A composite flocculant and a method for treating shield waste soil slurry

Abstract

The present invention discloses a composite flocculant and a treatment method for shield waste soil slurry. The composite flocculant includes flocculant A and flocculant B. Flocculant A includes a modified magnesium-iron flocculant and modified chitosan; flocculant B includes polyacrylamide and modified activated carbon. The composite flocculant provided by the present invention is prepared by compounding a modified magnesium-iron flocculant, modified chitosan, polyacrylamide, and modified activated carbon, and is added to shield slurry at different times. By adopting an inorganic-organic compounding method, it can make up for the many deficiencies of single-type flocculants, give play to their respective flocculation advantages, improve the treatment efficiency while reducing the treatment cost. The modified magnesium-iron flocculant, modified chitosan, polyacrylamide, and modified activated carbon provided by the present invention can significantly improve the treatment effect and efficiency of wastewater and waste slurry through the synergistic effects of flocculation-adsorption, charge neutralization, adsorption bridging, pore structure, and composite materials, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of flocculants, and particularly relates to a composite flocculant and a method for treating shield waste soil slurry. Background Art

[0002] Shield tunneling construction has the advantages of high tunneling efficiency and little impact on the surrounding environment, so it is widely used in subway construction projects. As an engineering auxiliary material, slurry is widely used in bored pile construction, shield tunneling construction and diaphragm wall construction. The slurry mainly plays the roles of protecting the wall, discharging slag, cleaning the hole and cooling. When problems such as increased viscosity and finer particles occur in the slurry, the slurry will be discarded. Due to the large output, high viscosity and difficult solid-liquid separation of the waste slurry, the disposal of the waste slurry has become a major problem in engineering construction. The generation of a large amount of waste slurry will not only cause waste of land area, but also may pollute the soil quality of the landfill. Therefore, the reduction treatment of waste slurry is a key step in resource treatment. The current common treatment methods include external transportation and landfill, mechanical pressure filtration, curing agent solidification treatment and flocculant precipitation dehydration. Even more, some directly discharge the waste slurry into rivers, which not only causes serious pollution, but also makes the water area silt up and the riverbed rise. External transportation and landfill is a treatment method with high cost but low treatment efficiency; although the efficiency of mechanical pressure filtration has been improved, the equipment operation cost is large and regular maintenance is required; the curing agent solidification treatment requires the soil to be treated to have a certain bearing capacity, otherwise it cannot be reused; the flocculation precipitation method can make the suspended particles in the slurry form larger flocs through the flocculant, and assist mechanical means to make the solid-liquid two phases easier to separate, which can reduce the discharge of waste slurry from the source and is a dehydration method that can be widely used in actual projects at present.

[0003] However, most of the current flocculants on the market have problems such as poor flocculation effect, slow flocculation speed and high cost. For example, Chinese Patent (CN109354141A) discloses a flocculant formula for treating shield waste slurry, which includes the following components: PAC with a purity of 30% and PAM with a molecular weight of 12 million. When the specific gravity of the waste slurry is 1.05 g / cm 3 ³, the dosage of PAC is 300 mg / L and the dosage of PAM is 45 mg / L. Although the formula of this patent screens out suitable flocculants and dosages according to the different specific gravities of the slurry to make the slurry undergo a flocculation reaction and concentration, its flocculation effect is limited and the flocculation speed is slow. Therefore, how to prepare a flocculant with good flocculation effect, fast flocculation speed, economic and environmental protection for shield slurry treatment is an urgent problem to be solved at present. Summary of the Invention

[0004] The main object of the present invention is to provide a composite flocculant and a method for treating shield waste soil slurry, aiming to solve the problems of poor flocculation effect and slow flocculation speed of existing flocculants.

[0005] To achieve the above object, the present invention provides a composite flocculant, comprising flocculant A and flocculant B. The flocculant A includes a modified magnesium-iron flocculant and modified chitosan; the flocculant B includes polyacrylamide and modified activated carbon.

