Five-step selective leaching method for determining germanium form in coal ash

Abstract

The invention relates to the field of research of germanium element in coal ash, in particular to a five-step selective leaching method for determining the form of germanium in coal ash, and provides a five-step selective leaching method for determining the form of germanium in coal ash by adopting various specific extraction reagents under specific operation conditions and processes according to the principle that the extraction reactivity of main germanium occurrence compounds in coal ash and different specific reagents is from weak to strong. Chemical forms mainly containing germanium elements, such as hexagonal germanium dioxide / exchange state, soluble germanate state, germanium sulfide / germanium-organic binding state, germanium-silicon binding state, tetragonal germanium dioxide / residual germanium, in the coal ash are sequentially and selectively leached. The extraction rate of the same extracting agent for the target germanium form reaches 100%, the extraction rate for germanium in other forms is lower than 10%, and the selectivity is excellent. And for various actual fly ash samples, the germanium recovery rate is stabilized between 90.8% and 100.1%. The developed step-by-step chemical extraction method special for the germanium form has the advantages that the operation steps are simple and convenient, the occurrence form of the main germanium in the coal ash can be rapidly and accurately determined at a low cost, and an important basis and a method reference can be provided for efficient extraction of the germanium in the coal.

Description

Technical Field

[0001] This invention relates to the field of germanium research in coal ash, and more particularly to a five-step selective leaching method for determining the speciation of germanium in coal ash. Background Technology

[0002] Germanium is an important strategic metal, indispensable in military and high-tech industries such as infrared detection systems, fiber optic communications, catalysis, semiconductors, solar panels, and polymer catalysis. Global germanium resources are mainly distributed in China, the United States, and Russia, with proven reserves of only 8,600 tons. In recent years, with the rapid development of high technology, the contradiction between the dramatic increase in global demand for germanium and its resource scarcity has become increasingly prominent.

[0003] The fly ash generated from the combustion of germanium-rich lignite is the main source of germanium extraction. In the process of germanium enrichment and extraction from lignite, the occurrence form of germanium in fly ash not only affects the extraction and utilization efficiency of the subsequent wet extraction process, but also serves as the scientific basis for whether germanium can be efficiently volatilized and enriched during the combustion of lignite.

[0004] Due to the low content, scattered distribution, and complex occurrence of germanium in coal ash, accurate quantitative determination of germanium occurrence forms presents a significant challenge. Although some progress has been made in the study of germanium occurrence forms in the combustion products of germanium-rich lignite both domestically and internationally, a unified testing and analysis method and standard have not yet been established for the analysis of germanium occurrence forms in coal ash. There are various methods for studying the occurrence state of germanium, a trace element, in coal ash. These methods can be broadly categorized into two types: indirect and direct methods. Direct methods, such as scanning electron microbeam microscopy with energy dispersive spectroscopy / wavelength spectroscopy (SEM-EDS / WDS), secondary ion mass spectrometry (SIMS), electron probe microanalysis (EPMA), ion probe mass spectrometry (IMMA), and synchrotron X-ray fluorescence spectrometry (SRXFM), can directly observe important information such as the distribution, chemical form, and structure of germanium in coal ash. However, they only provide local microscopic results and lack overall quantitative conclusions on germanium speciation, limiting their guiding significance for germanium extraction. Indirect speciation extraction methods, such as stepwise chemical extraction, offer advantages over direct methods, including ease of operation, low cost, and the ability to quantitatively obtain different germanium chemical speciations. However, previous reports have primarily referenced procedures and methods for determining trace heavy metal speciation in environmental geological samples such as soil and sediments. A typical example is the European Union's Community Bureau of Standards and Metrology (CESB). The standard BCR four-step extraction method proposed by the Reference Institute is used to assess the bioavailability, mobility and potential ecological risks of heavy metals in environmental geological samples. However, the reagents, extraction conditions and workflow used are difficult to apply to the smelting and extraction of germanium from coal ash. Bottlenecks exist, such as poor reagent selectivity, weak specificity and difficulty in accurately describing the occurrence of germanium in coal ash. Summary of the Invention

