Evaluation method suitable for electrostatic repulsion pressure among soil particles under field condition

Abstract

The invention relates to the field of measurement of mixed electrolyte systems, in particular to a method for evaluating electrostatic repulsion pressure among soil particles under field conditions. Comprising the following steps: (1) measuring the specific surface area of soil particles; (2) measuring the number of surface charges of the soil particles under different pH conditions; (3) evaluating the surface charge density of the soil particles under different pH conditions; (4) evaluating the surface potential of the soil particles under the field condition; and (5) evaluating the electrostatic repulsion pressure among soil particles under the field condition. According to the method, calculation of the electrostatic repulsion pressure between soil particles under the actual field condition is achieved.

Description

Technical Field

[0001] The present invention relates to the field of determination of mixed electrolyte systems, and in particular to an evaluation method for electrostatic repulsion pressure between soil particles under field conditions. Background Art

[0002] The electrostatic repulsion between soil particles is the repulsive force generated by the presence of surface charge. This force plays a crucial role in numerous soil processes and functions, including the formation and stabilization of soil aggregates, water / soil / solute migration, soil structure improvement, water and fertilizer conservation, and non-point source pollution control in farmland.

[0003] Currently, methods exist only to assess the electrostatic repulsion pressure of soil particles when the electrolyte type and concentration are known. Quantitative assessment of soil electrostatic repulsion pressure is not possible under mixed electrolyte conditions, or even under field conditions. For example, current methods are limited to single 1:1 and 2:1 electrolyte systems, as well as 1:1 + 2:1 mixed electrolyte systems. However, in actual field conditions, the electrolyte types and concentrations are very complex, and without corresponding assessment methods, targeted correlation studies of soil processes and functions based on soil electrostatic forces are impossible.

[0004] Therefore, there is an urgent need for an evaluation method for the electrostatic repulsion pressure between soil particles under field conditions to overcome the shortcomings of existing calculation methods and achieve new breakthroughs in the study of interfacial forces between materials. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to overcome the above-mentioned defects and provide an evaluation method for the electrostatic repulsion pressure between soil particles under field conditions, so as to realize the calculation of the electrostatic repulsion pressure between soil particles under actual field conditions.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for evaluating the electrostatic repulsion pressure between soil particles under field conditions, comprising the following main steps: (1) determining the specific surface area of ​​soil particles; (2) determining the amount of surface charge of soil particles under different pH conditions; (3) evaluating the surface charge density of soil particles under different pH conditions; (4) evaluating the surface potential of soil particles under field conditions; and (5) evaluating the electrostatic repulsion pressure between soil particles under field conditions.

[0008] The specific steps are:

[0009] (1) Determine the specific surface area of ​​soil particles;

[0010] Na-K ions are used as indicator ions, and the corresponding anions are Cl-1. - and OH - , the corresponding Cl -OH - with Na + , K + The compounds formed are NaCl / KCl and NaOH / KOH; the indicator ion Na + , K + It is a non-specific adsorbent of cations, and NaCl and KCl are water-soluble salts. First, the activity of the indicator ion in the equilibrium system is determined, which is recorded as a Na and a K ; Calculate the concentration of the indicator ion in the equilibrium system, denoted as c Na and c K , according to c Cl =Z Na c Na +Z K c K Calculate the corresponding anion Cl - The concentration of the indicator ion Na is calculated by substituting the measured ion concentration into the following formula. + , K + The adsorption amount on the surface of nano-micron particles is recorded as N Na and N K :

[0011]

[0012] Where N Na and N K The unit is mol / g; and Na + and K + The total volume of the ionic solution, in L; c and for Na + and K + Initial concentration of ions, c′ Na and c′ K for Na + and K + The equilibrium concentration of ions is expressed in mol / L; m is the oven-dried mass of the hydrogen-saturated soil sample in g.