[0006] Preferably, the preparation method of the modified magnesium-iron flocculant comprises the following steps:

[0007] Mix MgO and FeSO4·7H2O in a magnesium-iron molecular number ratio of (2-4):(6-8), then add concentrated sulfuric acid and stir evenly to obtain a mixed solution; dissolve NaClO3 in deionized water to obtain a NaClO3 solution, and add the NaClO3 solution to the mixed solution at one time while stirring, and then react at 25-35°C for 0.5-1.5 h, and cool to obtain the modified magnesium-iron flocculant.

[0008] Preferably, the preparation method of the modified chitosan comprises the following steps:

[0009] Add isopropanol and acetic acid to chitosan, stir to dissolve, then slowly add epichlorohydrin and heat to react to obtain an epoxidized chitosan product. Add cetyl dimethyl benzyl ammonium chloride to the epoxidized chitosan product and react at 50-70°C for 5-6 h to obtain modified chitosan.

[0010] Preferably, the dosage ratio of chitosan, epichlorohydrin, and cetyl dimethyl benzyl ammonium chloride is (10-30 g):(20-50 mL):(1-2 g);

[0011] The temperature of the heating reaction is 40-60°C, and the time of the heating reaction is 3-5 h.

[0012] Preferably, the mass ratio of flocculant A to flocculant B is (0.5-5):(0.1-0.5);

[0013] The mass ratio of the modified magnesium-iron flocculant to the modified chitosan is (2-5):(1-3);

[0014] The mass ratio of polyacrylamide to modified activated carbon is (3-6):(2-5).

[0015] Preferably, the preparation method of the modified activated carbon comprises the following steps:

[0016] The waste straw is crushed, screened, and then sodium hydroxide solution is added. After soaking for a period of time, it is carbonized at high temperature to obtain biochar. The biochar is washed, dried, ground, and screened to obtain activated carbon. Concentrated sulfuric acid is added to the activated carbon. After stirring, potassium permanganate is slowly added and continuously stirred. After reacting for a period of time, it is washed and dried to obtain oxidized activated carbon. Absolute ethanol is added to the oxidized activated carbon, and hydrochloric acid is added to adjust the pH value to 3-4. After stirring evenly, (3-mercaptopropyl)triethoxysilane and cetyltrimethylammonium bromide are slowly added dropwise, and heated to react to obtain modified activated carbon.

[0017] Preferably, the concentration of the sodium hydroxide solution is 1-2 mol / L, the temperature of the high-temperature carbonization is 650-850 °C, and the temperature of the heating reaction is 60-80 °C.

[0018] Preferably, the mass ratio of the activated carbon to potassium permanganate is 1:(2-4); the dosage ratio of the oxidized activated carbon, (3-mercaptopropyl)triethoxysilane, and cetyltrimethylammonium bromide is (6-10 g):(2-4 mL):(1-3 mL).

[0019] The present invention also provides a method for treating shield waste soil slurry. In the treatment project of shield waste soil slurry, the composite flocculant as described above is used.

[0020] Preferably, the method includes the following steps:

[0021] S1. Collect the waste soil slurry, let it stand for a period of time, and then filter it to obtain sand particles and the filtered slurry.

[0022] S2. Feed the filtered slurry in step S1 into a sedimentation tank, add a modified magnesium-iron flocculant, stir evenly, keep it warm and stand for 10-20 min, and then add modified chitosan, stir, and stand to obtain the preliminarily treated slurry; the sum of the masses of the modified magnesium-iron flocculant and the modified chitosan in the flocculant A accounts for 0.5%-5% of the slurry volume.

[0023] S3. Add flocculant B with a dosage of 0.1%-0.5% of the slurry volume to the preliminarily treated slurry, and stir evenly; the flocculant B includes polyacrylamide and modified activated carbon.

[0024] S4. Feed the slurry into a filter press for dehydration separation, and collect the separated clear liquid and cake.

[0025] S5. Use the sand particles in step S1 and the cake in step S4 as shield sand or for backfilling treatment; directly discharge the clear liquid in step 4.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The composite flocculant provided by the present invention is prepared by compounding an improved magnesium-iron flocculant, modified chitosan, polyacrylamide, and modified activated carbon, and is added to shield mud at different times. By adopting the inorganic-organic compounding method, it can make up for the many deficiencies of single-type flocculants, give play to their respective flocculation advantages, and improve the treatment efficiency while reducing the treatment cost.

