A flocculant for concrete mixture washed sand and a method for preparing the same

Abstract

The application discloses a flocculant for concrete mixture water-washed sand and a preparation method thereof. The flocculant is in a spherical configuration and is composed of a polystyrene inner core and a large number of polyacrylamide coating layers grafted on the surface of the polystyrene inner core. The preparation method comprises the following steps: firstly, preparing a styrene / hydroxyethyl acrylate / methoxy-terminated polyethylene glycol alkene copolymer P through free radical polymerization; then, performing ring-opening polymerization on the copolymer P by taking alpha-halogen-gamma-lactone as a polymerization monomer under the action of an organic metal catalyst to obtain a grafted poly(alpha-halogen-gamma-lactone) polymer S; then, adding magnesium powder to prepare a Grignard reagent polymer S-Mg-X; then, introducing carbon dioxide and hydrogen to prepare a carboxylic acid polymer S-COOH; then, filtering and removing magnesium carbonate precipitate; and finally, adding ammonia to perform amidation reaction to prepare the flocculant. The machine-made sand prepared by using the flocculant for concrete mixture water-washed sand has excellent initial plasticizing performance and good plasticizing retention capacity.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a flocculant for washed sand in concrete mixtures and its preparation method. Background Technology

[0002] With the continuous development of modern concrete technology and the increasing depletion of natural resources, manufactured sand prepared by ore crushing is now widely used. However, the crushing process inevitably leads to excessive mud and dust content in the manufactured sand. This mud and dust content causes poor workability of the concrete mix and insufficient initial plasticizing properties, as well as accelerated plasticizing loss over time. Flocculants can prevent the rapid settling of mud particles and stone powder in water. Therefore, flocculants are commonly used to separate stone powder and mud during the washing process of manufactured sand, thus avoiding the negative impact of excessive mud and dust content on the concrete mix. However, the use of flocculants leaves a small amount of flocculant residue on the surface of the manufactured sand. When this manufactured sand is used to mix concrete, it results in a serious over-limitation of water content in the concrete mix, and accelerated plasticizing loss. Currently, polyacrylamide flocculants are widely used as flocculants for washing sand in concrete mixes. Although the manufactured sand meets national standards after washing with flocculants, the problem of flocculant residue urgently needs to be addressed.

[0003] To address the negative effects of manufactured sand flocculants on concrete mixtures, Chinese patent CN113336462A discloses a method for degrading residual flocculants in washed manufactured sand used in concrete mixing. This method involves selecting washed manufactured sand with low residual flocculant content using a UV-Vis spectrophotometer and storing it in a sand silo. The stored manufactured sand is then transported by conveyor belt to a wear-resistant steel mixing silo for concrete preparation. During transport, the manufactured sand on the conveyor belt is irradiated with a low-pressure mercury lamp. Cement, mineral powder, and fly ash are added to the mixer and dry-mixed, followed by the addition of water and 2%–2.4% of a degradable polycarboxylate superplasticizer compounded with zinc sulfate and wet-mixed to obtain the finished concrete. Chinese patent CN114920509A discloses a method and application for combating the negative effects of polyacrylamide flocculants in manufactured sand. This method involves treating the manufactured sand or concrete or mortar containing manufactured sand with a chlorine-containing inorganic compound and a bromine-containing inorganic compound degrading agent. Chinese patent CN114349387A discloses a manufactured sand flocculant that does not affect concrete performance and its preparation method. The method specifically involves mixing 0.05–0.16% flocculant, 0.5–2% coagulant aid, 1–16% dispersant, 1–6% viscosity reducer, 15–19% retarder, and the remainder being water to prepare 100 parts of the manufactured sand flocculant. Chinese patent CN109179614A discloses a highly biodegradable oil sand tailings flocculant and its preparation method. This flocculant uses nano-titanium dioxide-coated kaolin as the inorganic composite particle core and polyacrylamide as the membrane. This method can effectively improve the photodegradation efficiency of polyacrylamide.

