Method for sequentially extracting forms of heavy metals in organic fertilizer

Abstract

The invention discloses a method for sequentially extracting forms of heavy metals in an organic fertilizer, which comprises the following steps: (1) mixing the organic fertilizer with a magnesium chloride solution, and separating to obtain a first filtrate and a first residue; (2) mixing and separating the first residue and an acetic acid-sodium acetate buffer solution to obtain a second filtrate and a second residue; (3) mixing and separating the second residue and a sodium pyrophosphate solution to obtain a third filtrate and a third residue; (4) mixing and separating the third residue and the hydrogen peroxide and nitric acid solution, and mixing and separating the obtained residue and an ammonium acetate solution to obtain a fourth filtrate and a fourth residue; (5) mixing and separating the fourth residue and a hydroxylamine hydrochloride solution to obtain a fifth filtrate and a fifth residue; (6) mixing the fifth residue with aqua regia, and filtering to obtain a sixth filtrate; (7) mixing the organic fertilizer with aqua regia, and filtering to obtain a seventh filtrate; and (8) detecting the contents of heavy metal elements in the first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate.

Description

Technical Field

[0001] The invention belongs to the field of heavy metal form analysis in organic fertilizers, and particularly relates to a method for sequentially extracting heavy metal forms in organic fertilizers. Background Art

[0002] As people become more aware of the hazards of heavy metals, the safety of heavy metals in organic fertilizers has received widespread attention. Detection methods based on total heavy metal concentrations tend to overestimate the potential risk of heavy metals, while the form of heavy metals can better characterize the environmental risk of heavy metals.

[0003] At present, the commonly used methods for the speciation analysis of heavy metals in organic fertilizers are the Tessier method, the BCR method, and corresponding improved methods. These traditional methods were originally extraction methods developed based on soil properties and have been widely applied to the analysis of heavy metals in organic fertilizers. The properties and components of organic fertilizers (see Table 1) are significantly different from those of soil. Soil is composed of approximately 90% minerals and 10% organic matter, with a high proportion of minerals. Organic manure is mainly formed by the mineralization or humification of organic matter from agricultural and sideline products such as livestock and poultry manure and straw. It has a low mineral content, while the organic matter content can be as high as 60%. For example, the organic matter content of composted livestock and poultry manure is usually 40%-60%, and can reach more than 60% after decomposition. The organic matter content of straw or kitchen waste fertilizers can exceed 70% after special treatment. The organic matter content of industrially produced organic fertilizers is mostly between 45% and 55%. Therefore, compared with soil, the probability of heavy metals in organic fertilizers combining with organic matter will be significantly increased. 80% of the organic matter in organic fertilizer is humus, among which humic acid has strong hydrophilicity and activity, and is the component in organic matter that is most easily precipitated and dissolved. Humic acid has cation exchange properties, complexing ability, colloidal properties, biological activity and other properties, and has a great influence on the activity of plants and soil microorganisms. If humic acid in organic fertilizer can be extracted and analyzed separately, it will greatly enrich the type information of organic matter in organic fertilizer. Therefore, it is necessary to add a humic acid extraction procedure for organic matter with high content and multiple types to obtain more information on the forms of heavy metals combined with organic matter.

[0004] Table 1 Technical index requirements for organic matter in common organic fertilizer standards

[0005]

[0006] At present, the heavy metal form analysis methods for organic fertilizers cannot effectively avoid the interference of organic matter on the reducible state, and there is a lack of information on the types of organic matter. It is necessary to conduct in-depth research on the form extraction and detection methods of heavy metals in organic fertilizers, and propose methods for heavy metal form analysis suitable for the properties of organic fertilizers, so as to provide basic support and scientific basis for the study of environmental risks of heavy metals in organic fertilizers. Summary of the Invention

[0007] The present invention aims to solve, at least to a certain extent, one of the technical problems in the related art. To this end, an object of the present invention is to provide a method for sequentially extracting heavy metal forms in organic fertilizers. The present invention effectively solves the problem of inaccurate distribution testing of heavy metal forms in organic fertilizers in existing traditional methods, improves the accuracy of the results of form analysis of heavy metals (As, Cd, Cr, Pb, Cu, Zn) in organic fertilizers, and provides a way to accurately assess the heavy metal risks of organic fertilizers.

[0008] The present invention proposes a method for sequentially extracting heavy metal forms from organic fertilizers. According to an embodiment of the present invention, the method comprises:

[0009] (1) Extraction of exchangeable heavy metals: mixing organic fertilizer with magnesium chloride solution and performing separation treatment to obtain a first filtrate and a first residue;

[0010] (2) Extraction of weakly acid-extractable heavy metals: mixing the first residue with an acetic acid-sodium acetate buffer solution and performing separation treatment to obtain a second filtrate and a second residue;

[0011] (3) Extraction of humic acid-bound heavy metals: the second residue is mixed with a sodium pyrophosphate solution and then separated to obtain a third filtrate and a third residue;

[0012] (4) Extraction of organically bound heavy metals: The third residue is mixed with hydrogen peroxide and nitric acid solution, and the residue obtained after separation is mixed with ammonium acetate solution and then separated to obtain a fourth filtrate and a fourth residue;

[0013] (5) Extraction of reducible heavy metals: mixing the fourth residue with a hydroxylamine hydrochloride solution and performing separation treatment to obtain a fifth filtrate and a fifth residue;

[0014] (6) Extraction of heavy metals from the residue: mixing the fifth residue with aqua regia and filtering the mixture to obtain a sixth filtrate;

[0015] (7) Full element extraction: the organic fertilizer is mixed with aqua regia and filtered to obtain a seventh filtrate;

[0016] (8) Detecting the heavy metal element content in the first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate respectively.

