Alkali-free environment-friendly composite flocculant and application thereof

Abstract

The invention relates to an alkali-free environment-friendly composite flocculant and application thereof. The alkali-free environment-friendly composite flocculant comprises anhydrous calcium chloride, hydroxypropyl methyl cellulose ether and sodium polyacrylate. The flocculation and dehydration effects are improved through the synergistic effect of the inorganic flocculant anhydrous calcium chloride, the organic flocculant hydroxypropyl methyl cellulose ether and the sodium polyacrylate, the problems that the alkalinity of the common inorganic flocculant calcium oxide is too strong, the flocculation efficiency of calcium chloride is low and the cost of the organic flocculant is high due to the need of pre-dissolving are solved, and high-efficiency and environment-friendly flocculation is realized.

Description

Technical Field

[0001] The invention relates to the technical field of waste sludge treatment, and in particular to an alkali-free environmentally friendly composite flocculant and application thereof. Background Art

[0002] The waste mud of bored piles has high water content, high fluidity, and fine particles, which makes it difficult to sink and separate naturally. Therefore, the disposal of waste mud of bored piles has long troubled construction units. In addition, the amount of mud discharged by bored piles and ground-connected walls is smaller and more intermittent than that of slurry shield construction. Therefore, the polymer-based flocculation system commonly used in slurry shields is usually not used to treat the waste mud. The characteristics of polymer flocculants are: high flocculation efficiency and no pollution, but they require pre-dissolution operation and a long dissolution time. They are suitable for mud treatment work with sufficient site, large processing volume, and strong continuity.

[0003] Therefore, in the on-site treatment of bored piles and ground-anchored wall mud, simple inorganic flocculants are usually used for direct dissolution and flocculation. This method is simple in process and only needs to be dissolved in the reaction tank and flocculated and precipitated with the waste mud. The flocculant composition is single, and the most commonly used is quicklime (calcium oxide), followed by inorganic flocculants such as aluminum hydroxide and polyferric sulfate (xanthate). Its principle is mainly to increase the zeta potential of the particle surface in the liquid environment (reduce the negative value), reduce the absolute value, reduce the electrostatic repulsion of the particles, and make the particles easier to aggregate and precipitate. Its disadvantages are: (1) The flocculant is highly alkaline, especially the most commonly used quicklime. The pH value of the mud cake after precipitation and filtration is high, which cannot meet the pH value range of 5.5 to 8.5 specified in GB 4284, and cannot be used for agricultural or backfilling; (2) The flocculation efficiency is low, so the amount of addition is large (much larger than that of polymer flocculants).

[0004] In the prior art, inorganic flocculants have the problem of strong alkalinity, and organic polymer flocculants need to be pre-dissolved and have high costs. Therefore, how to achieve efficient, environmentally friendly and economical waste mud flocculation has become a problem that needs to be solved urgently. Summary of the invention

[0005] In order to solve the above technical problems, the present invention aims to solve the contradiction between the need for predissolution of polymer flocculants and the strong alkalinity and low flocculation efficiency of inorganic flocculants, and to provide an alkali-free and environmentally friendly composite flocculant.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides an alkali-free environmentally friendly composite flocculant, which comprises: anhydrous calcium chloride, hydroxypropyl methyl cellulose ether and sodium polyacrylate.

[0008] The present invention improves the flocculation and dehydration effect through the synergistic effect of an inorganic flocculant anhydrous calcium chloride and an organic flocculant hydroxypropyl methyl cellulose ether and sodium polyacrylate. The organic flocculant hydroxypropyl methyl cellulose ether has strong adsorption and bridging effects. After the sodium polyacrylate is dissolved, the surface zeta potential is more positive, which can not only play a bridging role of the polymer chain but also reduce the absolute value of the surface charge of the particles. The two organic flocculants can play a synergistic role with the strong electrical neutralization of the inorganic flocculant, thereby enhancing the flocculation and dehydration effect, solving the problems of excessive alkalinity of the commonly used inorganic flocculant calcium oxide, low flocculation efficiency of calcium chloride, and the need for predissolution and high cost of the organic flocculant, thereby achieving high-efficiency and environmentally friendly flocculation.

[0009] As a preferred technical solution of the present invention, the alkali-free environmentally friendly composite flocculant includes, by weight: 78 to 85 parts of anhydrous calcium chloride, for example, 78 parts, 79 parts, 80 parts, 82 parts or 95 parts, etc., 12 to 17 parts of hydroxypropyl methylcellulose ether, for example, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts or 17 parts, etc., and 2 to 6 parts of sodium polyacrylate, for example, 2 parts, 3 parts, 4 parts, 5 parts or 6 parts, etc.