[0005] To address the problems existing in the background technology, a five-step selective leaching method for accurately determining the germanium speciation in coal ash is proposed. This method involves using multiple specific reagents under specific operating conditions and procedures, selectively leaching the chemical speciations of the main germanium elements in coal ash according to the principle of increasing reactivity of each germanium-containing speciation. These speciations include hexagonal germanium dioxide / exchangeable germanium, soluble germanate, germanium sulfide / germanium-organic bound, germanium-silicon bound, and tetragonal germanium dioxide / residual germanium. The specific steps of the method are as follows:

[0006] Step 1, Hexagonal germanium dioxide / exchangeable germanium extraction: Weigh the solid sample after air drying, impurity removal, grinding and sieving, disperse it in specific extraction reagent solution A, place the centrifuge tube in a benchtop constant temperature shaker, cool to room temperature after processing, then centrifuge, add deionized water to the filtrate and make up to volume for analysis;

[0007] Step 2, Soluble germanate extraction: Take the solid residue from Step 1, dry it, cool it to room temperature, and disperse it in specific extraction reagent solution B. Place the centrifuge tube in a benchtop constant temperature shaker, centrifuge after processing, and add deionized water to the filtrate for analysis.

[0008] Step 3, Germanium-organic bound / germanium sulfide extraction: Dry the solid residue from Step 2, cool it to room temperature, and disperse it in specific extraction reagent solution C. Place the centrifuge tube in a benchtop constant temperature shaker. After processing, cool it to room temperature, and add deionized water to the filtrate for analysis. Dry the solid residue again, add it to specific extraction reagent solution D, place the centrifuge tube in a benchtop constant temperature shaker, cool it to room temperature, and then centrifuge. Add deionized water to the filtrate for analysis.

[0009] Step 4, Germanium-silicon bound state extraction: Take the solid residue from Step 3, dry it, cool it to room temperature, and disperse it in specific extraction reagent solution E. Place the centrifuge tube in a benchtop constant temperature shaker, centrifuge after processing, and add deionized water to the filtrate for analysis.

[0010] Step 5, extraction of tetragonal germanium dioxide / residual germanium: The solid residue from Step 4 is dried and weighed, then nitric acid and hydrogen fluoride are added, and digested in a closed digestion tube. Before digestion, the coal sample is ashed to eliminate interference from organic matter. After the closed digestion is completed, the digestion tube is opened and placed in a graphite digester to heat and remove the acid to the size of a soybean. Nitric acid is then added to the sample and kept for a period of time. Deionized water is added to make up the volume for analysis.

[0011] Preferably, the samples described in step one are dried at 50°C for 24 hours to remove moisture and then passed through a 100-200 mesh sieve.

[0012] Preferably, the quantity of solid samples used in step one refers to germanium-containing industrial solid waste samples such as fly ash, gasification slag, and smelting slag; the specific extraction reagent A is a metal salt ion solution, specifically MgCl2, with a concentration of 1-3 mol / L; the extraction reaction conditions for hexagonal germanium dioxide / exchangeable germanium in step one are 60℃, 250 r / min, and 5 h.

[0013] Preferably, the specific extraction reagent B is a dilute mineral acid solution, such as an HCl solution with a concentration of 3-6 mol / L, and the soluble germanate extraction reaction conditions in step two are 25°C, 250 r / min, and 30 min.

[0014] Preferably, the specific extraction reagent C is a strong oxidizing solution, specifically a mixture of nitric acid and hydrogen peroxide. In step three, the extraction reaction conditions for germanium-organic bound state and germanium monosulfide are 90°C, 250 r / min, and 6 h.

[0015] Preferably, in step three, a (NH4)2S solution with a concentration of 20% or higher is added, and the shaking parameters are 60°C, 250 r / min, and 1 h.

[0016] Preferably, the specific extraction reagent E is a combined solution, specifically a 1-3M H2SO4 and NH4F mixed solution, and the germanium-silicon bound state extraction reaction conditions in step four are 60℃, 250r / min, and treatment for 1h.

