Method for detecting organic products in a bayer process complex

Abstract

The present application belongs to the field of analytical chemistry and metallurgical technology, and particularly relates to a detection method of organic products in a Bayer process complex system. The detection method comprises the following steps: taking a Bayer process mother liquor sample after reaction, filtering to remove solid impurities, adding an inorganic acid to adjust the pH to 1-2, adding an inorganic salt to the acidified sample to dissolve, then adding an organic solvent to extract, separating the organic phase, drying the separated organic phase to remove water, blowing dry with nitrogen at 35-40 DEG C to remove the organic solvent, and obtaining the extracted organic products; adding anhydrous pyridine to the extracted organic products to dissolve, then adding a silylating agent to perform a derivatization reaction, obtaining a sample to be tested, separating and detecting the sample to be tested by GC-MS, and obtaining the type and relative abundance information of the organic products in the sample. The present application effectively avoids the interference of a high-salt high-alkali matrix through an optimized pretreatment procedure, and realizes the accurate separation and identification of various hydroxyl-containing organic substances in the Bayer process mother liquor.

Description

Technical Field

[0001] This invention belongs to the fields of analytical chemistry and metallurgical technology, and specifically relates to a method for detecting organic products in complex Bayer processes. Background Technology

[0002] The Bayer process is the primary method for producing alumina, generating a large amount of highly alkaline red mud during production. During Bayer process production, organic matter introduced from bauxite and added organic additives (such as reducing agents and flocculants) undergo complex chemical transformations under high-temperature and high-alkali conditions, producing various organic acids, phenols, hydroxymethylfurans, and other hydroxyl-containing organic compounds. Studies have shown that these organic compounds can accumulate during process cycles, leading to problems such as increased solution viscosity, hindered alumina crystallization, decreased product purity, and increased alkali consumption. Therefore, establishing a method for accurately detecting hydroxyl-containing organic products in the Bayer process system is of great significance for process monitoring, additive screening, and risk assessment.

[0003] Several methods for treating organic matter in Bayer process mother liquor have been reported in the prior art. For example, patent CN121269774A discloses a method for removing organic matter from Bayer process alumina production solutions, which involves mixing the evaporation effluent with biogas digester residue and removing the organic matter through adsorption. Patent CN114655972A discloses a method for efficiently removing organic matter from Bayer process alumina solutions, which uses photocatalysis and ultrasound to convert the organic matter into oxalate crystals for separation. However, these methods mainly focus on the removal of organic matter and lack accurate detection methods for the types and contents of organic acids, thus failing to provide precise information on the organic matter composition for process optimization.

[0004] In the field of organic acid detection, patent CN115792031B discloses a quantitative detection method for organic acids, employing 3-nitrophenylhydrazine derivatization combined with liquid chromatography-tandem mass spectrometry (LC-MS / MS) for quantitative analysis. This method boasts high sensitivity and accuracy, but it primarily targets conventional matrices such as biological samples and does not consider the high-salt, high-alkali characteristics of Bayer process mother liquor. Patent CN109406704B discloses a method for determining the organic acid content in tobacco, using GC-MS combined with a standard curve for quantitative analysis. However, its sample pretreatment is relatively simple and difficult to directly apply to the complex composition of Bayer process mother liquor. Furthermore, methods for detecting other hydroxyl-containing organic compounds such as phenols and hydroxyfurans also lack optimization for the Bayer process system.

[0005] In summary, the Bayer process mother liquor has high alkalinity (Na₂O₂). kDue to the characteristics of high concentration (200-250 g / L), high aluminum concentration, and complex matrix, conventional organic acid detection methods are difficult to apply directly. Existing technologies mainly have the following problems: (1) High salt and high alkalinity matrices cause serious interference, affecting the accuracy of detection; (2) There are many types of hydroxyl-containing organic compounds with strong polarity, making it difficult to achieve effective separation; (3) There is a lack of standardized pretreatment methods for the complex Bayer process system. Summary of the Invention

[0006] In view of the shortcomings and deficiencies of the existing technology, the purpose of this invention is to provide a method for detecting organic products in complex Bayer processes.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for detecting organic products in a complex Bayer process system, comprising the following steps:

