-freezing box to achieve the following state.

[0060] Figure 7 (Example 25) The EDTA extract of sewage sludge incineration ash was adjusted to different pH values, placed in a quick-freezing oven for quick freezing, and then taken out to thaw and centrifuged to obtain white EDTA precipitate.

[0061] Figure 8 FESEM field emission scanning microscope image of the white EDTA precipitate separated by acidification, quick-freezing and thawing, and centrifugation of SSIA extract.

[0062] Figure 9 The EDS spectrum of the dried white EDTA precipitate, from... Figure 7 The 008 position was obtained by scanning.

[0063] Figure 10 In Example 27, the precipitates of sample #1 (with EDTA removed) and sample #2 (without EDTA removed) were obtained by SSIA extraction, and the precipitates #1-#6 were obtained by increasing the pH value to different values.

[0064] Figure 11 Example 28 describes the process of acidifying, quick-freezing, and thawing the extract from the filter residue of wastewater from an electronics factory to precipitate EDTA.

[0065] Figure 12In Example 28, the precipitate control of the filter residue extract of the electronics factory wastewater with EDTA removed (sample #3) and without EDTA removal (sample #4) was compared with the precipitate #7-#13 produced when the pH was increased to different values. Detailed implementation method:

[0066] Example 1

[0067] We conducted elemental composition analysis on several heavy metal pollutant ash residues (CPZ E-Sludge electronics factory wastewater filter residue, SSIA sewer sludge incineration ash, and IBA municipal solid waste incineration bottom ash) used in this application after thorough drying. Table 1 lists the chemical elemental composition of the several heavy metal pollutant ash residues after complete digestion and ICP-AES analysis. The dried sample of electronics factory wastewater filter residue mainly contained copper, nickel, iron, zinc, and tin, with contents of 4.2% wt., 1.1%, 0.4%, 0.24%, and 0.18%, respectively. The dried sample of sewer sludge incineration ash mainly contained silicon, phosphorus, calcium, aluminum, iron, potassium, sodium, titanium, zinc, and copper, with contents of 18.5% wt., 7.6%, 6.6%, 6.1%, 4.1%, 1.3%, 0.54%, 0.54%, 0.34%, and 0.20%, respectively. The dried ash samples from municipal solid waste incineration mainly contain calcium, iron, silicon, aluminum, sodium, zinc, phosphorus, copper, barium, lead, and manganese, with contents of 15.8% wt., 15.8%, 15.6%, 4.3%, 3.3%, 1.0%, 0.19%, 0.17%, 0.16%, 0.15%, and 0.13%, respectively.

[0068] Table 1. Chemical elemental composition of several heavy metal pollutants after complete digestion, analyzed by ICP-AES.

[0069]

[0070] Not tested*: Not tested due to cost control requirements.

[0071] Example 2

[0072] We conducted metal mobility analysis on several heavy metal pollutant ash residues (NSL CPZ E-Sludge filter residue from electronics factory wastewater, SSIA sewer sludge incineration ash, and IBA municipal solid waste incineration bottom ash) used in this application. We employed a modified BCR sequential extraction analysis method, the specific steps of which are as follows:

[0073] The sample was first dried and then ground and sieved using a ball mill to obtain a powder sample smaller than 125 micrometers.

[0074] Step 1: Add 1 gram of sample to 40 ml of 0.11 M acetic acid solution, shake on a shaking table at 22 rpm for 16 hours, and then centrifuge. This step is to extract the ion-exchangeable metal fraction.

[0075] Step 2: Add 40 mL of 0.5 M hydroxylamine hydrochloride (pH 1.5) to the separated residue, shake on a shaking table at 22 rpm for 16 hours, and then centrifuge. This step is to extract the reducible metal fraction.

[0076] Step 3: Add 10 ml of 8.8 M hydrogen peroxide to the separated residue, heat to 80 degrees Celsius and maintain for 1 hour, then add another 10 ml of 8.8 M hydrogen peroxide and heat to 80 degrees Celsius and maintain for 1 hour. Then add 50 ml of 1 M ammonium acetate, shake on a shaking bed at 22 rpm for 16 hours, and centrifuge. This step is to extract the oxidizable metals.

[0077] Step 4: Add 5 ml of concentrated nitric acid, 5 ml of concentrated hydrochloric acid, and 2 ml of concentrated hydrofluoric acid to the separated residue, and microwave digest until no residue remains. This step is to extract all the remaining metals.

[0078] ICP-AES analysis was performed on the supernatant produced in each step to calculate the amount of extracted metal elements.

[0079] The ion-exchangeable fraction extracted in the first step and the reducible fraction extracted in the second step are mobile metals. The oxidizable fraction extracted in the third step and the residue extracted in the fourth step are immobile metals.

[0080] Figure 2 This paper summarizes the normalized metal content calculated from sequential BCR extraction of sewage sludge incineration ash samples. The mobile fraction equals the sum of the ion-exchangeable fraction and the reducible fraction. Figure 2 It is evident that the mobile fraction content of most heavy metals in the sewage sludge incineration ash samples is low: Sn 0%, Cr 1.5%, Pb 2%, Fe 10%, Zn 10%, Ni 11%, Cu 18%, and V 18%. However, the mobile fraction content of barium and manganese is slightly higher: Ba 33% and Mn 41%. The average mobile fraction metal content is only 14.5%.