[0017] Preferably, in step five, the solid residue from step four is dried and weighed, and 0.1g of the sample is weighed into a PTFE digestion tube. HNO3+HF (2:1) is added to the coal sample, and the sample is sealed and digested at 80℃ for 1 hour. After the sealed digestion is completed, the digestion tube is opened and placed in a graphite digester to heat and remove the acid to the size of a soybean. Then, 4-5mL of nitric acid is added to the sample and kept for 20 minutes. After cooling, the sample is diluted with deionized water and ready for testing.

[0018] Preferably, in steps one through four, the centrifugation process involves washing the inner wall of the centrifuge tube with deionized water and transferring it to the extraction liquid to ensure that all extracted elements are transferred to the extraction liquid.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] (1) Compared with existing methods for quantifying germanium in fly ash samples, this invention redefines five main forms of germanium in fly ash based on the actual occurrence and extractability of germanium in fly ash: hexagonal germanium dioxide / exchangeable germanium, soluble germanate, germanium sulfide / germanium-organic bonded state, germanium-silicon bonded state, and tetragonal germanium dioxide / residual germanium.

[0021] (2) Based on the principle of increasing reactivity and decreasing selectivity, specific extraction reagents, operating conditions, and procedures for five different germanium forms were proposed. The extraction rate of germanium forms corresponding to the same extractant was 100%, while the extraction rate of other germanium forms was less than 10%, demonstrating excellent extraction selectivity and specificity. Extraction results from multiple actual fly ash samples of different types and germanium contents showed that the germanium recovery rate ranged from 90.8% to 100.1%, proving the reliability and wide applicability of the analytical method.

[0022] (3) The extraction operation is carried out under low temperature (<100℃) and normal pressure conditions. The specific extraction reagent is basically a dilute solution with weak acidity and corrosiveness. It can determine the germanium species in multiple coal ash samples in a large batch at one time. Compared with direct determination methods such as electron microbeam analysis, the extraction method of this invention has the advantages of simple operation steps and can quickly and accurately determine the main germanium species in fly ash at a low cost. Attached Figure Description

[0023] Figure 1 This is an experimental flowchart of the five-step selective leaching method for determining germanium speciation in coal ash in this invention.

[0024] Figure 2 (a) is a schematic diagram of the selectivity of leaching hexagonal germanium dioxide / exchangeable state by specific extraction reagent solution A (F1); (b) is a schematic diagram of the selectivity of leaching soluble germanate state by specific extraction reagent solution B (F2); (c) is a schematic diagram of the selectivity of leaching GeS and organically bound Ge by specific extraction reagent solution C (F3); (d) is a schematic diagram of the selectivity of leaching GeS2 by specific extraction reagent solution D. (e) is a schematic diagram of the selectivity of leaching Ge bound to silicate complex by specific extraction reagent solution E (F4).

[0025] Figure 3 Figure A shows the results of stepwise chemical extraction from germanium-rich fly ash and chlorination distillation residue; Figure B shows the absolute content of germanium in the three samples.

[0026] Figure 4 This is a schematic diagram showing the results of stepwise chemical extraction of a power plant sample with low germanium content.

[0027] Figure 5 This is a schematic diagram showing the absolute content of various forms of germanium in samples from power plants with low germanium content; A: AC power plant; B: DG power plant.

[0028] Figure 6 Figure A shows the results of traditional stepwise chemical extraction of germanium-rich fly ash and chlorination distillation residue; Figure B shows the absolute content of each form of germanium in the three samples.

[0029] Figure 7The image shows the results of traditional stepwise chemical extraction of samples from power plants.

[0030] Figure 8 The graph shows the absolute content of germanium in various forms after traditional stepwise chemical extraction of samples from power plants. A: AC power plant; B: DG power plant. Detailed Implementation

[0031] Corresponding to the conclusions of Examples 1 and 2 Figure 3 This represents the absolute germanium content (mg / 3g sample) during each step of the stepwise chemical extraction process from 3g of germanium-rich fly ash and chlorinated distillation residue sample. This corresponds to the conclusion of Example 3. Figure 5 This represents the absolute germanium content (μg / 2g sample) during each step of the step-by-step chemical extraction process of a 2g power plant sample with low germanium content.