[0017] Thus, in the method of the present invention, the organically bound state is subdivided into humic acid-bound heavy metals and organically bound heavy metals, and organic matter that is easily oxidized and easily extracted by sodium pyrophosphate is called humic acid-bound heavy metals, and organic matter that is tightly bound to heavy metals and difficult to extract is called organically bound heavy metals. The organic matter components with a higher proportion are classified and different extraction procedures are adopted to maximize the extraction efficiency of the organic matter. At the same time, the extraction of the organically bound heavy metals is performed first and then the extraction of the reducible heavy metals. During the extraction process of the organically bound heavy metals, the organic matter in the organically bound state can be fully extracted, and the iron minerals (iron oxides) will not be oxidized, which can avoid the interference of the extraction of the organically bound heavy metals with the extraction of the iron-manganese oxide heavy metal bound state, thereby ensuring the accuracy of the organically bound state determination.

[0018] In addition, the method for sequentially extracting heavy metal forms from organic fertilizer according to the above embodiment of the present invention may also have the following additional technical features:

[0019] In some embodiments of the present invention, in step (1), based on 1 g of the organic fertilizer, the amount of the magnesium chloride solution added is 20-30 mL.

[0020] In some embodiments of the present invention, the concentration of the magnesium chloride solution is 0.5-1.5 mol / L.

[0021] In some embodiments of the present invention, in step (2), based on 1 g of the organic fertilizer, the amount of the acetic acid-sodium acetate buffer solution added is 8-10 mL.

[0022] In some embodiments of the present invention, the pH of the acetic acid-sodium acetate buffer solution is 4.8-5.2.

[0023] In some embodiments of the present invention, in step (3), based on 1 g of the organic fertilizer, the amount of the sodium pyrophosphate solution added is 10-30 mL.

[0024] In some embodiments of the present invention, the concentration of the sodium pyrophosphate solution is 0.1-0.3 mol / L.

[0025] In some embodiments of the present invention, based on 1 g of the organic fertilizer, the amount of the nitric acid solution added is 2-6 mL, the amount of the hydrogen peroxide added is 7-13 mL, and the amount of the ammonium acetate solution added is 3-8 mL.

[0026] In some embodiments of the present invention, the concentration of the nitric acid solution is 0.01-0.05 mol / L, the mass concentration of the hydrogen peroxide is 20%-50%, and the concentration of the ammonium acetate solution is 3-3.5 mol / L.

[0027] In some embodiments of the present invention, in step (4), the hydrogen peroxide is added three times: the first addition amount of the hydrogen peroxide is 1-3 mL; the second addition amount of the hydrogen peroxide is 3-7 mL; and the third addition amount of the hydrogen peroxide is 3-7 mL.

[0028] In some embodiments of the present invention, in step (5), based on 1 g of the organic fertilizer, the amount of the hydroxylamine hydrochloride solution added is 10-20 mL.

[0029] In some embodiments of the present invention, the concentration of the hydroxylamine hydrochloride solution is 0.02-0.06 mol / L.

[0030] In some embodiments of the present invention, in step (6), the fifth residue is mixed with aqua regia and then heated on a hot plate for digestion treatment.

[0031] In some embodiments of the present invention, based on 0.1 g of the fifth residue, the amount of aqua regia added is 6-10 mL.

[0032] In some embodiments of the present invention, in step (6), the temperature of the digestion treatment is 160-190°C.

[0033] In some embodiments of the present invention, in step (7), the organic fertilizer is mixed with aqua regia and then heated on a hot plate for digestion treatment.

[0034] In some embodiments of the present invention, based on 0.1 g of the organic fertilizer, the amount of aqua regia added is 6-10 mL.

[0035] In some embodiments of the present invention, in step (7), the temperature of the digestion treatment is 160-190°C.

[0036] In some embodiments of the present invention, the first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate are filtered through filter membranes and then the heavy metal content therein is detected.

[0037] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0039] Figure 1 The present invention is a flow chart of a method for sequentially extracting heavy metal forms from organic fertilizer according to an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The embodiments of the present invention are described in detail below, which are intended to explain the present invention but are not to be construed as limiting the present invention.

[0041] The technical solution of this application was completed by the inventor based on the following findings:

[0042] Based on the properties of organic fertilizer derived from livestock and poultry manure, existing technology reclassifies heavy metal forms based on the classic Tessier method. This reclassification results in six forms: exchangeable, weakly acid-extractable, humic acid-bound, organically bound, reducible, and residual. Specifically, the exchangeable form is extracted using magnesium chloride; the weakly acid-extractable form is extracted using acetic acid-sodium acetate; the humic acid-bound form is extracted using sodium pyrophosphate; the strongly organically bound form is extracted using hydrogen peroxide; the reducible form is extracted using hydroxylamine hydrochloride; and the residual form is extracted using hydrochloric acid-nitric acid. X-ray diffraction (XRD) spectra of organic fertilizer extracted using the Tessier method for carbonate-bound and iron-manganese oxide-bound forms show that carbonates and iron-manganese oxides are not the primary components of the minerals bound to the heavy metals extracted using these two extraction methods. This is due to compositional differences between organic fertilizer and soil. Therefore, this method designates these two forms as weakly acid-extractable and reducible.

