A method for heavy metal speciation analysis in metallurgical sludge

Abstract

This invention relates to the field of metallurgical industry technology, and discloses a method for analyzing the heavy metal speciation in metallurgical sludge obtained from the chemical precipitation of acidic wastewater generated from non-ferrous metal smelting. The method includes the following steps: S1 Pretreatment: Take metallurgical sludge and add a compound plant root residue extract for fermentation; S2 Weak acid extraction state: Immerse in a weak acid solution, connect an electrode, perform electrolytic extraction, and centrifuge to obtain sludge X and extract A; S3 Reducible state: Take sludge X, add a reducing agent, add dilute nitric acid to adjust the pH value, shake and centrifuge to obtain sludge Y and extract B; S4 Oxidizable state: Take sludge Y, add oxidizing bacteria, add dilute nitric acid and ammonium acetate, adjust the pH value, shake and centrifuge to obtain sludge Z and extract C; S5 Residual state: Take sludge Z, add a mixed acid solution, digest with microwave, remove acid, wash with pure water, centrifuge to obtain extract D, and detect the metal element content of the extracts obtained in each step.

Description

Technical Field

[0001] This invention relates to the field of metallurgical industry technology, and more specifically, to a method for analyzing the speciation of heavy metals in metallurgical sludge. Background Technology

[0002] In the metallurgical industry, the smelting of metals generates a large amount of sludge produced by the chemical precipitation of acidic metallurgical wastewater. Heavy metals in this wastewater, after entering the solid phase, undergo precipitation, coagulation, and adsorption over a period of time, forming different forms. The toxicity of heavy metals in metallurgical sludge to surrounding plants, its environmental impact, migration and transformation rates, and the leaching effect depend not only on the total amount of heavy metals but also on their form in the solid phase. The form in which heavy metals exist refers to their physicochemical state in the environment and their combination with symbiotic elements, including the element's physical state, the type and form of compounds formed, and valence state. Due to these different forms, even the same type and amount of heavy metal can exhibit significant differences in activity, biotoxicity, and migration characteristics.

[0003] Currently, multi-stage continuous extraction methods, including the Tessior continuous extraction method and the BCR continuous extraction method, are commonly used for heavy metal speciation analysis in general soil. However, metallurgical sludge, being a highly alkaline sludge with high heavy metal content produced during metal smelting—essentially a waste product—has a complex elemental composition and numerous impurities, exhibiting significant differences in composition compared to general soil. It contains large amounts of metals such as lead, cadmium, copper, zinc, iron, calcium, and magnesium, making accurate speciation analysis of heavy metals in metallurgical sludge impossible using conventional soil heavy metal speciation analysis methods.

[0004] Therefore, we urgently need a method for analyzing the heavy metal speciation of metallurgical sludge obtained by chemical precipitation of acidic wastewater from non-ferrous metallurgy. Summary of the Invention

[0005] The technical problem to be solved by this invention:

[0006] Currently, the commonly used Tessior continuous extraction method, BCR continuous extraction method, and their improved methods are mainly used for the analysis of heavy metal speciation in general soil. They are not suitable for the speciation analysis of heavy metals in metallurgical sludge and cannot specifically analyze the speciation of heavy metals such as copper, zinc, lead, and cadmium in metallurgical sludge.

[0007] The technical solution adopted in this invention is as follows:

[0008] This invention provides a method for analyzing the speciation of heavy metals in metallurgical sludge, comprising the following steps:

[0009] S1 Pretreatment: Take metallurgical sludge, add compound plant root residue extract, and ferment.

[0010] S2 weak acid extraction state: Take the metallurgical sludge after fermentation in S1, immerse it in a weak acid solution, connect the electrode, perform electro-extraction, centrifuge, wash the sludge residue with pure water to obtain sludge residue X and extract A.

