CN111257541B - Method for continuously measuring isothermal adsorption curve of soil state - Google Patents
Method for continuously measuring isothermal adsorption curve of soil state Download PDFInfo
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Abstract
The invention discloses a method for continuously measuring an isothermal adsorption curve of a soil body state, which comprises the following steps: step one, adopting the concentration of
The source solution of the method is subjected to a penetrating soil column test with complete breakdown balance of pollutants; step two, CeContinuously keeping stable for four continuous periods; step three, testing the total mass m of the target pollutants in the samplea(ii) a Step four, calculating the concentration C of the target pollutant adsorbed on the soil sample particles of the soil columns(ii) a Fifthly, ensuring that the permeation speeds in the permeation tests of the concentrations of the sources are consistent; and step six, determining the curve with the best fitting degree as the isothermal adsorption curve of the soil sample. Has the advantages that: test errors caused by inconsistency of a plurality of soil samples are avoided. In the method except that
Besides, the initial values of the pore water concentration in the soil body and the adsorption concentration on the soil particles in the penetration test with the complete breakdown of the concentration of other sources are respectively C corresponding to the breakdown effluent with the previous concentration after the breakdown effluent reaches the balanceeAnd CsInstead of reaching the balance from a complete blank, the test efficiency is improved.
Description
Technical Field
The invention relates to a method for measuring an isothermal adsorption curve, in particular to a method for continuously measuring an isothermal adsorption curve of a soil body state.
Background
At present, the isothermal adsorption curve used to characterize the adsorption capacity of soil for contaminants is usually determined by the batch test method. The Batch test has the characteristics of simple and convenient operation and small occupied test space, thereby being widely applied. However, because the soil-water ratio, the contact time, the soil particle contact area and the like in the actual on-site soil body are different from the particulate state, the isothermal adsorption curve measured by the batch test is usually not consistent with the adsorption behavior in the soil body. The evaluation of the solute migration and adsorption conditions in soil body underground water based on the isothermal adsorption curve result of the batch test is not accurate. The soil column test method can directly measure the isothermal adsorption curve of the pollutants in the soil body state, and the migration and adsorption processes of solutes in the test process are similar to the actual state in the soil body in the nature, so the test result can be directly applied to solute migration analysis in the soil body in the field. However, the currently reported methods have some disadvantages: generally, the number of data points with different equilibrium concentrations on the isothermal adsorption curve is the number of soil columns needed to be arranged, so that the test workload is large; the method has the advantages that the method is used for testing various soil columns with different equilibrium concentrations, has good consistency and repeatability, has high requirements on preparation of soil column models, is usually used for remolding soil sample models, and is not suitable for undisturbed soil samples; the concentration of pollutants adsorbed by soil particles in each soil column test is increased from 0 to equilibrium concentration, and the time required for the test to reach equilibrium is long.
Disclosure of Invention
The invention aims to solve the problems that the existing soil column test method has large test workload, is not suitable for undisturbed soil samples, requires long time for test to reach balance and the like in the test process, and provides a method for continuously measuring the isothermal adsorption curve of the soil body state.
