A rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping of dredged soil

Abstract

The present invention discloses a rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping of dredged soil. The mass ratio of various heavy metals to the mass of the dredged soil sample is measured to obtain the solid content ratio of various heavy metals in the dredged soil. The water temperature is collected, the dredged soil is subjected to particle size grading, and the equilibrium distribution coefficient of dissolved and particulate heavy metals is calculated. A rapid calculation model for the concentration of dissolved heavy metals and particulate heavy metals in suspended matter in the overlying water body is established. According to the deposition thickness, mixing thickness, and dry bulk density in the sediment, the concentration of heavy metal-containing sediment and the total sediment concentration after the bottom bed sediment is mixed are calculated. A rapid calculation model for the concentration of dissolved heavy metals in the interstitial water and particulate heavy metals in the bottom bed is established. The present invention takes into account the environments of plankton and benthic organisms, realizes the monitoring, management, and treatment of toxic heavy metal environments during bottom dumping operations, and meets the evaluation requirements for the rapid, efficient, full-space, and multi-type heavy metal distribution during bottom dumping operations.

Description

Technical Field

[0001] The present invention relates to the technical field of dredged water heavy metal assessment, and particularly relates to a rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping process of dredged soil. Background Art

[0002] Currently, during the bottom dumping process of dredged soil in rivers or coastal waters, the diffusion and deposition problems of toxic heavy metals can cause great harm to the water ecosystem, especially to predators at the upper level of the food chain. The assessment of dissolved and particulate heavy metals during the bottom dumping operation often requires a large amount of manpower and material resources for sampling and measurement. At the same time, due to the dynamics of the bottom dumping process, the representativeness of sampling is also greatly limited. In addition, using mathematical models to calculate the distribution of heavy metals requires complex calculations of hydrodynamic, sediment, and multiple heavy metal variables. The process of model establishment is complicated, and the calculation timeliness is difficult to guarantee. At the same time, it is difficult for existing models to effectively calculate the heavy metal concentrations in bottom bed interstitial water and sediments. These limitations make the existing technical means difficult to meet the assessment requirements of rapid, efficient, full-space, and multi-type heavy metal distribution.

[0003] Therefore, we have designed a rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping process of dredged soil to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that the existing technical means for assessing heavy metals during the bottom dumping process of dredged soil are difficult to meet the assessment requirements of rapid, efficient, full-space, and multi-type heavy metal distribution. A rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping process of dredged soil is proposed. Based on each rapid calculation model, the distribution of multiple types of heavy metals in the entire water environment space during the bottom dumping process of dredged soil is rapidly calculated.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping process of dredged soil, the method mainly includes the following steps:

[0007] Step S1, pretreatment of the solid content ratio of heavy metals. Through drying and digestion treatment of dredged soil, the ratio of the mass of various heavy metals to the mass of the dredged soil sample is measured to obtain the solid content ratio of various heavy metals in the dredged soil.

[0008] Step S2, obtaining the equilibrium distribution coefficient of heavy metals. By collecting the water temperature, performing particle size grading screening on the dredged soil, and calculating the equilibrium distribution coefficients of dissolved and particulate heavy metals at different particle size grades.

[0009] Step S3, calculation of the concentrations of dissolved and particulate heavy metals in the overlying water body. According to the dredged soil bottom-dumping diffusion model, calculate the diffusion concentration of the dredged soil and the sediment thickness in the overlying water body, and establish a rapid calculation model for the concentrations of dissolved heavy metals and suspended particulate heavy metals in the overlying water body under the equilibrium state;

[0010] Step S4, calculation of the effective sediment concentration in the bottom bed sediment. According to the deposition thickness, mixing thickness, and dry bulk density in the sediment, considering the mixing process of the new sediment and the historical sediment, calculate the heavy metal-containing sediment concentration and the total sediment concentration after mixing of the bottom bed sediment;

[0011] Step S5, calculation of the concentrations of dissolved and particulate heavy metals in the interstitial water body. Establish a rapid calculation model for the concentrations of dissolved heavy metals in the interstitial water body and particulate heavy metals in the bottom bed, and achieve rapid acquisition of the concentrations of dissolved heavy metals in the interstitial water area and particulate heavy metals in the sediment bed area.

[0012] As a further preferred solution of the present invention, in step S1, the process for obtaining the solid content ratios of various heavy metals in the dredged soil is as follows:

[0013] Collect representative dredged soil samples from the dredged soil, ensure that the sampling points are evenly covered and have environmental representativeness, remove impurities from the dredged soil samples, and mix them evenly;

[0014] Dry the dredged soil samples to a constant weight, and grind the dredged soil samples into uniform fine powder with a mortar, and weigh the dry mass of the dredged soil samples;

[0015] Weigh the dredged soil samples according to wet digestion, add digestion reagents, place them in a microwave digestion instrument for digestion, and after completion, perform cooling and volume fixation, and measure the fixed volume;

[0016] Use atomic emission spectrometry to determine the mass concentrations of various heavy metals, and obtain the solid content ratios of various heavy metals according to the following formula :

[0017] .