[0043] The inventors further discovered that while the classic sequential heavy metal extraction method often extracts a certain proportion of water-soluble organic matter in the initial extraction steps (e.g., water-soluble, exchangeable, and carbonate-bound forms), more stable, less hydrolyzable organic matter components are not only distributed in the organically bound form, but also in forms such as iron-manganese oxide-bound forms. Extraction conditions for the iron-manganese oxide-bound and reducible forms often use reducing agents such as NH2OH·HCl to extract reducible materials primarily composed of iron-manganese oxides. However, during experiments, the inventors discovered that extracts from the reducible form contain 9-35% organic matter, a significantly higher content than organic matter extracted from other forms (excluding the organically bound form). This may be related to the high organic content of organic fertilizers. Organic matter in organic fertilizers is of various types and is often tightly bound to iron and manganese oxides. Reducing agents (such as NH2OH·HCl) not only reduce metal oxides but also destroy the structure of organic matter, resulting in the reduction of oxidized functional groups (such as carboxyl and phenolic hydroxyl groups) in the organic matter, thereby increasing its hydrophilicity and making it easier to enter the solution. In addition, the acidic reagents used in the extraction process promote the dissolution of organic matter in a reducing environment. Therefore, the reducible extraction procedure will precipitate a large amount of organic matter, reducing the subsequent extraction of organic matter in the bound state and increasing the test error.

[0044] To improve the accuracy of existing classical heavy metal speciation analysis methods, the inventors previously conducted accuracy verification tests using the Tessier method, finding that the iron-manganese oxide-bound state interferes with the extraction of the organic-bound state. Specifically, according to a formula, the relative error in the determination of the iron-manganese oxide-bound state ranges from 13.6% to 49.63%. The relative error in the determination of the organic-bound state ranges from 0.45% to 26.3%. Numerous studies and verifications have shown that, without changing the classical extraction sequence of the iron-manganese oxide-bound state and the organic-bound state, when the concentration of the iron-manganese oxide-bound state extractant (0.04-0.10 mol / L) and the extraction time (5-10 hours) are varied, the extraction concentration of iron ions does not significantly increase, resulting in insignificant results in the optimized extraction of iron-manganese oxide. Furthermore, the acidic and high-temperature digestion conditions used in the extraction process dissolve organic matter (9.04-35.00%), making it impossible to completely eliminate the interference with subsequent organic-bound state extraction. In order to avoid premature extraction of organic matter, the inventors changed the traditional extraction order and adjusted the reducible state extraction process to before the organic bound state extraction process, which can effectively avoid the interference of the reducible state extraction conditions on the organic bound state.

[0045] At the same time, organic fertilizer has a high organic matter content. The traditional sequential extraction method for soil only has one type of organic matter form, which is not suitable for the analysis of heavy metals in organic fertilizer. After the inventor tried to subdivide the organic bound state into two types: humic acid bound state and organic bound state, the extraction efficiency of organic matter was improved. Further, the inventor conducted extraction efficiency analysis on numerous extractants such as potassium permanganate, sodium hypochlorite, and NaOH through multiple studies and verifications. It was found that compared with other alkaline extractants, sodium pyrophosphate is stable in nature and not easy to decompose. Humic acid can be extracted under mild conditions (usually pH=7 or slightly alkaline), which can reduce the damage or degradation of organic matter structure. It will not precipitate with the target heavy metals. The spiked recovery rate of the target heavy metal is between 99.89% and 121.67%. There is no interference problem in the determination of heavy metals. It is an excellent extractant for humic acid.

[0046] In view of this, the present invention proposes a method for sequentially extracting heavy metal forms in organic fertilizers. Figure 1 , the method comprising:

[0047] S100: Mix organic fertilizer and magnesium chloride solution and separate them

[0048] In certain embodiments, fertilizer (such as livestock and poultry manure excrement) is air-dried after grinding and sieving (such as 100 mesh sieves), then the fertilizer sample powder is weighed in centrifuge tube, magnesium chloride solution is added, and fully mixed. The centrifuge tube covered with a lid is put into a constant temperature air oscillator and vibrates, and temperature is 25 DEG C, and speed is 180r / min, continuous oscillation. After vibration terminates, it is placed in centrifuge centrifugation, and speed is 4000r / min, and the time is 10min, so that supernatant and solid are separated completely. After centrifugation terminates, supernatant is temporarily stored in 50mL volumetric flask a. 8mL ultrapure water is added in centrifugal rear solid, and being fully mixed, it is placed in centrifuge centrifugation, and after terminating, water washing liquid is poured in volumetric flask a again, and is settled to scale with ultrapure water, namely obtains the first filtrate, 4 DEG C of storages are to be analyzed. The solid after solid-liquid separation is the first residue, namely according to the ion exchange of magnesium chloride, extracts the heavy metal element that can be released by ion exchange, i.e., exchangeable heavy metal, thus completes the extraction of exchangeable heavy metal.

[0049] Furthermore, in the above mixing process, based on 1g of the organic fertilizer, the amount of the magnesium chloride solution added is 20-30mL; the mixing time of the magnesium chloride solution and the organic fertilizer is 8-16h; and the concentration of the magnesium chloride solution is 0.5-1.5mol / L.