[0009] (1) Sample pretreatment: Take the Bayer process mother liquor sample after the reaction and filter to remove solid impurities;

[0010] (2) Acidification: Place the filtered sample in an ice bath and add inorganic acid dropwise while stirring to adjust the pH to 1.0-2.0;

[0011] (3) Salting out: Add inorganic salt to the acidified sample and stir until it is completely dissolved;

[0012] (4) Liquid-liquid extraction: Add an organic solvent to the salted-out sample for extraction to separate the organic phase;

[0013] (5) Drying: The separated organic phase is dried to remove water, and a dry organic phase extract is obtained;

[0014] (6) Nitrogen blowing concentration: The dried organic phase extract is dried with nitrogen at 35-40℃ to remove the organic solvent and obtain the extracted organic product;

[0015] (7) Derivatization: Anhydrous pyridine is added to the extracted organic product to dissolve it, and then a silanizing agent is added to carry out the derivatization reaction to obtain the sample to be tested;

[0016] (8) Gas chromatography-mass spectrometry analysis: The derivatives in the test sample are separated and detected by gas chromatography-mass spectrometry. The original compound types corresponding to each derivative are determined by searching the mass spectrometry database and comparing the retention time.

[0017] (9) Results analysis: Based on the detection results of step (8), the types and relative abundance of organic products in the Bayer process mother liquor sample are obtained.

[0018] Preferably, the inorganic acid in step (2) is hydrochloric acid or sulfuric acid, with a concentration of 3-6 mol / L.

[0019] Acidification converts charged carboxylate ions in a high-salt, high-alkalinity aqueous phase into molecular states, facilitating subsequent organic solvent extraction.

[0020] Preferably, the inorganic salt in step (3) is sodium chloride or sodium sulfate, and the concentration of the added inorganic salt is 80-100% of its saturated solubility in the added system. By adding an inorganic salt with near-saturated solubility, the partition coefficient of polar organic products (organic acids, phenols, hydroxyfurans, etc.) in the organic phase can be increased, thereby improving the extraction effect of subsequent organic solvent extraction.

[0021] Preferably, the organic solvent in step (4) is one or more of ethyl acetate, dichloromethane or diethyl ether, and the amount of organic solvent added is 0.8-1.2 times the volume of the sample after salting out.

[0022] The aforementioned organic solvents have a good extraction effect on the organic products in the samples of this invention, and have a low boiling point, making them easy to remove and avoiding interference with subsequent derivatization reactions.

[0023] Preferably, the extraction in step (4) is performed by repeated extraction 2-3 times, and the organic phases are combined.

[0024] Preferably, the drying and dehydration in step (5) refers to drying and dehydration using anhydrous sodium sulfate or anhydrous magnesium sulfate.

[0025] Drying and dehydration processes prevent interference with subsequent derivatization reactions and ensure the complete derivatization of organic products.

[0026] Step (6) can effectively avoid the loss of organic products by removing the organic solvent from the dried organic phase extract at a lower temperature of 35-40℃, thereby improving the accuracy of the detection results.

[0027] In step (7), the use of a specific anhydrous pyridine has good solubility for the extracted organic products, which is beneficial for the derivatization reaction.

[0028] Preferably, the silanizing agent in step (7) is one of BSTFA (bis(trimethylsilyl)trifluoroacetamide), BSTFA+1vt% TMCS (trimethylchlorosilane), or MSTFA (N-methyl-N-(trimethylsilane)trifluoroacetamide).

[0029] Preferably, the derivatization reaction in step (7) is carried out under sealed conditions at 60-80°C for 30-60 min.

[0030] Derivatization reactions using silanizing reagents convert hydroxyl-containing organic compounds (carboxylic acids, phenols, hydroxymethylfurans, etc.) into volatile trimethylsilyl esters or trimethylsilyl ether derivatives, improving chromatographic separation and mass spectrometry detection sensitivity. Finally, accurate identification of the target compounds is achieved through GC-MS combined with mass spectrometry database searching.

[0031] Preferably, the conditions for separating and detecting derivatives in the sample using gas chromatography-mass spectrometry in step (8) are as follows: the gas chromatography uses a non-polar or moderately polar capillary column with an injection port temperature of 250-300℃; the mass spectrometry uses an EI ionization source of 70 eV with a scanning range of m / z 50-500.