[0011] S3 Reducible State: Take mud X, add reducing agent, add dilute nitric acid to adjust pH to less than 2.5, shake and centrifuge to obtain mud Y and extract B;

[0012] S4 Oxidizable State: Take mud residue Y, add oxidizing bacteria, add dilute nitric acid and ammonium acetate, adjust the pH to 1.3-3.5, shake and centrifuge to obtain mud residue Z and extract C;

[0013] S5 Residue State: Take mud residue Z, add mixed acid solution, microwave digest, remove acid, wash with pure water, centrifuge to obtain extract D, and detect the metal element content of the extract obtained in each step.

[0014] Preferably, in step S1, the compound plant root residue extract includes one or more of *Solanum nigrum* root residue and *Polygonum cuspidatum* root residue; during fermentation, the fermentation temperature is controlled at 25-38℃ and the fermentation time is 4-28h.

[0015] Preferably, in step S2, the weak acid solution is a complexing agent of acetic acid and EDTA; after inserting a non-metallic electrode into the impregnation solution, electrolytic extraction is performed; the non-metallic electrode can be graphite or silica; during the extraction process, the weak acid solution is continuously added to maintain the pH value of the extract at 5-6.8.

[0016] Preferably, in step S3, the reducing agent is ascorbic acid and hydroxylamine hydrochloride.

[0017] Preferably, the oxidizing bacteria in step S4 include one or more of *Acidobacterium ferrooxidans* and *Acidobacterium thiooxidans*, as well as *Rhodotorula glutinis* as an auxiliary bacterium; after adding dilute nitric acid, the mixture is ultrasonically vibrated.

[0018] Preferably, in step S5, the mixed acid includes multiple types of hydrofluoric acid, nitric acid, and hydrochloric acid.

[0019] Technical mechanism and beneficial effects of the present invention:

[0020] Currently, existing methods for analyzing the speciation of heavy metals mainly employ the Tessior continuous extraction method, the BCR continuous extraction method, and their modified versions, but these are only used for analyzing the speciation of heavy metals in general soils.

[0021] Metallurgical sludge is a mixture containing various components, each exhibiting different forms due to its own physicochemical properties and the influence of other components. Its stability and sensitivity also vary. In the speciation analysis of different heavy metals, factors such as pH level, acid leaching time, added treatment agents, and treatment processes all affect whether the heavy metals in each speciation are leached sufficiently and effectively, thus influencing the results of the speciation analysis.

[0022] This invention addresses the sludge obtained from the chemical precipitation of acidic wastewater generated in non-ferrous metal smelting. By improving the treatment methods for each morphology and the overall treatment process during analysis, it achieves accurate and efficient morphological analysis of heavy metals in metallurgical sludge. It features high accuracy and strong targeting, and is suitable for morphological analysis of metallurgical sludge generated after metal smelting. It also boasts strong reproducibility, high accuracy, and strong comparability. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0024] This invention provides a method for analyzing the speciation of heavy metals in metallurgical sludge, comprising the following steps:

[0025] S1 Pretreatment: Metallurgical sludge is taken and a compound plant root residue extract is added for fermentation. The compound plant root residue extract includes one or more of the following: *Solanum lyratum* root residue and *Polygonum cuspidatum* root residue. The fermentation temperature is controlled at 25-38℃, and the fermentation time is 4-28 hours. By adding the compound plant root residue extract and fermenting it at a higher temperature for a period of time, the influence of the natural environment on the metallurgical sludge during the stacking process is simulated, activating the heavy metals that can be extracted by weak acid, thus promoting the subsequent analysis of the heavy metal speciation in the weak acid-extractable state.

[0026] S2 Weak Acid Extraction State: Take the metallurgical sludge from S1 after fermentation, and immerse it in a mixed solution of acetic acid and EDTA complexing agent at 32-37℃. After inserting a non-metallic electrode, electrolytic extraction is performed, followed by centrifugation to obtain sludge X and extract A. The non-metallic electrode can be graphite or silica. After electrolysis, the H in the acid extract... + Under the influence of electromigration and electroosmosis, it participates in promoting the acidification of metallurgical sludge and promotes the acid leaching process of weakly acid-extractable metals in metallurgical sludge.

[0027] S3 Reducible State: Take mud residue X, add reducing agent at 32-37℃, add dilute nitric acid to adjust the pH value to less than 2.5, shake for 12-16h, centrifuge to obtain mud residue Y and extract B; the reducing agent includes ascorbic acid and hydroxylamine hydrochloride.

