Method for rapidly and simultaneously determining cation exchange capacity and exchangeable salt-based ion content of soil

Abstract

The invention provides a method for rapidly and simultaneously measuring cation exchange capacity and exchangeable salt-based ion content of soil, which comprises the following steps: putting soil to be measured and a magnetic stirrer into a centrifugal tube, adding a cobalt hexammine trichloride solution without adding a sealing cover, putting the centrifugal tube on the magnetic stirrer, and magnetically stirring at 20 + / -2 DEG C to obtain the cation exchange capacity and exchangeable salt-based ion content of the soil. In the stirring process, vortexes are kept on the liquid level, the stirring time is 3-5 min, centrifuging is conducted, supernate is collected, and determination and analysis are conducted. The magnetic stirring method is used for measuring the cation exchange capacity and the exchangeable salt-based ion content of the soil through the cobalt hexammine trichloride method, and the synergistic effect of the two is achieved. According to the invention, the exchange reaction time is only 3 minutes, which can be saved by 57 minutes compared with the corresponding international standard time, and 95% of time is saved; when alkaline soil containing lime is measured, the step of preparing a calcium carbonate saturated solution can be omitted, and the working efficiency is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of determination of soil cation exchange capacity and exchangeable base ion content, and particularly relates to a method for rapidly and simultaneously determining soil cation exchange capacity and exchangeable base ion content. Background Art

[0002] Soil cation exchange capacity (CEC) refers to the capacity of soil to adsorb and exchange cations, expressed as centimoles of monovalent ions per kilogram of soil, i.e., cmol + / kg. The cation exchange capacity is related to the specific surface area and surface charge of soil colloids. Generally, the soil cation exchange capacity is obtained by substituting all the cations adsorbed by the soil with known cations and then measuring the adsorption amount of the known cations. Soil cation exchange capacity is a very important chemical property of soil, which directly reflects the fertilizer retention, fertilizer supply performance and buffering capacity of soil, and also plays an extremely important role in the migration and transformation process of soil pollutants.

[0003] Soil exchangeable base ions mainly refer to cations such as Ca 2+ , Mg 2+ , K + , Na + , etc. As one of the important criteria for evaluating soil quality, the content, saturation and different ion ratios of soil exchangeable bases reflect different soil physical and chemical properties, and also play an important role in maintaining soil nutrients and buffering soil acidification. Exchangeable Ca 2+ , Mg 2+ , K + are essential nutrient elements for plant growth, and their quantity and composition ratio affect the absorption and utilization of nutrients and water by plants, and further affect crop production, plant drought resistance, freezing resistance and pest resistance.

[0004] With the progress of agricultural technology, the determination of soil cation exchange capacity and exchangeable base ion content has become increasingly frequent in projects such as soil quality assessment, soil fertility improvement, soil improvement, soil pollution control, and the construction of high-standard farmland. For example, in the national soil environmental quality survey and local agricultural land soil fertility retention capacity survey, soil cation exchange capacity is a mandatory measurement index. The characteristics are a large number of samples, and a fast measurement speed is required. It is necessary to complete the detection of about 10,000 soil samples in 3 months. In ISO 23470:2018 (ISO 23470:2018. Soil quality - Determination of effective cation exchange capacity (CEC) and exchangeable cations using a hexamminecobalt(III)chloride solution (2nd ed.). 2018, International Organization for Standardization (ISO), Geneva, Switzerland.), during the determination of soil cation exchange capacity and exchangeable base ion content, only the exchange reaction operation requires shaking for 60 ± 5 min. And in the determination of the exchange properties of alkaline soils, in order to avoid the influence of calcium ions generated by the dissolution of calcium carbonate on the determination of exchangeable calcium, it is necessary to prepare a calcium carbonate saturated solution. The preparation process requires ultrasonic treatment for 30 min first, then magnetic stirring for 30 min, and finally the undissolved calcium carbonate needs to be left standing overnight. These operations further prolong the entire determination time and reduce the determination efficiency. To meet the needs of the rapid development of agricultural technology in the new situation, it has become increasingly urgent to improve the determination efficiency of soil cation exchange capacity and exchangeable base ion content. The 60-min shaking time during the exchange reaction process seems particularly long and urgently needs to be shortened. The overly long time for preparing and standing the calcium carbonate saturated solution also greatly reduces the determination efficiency and urgently needs to be improved.