[0010] As a preferred technical solution of the present invention, the alkali-free environmentally friendly composite flocculant includes, by weight: 80 to 82 parts of anhydrous calcium chloride, for example, 80 parts, 80.5 parts, 81 parts, 81.5 parts or 82 parts, etc., 13 to 15 parts of hydroxypropyl methylcellulose ether, for example, 13 parts, 13.5 parts, 14 parts, 14.5 parts or 15 parts, etc., and 3 to 5 parts of sodium polyacrylate, for example, 3 parts, 3.5 parts, 4 parts, 4.5 parts or 5 parts, etc.

[0011] The present invention adopts anhydrous calcium chloride as an inorganic flocculant, and increases the zeta potential of the surface of mud particles through calcium ions, so that the particles are more likely to aggregate and precipitate while having weaker alkalinity. The mud cake after precipitation and pressure filtration meets the pH value range of 5.5 to 8.5 specified in GB4284, and can be directly used for agriculture or backfilling. Hydroxypropyl methylcellulose ether and sodium polyacrylate are added as two high molecular polymers to further improve the flocculation efficiency. The proportion of several components is preferably selected so that they can work synergistically with the strong electrical neutralization of the inorganic flocculant to enhance the flocculation effect. While maintaining a high flocculation efficiency, the cost is low and no pre-dissolution is required.

[0012] As a preferred technical solution of the present invention, the average polymerization degree of the hydroxypropyl methylcellulose ether is 200,000 to 250,000, for example, it can be 200,000, 210,000, 220,000, 230,000, 240,000 or 250,000.

[0013] As a preferred technical solution of the present invention, the average degree of polymerization of the sodium polyacrylate is 8 to 12 million, for example, it can be 8 million, 9 million, 10 million, 11 million or 12 million.

[0014] As a preferred technical solution of the present invention, the anhydrous calcium chloride is industrial grade anhydrous calcium chloride.

[0015] In a second aspect, the present invention provides a method for preparing the alkali-free environmentally friendly composite flocculant described in the first aspect, wherein the preparation method comprises weighing anhydrous calcium chloride, hydroxypropyl methylcellulose ether and sodium polyacrylate in order according to parts by weight and stirring the mixture evenly.

[0016] In a third aspect, the present invention provides a use of the alkali-free environmentally friendly composite flocculant described in the first aspect in the flocculation treatment of waste mud.

[0017] As a preferred technical solution of the present invention, the application is: adding the alkali-free environmentally friendly composite flocculant into the waste mud, stirring it sufficiently, and then letting it stand to complete the flocculation treatment of the waste mud.

[0018] As a preferred technical solution of the present invention, the amount of the flocculant is controlled according to the specific gravity d of the waste mud, and the amount of the flocculant is (-7.143d 2 +17.571d-10.429~-7.429d 2 +18.314d-10.886)kg flocculant / m 3 mud.

[0019] The present invention reduces the use cost of the flocculant while maintaining a good flocculation effect by adopting the above flocculant dosage control.

[0020] As a preferred technical solution of the present invention, the standing time is 10 to 20 minutes, for example, it can be 10 minutes, 12 minutes, 14 minutes, 16 minutes, 18 minutes or 20 minutes.

[0021] Compared with the prior art, the present invention has at least the following beneficial effects:

[0022] (1) The main components of the composite flocculant of the present invention are anhydrous calcium chloride and organic polymers. The pH of the clear liquid and the bottom mud after flocculation is close to that of the incoming slurry. There is no problem of excessive alkalinity that cannot be recovered or discharged. The flocculant will not introduce heavy metals and no harmful substances will be dissolved.

[0023] (2) The amount of organic polymer added to the composite flocculant of the present invention is relatively small, and there is no problem that the organic polymer needs to be pre-dissolved. The prepared flocculant does not need to be pre-dissolved and can be directly put into use, which increases the convenience of use in intermittent drilling work.

[0024] (3) The flocculation efficiency of the composite flocculant of the present invention is higher than that of inorganic flocculants. The dehydration rate after standing for 10 minutes can reach 68%. The unit mud treatment cost is lower than that of organic flocculants and can reach 1.14 yuan / m3 , achieving high-efficiency and low-cost flocculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a comparison chart of the effects of recovering sludge for agricultural use after flocculation and dehydration in Example 1 and Comparative Examples 1 to 3.