[0018] As a further preferred solution of the present invention, in step S2, the process for obtaining the equilibrium distribution coefficient of heavy metals includes:

[0019] Collect the water temperature, perform particle size classification on the dredged soil using a laser particle size analyzer, and calculate the equilibrium distribution coefficients of dissolved and particulate forms of various heavy metals at different particle size classes:

[0020] ;

[0021] In the above formula, represents the th type of heavy metal, and the median particle size of the dredged soil is In the group number, when the temperature is T, the equilibrium distribution coefficient of heavy metals in dissolved and particulate forms; is the standard distribution coefficient, the factor characterizing the influence of temperature change on the equilibrium distribution coefficient, represents the median particle size of the dredged soil composition, the influence coefficient characterizing the different adsorption capacities of heavy metals due to different specific surface areas of different median particle size groups.

[0022] As a further preferred solution of the present invention, in step S3, a dredged soil bottom dumping diffusion model is used to calculate and obtain the sediment concentration and sediment thickness in the overlying water body during the dredged soil bottom dumping process, and a rapid acquisition model for the dissolved heavy metal concentration and suspended sediment particulate heavy metal concentration in the overlying water body under equilibrium conditions is established to achieve the rapid acquisition of the dissolved heavy metal concentration and suspended sediment particulate heavy metal concentration in the overlying water body;

[0023] Step S31, the calculation formula of the dredged soil bottom dumping diffusion model for the sediment concentration and sediment thickness of the dredged soil bottom dumping diffusion is as follows:

[0024] ;

[0025] ;

[0026] In the formula, is the calculated transitional sediment concentration before the sedimentation process occurs after the dredged soil diffusion process, is the mass of the dredged soil at point within the dredged material diffusion range, is the sediment concentration at point within the dredged material diffusion range, H is the water depth, K is the diffusion coefficient, represents the position coordinates of the dredged material dumping point, and are the transverse and longitudinal average flow velocities respectively, η is the cloud following coefficient, is the sediment settling velocity, is the calculation time step;

[0027] ;

[0028] In the formula, is the increased sediment thickness of the bottom bed after sedimentation at point within the dredged material diffusion range, is the porosity of the sediment deposited on the bottom bed, represents the dry bulk density of the sediment;

[0029] Step S32, according to the analysis theory of dissolved and particulate heavy metals in the overlying water body under equilibrium conditions, a rapid acquisition model for the dissolved heavy metal concentration in the overlying water body is established, and its expression is as follows:

[0030] ;

[0031] In the formula, represents the concentration of the th class of dissolved heavy metals in the overlying water at point within the dredged material diffusion range, represents the solid content ratio of the th class of heavy metals in the dredged material, represents the equilibrium distribution coefficient of the th class of heavy metals at a specific temperature, is the porosity in water;

[0032] Step S33: According to the analytical theory of dissolved and particulate heavy metals in the overlying water under equilibrium conditions, establish a rapid calculation model for the concentration of particulate heavy metals in the suspended matter of the overlying water, and its expression is as follows:

[0033] ;

[0034] In the formula, represents the concentration of the th class of particulate heavy metals in the suspended matter at point within the dredged material diffusion range, is the porosity in water.

[0035] As a further preferred solution of the present invention, in step S4, the calculation methods for the heavy metal sediment concentration and the total sediment concentration after mixing the bottom bed sediments are as follows:

[0036] Step S41: Utilize the exchange relationship between the new sediment and the surface sediment, and consider the mixing process of the new sediment and the historical sediment during the calculation of the heavy metal concentration distribution in the bottom bed sediment and the interstitial water, and calculate the heavy metal sediment concentration in the mixed bottom bed sediment :

[0037] ;

[0038] In the formula, represents the heavy metal sediment concentration in the mixed sediment at point within the dredged material diffusion range, is the increased sediment thickness of the bottom bed siltation after settlement at point within the dredged material diffusion range, is the cumulative increased sediment thickness of the bottom bed siltation after settlement at point within the dredged material diffusion range, represents the mixing thickness of the historical sediment of the bottom bed mixed with the new sediment under the action of dynamics and bioturbation, represents the dry bulk density of sediment;

[0039] Step S42, after mixing occurs, the particulate heavy metals in the bottom bed sediment and the dissolved heavy metals in the interstitial water reach equilibrium. At this time, the total sediment concentration after mixing of the bottom bed sediment :

[0040] ;

[0041] In the formula, represents the total sediment concentration after mixing at point within the dredged material diffusion range, is the porosity of the sediment in the bottom bed.