[0005] The above ISO 23470:2018 is an international standard for the determination of soil cation exchange capacity and exchangeable base ion content using the hexamminecobalt(III) chloride ([Co(NH3)6]Cl3) method. Its basic principle is as follows: Using hexamminecobalt(III) chloride as an exchanger, the soil to be measured is exchange-extracted by shaking under the condition of 20 ± 2 °C for 60 ± 5 min. The trivalent hexamminecobalt ions in the exchanger are used to replace the cations adsorbed on the soil particles. After the shaking exchange reaction is completed, centrifugation and filtration are carried out. The soil cation exchange capacity is calculated based on the difference in the concentration of hexamminecobalt before and after the exchange reaction in the exchanger. By measuring Ca 2+ 、Mg 2+ 、K + 、Na +Calculate the contents of soil exchangeable calcium, magnesium, potassium, and sodium based on the concentration. The concentration of the hexaamminecobalt(III) chloride solution is 0.0166 mol / L, and the amount of the solution added to each sample is 50 mL. Use a reciprocating shaker, and during the exchange reaction, ensure that the soil / exchanger mixture is always in a suspended state. The shaking temperature is 20 ± 2 °C. When measuring alkaline soil containing lime, prepare a calcium carbonate saturated solution to inhibit the dissolution of calcium carbonate during the exchange process, thus avoiding an overestimated value of the exchangeable calcium measurement. At this time, calculate the soil exchangeable calcium content by measuring the difference between the initial and final concentrations of calcium ions in the filtrate.

[0006] Ammonium chloride (NH4Cl), ammonium acetate (NH4Ac), and ammonium nitrate (NH4NO3) are also traditional exchangers for measuring soil cation exchange capacity and exchangeable base ion content. The principle is to use the monovalent ammonium ions therein to displace the cations adsorbed on the soil particles, and calculate the soil cation exchange capacity and exchangeable base ion content based on the concentrations of 2+ Mg 2+ K + Na + However, when using this traditional exchanger to measure soil cation exchange capacity and exchangeable base ion content in the prior art, the operation time of the exchange reaction is also very long. SUMMARY OF THE INVENTION

[0007] Aiming at the problems in ISO 23470:2018 that the exchange reaction process takes a long time and a calcium carbonate saturated solution needs to be prepared, which leads to low work efficiency, the present invention provides a method for quickly and simultaneously measuring the cation exchange capacity and exchangeable base ion content of various soils. By shortening the exchange reaction time and omitting the step of preparing the calcium carbonate saturated solution, the measurement efficiency of the soil cation exchange capacity and exchangeable base ion content is improved.

[0008] To achieve the object of the present invention, the technical solution provided by the present invention is as follows:

[0009] The present invention provides a method for quickly and simultaneously measuring the cation exchange capacity and exchangeable base ion content of soil. Put the soil to be measured and a magnetic stir bar into a centrifuge tube, add the hexaamminecobalt(III) chloride solution, do not cover with a sealing cap, place the centrifuge tube on a magnetic stirrer, and perform magnetic stirring at 20 ± 2 °C. During the stirring process, keep a vortex on the liquid surface. The stirring time is 3 - 5 min. Centrifuge and collect the supernatant, and conduct the determination and analysis of the soil cation exchange capacity and exchangeable base ion content. The determination and analysis method is as follows:

[0010] (1) The calculation formula for the soil cation exchange capacity CEC is:

[0011]

[0012] In the formula:

[0013] q: The number of moles of exchange per liter, mol / L;

[0014] V: The volume of cobalt(III) hexammine chloride solution used for each sample, mL;

[0015] m: The mass of the soil sample weighed, g;

[0016] w: The moisture content of the soil sample on a dry basis;

[0017] Among them,

[0018]

[0019] In the formula:

[0020] c0 ’ : The initial concentration of cobalt(III) hexammine in the exchanger, expressed in moles per liter, mol / L;

[0021] c ’ : The concentration of cobalt(III) hexammine in the test solution, expressed in moles per liter, mol / L;

[0022] (2) The calculation formula for the content of exchangeable base ions is:

[0023]

[0024]

[0025]

[0026]

[0027] In the formula:

[0028] c(Na, exchangeable): The content of exchangeable sodium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0029] c(K, exchangeable): The content of exchangeable potassium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0030] c(Ca, exchangeable): The content of exchangeable calcium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0031] c(Mg, exchangeable): The content of exchangeable magnesium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0032] ρ3: Concentrations of sodium, potassium, calcium, and magnesium in the dilution to be measured, expressed in milligrams per liter, mg / L;

[0033] ρ b1 : Concentrations of sodium, potassium, calcium, and magnesium in the dilution blank, expressed in milligrams per liter, mg / L;

[0034] m: Mass of the air-dried soil sample, expressed in grams, g;

[0035] w: Moisture content of the soil sample on a dry basis.