[0013] The specific surface area of ​​soil particles is obtained by solving the following two equations simultaneously:

[0014]

[0015] Where γ K and γ Na Na + and K + The charge coefficient, γ K =1.699,γ Na=1.110; Z K and Z Na Na + and K + valence of; Debye parameter, unit is dm -1 ; ε is the dielectric constant of water 8.9×10 -10 C 2 / (Jdm); S is the specific surface area, the unit is dm 2 / g; φ0′ is the surface potential of the Na-K measurement system, in V; R is the gas constant, which is 8.314 J / (mol K); T is the absolute temperature, which is 298 K at 25°C; e0 is the electron charge, which is 1.6×10 -19 C; F is the Faraday constant, which is 96485C / mol.

[0016] (2) Determine the surface charge of soil particles under different pH conditions;

[0017] By measuring the number of charges at different pH values, the functional relationship between pH and charge number is obtained, and then the pH under actual field conditions is measured. The actual field pH value is then substituted into the relationship between the measured number of charges and pH to obtain the surface charge number of soil particles at the actual field pH value.

[0018] The principle of this method is to take a hydrogen-saturated soil sample with the same specific surface area pretreatment as in step (1), put it into a beaker (if the soil salt content is high, take a wet hydrogen-saturated soil sample and calculate it using formula (2-2)), add a NaOH solution with a concentration of c0, record the total volume V1 of the NaOH solution, stir, and then adjust the pH with NaOH solution until the pH = 12 ± 0.2, and record the volume V2 of the NaOH solution added (if V1 is sufficient and the pH condition is met, then V2 = 0);

[0019] Add 0.5 mol / L acetic acid solution to the beaker, record the volume of acetic acid solution added V3, measure the pH of the suspension after exchange equilibrium, and repeatedly add acetic acid solution. After equilibrium, measure the pH and ion concentration c0′ of the suspension.

[0020] Calculate the surface charge in cmol according to the formula (+) / kg:

[0021]

[0022] If salt content needs to be considered, the following formula can be used for calculation:

[0023]

[0024] Where SCN is the surface charge of the soil, in cmol(+) / kg, c0 is the initial concentration of NaOH solution, c0′ is the Na ion concentration of the system at equilibrium, m0 is the mass of the air-dried soil sample, m0′ is the mass of the dried hydrogen-saturated soil sample, m1 is the mass of the centrifuge tube, m2 is the total mass of the soil sample and the centrifuge tube, ω is the soil moisture content, V1 is the total volume of NaOH solution added after all soil samples are transferred to the beaker, V2 is the volume of NaOH solution added to adjust the pH, V3 is the total volume of acetic acid solution added, 10 -3 The conversion factor for milliliters to liters is 10 5 mol (+) / g to cmol (+) / kg conversion factor.

[0025] (3) Evaluation of the surface charge density of soil particles under different pH conditions

[0026] The surface charge density under different pH conditions can be obtained by using the specific surface area and the surface charge number under different pH conditions:

[0027]

[0028] Where σ refers to the surface charge density (C / dm 2 ), 10 -5 cmol (+) / kg to mol (+) Conversion factor of / g.

[0029] (4) Evaluating the surface potential of soil particles under field conditions

[0030] The surface potential under field conditions was further estimated based on the obtained surface charge density using the following formula:

[0031]

[0032] Where π is the ratio of circumference to diameter; c is the ratio of circumference to diameter. i is the concentration of water-soluble cations in soil solution in mol / L; γ i is the effective charge coefficient of the water-soluble cation, where γ K =1.699,γ Na =1.110,γ Ca =1.403,γ Mg =1.183; Z i is the valence of a water-soluble cation.

[0033] Water-soluble cations (Na + , Ca 2+ , K + and Mg 2+) concentration determination method:

[0034] Soil water-soluble salts can be leached using a balance method at a certain soil-water ratio (usually 1:1), and then the Ca content in the leachate can be determined. 2+ , Mg 2+ , Na + , K + The concentration of major ions is then calculated based on the soil moisture content to determine the water-soluble salt concentration, expressed in mol / L. For methods for determining water-soluble base ions, refer to "Soil Testing - Part 16: Determination of Total Water-Soluble Base Content in Soil" (NY / T1121.16-2006) and "Analysis of Water-Soluble Salts in Forest Soils" (LY / T 1251-1999). If a specific soil sample contains a high concentration of other water-soluble base ions, refer to the methods for the corresponding ions.