[0042] As a further preferred solution of the present invention, in step S5, by establishing a rapid calculation model for the concentrations of dissolved heavy metals in the interstitial water and particulate heavy metals in the bottom bed, the rapid acquisition of the concentrations of dissolved heavy metals in the interstitial water area and particulate heavy metals in the sediment bed area is realized, including:

[0043] Step S51, using the analytical theory of dissolved and particulate heavy metals in the interstitial water, establish a rapid calculation model for the concentration of dissolved heavy metals in the interstitial water, and its expression is as follows:

[0044] ;

[0045] In the formula, represents the concentration of the th type of dissolved heavy metal in the interstitial water at point within the dredged material diffusion range, represents the solid content ratio of the th type of heavy metal in the dredged material, represents the concentration of sediment containing heavy metals after mixing at point within the dredged material diffusion range, represents the total sediment concentration after mixing of the sediment at point within the dredged material diffusion range, is the porosity of the sediment in the bottom bed, represents the th type of heavy metal's equilibrium distribution coefficient at a specific temperature;

[0046] Step S52, using the analytical theory of dissolved and particulate heavy metals in the interstitial water, establish a rapid calculation model for the concentration of particulate heavy metals in the bottom bed in the interstitial water, and its expression is as follows:

[0047] ;

[0048] In the formula, represents the point within the dredged material diffusion range The concentration of particulate heavy metals in the bottom bed sediment at class, represents the solid content ratio of the class of heavy metals in the dredged material, represents the concentration of heavy metal-containing sediment in the mixed sediment at point within the dredged material diffusion range, represents the total sediment concentration of the mixed sediment at point within the dredged material diffusion range, is the porosity of the bottom bed sediment, represents the class of heavy metals at a specific temperature.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows: The rapid calculation model of heavy metal distribution in the present invention does not require iterative calculation through traditional water flow-sediment-heavy metal coupling calculation equations, especially the convection-diffusion transport equations of multi-type heavy metal concentration parameters and the net flux equation of heavy metals from the sediment bed to the overlying water. Instead, it directly calculates and obtains the dissolved and particulate concentrations of heavy metals through the form of a rapid calculation model in the equilibrium state, improving the timeliness and simplicity of the calculation, and also avoiding the representativeness limitation of large-scale sampling and monitoring. By introducing the bottom bed sediment mixing process and the analysis process of the heavy metal concentration equilibrium state in the interstitial water, it is possible to simultaneously achieve the rapid calculation of the concentration distribution in the entire water environment space, including the dissolved state in the overlying water body, the dissolved state in the interstitial water body, the particulate state in the suspended matter, and the particulate state in the bottom bed sediment, thereby providing data support for the evaluation of the heavy metal environmental suitability of plankton and benthic organisms in the water body under actual conditions. By proposing calculation schemes for the equilibrium distribution coefficients of dissolved and particulate heavy metals under different types, different temperatures, and different particle size gradations, it is possible to better calculate the bottom dumping process of dredged materials under complex particle size gradations of dredged materials, water temperature changes, and multiple toxic heavy metal pollution conditions, thereby improving the evaluation reliability and accuracy of the heavy metal distribution and transport process.

[0050] The present invention takes into account the environments of plankton and benthic organisms, realizes the monitoring, management, and treatment of toxic heavy metals in the bottom dumping operation, and meets the evaluation requirements for the rapid, efficient, full-space, and multi-type heavy metal distribution in the bottom dumping process. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is a schematic flow chart of a rapid calculation method for the distribution of multi-type heavy metals during the bottom dumping process of dredged soil proposed by the present invention;

[0052] Figure 2 is a schematic diagram of the heavy metal transport process in the entire water environment space of the embodiment of the present invention;

[0053] Figure 3Schematic diagram of the calculation results of the dissolved heavy metal concentration diffusion in the overlying water at the points near the bottom dumping point in the embodiments of the present invention;

[0054] Figure 4 Schematic diagram of the calculation results of the sediment particulate heavy metal concentration diffusion in the interstitial water at the points near the bottom dumping point in the embodiments of the present invention;

[0055] Figure 5 It is the particle size distribution curve diagram in the embodiments of the present invention. Detailed implementation manners

[0056] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments.

[0057] Refer to Figure 1 A rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping of dredged soil proposed in this embodiment is a rapid calculation of the distribution of multiple types of heavy metals in the entire water environment during the bottom dumping of dredged soil based on a rapid calculation model. The method includes the following steps:

[0058] Step S1, pretreatment of the solid content ratio of heavy metals. Through drying and digestion treatment of the dredged soil, the ratio of the mass of various heavy metals to the mass of the dredged soil sample is measured to obtain the solid content ratio of various heavy metals in the dredged soil.

[0059] The various heavy metals referred to in this embodiment include heavy metals such as lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn).

[0060] The process of obtaining the solid content ratio of various heavy metals in the dredged soil is as follows:

[0061] Step S11, collect representative dredged soil samples from the dredged soil, ensure that the sampling points are evenly covered and have environmental representativeness, remove impurities from the dredged soil samples, and mix them evenly;

[0062] Step S12, dry the dredged soil samples pretreated above to a constant weight, and grind the dredged soil samples into uniform fine powder with a mortar, and weigh the dry mass of the dredged soil samples;

[0063] Step S13, according to wet digestion, weigh the digestion reagent added to the dredged soil sample (preferably polytetrafluoroethylene in this embodiment), place it in a microwave digestion instrument and digest it according to the set procedure, and after completion, perform cooling and volume fixation, and measure the fixed volume;

[0064] Step S14, use atomic emission spectrometry (preferably inductively coupled plasma emission spectrometry in this embodiment) to simultaneously measure the mass concentration of various heavy metals, and obtain the solid content ratio of various heavy metals according to the following formula :

[0065] 。

[0066] Detect the content ratio of Pb (lead), Cd (cadmium), Cu (copper) and Zn (zinc).