The invention provides a method for continuously measuring an isothermal adsorption curve of a soil body state, which comprises the following steps:
step one, setting the length to be L1The undisturbed soil column is filled into a pressure chamber of the permeameter according to the operation flow of the flexible wall permeameter, a pipeline is connected, and the confining pressure is set to be P in consideration of the lateral soil pressure received by the buried depth of the soil samplecSetting the osmotic pressure to P with reference to the actual head at the site1In a concentration of
Performing a penetrating soil column test of complete pollutant breakdown balance on the source solution;
step two, collecting the solution flowing out of the water outlet pipe in different periods, testing and collecting the concentration of the target pollutant in the solution by adopting a flame atomic absorption spectrometer, closing a valve to stop the test when the target pollutant solution completely breaks down the soil column, and achieving the breakdown standard: the concentration of the target contaminant in the effluent solution to be tested for three consecutive periods of time is no longer increased compared to the previous period of time, i.e. CeContinuously keeping stable for four continuous periods;
taking out the soil sample, cutting a section of soil sample with the length of 1-2cm from the lower part of the soil sample, taking a part of the cut soil sample, drying and testing the water content w of the part, and taking another part of the cut soil sample with the set mass of m1Carrying out digestion and testing the total mass m of the target pollutants in the solutiona；
Step four, calculating and adsorbing soil samples in the soil columnTarget contaminant concentration C on the particlesThe calculation formula is as follows:
in the formula: cs-the concentration of target contaminants adsorbed on soil sample particles of the soil column in mg/g;
ma-total mass of target contaminants in the wet soil sample in mg;
m1digesting the mass of the taken wet soil sample, wherein the unit is g;
w is the water content of the sample;
Ce-effluent concentration in mg/L when the column is punctured by contaminants;
ρwdensity of water at test temperature, in g/cm3；
Step five, continuously filling the residual soil sample into a flexible wall permeameter for permeation test, repeating the step one to the step four, and sequentially adopting the concentration from low to high as the permeation source solution
In the penetration test, the adopted soil sample is always the same, but the soil sample length is gradually shortened and is respectively L2、L3、……、Li、……Ln. In order to ensure the consistent conditions in each concentration experiment, the permeation pressure is gradually reduced according to the length of the permeation soil sample in the permeation experiment
Ensuring that the permeation speeds in the permeation tests of the concentrations of all the sources are consistent;
step six, testing the obtained stable outflow concentration C by using the concentration penetration test of each sourceeAnd the concentration C adsorbed on the soil particlessDrawing a graph respectively for the abscissa and the ordinate, fitting the test points by adopting each isothermal adsorption model, and determining the curve with the best fitting degree as the isothermal adsorption curve of the soil sample.
The invention has the beneficial effects that:
the isothermal adsorption curve in the method for continuously measuring the soil state isothermal adsorption curve provided by the invention is measured under the real confining pressure and real flow velocity of the soil state, can truly reflect the adsorption condition of soil particles in the migration process of target pollutants in the soil, and can be effectively used for the prediction analysis of the migration of the pollutants in the soil. The equilibrium reaction of all points of the isothermal adsorption curve always occurs in the same soil sample, and the test error caused by the inconsistency of a plurality of soil samples is avoided. In the method except that
Besides, the initial values of the pore water concentration in the soil body and the adsorption concentration on the soil particles in the penetration test with the complete breakdown of the concentration of other sources are respectively C corresponding to the breakdown effluent with the previous concentration after the breakdown effluent reaches the balanceeAnd CsRather than reaching equilibrium from a complete blank, the required adsorption equilibrium time becomes shorter and shorter (as shown in FIG. 1), increasing the efficiency of the assay.
Drawings
Fig. 1 is a schematic diagram of breakdown outflow curves corresponding to the actually measured source concentrations.
FIG. 2 is a schematic diagram of an isothermal adsorption curve of the actual measurement soil column state of the invention.
