A method for rapid coagulation separation of soil mineral-bound organic carbon
By using CaCl2 flocculation sedimentation and ethanol washing technology, the problem of time-consuming separation of soil mineral-bound organic carbon was solved, achieving rapid and effective solid-liquid separation and improving experimental efficiency and data quality.
Patent Information
- Application Number
- CN202611023170.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-10
- Publication Date
- 2026-11-06
AI Technical Summary
In existing technologies, the separation process of soil mineral-bound organic carbon (MAOC) suspensions is time-consuming and difficult to settle quickly, affecting experimental efficiency and data quality.
The CaCl2 flocculation sedimentation method was adopted. By adding CaCl2 solution to the suspension, the double electric layer of soil colloidal particles was compressed, which promoted the rapid aggregation of MAOC. The sample was then treated with ethanol washing or no washing to achieve rapid solid-liquid separation.
It significantly shortens the solid-liquid separation time, improves separation efficiency, avoids particle loss, reduces drying energy consumption, is suitable for batch sample processing, and improves experimental efficiency and data accuracy.
Smart Images
Figure CN123045809A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of chemical separation technology, specifically relating to a rapid sedimentation separation method for soil mineral-bound organic carbon. Background Technology
[0002] Particle size distribution (wet sieving) is currently the main physical method for separating particulate organic carbon (POC) and mineral-bound organic carbon (MAOC) in soil. The core principle is based on the difference in physical protection of soil organic carbon: particulate organic carbon (POC, >53 μm) mainly originates from plant residues, is exposed to microbial decomposition, and has a rapid turnover; while mineral-bound organic carbon (MAOC, <53 μm) forms complexes with clay minerals, is physically protected, and has strong stability. By physically separating the carbon at the 53 μm boundary, the content and dynamics of active and stable carbon pools can be quantitatively assessed.
[0003] The core process is as follows: Take air-dried soil samples, use sodium hexametaphosphate solution as a dispersant, and thoroughly break down the aggregates by shaking (18 h, 90 r / min). Then, separate the suspension by passing it through a 53 μm (approximately 300 mesh) sieve. The portion above the sieve is the POC soil sample, and the portion below the sieve is the MAOC soil sample. After drying at 60℃, weighing, grinding, and measuring the carbon content, POC and MAOC are obtained.
[0004] MAOCs are mainly composed of fine-sized clay particles (< 2 μm) and powder particles (2-53 μm). They readily form suspensions upon contact with water and are difficult to settle naturally by gravity. In the actual operation of this particle size grouping method, a large amount of deionized water is used to separate POCs and MAOCs through a 53 μm sieve. The MAOC fraction that passes through the sieve easily forms a suspension, and relying solely on gravity for natural sedimentation results in a very long waiting time, ranging from several hours to several days, according to Stokes' law. This leads to a long drying time required for drying the separated MAOC suspension at 60°C, becoming a significant bottleneck in batch experiments and affecting the experimental progress. Solving the problem of the long time required to obtain MAOCs that pass through the sieve is significant not only in saving time but also in improving experimental efficiency and data quality, and has a systematic improvement effect on the development of the discipline.
[0005] In summary, this invention addresses the problem of time-consuming MAOC (Massive Organic Carbon) extraction from soil by proposing a rapid sedimentation and separation method for soil mineral-bound organic carbon. Summary of the Invention
[0006] The purpose of this invention is to provide a rapid sedimentation separation method for soil mineral-bound organic carbon. The method uses CaCl2 flocculation sedimentation to achieve rapid sedimentation of fine soil particles to obtain MAOC, thus providing an improved means for the rapid sedimentation separation of soil mineral-bound organic carbon.
[0007] To achieve the above objectives, the technical solution of the present invention is as follows:
[0008] A rapid sedimentation separation method for soil mineral-bound organic carbon includes the following steps:
[0009] (1) Dispersion: Take an air-dried soil sample, use sodium hexametaphosphate solution as a dispersant, and shake to fully disperse the soil to form a suspension. Sodium hexametaphosphate eliminates the cation bridging effect by complexing with polyvalent cations such as calcium, magnesium, iron, and aluminum, thus fully dispersing the particles in the soil aggregates;
[0010] (2) Screening: The suspension after shaking is passed through a 53 μm sieve. The soil in the sieve is washed with deionized water in small amounts and multiple times until the water flowing under the sieve is colorless. The part above the sieve is particulate organic carbon component (>53 μm, POC), and the part below the sieve is mineral-bound organic carbon component (<53 μm, MAOC).