[0067] Step S2, obtaining the equilibrium distribution coefficient of heavy metals. By collecting the water temperature and performing particle size classification on the dredged soil, calculate the equilibrium distribution coefficients of dissolved and particulate heavy metals at different particle size levels. The process of obtaining the equilibrium distribution coefficient of heavy metals includes:

[0068] Collect the water temperature. The influence of temperature change on the distribution coefficient shows an exponential relationship, which can characterize the change of the distribution coefficient with the water temperature variable. At the same time, the distribution coefficient is related to the particle size level of the sediment, especially the difference in the adsorption capacity of clay and sand for heavy metals can be distinguished. Therefore, perform particle size classification on the sieve holes between the dredged soils. Calculate the equilibrium distribution coefficients of dissolved and particulate heavy metals of each type at different particle size levels:

[0069] ;

[0070] In the above formula, represents the type of heavy metal. In the group where the median particle size of the dredged soil is , when the temperature is T, the equilibrium distribution coefficients of dissolved and particulate heavy metals; is the standard distribution coefficient at 20 °C, characterizes the influence factor of temperature change on the equilibrium distribution coefficient, represents the median particle size of the dredged soil composition, characterizes the influence coefficient of different median particle size group ratios on the specific surface area and the heavy metal adsorption capacity. Generally, the smaller the particle size, the larger the surface area to volume ratio (specific surface area), and the stronger the ability to adsorb and transport heavy metals.

[0071] Step S3, calculating the concentrations of dissolved and particulate heavy metals in the overlying water. According to the bottom dumping diffusion model of the dredged soil, calculate the diffusion concentration of the dredged soil and the sediment thickness in the overlying water, and establish a rapid calculation model for the concentrations of dissolved heavy metals and suspended particulate heavy metals in the overlying water under equilibrium conditions. Figure 2 represents the heavy metal distribution in the water environment space where the bottom dumping vessel is located.

[0072] The dredged soil bottom dumping diffusion model is used to calculate and obtain the sediment concentration and sediment thickness in the overlying water body during the process of dredged soil bottom dumping. According to the analysis theory of dissolved heavy metals in the overlying water body, the heavy metal concentration distribution is quickly calculated, and a rapid acquisition model of the dissolved heavy metal concentration and the suspended solid particulate heavy metal concentration in the overlying water body under the equilibrium state is established to realize the rapid acquisition of the dissolved heavy metal concentration and the suspended solid particulate heavy metal concentration in the overlying water body.

[0073] The calculation steps are as follows:

[0074] Step S31, the calculation formula of the dredged soil bottom dumping diffusion model for the sediment concentration and sediment thickness of dredged soil bottom dumping diffusion is as follows:

[0075] ;

[0076] ;

[0077] Among them, is the calculated transitional sediment concentration before the sedimentation process occurs after the dredged soil diffusion process, is the mass of the dredged soil at point within the dredged material diffusion range, is the sediment concentration at point within the dredged material diffusion range, H is the water depth, K is the diffusion coefficient, represents the position coordinates of the dredged material dumping point, and are the transverse and longitudinal average flow velocities respectively, η is the cloud following coefficient, is the sediment settling velocity, is the calculation time step.

[0078] The calculation formula for obtaining the sediment thickness in the overlying water body during the dredged soil bottom dumping process by using the dredged soil bottom dumping diffusion model is as follows:

[0079] ;

[0080] In the formula, is the increased sediment thickness of the bottom bed after sedimentation at point within the dredged material diffusion range, is the porosity of the sediment deposited on the bottom bed, which can be taken as 1, represents the dry bulk density of the sediment.

[0081] Step S32, according to the analysis theory of dissolved and particulate heavy metals in the overlying water body under the equilibrium state, a rapid acquisition model of the dissolved heavy metal concentration in the overlying water body is established, and its expression is as follows:

[0082] ;

[0083] In the formula, Points within the dredged material diffusion range At the overlying water at the class dissolved heavy metal concentration, Represents the class solid content ratio of heavy metals in the dredged material, Represents the class equilibrium distribution coefficient of heavy metals at a specific temperature, Can represent various heavy metals such as lead (Pb), cadmium (Cd), copper (Cu), zinc (Zn), etc., Is the porosity in water.

[0084] Step S33, according to the analytical theory of dissolved and particulate heavy metals in the overlying water under equilibrium conditions, establish a rapid calculation model for the concentration of particulate heavy metals in the suspended matter of the overlying water, and its expression is as follows:

[0085] ;

[0086] In the formula, Points within the dredged material diffusion range At the suspended matter at the class particulate heavy metal concentration, Represents the class solid content ratio of heavy metals in the dredged material, Represents the class equilibrium distribution coefficient of heavy metals at a specific temperature, Can represent various heavy metals such as lead (Pb), cadmium (Cd), copper (Cu), zinc (Zn), etc., Is the porosity in water.