Detailed Description
Please refer to fig. 1 to 2:
the invention provides a method for continuously measuring a soil body state isothermal adsorption curve, which comprises the following steps:
step one, setting the length to be L1The undisturbed soil column is filled into a pressure chamber of the permeameter according to the operation flow of the flexible wall permeameter, a pipeline is connected, and the confining pressure is set to be P in consideration of the lateral soil pressure received by the buried depth of the soil samplecSetting the osmotic pressure to P with reference to the actual head at the site1In a concentration of
The source solution of the method is subjected to a penetrating soil column test with complete breakdown balance of pollutants;
step two, collecting the solution flowing out of the water outlet pipe in different periods, testing and collecting the concentration of the target pollutant in the solution by adopting a flame atomic absorption spectrometer, closing a valve to stop the test when the target pollutant solution completely breaks down the soil column, and achieving the breakdown standard: the concentration of the target contaminant in the effluent solution to be tested for three consecutive periods of time is no longer increased compared to the previous period of time, i.e. CeContinuously keeping stable for four continuous periods;
taking out the soil sample, cutting a section of soil sample with the length of 1-2cm from the lower part of the soil sample, taking a part of the cut soil sample, drying and testing the water content w of the part, and taking another part of the cut soil sample with the set mass of m1Carrying out digestion and testing the total mass m of the target pollutants in the solutiona；
Step four, calculating the concentration C of the target pollutant adsorbed on the soil sample particles of the soil columnsThe calculation formula is as follows:
in the formula: csThe concentration of target pollutants adsorbed on soil sample particles of the soil column is mg/g;
ma-total mass of target contaminants in the wet soil sample in mg;
m1digesting the mass of the taken wet soil sample, wherein the unit is g;
w is the water content of the sample;
Ce-effluent concentration in mg/L when the column is punctured by contaminants;
ρwdensity of water at test temperature, in g/cm3；
Step five, continuously filling the residual soil sample into a flexible wall permeameter for permeation test, repeating the step one to the step four, and sequentially adopting the concentration from low to high as
In the penetration test, the soil sample used is always the same, butThe soil sample length is gradually shortened and is respectively L2、L3、……、Li、……Ln. In order to ensure the consistent conditions in each concentration experiment, the permeation pressure is gradually reduced according to the length of the permeation soil sample in the permeation experiment
Ensuring that the permeation speeds in the permeation tests of the concentrations of all the sources are consistent;
step six, testing the obtained stable outflow concentration C by using the concentration penetration test of each sourceeAnd the concentration C adsorbed on the soil particlessDrawing a graph by respectively using the abscissa and the ordinate, fitting the test points by using each isothermal adsorption model, and determining the curve with the best fitting degree as the isothermal adsorption curve of the soil sample.
The target pollutant adopts Pb2+The soil sample is clay silt undisturbed soil sample. A soil column with the length of 100mm and the diameter of 101mm is cut, a latex film is sleeved on the side surface of the soil column, and the soil column is filled into a pressure chamber of a flexible wall permeameter. During the installation, care was taken to vent and maintain the seal, and the sample was then saturated. After saturation, Pb with a concentration of 50mg/L is used2+The solution was used to perform a penetrating soil column test with complete breakdown of the contaminants. The confining pressure can be set according to the actual buried depth of the sampling soil column, and here we set the confining pressure to be 20 kPa. Collecting effluent solution in different time periods during the penetration test, testing the concentration of the effluent solution, and if Pb in the effluent solution is tested in three consecutive time periods2+Concentration CeNo longer increasing compared to the previous period, i.e. CeAnd closing the valve and stopping the test when the stability is continuously kept continuously for four continuous time periods. Taking out the soil sample, cutting a soil sample with the thickness of 1.5cm from the bottom of the soil column, taking one part of the soil sample, drying to test the water content w, taking the other part of the soil sample, digesting, and testing Pb in the wet soil sample by adopting a flame atomic absorption spectrometer2+Total mass ma。
The remaining soil column continues to adopt the concentration C of the pollution source0The solution at 100mg/L was subjected to permeation test until the solution was completely broken down. Since the soil column is changed from 10cm to 8.5cm, in order to ensure the consistency of the flow velocity, the osmotic pressure is adjusted to be the front in the test8.5% of the value, a 1.5cm thick soil sample was cut from the bottom of the punctured soil sample for test analysis. Testing to obtain the water content w of the soil sample and the Pb in the wet soil sample2+Total mass ma。
Repeating the steps, and sequentially adopting 200, 400, 600 and 800mg/L Pb2+The solution is used as an osmotic source solution to carry out an osmotic test of complete breakdown. After the soil column was completely punctured, a 1.5cm thick soil sample was cut from the bottom of the punctured soil sample for testing and analysis. Testing to obtain the water content w of the soil sample and the Pb in the wet soil2+Total concentration Ca。
Fig. 1 is a breakdown outflow curve for each source concentration. As shown in the figure, the time required for the breakdown test was longer for a source concentration of 50mg/L, and then the breakdown equilibrium time was gradually shorter for each source concentration. In addition, the source concentration is
The initial concentration of the breakdown curves is all the source concentration
Equilibrium concentration of breakdown equilibrium test of
The target pollutant concentration adsorbed on soil particles of the soil column in the breakdown test of each source concentration is calculated by adopting the following formula:
in the formula: cs-target contaminant concentration (mg/g) adsorbed on earth-like particles of the earth pillar;
ma-total mass of target contaminants in the wet soil sample in mg;
m1digesting the mass of the taken wet soil sample, wherein the unit is g;
w is the water content of the sample;
Ce-effluent concentration (mg/L) when contaminants break down the column;
ρwthe density of water at the test temperature (g/cm 3).
