CN113000592A

CN113000592A - Method for electrically repairing heavy metal copper polluted soil

Info

Publication number: CN113000592A
Application number: CN202110193869.2A
Authority: CN
Inventors: 孙秀丽; 高程; 郑若璇; 任月萍; 王渝
Original assignee: Jiangnan University
Current assignee: Jiangnan University
Priority date: 2021-02-20
Filing date: 2021-02-20
Publication date: 2021-06-22

Abstract

The invention discloses a method for electrically repairing heavy metal copper polluted soil, which specifically comprises the steps of electrically repairing and electroosmosis drainage consolidation, wherein the anodes of the electrically repairing and electroosmosis drainage consolidation are both ruthenium-iridium-titanium plate plated on the surface, and the cathodes are both made of pure titanium materials; the electrokinetic repairing anode electrolyte is sodium chloride or sodium nitrate, and the cathode electrolyte is citric acid; the electroosmosis drainage consolidation grouting solution is a calcium chloride solution and a sodium silicate solution. The method combines electric restoration and electroosmosis drainage consolidation, realizes a whole set of operations of restoration of pollution and restoration of mechanical strength of heavy metal polluted soil with high water content, researches the influence of crack development at the soil junction in the electroosmosis consolidation process on the consolidation process, fills the crack by adopting a two-liquid grouting mode, obtains the optimal grouting time through experiments, and has a certain reference effect on the treatment and the reinforcement of the actual polluted site.

Description

Method for electrically repairing heavy metal copper polluted soil

Technical Field

The invention belongs to the technical field of environmental protection, and particularly relates to a method for electrically repairing heavy metal copper polluted soil.

Background

The soil plays an important role in human production and life, and meanwhile, the soil is also the foundation of the terrestrial ecosystem and plays an irreplaceable role in regulating the balance of the ecosystem. However, with the continuous development of the productivity of the human society and the continuous expansion of the urbanization process, the problem of heavy metal pollution of the soil caused by various human activities is more serious. According to the results of the national soil pollution survey bulletin issued by 2016 of China national resources department, the following results are shown: the total exceeding rate of the heavy metal content of the land in China reaches 16.1%, the exceeding rate of agricultural and forestry farmlands reaches 19.4%, the exceeding rate of the land around enterprises and plants polluted by heavy metal reaches 36.3%, and the exceeding rate of solid waste treatment and stacking fields reaches 21.3%. The serious damage of heavy metal pollution to the health of people and the development of national economy is behind the serial eye-touching and alarming numbers. The common heavy metal pollution is mainly mercury, cadmium, copper, zinc, lead, nickel, chromium and the like, and the heavy metal pollution mainly has the following three approaches to enter the environment: (1) sewage discharge pollution; (2) solid waste pollution; (3) air pollution.

Therefore, the environmental pollution problem is a problem which needs to be considered and is urgently needed to be solved, and needs to be considered in the whole society. After the soil is polluted by heavy metal for a long time, heavy metal ions slowly migrate and are fixed in the soil, particularly, the viscous soil is difficult to solve by a common treatment method or complicated in operation process due to low permeability coefficient, needs a large amount of manpower and material resources and is not cost-effective; meanwhile, in the present of rapid urban expansion, a large amount of waste slurry is generated in engineering construction or a refuse landfill and the like, the particle size of solid particles contained in the slurry is very small, the viscosity is high, the stability of formed colloid is good, clay particles are difficult to naturally precipitate and separate, the urban space is limited, large-area uniform stacking treatment is unrealistic, and the slurry contains heavy metal pollutants, so that certain danger can be generated to the environment.

Therefore, the problem to be solved by the technical personnel in the field is to provide a method for effectively repairing the heavy metal copper polluted soil.

Disclosure of Invention

In view of the above, the invention provides a method for electrically repairing heavy metal copper polluted soil, which combines electric repair and electroosmosis drainage consolidation, realizes a whole set of operations of pollution repair and mechanical strength repair of heavy metal polluted soil with high water content, fills cracks by adopting a double-liquid grouting mode by researching the influence of crack development at a plate-soil junction on the consolidation process in the electroosmosis consolidation process, obtains the optimal grouting time through experiments, and has a certain reference function on the treatment and reinforcement of an actual polluted site.

In order to achieve the purpose, the invention adopts the following technical scheme:

the method for electrically repairing heavy metal copper polluted soil specifically comprises electrically repairing and electroosmotic drainage consolidation, wherein anodes of the electrically repairing and the electroosmotic drainage consolidation are both provided with ruthenium-iridium-titanium plates plated on the surfaces, and cathodes of the electrically repairing and the electroosmotic drainage consolidation are both made of pure titanium materials;

the electrokinetic repairing anode electrolyte is sodium chloride or sodium nitrate, and the cathode electrolyte is citric acid; the electroosmosis drainage consolidation grouting solution is a calcium chloride solution and a sodium silicate solution.

