CN113716888B - Preparation method of hydrotalcite rust inhibitor based on single-point pH value control - Google Patents
Preparation method of hydrotalcite rust inhibitor based on single-point pH value control Download PDFInfo
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- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
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Abstract
A hydrotalcite rust inhibitor preparation method based on single-point pH value control comprises the following steps: (1) 12.49 parts by mass of magnesium nitrate hexahydrate is dissolved in 122 parts by mass of water to obtain a solution A; dissolving 1-2 parts by mass of sodium metaaluminate and 2.72-5.04 parts by mass of sodium hydroxide in 122 parts by mass of water to obtain solution B; (2) Keeping a certain temperature, introducing nitrogen, continuously stirring, and simultaneously dripping the solution A into the solution B, and controlling the pH = 11-13.5 of the mixed solution C after finishing dripping; (3) Continuously stirring for a certain time, and centrifugally washing an obtained precipitate; (4) Vacuum drying the centrifugally washed precipitate at 60 deg.c for 36-48 hr; (5) And grinding and sieving the dried product to obtain the hydrotalcite rust inhibitor.
Description
Technical Field
The invention relates to the field of concrete corrosion prevention and rust resistance, in particular to a preparation method of a hydrotalcite rust inhibitor based on single-point pH value control.
Background
The reinforced concrete is the most widely applied building material at present, and with the improvement of economic level, more and more reinforced concrete structures are in service in a chlorine salt environment, and chlorine salt corrosion is known to be one of main reasons of reinforcing steel bar corrosion, which causes huge economic loss due to the reinforcing steel bar corrosion every year. The rust inhibitor is one of effective ways for preventing the reinforcing steel bars from being corroded by chloride, and is widely applied to reinforced concrete structures due to the characteristics of convenience in use, low cost and good effect. Among them, the layered double hydroxides (also called hydrotalcite) have great potential in the field of corrosion prevention and rust inhibition of concrete due to their ion exchange characteristics.
In the existing research, chinese patent 201711254566.7 discloses a hydrotalcite intercalation 5-methylthio-1,3,4-thiadiazole-2-thioyl rust inhibitor and application thereof, the preparation method comprises slowly dripping a mixed solution of zinc nitrate and aluminum nitrate into a sodium nitrate solution, maintaining the pH of the mixed solution system to be =10 +/-0.5 at the moment of using sodium hydroxide, namely controlling the pH at multiple points, heating and crystallizing the obtained suspension in water bath to obtain zinc-aluminum hydrotalcite, and then obtaining the 5-methylthio-1,3,4-thiadiazole-2-thioyl rust inhibitor through ion exchange reaction. Chinese patent 202010779819.8 discloses an organic-inorganic composite intercalated hydrotalcite-based rust inhibitor and a preparation method thereof, the method comprises the steps of roasting hydrotalcite to obtain roasted hydrotalcite, then carrying out ion exchange reaction on the roasted hydrotalcite and nitrite to obtain hydrotalcite grafted with nitrite, and carrying out ion exchange reaction on the hydrotalcite grafted with nitrite and vitamin C to obtain the composite intercalated hydrotalcite rust inhibitor. Chinese patent 202010402322.4 discloses a concrete reinforcement corrosion inhibitor and a preparation method thereof, wherein the method comprises the steps of dissolving calcium nitrate tetrahydrate or magnesium nitrate hexahydrate and aluminum nitrate nonahydrate in boiling water to obtain a solution I; dissolving sodium lignosulfonate, sodium nitrate and sodium hydroxide in boiling water together to obtain a solution II; uniformly mixing the solution I and the solution II to obtain a reaction solution; and transferring the reaction liquid into a reaction kettle, carrying out hydrothermal reaction at 120-180 ℃ for 24-48 h, carrying out suction filtration and washing to obtain a filter cake, carrying out vacuum drying on the filter cake at 40-60 ℃, and then grinding to obtain the steel bar rust inhibitor. Chinese patent 201711223230.4 discloses a method for preparing zinc-aluminum hydrotalcite, which comprises mixing zinc nitrate and aluminum nitrate at room temperature to obtain a mixed solution, slowly dripping the mixed solution into a sodium carbonate solution, maintaining the pH of the mixed solution system to be =10 +/-0.5 by using sodium hydroxide, namely controlling the pH at multiple points, and then heating and crystallizing the suspension in a water bath to obtain the zinc-aluminum hydrotalcite.