[0026] Among them, 1 and 2-1 are the effects of sludge recovery for agricultural use for 7 days and 14 days in Example 1 of the present invention, respectively; 2 and 2-2 are the effects of sludge recovery for agricultural use for 7 days and 14 days in comparative example 1 of the present invention, respectively; 3 and 2-3 are the effects of sludge recovery for agricultural use for 7 days and 14 days in comparative example 2 of the present invention, respectively; 4 and 2-4 are the effects of sludge recovery for agricultural use for 7 days and 14 days in comparative example 3 of the present invention, respectively. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0028] Example 1

[0029] This embodiment provides an alkali-free environmentally friendly composite flocculant, which includes 81 parts of industrial-grade anhydrous calcium chloride, 14 parts of hydroxypropyl methylcellulose ether with an average polymerization degree of 250,000, and 4 parts of sodium polyacrylate with an average polymerization degree of 11 million. The alkali-free environmentally friendly composite flocculant is weighed in order according to weight and stirred evenly. The alkali-free environmentally friendly composite flocculant is added to the medium-weathered muddy siltstone waste mud with a specific gravity of 1.25 and stirred evenly. The amount of flocculant is 0.39Kg / m 3 , let it stand for 10 minutes to complete the flocculation treatment, and then test the dehydration rate of the waste mud.

[0030] Example 2

[0031] The present embodiment provides an alkali-free environmentally friendly composite flocculant, which includes 80 parts of industrial-grade anhydrous calcium chloride, 15 parts of hydroxypropyl methylcellulose ether with an average degree of polymerization of 200,000, and 3 parts of sodium polyacrylate with an average degree of polymerization of 12 million. The alkali-free environmentally friendly composite flocculant is weighed in order according to weight and stirred evenly. The alkali-free environmentally friendly composite flocculant is added to the medium-weathered muddy siltstone waste mud with a specific gravity of 1.25 and stirred evenly. The amount of flocculant is 0.375 kg / m 3 , let it stand for 10 minutes to complete the flocculation treatment, and then test the dehydration rate of the waste mud.

[0032] Example 3

[0033] The present embodiment provides an alkali-free environmentally friendly composite flocculant, which includes 82 parts of industrial-grade anhydrous calcium chloride, 13 parts of hydroxypropyl methylcellulose ether with an average polymerization degree of 230,000, and 5 parts of sodium polyacrylate with an average polymerization degree of 8 million. The alkali-free environmentally friendly composite flocculant is weighed in order according to weight and stirred evenly. The alkali-free environmentally friendly composite flocculant is added to the medium-weathered muddy siltstone waste mud with a specific gravity of 1.25 and stirred evenly. The amount of flocculant is 0.4Kg / m 3 , let it stand for 10 minutes to complete the flocculation treatment, and then test the dehydration rate of the waste mud.

[0034] Example 4

[0035] This embodiment provides an alkali-free environmentally friendly composite flocculant, which includes 85 parts of industrial-grade anhydrous calcium chloride, 17 parts of hydroxypropyl methylcellulose ether with an average polymerization degree of 230,000, and 6 parts of sodium polyacrylate with an average polymerization degree of 8 million. The alkali-free environmentally friendly composite flocculant is weighed in order according to weight and stirred evenly. The alkali-free environmentally friendly composite flocculant is added to the medium-weathered muddy siltstone waste mud with a specific gravity of 1.25 and stirred evenly. The amount of flocculant is 0.4Kg / m 3 , let it stand for 10 minutes to complete the flocculation treatment, and then test the dehydration rate of the waste mud.

[0036] Example 5

[0037] This embodiment provides an alkali-free environmentally friendly composite flocculant, which includes 78 parts of industrial-grade anhydrous calcium chloride, 12 parts of hydroxypropyl methylcellulose ether with an average polymerization degree of 230,000, and 2 parts of sodium polyacrylate with an average polymerization degree of 8 million. The alkali-free environmentally friendly composite flocculant is weighed in order and stirred evenly. The alkali-free environmentally friendly composite flocculant is added to the medium-weathered muddy siltstone waste mud with a specific gravity of 1.25 and stirred evenly. The amount of flocculant is 0.4Kg / m 3 , let it stand for 10 minutes to complete the flocculation treatment, and then test the dehydration rate of the waste mud.

[0038] Example 6

[0039] This embodiment is the same as Embodiment 1 except that the weight portion of sodium polyacrylate is 1 part.

[0040] Example 7

[0041] This embodiment is the same as Embodiment 1 except that the weight portion of sodium polyacrylate is 10 parts.

[0042] Example 8

[0043] This embodiment is the same as Example 1 except that the weight portion of anhydrous calcium chloride is 90 parts.

[0044] Example 9

[0045] This embodiment is the same as Example 1 except that the weight portion of anhydrous calcium chloride is 75 parts.