The results are shown in Table 1. The steady effluent concentration C obtained by the permeation test of each source concentrationeAnd the concentration C adsorbed on the soil particlessRespectively, abscissa and ordinate, plotted as figure 2. And (3) fitting the test points by adopting each isothermal adsorption model, determining the curve with the best fitting degree as the isothermal adsorption curve of the soil sample, and specifically fitting the curve as shown in figure 2.
TABLE 1 effluent concentration C for each source concentrationeAdsorption of pollutant concentration C by soil particless
Claims (1)
1. A method for continuously measuring the isothermal adsorption curve of a soil body state is characterized by comprising the following steps: the method comprises the following steps:
step one, setting the length to be L1The undisturbed soil column is filled into a pressure chamber of the permeameter according to the operation flow of the flexible wall permeameter, a pipeline is connected, and the confining pressure is set to be P in consideration of the lateral soil pressure received by the buried depth of the soil samplecSetting the permeate pressure to P with reference to the actual head at the site1With a concentration of C01, performing a penetrating soil column test of complete pollutant breakdown balance on the source solution;
step two, collecting the solution flowing out of the water outlet pipe in different periods, testing and collecting the concentration of the target pollutant in the solution by adopting a flame atomic absorption spectrometer, closing a valve to stop the test when the target pollutant solution completely breaks down the soil column, and achieving the breakdown standard: the concentration of the target contaminant in the effluent solution to be tested for three consecutive periods of time is no longer increased compared to the previous period of time, i.e. CeContinuously keeping stable for four continuous periods;
taking out the soil sample, cutting a section of soil sample with the length of 1-2cm from the lower part of the soil sample, taking a part of the cut soil sample, drying and testing the water content w of the part, and taking another part of the cut soil sample with the set mass of m1Performing digestion and testingWherein the total mass m of the target pollutanta；
Step four, calculating the concentration C of the target pollutant adsorbed on the soil sample particles of the soil columnsThe calculation formula is as follows:
in the formula: csThe concentration of target pollutants adsorbed on soil sample particles of the soil column is mg/g;
ma-total mass of target contaminants in the wet soil sample in mg;
m1digesting the mass of the taken wet soil sample, wherein the unit is g;
w is the water content of the sample;
Ce-effluent concentration in mg/L when the column is punctured by contaminants;
ρwdensity of water at test temperature, in g/cm3；
Step five, continuously filling the residual soil sample into a flexible wall permeameter for permeation test, repeating the step one to the step four, and sequentially adopting the concentration from low to high as the permeation source solution
In the penetration test, the adopted soil sample is always the same, but the soil sample length is gradually shortened and is respectively L2、L3、……、Li、……LnIn order to ensure the consistent conditions in each concentration experiment, the permeation pressure is gradually reduced according to the length of the permeation soil sample in the permeation experiment
Ensuring that the permeation speeds in the permeation tests of the concentrations of all the sources are consistent;
step six, testing the obtained stable outflow concentration C by using the concentration penetration test of each sourceeAnd the concentration C adsorbed on the soil particlessRespectively an abscissa and an ordinate, drawingAnd (4) mapping, fitting the test points by adopting each isothermal adsorption model, and determining the curve with the best fitting degree as the isothermal adsorption curve of the soil sample.
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