CN113716888B - Preparation method of hydrotalcite rust inhibitor based on single-point pH value control - Google Patents

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

A preparation method of hydrotalcite rust inhibitor based on single-point control of pH value

technical field

The invention relates to the field of concrete anti-corrosion and anti-rust, in particular to a method for preparing a hydrotalcite anti-rust agent based on single-point control of pH value.

Background technique

Reinforced concrete is currently the most widely used building material. With the improvement of the economic level, more and more reinforced concrete structures are serving in the chloride-salt environment. Chloride-salt corrosion is recognized as one of the main reasons for the corrosion of steel bars. Corrosion causes huge economic losses. The use of rust inhibitors is one of the effective ways to prevent the corrosion of steel bars caused by chloride corrosion. Rust inhibitors are widely used in reinforced concrete structures because of their convenient use, low cost and good effect. Among them, layered double metal hydroxide (also known as hydrotalcite) has great potential in the field of concrete anticorrosion and rust prevention because of its ion exchange properties.

In the existing research, Chinese patent 201711254566.7 discloses a hydrotalcite intercalated 5-methylthio-1,3,4-thiadiazole-2-mercapto rust inhibitor and its application. The preparation method is zinc nitrate The mixed solution with aluminum nitrate is slowly added dropwise to the sodium nitrate solution, and the pH of the mixed solution system is maintained at 10±0.5 by using sodium hydroxide at all times, that is, the pH is controlled at multiple points, and then the obtained suspension is heated and crystallized in a water bath to obtain zinc-aluminum water Talc, and then get 5-methylthio-1,3,4-thiadiazole-2-mercapto rust inhibitor through ion exchange reaction. Chinese patent 202010779819.8 discloses an organic-inorganic composite intercalated hydrotalcite-based rust inhibitor and its preparation method. The method involves roasting hydrotalcite to obtain roasted hydrotalcite, and then performing ion exchange reaction between roasted hydrotalcite and nitrite to obtain The hydrotalcite grafted with nitrite radicals, the composite intercalated hydrotalcite rust inhibitor is obtained by ion exchange reaction between the hydrotalcite grafted with nitrite radicals and vitamin C. Chinese patent 202010402322.4 discloses a rust inhibitor for concrete steel bars and a preparation method thereof. The method is to dissolve calcium nitrate tetrahydrate or magnesium nitrate hexahydrate and aluminum nitrate nonahydrate together in boiling water to obtain solution I; Dissolve sodium, sodium nitrate and sodium hydroxide together in boiling water to obtain solution II; mix the solution I with the solution II to obtain a reaction solution; move the reaction solution to a reaction kettle and put in water at 120-180°C After heat reaction for 24-48 hours, suction filtration and washing are performed to obtain a filter cake, which is vacuum-dried at 40-60° C. and then ground to obtain a steel bar rust inhibitor. Chinese patent 201711223230.4 discloses a method for preparing zinc-aluminum hydrotalcite. At room temperature, zinc nitrate and aluminum nitrate are mixed to obtain a mixed solution, and the mixed solution is slowly added dropwise to the sodium carbonate solution, and sodium hydroxide is used to maintain the mixed solution The pH of the system is 10±0.5, that is, the pH is controlled at multiple points, and then the suspension is heated and crystallized in a water bath to obtain zinc-aluminum hydrotalcite.

The above method can prepare the hydrotalcite rust inhibitor with excellent antirust effect, but there are also the following defects: (1) use aluminum nitrate to provide aluminum source, so that the consumption of sodium hydroxide is increased, and the effective utilization rate of resources is low; (2) ) The dropwise addition process needs to maintain the pH of the mixed solution at all times, that is, to control the pH at multiple points, the preparation conditions are harsher, and the steps are more loaded down with trivial details; (3) more waste materials are produced.

Contents of the invention

In view of the defects in the above methods, the present invention proposes a method for preparing a hydrotalcite rust inhibitor based on single-point pH control, using sodium metaaluminate as an aluminum source, dissolving sodium metaaluminate in water to provide part of OH ^- , reducing hydrogen The amount of sodium oxide is only needed to control the pH of the mixed solution C of magnesium nitrate, sodium metaaluminate and sodium hydroxide at a single point to 11-13.5, and this pH range is conducive to the stability of the hydrotalcite crystal. The invention can reduce synthesis process, lower synthesis cost, improve resource utilization rate, reduce generated nitrate waste, and the preparation process is simple and non-toxic.