[0028] (2) The improved magnesium-iron flocculant provided by the present invention has a lower cost compared with the traditional polyferric sulfate, and can be adsorbed by the negatively charged colloids in the mud, reducing the absolute value of the zeta potential on the surface of the colloids. The repulsive potential energy in the mud decreases, the stability of the colloid particles decreases, and the probability of collision between them increases. Eventually, the colloid is destabilized and settles to be separated from water. The modified chitosan provided by the present invention is obtained by first epoxidizing chitosan and then undergoing a substitution reaction to obtain modified chitosan with quaternary ammonium groups and benzyl groups, making the flocculant have strong surface activity and hydrophobic association effects. At the same time, the quaternary ammonium groups enhance the electro-neutralization ability of the flocculant, adsorb the colloid particles on the surface of the flocculant, and neutralize the negative charges on the surface of the colloid, reducing the zeta potential value on the surface of the colloid and the electrostatic repulsion, further destabilizing the colloid. Eventually, under the action of adsorption and electro-neutralization, the colloid particles are coagulated and aggregated for removal. The modified activated carbon provided by the present invention is prepared from waste straw, which has a wide source and saves resources. After carbonizing the waste straw and then modifying it to introduce mercapto groups, on the one hand, it improves the adsorption bridging effect of the flocculant, and on the other hand, it can enhance the ability to adsorb heavy metals such as copper, lead, and chromium in water, making the treated water meet the discharge standard. At the same time, there is a hydrogen bond interaction between the modified chitosan and the modified activated carbon, enhancing the effect of the flocculant in removing suspended particles during the flocculation and sedimentation processes, so as to more efficiently remove the colloids in water.

[0029] (3) The improved magnesium-iron flocculant, modified chitosan, polyacrylamide, and modified activated carbon provided by the present invention can greatly improve the treatment effect and efficiency of wastewater and waste mud through the synergistic effects of flocculation-adsorption, charge neutralization, adsorption bridging, pore structure, and composite materials, etc.

[0030] The realization of the purpose, functional characteristics, and advantages of the present invention will be further described in combination with the embodiments. Detailed Embodiments

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments without indicating the manufacturer are all conventional products that can be obtained through commercial purchase. In addition, the meaning of "and / or" appearing throughout the text includes three parallel scenarios. Taking "A and / or B" as an example, it includes Scenario A, or Scenario B, or the scenario where both A and B are satisfied simultaneously. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on what can be achieved by those of ordinary skill in the art. When the combination of technical solutions results in contradictions or cannot be achieved, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0032] The following further elaborates on the technical solutions of the present invention in combination with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0033] Example 1

[0034] A composite flocculant includes flocculant A and flocculant B with a mass ratio of 10:1. Flocculant A includes a modified magnesium-iron flocculant and modified chitosan with a mass ratio of 3:2. Flocculant B includes polyacrylamide and modified activated carbon with a mass ratio of 4:3.

[0035] Among them, the preparation method of the modified magnesium-iron flocculant includes the following steps:

[0036] Mix 12 g of MgO and 195 g of FeSO4·7H2O, then add 100 mL of concentrated sulfuric acid and stir evenly to obtain a mixed solution. Dissolve 10 g of NaClO3 in deionized water to obtain a NaClO3 solution. Add the NaClO3 solution to the mixed solution at one time while stirring, and then react at 30 °C for 1 h, and cool to obtain the modified magnesium-iron flocculant.

[0037] The preparation method of the modified chitosan includes the following steps:

[0038] Add 30 mL of isopropanol and 20 mL of acetic acid as solvents to 20 g of chitosan, stir to dissolve, then slowly add 30 mL of epichlorohydrin and react at 50 °C for 4 h to obtain an epoxidized chitosan product. Add 1.5 g of cetyl dimethyl benzyl ammonium chloride to the epoxidized chitosan product and react at 60 °C for 5.5 h to obtain the modified chitosan.