[0032] Example 1 presents a five-step selective leaching method for determining the germanium speciation in coal ash, using germanium-rich fly ash (circulating fluidized bed fly ash FA-1 and chain grate furnace fly ash FA-2).

[0033] Sample pretreatment: After drying in a 50℃ drying oven, the samples were sorted, ground, and sieved to ensure similar particle sizes (≤106μm), meeting the particle size range requirements for standard coal and fly ash samples. All experimental samples were stored in a desiccator.

[0034] Specific steps are as follows: Figure 1 , 2 As shown:

[0035] Step 1 (Extraction of hexagonal germanium dioxide and exchangeable germanium): Accurately weigh 3g of germanium-rich fly ash into a 100mL centrifuge tube (label the centrifuge tube before weighing and record its weight for subsequent calculation of the sample mass involved in the extraction of each form). Disperse the sample in specific reagent extraction solution A. Place the centrifuge tube in a benchtop constant temperature shaker at 60℃, 250r / min, for 5h. After processing, cool to room temperature, then centrifuge. Add deionized water to the filtrate and dilute to volume for analysis.

[0036] Step 2 (Soluble germanate extraction): The solid residue from Step 1 is dried in a 70°C oven, cooled to room temperature, weighed and recorded; specific extraction reagent solution B is added, and the centrifuge tube is placed in a benchtop constant temperature shaker at 25°C, 250 r / min for 30 min; the centrifugation and volume adjustment steps are the same as in Step 1.

[0037] Step 3 (Germanium-organic bound state and germanium sulfide): The solid residue from Step 2 is dried in a 70℃ oven, cooled to room temperature, weighed, and the weight recorded. It is then added to specific extraction reagent solution C, and the centrifuge tube is placed in a benchtop constant-temperature shaker at 90℃, 250 rpm for 6 hours. The centrifugation and volume adjustment steps are the same as in Step 1. Next, specific extraction reagent solution D is added, and the shaker parameters are: 60℃, 250 rpm for 1 hour. The centrifugation and volume adjustment steps are the same as in Step 1.

[0038] Step 4 (Germanium-Silicon Composite): The solid residue from Step 3 is dried in a 70°C oven, cooled to room temperature, weighed, and the weight recorded. It is then added to specific extraction reagent solution E, and the centrifuge tube is placed in a benchtop constant-temperature shaker at 60°C and 250 rpm for 1 hour. The centrifugation and volume adjustment steps are the same as in Step 1.

[0039] Step 5 (Tetragonal Germanium Dioxide / Residual Germanium): The solid residue from Step 4 is dried completely in a 70℃ oven. Weigh 0.1g of the sample into a PTFE digestion tube. Add 10mL of HNO3 and 5mL of HF to the coal sample. Digest the sample using a DS-360-36X graphite digester from Guangzhou Gedana Instruments Co., Ltd., following the set program. Digest at 80℃ for 1 hour. After digestion, open the digestion tube and heat it in the graphite digester until the acid is reduced to the size of a soybean. Then add 4-5mL of nitric acid to the sample and maintain for 20 minutes. After cooling, dilute to volume with deionized water for analysis.

[0040] Example 2 uses the five-step selective leaching method for determining germanium speciation in coal ash proposed in Example 1, except that the sample is chlorinated distillation residue (CR).