[0081] Example 3

[0082] BCR sequential extraction analysis was performed on filter residue samples from electronics factory wastewater. The analytical results are as follows: Figure 3 As shown. Figure 3 This paper summarizes the normalized metal content calculated from BCR sequential extraction of filter residue samples from electronics factory wastewater. The mobile fraction equals the sum of the ion-exchangeable and reducible fractions. Figure 3It is evident that most heavy metals exhibit high levels of mobile fractions in the wastewater filter residue samples from electronics factories: Sn 13%, Ni 37%, Co 37%, Cr 42%, and Fe 48%. However, the mobile fraction contents of lead, manganese, zinc, and copper are even higher: Pb 68%, Mn 72%, Zn 82%, and Cu 87%. The average mobile fraction metal content is as high as 54%.

[0083] Example 4

[0084] BCR sequential extraction analysis was performed on bottom ash samples from municipal solid waste incineration. The analytical results are as follows: Figure 4 As shown. Figure 4 This paper summarizes the normalized metal content calculated from BCR sequential extraction of bottom ash samples from municipal solid waste incineration. The mobile fraction equals the sum of the ion-exchangeable and reducible fractions. Figure 4 It is evident that most heavy metals exhibited very low mobile fraction content in the bottom ash samples from municipal solid waste incineration: Sn 0%, Ba 2%, Cr 4%, Ni 5%, Fe 7%, Co 10%, and Pb 17%. However, the mobile fraction content of manganese, copper, and zinc was slightly higher: Mn 26%, Cu 30%, and Zn 43%. The average mobile fraction metal content was only 14.6%.

[0085] Example 5

[0086] Extraction of sewage sludge incineration ash samples was performed using pure deionized water. The sewage sludge incineration ash samples were first thoroughly dried, ground using a ball mill, and sieved to obtain a powder sample smaller than 125 micrometers. One gram of the sewage sludge incineration ash powder sample was added to 15 ml of pure deionized water and shaken on a shaking bed at 22 rpm for 110 hours (approximately four and a half days), followed by centrifugation. The supernatant was analyzed by ICP-AES, and the extracted metal elements were calculated. The results are listed in Table 2. Table 2 clearly shows that deionized water was completely ineffective in extracting zinc, copper, nickel, chromium, lead, manganese, and iron from the sewage sludge incineration ash samples. The extraction efficiency for non-metallic phosphorus and silicon was also negligible. Only potassium was slightly soluble in water, with an extraction rate of 2.17%.

[0087] Table 2. Extraction efficiency of metals from sewage sludge incineration ash samples using deionized water.

[0088]

[0089] Example 6

[0090] Extraction of sewer sludge incineration ash samples was performed using a 0.6% wt. EDTA aqueous solution with a high liquid-to-solid ratio of 200 / 1 under 50W ultrasonic treatment. The sewer sludge incineration ash (SSIA) samples were first thoroughly dried, ground using a ball mill, and sieved to obtain a powder sample smaller than 125 micrometers. One gram of the SSIA powder sample was added to 200 mL of 0.6% wt. EDTA aqueous solution, stirred with 50W ultrasonic power for 1 hour, and then centrifuged. The supernatant was analyzed by ICP-AES to calculate the extracted metal element amounts, and the results are listed in Table 3. Table 3 clearly shows that, under ultrasonic treatment, a high liquid-to-solid ratio dilute EDTA solution can rapidly extract multiple heavy metals from sewer sludge incineration ash samples at room temperature (25℃). The extraction efficiency for arsenic, lead, molybdenum, copper, and manganese is high; the extraction efficiency for cobalt, vanadium, barium, zinc, and iron is moderate; and the extraction efficiency for chromium, silver, antimony, and nickel is very poor.

[0091] Table 3 shows the extraction efficiency of 0.6% wt. EDTA aqueous solution with a high liquid-to-solid ratio of 200 / 1 for 1 hour under 50W ultrasonic treatment on sewage sludge incineration ash samples.

[0092]

[0093] Example 7

[0094] Similar to Example 6, but with magnetic stirring at 300 rpm. One gram of sewer sludge incineration ash sample was added to 200 mL of 0.6% wt. EDTA aqueous solution, and the mixture was magnetically stirred at 300 rpm for 1 hour, followed by centrifugation. The supernatant was analyzed by ICP-AES, and the extracted metal elements were calculated. The results are listed in Table 4. Table 4 shows that under magnetic stirring at 300 rpm, a high liquid-to-solid ratio dilute EDTA solution can rapidly extract multiple heavy metals from sewer sludge incineration ash samples at room temperature (25°C). The extraction efficiency for arsenic and manganese is relatively high, while the extraction efficiency for cobalt, lead, molybdenum, copper, vanadium, barium, and iron is moderate. The extraction efficiency for zinc, chromium, silver, nickel, and tin is very poor. Compared with ultrasonic stirring (Example 6), magnetic stirring reduces the extraction efficiency for lead, molybdenum, copper, and zinc.

[0095] Table 4 shows the extraction efficiency of 0.6% wt. EDTA aqueous solution with a high liquid-to-solid ratio of 200 / 1 for 1 hour on sewage sludge incineration ash samples under magnetic stirring at 300 rpm.

[0096]

[0097] Example 8

[0098] Similar to Example 7, but using a high-concentration EDTA aqueous solution of 6% wt. One gram of sewage sludge incineration ash sample was added to 200 mL of 6% wt. EDTA aqueous solution, and the mixture was magnetically stirred at 300 rpm for 1 hour, followed by centrifugation. The supernatant was analyzed by ICP-AES, and the extracted metal elements were calculated. The results are listed in Table 5. Table 5 shows that, under magnetic stirring at 300 rpm, the high-concentration EDTA solution with a high liquid-to-solid ratio can rapidly extract various heavy metals from sewage sludge incineration ash samples at room temperature (25°C). The extraction efficiency for arsenic and manganese is relatively high, for cobalt, lead, molybdenum, vanadium, and barium it is moderate, and for zinc, copper, iron, chromium, silver, antimony, and tin it is very poor. Compared with the extraction efficiency of low-concentration EDTA (Example 7), the extraction efficiency of high-concentration EDTA did not increase; in fact, the extraction efficiency for nickel, copper, and iron decreased!