[0087] Step S4, calculate the effective sediment concentration in the bottom bed sediment. According to the sediment thickness, mixing thickness, and dry bulk density in the sediment, considering the mixing process of new sediment and historical sediment, calculate the heavy metal-containing sediment concentration and total sediment concentration after mixing of the bottom bed sediment.

[0088] The calculation methods for the heavy metal-containing sediment concentration and total sediment concentration after mixing of the bottom bed sediment are as follows:

[0089] Step S41, using the exchange relationship between new sediment and surface sediment, in the calculation process of the heavy metal concentration distribution in the bottom bed sediment and interstitial water, first consider the mixing process of new sediment and historical sediment, so as to calculate the heavy metal-containing sediment concentration in the bottom bed sediment after mixing :

[0090] ;

[0091] In the formula, Points within the dredged material diffusion range The concentration of sediment containing heavy metals in the sediment after mixing at is the point within the dredged material diffusion range where the sediment thickness increases due to the deposition of the bottom bed after settlement within the dredged material diffusion range, is the point within the dredged material diffusion range where the cumulative increased sediment thickness due to the deposition of the bottom bed after settlement within the dredged material diffusion range, represents the mixing thickness of the historical sediment on the bottom bed that is mixed with the new sediment under the action of dynamic and biological disturbances, represents the dry bulk density of the sediment.

[0092] In step S42, after the mixing occurs, the particulate heavy metals in the bottom bed sediment and the dissolved heavy metals in the interstitial water reach equilibrium. At this time, the total sediment concentration of the bottom bed sediment after mixing is :

[0093] ;

[0094] In the formula, represents the total sediment concentration of the sediment after mixing at the point within the dredged material diffusion range, is the porosity of the sediment deposited on the bottom bed.

[0095] In step S5, calculate the concentrations of dissolved and particulate heavy metals in the interstitial water, establish a rapid calculation model for the concentrations of dissolved heavy metals in the interstitial water and particulate heavy metals in the bottom bed, and achieve rapid acquisition of the concentrations of dissolved heavy metals in the interstitial water area and particulate heavy metals in the sediment bed area. The steps include:

[0096] In step S51, using the analysis theory of dissolved heavy metals in the interstitial water and particulate heavy metals in the bottom bed sediment, establish a rapid calculation model for the concentration of dissolved heavy metals in the interstitial water, and its expression is as follows:

[0097] ;

[0098] In the formula, represents the concentration of the th type of dissolved heavy metal in the interstitial water at the point within the dredged material diffusion range, represents the solid content ratio of the th type of heavy metal in the dredged material, represents the concentration of sediment containing heavy metals in the sediment after mixing at the point within the dredged material diffusion range, represents the total sediment concentration of the sediment after mixing at the point within the dredged material diffusion range, is the porosity of the sediment deposited on the bottom bed, represents the Equilibrium distribution coefficient of heavy metals at a specific temperature It can represent various heavy metals such as lead (Pb), cadmium (Cd), copper (Cu), zinc (Zn), etc.

[0099] Step S52: Using the theory of dissolved and sediment particle-bound heavy metals in interstitial water, establish a rapid calculation model for the concentration of sediment particle-bound heavy metals in interstitial water, and its expression is as follows:

[0100] ;

[0101] In the formula, represents the concentration of the -th type of sediment particle-bound heavy metal at point within the dredged material diffusion range, represents the solid content ratio of the -th type of heavy metal in the dredged material, represents the concentration of sediment with heavy metals in the mixed sediment at point within the dredged material diffusion range, represents the total sediment concentration in the mixed sediment at point within the dredged material diffusion range, is the porosity of the bottom sediment, represents the -th type of heavy metal's equilibrium distribution coefficient at a specific temperature, It can represent various heavy metals such as lead (Pb), cadmium (Cd), copper (Cu), zinc (Zn), etc.

[0102] In this example, the above method is further verified and studied in combination with experimental data, and its calculation process is as follows:

[0103] Step S1: Pretreatment of the solid content ratio of heavy metals. Through drying and digestion of the dredged soil, measure the ratio of the mass of various heavy metals to the mass of the dredged soil sample to obtain the solid content ratio of various heavy metals in the dredged soil.

[0104] The process of obtaining the solid content ratio of various heavy metals in the dredged soil is as follows:

[0105] Step S11: Collect 1.5 kg of representative dredged soil samples from the dredged soil, ensure that the sampling points are evenly covered and have environmental representativeness, remove impurities from the dredged soil samples, and mix them evenly;

[0106] Step S12: Dry the dredged soil sample to a constant weight, and grind the dredged soil sample into a uniform fine powder with a mortar, and weigh the dry mass of the dredged soil sample, with a mass of 1.2 kg;

[0107] Step S13: Weigh the dredged soil sample according to wet digestion method, add 12 kg of polytetrafluoroethylene, place it in a microwave digestion instrument and digest it according to the set procedure. After completion, cool it to room temperature of 25 °C and make up the volume. Measure that the made-up volume is 0.1 L.