[0035] For example:

[0036] 1) Calcium and magnesium ions are calculated using atomic absorption spectrophotometry using the following formula:

[0037] Soil water-soluble calcium (Ca 2+ ) content (g·kg -1 )=ρ(Ca 2+ )×50×ts×10-3 / m

[0038] Soil water-soluble calcium (Ca) content (cmol·kg -1 )=Ca 2+ (g·kg -1 ) / 0.040078

[0039] Soil water-soluble magnesium (Mg 2+ ) content (g·kg -1 )=ρ(Mg 2+ )×50×ts×10-3 / m

[0040] Soil water-soluble magnesium (Mg) content (cmol·kg -1 )=Mg 2+ (g·kg -1 ) / 0.024305

[0041] Where:

[0042] ρ(Ca 2+ ) or ρ(Mg 2+ ) is the mass concentration of calcium or magnesium measured in the suspension in μg / mL; ts is the fractionation multiple; 50 is the volume of the test solution in mL; 0.040078 and 0.024305 are Ca 2+ and Mg 2+ The molar mass is kg / mol; m is the mass of the soil sample in g.

[0043] 2) Potassium and sodium are calculated using flame photometry using the following formula:

[0044] Soil Na + ,% = obtained Na concentration mg / L×25 / V×5×10 -4

[0045] Na + , cmol / kg=Na%×100 / 23.0

[0046] Soil K + ,% = obtained K concentration mg / L×25 / V×5×10 -4

[0047] K + , cmol / kg=K%×100 / 39.1

[0048] Where V is the volume of soil leachate absorbed (ml); 25 is the constant volume (ml); 5 is the water-soil ratio

[0049] 10 -4 Factors for converting mg / L to %; 23.0 and 39.1 are respectively Na + and K + The millimolar mass is mg / mmol.

[0050] Determine the soil moisture content in the field and further evaluate the concentration of water-soluble cations in the soil solution:

[0051]

[0052] where c i is the concentration of water-soluble cations, the unit is mol / L; w i is the content of water-soluble cations, in cmol / kg; ρ is the density of water, in g / cm 3 ;ω is soil moisture content%; 10 -2 is the conversion factor from cmol / kg to mol / kg.

[0053] (5) Evaluate the electrostatic repulsion pressure between soil particles under field conditions

[0054] Calculate the midpoint potential between soil particles based on the surface potential obtained under field conditions

[0055]

[0056] Where ∑c1 and ∑c2 refer to the sum of the concentrations of monovalent and divalent water-soluble cations under field conditions, respectively, in mol / L; d is the distance between the surfaces of two adjacent particles, in nm; is the midpoint potential, in V; 10 -8 The conversion factor for converting nm to dm.

[0057] Electrostatic repulsion pressure P under field conditions EDL It can be calculated by the following formula:

[0058]

[0059] Where c i is the concentration of water-soluble cations in mol / L; γ i is the effective charge coefficient of the water-soluble cation; Z i is the valence state of the water-soluble cation; P EDL is the electrostatic repulsion pressure between soil particles, the unit is atm; 1000 / 101325 is the conversion factor from J / L to atm.

[0060] The specific operation of the further step (1) is as follows:

[0061] 1) Weigh an air-dried soil sample of mass m0 and place it in a centrifuge tube of mass m1;

[0062] 2) Add 0.10 mol / L HCl solution to the centrifuge tube at a solid-liquid mass ratio of 1:10, stir with a glass rod to disperse the sample until there are no lumps, and mix thoroughly for 2 minutes;

[0063] 3) Place the dispersed sample tube into a centrifuge. If the centrifugation is incomplete, increase the speed and time appropriately until the centrifugation is complete. Discard the supernatant.