[0004] In general, there are two main approaches to reducing the negative impact of residual flocculants in washed sand on concrete mixtures: ① Post-treatment of the washed sand with flocculants by adding various catalysts to degrade the flocculants remaining in the washed sand. This method is costly and too cumbersome. ② Adding other additives to counteract the negative effects of flocculants on concrete mixtures. Obviously, this method increases the cost of additives and cannot accurately control the dosage. Summary of the Invention

[0005] 1. The technical problem to be solved:

[0006] To address the aforementioned technical problems, this invention provides a flocculant for washed sand in concrete mixtures and its preparation method. The resulting flocculant has a spherical structure with a polystyrene core and a surface grafted with numerous polyacrylamide layers. These highly free polyacrylamide molecules exert a flocculating effect during the sand washing process, removing harmful powders and mud from the sand and gravel aggregates. Simultaneously, the flocculant residue on the surface of these washed sand particles utilizes the alkaline conditions of the concrete mixture itself to rapidly degrade the ester bonds in the polyacrylamide backbone, thereby reducing the impact of the polyacrylamide flocculant on the initial plasticizing properties and plasticizing retention capacity of the concrete mixture. Furthermore, after complete hydrolysis of the polyacrylamide structure, the core structure generates a polycarboxylate superplasticizer structure, providing continuous dispersing action and thus extending the plasticizing retention capacity of the concrete mixture.

[0007] 2. Technical Solution:

[0008] A flocculant for washed sand in concrete mixtures, characterized in that: the flocculant has a spherical configuration consisting of a polystyrene core and a large number of polyacrylamide coating layers grafted onto the surface of the polystyrene core; its main chain structure is composed of random copolymerization of styrene, hydroxyethyl acrylate, and polyethanol propylene ether; its side chain structure is composed of ring-opening polymerization of α-halogen-γ-lactone; its molecular formula is:

[0009]

[0010] In the above formula, a is an integer from 5 to 22; b is an integer from 39 to 121; c is an integer from 10 to 22; e is an integer from 0 to 4; f is an integer from 200 to 1000; g is an integer from 10 to 45; and R1 is one of O, CH2O, OCH2CH2O, OCH2CH2CH2O, OCH2CH2CH2CH2O, CH2OCH2CH2O, CH2OCH2CH2CH2O, and CH2OCH2CH2CH2CH2O.

[0011] A method for preparing a flocculant for washed sand in concrete mixtures includes the following steps:

[0012] Step 1: Add toluene solvent to a single-necked flask equipped with a stirrer, then add styrene, hydroxyethyl acrylate, and methoxy polyethylene glycol ether monomers to the single-necked flask and dissolve them completely. Add an initiator, heat to 50-80℃, and react for 20-24 hours to obtain styrene / hydroxyethyl acrylate / allyl polyethylene glycol ether copolymer P.

[0013] Step 2: Add copolymer P to a mixed solution of α-halogen-γ-lactone / toluene and carry out ring-opening polymerization for 8-10 hours under the action of an organometallic catalyst to obtain grafted poly(α-halogen-γ-lactone) polymer S;

[0014] Step 3: Add magnesium powder to polymer S and react at 30-40℃ for 20-24h to prepare Grignard reagent polymer S-Mg-X. Then, pass carboxylating gas through to prepare carboxylic acid polymer S-COOH and filter to remove magnesium carbonate precipitate.

[0015] Step 4: Ammonia, a dehydrating agent, and a catalyst are added to the polymer S-COOH, and an amidation reaction is carried out at a certain temperature and pressure for 8–10 hours. The mixture is then freeze-dried to prepare a flocculant for washed sand in concrete mixtures.

[0016] Furthermore, the methoxy polyethylene glycol ether is one or a combination of more than one of the following: methoxy polyethylene glycol vinyl ether, methoxy polyethylene glycol propylene ether, methoxy polyethylene glycol methoxyethylene ether, methoxy polyethylene glycol methoxypropylene ether, methoxy polyethylene glycol ethoxyethylene ether, methoxy polyethylene glycol ethoxypropylene ether, methoxy polyethylene glycol propoxyethylene ether, methoxy polyethylene glycol propoxypropylene ether, methoxy polyethylene glycol butoxyethylene ether, and methoxy polyethylene glycol butoxypropylene ether.

[0017] Furthermore, the initiator is one or a combination of more than one of azobisisobutyronitrile, azobisisoheptanenitrile, and azoisobutylcyanoformamide.

[0018] Further, the α-halogen-γ-lactone is one or a combination of more than one of α-chloro-γ-propiolactone, α-chloro-γ-butiolactone, α-chloro-γ-valerolactone, α-chloro-γ-caprolactone, α-bromo-γ-propiolactone, α-bromo-γ-butiolactone, α-bromo-γ-valerolactone, α-bromo-γ-caprolactone, α-iodo-γ-propiolactone, α-iodo-γ-butiolactone, α-iodo-γ-valerolactone, and α-iodo-γ-caprolactone.