[0046] Example 10

[0047] This embodiment is the same as the embodiment 1 except that the weight proportion of hydroxymethyl cellulose ether is 10 parts.

[0048] Embodiment 11

[0049] This embodiment is the same as the embodiment 1 except that the weight proportion of hydroxymethyl cellulose ether is 20 parts.

[0050] Example 12

[0051] In this embodiment, the amount of alkali-free environmentally friendly composite flocculant is 0.6Kg / m 3 Except for this, the rest are the same as in Example 1.

[0052] Example 13

[0053] In this embodiment, the amount of alkali-free environmentally friendly composite flocculant is 0.35Kg / m 3 Except for this, the rest are the same as in Example 1.

[0054] Comparative Example 1

[0055] This comparative example is the same as Example 1 except that the flocculant only contains hydroxypropyl methylcellulose ether.

[0056] Comparative Example 2

[0057] This comparative example is the same as Example 1 except that the flocculant only contains sodium polyacrylate.

[0058] Comparative Example 3

[0059] This comparative example is the same as Example 1 except that the flocculant only contains calcium oxide.

[0060] Comparative Example 4

[0061] This comparative example is the same as Example 1 except that the flocculant only contains industrial grade anhydrous calcium chloride.

[0062] Comparative Example 5

[0063] This comparative example is the same as Example 1 except that the flocculant only contains sodium carboxymethyl starch.

[0064] Comparative Example 6

[0065] This comparative example is the same as Example 1 except that the flocculant only contains hydroxypropyl starch ether.

[0066] Comparative Example 7

[0067] The flocculant provided in this comparative example does not contain hydroxypropyl methylcellulose ether component, and the reduced amount is supplemented by sodium polyacrylate according to the weight fraction. The rest is the same as Example 1.

[0068] Comparative Example 8

[0069] The flocculant provided in this comparative example does not contain the sodium polyacrylate component, and the reduced amount thereof is supplemented by hydroxypropyl methylcellulose ether according to the weight fraction, and the rest is the same as that in Example 1.

[0070] Test Method

[0071] The supernatant was extracted from the waste mud after flocculation in Examples 1 to 13 and Comparative Examples 1 to 8, and the dry basis moisture content of the waste mud before and after flocculation was tested according to the geotechnical test specification SL237-1999, and the dehydration rate of the waste mud was calculated. Wherein, dehydration rate = dry basis moisture content of the waste mud before flocculation - dry basis moisture content of the waste mud after flocculation. Then, the bottom mud was obtained by pressure filtration, and the pH values ​​of the supernatant and bottom mud were tested respectively according to GB / T 22592-2008 "General Rules for Determination of pH Value of Water Treatment Agents" and NY / T 1121.2-2006 Soil Testing Part 2: Determination of Soil pH. The bottom mud after flocculation and dehydration in Example 1 and Comparative Examples 1 to 3 was recycled for agricultural use, and four-season grass seeds were sprinkled, and the growth conditions after 7 days and 14 days were tested to characterize the effect of recycling the bottom mud for agricultural use.

[0072] The test results are shown in Table 1 and Figure 1 shown.

[0073] Table 1

[0074]

[0075]

[0076] The test results show that:

[0077] (1) It can be seen from Examples 1 to 5 that the present invention utilizes the synergistic effect of inorganic flocculants and organic flocculants. The calcium ions in the inorganic flocculants carry a positive charge, which compresses the double electric layer on the surface of the small-particle soil, increases the surface zeta potential, and reduces the repulsive force between particles, showing a tendency to flocculate. A small amount of organic polymer flocculants can simultaneously play multiple roles in the waste mud, such as adsorption bridging, electrical neutralization, and netting, so that the solid particles that have been initially flocculated can quickly aggregate into a larger floc structure, achieving a better flocculation and dehydration effect. At the same time, the pH value of the bottom mud is in the range of 7.6 to 8.4, which meets the range requirement of 5.5 to 8.5 for agricultural recycling, and the cost is also greatly reduced.

[0078] (2) It can be seen from Examples 1 to 3 and Examples 4 to 5 that the present invention can better balance the flocculation effect and the cost of flocculation treatment by further optimizing the proportion of each component in the alkali-free environmentally friendly composite flocculant. And it can be seen from Examples 1 and Examples 6 to 11 that the proportion of the organic polymer component in the present invention is too low, which will cause a significant decrease in the flocculation effect. Among them, when the weight proportion of hydroxymethyl cellulose ether is 10 parts, the dehydration rate of Example 10 drops to 54.6%. This is because the low proportion of organic components in the flocculant will lead to a decrease in the synergistic effect, the surface potential decreases, and the soil particles close to each other cannot be quickly adsorbed by the polymer to quickly form large-volume agglomerates. When the weight proportion of anhydrous calcium chloride is 75 parts, the ability of the flocculant to balance the surface potential of the particles decreases, and the adsorption bridging ability of the polymer caused by the excessively high surface potential decreases, and the dehydration rate drops to 59%.