[0050] S200: Mixing the first residue with an acetic acid-sodium acetate buffer solution and performing separation treatment

[0051] In certain embodiments, acetic acid-sodium acetate buffer solution (pH is 4.8-5.2, based on 1g of organic fertilizer, the addition amount of the acetic acid-sodium acetate buffer solution is 8-10mL) is added to the first residue and thoroughly mixed. The centrifuge tube with a lid is placed in a constant temperature air oscillator and vibrated, with a temperature of 25°C and a speed of 180r / min, for continuous oscillation for 5h. After oscillation terminates, it is placed in a centrifuge and centrifuged. After centrifugation terminates, the supernatant is temporarily stored in a 50mL volumetric flask b, 8mL of ultrapure water is added to the solid after centrifugation, and after being thoroughly mixed, it is placed in a centrifuge and centrifuged. After terminating, the washing liquid is poured into a volumetric flask b and is settled to the scale with ultrapure water, i.e., the second filtrate is obtained, and 4°C of storages are to be analyzed. The solid after solid-liquid separation is the second residue. Specifically, the weakly acid-extractable heavy metal extraction process is based on the acidity of the acetic acid-sodium acetate buffer solution, so that the metal substance forms a soluble salt, thereby realizing the extraction of the weakly acid-extractable heavy metal.

[0052] S300: Mix the second residue with the sodium pyrophosphate solution and perform separation treatment

[0053] In certain embodiments, it is sodium pyrophosphate solution (based on 1g of organic fertilizer, the addition amount of described sodium pyrophosphate solution is 10-30mL; The concentration of described sodium pyrophosphate solution is 0.1-0.3mol / L) that concentration is added to the second residue, thoroughly mix.The centrifuge tube with the lid is put into constant temperature air oscillator and vibrates, and temperature is 25 DEG C, and speed is 180r / min, and oscillation is continuous for 24h.After oscillation terminates, centrifuge is placed in centrifuge, after terminating, supernatant is temporarily stored in 50mL volumetric flask c, 8mL ultrapure water is added in the solid after centrifugation, after being thoroughly mixed, centrifuge is placed in centrifuge, after terminating, water washing liquid is poured in volumetric flask c and is settled to scale with ultrapure water, i.e. the third filtrate, 4 DEG C of storages are to be analyzed, and the solid after solid-liquid separation is the third residue. Specifically, humic acid binding state utilizes the characteristic that humic acid is soluble in alkali, and the heavy metal elements combined with the higher humus of this part activity are extracted with sodium pyrophosphate solution, and the extraction of humic acid binding state heavy metals can be realized.

[0054] S400: The third residue is mixed with hydrogen peroxide and nitric acid solution, and the separated residue is mixed with ammonium acetate solution and then separated.

[0055] In some embodiments, the residue obtained by mixing and separating the third residue with hydrogen peroxide and nitric acid solution is mixed with ammonium acetate solution and then separated to obtain a fourth filtrate and a fourth residue.

[0056] In some embodiments, based on 1g of the organic fertilizer, the amount of the nitric acid solution added is 2-6mL, the amount of the hydrogen peroxide added is 7-13mL, and the amount of the ammonium acetate solution added is 3-8mL; the concentration of the nitric acid solution is 0.01-0.05mol / L, the mass concentration of the hydrogen peroxide is 20-50%, and the concentration of the ammonium acetate solution is 3-3.5mol / L.

[0057] In some embodiments, the hydrogen peroxide is added in three times: the first addition amount of the hydrogen peroxide is 1-3 mL; the second addition amount of the hydrogen peroxide is 3-7 mL; and the third addition amount of the hydrogen peroxide is 3-7 mL.

[0058] As an example, add 1-3 mL of 0.01-0.05 mol / L nitric acid solution and 1-3 mL of hydrogen peroxide solution to the third residue. Be careful to add slowly and tighten the lid to avoid a violent reaction that could cause sample overflow. Let it sit for a while until the reaction subsides (sometimes at least 1 hour). Gently shake the centrifuge tube to break up any bubbles, then slowly add 3-7 mL of hydrogen peroxide solution. This can be added in multiple doses. Mix thoroughly and immediately tighten the lid. Let it sit until bubbling subsides. Gently shake the centrifuge tube to break up any bubbles, then place the opened centrifuge tube in a thermostatic water bath at 85°C for 2 hours, shaking the tube every 10 minutes to ensure adequate contact between the reagents and the sample. Then add 1-3 mL of nitric acid solution and 3-7 mL of hydrogen peroxide solution. Place the centrifuge tube in a thermostatic water bath at 85°C and wait until the liquid evaporates to approximately 0.5 mL. This is sufficient to prevent the liquid from flowing out when the tube is inverted. After cooling, add 3-8mL of ammonium acetate solution and 15mL of ultrapure water, and place the covered centrifuge tube in a constant temperature air oscillator for oscillation at a temperature of 25°C and a speed of 180r / min for continuous oscillation for 0.5h. After the oscillation is completed, place it in a centrifuge for centrifugation. After the completion, temporarily store the supernatant in a 50mL volumetric flask d, add 8mL of ultrapure water to the solid after centrifugation, mix thoroughly and place it in a centrifuge for centrifugation. After the completion, pour the water washing liquid into the volumetric flask d and make up to the scale with ultrapure water to obtain the fourth filtrate. Store at 4°C for analysis. The solid after solid-liquid separation is the fourth residue. Specifically, the oxidation effect of nitric acid and hydrogen peroxide can be used to oxidize organic matter that is difficult to decompose for a long time, thereby realizing the extraction of organically bound heavy metals.