[0019] Furthermore, the organometallic base catalyst is one or more of 1,8-diazabicyclo[5.4.0]undec-7-ene, stannous isooctanoate, and aluminum isopropoxide.

[0020] Furthermore, the carboxylating gas is a mixture of carbon dioxide and hydrogen, with a molar ratio of carbon dioxide to hydrogen of 4:1.

[0021] Further, the dehydrating agent is one or more of dicyclohexylcarbodiimide and N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide hydrochloride;

[0022] Further, the catalyst is one or a combination of more than one of N,N,N′,N′-tetramethyl-O-(7-azabenzotriazol-1-yl)hexafluorophosphate, N,N-dimethyl-4-pyridinium, N,N-carbonyldiimidazole, and 1-hydroxybenzotriazole.

[0023] Furthermore, the specified temperature and pressure are: temperature 50–120°C, pressure 1.2–1.5 MPa.

[0024] 3. Beneficial effects:

[0025] (1) The flocculant for washing sand in concrete mixture prepared by the present invention has a spherical structure, the core of which is made of polystyrene. A large number of polyacrylamide coating layers are grafted onto the surface of the polystyrene core. These highly free polyacrylamides play a flocculation role in the washing sand process, removing harmful powder and mud from the sand and gravel aggregate.

[0026] (2) The flocculant for washed sand in concrete mixture prepared by the present invention has a rapid alkaline degradation rate. The flocculant for washed sand in concrete mixture remaining on the surface of the washed sand can utilize the alkaline conditions of the concrete mixture itself to rapidly degrade the ester bonds in the polyacrylamide main chain, thereby reducing the effect of polyacrylamide flocculant on the initial plasticizing performance and plasticizing retention capacity of the concrete mixture.

[0027] (3) After the flocculant structure of the concrete mixture prepared by the present invention is completely hydrolyzed, the core structure will generate a polycarboxylate superplasticizer structure, which provides a continuous dispersing effect, thereby extending the plasticizing retention capacity of the concrete mixture.

[0028] (4) After the structure of the flocculant for the washed sand in the concrete mixture prepared by the present invention is completely hydrolyzed, a large number of amino acid molecules and oligoamino acid molecules will be generated. These small molecular structures can act as retarder in the concrete mixture, thereby further extending the plasticizing time of the concrete mixture. Detailed Implementation

[0029] The embodiments of the present invention are described in detail below. The implementation is based on the technical solution of the present invention, and detailed implementation methods and operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments.

[0030] Example 1

[0031] Step S01: Add 1 mol of toluene solvent to a single-necked flask equipped with a stirrer, then add 0.01 mol of styrene, 0.08 mol of hydroxyethyl acrylate, and 0.02 mol of methoxy polyethylene glycol ether (molecular weight 2038 g / mol) to the single-necked flask and dissolve them completely. Add 0.001 mol of initiator, heat to 65°C, and react for 20 hours to obtain styrene / hydroxyethyl acrylate / allyl polyethylene glycol ether copolymer P-1; Step S02: Add copolymer P-1 to a sealed reaction vessel containing a mixed solution of 16 mol of α-bromo-γ-butyrolactone and 50 mol of toluene, and carry out ring-opening polymerization for 8 hours under the action of 0.03 mol of stannous isooctanoate catalyst to obtain... Grafted poly(α-bromo-γ-butyrolactone) polymer S-1; Step S03: Add 16 mol of magnesium powder to polymer S-1 and react at 35℃ for 24 h to prepare Grignard reagent polymer S-1-Mg-X. Then, pass a mixed gas (32 mol of carbon dioxide and 8 mol of hydrogen) to prepare carboxylic acid polymer S-1-COOH. Filter to remove magnesium carbonate precipitate; Step S04: Add 16 mol of ammonia, 16 mol of dicyclohexylcarbodiimide dehydrating agent and 0.01 mol of N,N-dimethyl-4-pyridinium amine catalyst to polymer S-1-COOH and carry out amidation reaction at 75℃ and 1.2 MPa for 8 h. Freeze-dry to prepare flocculant for washed sand in concrete mixtures. The structural formula is shown below.