[0079] (3) It can be seen from Examples 1 and 12 to 13 that the present invention optimizes the dosage of the alkali-free environmentally friendly composite flocculant and fits it into a formula. When the dosage of the alkali-free environmentally friendly composite flocculant is too small, the flocculation effect will decrease. When the dosage is too large, the flocculation effect will not be improved and the cost will be too high.

[0080] (4) It can be seen from Example 1 and Comparative Examples 1 to 6 that the present invention can obtain a good flocculation effect by selecting the types of organic high molecular polymer flocculants and inorganic flocculants. The dehydration rate of the alkali-free environmentally friendly composite flocculant provided by the present invention is higher than that of the commonly used organic high molecular flocculants on the market. Directly adding an organic high molecular flocculant is extremely costly and dissolves slowly, resulting in flocculant agglomeration and low flocculation efficiency, and is higher than that of calcium oxide and calcium chloride flocculants. It can be seen from Example 1 and Comparative Examples 7 to 8 that the three components of the present invention work synergistically to achieve a flocculation effect higher than the combination of an inorganic flocculant and any one of the organic high molecular flocculants.

[0081] (5) It can be seen from Example 1 and Comparative Examples 1 to 3 that the waste mud sludge after flocculation by the alkali-free environmentally friendly composite flocculant of the present invention can be directly recycled for agricultural use. Compared with calcium oxide as a flocculant, the four-season grass seeds grow well on the sludge.

[0082] In summary, the present invention promotes the flocculation of waste sludge through the synergistic effect of the inorganic flocculant anhydrous calcium chloride and the organic polymer flocculants hydroxypropyl methylcellulose ether and sodium polyacrylate. The alkali-free environmentally friendly composite flocculant of the present invention has a dehydration rate that is better than that of any component used alone and the combination of the two components, while reducing costs and avoiding the problem of difficult agricultural recycling caused by excessive alkalinity.

[0083] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. An alkali-free environmentally friendly composite flocculant, characterized in that: The alkali-free environmentally friendly composite flocculant comprises: anhydrous calcium chloride, hydroxypropyl methyl cellulose ether and sodium polyacrylate.

2. The alkali-free environmentally friendly composite flocculant according to claim 1, characterized in that: The alkali-free environmentally friendly composite flocculant comprises, by weight: 78-85 parts of anhydrous calcium chloride, 12-17 parts of hydroxypropyl methylcellulose ether and 2-6 parts of sodium polyacrylate.

3. The alkali-free environmentally friendly composite flocculant according to claim 1 or 2, characterized in that: The alkali-free environmentally friendly composite flocculant comprises, by weight: 80-82 parts of anhydrous calcium chloride, 13-15 parts of hydroxypropyl methylcellulose ether and 3-5 parts of sodium polyacrylate.

4. The alkali-free environmentally friendly composite flocculant according to any one of claims 1 to 3, characterized in that: The average polymerization degree of the hydroxypropyl methylcellulose ether is 200,000 to 250,000.

5. The alkali-free environmentally friendly composite flocculant according to any one of claims 1 to 4, characterized in that: The average degree of polymerization of the sodium polyacrylate is 8 to 12 million.

6. The alkali-free environmentally friendly composite flocculant according to any one of claims 1 to 5, characterized in that: The anhydrous calcium chloride is industrial grade anhydrous calcium chloride.

7. A method for preparing an alkali-free environmentally friendly composite flocculant as claimed in any one of claims 1 to 6, characterized in that: The preparation method comprises weighing anhydrous calcium chloride, hydroxypropyl methylcellulose ether and sodium polyacrylate in order according to weight proportions and then stirring them evenly.

8. Use of the alkali-free environmentally friendly composite flocculant as claimed in any one of claims 1 to 6 in the flocculation treatment of waste mud.

9. The use according to claim 8, characterized in that: The application includes: adding the alkali-free environmentally friendly composite flocculant into waste mud, stirring it fully, and then letting it stand to complete the flocculation treatment of the waste mud.

10. The use according to claim 9, characterized in that: The amount of the alkali-free environmentally friendly composite flocculant is controlled according to the specific gravity d of the waste mud. The amount of the alkali-free environmentally friendly composite flocculant is (-7.143d 2 +17.571d-10.429~-7.429d 2 +18.314d-10.886)kg flocculant / m 3 mud.

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