The hydrotalcite rust inhibitor with excellent rust inhibition effect can be prepared by the method, but the method also has the following defects: (1) Aluminum nitrate is used for providing an aluminum source, so that the using amount of sodium hydroxide is increased, and the effective utilization rate of resources is low; (2) The pH of the mixed solution needs to be maintained at any time in the dripping process, namely the pH is controlled at multiple points, the preparation conditions are harsh, and the steps are complex; and (3) the generated waste is high.
Disclosure of Invention
Aiming at the defects of the method, the invention provides a method for preparing a hydrotalcite rust inhibitor based on single-point pH control, which uses sodium metaaluminate to provide an aluminum source, and the sodium metaaluminate is dissolved in water to provide partial OH - And the use amount of sodium hydroxide is reduced, and the pH = 11-13.5 of the mixed solution C of magnesium nitrate, sodium metaaluminate and sodium hydroxide is controlled only by a single point, so that the stability of hydrotalcite crystals is facilitated in the pH range. The invention can reduce the synthetic procedures, reduce the synthetic cost, improve the resource utilization rate and reduce the generated nitrate waste, and the preparation process is simple and nontoxic.
In order to achieve the purpose, the invention adopts the technical scheme that: a hydrotalcite rust inhibitor based on single-point pH value control comprises the following raw materials in parts by weight: 12.49 parts of magnesium nitrate hexahydrate, 2.72-5.04 parts of sodium hydroxide and 1-2 parts of sodium metaaluminate.
The preparation method of the hydrotalcite rust inhibitor based on single-point pH value control is carried out according to the following chemical reaction equation:
2Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(2+x)NaOH+(n+2)H 2 O＝Mg 2 Al(OH) 6 (OH) x (NO 3 ) 1-x ·nH 2 O+(3+x)NaNO 3 +6H 2 O(1)
3Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(4+x)NaOH+(n+2)H 2 O＝Mg 3 Al(OH) 8 (OH) x (NO 3 ) 1-x ·nH 2 O+(5+x)NaNO 3 +6H 2 O(2)
4Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(6+x)NaOH+(n+2)H 2 O＝Mg 4 Al(OH) 10 (OH) x (NO 3 ) 1-x ·nH 2 O+(7+x)NaNO 3 +6H 2 O(3)
the preparation method of the hydrotalcite rust inhibitor based on single-point pH value control comprises the following steps:
(1) Weighing 12.49 parts by mass of magnesium nitrate hexahydrate, and dissolving the magnesium nitrate hexahydrate in 122 parts by mass of water to obtain a solution A; weighing 1-2 parts by mass of sodium metaaluminate and 2.72-5.04 parts by mass of sodium hydroxide, and dissolving in 122 parts by mass of water to obtain a solution B;
(2) Keeping the temperature at 20-80 ℃, introducing nitrogen, continuously stirring, and simultaneously dripping the solution A into the solution B to obtain a mixed solution C, wherein the pH = 11-13.5;
(3) Continuously stirring the mixed solution C for 1-24 hours, and centrifugally washing the obtained precipitate for 1-3 times by using 200mL of water;
(4) Vacuum drying the centrifugally washed precipitate at 60 deg.c for 36-48 hr;
(5) And grinding and sieving the dried product with a 200-mesh sieve to obtain the hydrotalcite rust inhibitor.