[0099] Table 5 shows the extraction efficiency of 6% wt. high-concentration EDTA aqueous solution with a high solid-liquid ratio of 200 / 1 for 1 hour on sewage sludge incineration ash samples under magnetic stirring at 300 rpm.

[0100]

[0101]

[0102] Example 9

[0103] Similar to Example 8, but with a smaller amount of extractant, 20 mL. The experimental results are listed in Table 6. Table 6 shows that, under magnetic stirring at 300 rpm, a high-concentration EDTA solution with a low liquid-to-solid ratio can rapidly extract multiple heavy metals from sewage sludge incineration ash samples at room temperature (25°C). It exhibits high extraction efficiency for arsenic, moderate efficiency for manganese and vanadium, and very poor efficiency for zinc, cobalt, lead, molybdenum, copper, iron, chromium, barium, silver, nickel, and tin. Compared to the high liquid-to-solid ratio EDTA extraction efficiency (Example 8), the low liquid-to-solid ratio EDTA extraction efficiency decreases for barium, lead, manganese, molybdenum, zinc, and iron, but improves for copper and nickel.

[0104] Table 6 shows the extraction efficiency of a 6% wt. high-concentration EDTA aqueous solution with a low solid-liquid ratio of 20 / 1 for 1 hour using a magnetically stirred solution at 300 rpm for extraction of sewage sludge incineration ash samples.

[0105]

[0106] Example 10

[0107] Similar to Example 9, but with ultrasonic stirring at 50 watts. The experimental results are listed in Table 7. Table 7 shows that under ultrasonic stirring, the high-concentration EDTA solution with a low liquid-to-solid ratio can rapidly extract various heavy metals from sewage sludge incineration ash samples at room temperature (25°C). It exhibits high extraction efficiency for arsenic and manganese, moderate efficiency for barium, lead, molybdenum, copper, iron, and vanadium, and very poor efficiency for zinc, cobalt, silver, nickel, tin, and chromium. Compared to the EDTA extraction efficiency with magnetic stirring at 300 rpm (Example 9), ultrasonically stirred EDTA shows improved extraction efficiency for barium, lead, manganese, molybdenum, copper, iron, zinc, and nickel. Compared to the low-concentration EDTA solution with a high solid-to-liquid ratio in Example 6, the high-concentration EDTA solution with a low liquid-to-solid ratio in this example shows reduced extraction efficiency for barium, lead, manganese, molybdenum, copper, and zinc.

[0108] Table 7 shows the extraction efficiency of a 6% wt. high-concentration EDTA aqueous solution with a low solid-liquid ratio of 20 / 1 for 1 hour using ultrasonic stirring at 50 watts.

[0109]

[0110] Example 11

[0111] Under similar conditions to Example 6, but with the addition of 3% ammonium chloride to the extract, the extraction efficiency of iron increased from 12.2% to 14.7%, with little effect on the extraction efficiency of the other metals.

[0112] Example 12

[0113] Dry samples (less than 125 micrometers) of sewage sludge incineration ash were extracted with a 6% wt. high-concentration EDTA aqueous solution at a low liquid-to-solid ratio of 15 / 1 without mechanical stirring. Sample 1 was added to 15 mL of the 6% wt. EDTA aqueous solution, heated at 160 °C for 2 hours, and then centrifuged. The supernatant was analyzed by ICP-AES, and the extracted metal elements were calculated. The results are listed in Table 8. Table 8 shows that the high-concentration EDTA solution with a low liquid-to-solid ratio can rapidly extract multiple heavy metals from sewage sludge incineration ash samples at a relatively high temperature (160 °C). The extraction efficiency for iron and copper was high (28.8% and 26.5%, respectively), the extraction efficiency for zinc and nickel was moderate (12.7% and 14.2%, respectively), and the extraction efficiency for chromium was very poor (7.4%). Figure 2It has been shown that the mobile fractions of iron, copper, zinc, nickel, and chromium in dried sewage sludge incineration ash samples are 10%, 18%, 10%, 11%, and 1.5%, respectively. This means that the extraction rate of the mobile fraction determined by the low liquid-to-solid ratio, high-concentration EDTA solution at a higher temperature (160℃) for 2 hours is higher than that determined by the accepted standard BCR sequential extraction method (16 hours). This implies that extraction with a low liquid-to-solid ratio, high-concentration EDTA solution at a higher temperature (160℃) for 2 hours can completely extract the mobile fractions of heavy metals, achieving the purpose of cleaning. The immobile fractions of heavy metals, due to their immobility, are not easily leaked into the environment and pose little threat to the environment.

[0114] Table 8 shows the extraction efficiency of a 6% wt. high-concentration EDTA aqueous solution with a low liquid-to-solid ratio of 15 / 1 for 2 hours on dried sewage sludge incineration ash samples without mechanical stirring.