[0036] Preferably, the soil to be measured further includes at least one of acidic soil, neutral soil, and alkaline soil.

[0037] More preferably, the soil to be measured is alkaline soil containing lime.

[0038] Preferably, the stirring time is 3 min.

[0039] Preferably, the depth of the vortex is 2 - 5 mm.

[0040] Preferably, the centrifuge tube is vertically placed on the magnetic stirrer.

[0041] Preferably, the centrifuge tube is a round-bottom centrifuge tube.

[0042] Preferably, the type of the magnetic stir bar is Type A.

[0043] Preferably, the concentration of the hexaamminecobalt(III) chloride solution is 0.0166 mol / L.

[0044] Preferably, it further includes the step of establishing the standard curves of Co, Ca, K, Mg, and Na.

[0045] The beneficial effects of the present invention are as follows:

[0046] The present invention applies the magnetic stirring method to the ion exchange reaction process in the determination of soil cations by the hexaamminecobalt(III) chloride method, giving play to the synergistic effect of the two. In the ISO 23470:2018 standard for determining the cation exchange capacity and exchangeable base ion content of soil, it takes 60 min to complete the whole exchange reaction. By using the present invention, the exchange reaction time only needs 3 min, saving 57 min, which is 95% of the time saved; when the existing standard measures the cation exchange capacity and exchangeable base ion content of alkaline soil containing lime, it is necessary to prepare a calcium carbonate saturated solution, while the present invention omits this step. Therefore, the method of the present invention is applicable to the ion exchange reaction process of determining the cation exchange capacity and exchangeable base ion content of alkaline soil containing lime by the hexaamminecobalt(III) chloride method, and has the effect of significantly improving work efficiency. Specific Embodiments

[0047] The following embodiments facilitate a better understanding of the present invention, but do not limit the present invention. The experimental methods in the following embodiments are all conventional methods unless otherwise specified. The test materials used in the following embodiments are all purchased from conventional biochemical reagent companies unless otherwise specified. In the following embodiments, quantitative tests are all set with three repeated experiments, and the results are averaged.

[0048] Compared with the detection method in ISO 23470:2018 standard, the present invention is different in that: the present invention uses a magnetic stir bar for stirring and defines specific conditions related to magnetic stirring; when measuring the cation exchange capacity and exchangeable base ion content of alkaline soil containing lime, the step of preparing a calcium carbonate saturated solution is omitted. The remaining steps are the same as the detection method in ISO 23470:2018 standard.

[0049] The present invention provides a method for quickly and simultaneously measuring the cation exchange capacity and exchangeable base ion content of soil, comprising the following steps:

[0050] Weigh the corresponding mass of the soil to be tested according to the numerical range of the cation exchange capacity (CEC), and place it together with a magnetic stir bar in a 100 mL round-bottom centrifuge tube. Add 50 mL of hexaamminecobalt(III) chloride solution as an exchanger, without adding a sealing cap. Place the centrifuge tube vertically on a magnetic stirrer and perform magnetic stirring at 20 ± 2 °C. During the stirring process, maintain a vortex with a depth of 2 - 5 mm on the liquid surface. The stirring time is 3 - 5 min, and the preferred stirring time is 3 min. After sufficient stirring by the magnetic stirrer, send it to a centrifuge and centrifuge at 4000 r / min for 20 min. Collect the supernatant for the determination and analysis of the cation exchange capacity and exchangeable base ion content of the soil. The determination and analysis methods are as follows:

[0051] (1) The calculation formula for the soil cation exchange capacity CEC is:

[0052]

[0053] In the formula:

[0054] q: The number of exchange moles per liter, mol / L;

[0055] V: The volume of hexaamminecobalt(III) chloride solution used for each sample, mL;

[0056] m: The mass of the soil sample weighed, g;

[0057] w: The moisture content of the soil sample based on the dry basis;

[0058] Among them,

[0059]

[0060] In the formula:

[0061] c0 ’ : The initial concentration of hexaamminecobalt in the exchanger, expressed in moles per liter, mol / L;

[0062] c ’ : The concentration of hexaamminecobalt in the test solution, expressed in moles per liter, mol / L;

[0063] (2) The calculation formula for the content of exchangeable base cations is:

[0064]

[0065]

[0066]

[0067]

[0068] In the formula:

[0069] c(Na, exchangeable): The content of exchangeable sodium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0070] c(K, exchangeable): The content of exchangeable potassium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0071] c(Ca, exchangeable): The content of exchangeable calcium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0072] c(Mg, exchangeable): The content of exchangeable magnesium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0073] ρ3: The concentrations of sodium, potassium, calcium and magnesium in the test dilution solution, expressed in milligrams per liter, mg / L;

[0074] ρ b1 : The concentrations of sodium, potassium, calcium and magnesium in the dilution blank solution, expressed in milligrams per liter, mg / L;

[0075] m: The mass of the air-dried soil sample, expressed in grams, g;

[0076] w: The moisture content of the soil sample based on the oven-dry basis.