The preparation method of the hydrotalcite rust inhibitor based on single-point pH value control comprises the following steps of (2) controlling the pH value of the mixed solution C: according to Mg in the equation (2～4) Al(OH) (6～10) NO 3 Calculating to obtain OH required by the reaction - Mass m of 1 4.88 to 5.85 portions of sodium metaaluminate, which is dissolved in water to provide OH - Mass m of 2 1.95-3.9 parts of the total OH required for calculating the pH = 11-13.5 of the single-point control mixed solution C according to the volume of the mixed solution C - Mass m 3 0.01 to 3.09 portions, namely the mass m = m of the sodium hydroxide of the solution B in the step (1) 1 －m 2 +m 3 2.72 to 5.04 portions.
In the preparation method of the hydrotalcite rust inhibitor based on single-point pH value control, the sodium metaaluminate is dissolved in water to provide OH - The chemical formula is as follows:
NaAlO 2 +H 2 O＝Na[Al(OH) 4 ] (4)。
the invention has the beneficial effects that:
1. sodium metaaluminate is used as raw material to provide partial OH required by reaction - Improve resourcesThe utilization rate, the generated waste materials are reduced, and the preparation cost is reduced.
2. The pH of the mixed solution of magnesium nitrate, sodium metaaluminate and sodium hydroxide is controlled only by a single point, and compared with the traditional preparation method in which the pH of the mixed solution is constantly maintained in the dropping process, namely the pH is controlled by multiple points, the preparation is more efficient, simpler and more convenient.
Drawings
FIG. 1 is an XRD pattern of hydrotalcite rust inhibitor prepared in examples 1, 2 and 3;
FIG. 2 shows the self-etching potentials as a function of c (Cl) for each of the groups of examples 1, 2 and 3 - ) (ii) an incremental change map;
FIG. 3 shows the steel bars of each group of examples 1, 2 and 3 in a soaking period of 8 days (c (Cl) - ) Electrochemical impedance spectrum when =0.08 mol/L);
FIG. 4 shows the values of the polarization resistance Rp with c (Cl) for each set of steel bars in examples 1, 2 and 3 - ) (ii) an incremental change map;
Detailed Description
The technical solution of the present invention is further described in detail with reference to the following examples, which should be construed as limiting the scope of the present invention.
Example 1
According to an embodiment of the preparation method of the hydrotalcite rust inhibitor based on single-point pH control, the reaction chemical equation is as follows:
2Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(2+x)NaOH+(n+2)H 2 O＝Mg 2 Al(OH) 6 (OH) x (NO 3 ) 1-x ·nH 2 O+(3+x)NaNO 3 +6H 2 O (1)
the method comprises the following steps:
(1) Weighing 12.49 parts by mass of magnesium nitrate hexahydrate, and dissolving the magnesium nitrate hexahydrate in 122 parts by mass of water to obtain a solution A; 2 parts by mass of sodium metaaluminate and 7.31 parts by mass of sodium hydroxide are weighed and dissolved in 122 parts by mass of water to obtain a solution B.
(2) Pouring the solution A into a constant-pressure burette, pouring the solution B into a three-neck flask, placing the three-neck flask into a temperature-controlled magnetic stirrer, setting the temperature to be 60 ℃, introducing nitrogen, continuously stirring, and dripping the solution A into the solution B to obtain a mixed solution C, wherein the pH of the mixed solution C is =13.5 after the dripping is finished.
(3) After the addition was completed, stirring was continued for 12 hours, and the resulting precipitated product was washed 3 times by centrifugation with 200mL of water each time.
(4) The precipitated product after centrifugal washing was put into a vacuum drying oven and vacuum-dried at 60 ℃ for 48 hours.
(5) And grinding the dried product and sieving the ground product with a 200-mesh sieve to obtain the hydrotalcite rust inhibitor named LDHs-1. The theoretical mass produced was 3.88g, the actual mass produced was 3.55g, and the mass conversion was 91.5%.