[0059] S500: Mix the fourth residue with the hydroxylamine hydrochloride solution and then separate it

[0060] In some embodiments, the hydroxylamine hydrochloride solution added to the fourth residue (based on 1g of the organic fertilizer, the amount of the hydroxylamine hydrochloride solution added is 10-20mL; the concentration of the hydroxylamine hydrochloride solution is 0.02-0.06mol / L) is thoroughly mixed. The covered centrifuge tube is placed in a constant temperature water bath for 6 hours at 96°C. Note that the lid needs to be loose so that the gas can escape to avoid the centrifuge tube from bursting due to excessive pressure. Shake the centrifuge tube every 30 minutes to ensure that the reagent is in full contact with the sample. Cool to room temperature after the water bath ends. Place in a centrifuge for centrifugation. After the end, temporarily store the supernatant in a 50mL volumetric flask e, add 8mL of ultrapure water to the solid after centrifugation, mix thoroughly and place in a centrifuge for centrifugation. After the end, pour the water washing liquid into the volumetric flask e and make up to the scale with ultrapure water to obtain the fifth filtrate, which is stored at 4°C for analysis. The solid after solid-liquid separation is the fifth residue. Specifically, based on the reducing effect of hydroxylamine hydrochloride, heavy metal elements bound to amorphous iron oxide and manganese in the fourth residue and elements in heavy metal oxides can be extracted, thereby achieving the extraction of reducible heavy metals.

[0061] S600: Mix the fifth residue with aqua regia and filter

[0062] In some embodiments, the centrifuge tube containing the fifth residue is placed in a constant temperature drying oven, and the solid in the centrifuge tube is dried at 50°C. The total mass of the centrifuge tube and the solid sample after drying is weighed, and the difference between this value and the mass of the hollow centrifuge tube is the mass of the fifth residue. The sample is then ground into powder with an agate mortar and stored at room temperature. For example, 0.10g of the fifth residue sample is accurately weighed, placed in a 100mL conical flask, 6-10mL of aqua regia is added, covered with a glass funnel, and placed on a hot plate for heating and digestion for 2h at a temperature of 160-190°C. During this period, the aqua regia vapor is kept refluxed on the wall of the conical flask and the glass funnel, but the reaction should not be too violent to cause the sample to overflow. After the digestion is completed, it is allowed to stand and cool to room temperature, filtered with slow quantitative filter paper, and after the end, the filtrate is transferred to a 50mL volumetric flask f and fixed to the scale with ultrapure water to obtain the sixth filtrate.

[0063] S700: Mix organic fertilizer with aqua regia and filter

[0064] In some embodiments, the organic fertilizer ground and sieved in step S100 is placed in a constant temperature drying oven and dried under the conditions of 50 ° C. For example, 0.10g organic fertilizer sample is accurately weighed, placed in a 100mL conical flask, 6-10mL aqua regia is added, a glass funnel is covered, and it is placed on a hot plate and heated for 2 hours at a temperature of 160-190 ° C. During this period, aqua regia vapor is kept to reflux on the wall of the conical flask and the glass funnel, but the reaction can not be too violent and cause the sample to overflow. After digestion, it is left to stand and cool to room temperature, filtered with slow quantitative filter paper, and after terminating, the filtrate is transferred to a 50mL volumetric flask g, and is settled to the scale with ultrapure water, which is the seventh filtrate. Specifically, thereby by directly carrying out aqua regia digestion to organic fertilizer, all heavy metals can be dissolved, so that the total amount of heavy metals can be measured.

[0065] S800: Detect the heavy metal content in the first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate respectively

[0066] In some embodiments, the first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate are respectively filtered through a 0.45 μm filter membrane, and then the heavy metal elements therein are detected to obtain the content of exchangeable heavy metals, the content of weakly acid-extractable heavy metals, the content of humic acid-bound heavy metals, the content of organically bound heavy metals, the content of reducible heavy metals, the content of residual heavy metals and the content of total heavy metals in the organic fertilizer, and then the extraction rate data of each bound heavy metal can be obtained.

[0067] In some embodiments, the first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate are stored at 4° C. and are stored for a long time to avoid generating additional precipitation. The test must be completed within one week.

[0068] Specifically, the first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate can be measured respectively using inductively coupled plasma emission mass spectrometry (ICP-MS) or spectroscopy (ICP), and the exchangeable heavy metals, weakly acid extractable heavy metals, humic acid bound heavy metals, organic bound heavy metals, reducible heavy metals, residual heavy metals and the As, Cd, Cr, Pb, Cu, and Zn element contents in the total amount of the analytical extract can be measured, and then the extraction rate data of each bound heavy metal can be obtained. Preferably, the As, Cd, Cr, and Pb element contents are measured using ICP-MS, and the Cu and Zn element contents are measured using ICP.

[0069] The present invention is described below with reference to specific examples. It should be noted that these examples are merely illustrative and do not limit the present invention in any way.

[0070] Example 1

[0071] (1) After air-drying the pig manure, grind it through a 100-mesh sieve. Then weigh 1.00 g of the organic fertilizer sample powder into a 50 mL centrifuge tube, add 30 mL of a 1.00 mol / L magnesium chloride solution, and mix thoroughly. Place the covered centrifuge tube in a constant temperature air oscillator and oscillate at a temperature of 25°C and a speed of 180 r / min for 12 hours. After the oscillation is completed, place it in a centrifuge for centrifugation at a speed of 4000 r / min for 10 minutes to completely separate the supernatant and the solid. After the centrifugation is completed, temporarily store the supernatant in a 50 mL volumetric flask a. Add 8 mL of ultrapure water to the solid after centrifugation, mix thoroughly, and place it in a centrifuge for centrifugation. After the end, pour the water washing liquid into the volumetric flask a again and dilute to the scale with ultrapure water to obtain the first filtrate, which is stored at 4°C for analysis. The solid after solid-liquid separation is the first residue.