[0077] Among them, when measuring the cation exchange capacity and the content of exchangeable base cations in alkaline soil containing lime, the hexaamminecobalt(III) chloride solution is still used, and the step of preparing the calcium carbonate saturated solution is omitted.

[0078] The depth of the vortex is maintained at 2 - 5 mm, which can ensure that the soil / exchanger mixture is always in a suspended state.

[0079] The concentration of the hexaamminecobalt(III) chloride solution is 0.0166 mol / L.

[0080] The type of the magnetic stir bar is preferably type A. The stir bar of this shape can rotate freely at the bottom of the round-bottom centrifuge tube, and neither end will rub against the bottom of the centrifuge tube.

[0081] The centrifuge tube is a round-bottom centrifuge tube. Only such a centrifuge tube can give full play to the stirring effect of the magnetic stir bar.

[0082] The method of the present invention is applicable to the determination of acidic soil, neutral soil and alkaline soil.

[0083] The method of the present invention is applicable to the determination of alkaline soil containing lime.

[0084] Comparative Example 1 Method for determining the cation exchange capacity and the content of exchangeable base cations in soil in ISO 23470:2018 standard

[0085] 1 Reagents

[0086] Only reagents certified as analytical pure can be used.

[0087] 1.1 Distilled water or deionized water: free of the elements to be analyzed, with a conductivity less than 0.5 μS / cm.

[0088] 1.2 Hexaamminecobalt(III) chloride solution, c[Co(NH3)6Cl3] = 0.0166 mol / L.

[0089] The adsorbed water of hexaamminecobalt(III) chloride should be removed before use. Weigh 4.458 g of hexaamminecobalt(III) chloride solid and place it in a 1 L volumetric flask containing 700 mL of water. Dissolve, make up to the mark and mix well.

[0090] 1.3 Ca 2+ 、K + 、Mg 2+ 、Na + Standard stock solution, = 1000 g / L.

[0091] 1.4 Hexaamminecobalt(III) chloride calcium carbonate saturated solution

[0092] Take a 2L beaker and fill it with hexamminecobalt(III) chloride solution (Reagent 1.2). Add 2g of finely ground calcium carbonate. Place this mixture in an ultrasonic reactor and sonicate for 30 min. To reduce the influence of temperature effects on the dissolution of calcium carbonate, stir the sonicated solution with a magnetic stirrer for another 30 min. After removing the magnetic stir bar, let the solution stand overnight to promote further dissolution of the undissolved calcium carbonate. Cover the 2L beaker with a plastic film during the calcium carbonate saturation process. Treat the solution by decantation or filtration, taking care to avoid getting the undissolved calcium carbonate into the supernatant or filtrate.

[0093] 2 Equipment

[0094] 2.1 Analytical balance: The weighing uncertainty range does not exceed ±0.1% of the weighed mass.

[0095] 2.2 Round-bottom centrifuge tube: Capacity is 100 mL, with a sealed lid.

[0096] 2.3 50 mL pipette: The error range is ±0.25 mL.

[0097] 2.4 Reciprocating shaker: During the exchange reaction, it can ensure that the soil / exchanger mixture remains in a suspended state all the time, and the oscillation temperature is 20 ± 2 °C.

[0098] 2.5 Centrifuge: It can ensure centrifugation at 4000 r / min for 20 min, and can fully achieve solid-liquid separation.

[0099] 2.6 Inductively coupled plasma optical emission spectrometer.

[0100] 2.7 Ultrasonic reactor.

[0101] 3 Procedures

[0102] 3.1 Sampling

[0103] Weigh the corresponding mass of the soil to be measured into a centrifuge tube according to the CEC value range shown in Table 1.