Electrochemical testing:
the saturated calcium hydroxide solution with the pH value of 12.5 is taken as a simulated concrete pore solution, the rust inhibitor LDHs-1 prepared in the example 1 is doped into the simulated concrete pore solution according to 0.5 percent of the mass of the simulated concrete pore solution, the label is LDHs-1 (0.5 percent), and the control group B is the simulated concrete pore solution without any rust inhibitor. Cutting a HPB300 steel bar with the diameter of 10mm into short steel bars with the length of 10mm, connecting one end face by using a lead, taking the other end face as a working face, sealing the rest faces except the working face by using epoxy resin, gradually polishing the working face into a mirror surface by using 180# -1500# alumina gold phase sand paper, passivating a working electrode in a simulated concrete pore solution for 10 days, and then adding sodium chloride into a sample to be measured every day to ensure that Cl in the sample to be measured is Cl - The concentration of the chlorine ions is increased by 0.01mol/L every day, slow erosion of the chlorine ions to the steel bars in the actual environment is simulated, a CS235OH electrochemical workstation is adopted, a three-electrode system (the steel bars are used as working electrodes, platinum electrodes are used as auxiliary electrodes, and saturated calomel electrodes are used as reference electrodes) is adopted as a test system, and the self-corrosion potential in each group is tested along with Cl - A graph of the change in the increase in the added concentration and an electrochemical impedance spectrum.
Example 2
According to another embodiment of the preparation method of the hydrotalcite rust inhibitor based on single-point pH control, the reaction chemical equation is as follows:
3Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(4+x)NaOH+(n+2)H 2 O＝Mg 3 Al(OH) 8 (OH) x (NO 3 ) 1-x ·nH 2 O+(5+x)NaNO 3 +6H 2 O (2)
the method comprises the following steps:
(1) Weighing 9.62 parts by mass of magnesium nitrate hexahydrate, and dissolving the magnesium nitrate hexahydrate in 122 parts by mass of water to obtain a solution A;1 part by mass of sodium metaaluminate and 2.72 parts by mass of sodium hydroxide are weighed and dissolved in 122 parts by mass of water to obtain a solution B.
The remaining steps were similar to example 1 except that the temperature was set to 20 ℃ in step (2), and the pH of the mixed solution C was controlled to =12; stirring for 24 hours in the step (3). The hydrotalcite rust inhibitor named LDHs-2 is prepared. The theoretical mass produced was 5.04g, the actual mass produced was 4.58g, and the mass conversion was 90.9%.
Electrochemical testing:
saturated calcium hydroxide solution with pH value of 12.5 is used as simulated concrete pore solution, the rust inhibitor LDHs-2 prepared in example 2 is added into the simulated concrete pore solution according to 1.5% of the mass of the simulated concrete pore solution, and is marked as LDHs-2 (1.5%), and the control group B is the simulated concrete pore solution without any rust inhibitor. The remaining specific test procedures were the same as in example 1.
Example 3
In another embodiment of the method for preparing the hydrotalcite rust inhibitor based on single-point pH control, the reaction chemical equation is as follows:
4Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(6+x)NaOH+(n+2)H 2 O＝Mg 4 Al(OH) 10 (OH) x (NO 3 ) 1-x ·nH 2 O+(7+x)NaNO 3 +6H 2 O (3)
the method comprises the following steps:
(1) Weighing 12.49 parts by mass of magnesium nitrate hexahydrate, and dissolving the magnesium nitrate hexahydrate in 122 parts by mass of water to obtain a solution A;1 part by mass of sodium metaaluminate and 2.94 parts by mass of sodium hydroxide are weighed and dissolved in 122 parts by mass of water to obtain a solution B.
The remaining steps were similar to example 1 except that in step (2), the temperature was set to 80 ℃ and the pH of the mixed solution C was controlled =11; stirring for 6 hours in the step (3). Preparing the hydrotalcite rust inhibitor LDHs-3. The theoretical mass produced was 5.93g, the actual mass produced was 6.2g, and the mass conversion was 95.8%.