[0064] 4) Repeat steps 2) and 3) 4 times; after the last centrifugation, use pH test paper to test the pH of the supernatant. If pH ≤ 2.00, it means that the sample has been completely absorbed by H. + Saturation; if pH>2.00, continue to add the same volume of 0.10 mol / L HCl solution as in 2) and increase the number of treatments according to 2) and 3) until pH≤2.00;

[0065] 5) Add pure water to the centrifuge tube at a solid-liquid mass ratio of 1:10, stir with a glass rod to disperse the sample until there are no lumps, and mix thoroughly for 2 minutes;

[0066] 6) Repeat step 3);

[0067] 7) a. Record the total mass m2 of the soil sample and centrifuge tube at this point. This sample is a wet hydrogen-saturated soil sample and can be used to determine the surface charge of soil particles in an air-dried soil sample (taking into account the salt content).

[0068] b. Transfer all the samples in the centrifuge tube to the mortar (you can rinse the centrifuge tube with a small amount of pure water and transfer the rinsed suspension to the mortar together), then place the mortar containing the sample in an oven at 70°C to dry (the recommended drying time is not less than 24 hours);

[0069] 8) Remove the mortar containing the dried soil sample from 7)b. After cooling, grind the sample until it passes through a 0.25 mm sieve. Mix thoroughly, seal the sample in a ziplock bag, and store at room temperature. Grind and sieve the dried soil sample together, mix thoroughly, and place it in the same ziplock bag. This sample is hydrogen-saturated and can be used to directly determine the surface charge of soil particles (regardless of salt content) and the specific surface area of ​​the soil.

[0070] 9) Weigh m (g) of hydrogen-saturated sample into a sample cup, add a prepared alkali solution (NaOH + KOH mixed solution) of known concentration, and stir on a magnetic stirrer for 60 minutes;

[0071] 10) Use a pH electrode to measure the pH of the suspension to be tested in 9). If the pH is too low, add a mixed alkali solution; if the pH is too high, add a hydrogen-saturated soil sample. Stir for 10 minutes after addition. Repeat the above steps until the pH is between 7.2 ± 0.2.

[0072] 11) Use Na + , K + Determination of Na in suspension by ion selective electrode + , K + activity;

[0073] 12) In the iterative operation, the measured Na + , K + Activity a Na 、a K Set to Na + , K + The initial concentration value, c Na (0) = a Na , c K (0) = a K , then the Na of the first iteration + , K + The concentration is:

[0074]

[0075] In the formula π is the circumference of a circle, F is the Faraday constant 96485C / mol, e0 is the charge of an electron 1.6×10 -19 C, ε is the dielectric constant of water 8.9×10 -10 C 2 / (J dm), R is the gas constant 8.314 J / (mol K), T is the system temperature in Kelvin (298 K at 25 °C); I(0) is the initial ionic strength and I(0) = c Na (0)+c K (0);

[0076] 13) According to the Na calculated in the first iteration + , K + Concentration c Na (1) and c K (1), the second iteration is calculated by the following equation:

[0077]

[0078] Where I(1) is the initial ionic strength and I(1)=c Na (1)+c K (1);

[0079] 14) Similarly, repeat the above process until the difference between the results of the nth and n+1th times is [c(n+1)-c(n)] / c(n+1)<0.001. At this time, the iteration Na + , K + The concentration is the Na in the suspension at the corresponding pH + , K + Concentration, i.e. c Na and c K Substitute the measured ion concentration into the following formula to calculate the indicator ion Na + , K + The adsorption amount on the surface of nano-micron particles is recorded as N Na and N K :

[0080]

[0081] Where N Na and N K The unit is mol / g; and Na + and K + The total volume of the ionic solution, in L; c and for Na + and K + Initial concentration of ions, c′ Na and c′ K for Na + and K + The equilibrium concentration of ions is in mol / L; m is the oven-dried mass of the hydrogen-saturated soil sample in g;

[0082] The specific surface area of ​​soil particles is obtained by solving the following two equations simultaneously:

[0083]