[0028] S4 Oxidizable State: Take sludge Y, add oxidizing bacteria at 20-28℃, add dilute nitric acid and ammonium acetate, adjust the pH to 1.3-3.5, sonicate for 12-36 hours, centrifuge to obtain sludge Z and extract C; the oxidizing bacteria include one or more of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, as well as Rhodotorula glutinis as a helper. Unlike oxidizable heavy metals in general soil that exist in organic matter-bound form, oxidizable heavy metals in metallurgical sludge are mostly in sulfide-bound form, which can be decomposed by the aforementioned oxidizing bacteria.

[0029] S5 Residual State: Take mud residue Z, put it into a digestion vessel, add mixed acid solution, stir for 10-35 min, and age for 0.5-2.5 h. Then, place the digestion vessel in a microwave digester and set the program for microwave digestion. After digestion, use an acid removal device to remove the acid, then wash with pure water, centrifuge, and obtain extract D. Detect the metal element content of the extract obtained in each step; the mixed acid includes multiple types of hydrofluoric acid, nitric acid, and hydrochloric acid. By adding a mixed acid solution containing multiple types of hydrofluoric acid, nitric acid, and hydrochloric acid, the mineral lattice structure of mud residue Z can be destroyed, thereby extracting the residual heavy metals.

[0030] <Example>

[0031] Example 1

[0032] This embodiment provides a method for analyzing the speciation of heavy metals in metallurgical sludge, including the following steps:

[0033] S1 preprocessing:

[0034] Take metallurgical sludge, add a compound plant root extract including root residue of Sauvignon Blanc and root residue of Polygonum cuspidatum, gradually raise the temperature to 32°C, and ferment for about 5.5 hours.

[0035] S2 weak acid extraction state:

[0036] Take the metallurgical sludge fermented in S1 and immerse it in a mixed solution containing 0.2 mol / L acetic acid and 0.05 mol / L EDTA complexing agent at 35℃ for 2.5 h. Then insert a graphite electrode, apply current, and control the electric field strength to 1.5-5 V / cm for 15 h of extraction. After centrifugation, wash the sludge residue with pure water to obtain sludge residue X and extract A. The current is paused for 0.5 h after every 1 h of energization until the extraction is completed.

[0037] S3 reducible state:

[0038] Take mud residue X, add a mixed reducing agent including ascorbic acid and hydroxylamine hydrochloride at 35℃, add 0.2mol / L dilute nitric acid to adjust the pH to 2.0, shake for 14h, and centrifuge to obtain mud residue Y and extract B.

[0039] S4 oxidizable state:

[0040] Take mud residue Y, add oxidizing bacteria at 25℃, add dilute nitric acid and ammonium acetate, adjust the pH to about 2.0, sonicate for 14 hours, centrifuge to obtain mud residue Z and extract C; the oxidizing bacteria are a mixed genus including acidophilic ferrooxidizing bacillus and Rhodotorula glutinis auxiliary bacteria.

[0041] S5 residual state:

[0042] Take mud residue Z and place it in a digestion vessel. Add a mixed acid solution containing hydrofluoric acid, nitric acid, and hydrochloric acid, stir for 15 minutes, and age for 2 hours. Then, place the digestion vessel in a microwave digester and set a program for microwave digestion. After digestion, remove the acid using an acid removal device, wash with pure water, and centrifuge to obtain extract D. Analyze the metal element content of the extracts obtained in each step. High-concentration acid solutions were used for hydrofluoric acid, nitric acid, and hydrochloric acid.

[0043] Example 2

[0044] This embodiment provides a method for analyzing the speciation of heavy metals in metallurgical sludge, including the following steps:

[0045] S1 preprocessing:

[0046] Take metallurgical sludge, add a compound plant root extract including root residue of Sauvignon Blanc and root residue of Polygonum cuspidatum, gradually raise the temperature to 27°C, and ferment for about 15 hours.