The saturated calcium hydroxide solution with the pH value of 12.5 is taken as a simulated concrete pore solution, the rust inhibitor LDHs-3 prepared in the example 3 is respectively mixed into the simulated concrete pore solution according to 3 percent of the mass of the simulated concrete pore solution, the mixture is marked as LDHs-3 (3 percent), and the control group B is the simulated concrete pore solution without any rust inhibitor. The remaining specific test procedures were the same as in example 1.
The results of the examples are as follows:
FIG. 1 is an XRD pattern of MgAl-LDHs prepared in examples 1, 2 and 3. Wherein, a, b and c in figure 1 correspond to XRD patterns of LDHs-1, LDHs-2 and LDHs-3 respectively. As can be seen from figure 1, LDHs-2 and LDHs-3 all have the characteristic peak of hydrotalcite, which indicates that the magnalium hydrotalcite rust inhibitor is successfully synthesized by the invention. The interlayer distances of 0.776nm, 0.779nm and 0.790nm are respectively calculated from the 003 peak of the plane index by using Jade software, and the interlayer distances are increased along with the increase of the magnesium-aluminum ratio.
FIG. 2 shows the self-corrosion potential of LDHs-1 (0.5%), LDHs-2 (1.5%), LDHs-3 (3%), control group B with Cl - Concentration trend plot, control group B at c (Cl) - ) The autogenous corrosion potential is-334 mV < -250mV at 0.08mol/L, the steel bars in the control group may begin to corrode according to the Standard of the Ministry of Chinese metallurgy, and the autogenous corrosion potentials of LDHs-1 (0.5%), LDHs-2 (1.5%) and LDHs-3 (3%) are-62 mV, -57mV, -44mV respectively at the time, and the steel bars are not corroded. Control group B at c (Cl) - ) The self-corrosion potential is-507 mV < -400mV at 0.15mol/L, the steel bars in the control group are corroded according to the Standard of the Ministry of Chinese metallurgy, and the self-corrosion potentials of LDHs-1 (0.5%), LDHs-2 (1.5%) and LDHs-3 (3%) are-41 mV, -56mV, -53mV at the time, and the steel bars are not corroded.
FIG. 3 shows the lengths of the groups of steel bars in the soaking period of 8 days (c (Cl) - ) =0.08 mol/L), and qualitatively determining the magnitude of the polarization resistance Rp of the steel bar according to the slope of the corresponding curve, as can be seen from fig. 3, the magnitudes of the Rp values in each group are: LDHs-2 (1.5%) > LDHs-3 (3%) > LDHs-1 (0.5%) > control group B, and the corresponding Rp value obtained by fitting is: 7.4E +05 > 5.5E +05 > 3.4E +05 > 8.3E +04. The Rp values of the experimental groups added with LDHs are all higher by one order of magnitude than those of the control group B.
Fig. 4 is a graph of the change of the polarization resistance Rp of each set of steel bar electrodes along with the increase of the chloride ion concentration, and it can be known from the graph that the Rp value of the experimental group added with the LDHs is always larger than that of the control group B along with the increase of the chloride ion concentration, the rust inhibition efficiency is calculated by the Rp value at the 15 th day, and the calculation formula of the rust inhibition efficiency is as follows:
calculated to obtain the rust resistance efficiencies of LDHs-1 (0.5%), LDHs-2 (1.5%) and LDHs-3 (3%) of 99%, 99.6% and 99.5%, respectively.