[0084] Where γ K and γ Na Na + and K + The charge coefficient, γ K =1.699,γ Na =1.110; Z K and Z Na Na + and K + valence of; Debye parameter, unit is dm -1 ; ε is the dielectric constant of water 8.9×10 -10 C 2 / (J dm); S is the specific surface area, the unit is dm 2 / g; is the surface potential of the Na-K measurement system, in V; R is the gas constant, which is 8.314 J / (mol K); T is the absolute temperature, which is 298 K at 25 °C; e0 is the electron charge, which is 1.6×10 -19 C; F is the Faraday constant, which is 96485C / mol. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 Graph showing the surface charge quantity of soil particles under different pH conditions in the embodiment;

[0086] Figure 2 Surface charge density diagram of soil particles under different pH conditions in the embodiment;

[0087] Figure 3 Graph showing the concentrations of major water-soluble cations under different soil moisture conditions in the embodiment;

[0088] Figure 4 Graph showing how the electrostatic repulsion pressure between soil particles varies with distance in the embodiment. DETAILED DESCRIPTION

[0089] In this embodiment, soil samples (upland yellow soil) were collected from the field, and the electrostatic repulsion pressure between soil particles was calculated according to the steps of the present invention. The specific steps are as follows:

[0090] (1) Specific surface area of ​​soil particles:

[0091] 1) Weigh 100 g of yellow soil sample into a beaker;

[0092] 2) Add 0.10 mol / L HCl solution to the beaker at a solid-liquid mass ratio of 1:10, stir with a glass rod to disperse the sample until there are no lumps, and mix thoroughly for 2 minutes;

[0093] 3) Transfer the dispersed sample to a centrifuge tube and centrifuge. If the centrifugation is incomplete, increase the speed and time appropriately until the centrifugation is complete. Discard the supernatant after centrifugation.

[0094] 4) Repeat steps 2) and 3) 4 times; after the last centrifugation, use pH test paper to test the pH of the supernatant. If pH ≤ 2.00, it means that the sample has been completely absorbed by H. + Saturation; if pH>2.00, continue to add the same volume of 0.10 mol / L HCl solution as in 2) and increase the number of treatments according to 2) and 3) until pH≤2.00;

[0095] 5) Add pure water to the beaker at a solid-liquid mass ratio of 1:10, stir with a glass rod to disperse the sample until there are no lumps, and mix thoroughly for 2 minutes;

[0096] 6) Repeat step 3);

[0097] 7) Transfer all the samples in the centrifuge tube to a mortar (you can rinse the centrifuge tube with a small amount of pure water and transfer the rinsed suspension to the mortar), then place the mortar containing the sample in an oven at 70°C to dry (the recommended drying time is at least 24 hours);

[0098] 8) Remove the dried sample from the mortar and grind it until it passes through a 0.25 mm sieve after cooling. Mix thoroughly and seal the mixture in a ziplock bag. Store at room temperature. Grind, sieve, and mix the same sample from the same batch together and place it in the same ziplock bag. This sample is the hydrogen-saturated soil sample.

[0099] 9) Weigh 5.00 g (round to two decimal places) of soil sample into a sample cup. Add a 0.005 mol / L NaOH + KOH solution. After adding the alkali solution, stir on a magnetic stirrer for 60 minutes.

[0100] 10) Use a pH electrode to measure the pH of the suspension to be tested in 9). If the pH is too low, add a small amount of mixed alkali solution. If the pH is too high, add a small amount of hydrogen-saturated soil sample. Stir for 10 minutes after addition. Repeat the above steps until the pH value is between 7.2 ± 0.2.

[0101] 11) Use Na + , K + Determination of Na in suspension by ion selective electrode + , K + activity.

[0102] 12) In the iterative operation, the measured Na + , K + Activity a Na 、a K Set to Na + , K + The initial concentration value, c Na (0) = a Na , c K (0) = a K , then the Na of the first iteration + , K + The concentration is:

[0103]

[0104] In the formula π is the circumference of a circle, F is the Faraday constant 96485C / mol, e0 is the charge of an electron 1.6×10 -19 C, ε is the dielectric constant of water 8.9×10 -10 C 2 / (J dm), R is the gas constant 8.314 J / (mol K), T is the system temperature in Kelvin (298 K at 25 °C), I(0) is the initial ionic strength and

[0105] I(0)=c Na (0)+c K (0).