[0104] Table 1

[0105]

[0106] 3.2 Exchange reaction

[0107] The exchange reaction steps in ISO 23470:2018 standard are as follows: Add 50 mL of 0.0166 mol / L hexaamminecobalt(III) chloride solution (Reagent 1.2) to the centrifuge tube containing the soil sample, tighten the seal of the centrifuge tube, and place it on a reciprocating shaker to shake at 20 ± 2 °C for 60 ± 5 min. Place the centrifuge tube in a centrifuge and centrifuge at 4000 r / min for 20 min, collect the supernatant for determination and analysis. Conduct a blank experiment without adding the soil sample under the same conditions. When determining alkaline soil containing lime, the exchanger needs to be prepared into a saturated solution of hexaamminecobalt(III) chloride calcium carbonate with a concentration of 0.0166 mol / L (Reagent 1.4).

[0108] 3.3 Determination of CEC and exchangeable Ca, Mg, K, Na

[0109] Determine the CEC and the contents of exchangeable Ca, Mg, K, Na by measuring the concentrations of total cobalt and Ca 2+ , Mg 2+ , K + , Na + in the solution using an inductively coupled plasma optical emission spectrometer.

[0110] 3.4 Calculation of CEC

[0111] The calculation formula for the number of moles of exchange per liter is as follows:

[0112] (1)

[0113] In the formula:

[0114] c0 ’ : The initial concentration of hexaamminecobalt in the exchanger, expressed in moles per liter, mol / L;

[0115] c ’ : The concentration of hexaamminecobalt in the test solution, expressed in moles per liter, mol / L.

[0116] The calculation formula for CEC is as follows:

[0117] (2)

[0118] In the formula:

[0119] q: The number of moles of exchange per liter, mol / L;

[0120] V: The volume of hexaamminecobalt(III) chloride solution used for each sample, mL;

[0121] m: The mass of the soil sample weighed, g;

[0122] w: The moisture content of the soil sample based on the dry basis.

[0123] Preparation of 3.5 Exchangeable Base Cation Standard Solution

[0124] The hexaamminecobalt(III) chloride solution (Reagent 1.2) is the blank solution (Standard 0) for the determination of exchangeable base cations. For each element, transfer the corresponding volumes of Ca, K, Mg, and Na standard stock solutions (Reagent 1.3) as shown in Table 2 into a 500 mL volumetric flask. Add 2.229 g of solid hexaamminecobalt(III) chloride and dissolve it. Make up the volume to the mark with water and mix well. This solution contains the highest concentration of cations (Standard 3).

[0125] Table 2

[0126]

[0127] Transfer 50 mL of Standard 3 to a 100 mL volumetric flask, make up the volume to the mark with Standard 0, and mix well to obtain Standard 2.

[0128] Transfer 25 mL of Standard 3 to a 100 mL volumetric flask, make up the volume to the mark with Standard 0, and mix well to obtain Standard 1.

[0129] 3.6 Establishment of Cobalt Standard Curve

[0130] Weigh a certain amount of solid hexaamminecobalt(III) chloride, dissolve it in 1000 mL of water, and establish a cobalt standard curve. The weighing amounts are shown in Table 3.

[0131] Table 3

[0132]

[0133] 3.7 Determination of Exchangeable Base Cations

[0134] Inject the samples of Standards 0 - 3 (3.5) and measure the emission intensity according to the instrument reference test conditions. Use the emission intensity values as the ordinate and the Ca, K, Mg, and Na series concentrations as the abscissa to establish the Ca, K, Mg, and Na standard curves.

[0135] 3.8 Determination of Cobalt

[0136] Use distilled water or deionized water without hexaamminecobalt(III) chloride as the blank sample to calibrate the instrument zero point. Inject the samples numbered 0 - 3 in Table 3 and measure the emission intensity according to the instrument reference test conditions. Use the emission intensity values as the ordinate and the cobalt series concentrations as the abscissa to establish the cobalt standard curve.

[0137] 3.9 Calculation of Exchangeable Base Cations

[0138] Calculate the contents of exchangeable sodium, potassium, calcium, and magnesium in the soil using the following formulas (3) - (6):

[0139]

[0140]

[0141]

[0142]

[0143] In the formula:

[0144] c(Na, exchangeable): The content of exchangeable sodium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0145] c(K, exchangeable): The content of exchangeable potassium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0146] c(Ca, exchangeable): The content of exchangeable calcium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0147] c(Mg, exchangeable): The content of exchangeable magnesium in the soil, expressed in centimoles of positive charge per kilogram, cmol + / kg;

[0148] ρ3: The concentrations of sodium, potassium, calcium and magnesium in the diluted solution to be measured, expressed in milligrams per liter, mg / L;

[0149] ρ b1 : The concentrations of sodium, potassium, calcium and magnesium in the diluted blank solution, expressed in milligrams per liter, mg / L;

[0150] m: The mass of the air-dried soil sample, expressed in grams, g;

[0151] w: The moisture content of the soil sample based on the oven-dry basis.