[0032]

[0033] Example 2

[0034] Step S01: Add 1 mol of toluene solvent to a single-necked flask equipped with a stirrer, then add 0.01 mol of styrene, 0.09 mol of hydroxyethyl acrylate, and 0.033 mol of methoxy polyethylene glycol ether (molecular weight 996 g / mol) to the single-necked flask and dissolve them completely. Add 0.001 mol of initiator, heat to 75°C, and react for 24 hours to obtain styrene / hydroxyethyl acrylate / allyl polyethylene glycol ether copolymer P-2; Step S02: Add copolymer P-2 to a sealed reaction vessel containing a mixed solution of 45 mol of α-bromo-γ-propiolactone and 100 mol of toluene, and carry out ring-opening polymerization for 9 hours under the action of 0.06 mol of stannous isooctanoate catalyst to obtain grafted copolymer. Poly(α-bromo-γ-butyrolactone) polymer S-2; Step S03: Add 45 mol of magnesium powder to polymer S-2 and react at 30℃ for 20 h to prepare Grignard reagent polymer S-2-Mg-X. Then, pass a mixed gas (90 mol of carbon dioxide and 22.5 mol of hydrogen) to prepare carboxylic acid polymer S-2-COOH. Filter to remove magnesium carbonate precipitate; Step S04: Add 45 mol of ammonia, 45 mol of dicyclohexylcarbodiimide dehydrating agent and 0.03 mol of N,N-dimethyl-4-pyridinium amine catalyst to polymer S-2-COOH and carry out amidation reaction at 105℃ and 1.3 MPa for 10 h. Freeze-dry to prepare flocculant for washed sand of concrete mixture, the structural formula of which is shown below.

[0035]

[0036] Example 3

[0037] Step S01: Add 1 mol of toluene solvent to a single-necked flask equipped with a stirrer, then add 0.01 mol of styrene, 0.045 mol of hydroxyethyl acrylate, and 0.02 mol of methoxy polyethylene glycol propylene ether (molecular weight 1172 g / mol) to the single-necked flask and dissolve them completely. Add 0.001 mol of initiator, heat to 55°C, and react for 22 hours to obtain styrene / hydroxyethyl acrylate / allyl polyethylene glycol ether copolymer P-3; Step S02: Add copolymer P-3 to a sealed reaction vessel containing a mixed solution of 18 mol of α-chloro-γ-butyrolactone and 50 mol of toluene, and carry out ring-opening polymerization for 8 hours under the action of 0.03 mol of stannous isooctanoate catalyst to obtain... Grafted poly(α-chloro-γ-butyrolactone) polymer S-3; Step S03: Add 18 mol of magnesium powder to polymer S-3 and react at 35℃ for 24 h to prepare Grignard reagent polymer S-3-Mg-X. Then, pass a mixed gas (36 mol of carbon dioxide and 9 mol of hydrogen) to prepare carboxylic acid polymer S-3-COOH. Filter to remove magnesium carbonate precipitate; Step S04: Add 18 mol of ammonia, 18 mol of dicyclohexylcarbodiimide dehydrating agent and 0.01 mol of N,N-dimethyl-4-pyridinium amine catalyst to polymer S-3-COOH and carry out amidation reaction at 85℃ and 1.3 MPa for 9 h. Freeze-dry to prepare flocculant for washed sand of concrete mixture, the structural formula of which is shown below.

[0038]

[0039] Example 4

[0040] Step S01: Add 1 mol of toluene solvent to a single-necked flask equipped with a stirrer, then add 0.01 mol of styrene, 0.06 mol of hydroxyethyl acrylate, and 0.014 mol of methoxy polyethylene glycol methoxyethylene ether (molecular weight 1848 g / mol) to the single-necked flask and dissolve them completely. Add 0.001 mol of initiator, heat to 50°C, and react for 24 hours to obtain styrene / hydroxyethyl acrylate / allyl polyethylene glycol ether copolymer P-4; Step S02: Add copolymer P-4 to a sealed reaction vessel containing a mixed solution of 21.3 mol of α-chloro-γ-butyrolactone and 50 mol of toluene, and carry out ring-opening polymerization for 8 hours under the action of 0.03 mol of stannous isooctanoate catalyst to obtain grafted copolymer. (α-Chloro-γ-Butyrolactone) polymer S-4; Step S03: Add 21.3 mol of magnesium powder to polymer S-4 and react at 35℃ for 22 h to prepare Grignard reagent polymer S-4-Mg-X. Then, pass a mixed gas (42.6 mol of carbon dioxide and 10.65 mol of hydrogen) to prepare carboxylic acid polymer S-4-COOH. Filter to remove magnesium carbonate precipitate; Step S04: Add 21.3 mol of ammonia, 21.3 mol of dicyclohexylcarbodiimide dehydrating agent and 0.01 mol of N,N-dimethyl-4-pyridinium amine catalyst to polymer S-4-COOH and carry out amidation reaction at 95℃ and 1.5 MPa for 8 h. Freeze-dry to prepare flocculant for washed sand of concrete mixture, the structural formula of which is shown below.