[0106] 13) According to the Na calculated in the first iteration + , K + Concentration c Na (1) and c K (1), the second iteration is calculated by the following equation:

[0107]

[0108] Where I(1) is the initial ionic strength and I(1)=c Na 1)+c K (1).

[0109] 14) Similarly, repeat the above process until the difference between the results of the nth and n+1th times is [c(n+1)-c(n)] / c(n+1)<0.001. At this time, the iteration Na + , K + The concentration is the Na in the suspension at the corresponding pH + , K + Concentration, c′ Na and c′ K Substitute the measured ion concentration into the following formula to calculate the indicator ion Na+ , K + The adsorption amount on the surface of nano-micron particles is recorded as N Na and N K :

[0110]

[0111] Where N Na and N K The unit is mol / g; and Na + and K + The total volume of the ionic solution, in L; c and for Na + and K + Initial concentration of ions, c′ Na and c′ K for Na + and K + The equilibrium concentration of ions is expressed in mol / L; m is the oven-dried mass of the hydrogen-saturated soil sample in g.

[0112] The specific surface area of ​​soil particles is obtained by solving the following two equations simultaneously:

[0113]

[0114]

[0115] Where γ K and γ Na Na + and K + The charge coefficient, γ K =1.699,γ Na =1.110; Z K and Z Na Na + and K + valence of; Debye parameter, unit is dm -1 ; ε is the dielectric constant of water 8.9×10 -10 C 2 / (J dm); S is the specific surface area, the unit is dm 2 / g; is the surface potential of the Na-K measurement system, in V; R is the gas constant, which is 8.314 J / (mol K); T is the absolute temperature, which is 298 K at 25 °C; e0 is the electron charge, which is 1.6×10 -19 C; F is the Faraday constant, which is 96485C / mol.

[0116] The values ​​of relevant parameters are obtained through the above experiments, as shown in Figure 1, and then these parameters are used to calculate the specific surface area of ​​soil particles:

[0117] Table 1 Values ​​of relevant parameters

[0118]

[0119] (2) Determination of the surface charge of soil particles under different pH conditions:

[0120] Weigh the hydrogen-saturated dried soil sample with a mass of m′0 obtained according to step (1) into a 100 mL sample cup, mix it evenly with a sodium hydroxide solution with a volume of V1 and a concentration of c0, adjust the pH with the sodium hydroxide solution until the pH is 12±0.2, record the volume of the alkaline solution added to adjust the pH V2, add 0.5 mol / L acetic acid solution to the beaker, record the volume of the acetic solution added V3, measure the pH of the suspension after exchange equilibrium, repeatedly add acetic solution, and measure the pH and ion concentration c0′ of the suspension after equilibrium. The salt content of this sample is low, so the salt content is not considered. The soil surface charge is calculated using the following formula:

[0121]

[0122] Where SCN is the soil cation exchange capacity, in cmol (+) / kg, c0 is the initial concentration of NaOH solution, c'0 is the Na ion concentration of the system at equilibrium, m0' is the mass of the dried hydrogen-saturated soil sample, V1 is the total volume of NaOH solution added after all soil samples are transferred to the beaker, V2 is the volume of NaOH solution added to adjust the pH, and V3 is the total volume of acetic acid solution added, the unit is ml; 10 -3 The conversion factor for milliliters to liters is 10 5 mol (+) / g to cmol (+) After adjusting the pH of the system to 12 ± 0.2 with sodium hydroxide solution, gradually add different volumes of acetic acid solution to change the pH of the system. In each step, record the corresponding pH value and related parameters, and calculate the surface charge of soil particles under different pH conditions according to the formula:

[0123] Table 2 Parameter values ​​recorded

[0124]

[0125] like Figure 1According to the fitting equation y = a*[1-exp(-b*x)], the actual surface charge of soil particles in the field at the actual pH = 5.64 is 6.67 cmol. (+) / kg.

[0126] (3) Evaluation of the surface charge density of soil particles under different pH conditions:

[0127] The surface charge density under different pH conditions can be obtained by the specific surface area obtained above and the number of surface charges under different pH conditions:

[0128]

[0129] Where σ refers to the surface charge density (C / dm 2 ),10 -5 cmol (+) / kg to mol (+) Conversion factor of / g.