[0072] (2) Add 8 mL of 1.00 mol / L acetic acid-sodium acetate buffer solution (pH 5) to the first residue and mix thoroughly. Place the covered centrifuge tube in a constant temperature air oscillator and oscillate at a temperature of 25°C and a speed of 180 r / min for 5 hours. After the oscillation is completed, place it in a centrifuge for centrifugation. After the centrifugation is completed, temporarily store the supernatant in a 50 mL volumetric flask b, add 8 mL of ultrapure water to the solid after centrifugation, mix thoroughly and place it in a centrifuge for centrifugation. After the end, pour the water washing liquid into the volumetric flask b and dilute to the scale with ultrapure water to obtain the second filtrate, which is stored at 4°C for analysis. The solid after solid-liquid separation is the second residue.

[0073] (3) Add 20 mL of 0.10 mol / L sodium pyrophosphate solution to the second residue and mix thoroughly. Place the covered centrifuge tube in a constant temperature air oscillator and oscillate at a temperature of 25°C and a speed of 180 r / min for 24 hours. After the oscillation is completed, place it in a centrifuge for centrifugation. After the completion, temporarily store the supernatant in a 50 mL volumetric flask c. Add 8 mL of ultrapure water to the solid after centrifugation, mix thoroughly and place it in a centrifuge for centrifugation. After the completion, pour the water washing liquid into the volumetric flask c and dilute to the scale with ultrapure water, i.e., the third filtrate. Store at 4°C for analysis. The solid after solid-liquid separation is the third residue.

[0074] (4) Add 3 mL of 0.02 mol / L nitric acid solution and 1 mL of hydrogen peroxide solution to the third residue. Be careful to add slowly and tighten the lid to avoid a violent reaction that may cause the sample to overflow. Let it stand for a while until the reaction is not violent (sometimes at least 1 hour). Gently shake the centrifuge tube to break the foam and then slowly add 4 mL of hydrogen peroxide solution. It can be added in multiple times. Mix well and immediately tighten the lid. Let it stand until the bubbles are not violent. Gently shake the centrifuge tube to break the foam and then place the opened centrifuge tube in a constant temperature water bath for 2 hours at 85°C. During this period, shake the centrifuge tube once every 10 minutes to ensure that the reagents are in full contact with the sample. Then add 3 mL of nitric acid solution and 5 mL of hydrogen peroxide solution and place the centrifuge tube in a constant temperature water bath at 85°C until the liquid evaporates and the remaining amount is about 0.5 mL. The liquid will not flow out when the centrifuge tube is tilted. After cooling, add 5 mL of ammonium acetate solution and 15 mL of ultrapure water. Place the capped centrifuge tube in a constant-temperature air oscillator and oscillate at 25°C and 180 rpm for 0.5 h. After oscillation, centrifuge the tube. Transfer the supernatant to a 50 mL volumetric flask (d). Add 8 mL of ultrapure water to the solid solution, mix thoroughly, and centrifuge the tube. Pour the wash solution into a volumetric flask (d) and dilute to the mark with ultrapure water to obtain the fourth filtrate. Store at 4°C until analysis is complete. The solid after solid-liquid separation is the fourth residue.

[0075] (5) Add 20 mL of 0.04 mol / L hydroxylamine hydrochloride solution to the fourth residue and mix thoroughly. Place the covered centrifuge tube in a constant temperature water bath at 96°C for 6 hours. Note that the lid must be loose to allow the gas to escape and to avoid the centrifuge tube from rupturing due to excessive pressure. Shake the centrifuge tube every 30 minutes to ensure that the reagent and sample are in full contact. Cool to room temperature after the water bath. Centrifuge and store the supernatant in a 50 mL volumetric flask e. Add 8 mL of ultrapure water to the solid after centrifugation, mix thoroughly, and centrifuge. Pour the water wash into the volumetric flask e and dilute to the mark with ultrapure water to obtain the fifth filtrate. Store at 4°C for analysis. The solid after solid-liquid separation is the fifth residue.

[0076] (6) Place the centrifuge tube containing the fifth residue in a constant temperature drying oven and dry the solid in the centrifuge tube at 50°C. Weigh the total mass of the dried centrifuge tube and the solid sample. The difference between this value and the mass of the hollow centrifuge tube is the mass of the fifth residue. Then use an agate mortar to grind the sample into powder and store it at room temperature. Accurately weigh 0.10g of the fifth residue sample, place it in a 100mL conical flask, add 6mL of aqua regia, cover it with a glass funnel, and place it on a hot plate for heating and digestion for 2 hours at a temperature of 180°C. During this period, keep the aqua regia vapor reflux on the wall of the conical flask and the glass funnel, but the reaction should not be too violent to cause the sample to overflow. After the digestion is completed, let it cool to room temperature and filter it with slow quantitative filter paper. After the end, transfer the filtrate to a 50mL volumetric flask f and dilute to the scale with ultrapure water, which is the sixth filtrate.

[0077] (7) The ground and sieved pig feces in step (1) are placed in a constant temperature drying oven and dried at 50°C. Accurately weigh 0.10g of sample, place it in a 100mL conical flask, add 6mL of aqua regia, cover it with a glass funnel, place it on a hot plate and heat it for 2h at a temperature of 180°C. During this period, keep the aqua regia vapor reflux on the wall of the conical flask and the glass funnel, but the reaction should not be too violent to cause the sample to overflow. After the digestion is completed, let it stand and cool to room temperature, filter with slow quantitative filter paper, and transfer the filtrate to a 50mL volumetric flask g after completion. Use ultrapure water to make up to the scale, which is the seventh filtrate.

[0078] (8) The first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate are filtered through a 0.45 μm filter membrane respectively, and then the first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate are respectively determined by inductively coupled plasma emission mass spectrometry or spectroscopy, so as to obtain the exchangeable heavy metals, weakly acid extractable heavy metals, humic acid bound heavy metals, organic bound heavy metals, reducible heavy metals, residual heavy metals and the As, Cd, Cr, Pb, Cu and Zn element contents in the total amount of the analysis extract, and then the extraction rate data of each bound heavy metal can be obtained.