[0041]

[0042] Example 5

[0043] Step S01: Add 1 mol of toluene solvent to a single-necked flask equipped with a stirrer, then add 0.01 mol of styrene, 0.11 mol of hydroxyethyl acrylate, and 0.032 mol of methoxy polyethylene glycol ethoxylate (molecular weight 765 g / mol) to the single-necked flask and dissolve them completely. Add 0.001 mol of initiator, heat to 65°C, and react for 24 hours to obtain styrene / hydroxyethyl acrylate / allyl polyethylene glycol ether copolymer P-5; Step S02: Add copolymer P-5 to a sealed reaction vessel containing a mixed solution of 23.65 mol of α-chloro-γ-butyrolactone and 50 mol of toluene, and carry out ring-opening polymerization for 10 hours under the action of 0.03 mol of stannous isooctanoate catalyst to obtain grafted poly(α-chloro-γ-butyrolactone) Step S03: Add 23.65 mol of magnesium powder to polymer S-5 and react at 30℃ for 24 h to prepare Grignard reagent polymer S-5-Mg-X. Then, pass a mixed gas (47.3 mol of carbon dioxide and 11.825 mol of hydrogen) to prepare carboxylic acid polymer S-5-COOH. Filter to remove magnesium carbonate precipitate. Step S04: Add 23.65 mol of ammonia, 23.65 mol of dicyclohexylcarbodiimide dehydrating agent and 0.01 mol of N,N-dimethyl-4-pyridinium amine catalyst to polymer S-5-COOH and carry out amidation reaction at 105℃ and 1.5 MPa for 10 h. Freeze-dry to prepare flocculant for washed sand in concrete mixtures. The structural formula is shown below.

[0044]

[0045] Test example: flocculation ability

[0046] Manufactured sand prepared from crushed ore was subjected to water washing treatment. The mud content of unwashed manufactured sand, manufactured sand washed with tap water, and manufactured sand washed with a 1% flocculant tap water solution were tested. The flocculants included the samples prepared in Examples 1-5 and two commercially available polyacrylamide flocculants. The mud content was tested according to the relevant methods in GB / T 14684-2022 "Construction Sand".

[0047] Table 1. Mud Content in Manufactured Sand

[0048]

[0049]

[0050] As shown in Table 1, the flocculant for washed sand in concrete mixtures prepared by this invention has similar flocculation ability to commercially available flocculants for washed sand in concrete mixtures, and can achieve a mud removal rate of over 90% for manufactured sand.

[0051] Test Example: The Effect of Flocculants on the Plasticizing Properties of Concrete

[0052] Concrete mixture performance tests were conducted according to GB / T 8076-2012 "Concrete Admixtures". The mix design used manufactured sand treated with the same method as in the test examples, along with the same dosage of concrete water-reducing agent. Specific mix designs are shown in Table 2 below. Initial slump and spread were used to evaluate the effect of flocculant on the initial plasticizing properties of the concrete mixture, while 1-hour slump and spread were used to evaluate the effect of flocculant on the time-dependent loss of initial plasticizing properties of the concrete mixture.

[0053] Table 2 Concrete mix proportions (kg / m³) 3 )

[0054] benchmark cement Manufactured sand pebbles Water consumption admixtures 360 785 1040 165 3.6

[0055] Table 3 Plasticizing properties of concrete mixtures

[0056]

[0057] As shown in Table 3, the concrete mixed with machine-made sand treated with the flocculant prepared by the present invention exhibits better initial plasticization effect and plasticization retention ability, which can significantly improve the construction performance of the concrete mixture.

[0058] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be defined by the scope of the claims of this application.

Claims

1. A flocculant for washing sand in concrete mixtures, characterized in that: The flocculant for washed sand in concrete mixtures has a spherical configuration consisting of a polystyrene core and a large number of polyacrylamide coating layers grafted onto the surface of the polystyrene core; its main chain structure is composed of random copolymerization of styrene, hydroxyethyl acrylate, and polyethanol propylene ether; its side chain structure is composed of ring-opening polymerization of α-halogen-γ-lactone; its molecular formula is: In the above formula, a is an integer from 5 to 22; b is an integer from 39 to 121; c is an integer from 10 to 22; e is an integer from 0 to 4; f is an integer from 200 to 1000; g is an integer from 10 to 45; and R1 is one of O, CH2O, OCH2CH2O, OCH2CH2CH2O, OCH2CH2CH2CH2O, CH2OCH2CH2O, CH2OCH2CH2CH2O, and CH2OCH2CH2CH2CH2O.