[0011] (3) Sedimentation: Add CaCl2 solution to the suspension through the sieve while stirring to cause MAOC to precipitate. 2+ Compression of the double electric layer on the surface of soil colloidal particles reduces the electrostatic repulsion between particles, promoting rapid aggregation of MAOC.
[0012] (4) Settling: Let stand until MAOC settles at the bottom, remove the supernatant to obtain MAOC precipitate;
[0013] (5) Remove CaCl2 salts from the MAOC precipitate to obtain a MAOC sample suitable for subsequent detection. One of two methods can be used:
[0014] Method 1 (Applicable to elemental analyzers): After drying the MAOC precipitate, weigh the total mass. Subtract the mass of added CaCl2 by calculation to obtain the dry mass of MAOC. When determining the total carbon content using an elemental analyzer, Cl... - It does not generate interference signals, therefore there is no need to add Cl - Physical removal from the sample simply requires deducting the contribution of CaCl2 from the mass calculation.
[0015] Method 2 (applicable to solution method): Wash the MAOC precipitate with ethanol to remove Cl. - After drying, the dry weight of MAOC is obtained. Ethanol washing does not redisperse the aggregated particles, thus avoiding the loss of MAOC caused by water washing.
[0016] Preferably, the concentration of sodium hexametaphosphate is 5 g / L, and the mass ratio of sodium hexametaphosphate to soil sample is 1:800.
[0017] Another object of the present invention is to provide a MAOC dry sample obtained according to the above method.
[0018] The present invention also aims to provide the application of the method described above in the rapid quantitative assessment of the content and dynamics of activated carbon libraries and stable carbon libraries.
[0019] The beneficial effects of this invention are:
[0020] To address the difficulties in solid-liquid separation and excessively long drying cycles of MAOC suspensions in conventional particle size distribution methods, this invention introduces CaCl2 solution as a flocculant, promoting rapid sedimentation of fine soil particles within 1-2 hours, achieving efficient solid-liquid separation, and significantly reducing the moisture content of the samples to be dried. This method, without compromising the accuracy of organic carbon determination, restructures the entire solid-liquid separation-drying process into predictable and standardized operational steps, significantly improving the throughput and efficiency of batch sample processing.
[0021] The advantages of this invention are as follows:
[0022] ① Shorten solid-liquid separation time: For the MAOC suspension after sieving, conventional methods make it difficult for particles to settle by gravity due to their small size. The improved method introduces CaCl2 solution to compress the colloidal double layer, which promotes the rapid flocculation and sedimentation of the particles within 1-2 hours, improving the solid-liquid separation efficiency by more than 95%.
[0023] ② Avoid particle loss. For elemental analyzer detection, mass deduction is used instead of water washing for desalination, fundamentally avoiding MAOC loss during the washing process. For solution-based detection, ethanol washing is used instead of water washing to avoid redispersing of already precipitated particles.
[0024] ③ Reduced drying energy consumption: The improved method directly removes the supernatant through solid-liquid separation (Method 1) or washing with ethanol (Method 2), resulting in a significantly reduced moisture content compared to the suspension produced by conventional methods. This eliminates the need for direct evaporation of large amounts of supernatant as in conventional methods. The drying time for a single sample is reduced from the conventional 10-12 days to 4 hours.
[0025] ④ The method is highly versatile. Two pretreatment schemes are provided, one for elemental analyzers and the other for solution methods, allowing operators to choose based on their laboratory's existing equipment.
[0026] ⑤ It is easy to operate and suitable for batch sample processing. Attached Figure Description
[0027] Figure 1 This is a flowchart comparing the improved methods (method 1 and method 2) of this invention with the conventional method (drying temperature is 60°C for both).
[0028] Figure 2 This is a physical image of the sedimentation effect in this invention. Detailed Implementation
[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.
[0030] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.
[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0032] Example 1 (Applicable to elemental analyzers)
[0033] 1. Experimental Objectives and Procedures
[0034] Experimental objective: To shorten the soil MAOC collection time using CaCl2 flocculation and sedimentation method, achieve solid-liquid separation, reduce drying energy consumption, and improve experimental efficiency.