The invention combines electric restoration and electroosmosis drainage consolidation, realizes a whole set of operations of pollution restoration and mechanical strength restoration of heavy metal polluted soil with high water content, and fills the cracks by adopting a two-liquid grouting mode by researching the influence of crack development at the plate soil junction on the consolidation process in the electroosmosis consolidation process. The method can effectively repair the heavy metal copper polluted soil and has a certain reference function.

Preferably, the concentration of the sodium chloride or the sodium nitrate is 0.1 to 0.3mol/L

Preferably, the concentration of the sodium chloride or the sodium nitrate is 0.1 mol/L.

Preferably, the concentration of the citric acid is 0.2-0.5 mol/L.

Preferably, the concentration of the citric acid is 0.2 mol/L.

In the electric restoration, the soil body close to the cathode part is subjected to OH generated by the cathode^-The alkalinity of the soil body is very high, if the pH is not controlled, a large amount of copper hydroxide precipitation substances are generated at the position close to the cathode to block the pores, so that the repairing effect is influenced, and meanwhile, the water molecules flow out of the cathode during the subsequent electroosmosis drainage consolidation is greatly hindered; citric acid as a green small-molecule organic acid carries H⁺Is beneficial to neutralizing OH generated by the cathode^-Prevention of Cu²⁺The ions are precipitated, and simultaneously the organic ligand carried by the ions and Cu²⁺Complex reaction is carried out to generate coordination compound to further promote Cu²⁺Desorption of ions from the soil particles; the electric restoration effect and the ion form of heavy metal have a great relationship, the organic combination state and the residue state in a stable state in soil are difficult to remove by a method of controlling the cathode pH value through citric acid, the optimum concentration of the citric acid in the test is 0.2mol/L along with the slow increase of the citric acid concentration, the restoration efficiency is basically unchanged, the excessive citric acid concentration can cause overlarge current, so that the temperature rise of the soil body is caused, the energy consumption is wasted, and the optimum citric acid concentration is 0.2 mol/L.

Preferably, the mass concentration of the calcium chloride solution and the mass concentration of the sodium silicate solution are both 20-30%.

The cracks at the plate-soil junction are always generated in preference to the soil body cracks, and the occurrence of the cracks at the plate-soil junction can greatly reduce the electroosmosis consolidation efficiency.

Preferably, the volume ratio of the calcium chloride solution to the sodium silicate solution is 1: 1.

Preferably, the grouting time is between 1/3 and the full-growth time of the fracture.

Preferably, the grouting time is 2/3 time of the crack growth vigorous development time.

In order to prevent the water content mutation phenomenon in the anode region, grouting before the development and vigorous crack development moment of 1/3 is avoided as much as possible, and the chemical grouting time capable of realizing the optimal electroosmosis benefit is about 2/3 moment of the vigorous crack development time of the plate-soil junction, which is mainly reflected in the advantages of large water discharge, low unit energy consumption and relatively high average shear strength of the soil sample.

Preferably, the grouting position is a cathode of the electroosmotic drainage consolidation.

The electroosmosis consolidation can improve the pH of the small section of soil body close to the cathode, so that the pH of the electrokinetic remediation acidic soil is partially improved, the effect of the electrokinetic remediation combined chemical grouting method is more obvious, and the pH of the soil body near the cathode can be changed from acidity to neutrality or alkalescence.

Preferably, the temperature of the electroosmotic drainage consolidation is 25-40 ℃.

Compared with the prior art, the invention has the following beneficial effects: the invention provides a method for electrically repairing heavy metal copper polluted soil, which combines electric repair and electroosmosis drainage consolidation, realizes a whole set of operations of pollution repair and mechanical strength repair of heavy metal polluted soil with high water content, fills cracks by adopting a double-liquid grouting mode by exploring the influence of crack development at a plate-soil junction on the consolidation process in the electroosmosis consolidation process, obtains the optimal grouting time through experiments, and has a certain reference effect on the treatment and reinforcement of an actual polluted site.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a graph of time-current change in experimental examples 1T1 to T3 according to the present invention;

FIG. 2 is a graph showing the pH variation with position of soil bodies T1-T3 in experimental example 1 of the present invention;

FIG. 3 is a graph showing the ratio of copper at each position before and after repair in Experimental example 1T 1-T3;

FIG. 4 is a graph of time-current variation for different concentrations of test groups from T3 to T8 in Experimental example 1;

FIG. 5 is a graph of current and temperature increase over time for Experimental example 1T8 in accordance with the present invention;

FIG. 6 is a graph showing the pH variation with soil location for test groups of different concentrations in Experimental example 1 of the present invention;

FIG. 7 is a graph showing the ratio of copper before and after repair at each position of groups having different concentrations from T3 to T8 in Experimental example 1 of the present invention;

FIG. 8 is a graph showing the variation of the removal rates of T3-T8 with the concentration of citric acid in Experimental example 1;

FIG. 9 is a graph showing the change of conductivity with soil location after remediation by groups of different concentrations from T3 to T8 in Experimental example 1 of the present invention;