[0032] Preferably, the relative abundance information in step (9) is obtained by peak area normalization.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] (1) This invention provides a method for detecting organic products in complex systems with strong base, high salt, and high aluminum in the Bayer process. By optimizing the pretreatment process of acidification-salting out-extraction-derivative, the interference of high salt and high base matrices is effectively removed, solving the technical problem that traditional methods are difficult to apply directly to Bayer process mother liquor.

[0035] (2) To address the low derivatization efficiency of the Bayer process mother liquor, this invention employs drying, nitrogen blowing, and anhydrous pyridine reconstitution to remove water and residual solvents that interfere with the derivatization reaction. This ensures that the silanizing reagent is fully used for the derivatization of the target compound, significantly improving detection sensitivity. This method exhibits good derivatization effects on hydroxyl-containing organic compounds such as carboxylic acids, phenols, and hydroxymethylfurans.

[0036] (3) The method of the present invention is simple to operate and has good repeatability. It can be widely used in the detection of various organic products in the Bayer process, providing key technical means for process monitoring and risk assessment of organic matter accumulation. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the process used in Example 1 for detecting organic products in the simulated reduction Bayer dissolution system.

[0038] Figure 2 The image shows the GC-MS total ion chromatogram of the SHG system (glucose-Bayer mother liquor-hematite) in Example 1.

[0039] Figure 3 The GC-MS total ion chromatograms of different reaction systems in Example 2 are compared, where (a) is the WG system (glucose-aqueous solution) and (b) is the SG system (glucose-Bayer mother liquor). Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0041] Example 1

[0042] This embodiment uses the method of the present invention to detect organic products in a simulated reduction Bayer leaching system (i.e., glucose-Bayer mother liquor-hematite system, SHG). The flowchart is shown below. Figure 1 As shown, it includes the following steps:

[0043] (1) Sample pretreatment: Take 10 mL of Bayer process mother liquor sample after simulated high temperature dissolution reaction (reaction conditions: 270℃, initial addition of glucose, glucose to hematite mass ratio of 40%, reaction for 60 min), cool to room temperature and filter through a 0.45 μm filter membrane.

[0044] (2) Acidification: Place the filtered sample in an ice bath and slowly add 6 mol / L HCl while stirring to adjust the pH to 1.5.

[0045] (3) Salting out: Add 3 g NaCl until nearly saturated and stir to dissolve.

[0046] (4) Liquid-liquid extraction: Add 10 mL of ethyl acetate and extract 3 times, then combine the organic phases.

[0047] (5) Drying: Add anhydrous Na2SO4 and dry for 30 min, then filter.

[0048] (6) Nitrogen blowing concentration: The dried organic phase is dried by nitrogen blowing at 35-40℃.

[0049] (7) Derivatization: Add 50 μL of anhydrous pyridine to dissolve the residue, then add 50 μL of BSTFA + 1% TMCS, and react at 70℃ for 30 min. After cooling, add 900 μL of ethyl acetate to dilute and obtain the sample to be tested.

[0050] (8) GC-MS Analysis: Analysis was performed using a gas chromatography-mass spectrometry (GC-MS) system. The chromatographic column was an SH-I-5sil MS capillary column (30 m × 0.25 mm × 0.25 μm). The injection port temperature was 280℃, and the split ratio was 30:1. The temperature program was as follows: initial temperature 60℃, held for 2 min, increased to 90℃ at 10℃ / min, continued to increase to 200℃ at 4℃ / min, and then increased to 280℃ at 20℃ / min, held for 5 min. The EI ionization source was 70 eV, and the scan range was m / z 50-500. The corresponding detection chromatograms are shown below. Figure 2 As shown.

[0051] (9) Results Analysis: Multiple organic acid derivatives were detected. Through mass spectrometry database search (NIST library) and retention time comparison, combined with the correspondence between the derivatives and the original organic acids (increased molecular weight after silanization, characteristic fragment ions, etc.), the corresponding original organic acids were identified as methyl succinic acid (MeSA), succinic acid (SA), α-hydroxyisobutyric acid (α-HIBA), 2-methylglutaric acid (2-MGA), glycolic acid (GA), etc. The relative contents of each organic product were obtained by peak area normalization method, and the results are shown in Table 1.