In order to achieve the above object, the technical solution adopted in the present invention is: a hydrotalcite rust inhibitor based on single-point control of pH value, its raw material composition and mass parts are: 12.49 parts of magnesium nitrate hexahydrate, 2.72 to 5.04 parts of sodium hydroxide 1-2 parts of sodium metaaluminate.

The preparation method of the hydrotalcite rust inhibitor based on the single-point control pH value 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 the single-point control pH value comprises the following steps:

(1) Weigh 12.49 parts by weight of magnesium nitrate hexahydrate and dissolve it in 122 parts by weight of water to obtain solution A; weigh 1 to 2 parts by weight of sodium metaaluminate and 2.72 to 5.04 parts by weight of sodium hydroxide and dissolve it in 122 parts by weight of In water, solution B is obtained;

(2) Keeping the temperature at 20°C to 80°C, injecting nitrogen gas and stirring continuously, drop solution A into solution B, obtain mixed solution C after the dropwise addition, and control the pH of mixed solution C to 11 to 13.5;

(3) The mixed solution C was continuously stirred for 1 to 24 hours, and the obtained precipitated product was centrifuged and washed with 200 mL of water for 1 to 3 times;

(4) Vacuum-dry the precipitated product after centrifugation and washing at 60° C. for 36 to 48 hours;

(5) Grinding and sieving the dried product through a 200-mesh sieve to obtain a hydrotalcite rust inhibitor.

In the preparation method of the hydrotalcite rust inhibitor based on single-point control of the pH value, the method for controlling the pH of the mixed solution C in step (2) is: according to the formula Mg _(2～4) Al(OH) _(6～10) The mass m ₁ of OH ^- required for the reaction is 4.88 to 5.85 parts by NO ₃ calculation, and the mass m ₂ of OH ^- provided by dissolving sodium metaaluminate in water is 1.95 to 3.9 parts, and then calculated based on the volume of the mixed solution C to obtain a single point Control the pH of the mixed solution C to 11-13.5 and the required OH ^- mass _m3 is 0.01-3.09 parts, that is, the sodium hydroxide mass m= _m1 - _m2 + _m3 of the solution B in step (1) is 2.72- 5.04 copies.

In the preparation method of the hydrotalcite rust inhibitor based on single-point control of pH value, the sodium metaaluminate is dissolved in water to provide ^OH- , and its chemical equation is:

NaAlO ₂ +H ₂ O=Na[Al(OH) ₄ ] (4).

The beneficial effects of the present invention are:

1. Sodium metaaluminate is used as a raw material to provide part of OH ^- required for the reaction, which improves resource utilization, reduces waste generated, and reduces preparation costs.

2. It only needs to control the pH of the mixed solution of magnesium nitrate, sodium metaaluminate and sodium hydroxide at a single point. Compared with the traditional preparation method of maintaining the pH of the mixed solution during the dropping process, that is, controlling the pH at multiple points, the preparation is more efficient and simple.

Description of drawings

Fig. 1 is the hydrotalcite rust inhibitor XRD pattern prepared in embodiment 1,2,3;

Fig. 2 is the change graph of each group's self-corrosion potential with the increase of c(Cl ^- ) in Examples 1, 2, and 3;

Fig. 3 is the electrochemical impedance spectrum of each group of steel bars in Examples 1, 2, and 3 when the soaking age is 8 days (c(Cl ⁻ )=0.08mol/L);

Fig. 4 is the change diagram of the polarization resistance Rp value of each group of steel bars with the increase of c(Cl ^- ) in Examples 1, 2, and 3;

Detailed ways

The technical solution of the present invention will be described in further detail below in conjunction with the examples. It should be noted that the examples do not constitute a limitation to the protection scope of the present invention.

Example 1

An example of a hydrotalcite rust inhibitor preparation method based on single-point control of pH value according to the present invention, the reaction chemical equation is:

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)

Including the following steps:

(1) Weigh 12.49 parts of quality magnesium nitrate hexahydrate and dissolve it in 122 parts of quality water to obtain solution A; weigh 2 parts of quality sodium metaaluminate and 7.31 parts of quality sodium hydroxide and dissolve it in 122 parts of quality water to obtain a solution b.