FIG. 10 is a diagram showing the change of the water content of the soil body with the soil position after the remediation of groups with different concentrations from T3 to T8 in the experimental example 1 of the invention;

FIG. 11 shows Cu before and after T6 repair in Experimental example 1 of the present invention²⁺The change situation of the ion form along with the soil position is shown;

FIG. 12 is a graph of time-current change in experimental examples 2D0 and D1 according to the present invention;

FIG. 13 is time-displacement curves of D0 and D1 according to experimental examples of the present invention;

FIG. 14 is a graph of time-clay crack width variation for Experimental examples 2D0 and D1 according to the present invention;

FIG. 15 is a graph showing time-current changes in experimental examples 2D2 to D6 according to the present invention;

FIG. 16 is a graph showing the change in the position-water content in Experimental examples 2D1 to D6 according to the present invention;

FIG. 17 is a graph showing the change in position-shear strength of experimental examples 2D1 to D6 according to the present invention;

FIG. 18 is a graph showing the pH of the soil after electroosmotic consolidation in Experimental examples 2D1 and D5.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

Example 1

A method for electrically repairing heavy metal copper polluted soil specifically comprises electrically repairing and electroosmotic drainage consolidation, wherein anodes of the electrically repairing and the electroosmotic drainage consolidation are all ruthenium-iridium-titanium plate plated on the surface, and cathodes are all made of pure titanium materials;

wherein, the electrokinetic repairing anolyte is sodium chloride, and the concentration is 0.1 mol/L; the electrolyte of the cathode is citric acid, and the concentration is 0.2 mol/L;

the electroosmotic drainage consolidation grouting solution comprises a calcium chloride solution and a sodium silicate solution, the mass concentration of the calcium chloride solution and the sodium silicate solution is 20%, the volume ratio of the calcium chloride solution to the sodium silicate solution is 1:1, the grouting time is between 1/3 and the growth of the fracture, and is preferably 2/3 of the growth and the growth of the fracture; the grouting position is near the cathode of electroosmosis drainage consolidation; the temperature for electroosmotic drainage consolidation was 25 ℃.

Example 2

wherein the electrokinetic repairing anolyte is sodium nitrate, and the concentration is 0.3 mol/L; the electrolyte of the cathode is citric acid, and the concentration is 0.5 mol/L;

the electroosmotic drainage consolidation grouting solution comprises a calcium chloride solution and a sodium silicate solution, the mass concentration of the calcium chloride solution and the sodium silicate solution is 30%, the volume ratio of the calcium chloride solution to the sodium silicate solution is 1:1, the grouting time is between 1/3 time of the crack growth vigorous time and the crack growth vigorous time, and is preferably 2/3 time of the crack growth vigorous time; the grouting position is near the cathode of electroosmosis drainage consolidation; the temperature for electroosmotic drainage consolidation is 40 ℃.

Experimental example 1

The invention designs an organic glass electric repair tank and an electroosmosis drainage consolidation tank object, wherein the electric repair tank mainly comprises a middle soil chamber and cathode and anode solution chambers at two sides; wherein, the inner size of the soil chamber is 200mm 100mm, the soil chamber and the cathode and anode solution chambers are separated by an open pore clapboard, which is convenient for the free inlet and outlet of the solution and the ions in the soil, and the thickness of the clapboard is 5 mm; the inner size of the solution chamber is 50mm 100mm, overflow ports are formed at positions with the heights of both sides being 80mm, and the height of a soil body is also 80mm during the test, so that the cathode and anode solutions and the soil body are kept on the same horizontal plane, and the influence of hydraulic seepage on the test is eliminated; when in electric repair, the electrode plate is directly inserted into the cathode and anode solution chamber; updating the cathode and anode solution by a micro peristaltic pump;

the electroosmosis consolidation tank and the soil chamber of the electric restoration tank have the same size, the electroosmosis consolidation tank omits an anode solution chamber, electrode plates are directly inserted into two opposite sides of the soil, a cathode plate is arranged on the wall of the soil chamber on one side of the diet chamber, a cathode chamber is a water storage chamber, the inner size is 30mm 100mm, and a small hole is formed in the bottom of the cathode chamber to facilitate the water drained by electroosmosis to flow out; the perforated partition plate is also arranged between the cathode chamber and the soil chamber so as to facilitate the flow of pore water; the cathode plate of the electric repair test is made of a pure titanium plate material without holes, and the electroosmosis consolidation test adopts a pure titanium net with holes;

the current sensor is an 8-circuit thermal resistance module of a JF-8PT100-4-003 model, is matched with a 12-24 VDC power supply, has the maximum measuring current of 1A, and has an output port of an RS485 communication interface; the voltage sensor is a 24-path full-isolation direct-current voltage acquisition module of ZH-44241-14F2, is matched with a 9-30VDC power supply, has a measuring range of 60V, and has an output end also serving as an RS485 communication interface; both convert the electric signal into digital signal and transmit to the acquisition software; in the test, the current collector and the voltage collector use the same analysis software, namely 32-path analog quantity collection module test software, and respectively use two different ports to read data;

the test power supply is a RIGIO DP832 programmable direct current output power supply, three independent output ports are provided in total, the output range of each port is 0-30V, and the output voltage precision can be adjusted to 0.01V.