[0115]

[0116] Example 13

[0117] Extraction of dried CPZ E-Sludge (smaller than 125 micrometers) from electronic factory wastewater filter residue was performed using a 6% wt. high-concentration EDTA aqueous solution with a low liquid-to-solid ratio of 15 / 1 without mechanical stirring. 10 g of sample was added to 150 mL of 6% wt. EDTA aqueous solution, and the reaction was carried out at 160 °C for 2 hours, followed by centrifugation. The supernatant was analyzed by ICP-AES, and the extracted metal element amounts were calculated. The results are listed in Table 9. Table 9 shows that the high-concentration EDTA solution with a low liquid-to-solid ratio can rapidly extract multiple heavy metals from the dried electronic factory wastewater filter residue at a relatively high temperature (160 °C). The extraction efficiency for zinc, lead, and copper reached 100%, while the extraction efficiencies for manganese, cobalt, nickel, chromium, and iron were relatively high, at 73.2%, 78.3%, 48.4%, 46.7%, and 44.7%, respectively. The extraction efficiency for vanadium was moderate at 28.5%, while the extraction efficiency for antimony, molybdenum, and silver was very poor (0%). However, their dry concentrations in the original sample were extremely low: vanadium 56 mg / kg, antimony 8 mg / kg, molybdenum 2 mg / kg, and silver 16 mg / kg, respectively. The concentrations of antimony, molybdenum, and silver were so low that they could be considered negligible. Figure 3Studies have shown that the mobile fractions of zinc, lead, and copper in dried samples of wastewater filter residue from electronics factories are 82%, 68%, and 87%, respectively, while the mobile fractions of manganese, cobalt, nickel, chromium, and iron are 72%, 37%, 37%, 42%, and 48%, respectively. This means that the extraction rates of major heavy metals zinc, lead, copper, manganese, cobalt, nickel, chromium, and iron using a high-concentration EDTA solution with a low liquid-to-solid ratio at a higher temperature (160°C) for 2 hours are higher than those measured by the accepted standard BCR sequential extraction method (16 hours). This implies that extraction with a high-concentration EDTA solution with a low liquid-to-solid ratio at a higher temperature (160°C) for 2 hours can completely extract the mobile fractions of major heavy metals, achieving the purpose of cleaning. The immobile fractions of heavy metals, due to their immobility, are unlikely to leak into the environment and pose little threat to environmental protection.

[0118] Table 9 shows the extraction efficiency of a dried sample of wastewater filter residue from an electronics factory extracted with a 6% wt. high-concentration EDTA aqueous solution (liquid-solid ratio 15 / 1) for 2 hours without mechanical stirring.

[0119]

[0120]

[0121] Example 14

[0122] Dry samples of municipal solid waste incineration bottom ash (particle size less than 125 μm) were extracted using a 0.6% wt. EDTA aqueous solution with a high liquid-to-solid ratio of 200 / 1 under mechanical stirring at 300 rpm. One gram of sample was added to 200 mL of 0.6% wt. EDTA aqueous solution, and the reaction was carried out for 1 hour under mechanical stirring at 300 rpm, followed by centrifugation. The supernatant was analyzed by ICP-AES, and the extracted metal elements were calculated. The results are listed in Table 10. Table 10 clearly shows that, under mechanical stirring at 300 rpm, the high liquid-to-solid ratio dilute EDTA solution can rapidly extract multiple heavy metals from the dry samples of municipal solid waste incineration bottom ash at room temperature (25 °C). The extraction efficiency for copper, lead, and zinc was relatively high, at 47.0%, 46.2%, and 62.4%, respectively; the extraction efficiency for manganese and barium was moderate; and the extraction efficiency for iron, cadmium, chromium, cobalt, nickel, vanadium, molybdenum, and tin was very poor.

[0123] Table 10 shows the extraction efficiency of a 0.6% wt. EDTA aqueous solution with a high liquid-to-solid ratio of 200 / 1 for 1 hour from dried municipal solid waste incineration bottom ash under mechanical stirring at 300 rpm.

[0124]

[0125]

[0126] Example 15

[0127] Similar to Example 14, but using a low liquid-to-solid ratio of 20 / 1 and a high concentration of 6% wt. EDTA. One gram of dried municipal solid waste incineration ash sample (particle size less than 125 micrometers) was added to 20 mL of a 6% wt. high concentration EDTA aqueous solution. The mixture was reacted for 1 hour with mechanical stirring at 300 rpm, followed by centrifugation. The supernatant was analyzed by ICP-AES, and the extracted metal elements were calculated. The results are listed in Table 11. Table 11 clearly shows that, under mechanical stirring at 300 rpm, the low liquid-to-solid ratio high concentration EDTA solution can rapidly extract multiple heavy metals from dried municipal solid waste incineration ash samples at room temperature (25°C). The extraction efficiencies for manganese, lead, cadmium, and zinc are relatively high, at 31.9%, 64.0%, 50.0%, and 70.8%, respectively. The extraction efficiencies for copper, cobalt, and nickel are moderate, while the extraction efficiencies for iron, barium, chromium, vanadium, molybdenum, and tin are very poor.

[0128] Table 11 shows the extraction efficiency of a 6% wt. high-concentration EDTA aqueous solution with a low liquid-to-solid ratio of 20 / 1 for 1 hour using a mechanically stirred sample at 300 rpm.

[0129]

[0130] Example 16

[0131] Similar conditions to Example 14, but with a reaction time of 3 hours. 1 gram of dried municipal solid waste incineration ash sample (particle size less than 125 micrometers) was added to 200 mL of 0.6% wt. EDTA aqueous solution, and reacted for 3 hours with mechanical stirring at 300 rpm, followed by centrifugation.

[0132] The supernatant was analyzed by ICP-AES, and the amount of extracted metal elements was calculated. The results are listed in Table 12. Table 12 clearly shows that, under mechanical stirring at 300 rpm, a high liquid-to-solid ratio dilute EDTA solution can rapidly extract multiple heavy metals from dried municipal solid waste incineration ash samples at room temperature (25°C). The extraction efficiencies for copper, lead, manganese, and zinc are relatively high, at 42.3%, 63.8%, 39.5%, and 76.6%, respectively, while the extraction efficiency for iron is moderate.