[0052] Table 1. GC-MS analysis results of major organic products in the Bayer process mother liquor sample of Example 1

[0053] Retention time (min) Compound Name Relative content (%) Matching degree (SI) 7.59 α-Hydroxyisobutyric acid (α-HIBA) 10.35 96 7.89 Glycolic acid (GA) 1.53 97 9.31 2-Hydroxy-2-methylbutyric acid (2-Me-2-HB) 3.26 94 14.45 Succinic acid (SA) 9.52 94 14.80 Methylsuccinic acid (MeSA) 59.5 94 16.91 2,2-Dimethylsuccinic acid (2,2-diMeSA) 3.32 86 17.22 Glutaric acid (GlrA) 1.69 87 17.50 2-Methylglutaric acid (2-MGA) 6.67 88

[0054] Note: The compound names in the table are the original parent compounds; the actual targets detected are their trimethylsilyl ester derivatives. Relative contents are calculated using peak area normalization; only compounds with a relative content >1% are listed. The similarity index (SI) is used for mass spectrometry database searches (>85 indicates a good match), and the same applies below.

[0055] Example 2

[0056] Organic products in the post-reaction liquid phase of the organic auxiliary agent-aqueous solution system (WG) and the organic auxiliary agent-Bayer mother liquor system (SG) were detected according to the method of Example 1. The WG system did not require acidification and salting-out steps; the aqueous solution was directly subjected to liquid-liquid extraction, drying, nitrogen blowing concentration, derivatization, and GC-MS analysis. Glucose was used as the organic auxiliary agent, and the amount of glucose and other reaction conditions were the same as in Example 1. The corresponding detection chromatograms are shown below. Figure 3 As shown in Tables 2 and 3, the relative contents of each organic product were obtained by peak area normalization.

[0057] Table 2. GC-MS analysis results of major organic products in the WG system

[0058] Retention time (min) Compound Name Relative content (%) Matching degree (SI) 7.51 Lactic acid (LA) 3.29 95 7.89 Glycolic acid (GA) 9.41 97 9.31 Lev (levulinic acid) 21.87 96 14.35 5-Hydroxymethylfurfural (5-HMF) 22.26 93 17.05 Resorcinol (Res) 2.41 86 22.89 pyrogallol (PG) 40.76 92

[0059] Table 3. GC-MS analysis results of major organic products in the SG system

[0060] Retention time (min) Compound Name Relative content (%) Matching degree (SI) 7.51 Lactic acid (LA) 68.05 96 7.59 α-Hydroxyisobutyric acid (α-HIBA) 14.06 96 7.89 Glycolic acid (GA) 1.96 97 9.12 2-Hydroxybutyric acid (2-HB) 6.36 97 9.31 2-Hydroxy-2-methylbutyric acid (2-H-2-MBA) 2.19 93 22.26 2-Hydroxyglutaric acid (2-HG) 2.59 92 22.35 2-Methyl-2-hydroxyglutaric acid (2-Me-2-HG) 1.26 93

[0061] As shown in Tables 2-3, there are significant differences in the composition of organic products in different systems: phenols and hydroxymethylfurans are predominant in the WG system, while hydroxy acids such as lactic acid are predominant in the SG system. These results demonstrate that the method of this invention is not only applicable to the detection of organic acids, but also exhibits good derivatization effects and detection sensitivity for hydroxyl-containing organic compounds such as phenols and hydroxymethylfuran derivatives, verifying the applicability of this method to the detection of organic products in complex Bayer process systems.

[0062] Comparative Example 1

[0063] Compared with Example 1, this comparative example lacks step (6) of nitrogen blowing concentration, but the rest are the same.

[0064] The results showed that the detection signals of major organic acid derivatives were significantly weakened, and some low-abundance organic acids were difficult to detect, indicating that residual moisture consumed the silanizing reagent, resulting in incomplete derivatization.