The samples were prepared as follows:

the soil is stannum-free Taihu lake sludge collected on the bank side of the Taihu lake and is clay with high water content, the sampling depth is 10-30 cm, the collected soil is air-dried and mashed to remove grass roots, shells and other impurities, the soil is dried at 105 ℃ for 8 hours to constant weight, the soil is crushed by a crusher and then passes through a 2mm sieve, and the soil is sealed by a black plastic bag until the soil is stored in a dark place; the physical and chemical properties are shown in Table 1.

TABLE 1 physicochemical Properties of Taihu lake sludge

pH value	EC(mS/cm)	Water content (%)	Liquid limit (%)	Plastic limit (%)	Copper content (mg/kg)
						7.2	1.24	31	49	21	18.6

In order to simulate the actual heavy metal polluted silt soil, the initial water content of the polluted soil in the test is above the liquid limit and is 55%, and the prepared soil sample is in a flowable state; the copper ion pollution medicine is copper sulfate pentahydrate with the chemical formula of CuSO₄·5H₂O, the relative molecular mass is 250, the crystal is a blue crystal, is relatively stable in air, and does not deliquesce; the preparation method comprises the following specific steps: (1) taking out the required soil from the previously sealed plastic bag, drying the soil in an oven for 1h to remove the influence of water vapor in the air on the water content, and spreading and cooling the soil to room temperature after drying; (2) weighing the calculated mass of the blue copperas crystal by using a high-precision electronic balance, dissolving the blue copperas crystal in a certain amount of deionized water, and fully stirring until the crystal is completely dissolved; (3) weighing a certain amount of soil sample, placing the soil sample in a plastic barrel, slowly pouring a copper sulfate solution while stirring, and continuously stirring for more than 10min by using a mechanical stirrer after the solution is completely poured; (4) sealing the plastic barrel by using a black sealing bag, placing the plastic barrel in an indoor dark place, and aging for 7d to ensure that copper ions and soil particles are fully reacted by triggering; (5) the soil sample is stirred again before the restoration test is started and the water content is measured, and corresponding deionized water is added to supplement the evaporated water, so that the water content of the soil sample before restoration is kept near 55%.

Test protocol

The test is mainly divided into two parts, wherein the first part is used for researching the influence of controlling the pH value of catholyte on the repair effect, and the second part is used for researching the optimal concentration of the citric acid solution added into the cathode tank under the test condition; the total number of the tests was 8 groups, and the specific test conditions are shown in Table 2.

TABLE 2 test conditions

Numbering	Anode electrolyte	Catholyte solution	Voltage of	Repair time
					T1	Deionized water	Deionized water	30V	5d
T2	0.1mol/L sodium chloride	Deionized water	30V	5d
					T3	0.1mol/L sodium chloride	0.1mol/L citric acid	30V	5d
T4	0.1mol/L sodium chloride	0.05mol/L citric acid	30V	5d
					T5	0.1mol/L sodium chloride	0.15mol/L citric acid	30V	5d
T6	0.1mol/L sodium chloride	0.2mol/L citric acid	30V	5d
					T7	0.1mol/L sodium chloride	0.3mol/L citric acid	30V	5d
T8	0.1mol/L sodium chloride	0.5mol/L citric acid	30V	5d

(Note: the water content of all contaminated soils was 55% and the copper concentration was 3000 mg/kg.)

Test procedure

(1) Pasting qualitative filter paper on a partition plate between a soil tank and a cathode-anode tank to prevent soil particles from entering in the remediation process, uniformly coating vaseline on the inner wall of organic glass to reduce the influence of side wall friction on a soil sample, filling polluted soil into the organic glass remediation tank in 3 layers, fully vibrating the tank body every time one layer is filled to discharge large air bubbles in the soil, and scraping the surface of the soil sample after the soil filling is finished;

(2) connecting a current collector in series into the circuit and well connecting the circuit, and well debugging current collection software on a computer;

(3) pouring the prepared cathode and anode electrolyte into a cathode and anode tank, and standing for 12h to make the system reach balance;

(4) after 12h, inserting the cathode and anode electrode plates into the solution of the cathode and anode tanks respectively, and turning on a power supply to carry out electric repair;

(5) updating the electrolyte in the cathode and anode solution tanks every 24 hours, collecting the waste electrolyte by using a glass container, and properly processing the waste electrolyte after the test is finished;

(6) after the test is finished, 5 sections from the anode to the cathode are equally divided into S1-S5, three soil samples are collected from each section, and the three soil samples are fully mixed for measuring the Cu after the repair²⁺Concentration, pH, conductivity and other indexes; the results are shown in FIGS. 1-11.