[0108] Step S14: Use inductively coupled plasma emission spectrometry to calculate the solid content ratio of various heavy metals according to the measured mass concentration of various heavy metals. As follows:

[0109] The detected Pb (lead) content ratio is 200 mg / kg, the Cd (cadmium) content ratio is 5 mg / kg, the Cu (copper) content ratio is 250 mg / kg, and the Zn (zinc) content ratio is 100 mg / kg.

[0110] Step S2: Obtain the equilibrium distribution coefficient of heavy metals. By collecting the water temperature, perform particle size classification on the dredged soil, and calculate the equilibrium distribution coefficient of dissolved and particulate heavy metals at different particle size levels. The process of obtaining the equilibrium distribution coefficient of heavy metals includes:

[0111] Collect the water temperature at 20 degrees Celsius. The influence of temperature change on the distribution coefficient shows an exponential relationship, which can characterize the change of the distribution coefficient with the water temperature variable. At the same time, the distribution coefficient is related to the sediment particle size level, especially the adsorption capacity difference of clay and sand and gravel for heavy metals can be distinguished. Therefore, perform particle size classification on the dredged soil using a sieve hole between 10 mesh and 30 mesh. The particle size distribution of the dredged soil is shown in Table 1, and the particle size distribution curve is shown in Figure 5 .

[0112] Table 1: Particle size distribution composition table of dredged soil

[0113]

[0114] The calculation method of the distribution coefficient covers different sediment particle size levels. Calculate the equilibrium distribution coefficient of dissolved and particulate heavy metals of various types at different particle size levels. It can be calculated that taking the dredged soil with a particle size level of 0.075 mm as an example, the equilibrium distribution coefficient of Pb (lead) is 750 L / kg, the equilibrium distribution coefficient of Cd (cadmium) is 75 L / kg, the equilibrium distribution coefficient of Cu (copper) is 750 L / kg, and the equilibrium distribution coefficient of Zn (zinc) is 75 L / kg.

[0115] Step S3: Use the bottom dumping diffusion model of dredged soil to calculate and obtain the sediment concentration and sediment thickness in the overlying water during the bottom dumping process of dredged soil. According to the dissolution theory of dissolved heavy metals in the overlying water, quickly calculate and obtain the heavy metal concentration distribution, establish a rapid acquisition model for the dissolved heavy metal concentration and the suspended sediment particulate heavy metal concentration in the overlying water under equilibrium conditions, and realize the rapid acquisition of the dissolved heavy metal concentration and the suspended sediment particulate heavy metal concentration in the overlying water. Next, take Pb (lead) as the research object.

[0116] Step S31, the calculation formula of the dredged soil bottom dumping diffusion model for the diffusion sediment concentration and sediment thickness is as follows:

[0117] ;

[0118] ;

[0119] Among them, is the calculated transitional sediment concentration before the sedimentation process occurs after the dredged soil diffusion process, is the mass of dredged soil at point within the dredged material diffusion range, which is 20,000 t, is the sediment concentration at point within the dredged material diffusion range, H is the water depth, with an average value of 90 m, K is the diffusion coefficient of 10 -6 , and are the average lateral and longitudinal flow velocities respectively, which are 0.3 m / s, η is the cloud following coefficient, is the sediment settlement velocity, is the calculation time step, which is taken as 60 s. The calculated diffusion sediment concentration at the mud dumping point is 40 mg / L.

[0120] The calculation formula for obtaining the sediment thickness in the overlying water during the dredged soil bottom dumping process using the dredged soil bottom dumping diffusion model is as follows:

[0121] ;

[0122] In the formula, is the increased sediment thickness of the bottom bed after sedimentation at point within the dredged material diffusion range, is the porosity of the sediment in the bottom bed, which can be taken as 1, represents the dry bulk density of sediment, which is 2650 kg / m 3 . The calculated bottom bed siltation thickness is 1.7 m.

[0123] Step S32, according to the analytical theory of dissolved and particulate heavy metals in the overlying water under the equilibrium state, a rapid acquisition model for the concentration of dissolved heavy metals in the overlying water is established, and its expression is as follows:

[0124] ;

[0125] In the formula, represents lead (Pb), is the porosity in water, which can be directly taken as 1. The calculation result of the concentration of dissolved heavy metals in the overlying water changes with time as Figure 3 .

[0126] It can be calculated that the maximum concentration of Pb (lead) in the overlying water in the mud dumping area is about 0.8 mg / L. The maximum concentration of Pb (lead) in the overlying water in the area 100 m away from the mud dumping point is about 0.4 mg / L.

[0127] Step S33: According to the analytical theory of dissolved and particulate heavy metals in the overlying water under the equilibrium state, a rapid calculation model for the concentration of particulate heavy metals in the suspended solids of the overlying water is established, and its expression is as follows:

[0128] ;

[0129] In the formula, represents the concentration of the th type of particulate heavy metal in the suspended solids at point within the dredged material diffusion range, represents the solid content ratio of the th type of heavy metal in the dredged material, represents the equilibrium distribution coefficient of the th type of heavy metal at a specific temperature, represents lead (Pb), is the porosity of the water and can be directly taken as 1.