[0133] Table 12 shows the extraction efficiency of a 0.6% wt. EDTA aqueous solution with a high liquid-to-solid ratio of 200 / 1 for 3 hours on a mechanically stirred sample at 300 rpm.

[0134]

[0135] Example 17

[0136] Under similar conditions to Example 15, but with a reaction time of 3 hours, 1 gram of dried municipal solid waste incineration bottom ash sample (particle size less than 125 micrometers) was added to 20 mL of 6% wt. high-concentration EDTA aqueous solution. The mixture was reacted for 3 hours with mechanical stirring at 300 rpm, followed by centrifugation. The supernatant was analyzed by ICP-AES, and the extracted metal elements were calculated. The results are listed in Table 13. Table 13 clearly shows that, under mechanical stirring at 300 rpm, the high-concentration EDTA solution with a low liquid-to-solid ratio can rapidly extract multiple heavy metals from the dried municipal solid waste incineration bottom ash sample at room temperature (25°C). The extraction efficiency for manganese, lead, and zinc was relatively high, at 43.8%, 68.9%, and 86.5%, respectively. The extraction efficiency for copper was moderate (22.3%), and the extraction efficiency for iron was poor (7.8%).

[0137] Table 13 shows the extraction efficiency of a 6% wt. high-concentration EDTA aqueous solution with a low liquid-to-solid ratio of 20 / 1 for 3 hours using a mechanically stirred solution at 300 rpm.

[0138]

[0139] Example 18

[0140] Dry samples of municipal solid waste incineration bottom ash (particle size less than 125 μm) were extracted using a 0.6% wt. EDTA aqueous solution with a high liquid-to-solid ratio of 200 / 1 under mechanical stirring at 300 rpm. One gram of sample was added to 200 mL of 0.6% wt. EDTA aqueous solution, and the reaction was carried out for 8 hours under mechanical stirring at 300 rpm, followed by centrifugation. The supernatant was analyzed by ICP-AES, and the extracted metal elements were calculated. The results are listed in Table 14. Table 14 clearly shows that, under mechanical stirring at 300 rpm, a low concentration of 0.6% wt. EDTA aqueous solution with a high liquid-to-solid ratio can extract multiple heavy metals from the dry samples of municipal solid waste incineration bottom ash within 8 hours at room temperature (25°C). The extraction efficiency for lead, zinc, cadmium, and manganese was relatively high, at 59.7%, 49.4%, 71.0%, and 55.5%, respectively. The extraction efficiency for vanadium, nickel, cobalt, molybdenum, copper, and barium was moderate, while the extraction efficiency for iron, chromium, and tin was poor.

[0141] Table 14 shows the extraction efficiency of a low-concentration 0.6% wt. EDTA aqueous solution with a high liquid-to-solid ratio of 200 / 1 for 8 hours on a mechanically stirred sample at 300 rpm.

[0142]

[0143] Example 19

[0144] Similar to Example 18, but the extraction solvent was changed to a 0.5% wt. EDTA + 0.1% wt. sodium persulfate aqueous solution. Extraction was performed on dried samples (particle size less than 125 micrometers) of municipal solid waste incineration bottom ash. 1 gram of sample was added to 200 mL of a 0.5% wt. EDTA + 0.1% wt. sodium persulfate aqueous solution, and the reaction was carried out for 8 hours with mechanical stirring at 300 rpm, followed by centrifugation. The supernatant was analyzed by ICP-AES, and the amount of extracted metal elements was calculated. The results are listed in Table 15. Table 15 clearly shows that, under mechanical stirring at 300 rpm, a low-concentration aqueous solution of 0.5% wt. EDTA + 0.1% wt. sodium persulfate with a high liquid-to-solid ratio can extract multiple heavy metals from dried samples of municipal solid waste incineration bottom ash within 8 hours at room temperature (25°C). The extraction efficiencies for copper, lead, zinc, cadmium, manganese, and cobalt are relatively high, with extraction efficiencies of 64.4%, 66.8%, 78.3%, 71.4%, 46.0%, and 50.4%, respectively. The extraction efficiencies for vanadium, molybdenum, nickel, and barium are moderate, while the extraction efficiencies for iron, chromium, and tin are very poor.

[0145] Table 15 shows the extraction efficiency of a low-concentration (0.5% wt. EDTA + 0.1% wt. sodium persulfate) aqueous solution with a high liquid-to-solid ratio of 200 / 1 for 8 hours on a mechanically stirred sample at 300 rpm.

[0146]

[0147] Example 20

[0148] Comparing Examples 18 and 19, as shown in Table 16, the extraction effect of 0.5% wt. EDTA + 0.1% wt. sodium persulfate aqueous solution is better than that of 0.6% wt. EDTA alone. The extraction rates of copper, zinc, and cobalt are significantly improved, increasing by 3.7 times, 1.6 times, and 1.8 times, respectively. The extraction rates of lead, cadmium, nickel, vanadium, and molybdenum are also improved. Sodium persulfate has strong oxidizing properties and can oxidize low-valence metals and organic matter. Combined with chelating agents, it allows the oxidizable (immobile) portion of heavy metals to be extracted. In other words, 0.5% wt. EDTA + 0.1% wt. sodium persulfate aqueous solution can extract heavy metals from the ion-exchangeable, reducible (collectively referred to as the mobile portion), and oxidizable (immobile) portions. However, 0.5% wt. EDTA alone can only extract heavy metals from the ion-exchangeable and reducible portions (collectively referred to as the mobile portion). Therefore, under these extraction conditions, the extraction effect of 0.5% wt. EDTA + 0.1% wt. sodium persulfate aqueous solution is better than that of 0.6% wt. EDTA alone. (Referring to Example 19 and...) Figure 4 Comparing the BCR sequential extraction results, it's easy to see that the extraction efficiency of most heavy metals in Example 19 is higher than that in Example 19. Figure 4 The content of movable components is high. For example, the extraction efficiencies of copper, lead, zinc, manganese, cobalt, and nickel in Example 19 were 64.4%, 66.8%, 78.3%, 46.0%, 50.4%, and 23.2%, respectively, which are far higher than those in other samples. Figure 4 The BCR sequential extraction results revealed that the total mobile fractions of copper, lead, zinc, manganese, cobalt, and nickel were 30%, 17%, 43%, 26%, 10%, and 5%, respectively. This further demonstrates that the strong oxidant sodium persulfate can oxidize low-valence metals and organic matter. Combined with chelating agents, it allows the oxidizable fractions (immobile fractions) of heavy metals to be extracted, significantly enhancing the extraction efficiency of the main extractant and chelating agent, making it a highly effective auxiliary extractant.