TABLE 1 Experimental conditions and Corrosion resistance of the invention
| Rust inhibitor | pH | Temperature (. Degree. C.) | Mixing time (hours) | Amount of incorporation (%) | Rust-proof efficiency (%) |
| LDHs-1 | 13.5 | 60 | 12 | 0.5 | 99 |
| LDHs-2 | 12 | 20 | 24 | 1.5 | 99.6 |
| LDHs-3 | 11 | 80 | 6 | 3 | 99.5 |
The invention also has the following advantages:
1. sodium metaaluminate, magnesium nitrate hexahydrate and sodium hydroxide are used as raw materials, so that the resource utilization rate is improved, and the generated waste is reduced. The reaction equation for the preparation is as follows:
the reaction equation for the preparation is as follows:
2Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(2+x)NaOH+(n+2)H 2 O＝Mg 2 Al(OH) 6 (OH) x (NO 3 ) 1-x ·nH 2 O+(3+x)NaNO 3 +6H 2 O (1)
3Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(4+x)NaOH+(n+2)H 2 O＝Mg 3 Al(OH) 8 (OH) x (NO 3 ) 1-x ·nH 2 O+(5+x)NaNO 3 +6H 2 O (2)
4Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(6+x)NaOH+(n+2)H 2 O＝Mg 4 Al(OH) 10 (OH) x (NO 3 ) 1-x ·nH 2 O+(7+x)NaNO 3 +6H 2 O (3)
the conventional preparation reaction equation is as follows:
2Mg(NO 3 ) 2 ·6H 2 O+Al(NO 3 ) 3 ·9H 2 O+(6+x)NaOH+NaNO 3 +nH 2 O＝Mg 2 Al(OH) 6 (OH) x (NO 3 ) 1-x ·nH 2 O+(7+x)NaNO 3 +15H 2 O (6)
3Mg(NO 3 ) 2 ·6H 2 O+Al(NO 3 ) 3 ·9H 2 O+(8+x)NaOH+NaNO 3 +nH 2 O＝Mg 3 Al(OH) 8 (OH) x (NO 3 ) 1-x ·nH 2 O+(9+x)NaNO 3 +15H 2 O (7)
4Mg(NO 3 ) 2 ·6H 2 O+Al(NO 3 ) 3 ·9H 2 O+(10+x)NaOH+NaNO 3 +nH 2 O＝Mg 4 Al(OH) 10 (OH) x (NO 3 ) 1-x ·nH 2 O+(11+x)NaNO 3 +15H 2 O (8)
the comparative example of the present invention and the conventional preparation method is shown in table 2:
TABLE 2 comparison of the present invention with conventional preparation methods
As can be seen from Table 2, the present invention saves 4mol of NaOH and reduces 4mol of NaNO compared to the conventional preparation method 3 And (4) waste materials. For example, 1mol of Mg is prepared 2 Al(OH) 6 (OH) x (NO 3 ) 1-x ·nH 2 O, the invention only needs (2+x) NaOH to produce (3+x) mol NaNO 3 The waste material, the traditional preparation method needs (6+x) NaOH to produce (7+x) mol NaNO 3 And (4) waste materials. Similarly, 1mol of Mg was prepared 3 Al(OH) 8 (OH) x (NO 3 ) 1-x ·nH 2 O and Mg 4 Al(OH) 10 (OH) x (NO 3 ) 1-x ·nH 2 Compared with the traditional preparation method, the invention saves 4mol of NaOH and reduces 4mol of NaNO 3 。
2. The preparation cost is reduced, and according to the data provided by Nanning blue sky experimental equipment Co., ltd, the cost of each reagent is shown in Table 3:
TABLE 3 cost of reagents
| Reagent | Specification of | Producing area | Unit price of |
| NaOH | AR500g | Guangdong/Guanghua | 7.5 yuan/bottle |
| NaNO 3 | AR500g | Guangdong/Guanghua | 10.6 yuan/bottle |
| Mg(NO 3 ) 2 ·6H 2 O | AR500g | Guangdong/Guanghua | 19.6 yuan/bottle |
| Al(NO 3 ) 3 ·9H 2 O | AR500g | Guangdong/Guanghua | 17.9 Yuan/bottle |
| NaAlO 2 | AR500g | Tianjin/ |
20 yuan/bottle |
Calculated from the reaction equation of the present invention:
preparation of 194g Mg 2 Al(OH) 6 (OH) x (NO 3 ) 1-x ·nH 2 O, needs 20.07+, 3.28+, 1.2=24.55 yuan in total.
Calculated from the reaction equation of the conventional preparation method:
preparation of 194g Mg 2 Al(OH) 6 (OH) x (NO 3 ) 1-x ·nH 2 O, 20.07+, 13.4+, 3.6+, 1.8=38.87 yuan is needed.