Test results

1. Effect of cathode pH control on electrokinetic remediation Effect

As shown in fig. 1, the current magnitudes of three groups of experiments in the whole process from T1 to T3 are obviously different, and it can be seen that the addition of citric acid solution in the cathode cell makes the pH of the cathode cell within the acidic range of 2 to 4, so that the cathode cell has obvious advantages in current; in one aspect, the citric acid contains a significant amount of H⁺Can neutralize OH produced by cathode reduction^-So that the cathode soil section is acidic, and the generation of precipitate is avoided; on the other hand, the citric acid is a good complexing agent and can generate a complexing reaction with copper ions in soil to generate a soluble compound so that copper is transferred into a liquid phase;

as shown in FIG. 2, the initial non-contaminated Taihu lake sludge pH was 7.2 and was neutral, and since the copper sulfate solution was weakly acidic, the initial soil pH before the test remediation was 6.4; as is obvious from the figure, the T3 test group for controlling the cathode pH is greatly different from the T1 test group and the T2 test group, and the pH of the whole soil section is maintained in an acidic range because the T3 test group adopts 0.1mol/L citric acid solution to keep the pH of the cathode solution between 2 and 4 at the moment; the pH value of the soil body is slowly increased from 2.9 to 5.5 from the anode to the cathode, and in the anode area, a large amount of H is generated due to the oxidation reaction of the electrode plate⁺The Cu adsorbed on the surface of the soil particles is replaced by Cu existing in pore liquid of the soil or through the action of competitive adsorption²⁺Therefore, the pH value is lower as the pH value is closer to the anode and higher as the pH value is closer to the cathode, and although the method of controlling the pH of the catholyte is adopted, the cathode generates large ions during the testAmount of OH^-Will neutralize H⁺Consuming a part of H⁺Therefore, the pH of the S5 soil segment is weakly acidic.

As can be seen from Table 3 and FIG. 3, the repairing effect of the T3 test using the control of cathode pH is greatly improved, the total removal rate reaches 66.6%, and is much higher than that of Cu at the positions of T1, T2, S4 and S5²⁺The deposition condition is obviously improved, and the removal rates of the two sections are respectively 60% and 51%; as can be seen in FIG. 3, the pH of S4 and S5 is slightly acidic, resulting in some Cu²⁺The generated precipitate is fixed in the soil and is due to Cu of the whole soil section²⁺Both migrate from the anode to the cathode and thus some of the copper migrating from the anode region accumulates there and has not yet gained access to the cathode bath at S4 and S5, so that in electrokinetic remediation tests, it is important to focus on the remediation effect near the cathode region where the alkalinity is high and if the relevant method of controlling the cathode pH is not used, a significant amount of precipitated material tends to block the "drain" and cause poor remediation.

TABLE 3 removal rates at each position T1-T3

Group of	S1	S2	S3	S4	S5
						T-EK01	67％	40％	15％	-30％	-45％
T-EK02	75％	55％	47％	5％	8％
						T-EK03	82％	75％	65％	60％	51％

2. Effect of cathode citric acid concentration on electrokinetic remediation Effect

As shown in fig. 4, the current gradually increased with the increase of the citric acid concentration, and the current of 6 sets of tests all had a peak value around 20h, and then the current slowly decreased; however, the temperature of the test group T8 (0.5mol/L citric acid) is increased compared with that of other test groups, and the change of the current and the temperature increment of the test group T8 along with the time is shown in FIG. 5, and it can be seen that although the higher the citric acid concentration is, the higher the current value is, a part of the electric energy is used for heating the soil body, and the waste of energy consumption is caused.

As can be seen from fig. 6, the higher the concentration of citric acid, the better the control of acidity for the whole soil mass; the soil body pH of the test group using the cathode pH control method is smaller than the initial value, and H released by citric acid⁺Effectively neutralize OH generated at the cathode^-And complex out of the adsorption on the surface of soil particlesThe copper ions increase the soil body current, and the higher the current is, the H generated by the anode⁺The more, a large amount of H⁺The pH value of the solution is increased, and the solution is pushed towards the cathode and contributes to the reduction of the alkalinity of the area close to the cathode.

As shown in FIGS. 7 and 8, the total removal rate and the removal rate of each small segment are increased with the increase of the citric acid concentration, but the repair efficiency is not always increased with the increase of the citric acid concentration, and the repair rates of the three groups of 0.2, 0.3 and 0.5mol/L are very close, which indicates that H is released by 0.2mol/L citric acid⁺And organic ligands are enough to desorb and complex most of Cu in soil²⁺Ions and residual copper ions cannot be desorbed or complexed only by citric acid due to the ionic form, and even if the citric acid concentration is increased, the citric acid concentration is not compensated, so that the excessive citric acid concentration not only wastes a repairing agent, but also causes excessive current and energy consumption, and the optimal concentration of the catholyte is 0.2 mol/L.