[0041] like Figure 3As shown, the total recoveries of the samples were 93.59% for FA-1, 100.10% for FA-2, and 90.88% for CR. In the circulating fluidized bed fly ash FA-1, germanium was mainly found in hexagonal germanium dioxide, germanates, germanium sulfides, and germanium-carbon compounds, accounting for approximately 89.62% in total. In the chain grate fly ash FA-2, the readily soluble forms of germanium (hexagonal germanium dioxide, germanates, germanium sulfides, and germanium-carbon compounds) accounted for 53%, while the insoluble forms (germanium-silicon compounds, tetragonal germanium dioxide, and encapsulated forms) accounted for 47%. Comparing the stepwise chemical extraction results of germanium-rich fly ash samples from the two types of furnaces, it can be found that both contain a large amount of hexagonal germanium dioxide and germanates, indicating that there may have been high-temperature interactions between germanium and coal minerals in the boiler. The significant differences in the occurrence forms of germanium in the two fly ash samples indicate that different combustion processes and combustion temperatures have a significant impact on the occurrence forms of germanium. The morphological distribution of CR in the chlorination distillation residue confirmed the bottleneck in the process: 83.82% of germanium existed in insoluble forms (germanium-silicon solid solution, tetragonal germanium dioxide, and encapsulated forms), which is highly consistent with previous studies suggesting the reason for the low germanium extraction rate. This result reveals the essential reason for the low extraction rate (<20%) of germanium-rich fly ash through chlorination distillation from the perspective of germanium occurrence morphology, providing a clear direction for process optimization. Key breakthroughs are needed in the conversion technologies of germanium-silicon bound states and tetragonal germanium dioxide.

[0042] Example 3 uses the five-step selective leaching method for determining germanium speciation in coal ash proposed in Example 1. The difference is that the samples are 26 ash samples from various coal-fired power plants in China, with a sample weight of 2g.

[0043] like Figure 4 As shown, through stepwise chemical extraction tests, the germanium recovery rate of the low-germanium-content power plant samples was 82%-93%. Analysis indicates that germanium is mainly found in insoluble states (including germanium-silicon bound states, tetragonal germanium dioxide, and encapsulated states), reflecting that the combustion process parameters (such as temperature and atmosphere) of conventional coal-fired power plants may be unfavorable for effective germanium extraction. Notably, high levels of active germanium (including hexagonal germanium dioxide, germanates, germanium sulfides, and germanium-carbon bound states) were detected in some power plant bottom ash, suggesting that some germanium may have undergone high-temperature interactions with coal minerals during combustion and remained in the bottom ash phase. Combined with ash composition analysis data, this batch of power plant bottom ash had a high sulfur content, suggesting that germanium may mainly exist in the form of germanium sulfides and germanium-carbon bound compounds. This finding provides a new technical approach for the targeted enrichment of germanium through optimizing combustion parameters.

[0044] like Figure 5As shown, although the fly ash from low-germanium power plants also exhibits a high proportion of insoluble germanium, similar to the germanium-rich sample FA-2, their absolute contents differ by orders of magnitude. Specifically, the content of germanium in all forms in the low-germanium sample is below 16 μg (based on a 2g sample baseline), with most below 5 μg; while the absolute content of insoluble germanium in the FA-2 sample reaches 8.92 mg (based on a 3g sample baseline), a difference of three orders of magnitude.

[0045] Analysis of the three samples revealed that assessing resource recoverability solely based on the proportion of occurrence forms may lead to misjudgment. Although the proportion of insoluble forms in both types of samples exceeded 40%, seemingly resulting in extraction losses of germanium resources, the FA-2 sample, with its high absolute content (8.92 mg / 3g sample), still possesses significant economic extraction value. Conversely, the low-germanium fly ash samples (content below 16 μg / 2g sample) suffer from a severe imbalance between extraction costs and economic benefits due to their extremely low absolute content. Therefore, the industrial recovery of germanium resources must simultaneously meet the dual standards of technical extractability and economic feasibility. Based on current process conditions, low-germanium fly ash currently lacks the value for large-scale development.

[0046] Comparative Example 1: In this example, the sample was germanium-rich fly ash (circulating fluidized bed fly ash FA-1 and chain grate furnace fly ash FA-2). The specific steps for determining the germanium speciation in the fly ash included:

[0047] Step 1 (Exchangeable State): 3g ash + 20mL 1mol / L NH4Ac, shake and react for 6h, centrifuge / filter; take 10mL deionized water, add it and shake and react again for 15min, then take out the sample and centrifuge; wash the centrifuge tube three times with deionized water, transfer all the washing liquid to the extraction liquid, and squeeze out a small amount of deionized water with a wash bottle to rinse the liquid adhering to the inner wall of the centrifuge tube during centrifugation, to ensure that all extracted elements are transferred to the extraction liquid; add deionized water to the supernatant after centrifugation and set aside for analysis.