[0065] Comparative Example 2

[0066] Compared with Example 1, this comparative example lacks the derivatization process of step (7). The residue after nitrogen blowing concentration was diluted with 900 μL of ethyl acetate and then analyzed by GC-MS.

[0067] The results showed that only a small amount of low-boiling-point substances were detected. Dicarboxylic acids such as methyl succinic acid and succinic acid could not be detected due to their high polarity and low volatility, thus failing to achieve effective detection of organic products. This indicates that derivatization is a necessary step for the detection of polar organic products.

[0068] Comparative Example 3

[0069] Compared with Example 1, this comparative example lacks step (3) salting out, but the rest are the same.

[0070] The results showed that the detection signals of polar organic acids such as methyl succinic acid and succinic acid were significantly weakened, indicating that salting out plays an important role in improving the extraction efficiency of polar organic acids.

[0071] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for detecting organic products in complex Bayer processes, characterized in that... Includes the following steps: (1) Sample pretreatment: Take the Bayer process mother liquor sample after the reaction and filter to remove solid impurities; (2) Acidification: Place the filtered sample in an ice bath and add inorganic acid dropwise while stirring to adjust the pH to 1.0-2.0; (3) Salting out: Add inorganic salt to the acidified sample and stir until it is completely dissolved; (4) Liquid-liquid extraction: Add an organic solvent to the salted-out sample for extraction to separate the organic phase; (5) Drying: The separated organic phase is dried to remove water, and a dry organic phase extract is obtained; (6) Nitrogen blowing concentration: The dried organic phase extract is dried with nitrogen at 35-40℃ to remove the organic solvent and obtain the extracted organic product; (7) Derivatization: Anhydrous pyridine is added to the extracted organic product to dissolve it, and then a silanizing agent is added to carry out the derivatization reaction to obtain the sample to be tested; (8) Gas chromatography-mass spectrometry analysis: The derivatives in the test sample are separated and detected by gas chromatography-mass spectrometry. The original compound types corresponding to each derivative are determined by searching the mass spectrometry database and comparing the retention time. (9) Results analysis: Based on the detection results of step (8), the types and relative abundance of organic products in the Bayer process mother liquor sample are obtained.

2. The method for detecting organic products in a complex Bayer process system according to claim 1, characterized in that: The inorganic acid mentioned in step (2) is hydrochloric acid or sulfuric acid, with a concentration of 3-6 mol / L.

3. The method for detecting organic products in a complex Bayer process system according to claim 1, characterized in that: The inorganic salt mentioned in step (3) is sodium chloride or sodium sulfate, and the concentration of the added inorganic salt is 80-100% of its saturated solubility in the added system.

4. The method for detecting organic products in a complex Bayer process system according to claim 1, characterized in that: The organic solvent mentioned in step (4) is one or more of ethyl acetate, dichloromethane or diethyl ether, and the amount of organic solvent added is 0.8-1.2 times the volume of the sample after salting out.

5. The method for detecting organic products in a complex Bayer process system according to claim 4, characterized in that: The extraction process involves repeated extraction 2-3 times, followed by combining the organic phases.

6. The method for detecting organic products in a complex Bayer process system according to claim 1, characterized in that: The drying and dehydration mentioned in step (5) refers to drying and dehydration using anhydrous sodium sulfate or anhydrous magnesium sulfate.

7. The method for detecting organic products in a complex Bayer process system according to claim 1, characterized in that: The silanizing agent mentioned in step (7) is one of BSTFA, BSTFA+1vt% TMCS or MSTFA.

8. The method for detecting organic products in a complex Bayer process system according to claim 1, characterized in that: The derivatization reaction described in step (7) is carried out under sealed conditions at 60-80℃ for 30-60 min.

9. The method for detecting organic products in a complex Bayer process system according to claim 1, characterized in that: The conditions for separating and detecting derivatives in the sample using gas chromatography-mass spectrometry in step (8) are as follows: gas chromatography uses a non-polar or moderately polar capillary column with an injection port temperature of 250-300℃; mass spectrometry uses an EI ionization source of 70 eV with a scanning range of m / z 50-500.

10. The method for detecting organic products in a complex Bayer process system according to claim 1, characterized in that: The relative abundance information mentioned in step (9) is obtained by peak area normalization.

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