[0152] Example 1 A method for rapidly and simultaneously determining the cation exchange capacity and the content of exchangeable base cations in soil

[0153] The differences between this example and Comparative Example 1 are as follows in (1)-(3):

[0154] (1) This example does not require the preparation of the cobalt(III) hexammine carbonate calcium carbonate saturated solution in step 1.4 of Comparative Example 1.

[0155] (2) This example uses a magnetic stirrer and a magnetic stir bar: The stirring temperature is 20±2 °C, and a type A magnetic stir bar is used.

[0156] (3) The exchange reaction step in step 3.2 of this example is different from that of Comparative Example 1.

[0157] In this example, the exchange reaction steps are as follows: Add 50 mL of 0.0166 mol / L hexaamminecobalt(III) chloride solution (Step 1.2 of Comparative Example 1) to a centrifuge tube containing a soil sample, place a Type A magnetic stir bar in it, do not add a sealing cap, vertically place the centrifuge tube on a magnetic stirrer, perform magnetic stirring at 20 ± 2 °C, adjust the stirring speed to keep a 2 - 5 mm deep vortex on the liquid surface during stirring, and the stirring time is 3 min. Place the centrifuge tube in a centrifuge and centrifuge at 4000 r / min for 20 min, collect the supernatant for determination and analysis. Do a blank experiment without adding a soil sample under the same conditions. When measuring alkaline soil containing lime, the exchanger does not need to be prepared into a calcium carbonate saturated solution of 0.0166 mol / L hexaamminecobalt(III) chloride (Step 1.4 of Comparative Example 1).

[0158] The remaining steps and parameters are the same as those in Comparative Example 1.

[0159] Comparative Example 2: Determination of CEC and exchangeable base ion contents of standard soils at different reaction times

[0160] Select 2 kinds of standard soils. TMQC0253 is a neutral soil with a pH value of 7.04 ± 0.10 and no calcium carbonate; GBW(E)070374 is a calcareous soil with a pH value of 8.27 ± 0.16 and a calcium carbonate content of 18.1 ± 2.2%. Use the method of Example 1 of the present invention to determine the CEC and exchangeable base ion contents at different reaction times. The reaction times are set to 0.5 min, 1 min, 3 min, and 5 min. Set 3 parallel experiments for each sample and take the average value. The results are shown in Table 4.

[0161] As can be seen from Table 4, for the two standard soils, the CEC values obtained at reaction times of 0.5 min, 1 min, 3 min, and 5 min are all within the standard value range, but the measured values of the contents of exchangeable Ca 2+ , Mg 2+ , K + , Na + need to reach the standard value range at a reaction time of 3 min. The measured values at reaction times of 0.5 min and 1 min are lower than the standard value range, and there is no significant change in the measurement results between 5 min and 3 min. Therefore, a reaction time of 3 min is sufficient to complete the cation exchange reaction of the soil. At this time, the simultaneous determination of soil CEC and exchangeable base ions can be achieved.

[0162] Table 4

[0163]

[0164] Experimental Example 2: Determination of CEC and exchangeable base ion contents of standard soils with different properties

[0165] Three standard soils with different properties were selected. GBW(E)070334 is an acidic soil with a pH value of 6.25±0.09 and no calcium carbonate; TMQC0253 is a neutral soil with a pH value of 7.04±0.10 and no calcium carbonate; GBW(E)070374 is a calcareous soil with a pH value of 8.27±0.16 and a calcium carbonate content of 18.1±2.2%. The CEC and exchangeable base ion contents were measured by the methods of Comparative Example 1 and Example 1 respectively. Three parallel experiments were set for each sample, and the average value was taken. The results are shown in Table 5.

[0166] As can be seen from Table 5, the measured values of the CEC and exchangeable base ion contents of acidic, neutral and alkaline soils under ISO 23470:2018 and the method of Example 1 of the present invention are all within the standard value range, and accurate results can be obtained by both operation steps.

[0167] Compared with ISO 23470:2018, the exchange reaction time of the present invention only needs 3 min, which can save 57 min and 95% of the time; when measuring the CEC and exchangeable base ion contents of calcareous alkaline soils containing lime, the step of preparing a calcium carbonate saturated solution is omitted.