[0130] Calculated according to the above formula, the particulate concentration of Pb (lead) in the overlying water in the mud dumping area is 0.8 mg / L.

[0131] Step S4: The calculation methods for the heavy metal sediment concentration and the total sediment concentration after the bottom bed sediment is mixed are as follows:

[0132] Step S41: Using the exchange relationship between the new sediment and the surface sediment, in the calculation process of the heavy metal concentration distribution in the bottom bed sediment and the interstitial water, first consider the mixing process of the new sediment and the historical sediment, so as to calculate the heavy metal sediment concentration in the bottom bed sediment after mixing.

[0133] Step S42: After the mixing occurs, the particulate heavy metals in the bottom bed sediment and the dissolved heavy metals in the interstitial water reach equilibrium. At this time, the total sediment concentration :

[0134] ;

[0135] In the formula, represents the total sediment concentration after the sediment mixing at point within the dredged material diffusion range, is the porosity of the bottom bed sediment. It can be calculated that the total mixed concentration of Pb (lead) in the bottom bed in the mud dumping area is 0.15 mg / L.

[0136] Step S5: Calculate the concentrations of dissolved and particulate heavy metals in the interstitial water, establish a rapid calculation model for the concentrations of dissolved heavy metals in the interstitial water and particulate heavy metals in the bottom bed, and achieve rapid acquisition of the concentrations of dissolved heavy metals in the interstitial water area and particulate heavy metals in the sediment bed area.

[0137] Step S51: Utilize the analytical theory of dissolved and particulate heavy metals in the interstitial water and the bottom bed sediment to establish a rapid calculation model for the concentration of dissolved heavy metals in the interstitial water. The expression is as follows:

[0138] ;

[0139] The calculated dissolved concentration of Pb (lead) in the interstitial water in the dredged spoil area is 82 mg / L.

[0140] Step S52: Utilize the analytical theory of dissolved and particulate heavy metals in the interstitial water and the bottom bed sediment to establish a rapid calculation model for the concentration of particulate heavy metals in the bottom bed of the interstitial water. According to the following formula:

[0141] ;

[0142] The calculation results of the concentration of particulate heavy metals in the sediment of the interstitial water change with time as Figure 4 , and finally, the calculated particulate concentration of Pb (lead) in the interstitial water in the dredged spoil area is 8.5 mg / L.

[0143] In the present invention, through the drying and digestion treatment of dredged soil samples, the mass ratios of various types of heavy metals such as lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) to the mass of the dredged soil samples are measured respectively to obtain the solid content ratios of various heavy metals in the bottom-dumped dredged soil; the water temperature is collected, the particle size groups of different particle size gradations of the dredged material are distinguished, and the equilibrium distribution coefficients of dissolved and particulate heavy metals of various types are calculated; according to the bottom-dumping diffusion model of dredged soil, the sediment concentration in the overlying water is calculated, and a rapid calculation model for the concentrations of dissolved heavy metals in the overlying water and particulate heavy metals in the suspended sediment is established to achieve rapid acquisition of the concentrations of dissolved heavy metals in the overlying water area and particulate heavy metals in the suspended sediment; according to the sediment deposition thickness, mixing thickness, and porosity, a rapid calculation model for the concentrations of dissolved heavy metals in the interstitial water and particulate heavy metals in the bottom bed is established to achieve rapid acquisition of the concentrations of dissolved heavy metals in the interstitial water and particulate heavy metals in the sediment of the sediment bed area. The present invention can achieve rapid calculation and evaluation of the concentration distributions of various types of heavy metal substances in the entire water environment space, such as dissolved in the overlying water, dissolved in the interstitial water, particulate in the suspended sediment, and particulate in the bottom bed sediment during the bottom-dumping process of dredged soil, taking into account the plankton and benthic organism environments, providing a practical tool for toxic heavy metal environmental monitoring, management, and treatment during bottom-dumping operations, and is suitable for wide application in actual operations.

[0144] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes, shall be covered by the protection scope of the present invention.