[0149] Table 16 compares the extraction efficiency of two low-concentration extraction solutions (0.6% wt. EDTA aqueous solution or 0.5% wt. EDTA + 0.1% wt. sodium persulfate aqueous solution) for 8 hours on dried samples of municipal solid waste incineration bottom ash under mechanical stirring at 300 rpm and a high liquid-to-solid ratio of 200 / 1.

[0150]

[0151] Example 21

[0152] Similar to Example 18, but using a high-concentration 6% wt. EDTA aqueous solution with a low liquid-to-solid ratio of 20 / 1, extraction was performed on dried samples of municipal solid waste incineration bottom ash (particle size less than 125 micrometers). 1 gram of sample was added to 20 mL of 6% wt. EDTA aqueous solution, and the reaction was carried out for 8 hours with mechanical stirring at 300 rpm, followed by centrifugation. The supernatant was analyzed by ICP-AES, and the extracted metal elements were calculated. The results are listed in Table 17. Table 17 clearly shows that, under mechanical stirring at 300 rpm, a high-concentration 0.6% wt. EDTA aqueous solution with a low liquid-to-solid ratio can extract multiple heavy metals from dried municipal solid waste incineration bottom ash samples within 8 hours at room temperature (25°C). The extraction efficiency for copper, lead, zinc, cadmium, and manganese was high, at 68.6%, 72.7%, 88.9%, 71.3%, and 53.6%, respectively. The extraction efficiency for iron, vanadium, nickel, and molybdenum was moderate, while the extraction efficiency for barium, chromium, cobalt, and tin was poor. The extraction effect was better than in Example 18. This indicates that the extraction effect of a low liquid-to-solid ratio, high-concentration extractant is not worse than that of a high liquid-to-solid ratio, low-concentration extractant. When the solid content is very large, a low liquid-to-solid ratio requires less space and has considerable application advantages.

[0153] Table 17 shows the extraction efficiency of a high-concentration 6% wt. EDTA aqueous solution with a low liquid-to-solid ratio of 20 / 1 for 8 hours on a mechanically stirred sample at 300 rpm.

[0154]

[0155] Example 22

[0156] Similar to Example 12, but three identical samples were extracted sequentially using one extraction buffer. The amount of extraction buffer and sample was 100 times that of Example 12. The pH of the extraction buffer was 3.2. The concentration of heavy metal ions in the extraction buffer increased cumulatively, and the results are listed in Table 18. The extraction buffer contained phosphate, iron, aluminum, silicon, zinc, copper, chromium, and lead.

[0157] Table 18 shows the heavy metal concentrations in the final extracts of three identical dried sewage sludge incineration ash samples extracted sequentially with a 6% wt. high-concentration EDTA aqueous solution (low liquid-to-solid ratio 15 / 1) for 2 hours each time, without mechanical stirring.

[0158]

[0159] Example 23

[0160] Take 10 mL of the final extract from Example 22, pH 3.2. Six parallel control experiments were conducted. Sulfuric acid was added to adjust the pH to 1.65, 1.38, 1.12, 0.94, 0.76, and 0.70, respectively. Figure 5 As shown, the extract is brown to light brown in pH 3.2 to 1.65, and pink to light purple in pH below 0.94.

[0161] Example 24

[0162] The pH-adjusted extract from Example 23 was placed in a -20°C quick-freezing oven, and it quickly froze into an ice-like solid after 30-60 minutes. Figure 6 As shown, EDTA precipitates during the quick-freezing process, while heavy metals do not. At room temperature, EDTA takes about one day to begin precipitating and approximately five days to complete the precipitation process. The quick-freezing process significantly accelerates the precipitation of EDTA. Compared to room temperature precipitation, the precipitation rate is approximately 120 times faster.

[0163] Example 25

[0164] The quick-frozen extract from Example 24 was removed from the freezer and left at room temperature for approximately 30 minutes, allowing it to slowly thaw and become liquid. The precipitated EDTA was then visible at the bottom. After centrifugation, the precipitated EDTA appeared as shown in the image. Figure 7 As shown, the amount of EDTA precipitated is related to pH. At pH values ​​of 0.70, 0.76, and 0.94, the amount of EDTA precipitated is essentially the same. At pH 1.12, the amount of EDTA precipitated is significantly less than at pH values ​​of 0.70, 0.76, and 0.94.

[0165] Example 26

[0166] After rapidly freezing the extract at pH 0.76 from Example 25 to precipitate EDTA, centrifugation yielded a white solid EDTA precipitate and supernatant. The white solid EDTA precipitate, after drying, weighed 0.59 g, with a yield of 98.3%. Its SEM morphology is shown below. Figure 8 As shown. In Figure 8 An EDS spectral scan was performed at position 008 to obtain... Figure 9 The energy dispersive spectroscopy (EDS) showed a carbon peak of 68.0%, an oxygen peak of 31.2%, and a phosphorus peak of 0.8%. The EDS spectrum indicated that the precipitated white EDTA was 99.2% pure, containing a small amount of phosphate, which did not affect its reuse and could be recovered for continued use in the next cycle.