[0079] Comparative Example 1

[0080] The difference between the analysis method and Example 1 is that the water-soluble phase extraction is performed first, followed by the exchangeable phase extraction, carbonate-bound phase extraction, iron-manganese oxide-bound phase extraction, organic-bound phase extraction, and residue phase extraction in sequence. The carbonate-bound phase in Comparative Example 1 roughly corresponds to the weakly acid-extractable phase in Example 1, and the iron-manganese oxide-bound phase in Comparative Example 1 roughly corresponds to the reducible phase in Example 1. The specific extraction process is as follows:

[0081] The pig manure organic fertilizer sample was air-dried and ground through a 100-mesh sieve, and then the stand-by solutions were prepared: ultrapure water as solution A, 1mol / L MgCl2 (pH = 7, adjusted by HCl and NaOH) as solution B, 1mol / L CH3COONa (pH = 5, adjusted by CH3COOH) as solution C, 0.10mol / L NH2OH-HCl (containing 25% CH3COOH) as solution D, 0.02mol / L HNO3 as solution E, 30% H2O2 as solution F, 3.2mol / L CH3COONH4 as solution G, and aqua regia as solution H.

[0082] Take 1.00g of pig manure organic fertilizer sample, add 23mL of solution A, shake at 25℃ for 33h, centrifuge at 4000r / min for 10min, adjust the volume of the supernatant and filter through 0.45μm filter membrane, and use inductively coupled plasma atomic emission spectrometer (ICP-MS) to determine the metal ion content. The measured value is the water-soluble state of heavy metals, and the precipitate is washed with water. Add 8mL of solution B to the washed precipitate, shake at 25℃ for 1h, centrifuge at 4000r / min for 10min, adjust the volume of the supernatant and filter through 0.45μm filter membrane, and use inductively coupled plasma atomic emission spectrometer (ICP-MS) to determine the metal ion content. The measured value is the exchangeable state of heavy metals, and the precipitate is washed with water. After washing, add 8 mL of solution C to the precipitate, shake at 25°C for 5 h, centrifuge at 4000 r / min for 10 min, adjust the volume of the supernatant to a volume, filter through a 0.45 μm filter, and determine the metal ion content using inductively coupled plasma atomic emission spectrometry (ICP-MS). The measured value is the heavy metal carbonate-bound state, and the precipitate is washed with water. After washing, add 20 mL of solution D to the precipitate, water bath at 96°C for 6 h, cool, and centrifuge at 4000 r / min for 10 min. After adjusting the volume of the supernatant to a volume, filter through a 0.45 μm filter, and determine the metal ion content using inductively coupled plasma atomic emission spectrometry (ICP-MS). The measured value is the heavy metal iron and manganese oxide-bound state, and the precipitate is washed with water. After washing, add 3 mL of solution E and 5 mL of solution F to the precipitate, incubate in a water bath at 85°C for 3 h until nearly dry (about 0.5 mL of liquid remains), repeat the addition of solution and water bath operation twice, add 5 mL of solution G, dilute to 20 mL with deionized water, centrifuge at 4000 r / min for 10 min, adjust the supernatant to volume, filter through a 0.45 μm filter, and determine the metal ion content using inductively coupled plasma atomic emission spectrometry (ICP-MS). The measured value is the organically bound heavy metal state. The precipitate is washed with water. The washed precipitate is dried and ground. Take 0.10 g of sample, add 6 mL of solution H, digest on a hot plate at 180°C for 2 h, filter and adjust the volume, and determine the metal ion content using inductively coupled plasma atomic emission spectrometry (ICP-MS). The measured value is the heavy metal residual state.

[0083] Table 2 Test errors of different forms (%)

[0084]

[0085] Note: - indicates that the sample was not tested for this morphology

[0086] Compared with the comparative example, the method of the present invention can obtain more detailed morphological distribution information and adds the extraction of humic acid-bound heavy metals. The biological activity and toxicity of humic acid-bound heavy metals are relatively significant. Understanding the content of this part of heavy metals in fertilizers is of great significance for evaluating the safety of organic fertilizers. Therefore, adding the extraction of humic acid-bound heavy metals can obtain more information on bioavailable heavy metals.

[0087] The Tessier method is a study conducted on sediments and soils, and is an internationally recognized method for heavy metal speciation analysis. Since the morphological classification referred to here is the morphology at the operational level, the accuracy of the method cannot be directly defined. To solve this problem, the inventor used Tessier's test data as the benchmark value, used calcium, iron, manganese, silicon, sulfur, and carbon as characterization indicators, and supplemented it with mineral component (X-ray diffraction XRD) analysis to establish an evaluation formula for the test error of heavy metal speciation analysis. Based on the benchmark value of the Tessier method, the test errors of other methods were calculated. After calculation, this method reduced the test error of the reducible state (iron-manganese oxide bound state) from 20.08% to 10.40%, and reduced the test error of the organic bound state from 20.66% to 10.98%, thereby improving the accuracy of heavy metal speciation detection.

[0088] Table 3 Total carbon content of different forms of extraction (%)

[0089]

[0090] Note: - indicates that the sample has not been tested for this form; ND indicates that the sample component has not been tested

[0091] The data in Table 3 show that the organic carbon in Example 1 is mainly distributed in the humic acid-bound state and the organic-bound state, with a total proportion of up to 64.75%-81.82%. The subsequent reducible state contains only 2.03% organic matter. Compared with Comparative Example 1, the preferential extraction of the organic-bound state reduces the organic matter content of the reducible state, avoids interference with the reducible state, and the measured organic-bound heavy metal content is more accurate.