[0048] Step 2 (carbonate-bound state): The solid residue from Step 1 was dried in a 60°C oven, cooled to room temperature, weighed and recorded; 20 mL of 0.11 mol / L HAc was added, and the reaction was carried out at room temperature for 12 h. The centrifugation and volume adjustment steps were the same as in Step 1.

[0049] Step 3 (Fe-Mn oxide bound state): The solid residue from step 2 was dried in a 60℃ oven, cooled to room temperature, weighed and recorded; 20 mL of 0.1 mol / L NH2OH·HCl (pH adjusted to 2 with nitric acid) was added, and the reaction was carried out for 12 h. The centrifugation and volume adjustment steps were the same as in step 1.

[0050] Step 4 (Organic / Sulfide Bound State): The solid residue from Step 3 is dried in a 60℃ oven, cooled to room temperature, weighed, and recorded. 20 mL of 2 mol / L HNO3 solution is added, and the centrifuge tube is placed in a benchtop constant-temperature shaker. The shaker parameters are: 85℃, 250 r / min, for 12 h. Centrifugation and volume adjustment are the same as in Step 1.

[0051] Step 5 (Residual State): Dry the solid residue from Step 4 in a 70℃ oven until completely dry. Weigh 0.1g of the sample into a PTFE digestion tube. Add 10mL of HNO3 and 5mL of HF to the coal sample. Digest the sample using a DS-360-36X graphite digester from Guangzhou Gedana Instruments Co., Ltd., following the set program. After closed digestion, open the digestion tube and heat it in the graphite digester until the acid is removed to the size of a soybean. Then add 5mL of nitric acid to the sample and maintain for 20 minutes. After cooling, dilute to volume with deionized water for analysis.

[0052] Comparative Example 2 used the same method for determining germanium speciation in coal ash as Comparative Example 1, except that the sample was chlorination distillation residue (CR).

[0053] like Figure 6 As shown in (A), the conventional method yielded germanium recoveries of 92.63%–105.81%, which is within the methodologically acceptable range. Speciation characteristics revealed that circulating fluidized bed fly ash FA-1 contained a high proportion of exchangeable and residual germanium, while germanium in chain grate fly ash FA-2 and chlorination distillation residue CR was predominantly residual germanium, exceeding 50%, and even exceeding 80% in the CR sample. This indicates a significant limitation of conventional methods in identifying the active forms of germanium in coal ash. Using conventional methods, the exact chemical form of "residual" germanium remains elusive. Certain amounts of germanium were detected in carbonates, Fe-Mn oxides, and organic matter / sulfides. In contrast, the newly designed SLM procedure determined significantly lower levels of residual forms. These findings, combined with the different germanium-containing phases and their quantitative distribution, highlight the complex heterogeneous reactions between germanium, coal minerals, and unburned carbon during combustion. These comprehensive data provide an important foundation for developing advanced germanium enrichment and extraction technologies.

[0054] Figure 6 (B) provides the absolute content values ​​for each form of germanium in the three samples. For example... Figure 6As shown in (B), samples FA-1 and FA-2 still contain a certain amount of carbonate-bound, Fe-Mn oxide-bound, and organic / sulfide-bound germanium, ranging from approximately 2 mg to 4 mg. However, carbonate minerals rarely form under high-temperature combustion conditions, and there is no empirical evidence to support the use of Fe-Mn oxides as a germanium scavenging or recovery agent during coal combustion. Traditional stepwise chemical extraction methods lack phase specificity, severely limiting their practical significance in optimizing wet germanium extraction and elucidating the germanium enrichment mechanism during coal combustion.

[0055] Comparative Example 3 used the same method for determining germanium speciation in coal ash as Comparative Example 1, except that the sample consisted of 26 ash samples from various coal-fired power plants in China, with a sample weight of 2g.