[0130] According to the actual field pH = 5.64, the actual surface charge of soil particles in the field is 6.67 cmol (+) / kg, the surface charge density of soil particles at the actual pH in the field can be calculated to be 0.001978C / dm 2 ,like Figure 2 . ,

[0131] (4) Evaluate the surface potential of soil particles under field conditions:

[0132] Surface potential under field conditions Calculated by the following formula:

[0133]

[0134] Where π is the ratio of circumference to diameter; c is the ratio of circumference to diameter. i is the concentration of water-soluble cations in soil solution in mol / L; γ i is the effective charge coefficient of the water-soluble cation, where γ K =1.699,γ Na =1.110,γ Ca =1.403,γ Mg =1.183; Z i It is the valence state of a water-soluble cation.

[0135] Because the soil type collected is dry yellow soil, the determination method of water-soluble cations can refer to the soil agrochemical analysis textbook. i(i is K, Na, Ca and Mg, the unit is cmol / kg)), and then the volume of water per kilogram of soil is obtained according to the measured field soil moisture content (refer to the agricultural chemical analysis textbook), thereby evaluating the water-soluble cation concentration (mol / L) in the soil solution. The formula is as follows:

[0136]

[0137] where c i is the concentration of water-soluble cations, the unit is mol / L; w i is the content of water-soluble cations, in cmol / kg; ρ is the density of water, in g / cm 3 ; ω is soil moisture%, 10 -2 is the conversion factor from cmol / kg to mol / kg.

[0138] Through the relationship between the soil moisture content above and the concentration of water-soluble cations, e.g. Figure 3 , the actual concentration of major water-soluble cations in the field can be obtained according to the actual soil moisture content in the field, and the surface potential of soil particles under field conditions can be calculated using the above formula:

[0139] Table 3 Calculated parameter values

[0140]

[0141] (5) Evaluate the electrostatic repulsion pressure between soil particles under field conditions:

[0142] The midpoint potential of the mixed electrolyte system is calculated by the following formula

[0143]

[0144] Where ∑c1 and ∑c2 refer to the sum of the concentrations of monovalent and divalent water-soluble cations under field conditions, respectively, in mol / L; d is the distance between the surfaces of two adjacent particles, in nm; is the midpoint potential, in V; 10 -8 The conversion factor for converting nm to dm.

[0145] Electrostatic repulsion pressure P under field conditions EDL Calculated by the following formula:

[0146]

[0147] Where c i is the concentration of water-soluble cations in mol / L; γ i is the effective charge coefficient of the water-soluble cation; Z iis the valence state of the water-soluble cation; P EDL is the electrostatic repulsion pressure between soil particles, the unit is atm; 1000 / 101325 is the conversion factor from J / L to atm.

[0148] Figure 4 This is the law of variation of electrostatic repulsion pressure between soil particles with distance under field conditions when the actual field pH is 5.64 and the soil moisture content is 6.5%.

Claims

1. A method for evaluating the electrostatic repulsion pressure between soil particles under field conditions, characterized in that: The following steps are involved: (1) Determine the specific surface area of ​​soil particles; (2) Determine the surface charge of soil particles under different pH conditions; By measuring the number of charges at different pH values, the functional relationship between pH and the number of charges is obtained, and then the pH under actual field conditions is measured. Then, the actual field pH value is substituted into the relationship between the measured number of charges and pH to obtain the surface charge number of soil particles under the actual field pH value; (3) evaluate the surface charge density of soil particles under different pH conditions; The surface charge density under different pH conditions can be obtained by using the specific surface area obtained above and the surface charge quantity under different pH conditions; (4) Evaluate the surface potential of soil particles under field conditions; The surface potential under field conditions was evaluated based on the obtained surface charge density; (5) Evaluate the electrostatic repulsion pressure between soil particles under field conditions; Based on the surface potential under field conditions, the midpoint potential between soil particles is calculated; and the electrostatic repulsion pressure between soil particles under field conditions is further evaluated based on the obtained midpoint potential.