Cost saving (38.87-24.55)/38.87 =36.8%
Similarly, mg 3 Al(OH) 8 (OH) x (NO 3 ) 1-x ·nH 2 O、Mg 4 Al(OH) 10 (OH) x (NO 3 ) 1-x ·nH 2 The calculation procedure for O was the same as above, and the calculation results of the preparation are shown in Table 4.
TABLE 4 comparison of the cost of the present invention with that of the conventional preparation method
| Rust inhibitor | Cost of the invention (yuan) | Conventional preparation method (Yuan) | Saving cost (%) |
| LDHs-1 | 24.55 | 38.87 | 36.8 |
| LDHs-2 | 35.78 | 50.01 | 28.6 |
| LDHs-3 | 47.02 | 61.34 | 23.3 |
Claims (3)
1. A preparation method of a hydrotalcite rust inhibitor based on single-point pH value control is characterized by comprising the following raw materials in parts by weight: 12.49 parts of magnesium nitrate hexahydrate, 2.72-5.04 parts of sodium hydroxide and 1-2 parts of sodium metaaluminate, and the method is carried out according to the following chemical reaction equation:
2Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(2+x)NaOH+(n+2)H 2 O＝Mg 2 Al(OH) 6 (OH) x (NO 3 ) 1-x ·nH 2 O+(3+x)NaNO 3 +6H 2 O(1)
3Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(4+x)NaOH+(n+2)H 2 O＝Mg 3 Al(OH) 8 (OH) x (NO 3 ) 1-x ·nH 2 O+(5+x)NaNO 3 +6H 2 O(2)
4Mg(NO 3 ) 2 ·6H 2 O+NaAlO 2 +(6+x)NaOH+(n+2)H 2 O＝Mg 4 Al(OH) 10 (OH) x (NO 3 ) 1-x ·nH 2 O+(7+x)NaNO 3 +6H 2 O(3)；
the method comprises the following steps:
(1) Weighing 12.49 parts by mass of magnesium nitrate hexahydrate, and dissolving the magnesium nitrate hexahydrate in 122 parts by mass of water to obtain a solution A; weighing 1-2 parts by mass of sodium metaaluminate and 2.72-5.04 parts by mass of sodium hydroxide, and dissolving in 122 parts by mass of water to obtain a solution B;
(2) Keeping the temperature at 20-80 ℃, introducing nitrogen, continuously stirring, and simultaneously dripping the solution A into the solution B to obtain a mixed solution C, wherein the pH = 11-13.5;
(3) Continuously stirring the mixed solution C for 1-24 hours, and centrifugally washing the obtained precipitate for 1-3 times by using 200mL of water;
(4) Vacuum drying the centrifugally washed precipitate at 60 deg.c for 36-48 hr;
(5) And grinding and sieving the dried product with a 200-mesh sieve to obtain the hydrotalcite rust inhibitor.
2. The preparation method of the hydrotalcite rust inhibitor based on single-point pH control according to claim 1, wherein the step (2) of controlling the pH of the mixed solution C comprises the following steps: according to Mg in the equation (2～4) Al(OH) (6～10) NO 3 Calculating to obtain OH required by the reaction - Mass m of 1 4.88 to 5.85 parts of sodium metaaluminate, which is dissolved in water to provide OH - Mass m of 2 Is 1.95E3.9 parts of the total amount of the mixed solution C, and calculating OH required for controlling the pH = 11-13.5 of the mixed solution C at a single point according to the volume of the mixed solution C - Mass m 3 0.01 to 3.09 portions, namely the mass m = m of the sodium hydroxide of the solution B in the step (1) 1 －m 2 +m 3 2.72 to 5.04 portions.
3. The method of claim 1, wherein the sodium metaaluminate is dissolved in water to provide OH - The chemical formula is as follows:
NaAlO 2 +H 2 O＝Na[Al(OH) 4 ] (4)。
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