[0056] like Figure 7 As shown, the traditional method yielded a germanium recovery rate of 81%-108%, which is within the methodologically acceptable range. Speciation characteristics revealed that the proportion of residual germanium was generally higher than 70% (reaching 95% in some samples), indicating a significant limitation in identifying the active forms of germanium in coal ash using the traditional method. The proportion of exchangeable germanium (defined as metal elements adsorbed on soil, humus, and other components, representing a simple adsorption state) was generally lower than 5% (only 5-10% in a few samples). The proportion of carbonate-bound germanium (defined as co-precipitated germanium formed by metal elements in the soil on carbonate minerals) was significantly higher than that of Fe-Mn oxide-bound germanium (defined as existing as mineral encapsulations and finely dispersed particles; active iron-manganese oxides have a large specific surface area and are formed by adsorbing or co-precipitating anions). This comparison indicates two significant differences in the application of the traditional method to the coal ash system: firstly, it lacks specific identification ability for the active forms of germanium in high-temperature combustion products; secondly, the accuracy of speciation analysis is insufficient.

[0057] However, comparing relative percentage content can lead to misjudgments, while comparing absolute content is more accurate. Therefore, Figure 8 The absolute germanium content values ​​for each step of the chemical process in the low-germanium power plant sample are given. Figure 8 and Figure 4In comparison, traditional stepwise chemical extraction methods show low extraction efficiency and significantly poor results for carbonate-bound forms, mainly due to insufficient acid strength of the 0.11 mol / L acetic acid solution. Despite a longer extraction time, it is still difficult to effectively dissociate the germanium-carbonate complex. The extraction rate for organic / sulfide-bound forms is also low, reaching a maximum of approximately 20% and a minimum of only about 1%, mostly falling within the 3%-10% range. There are two main reasons for this: firstly, the limited oxidizing power of nitric acid (2 mol / L) alone is insufficient to completely decompose germanium-organic compounds and germanium sulfides; secondly, the low solid-liquid ratio during extraction means that a 20 mL reagent volume is insufficient to fully extract 2 g of ash sample. In contrast, the method developed in this invention overcomes the limitations of traditional methods: the increased solid-liquid ratio and the nitric acid-hydrogen peroxide mixture ensure sufficient oxidizing power and extractability, providing methodological assurance for the accurate analysis of the active forms of germanium in coal ash.

[0058] Traditional stepwise chemical extraction methods primarily serve for soil heavy metal environmental risk assessment. Their speciation systems (exchangeable forms, carbonate-bound forms, etc.) are insufficient to accurately determine the specific occurrence forms of germanium in coal ash systems, resulting in significant limitations. In contrast, the stepwise chemical extraction method for germanium speciation developed in this invention not only clearly identifies the specific forms of germanium but has also been verified to possess a certain degree of accuracy.

[0059] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A five-step selective leaching process for determining germanium speciation in coal ash, characterized in that, The occurrence state of germanium in coal fly ash is quantitatively determined by using multiple reagents and through a five-step selective leaching method, including hexagonal germania / exchangeable germanium, soluble germanate, germanium sulfide / germanium-organic combination state, germanium-silicon combination state and tetragonal germania / residual germanium.