[0035] Core principle: Adding Ca to the MAOC suspension 2+ The compression of the double electric layer of the viscous particles causes them to rapidly agglomerate into large flocs and settle, thereby achieving rapid solid-liquid separation.
[0036] Operating steps:
[0037] (1) Dispersion. Accurately weigh m grams (20 grams) of air-dried soil sample (passed through a 2 mm sieve and mixed evenly), place it in a 250 mL Erlenmeyer flask or centrifuge bottle, add 50 mL of 5 g / L sodium hexametaphosphate solution, cover and place on a reciprocating shaker, shake at 90 r / min for 15 h to fully disperse the soil and form a suspension.
[0038] (2) Sieving. The shaken suspension was passed through a 53 μm sieve. The soil in the sieve was rinsed with deionized water in small amounts and multiple times until the water flowing under the sieve was colorless. The part above the sieve was particulate organic carbon component (>53 μm, POC), and the part below the sieve was mineral-bound organic carbon component (<53 μm, MOC). The soil suspension below the sieve was collected in a 1 L beaker.
[0039] (3) Sedimentation. Slowly add 25 mL of 0.5 mol / L CaCl2 solution to the suspension while stirring.
[0040] (4) Let stand. Let stand for 1-2 hours until the supernatant is clear and MAOC settles at the bottom.
[0041] (5) Remove the supernatant. Remove the supernatant using a pipette or siphon, removing as much as possible without disturbing the bottom sediment. Do not wash with water.
[0042] (6) Drying. Transfer the bottom MAOC wet sample along with the container to an oven and dry at 60°C to constant weight.
[0043] (7) Weighing. Record the total dry mass W (unit: g) after drying.
[0044] (8) Calculate the dry mass of MAOC. The mass of CaCl2 added, W(CaCl2) = 0.5 × 0.025 × 110.98 = 1.387 g. The dry mass of MAOC, W(MAOC) = W(total) – W(CaCl2).
[0045] (9) Determination of organic carbon. Take a portion of the dry sample, grind it evenly, and determine the total carbon content C (%) using an elemental analyzer. The absolute carbon mass of MAOC m(MAOC-C) = W(MAOC) × C / 100.
[0046] (10) Results presentation. The carbon mass per gram of soil MAOC is expressed as: MAOC = m(MAOC-C) / m.
[0047] 2. Experimental equipment
[0048] The experimental equipment used in this embodiment is shown in Table 1.
[0049] Table 1. Experimental equipment used in the improved method (Method 1)
[0050]
[0051] Example 2 (Method 2: Solution Method)
[0052] 1. Experimental Objectives and Procedures
[0053] Experimental Objective: To utilize the CaCl2 flocculation and sedimentation method to shorten the collection time of MAOC in soil while eliminating Cl-. - It interferes with the results of organic carbon content determination.
[0054] Core principle: Adding Ca to the MAOC suspension 2+ The compression of the double electric layer of the particles causes them to rapidly aggregate into large flocs and settle, thus achieving rapid solid-liquid separation. Washing with 95% ethanol instead of water avoids redispersing of the aggregated particles.
[0055] Operating steps:
[0056] (1) Dispersion. Accurately weigh m grams (20 grams) of air-dried soil sample (passed through a 2 mm sieve), place it in a 250 mL Erlenmeyer flask or centrifuge bottle, add 50 mL of 5 g / L sodium hexametaphosphate solution, cover the flask, and place it on a reciprocating shaker at 90 r / min for 15 h to fully disperse the soil.
[0057] (2) Sieving. The shaken suspension was passed through a 53 μm sieve. The soil in the sieve was rinsed with deionized water in small amounts and multiple times until the water flowing under the sieve was colorless. The part above the sieve was particulate organic carbon component (>53 μm, POC), and the part below the sieve was mineral-bound organic carbon component (<53 μm, MAOC). The soil suspension below the sieve was collected in a 1 L beaker.
[0058] (3) Sedimentation. Transfer the dispersed suspension to a suitable container, slowly add 25 mL of 0.5 mol / L CaCl2 solution while stirring, and continue stirring for 5 min.
[0059] (4) Let stand. Let stand for 1-2 hours until the supernatant is clear and MAOC settles at the bottom of the container.
[0060] (5) Remove the supernatant. Use a pipette or siphon to remove the supernatant, trying to remove it as completely as possible without disturbing the bottom sediment.