As shown in fig. 9, the overall conductivity of the soil body after remediation of each group at different concentrations of citric acid is smaller than that before remediation, which indicates that a large amount of copper ions migrate out of the soil, the conductivity is reduced due to the reduction of the number of conductive ions existing in the soil, and the overall conductivity of the soil body after remediation is lower as the concentration of citric acid is higher, because of the Cu migrating out of the soil body²⁺The greater the number of ions; the conductivity of the original plain soil is 1.28ms/cm, and the conductivity of the soil body after all groups of repairing is greater than that of the repaired original plain soil, because the cathode and the anode generate conductive H in the repairing process⁺And OH^-Ions which enter the soil, thereby increasing the conductivity of the soil.

As can be seen from FIG. 10, the water content before and after the restoration of all the test groups did not change much; the water content in the positions S1 and S5 close to the two-stage electrolytic cell is slightly higher, mainly because the positions S1 and S5 are supplemented by the continuous electrolyte in the anode-cathode electrolytic cell, so that the water content in the two positions is higher.

As shown in FIG. 11, Cu was contained in the soil at each position after remediation and in the soil before remediation in 0.2mol/L citric acid group²⁺Ion(s)The form is detected, the proportion of the extractable weak acid in an unstable state in the initial polluted soil is the largest and reaches 73.1%, after electric restoration, the extractable weak acid state is not detected in the S1 area close to the anode, which indicates that the extractable weak acid state is completely eliminated, mainly because the S1 area has the strongest acidity and H is 1 area⁺Displacing Cu adsorbed on the surface of the soil particles²⁺The closer the ions are to the cathode, the more weak acid remaining in the soil can be extracted, due to OH^-The presence of (2) consumes part H⁺Resulting in a small fraction of the weakly acid extractable Cu²⁺Ions are not removed; in general, the removal of the extractable state of the weak acid makes a great contribution to the removal of the total copper, the proportion of the extractable state of the total weak acid in the tested soil is only 2.42 percent, and 96.6 percent of the extractable state of the weak acid is removed; at the same time, the proportion of oxide bound state at each site also decreased, and the overall trend was to increase slowly from anode to cathode, which was primarily pH dependent, but the total oxide bound state in the soil was reduced by 53.7% compared to that before remediation.

After physical and mechanical characteristics and microstructures of copper polluted soil with different concentrations and copper polluted soil subjected to electric restoration are observed, the thickness of double electric layers on the surfaces of soil particles is reduced along with the increase of the concentration of copper in the soil, so that the gravitation in the soil is increased, agglomeration is formed among the soil particles, the content of sticky particles is reduced, the content of particles with large particle sizes is increased, the specific surface area of a soil body is reduced, and the plasticity index of the soil body is reduced; meanwhile, copper ions can also cause certain corrosion to soil particles and cementing substances in the soil, so that the bonds between the particles are weakened, and the shearing strength and the compression resistance of the copper polluted soil are poor. After electric restoration, most of copper ions are removed, but the removal of the copper ions depends on an acid environment, so that the restored soil body has strong acidity, and a large amount of H exists in the soil⁺Replace the original Cu²⁺The carbon is adsorbed on the surface of soil particles, so that the thickness of a double electric layer is reduced, and the soil particles are agglomerated; at the same time H⁺Has great erosion effect on soil particles and cementing substances in soil, and is accompanied with expensive Cu²⁺Removal and bulk H⁺The engineering property of the soil body is not improved in the comprehensive view.

Experimental example 2

The test soil body is the soil body repaired by the optimal citric acid concentration group for controlling the cathode pH in the experimental example 1, namely the T6 group and the 0.2mol/L citric acid group, the water content of the soil body is 55%, meanwhile, as the properties of the soil body after electric repair are changed, in order to explore the influence of the change of the properties of the soil body after electric repair on electroosmosis consolidation, a group of plain soil test groups which are not polluted and are not subjected to electric repair are arranged at this time, and the properties of the soil body are shown in the table 4.

Table 4 test soil properties

Test protocol

7 groups of tests are set, D0 is an electroosmosis consolidation test of plain soil without electric restoration, D1 is an electroosmosis consolidation test of polluted soil after electric restoration, and the rest groups are grouting control test groups; the purpose of setting D0 and D1 test groups is to research the change of electroosmosis characteristics of plain soil and electroosmosis polluted soil caused by the difference of soil properties, and the D1 test is used as a benchmark test of the D2-D6 groups and is to find out the development rule of cracks at the plate-soil interface under the condition of no grouting so as to determine the vigorous development time t of the cracks at the plate-soil interface_crDetermining the grouting time of D2-D6 on the basis of the results of the D1 test group; the voltage of all test groups is 30V, namely the voltage gradient is 1.5V/cm, the test temperature is kept at 25 ℃, and the test running time is 23 h; the test conditions are shown in Table 6.