[0039] The preparation method of the modified activated carbon comprises the following steps:

[0040] Crush 100 g of waste straw, sieve it, then add 1.5 mol / L sodium hydroxide solution, soak for a period of time, and then carry out high-temperature carbonization at 700 °C to obtain biochar. Wash, dry, grind and sieve the biochar to obtain activated carbon; add 200 mL of concentrated sulfuric acid to 10 g of activated carbon, stir, then slowly add 30 g of potassium permanganate and continuously stir. After reacting for a period of time, wash and dry to obtain oxidized activated carbon; add absolute ethanol to 8 g of oxidized activated carbon, and add 1 mol / L hydrochloric acid to adjust the pH value to 3.5. After stirring evenly, slowly dropwise add 3 mL of (3-mercaptopropyl)triethoxysilane and 2 mL of cetyltrimethylammonium bromide, and heat to 70 °C and react for 5 h to obtain modified activated carbon.

[0041] Example 2

[0042] A composite flocculant comprises flocculant A and flocculant B with a mass ratio of 5:1. The flocculant A comprises a modified magnesium-iron flocculant and modified chitosan with a mass ratio of 2:1; the flocculant B comprises polyacrylamide and modified activated carbon with a mass ratio of 3:2.

[0043] Among them, the preparation method of the modified magnesium-iron flocculant comprises the following steps:

[0044] Mix 8 g of MgO and 167 g of FeSO4·7H2O, then add 90 mL of concentrated sulfuric acid and stir evenly to obtain a mixed solution; dissolve 10 g of NaClO3 in deionized water to obtain a NaClO3 solution, and add the NaClO3 solution to the mixed solution at one time while stirring, and then react at 30 °C for 1 h, and cool to obtain the modified magnesium-iron flocculant.

[0045] The preparation method of the modified chitosan comprises the following steps:

[0046] Add 20 mL of isopropyl alcohol and 20 mL of acetic acid as solvents to 10 g of chitosan, stir to dissolve, then slowly add 20 mL of epichlorohydrin, and react at 40 °C for 6 h to obtain an epoxidized chitosan product. Add 1 g of cetyl dimethyl benzyl ammonium chloride to the epoxidized chitosan product and react at 50 °C for 6 h to obtain modified chitosan.

[0047] The preparation method of the modified activated carbon comprises the following steps:

[0048] 80 g of waste straw was crushed, sieved, and then added to 1 mol / L sodium hydroxide solution and soaked for a period of time. Subsequently, it was carbonized at 650 °C to obtain biochar. The biochar was washed, dried, ground, and sieved to obtain activated carbon. 180 mL of concentrated sulfuric acid was added to 6 g of activated carbon, and after stirring, 12 g of potassium permanganate was slowly added while continuously stirring. After reacting for a period of time, it was washed and dried to obtain oxidized activated carbon. Absolute ethanol was added to 6 g of oxidized activated carbon, and 1 mol / L hydrochloric acid was added to adjust the pH value to 3. After stirring evenly, 2 mL of (3-mercaptopropyl)triethoxysilane and 1 mL of cetyltrimethylammonium bromide were slowly added dropwise, and the mixture was heated to 70 °C and reacted for 5 h to obtain modified activated carbon.

[0049] Example 3

[0050] A composite flocculant, comprising flocculant A and flocculant B with a mass ratio of 50:1. Flocculant A comprises a modified magnesium-iron flocculant and modified chitosan with a mass ratio of 5:3. Flocculant B comprises polyacrylamide and modified activated carbon with a mass ratio of 6:5.

[0051] Among them, the preparation method of the modified magnesium-iron flocculant comprises the following steps:

[0052] 16 g of MgO and 220 g of FeSO4·7H2O were mixed, and then 110 mL of concentrated sulfuric acid was added and stirred evenly to obtain a mixed solution. 10 g of NaClO3 was dissolved in deionized water to obtain a NaClO3 solution. The NaClO3 solution was added to the mixed solution at one time while stirring, and then reacted at 30 °C for 1 h and cooled to obtain the modified magnesium-iron flocculant.