2. A method for preparing a flocculant for washed sand in concrete mixtures, used to prepare the flocculant of claim 1, characterized in that: Includes the following steps: Step 1: Add toluene solvent to a single-necked flask equipped with a stirrer, then add styrene, hydroxyethyl acrylate, and methoxy polyethylene glycol ether monomers to the single-necked flask and dissolve them completely. Add an initiator, heat to 50-80℃, and react for 20-24 hours to obtain styrene / hydroxyethyl acrylate / allyl polyethylene glycol ether copolymer P. Step 2: Add copolymer P to a mixed solution of α-halogen-γ-lactone / toluene and carry out ring-opening polymerization for 8-10 hours under the action of an organometallic catalyst to obtain grafted poly(α-halogen-γ-lactone) polymer S; Step 3: Add magnesium powder to polymer S and react at 30-40℃ for 20-24h to prepare Grignard reagent polymer S-Mg-X. Then, pass carboxylating gas through to prepare carboxylic acid polymer S-COOH and filter to remove magnesium carbonate precipitate. Step 4: Add ammonia, dehydrating agent and catalyst to polymer S-COOH and carry out amidation reaction for 8-10 hours under certain temperature and pressure. Freeze-dry to prepare flocculant for washing sand in concrete mixture.

3. The method for preparing a flocculant for washed sand in concrete mixtures according to claim 2, characterized in that: The methoxy polyethylene glycol ether is one or a combination of one or more of the following: methoxy polyethylene glycol vinyl ether, methoxy polyethylene glycol propylene ether, methoxy polyethylene glycol methoxy vinyl ether, methoxy polyethylene glycol methoxy vinyl ether, methoxy polyethylene glycol ethoxy vinyl ether, methoxy polyethylene glycol ethoxy vinyl ether, methoxy polyethylene glycol propoxy vinyl ether, methoxy polyethylene glycol propoxy vinyl ether, methoxy polyethylene glycol butoxy vinyl ether, and methoxy polyethylene glycol butoxy vinyl ether.

4. The method for preparing a flocculant for washed sand in concrete mixtures according to claim 2, characterized in that: The initiator is one or a combination of one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and azoisobutylcyanoformamide.

5. The method for preparing a flocculant for washed sand in concrete mixtures according to claim 2, characterized in that: The α-halogen-γ-lactone is one or a combination of one or more of the following: α-chloro-γ-propiolactone, α-chloro-γ-butiolactone, α-chloro-γ-valerolactone, α-chloro-γ-caprolactone, α-bromo-γ-propiolactone, α-bromo-γ-butiolactone, α-bromo-γ-valerolactone, α-bromo-γ-caprolactone, α-iodo-γ-propiolactone, α-iodo-γ-butiolactone, α-iodo-γ-valerolactone, and α-iodo-γ-caprolactone.

6. The method for preparing a flocculant for washed sand in concrete mixtures according to claim 2, characterized in that: The organometallic base catalyst is one or more of 1,8-diazabicyclo[5.4.0]undec-7-ene, stannous isooctanoate, and aluminum isopropoxide.

7. The method for preparing a flocculant for washed sand in concrete mixtures according to claim 2, characterized in that: The carboxylating gas is a mixture of carbon dioxide and hydrogen, with a molar ratio of carbon dioxide to hydrogen of 4:

1.

8. The method for preparing a flocculant for washed sand in concrete mixtures according to claim 2, characterized in that: The dehydrating agent is one or more of dicyclohexylcarbodiimide and N-ethyl-N′-(3-dimethylaminopropyl)carbodiimide hydrochloride.

9. The method for preparing a flocculant for washed sand in concrete mixtures according to claim 2, characterized in that: The catalyst is one or a combination of one or more of N,N,N′,N′-tetramethyl-O-(7-azabenzotriazol-1-yl)hexafluorophosphate, N,N-dimethyl-4-pyridinium, N,N-carbonyldiimidazole, and 1-hydroxybenzotriazole.

10. The method for preparing a flocculant for washed sand in concrete mixtures according to claim 2, characterized in that: The specified temperature and pressure are: temperature 50~120℃, pressure 1.2~1.5Mpa.

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