TABLE 6 test conditions

Test procedure

(1) Evenly coating vaseline on the inner wall of the organic glass groove to reduce the friction between the soil body and the inner wall of the organic glass groove;

(2) placing an electrode plate, simultaneously placing filter paper between the cathode electrode plate and the perforated partition plate, placing a water collecting measuring cylinder, and installing a camera for observing during the test;

(3) pouring the test muddy soil into an organic glass tank for three times, and uniformly vibrating each time to discharge bubbles in the soil body;

(4) after the circuit is connected, a power supply is started to carry out a test, and a camera, a current acquisition device and the like are started to record test data;

(5) and (4) grouting by using a needle tube injector at a specified time. The grouting method comprises the following steps: respectively filling the calcium chloride solution and the sodium silicate solution into two syringes (each 25ml, the concentration is 20%), and sequentially and tightly injecting the two syringes of the solution into the crack at one time;

(6) measuring the test current every 1min, reading the water yield every 0.5h, and carrying out the test for 23 h;

(7) after the test is finished, indexes such as water content, shear strength and the like of the soil sample are detected immediately, and the shear strength of the soil body is measured by a miniature cross plate shearing instrument.

Results of the experiment

The current diagrams of D0 and D1 are shown in FIG. 12, and the overall shapes of the two curves are very similar; however, the currents of D1 were all higher than D0; the water discharge and the water discharge rate of D0 and D1 are shown in FIG. 13, the water discharge and the water discharge rate of the two groups are very close to each other in the 0-2 h stage of the test, after 2h, the water discharge of D0 is obviously higher than that of D1, and at the end of the test, the water discharge volume of D0 is 212ml, the water discharge volume of D1 is 181ml, and the water discharge volume of D0 is 17.3% more than that of D1.

As can be seen from the current diagram and the drainage quantity diagram: the current value of D0 was less than D1 at all times, but D1 was always less drained than D0 except in the first 2h of the test, which is due to the different initial properties of the D0 and D1 soils in the test, the most important reason being the different initial pH of the soil.

2. Plotted against the measured change in the width of the earth crack throughout the testTime-plate soil crack width curves of D0 and D1, as shown in FIG. 14, the repaired contaminated soil has a strong crack growth time t at the plate soil boundary_cr7h, so as to carry out subsequent experiments from D2 to D6.

The time-current change curves of 3, D2-D6 are shown in FIG. 15, and the current reduction rate conditions in the early stage (within 4-5 h after grouting) after grouting of each group of tests are as follows: d6> D5 ≈ D4> D3 ≈ D2, namely, the current of the later grouted group is reduced at a higher speed, because the crack between the electrode plate and the soil body before grouting is already obvious in the later grouted group, and although the deposit generated by grouting can make up the crack between the electrode plate and the soil body, the current is reduced sharply because the crack is too large and is only re-cracked again in the subsequent time; in the early grouting group, the electrode plates and the soil body are tightly bonded, and the connection between the plate and the soil body is further strengthened by the sediment generated by grouting at the moment, so the current reduction rate is relatively slow;

the final water displacement of D1-D6 is shown in Table 7:

TABLE 7D 1-D6 Final displacement

Group of	T1	T2	T3	T4	T5	T6
							Final drainage (ml)	181	230	271	282	295	259

As can be seen from the above, the amount of water discharged by each group is D5>D4>D3>D6>D2>The water discharge of the D1 and D2 single-liquid grouting test groups is far less than that of the D3-D6 double-liquid grouting groups, the grouting solution selected by the D2 test group is NaCl which is one of reaction products of the D3-D6 double-liquid grouting solutions, and the CaCl is proved₂And Na₂SiO₃CaSiO generated after reaction₃The effect of the precipitate on the electroosmotic drainage is greater than the effect of the generated NaCl on the electroosmotic drainage, i.e., it can be confirmed that CaSiO₃The generation of the sediment is really beneficial to the process of electroosmosis consolidation, and is mainly reflected in the function of filling cracks at the boundary of the plate soil so as to effectively reduce the interface resistance; d5 obtained the maximum displacement in this test, that is, when the grouting time was about 2/3 of the vigorous development time of the crack at the plate-soil boundary, the electroosmotic drainage efficiency was the highest.

5. After the test is finished, scraping off precipitated substances and other impurities on the surface of the soil body, and then carrying out local sampling to determine the water content and the shear strength; the sampling positions are 3cm, 7cm, 10cm, 18cm (close to the cathode), 18cm (close to the anode) and 20cm away from the cathode, and a position-water content change diagram 16 is obtained, so that the earlier the grouting time is, the more obvious the water content mutation phenomenon is, and the later the grouting is, the more the number of water molecules in the anode region moving to the cathode is, and the weaker the water content mutation phenomenon is; the average moisture content of the D5 test group was 39%, which was the lowest of all test groups;

the shear strength of the soil body is measured immediately after the test is finished, a position-shear strength change situation figure 17 is obtained, and it can be seen that the grouting time is very longIn the early D3 and D4 groups, the strength at 20cm and 18cm close to the anode is lower, because the grouting time is too early, a large amount of generated precipitates block pores, the moisture content of the small block is too high, and the shear strength is weakened; the average shear strength of D5 was 19.8kPa, 55% higher than the lowest D1, and therefore was 2/3t under the conditions of this test_crThe grouting can have the best effect on improving the shear strength of the soil body;