[0047] S2 weak acid extraction state:

[0048] Take the metallurgical sludge fermented in S1 and immerse it in a mixed solution containing 0.2 mol / L acetic acid and 0.05 mol / L EDTA complexing agent at 37℃ for 2.5 h. Then insert a graphite electrode, apply current, and control the electric field strength to 1.5-5 V / cm for 15 h of extraction. Centrifuge to obtain sludge X and extract A. The current is paused for 0.5 h after every 1 h of energizing until the extraction is completed.

[0049] S3 reducible state:

[0050] Take mud residue X, add a mixed reducing agent including ascorbic acid and hydroxylamine hydrochloride at 37℃, add 0.2 mol / L dilute nitric acid to adjust the pH to 2.0, shake for 14 h, and centrifuge to obtain mud residue Y and extract B.

[0051] S4 oxidizable state:

[0052] Take mud residue Y, add oxidizing bacteria at 22℃, add dilute nitric acid and ammonium acetate, adjust the pH to about 2.0, sonicate for 14 hours, centrifuge to obtain mud residue Z and extract C; the oxidizing bacteria are a mixed genus including acidophilic sulfur-oxidizing bacteria and Rhodotorula glutinis auxiliary bacteria.

[0053] S5 residual state:

[0054] Take mud residue Z and place it in a digestion vessel. Add a mixed acid solution containing hydrofluoric acid, nitric acid, and hydrochloric acid, stir for 30 minutes, and age for 1 hour. Then, place the digestion vessel in a microwave digester and set a program for microwave digestion. After digestion, remove the acid using an acid removal device, then wash with pure water and centrifuge. High-concentration acid solutions were used for hydrofluoric acid, nitric acid, and hydrochloric acid.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for analyzing the speciation of heavy metals in metallurgical sludge, characterized in that, Includes the following steps: S1 Pretreatment: Take metallurgical sludge, add compound plant root residue extract, the compound plant root residue extract includes one or more of sour grass root residue and Japanese knotweed root residue, ferment, control the fermentation temperature at 25-38℃, and fermentation time at 4-28h. S2 Weak acid extraction state: Take the metallurgical sludge after fermentation in S1, immerse it in a weak acid solution, connect the electrode, control the pH value of the extract to be maintained at 5-6.8, perform electro-extraction, centrifuge, wash the sludge with pure water, and obtain sludge X and extract A. S3 Reducible state: Take mud X, add reducing agent, add dilute nitric acid to adjust the pH value to less than 2.5, shake and centrifuge to obtain mud Y and extract B; S4 Oxidizable state: Take mud residue Y, add oxidizing bacteria, including one or more of Acidobacterium ferrooxidans and Acidobacterium thiooxidans, as well as Rhodotorula glutinis auxiliary bacteria, then add dilute nitric acid and ammonium acetate, sonicate to adjust the pH to 1.3-3.5, centrifuge to obtain mud residue Z and extract C; S5 Residual state: Take mud residue Z, add mixed acid solution, microwave digest, remove acid, wash with pure water, centrifuge to obtain extract D, and detect the metal element content of the extract obtained in each step.

2. The method for analyzing the speciation of heavy metals in metallurgical sludge according to claim 1, characterized in that, In step S2, the weak acid solution includes acetic acid and EDTA complexing agent.

3. The method for analyzing the speciation of heavy metals in metallurgical sludge according to claim 2, characterized in that, In step S2, during the extraction process, a weak acid solution is continuously added to adjust the pH value of the extract.

4. The method for analyzing the speciation of heavy metals in metallurgical sludge according to claim 2, characterized in that, In step S2, a non-metallic electrode is inserted into the impregnation solution and then subjected to electro-extraction; the non-metallic electrode is selected from graphite or silica.

5. The method for analyzing the speciation of heavy metals in metallurgical sludge according to claim 1, characterized in that, In step S3, the reducing agents include ascorbic acid and hydroxylamine hydrochloride.

6. The method for analyzing the speciation of heavy metals in metallurgical sludge according to claim 1, characterized in that, In step S5, the mixed acid includes multiple types of hydrofluoric acid, nitric acid, and hydrochloric acid.