(2) Pour solution A into a constant pressure burette, solution B into a three-necked flask, place the three-necked flask in a temperature-controlled magnetic stirrer, set the temperature at 60°C, and pour solution A into the solution while feeding nitrogen gas and stirring continuously B. A mixed solution C is obtained after the dropwise addition, and the pH of the mixed solution C is made to be 13.5.

(3) After the dropwise addition, the stirring was continued for 12 hours, and the obtained precipitated product was centrifuged and washed 3 times with 200 mL of water each time.

(4) Put the precipitated product after centrifugal washing into a vacuum drying oven, and vacuum dry at 60° C. for 48 hours.

(5) Grinding the dried product through a 200-mesh sieve to obtain a hydrotalcite rust inhibitor, named LDHs-1. The theoretical production mass is 3.88g, the actual production mass is 3.55g, and the mass conversion rate is 91.5%.

Electrochemical test:

The saturated calcium hydroxide solution with a pH value of 12.5 is the simulated concrete pore solution, and the rust inhibitor LDHs-1 prepared in Example 1 is mixed in the simulated concrete pore solution by 0.5% of the simulated concrete pore solution quality, marked as LDHs- 1 (0.5%), the control group B is a simulated concrete hole solution without any rust inhibitor. Cut the HPB300 steel bar with a diameter of 10mm into short steel bars with a length of 10mm, one end face is connected with a wire, and the other end face is used as a working surface, and the rest of the working surface is sealed with epoxy resin, and the working surface is oxidized with 180#-1500# Aluminum metallographic sandpaper was polished into a mirror surface step by step, the working electrode was passivated in the simulated concrete pore solution for 10 days, and then sodium chloride was added to the sample to be tested every day, so that the concentration ^of Cl in the sample to be tested was increased by 0.01mol/ L increases gradually to simulate the slow corrosion of steel bars by chloride ions in the actual environment. The CS235OH electrochemical workstation is used. The test system adopts a three-electrode system (the steel bar is the working electrode, the platinum electrode is the auxiliary electrode, and the saturated calomel electrode is the reference electrode). The changes of self-corrosion potential with the increase of Cl ^- concentration in each group and electrochemical impedance spectroscopy.

Example 2

Another example of a hydrotalcite rust inhibitor preparation method based on single-point control of pH value according to the present invention, the reaction chemical equation is:

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)

Including the following steps:

(1) Weigh 9.62 parts of quality magnesium nitrate hexahydrate and dissolve it in 122 parts of quality water to obtain solution A; weigh 1 part of quality sodium metaaluminate and 2.72 parts of quality sodium hydroxide and dissolve it in 122 parts of quality water to obtain solution b.

The rest of the steps are similar to Example 1, except that the temperature is set at 20° C. in step (2), and the pH of the mixed solution C is controlled to be 12; and stirred for 24 hours in step (3). The obtained hydrotalcite rust inhibitor was named LDHs-2. The theoretical production mass is 5.04g, the actual production mass is 4.58g, and the mass conversion rate is 90.9%.

Electrochemical test:

The saturated calcium hydroxide solution with a pH value of 12.5 is the simulated concrete hole solution, and the rust inhibitor LDHs-2 prepared in Example 2 is mixed in the simulated concrete hole solution by 1.5% of the quality of the simulated concrete hole solution, and is marked as LDHs- 2 (1.5%), control group B is a simulated concrete hole solution without any rust inhibitor. Remaining concrete test steps are identical with embodiment 1.

Example 3

Another example of the preparation method of a hydrotalcite rust inhibitor based on single-point control of pH value according to the present invention, the reaction chemical equation is:

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)

Including the following steps:

(1) Weigh 12.49 parts of quality magnesium nitrate hexahydrate and dissolve it in 122 parts of quality water to obtain solution A; weigh 1 part of quality sodium metaaluminate and 2.94 parts of quality sodium hydroxide and dissolve it in 122 parts of quality water to obtain a solution b.

The rest of the steps are similar to Example 1, except that in step (2), the set temperature is 80° C., and the pH of the mixed solution C is controlled to be 11; in step (3), it is stirred for 6 hours. The hydrotalcite rust inhibitor LDHs-3 was prepared. The theoretical production mass is 5.93g, the actual production mass is 6.2g, and the mass conversion rate is 95.8%.

The saturated calcium hydroxide solution with a pH value of 12.5 is the simulated concrete pore solution, and the rust inhibitor LDHs-3 prepared in Example 3 is mixed into the simulated concrete pore solution by 3% of the simulated concrete pore solution quality, marked as LDHs -3 (3%), control group B is a simulated concrete hole solution without any rust inhibitor. Remaining concrete test steps are identical with embodiment 1.