[0168] Table 5

[0169]

[0170] Experimental Example 3 Determination of CEC and Exchangeable Base Ion Contents of Alkaline Soils with Different Calcium Carbonate Contents

[0171] The standard calcareous soil numbered GBW(E)070374 with a pH value of 8.27±0.16 and a calcium carbonate content of 18.1±2.2% was selected. Taking this as the reference soil, a certain amount of analytical pure calcium carbonate was added to prepare calcareous soils with calcium carbonate contents of 20%, 40%, 60% and 80%. The CEC and exchangeable base ion contents were measured by the methods of Comparative Example 1 and Example 1 respectively. Three parallel experiments were set for each sample, and the average value was taken. The measured values of the CEC and exchangeable base ion contents of the 5 soils under ISO 23470:2018 and the method of Example 1 of the present invention are shown in Table 6.

[0172] As can be seen from Table 6, the CEC and exchangeable Ca 2+ , Mg 2+ , K + , Na +The measured values of the content are all within the standard value range, and accurate results can be obtained by both operation procedures. Compared with ISO 23470:2018, the exchange reaction time of the present invention only needs 3 minutes, which can save 57 minutes, saving 95% of the time; and the step of preparing a saturated calcium carbonate solution is omitted. The measurement efficiency is greatly improved.

[0173] Table 6

[0174]

[0175] Experimental Example 4 Determination of CEC and exchangeable base ion content in actual alkaline soils with different calcium carbonate contents

[0176] Five actual alkaline soils with different calcium carbonate contents were selected, and the CEC and exchangeable base ion contents were measured by the methods of Comparative Example 1 and Example 1 respectively. Three parallel experiments were set for each sample, and the average value was taken. The measured values of the five soils under ISO 23470:2018 and the method of Example 1 of the present invention are shown in Table 7.

[0177] As can be seen from Table 7, the measurement results of the CEC and exchangeable base ion contents of the five soils under ISO 23470:2018 and the method of Example 1 of the present invention are basically the same, and accurate measurement results can be obtained by both methods. Compared with ISO 23470:2018, the exchange reaction time of the present invention only needs 3 minutes, which can save 57 minutes, saving 95% of the time; and the step of preparing a saturated calcium carbonate solution is omitted. The measurement efficiency is greatly improved.

[0178] Table 7

[0179]

[0180] Experimental Example 5 Determination of CEC and exchangeable base ion content in actual soils with different properties

[0181] Three actual soils with different properties were selected, and the CEC and exchangeable base ion contents were measured by the methods of Comparative Example 1 and Example 1 respectively. Three parallel experiments were set for each sample, and the average value was taken. The results are shown in Table 8.

[0182] As can be seen from Table 8, relatively consistent measurement results of the CEC and exchangeable base ion contents of acidic, neutral and alkaline soils can be obtained under ISO 23470:2018 and the method of Example 1 of the present invention. Compared with ISO 23470:2018, the exchange reaction time of the present invention only needs 3 minutes, which can save 57 minutes, saving 95% of the time; and the step of preparing a saturated calcium carbonate solution is omitted when measuring the CEC and exchangeable base ion contents of alkaline soils containing lime.

[0183] Table 8

[0184]

[0185] Experimental Example 6 Determination of Standard Soil CEC and Exchangeable Base Cation Content at a Reaction Time of 3 min with Different Exchangers

[0186] Three common exchangers NH4Cl, NH4Ac, and NH4NO3 used in the determination of soil CEC and exchangeable base cation content were configured into concentrations equivalent to that of the hexaamminecobalt(III) chloride solution. According to the method of Example 1 of the present invention, they were reacted with 4 standard soils for 3 min under the same conditions respectively, and the remaining steps were all kept the same. Three parallel experiments were set for each sample, and the average value was taken. The measurement results are shown in Table 9.

[0187] As can be seen from Table 9, the CEC and exchangeable base cation content values obtained by the three common exchangers within a reaction time of 3 min are all lower than the standard value range, indicating that the three traditional exchangers did not achieve complete exchange of cations in the soil to be measured within a reaction time of 3 min. However, the measured values of CEC and exchangeable base cation content under the method of Example 1 of the present invention are all within the standard value range, indicating that only the method of the present invention can complete the cation exchange reaction of the soil to be measured in such a short time. It shows that there is a synergistic effect between the magnetic stirring method in the present invention and the hexaamminecobalt(III) chloride exchanger.

[0188] Table 9

[0189]

[0190] In summary, it takes 60 min to complete the entire exchange reaction in ISO 23470:2018, while only 3 min is required using the present invention, which can save 57 min, saving 95% of the time. When measuring alkaline soils containing lime, ISO 23470:2018 requires the preparation of a calcium carbonate saturated solution, which is omitted in the present invention. At the same time, it can also be seen that although the magnetic stirring method has a good stirring effect, there is no synergistic effect with the monovalent ammonium ion, resulting in the inability to complete the full exchange of soil cations within 3 min. Only in combination with the trivalent hexaamminecobalt ion does it have a synergistic effect.