[0053] The preparation method of the modified chitosan comprises the following steps:

[0054] 30 mL of isopropanol and 20 mL of acetic acid, as solvents, were added to 30 g of chitosan and stirred until dissolved. Then 50 mL of epichlorohydrin was slowly added and reacted at 60 °C for 3 h to obtain an epoxidized chitosan product. 2 g of cetyl dimethyl benzyl ammonium chloride was added to the epoxidized chitosan product and reacted at 70 °C for 5 h to obtain modified chitosan.

[0055] The preparation method of the modified activated carbon comprises the following steps:

[0056] 100 g of waste straw was crushed, sieved, and then added with a 2 mol / L sodium hydroxide solution. After soaking for a period of time, it was carbonized at 850 °C to obtain biochar. The biochar was washed, dried, ground, and sieved to obtain activated carbon. 200 mL of concentrated sulfuric acid was added to 10 g of activated carbon, and after stirring, 40 g of potassium permanganate was slowly added while continuously stirring. After reacting for a period of time, it was washed and dried to obtain oxidized activated carbon. Anhydrous ethanol was added to 10 g of oxidized activated carbon, and 1 mol / L hydrochloric acid was added to adjust the pH value to 4. After stirring evenly, 4 mL of (3-mercaptopropyl)triethoxysilane and 3 mL of cetyltrimethylammonium bromide were slowly added dropwise, and the mixture was heated to 70 °C and reacted for 5 h to obtain modified activated carbon.

[0057] Comparative Example 1

[0058] A composite flocculant, comprising flocculant A and flocculant B with a mass ratio of 10:1. The flocculant A comprises modified chitosan; the flocculant B comprises polyacrylamide and modified activated carbon with a mass ratio of 4:3.

[0059] Among them, the preparation method of the modified chitosan comprises the following steps:

[0060] 20 g of chitosan was added with 30 mL of isopropanol and 20 mL of acetic acid as solvents, stirred and dissolved, and then 30 mL of epichlorohydrin was slowly added. The reaction was carried out at 50 °C for 4 h to obtain an epoxidized chitosan product. 1.5 g of cetyl dimethyl benzyl ammonium chloride was added to the epoxidized chitosan product, and the reaction was carried out at 60 °C for 5.5 h to obtain modified chitosan.

[0061] The preparation method of the modified activated carbon comprises the following steps:

[0062] 100 g of waste straw was crushed, sieved, and then added with a 1.5 mol / L sodium hydroxide solution. After soaking for a period of time, it was carbonized at 700 °C to obtain biochar. The biochar was washed, dried, ground, and sieved to obtain activated carbon. 200 mL of concentrated sulfuric acid was added to 10 g of activated carbon, and after stirring, 30 g of potassium permanganate was slowly added while continuously stirring. After reacting for a period of time, it was washed and dried to obtain oxidized activated carbon. Anhydrous ethanol was added to 8 g of oxidized activated carbon, and 1 mol / L hydrochloric acid was added to adjust the pH value to 3.5. After stirring evenly, 3 mL of (3-mercaptopropyl)triethoxysilane and 2 mL of cetyltrimethylammonium bromide were slowly added dropwise, and the mixture was heated to 70 °C and reacted for 5 h to obtain modified activated carbon.

[0063] Comparative Example 2

[0064] A composite flocculant, comprising flocculant A and flocculant B with a mass ratio of 10:1, wherein flocculant A comprises a modified magnesium-iron flocculant; and flocculant B comprises polyacrylamide and modified activated carbon with a mass ratio of 4:3.

[0065] Among them, the preparation method of the modified magnesium-iron flocculant comprises the following steps:

[0066] Mix 12 g of MgO and 195 g of FeSO4·7H2O, then add 100 mL of concentrated sulfuric acid and stir evenly to obtain a mixed solution; dissolve 10 g of NaClO3 in deionized water to obtain a NaClO3 solution, and add the NaClO3 solution to the mixed solution at one time while stirring, then react at 30 °C for 1 h, and cool to obtain the modified magnesium-iron flocculant.