[0061] (6) Ethanol washing. Add 20-30 mL of 95% ethanol to the sediment, shake gently (avoid vigorous shaking), let stand for 10-15 min, then centrifuge (4000-5000 rpm, 5-10 min) and discard the supernatant. Repeat washing 2-3 times.
[0062] (7) Cl⁻ test. Take the supernatant from the last wash and add 2-3 drops of 0.1 mol / L AgNO₃ solution. If no white precipitate forms, it indicates that Cl⁻ is present. - Completely removed. If white precipitate remains, wash once more with ethanol.
[0063] (8) Drying. Transfer the bottom MAOC wet sample along with the container to an oven and dry at 60°C to constant weight.
[0064] (9) Weighing and Calculation. Record the dry mass W(MAOC) of MAOC after drying. Ethanol washing has removed Cl... - Completely removed; the added CaCl2 has been eluted, so no salt deduction is needed.
[0065] (10) Determination of organic carbon. Take a portion of the dry sample, grind it evenly, and determine the organic carbon content C (%) according to the corresponding solution method. The absolute carbon mass of MAOC m(MAOC-C) = W(MAOC) × C / 100.
[0066] (11) Results presentation. MAOC is expressed as the carbon mass per gram of soil: MAOC = m(MAOC-C) / m.
[0067] 2. Experimental equipment
[0068] The experimental equipment used in this embodiment is shown in Table 2.
[0069] Table 2 Experimental equipment used in the improved method (method 2)
[0070]
[0071] Compared with traditional methods, the method according to this embodiment has the following advantages (Table 3):
[0072] (1) Shorten solid-liquid separation time: For the MAOC suspension after sieving, conventional methods make it difficult for particles to settle by gravity due to their small size. The improved method introduces CaCl2 solution to compress the double electric layer of soil colloids, which promotes the rapid flocculation and sedimentation of clay particles within 1-2 hours, thereby improving the solid-liquid separation efficiency by more than 95%.
[0073] (2) Reduced drying energy consumption: After centrifugation and washing, the improved method significantly reduces the moisture content of the suspension compared to conventional methods, eliminating the need for direct evaporation of large amounts of supernatant as in conventional methods. The drying time for a single sample is reduced from the conventional 10-12 days to 4 hours.
[0074] (3) Reduced batch experiment time: This experiment separates a standard soil sample (washing out about 1 L of suspension). Conventional drying method requires evaporating a large amount of water in the oven, which takes 10-12 days. The improved method only requires 2 h of sedimentation, 1.5 h of centrifugation and washing, and 10 h of drying, reducing the total time by more than 94%.
[0075] Table 3 Comparison of the advantages and disadvantages of the methods
[0076]
[0077] In summary, the CaCl2 flocculation sedimentation method proposed in this invention can achieve extremely high separation efficiency, reducing the total separation time by more than 94%, and can be used for rapid quantitative assessment of the content and dynamics of activated carbon and stable carbon libraries.
[0078] The above-described embodiments are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.
Claims
1. A method for rapid flocculation separation of soil mineral-bound organic carbon, characterized by, The method specifically includes: (1) Dispersion: Take an air-dried soil sample, use sodium hexametaphosphate solution as a dispersant, shake to fully disperse the soil and form a suspension; (2) Screening: The suspension after shaking is passed through a 53 μm sieve. The soil in the sieve is washed with deionized water. The part above the sieve is particulate organic carbon component, and the part below the sieve is mineral-bound organic carbon component, which is MAOC with a diameter <53 μm. (3) Sedimentation: CaCl2 solution was slowly added dropwise to the suspension while stirring; (4) Let stand: Let stand for 1-2 hours until the supernatant is clear and MAOC is deposited at the bottom; (5) Desalination: pour off the supernatant, dry the MAOC precipitate and weigh the total mass, calculate the mass of CaCl2 added and obtain the dry mass of MAOC or wash the MAOC precipitate with ethanol to remove Cl - and dry, to obtain the dry mass of MAOC.
2. The method of claim 1, wherein, The concentration of sodium hexametaphosphate is 5 g / L, and the mass ratio of sodium hexametaphosphate to soil sample is 1:
800.
3. The MAOC dry sample obtained by the method according to claim 1.
4. The application of the method as described in claim 1 in the rapid quantitative assessment of the content and dynamics of the active carbon library and the stable carbon library.