[0167] Example 27

[0168] Comparing 10 mL of the EDTA-removed supernatant from Example 26 (pH 0.76, sample #1) with 10 mL of the final extract from Example 22 (pH 3.2, sample #2) without EDTA removal, the pH was adjusted to precipitate and separate the heavy metals. First, the pH of sample #1 was adjusted to 3.2, producing a small amount of slightly yellowish precipitate (precipitate #1), which was then separated by centrifugation. The separated precipitates are shown below. Figure 10 As shown. The pH of the supernatant was further adjusted to 6.0, producing a large amount of light blue precipitate (precipitate #2), which was separated by centrifugation. The pH of the supernatant was further adjusted to 9.8, producing a small amount of yellowish-white precipitate (precipitate #3), which was separated by centrifugation. The pH of the supernatant was further adjusted to 12.5, producing a very small amount of reddish-brown precipitate (precipitate #4), which was separated by centrifugation. The pH of the supernatant was further adjusted to 13.8, and no precipitate was produced.

[0169] Control experiment. The pH of sample #2 was increased to 6.0, and no precipitation was observed. The pH was further increased to 9.8, resulting in a small amount of brown precipitate (precipitate #5), which was separated by centrifugation. The pH of the supernatant was further increased to 12.5, resulting in a large amount of brown precipitate (precipitate #6), which was separated by centrifugation. The pH of the supernatant was further increased to 13.8, and no precipitation was formed.

[0170] After EDS and ICP-MS identification, precipitate #1 was high-purity ferric phosphate; precipitate #2 contained aluminum hydroxide, nickel hydroxide, copper hydroxide and zinc hydroxide, which need to be further separated; precipitate #3 was mainly lead chromate; precipitate #4 was ferric hydroxide; precipitate #5 was mainly ferric hydroxide; precipitate #6 was mainly ferric hydroxide.

[0171] This clearly demonstrates that in sample #1, after removing EDTA from the sewer sludge incineration ash extract through acidification, quick-freeze-thaw, and centrifugation, heavy metals can be precipitated sequentially with high purity by controlling and adjusting the pH value. Only a few precipitates are co-precipitates, such as precipitate #2 in this example, requiring further separation. As a control, in sample #2, where EDTA was not removed, it was extremely difficult to precipitate heavy metals from the chelates between EDTA and heavy metals; most heavy metals remained stubbornly in the extract and could not be separated. Even if a large amount of alkali were used to precipitate them, separating so many co-precipitates of heavy metals would be very time-consuming and laborious. Even using electrochemical electroplating methods, with the presence of EDTA, electroplating heavy metals from the chelates between EDTA and heavy metals would be very difficult.

[0172] Example 28

[0173] In Example 13, the EDTA extract of the sludge filter residue from the electronics factory was blue, with a pH of 6.21, and contained 3350 ppm Cu, 466.7 ppm Ni, 167.8 ppm Zn and 103.3 ppm Fe. The total amount of other heavy metals, chromium, cobalt, lead, manganese, vanadium and tin, was 11.8 ppm, which can be ignored.

[0174] like Figure 11 As shown, 10 ml of the extract was taken and the pH was adjusted to 0.84 by acidification. It was then placed in a -20°C freezer for 30-60 minutes to precipitate EDTA. After solidification, it was removed and allowed to thaw naturally at room temperature for 30 minutes, resulting in precipitated EDTA settling at the bottom. Centrifugation was used to separate the EDTA. After washing and drying, EDS spectroscopy confirmed it to be high-purity EDTA, free of heavy metals. At room temperature, EDTA would begin to precipitate slowly after one day and complete precipitation in approximately five days. The quick-freezing process significantly accelerated EDTA precipitation. Compared to room-temperature precipitation, quick-freezing increased the precipitation rate by approximately 120 times.

[0175] Example 29

[0176] Comparing 10 mL of the EDTA-removed supernatant (pH 0.84, sample #3) from Example 28 with EDTA removal and 10 mL of the final extract (pH 6.21, sample #4) from Example 13 without EDTA removal, the pH was adjusted to precipitate and separate the heavy metals. First, the pH of sample #3 was adjusted to 4.33, resulting in a large amount of blue precipitate (precipitate #7), which was then separated by centrifugation. The separated precipitates are shown below. Figure 12As shown. The pH of the supernatant was further adjusted to 5.24, producing a large amount of blue precipitate (precipitate #8), which was separated by centrifugation. The pH of the supernatant was further adjusted to 8.65, producing a moderate amount of brownish-blue precipitate (precipitate #9), which was separated by centrifugation. The pH of the supernatant was further adjusted to 11.34, producing a moderate amount of blue precipitate (precipitate #10), which was separated by centrifugation. The pH of the supernatant was further adjusted to 12.38, producing a very small amount of blue precipitate (precipitate #11), which was separated by centrifugation. The pH of the supernatant was further adjusted to 13.3, and no precipitate was produced.

[0177] Control experiment. The pH of sample #4 was adjusted to 8.67, producing a moderate amount of brownish-blue precipitate (precipitate #12), which was separated by centrifugation. The pH of its supernatant was further adjusted to 12.35, producing a small amount of brown precipitate (precipitate #13), which was separated by centrifugation. The pH of its supernatant was further adjusted to 13.3, with no precipitate forming.