6. according to the observation of the cracks of the soil body after electroosmosis, the phenomenon of plate soil separation of D2 is very obvious, a plurality of irregular cracks are arranged at two ends of the soil body, and the shape of the cracks at the plate soil junction is kept relatively complete due to the bridging effect of the sediment substances at the two ends of the soil body in the groups D3-D6; the results of the horizontal retraction are shown in table 8:

TABLE 8D 1-D6 soil State

As can be seen from the above, D2 has no compensation effect of the sediment substances, the shrinkage of the two ends of the soil body relative to the electrode plates is large, and therefore the horizontal shrinkage is severe; although cracks at the plate-soil boundary are compensated for in D3, D5 and D6, substances generated after grouting firmly adsorb soil particles, and precipitates and the soil particles can be considered to be integrated, so that once soil bodies and electrode plates are separated again, the shrinkage is large, and the horizontal shrinkage is large; d4 reduces the shrinkage of the soil body along the horizontal direction due to the appearance and development of a plurality of wide cracks in the soil body, so that the final horizontal shrinkage is reduced compared with other groups;

according to the condition of the cracks at the plate-soil junction in the table, the time t for the cracks to develop vigorously at the plate-soil junction can be seen_crGrouting at any time can play a role in delaying the occurrence of cracks in the soil.

7. The drainage energy consumption of each group is shown in table 9;

TABLE 9D 2-D6 energy consumption cases

Group of	T2	T3	T4	T5	T6
						Total energy consumption (W h)	340.08	218.94	199.73	199.67	201.95
Unit drainage energy consumption (W x h/ml)	1.5048	0.7991	0.7083	0.6862	0.7679

From the perspective of unit drainage energy consumption: d5< D4< D6< D3< D2, so it can be seen that the chemical grouting time to achieve the best electroosmotic benefit is about 2/3 at which the cracks at the plate-soil interface develop vigorously.

8. The change of the pH of the soil body after electroosmotic consolidation is shown in fig. 18, it can be seen that electroosmotic consolidation has a certain improvement effect on the pH of the soil body close to the cathode, the acidity of the soil body is weakened, the effect of electroosmotic combined grouting is more obvious, and the pH of the soil body in the areas of S4 and S5 is changed from acidity to neutrality and is slightly alkaline.

The invention combines electric restoration and electroosmosis drainage consolidation, realizes a whole set of operations of pollution restoration and mechanical strength restoration of heavy metal polluted soil with high water content, adopts a two-liquid grouting form to fill the cracks by exploring the influence of crack development at the plate-soil junction on the consolidation process in the electroosmosis consolidation process, obtains the optimal grouting time through experiments, and has a certain reference effect on the treatment and the reinforcement of the actual polluted site.

The embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The method for electrically repairing the heavy metal copper polluted soil is characterized by specifically comprising the steps of electrically repairing and electroosmosis drainage consolidation, wherein the anodes of the electrically repairing and electroosmosis drainage consolidation are both ruthenium-iridium-titanium plate plated on the surface, and the cathodes of the electrically repairing and electroosmosis drainage consolidation are both made of pure titanium materials;

2. The method for electrokinetic remediation of soil contaminated by heavy metal copper according to claim 1, wherein the concentration of the sodium chloride or the sodium nitrate is 0.1-0.3 mol/L.

3. The method for electrokinetic remediation of soil contaminated by heavy metal copper according to claim 1, wherein the concentration of the citric acid is 0.2-0.5 mol/L.

4. The method for electrokinetic remediation of soil contaminated by heavy metal copper according to claim 3, wherein the concentration of the citric acid is 0.2 mol/L.

5. The method for electrokinetic remediation of soil contaminated by heavy metal copper according to claim 1, wherein the mass concentration of the calcium chloride solution and the sodium silicate solution is 20-30%.

6. The method for electrokinetic remediation of soil contaminated by heavy metal copper according to claim 5, wherein the volume ratio of the calcium chloride solution to the sodium silicate solution is 1: 1.

7. The method for electrokinetic remediation of soil contaminated by heavy metal copper according to claim 1, wherein the grouting time is between 1/3 and 1/3 of the crack growth vigorous time.

8. The method for electrokinetic remediation of soil contaminated by heavy metal copper according to claim 7, wherein the grouting time is 2/3 times of the time when the cracks develop vigorously.

9. The method for electrokinetic remediation of heavy metal copper contaminated soil according to claim 1, wherein the grouting location is the electroosmotic drainage consolidated cathode.

10. The method for electrokinetic remediation of heavy metal copper contaminated soil according to claim 1, wherein the temperature of the electro-osmotic drainage consolidation is 25-40 ℃.