[0092] Example 2 Results of implementation of Example 1 by laboratories in different regions of China

[0093] The present embodiment adopts respectively one domestic North China, Northeast China and Southwest China each to have the inspection and testing qualification (CMA) laboratory to analyze the metal form of pig manure organic fertilizer, and method is the same as Example 1. Each laboratory uses its own instrument and reagent to test, and test personnel are also selected by each laboratory. Used is the same batch of pig manure organic fertilizer, and adopts the same sample preparation method to prepare and distribute to each laboratory.

[0094] Taking the total amount of the element as the standard, compare it with the sum of each form and calculate the index recovery rate R (%):

[0095]

[0096] where m i is the mass of each form of the element, m 全The results show that the recoveries of all three elements met the requirements, with the exception of the high test error caused by low chromium content. The data are reliable.

[0097] Table 4 Element recovery rates of speciation analysis in three laboratories

[0098]

[0099] The same sample was repeated seven times, and the RSD of each replicate analysis was calculated, with an RSD requirement of ≤30%. The RSDs of each replicate analysis across the three laboratories met the recovery requirements for all elements, except for some forms of chromium, cadmium, and lead.

[0100] Table 5 Element recovery rates of speciation analysis in each laboratory

[0101]

[0102] “-” Not detected

[0103] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0104] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for sequentially extracting heavy metal forms in organic fertilizers, characterized in that: include: (1) Extraction of exchangeable heavy metals: mixing organic fertilizer with magnesium chloride solution and performing separation treatment to obtain a first filtrate and a first residue; (2) Extraction of weakly acid-extractable heavy metals: mixing the first residue with an acetic acid-sodium acetate buffer solution and performing separation treatment to obtain a second filtrate and a second residue; (3) Extraction of humic acid-bound heavy metals: the second residue is mixed with a sodium pyrophosphate solution and then separated to obtain a third filtrate and a third residue; (4) Extraction of organically bound heavy metals: The third residue is mixed with hydrogen peroxide and nitric acid solution, and the residue obtained after separation is mixed with ammonium acetate solution and then separated to obtain a fourth filtrate and a fourth residue; (5) Extraction of reducible heavy metals: mixing the fourth residue with a hydroxylamine hydrochloride solution and performing separation treatment to obtain a fifth filtrate and a fifth residue; (6) Extraction of heavy metals in the residue: mixing the fifth residue with aqua regia and filtering to obtain a sixth filtrate; (7) Full element extraction: the organic fertilizer is mixed with aqua regia and filtered to obtain a seventh filtrate; (8) Detecting the heavy metal element content in the first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate respectively.

2. The method according to claim 1, characterized in that In step (1), based on 1g of the organic fertilizer, the amount of the magnesium chloride solution added is 20-30mL; and / or The mixing time of the magnesium chloride solution and the organic fertilizer is 8-16 hours; and / or The concentration of the magnesium chloride solution is 0.5-1.5 mol / L.

3. The method according to claim 1 or 2, characterized in that In step (2), based on 1g of the organic fertilizer, the amount of the acetic acid-sodium acetate buffer solution added is 8-10mL; and / or The pH of the acetic acid-sodium acetate buffer solution is 4.8-5.

2.

4. The method according to claim 1, wherein In step (3), based on 1g of the organic fertilizer, the amount of the sodium pyrophosphate solution added is 10-30mL; and / or The concentration of the sodium pyrophosphate solution is 0.1-0.3 mol / L.

5. The method according to claim 1 or 4, characterized in that In step (4), based on 1g of the organic fertilizer, the amount of the nitric acid solution added is 2-6mL, the amount of the hydrogen peroxide added is 7-13mL, and the amount of the ammonium acetate solution added is 3-8mL; and / or The concentration of the nitric acid solution is 0.01-0.05 mol / L, the mass concentration of the hydrogen peroxide is 20-50%, and the concentration of the ammonium acetate solution is 3-3.5 mol / L.

6. The method according to claim 1 or 5, characterized in that In step (4), the hydrogen peroxide solution is added three times: The amount of hydrogen peroxide added for the first time is 1-3 mL; and / or The second addition amount of hydrogen peroxide is 3-7 mL; and / or The amount of hydrogen peroxide added for the third time is 3-7 mL.

7. The method according to claim 1 or 2, characterized in that In step (5), based on 1g of the organic fertilizer, the amount of the hydroxylamine hydrochloride solution added is 10-20mL; and / or The concentration of the hydroxylamine hydrochloride solution is 0.02-0.06 mol / L.

8. The method according to claim 1 or 2, characterized in that In step (6), the fifth residue is mixed with aqua regia and then heated on a hot plate for digestion treatment; and / or Based on 0.1 g of the fifth residue, the amount of aqua regia added is 6-10 mL; and / or The temperature of the digestion treatment is 160-190°C.

9. The method according to claim 1 or 2, characterized in that In step (7), the organic fertilizer is mixed with aqua regia and then heated on a hot plate for digestion treatment; and / or Based on 0.1 g of the organic fertilizer, the amount of the aqua regia added is 6-10 mL; and / or The temperature of the digestion treatment is 160-190°C.

10. The method according to claim 1 or 2, characterized in that The first filtrate, the second filtrate, the third filtrate, the fourth filtrate, the fifth filtrate, the sixth filtrate and the seventh filtrate are respectively filtered through filter membranes and then the heavy metal element contents therein are detected.

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