[0178] After EDS and ICP-MS identification, precipitates #7, #8 and #11 were high-purity copper hydroxide; precipitate #9 mainly contained iron hydroxide, zinc hydroxide and nickel hydroxide, and needed further separation; precipitate #10 mainly contained nickel hydroxide; precipitate #12 contained iron hydroxide and nickel hydroxide; precipitate #13 mainly contained iron hydroxide.

[0179] This clearly demonstrates that in sample #3, after removing EDTA from the extract of wastewater filter residue from the electronics factory through acidification, quick-freezing, thawing, and centrifugation, the heavy metals can be precipitated sequentially with high purity by controlling and adjusting the pH value. Only a few precipitates are co-precipitates, such as precipitate #9 in this example, which require further separation. As a control, in sample #4, where EDTA was not removed, it was extremely difficult to precipitate heavy metals from the chelates between EDTA and heavy metals. The most abundant heavy metal, copper, did not precipitate at all; only a small amount of iron and nickel precipitated, while most of the heavy metals remained stubbornly in the extract and could not be separated. Even if a large amount of alkali were used to precipitate them, separating so many co-precipitates of heavy metals would be extremely time-consuming and laborious. Even using electrochemical electroplating methods, with the presence of EDTA, electroplating heavy metals from the chelates between EDTA and heavy metals would be very difficult.

[0180] In summary, the process of this invention provides a feasible solution to the problems of extracting heavy metals from non-combustible solid waste contaminated with heavy metals, and even more so, separating high-purity heavy metals and high-purity chelating agents from heavy metal chelates for recycling. This invention employs an innovative extraction agent composition using EDTA as the main extractant and sodium persulfate and ammonium chloride as auxiliary extractants. It performs aqueous phase extraction on sewage sludge incineration ash, electronic factory wastewater filter residue, and municipal solid waste incineration bottom ash. The extraction efficiency is higher than the sum of the exchangeable, reducible, and oxidizable fractions in the standard BCR extraction method, leaving only the heavy metal fraction that can be extracted by digestion in the final residue. This thoroughly cleans the heavy metal-contaminated solid waste, providing a fundamental justification for its further application rather than landfilling. The innovative method of rapid freezing and centrifugation separation of the main precipitant EDTA allows for very rapid and effective separation of the chelated chelating agent and heavy metals, and the recycling of the chelating agent. The high-purity heavy metals separated by sequential precipitation and co-precipitation are important industrial raw materials. The process of this invention consumes less acid and alkali, has lower cost, and has broad application prospects.

[0181] The present invention has been described in an illustrative rather than restrictive manner according to embodiments thereof. However, it should be understood that the scope of protection of the present invention is not limited thereto. Without departing from the relevant scope of protection defined by the claims, those skilled in the art can make changes and / or modifications. Any modifications, equivalent substitutions, etc., based on this should be covered within the scope of protection of the present invention.

Claims

1. A method for heavy metal extraction and recovery, characterized in that, Includes the following steps: S1, prepare an aqueous solution containing the main extractant EDTA, the auxiliary extractant sodium persulfate and ammonium chloride; S2, the aqueous solution is contacted with solid waste contaminated with heavy metals to extract the heavy metals from the solid waste, wherein the solid waste is selected from one or more of the following: sewage sludge incineration ash, wastewater filter residue from electronics factories, and bottom ash from municipal solid waste incineration; then solid-liquid separation is performed to obtain an extract containing heavy metals. S3, acidify the heavy metal-containing extract obtained in step S2 to pH 0.5-1.0, then quickly freeze it at -10℃ to -30℃, and then thaw it to precipitate the main extractant EDTA, while the heavy metals and the auxiliary extractant remain in the liquid phase. S4, perform solid-liquid separation on the system obtained in step S3, and recover the EDTA precipitate; S5, the liquid phase obtained in step S4 is subjected to sequential precipitation and / or co-precipitation separation to recover individual heavy metal compounds and obtain a recyclable auxiliary extract after heavy metal separation. S6. The EDTA recovered in step S4 is redissolved in the recyclable auxiliary extraction solution obtained in step S5, and the pH is adjusted to 3.2-4.0 to obtain a recyclable extraction solution.

2. The method according to claim 1, characterized in that, The pH used for extraction in step S2 is 3.2-4.

0.

3. The method according to claim 1 or 2, characterized in that, The quick-freezing process described in step S3 is carried out at -20°C for 30-60 minutes.

4. The method according to claim 1, characterized in that, When the solid waste is sewer sludge incineration ash, the liquid phase after EDTA removal in step S5 is sequentially subjected to precipitation separation by raising the pH to 3.2, 6.0, 9.8 and 12.5, in order to recover ferric phosphate, coprecipitate containing aluminum / nickel / copper / zinc, lead chromate and ferric hydroxide, respectively.

5. The method according to claim 4, characterized in that, The coprecipitate containing aluminum / nickel / copper / zinc is further separated by dissolution-reprecipitation: zinc is first dissolved using a pH 11-12 solution and zinc hydroxide is recovered at pH 9-10; The remaining components were dissolved in dilute acid, then potassium iodide and sodium thiosulfate were added and the pH was adjusted to 4.2 to recover cuprous iodide. Then dimethylglyoxime was added and the pH was adjusted to 4.6 to recover nickel dimethylglyoxime. Finally, the pH was adjusted to 7.5 to recover aluminum hydroxide.

6. The method according to claim 1, characterized in that, When the solid waste is filter residue from wastewater from an electronics factory, the liquid phase after EDTA removal in step S5 is sequentially subjected to precipitation separation by raising the pH to 4.33, 5.24, 8.65, 11.34 and 12.38 to recover copper hydroxide, copper hydroxide, coprecipitates containing iron / zinc / nickel, nickel hydroxide and copper hydroxide.

Images