Claims

1. A rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping of dredged soil, characterized in that, It includes the following steps: Step S1: Through dredged soil drying and digestion treatment, measure the ratio of the mass of various heavy metals to the mass of the dredged soil sample to obtain the solid content ratio of various heavy metals in the dredged soil; Step S2: By collecting the water temperature, conduct particle size grading on the dredged soil, and calculate the equilibrium distribution coefficient of dissolved and particulate heavy metals at different particle size grades; ； In the above formula, represents the type of heavy metal. In the group where the median particle size of the dredged soil is , when the temperature is T, it is the equilibrium distribution coefficient between the dissolved state and the particulate state of the heavy metal; is the standard distribution coefficient, is the influence factor characterizing the effect of temperature change on the equilibrium distribution coefficient, represents the median particle size of the dredged soil composition, is the influence coefficient characterizing the effect of different specific surface areas of different median particle size groups on the heavy metal adsorption capacity; Step S3: According to the bottom dumping diffusion model of dredged soil, calculate the diffusion concentration of dredged soil and sediment thickness in the overlying water body, and establish a rapid calculation model for the dissolved heavy metal concentration and suspended sediment particulate heavy metal concentration in the overlying water body under equilibrium conditions; The expression of the rapid calculation model for dissolved heavy metal concentration is as follows: ； In the formula, represents the concentration of the th type of dissolved heavy metal in the overlying water at point within the dredged material diffusion range, represents the solid content ratio of the th type of heavy metal in the dredged material, represents the equilibrium distribution coefficient of the th type of heavy metal, is the porosity in water; The expression of the rapid calculation model for suspended sediment particulate heavy metal concentration is as follows: ； In the formula, represents the concentration of the th type of particulate heavy metal in the suspended solids at point within the dredged material diffusion range, is the porosity in water, is the sediment concentration at point within the dredged material diffusion range; Step S4: According to the deposition thickness, mixing thickness, and dry bulk density in the sediment, considering the mixing process of new sediment and historical sediment, calculate the heavy metal-containing sediment concentration and total sediment concentration after the bottom bed sediment is mixed; ； In the formula, represents the concentration of sediment containing heavy metals in the mixed sediment at point within the dredged material diffusion range, is the increased sediment thickness of the bottom bed siltation after settlement at point within the dredged material diffusion range, is the cumulative increased thickness of the sediment of the bottom bed siltation after settlement at point within the dredged material diffusion range, represents the mixing thickness of the historical sediment of the bottom bed mixed with the new sediment under the action of dynamic and biological disturbance, represents the dry unit weight of sediment; ； In the formula, represents the total sediment concentration of the mixed sediment at point within the dredged material diffusion range, is the porosity of the sediment deposited on the bottom bed; Step S5: Establish a rapid calculation model for the dissolved heavy metal concentration in the interstitial water and the particulate heavy metal concentration in the bottom bed, and realize the rapid acquisition of the dissolved heavy metal concentration in the interstitial water area and the particulate heavy metal concentration in the sediment bed area.

2. The rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping of dredged soil according to claim 1, wherein, In Step S1, the process of obtaining the solid content ratio of various heavy metals in the dredged soil is as follows: Collect representative dredged soil samples from the dredged soil, ensure that the sampling points are evenly covered and have environmental representativeness, remove impurities from the dredged soil samples, and mix them evenly; Dry the dredged soil sample to a constant weight, and grind the dredged soil sample into uniform fine powder with a mortar, and weigh the dry mass of the dredged soil sample; Weigh the dredged soil sample according to wet digestion, add digestion reagents, place it in a microwave digestion instrument for digestion, cool and make up the volume after completion, and measure the made-up volume; Determine the mass concentration of various heavy metals by atomic emission spectrometry, and obtain the solid content ratio of various heavy metals according to the following formula : 。 3. A rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping of dredged soil according to claim 1, characterized in that, In Step S3, Sediment concentration at points within the dredged material diffusion range is calculated as follows: The calculation method is as follows: ; For the calculated transitional sediment concentration after the dredged soil diffusion process and before the settlement process, the calculation method is as follows: ； In the formula, is the mass of dredged soil at point within the dredged material diffusion range, H is the water depth, K is the diffusion coefficient, represents the position coordinates of the dredged material dumping point, and are the transverse and longitudinal average flow velocities respectively, η is the cloud following coefficient, is the sediment settling velocity, is the calculation time step; Points within the dredged material diffusion range The sediment thickness of the bottom bed siltation increase after settlement at the location The calculation method is as follows: ； In the formula, is the porosity of the sediment deposited on the bottom bed, represents the dry unit weight of the sediment.

4. A rapid calculation method for the distribution of multiple types of heavy metals during the bottom dumping of dredged soil according to claim 1, characterized in that In Step S5, by establishing a rapid calculation model for the dissolved heavy metal concentration in the interstitial water and the particulate heavy metal concentration in the bottom bed, the rapid acquisition of the dissolved heavy metal concentration in the interstitial water area and the particulate heavy metal concentration in the sediment bed area is realized, including: Step S51: Using the analysis theory of dissolved and bottom bed sediment particulate heavy metals in the interstitial water, establish a rapid calculation model for the dissolved heavy metal concentration in the interstitial water, and its expression is as follows: ； In the formula, represents the concentration of the th type of dissolved heavy metal in the interstitial water at point within the dredged material diffusion range, represents the solid content ratio of the th type of heavy metal in the dredged material, represents the concentration of sediment containing heavy metals in the mixed sediment at point within the dredged material diffusion range, represents the total sediment concentration in the mixed sediment at point within the dredged material diffusion range, is the porosity of the bottom bed sediment, represents the th type of heavy metal equilibrium distribution coefficient;​ Step S52: Using the analysis theory of dissolved and bottom bed sediment particulate heavy metals in the interstitial water, establish a rapid calculation model for the bottom bed particulate heavy metal concentration in the interstitial water, and its expression is as follows: ； In the formula, represents the concentration of the th type of particulate heavy metal in the bed sediment at point within the dredged material diffusion range.

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