[0191] NH4Cl, NH4Ac, and NH4NO3 are traditional exchangers for determining soil cation exchange capacity and exchangeable base cation content. The principle is to use the monovalent ammonium ion therein to displace the cations adsorbed on soil particles, and by measuring the ammonium ion and Ca 2+ 、Mg 2+ 、K + 、Na +Calculate the soil cation exchange capacity and the content of exchangeable base cations. The present invention believes that it may be due to the different charges and volumes of the monovalent ammonium ion and the trivalent hexaamminecobalt ion, and their effects are also different during the exchange with the cations adsorbed by the soil. The monovalent ammonium ion cannot completely displace the cations adsorbed by the soil to be measured within 3 minutes, while the trivalent hexaamminecobalt ion can complete all exchanges. Based on the characteristic that the magnetic stirring method can make the soil particles fully contact with the exchanger, and combined with the characteristics of the trivalent hexaamminecobalt ion itself, the synergistic effect of the two is realized. It can be seen from the implementation effect that although the magnetic stirring method has a good stirring effect, there is no synergistic effect with the monovalent ammonium ion, resulting in the inability to complete all exchanges of soil cations within 3 minutes. Only when combined with the trivalent hexaamminecobalt ion in the present invention does it have a synergistic effect.

[0192] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for rapidly and simultaneously determining the cation exchange capacity and exchangeable base ion content of soil, characterized in that: Place the soil to be tested and a magnetic stirrer into a centrifuge tube, add the hexaamminecobalt trichloride solution, without a sealing cover, place the centrifuge tube on a magnetic stirrer, and perform magnetic stirring at 20±2°C. During the stirring process, keep a vortex on the liquid surface. The stirring time is 3-5 minutes. Centrifuge and collect the supernatant to determine and analyze the soil cation exchange capacity and exchangeable base ion content. The determination and analysis method is as follows: (1) The calculation formula of soil cation exchange capacity (CEC) is: Where: q: number of exchange moles per liter, mol / L; V: volume of hexaamminecobalt trichloride solution used for each sample, mL; m: mass of soil sample, g; w: moisture content of soil sample on oven-dry basis; in, Where: c0 ’ : initial concentration of hexaamminecobalt in the exchanger, expressed in moles per liter, mol / L; c ’ : The concentration of hexaaminecobalt in the test solution, expressed in moles per liter, mol / L; (2) The calculation formula for the exchangeable base ion content is: Where: c (Na, exchangeable): The exchangeable sodium content in the soil, expressed as centimoles of positive charge per kilogram, cmol + / kg; C (K, exchangeable): exchangeable potassium content in soil, expressed as centimoles of positive charge per kilogram, cmol + / kg; c (Ca, exchangeable): The exchangeable calcium content in the soil, expressed as centimoles of positive charge per kilogram, cmol + / kg; c (Mg, exchangeable): The exchangeable magnesium content in the soil, expressed as centimoles of positive charge per kilogram, cmol + / kg; ρ3: the concentration of sodium, potassium, calcium and magnesium in the dilution to be tested, expressed in milligrams per liter, mg / L; ρ b1 : The concentrations of sodium, potassium, calcium and magnesium in the diluted blank solution, expressed in milligrams per liter, mg / L; m: mass of air-dried soil sample, expressed in grams, g; w: moisture content of soil sample on an oven-dry basis.

2. The method according to claim 1, characterized in that: The soil to be tested also includes at least one of acidic soil, neutral soil and alkaline soil.

3. The method according to claim 2, characterized in that: The soil to be tested is alkaline soil containing lime.

4. The method according to any one of claims 1 to 3, characterized in that: The stirring time is 3 min.

5. The method according to any one of claims 1 to 3, characterized in that: The depth of the vortex is 2-5 mm.

6. The method according to any one of claims 1 to 3, characterized in that: Place the centrifuge tube vertically on a magnetic stirrer.

7. The method according to any one of claims 1 to 3, characterized in that: The centrifuge tube is a round-bottom centrifuge tube.

8. The method according to any one of claims 1 to 3, characterized in that: The magnetic stirrer is of type A.

9. The method according to any one of claims 1 to 3, characterized in that: The concentration of the hexaamminecobalt trichloride solution is 0.0166 mol / L.

10. The method according to any one of claims 1 to 3, characterized in that: Also included are steps for establishing standard curves for Co, Ca, K, Mg, and Na.

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