2. The five step selective leaching process for determination of germanium species in coal ash as claimed in claim 2 wherein, The method comprises the following steps: Step one, hexagonal germania / exchangeable germanium extraction: the solid sample after being air-dried, impurity-removed, ground and sieved is dispersed in a specific extraction reagent solution A, the centrifugal tube is placed in a table type constant temperature oscillator, after the treatment is completed, it is cooled to room temperature, then centrifugal separation is conducted, and the filtrate is added with deionized water for constant volume before measurement; Step two, soluble germanate extraction: the solid residue in step one is dried, and after being cooled to room temperature, it is dispersed in a specific extraction reagent solution B, the centrifugal tube is placed in a table type constant temperature oscillator, after the treatment is completed, centrifugal separation is conducted, and the filtrate is added with deionized water for constant volume before measurement; Step three, germanium-organic combination state / germanium sulfide extraction: the solid residue in step two is dried, and after being cooled to room temperature, it is dispersed in a specific extraction reagent solution C, the centrifugal tube is placed in a table type constant temperature oscillator, after the treatment is completed, it is cooled to room temperature, the filtrate is added with deionized water for constant volume before measurement; the solid residue is dried, and then added with a specific extraction reagent solution D, the centrifugal tube is placed in a table type constant temperature oscillator, after the treatment is completed, it is cooled to room temperature, then centrifugal separation is conducted, and the filtrate is added with deionized water for constant volume before measurement; Step four, germanium-silicon combination state extraction: the solid residue in step three is dried, and after being cooled to room temperature, it is dispersed in a specific extraction reagent solution E, the centrifugal tube is placed in a table type constant temperature oscillator, after the treatment is completed, centrifugal separation is conducted, and the filtrate is added with deionized water for constant volume before measurement; Step five, tetragonal germania / residual germanium extraction: the solid residue in step four is dried, and then added with nitric acid and hydrogen fluoride, and is digested in a closed digestion tube; before the digestion, the coal sample is subjected to ashing treatment to eliminate the interference of organic matters; after the closed digestion is completed, the digestion tube is opened, and is placed in a graphite digestion instrument to be heated to chase the acid to the size of a soybean, then nitric acid is added in the sample, and is kept for a period of time, and deionized water is added for constant volume before measurement.

3. The five step selective leaching process for determination of germanium species in coal ash as claimed in claim 2 wherein, The sample in step one is dried at 50 DEG C for 24 hours to remove water, and is sieved through a 100-200 mesh sieve.

4. The five step selective leaching process for determination of germanium species in coal ash as claimed in claim 2 wherein, The solid sample used in step one is a fly ash, a gasification slag, a smelting slag or the like containing germanium industrial solid waste sample; the specific extraction reagent A is a metal salt ion solution, specifically MgCl2, and the concentration is 1-3 mol / L; the hexagonal germania / exchangeable germanium extraction reaction condition in step one is 60 DEG C, 250 r / min, and the treatment time is 5 hours.

5. The five step selective leaching process for the determination of germanium species in coal ash as claimed in claim 2 wherein, The specific extraction reagent B is a dilute mineral acid solution, such as an HCl solution with a concentration of 3-6 mol / L, and the soluble germanate extraction reaction condition in step two is 25 DEG C, 250 r / min, and the treatment time is 30 minutes.

6. The five step selective leaching process for the determination of germanium species in coal ash as claimed in claim 2 wherein, The specific extraction reagent C is a strong oxidizing solution, specifically a nitric acid+hydrogen peroxide mixed solution, and the germanium-organic combination state and germanium sulfide extraction reaction condition in step three is 90 DEG C, 250 r / min, and the treatment time is 6 hours.

7. The five step selective leaching process for the determination of germanium species in coal ash as claimed in claim 2 wherein, The specific extraction reagent D is an ammonium salt solution, specifically a (NH4)2S solution with a concentration of 20% or more, and the germanium disulfide extraction reaction condition in step three is 60 DEG C, 250 r / min, and 1 h of treatment.

8. The five step selective leaching process for the determination of germanium species in coal ash as claimed in claim 2 wherein, The specific extraction reagent E is a combined solution, specifically a 1-3 M H2SO4+NH4F mixed solution, and the germanium-silicon combined state extraction reaction condition in step four is 60 DEG C, 250 r / min, and 1 h of treatment.

9. The five step selective leaching process for the determination of germanium species in coal ash as claimed in claim 2 wherein, In step five, the solid residue in step four is dried and weighed, 0.1 g of the sample is weighed into a PTFE digestion tube, HNO3+HF (2:1) is added to the coal sample, and the closed digestion is carried out at 80 DEG C for 1 h; after the closed digestion is completed, the digestion tube is opened, placed in a graphite digestion instrument, and heated to chase the acid to the size of a soybean, then 4-5 mL of nitric acid is added to the sample, and maintained for 20 minutes; after cooling, the sample is diluted with deionized water and measured.

10. The five step selective leaching process for the determination of germanium species in coal ash as claimed in claim 2 wherein, In steps one to four, the inner wall of the centrifugal tube is washed with deionized water to transfer it to the extraction liquid together, so as to ensure that all elements are transferred to the solution to be measured.

Images