2. A method for evaluating the electrostatic repulsion pressure between soil particles under field conditions according to claim 1, characterized in that: The specific method of step (1) determining the specific surface area of ​​soil particles is as follows: Na-K ions are used as indicator ions, and the corresponding anions are Cl-1. - and OH - , the corresponding Cl - OH - with Na + , K + The compounds formed are NaCl / KCl and NaOH / KOH; the indicator ion Na + , K + It is a non-specific adsorbent of cations, and NaCl and KCl are water-soluble salts; First, determine the activity of the indicator ion in the equilibrium system, denoted as a Na and a K ; Calculate the concentration of the indicator ion in the equilibrium system, denoted as c Na and c K , according to c Cl =Z Na c Na +Z K c K Calculate the corresponding anion Cl - The concentration of the indicator ion Na is calculated by substituting the measured ion concentration into the following formula. + , K + The adsorption amount on the surface of nano-micron particles is recorded as N Na and N K : Where N Na and N K The unit is mol / g; and Na + and K + The total volume of the ionic solution, in L; and for Na + and K + Initial concentration of ions, c′ Na and c′ K for Na + and K + The equilibrium concentration of ions is in mol / L; m is the oven-dried mass of the hydrogen-saturated soil sample in g; The specific surface area of ​​soil particles is obtained by solving the following two equations simultaneously: Where γ K and γ Na Na + and K + The charge coefficient, γ K =1.699,γ Na =1.110; Z K and Z Na Na + and K + valence of; Debye parameter, unit is dm -1 ; ε is the dielectric constant of water 8.9×10 -10 C 2 / (J dm); S is the specific surface area, the unit is dm 2 / g; is the surface potential of the Na-K measurement system, in V; R is the gas constant, which is 8.314 J / (mol K); T is the absolute temperature, which is 298 K at 25 °C; e0 is the electron charge, which is 1.6×10 - 19 C; F is the Faraday constant, which is 96485C / mol.

3. A method for evaluating the electrostatic repulsion pressure between soil particles under field conditions according to claim 1, characterized in that: Step (3) Surface charge density under different pH conditions: Where σ refers to the surface charge density C / dm 2 ; 10 -5 cmol (+) / kg to mol (+) Conversion factor of / g.

4. A method for evaluating electrostatic repulsion pressure between soil particles under field conditions according to claim 1, characterized in that: The specific method of step (4) is: The surface potential under field conditions was further estimated based on the obtained surface charge density using the following formula: Where π is the ratio of circumference to diameter; c is the ratio of circumference to diameter. i is the concentration of water-soluble cations in soil solution in mol / L; γ i is the effective charge coefficient of the water-soluble cation, where γ K =1.699,γ Na =1.110,γ Ca =1.403,γ Mg =1.183; Z i is the valence of the water-soluble cation; Determine the soil moisture content in the field and further evaluate the concentration of water-soluble cations in the soil solution: where c i is the concentration of water-soluble cations, the unit is mol / L; w i is the content of water-soluble cations, in cmol / kg; ρ is the density of water, in g / cm 3 ;ω is soil moisture content%; 10 -2 is the conversion factor from cmol / kg to mol / kg.

5. The method for evaluating the electrostatic repulsion pressure between soil particles under field conditions according to claim 1, characterized in that: The specific method of step (5) is: Calculate the midpoint potential between soil particles based on the surface potential obtained under field conditions Where ∑c1 and ∑c2 refer to the sum of the concentrations of monovalent and divalent water-soluble cations under field conditions, respectively, in mol / L; d is the distance between the surfaces of two adjacent particles, in nm; is the midpoint potential, in V; 10 -8 The conversion factor from nm to dm; Electrostatic repulsion pressure P under field conditions EDL Calculated by the following formula: Where c i is the concentration of water-soluble cations in mol / L; γ i is the effective charge coefficient of the water-soluble cation; Z i is the valence state of the water-soluble cation; P EDL is the electrostatic repulsion pressure between soil particles, the unit is atm; 1000 / 101325 is the conversion factor from J / L to atm.

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