[0067] The preparation method of the modified activated carbon comprises the following steps:

[0068] Crush 100 g of waste straw, sieve it, then add 1.5 mol / L sodium hydroxide solution, soak for a period of time, and then carbonize at 700 °C to obtain biochar. Wash, dry, grind and sieve the biochar to obtain activated carbon; add 200 mL of concentrated sulfuric acid to 10 g of activated carbon, stir, then slowly add 30 g of potassium permanganate and keep stirring. After reacting for a period of time, wash and dry to obtain oxidized activated carbon; add absolute ethanol to 8 g of oxidized activated carbon, and add 1 mol / L hydrochloric acid to adjust the pH value to 3.5. Stir evenly and then slowly dropwise add 3 mL of (3-mercaptopropyl)triethoxysilane and 2 mL of cetyltrimethylammonium bromide, and heat to 70 °C to react for 5 h to obtain the modified activated carbon.

[0069] Comparative Example 3

[0070] A composite flocculant, comprising flocculant A and flocculant B with a mass ratio of 10:1, wherein flocculant A comprises a modified magnesium-iron flocculant and modified chitosan with a mass ratio of 3:2; and flocculant B comprises polyacrylamide.

[0071] Among them, the preparation method of the modified magnesium-iron flocculant comprises the following steps:

[0072] Mix 12 g of MgO and 195 g of FeSO4·7H2O, then add 100 mL of concentrated sulfuric acid and stir evenly to obtain a mixed solution; dissolve 10 g of NaClO3 in deionized water to obtain a NaClO3 solution, and add the NaClO3 solution to the mixed solution at one time while stirring, then react at 30 °C for 1 h, and cool to obtain the modified magnesium-iron flocculant.

[0073] The preparation method of the modified chitosan comprises the following steps:

[0074] Add 30 mL of isopropanol and 20 mL of acetic acid as solvents to 20 g of chitosan, stir to dissolve, then slowly add 30 mL of epichlorohydrin, and react at 50 °C for 4 h to obtain an epoxidized chitosan product. Add 1.5 g of cetyl dimethyl benzyl ammonium chloride to the epoxidized chitosan product and react at 60 °C for 5.5 h to obtain modified chitosan.

[0075] Testing methods and results

[0076] Collect shield mud, filter it, and divide it into six portions. Add the composite flocculants in Examples 1 - 3 and Comparative Examples 1 - 3 to the six portions of mud in equal amounts. First add the modified magnesium - iron flocculant in Flocculant A, stir evenly, keep warm and stand still for 15 min, then add modified chitosan. The sum of the masses of the magnesium - iron flocculant and modified chitosan accounts for 1% of the mud volume. Then add Flocculant B with a volume of 0.3% of the mud volume, and stir evenly; after standing for 1 h, send the mud to a filter press for dehydration separation, collect the separated clear liquid and filter cake, measure the turbidity, total phosphorus, total nitrogen, COD value of the clear liquid and the moisture content of the filter cake, and calculate the turbidity removal rate.

[0077] Turbidity removal rate = [(turbidity of shield silt - turbidity of filtrate) / turbidity of shield silt] * 100%

[0078] Moisture content of filter cake = [(weight of filter cake obtained by filter pressing - weight of filter cake after drying and drying) / weight of filter cake obtained by filter pressing] * 100%.

[0079] The representative pollutant contents of shield mud are shown in Table 1 below.

[0080] Table 1 Representative pollutant content table of shield mud

[0081]

[0082] Respectively take the clear liquids of Examples 1 - 3 and Comparative Examples 1 - 3, and use an atomic absorption spectrophotometer to measure the remaining concentrations of copper, lead, and chromium, as well as the turbidity, total phosphorus, total nitrogen, COD value of the clear liquid and the moisture content of the filter cake, as shown in Table 2 below.

[0083] Table 2 Turbidity, total phosphorus, total nitrogen, COD value, moisture content of filter cake and heavy metal content in clear liquid

[0084]

[0085] As can be seen from Table 1 and Table 2 above, compared with Comparative Examples 1 - 3, the flocculants prepared in Examples 1 - 3 of the present invention have better turbidity removal effects, significantly reduce the moisture content of the filter cake, and have strong adsorption capabilities for both pollutants and heavy metals in the mud, achieving a better purification effect and making the purified water meet the discharge standards.

[0086] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the patent protection scope of the present invention.

Claims

1. A method for treating shield waste soil slurry, characterized in that, In the treatment project of shield waste soil slurry, a composite flocculant is used, and the method includes the following steps: S1. Collect the waste soil slurry, let it stand for a period of time, and then filter it to obtain sand particles and the filtered slurry; S2. Feed the filtered slurry in step S1 into a sedimentation tank, add a modified magnesium-iron flocculant, stir evenly, keep it warm and stand for 10 - 20 min, and then add modified chitosan, stir, and stand to obtain the preliminarily treated slurry; where the sum of the masses of the modified magnesium-iron flocculant and modified chitosan in flocculant A accounts for 0.5% - 5% of the slurry volume; S3. Add flocculant B with a volume of 0.1% - 0.5% of the slurry volume to the preliminarily treated slurry, and stir evenly; where flocculant B includes polyacrylamide and modified activated carbon; S4. Feed the slurry into a filter press for dehydration separation, and collect the separated clear liquid and cake; S5. Use the sand particles in step S1 and the cake in step S4 as shield sand or for backfilling; directly discharge the clear liquid in step 4; The composite flocculant includes flocculant A and flocculant B, the flocculant A includes a modified magnesium-iron flocculant and modified chitosan; the flocculant B includes polyacrylamide and modified activated carbon; The preparation method of the modified magnesium-iron flocculant includes the following steps: Mix MgO and FeSO4·7H2O according to the magnesium-iron molecular number ratio of (2 - 4):(6 - 8), then add concentrated sulfuric acid and stir evenly to obtain a mixed solution; dissolve NaClO3 in deionized water to obtain a NaClO3 solution, and add the NaClO3 solution to the mixed solution at one time while stirring, and then react at 25 - 35 °C for 0.5 - 1.5 h, and cool to prepare the modified magnesium-iron flocculant; The preparation method of the modified chitosan includes the following steps: Add isopropanol and acetic acid to chitosan, stir to dissolve, and then slowly add epichlorohydrin and heat to react to obtain an epoxidized chitosan product. Add cetyl dimethyl benzyl ammonium chloride to the epoxidized chitosan product and react at 50 - 70 °C for 5 - 6 h to obtain modified chitosan; The preparation method of the modified activated carbon includes the following steps: Crush the waste straw, sieve it, then add sodium hydroxide solution and soak for a period of time, and then perform high-temperature carbonization to obtain biochar. Wash, dry, grind and sieve the biochar to obtain activated carbon; add concentrated sulfuric acid to the activated carbon, stir, then slowly add potassium permanganate and keep stirring. After reacting for a period of time, wash and dry to obtain oxidized activated carbon; add absolute ethanol to the oxidized activated carbon, and add hydrochloric acid to adjust the pH value to 3 - 4. Stir evenly and then slowly dropwise add (3-mercaptopropyl)triethoxysilane and cetyl trimethyl ammonium bromide, and heat to react to obtain modified activated carbon; The mass ratio of flocculant A to flocculant B is (0.5 - 5):(0.1 - 0.5); The mass ratio of the modified magnesium-iron flocculant to modified chitosan is (2 - 5):(1 - 3); The mass ratio of polyacrylamide to modified activated carbon is (3 - 6):(2 - 5).

2. The treatment method of shield waste soil slurry according to claim 1, wherein, The dosage ratio of the chitosan, epichlorohydrin, and cetyl dimethyl benzyl ammonium chloride is (10~30 g):(20~50 mL):(1~2 g); The temperature of the heating reaction is 40~60 °C, and the time of the heating reaction is 3~5 h.

3. The treatment method of shield waste soil slurry according to claim 1, characterized in that, The concentration of the sodium hydroxide solution is 1~2 mol / L, the temperature of the high-temperature carbonization is 650~850 °C, and the temperature of the heating reaction is 60~80 °C.

4. The treatment method of shield waste soil slurry according to claim 1, characterized in that, The mass ratio of the activated carbon to potassium permanganate is 1:(2~4); the dosage ratio of the oxidized activated carbon, (3-mercaptopropyl)triethoxysilane, and cetyl trimethyl ammonium bromide is (6~10 g):(2~4 mL):(1~3 mL).

Images