Embodiment result is as follows:

FIG. 1 is the XRD patterns of MgAl-LDHs prepared in Examples 1, 2, and 3. Among them, a, b, and c in Figure 1 correspond to the XRD patterns of LDHs-1, LDHs-2, and LDHs-3, respectively. It can be seen from Figure 1 that LDHs-1, LDHs-2, and LDHs-3 all have characteristic peaks of hydrotalcite, indicating that the present invention has successfully synthesized magnesium aluminum hydrotalcite rust inhibitor. Using Jade software to calculate the interlayer spacing from the crystal plane index 003 peak is 0.776nm, 0.779nm, 0.790nm, indicating that the interlayer spacing increases with the increase of the magnesium-aluminum ratio.

Fig. 2 is the trend diagram of the self-corrosion potential of LDHs-1 (0.5%), LDHs-2 (1.5%), LDHs-3 (3%), and the control group B with the concentration of Cl ^- , and the control group B is at c(Cl ^- ) When =0.08mol/L, the self-corrosion potential is -334mV<-250mV. According to the "Standards of the Ministry of Metallurgy of China", the steel bars in the control group may have begun to corrode, and at this time LDHs-1 (0.5%), LDHs-2 (1.5%) , LDHs-3 (3%) self-corrosion potentials are -62mV, -57mV, -44mV respectively, and the steel bars are not corroded. The self-corrosion potential of control group B is -507mV<-400mV when c(Cl ^- )=0.15mol/L. The self-corrosion potentials of LDHs-2 (1.5%) and LDHs-3 (3%) are -41mV, -56mV, -53mV respectively, and the steel bars do not corrode.

Figure 3 is the electrochemical impedance spectrum of each group of steel bars when the soaking age is 8 days (c(Cl ^- ) = 0.08mol/L), and the polarization resistance Rp of the steel bars is qualitatively judged according to the slope of the corresponding curve. Figure 3 shows that the Rp value of each group is: 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 group added with LDHs were all an order of magnitude higher than that of the control group B.

Figure 4 shows the change diagram of the polarization resistance Rp of steel bar electrodes in each group with the increase of chloride ion concentration. It can be seen from the figure that with the increase of chloride ion concentration, the Rp value of the experimental group added with LDHs is always greater than that of the control group B. From the 15th day Rp Calculate the rust-inhibiting efficiency, the formula for calculating the rust-inhibiting efficiency is as follows:

The calculated antirust efficiencies of LDHs-1 (0.5%), LDHs-2 (1.5%) and LDHs-3 (3%) are 99%, 99.6%, and 99.5%, respectively.

Table 1 Experimental conditions and antirust performance of the present invention

rust inhibitor pH temperature(℃) Stirring time (hours) Dosage (%) Anti-rust efficiency (%) LDHs-1 13.5 60 12 0.5 99 LDHs-2 12 20 twenty four 1.5 99.6 LDHs-3 11 80 6 3 99.5

The present invention also has the following advantages:

1. Use sodium metaaluminate, magnesium nitrate hexahydrate, and sodium hydroxide as raw materials to improve resource utilization and reduce waste. The prepared reaction equation is as follows:

The prepared reaction 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)

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 traditional 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 present invention compares with traditional preparation method as shown in table 2:

Table 2 The present invention compares with traditional preparation method

As can be seen from Table 2, the present invention saves 4 mol NaOH and reduces ₄ mol NaNO3 waste material compared with the traditional preparation method. For example, to prepare 1mol Mg ₂ Al(OH) ₆ (OH) _x (NO ₃ ) _1-x nH ₂ O, the present invention only needs (2+x) NaOH to produce (3+x) mol NaNO ₃ waste material, traditional The preparation method requires (6+x) NaOH and produces (7+x) mol NaNO ₃ waste. Similarly, to prepare 1mol of Mg 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 O, Compared with the traditional preparation method, the present invention saves 4 mol NaOH and reduces 4 mol NaNO ₃ .

2. The preparation cost is reduced. According to the data provided by Nanning Lantian Experimental Equipment Co., Ltd., the cost of each reagent is shown in Table 3:

Table 3 Reagent costs

Reagent Specification place of origin unit price NaOH AR500g Guangdong/Guanghua 7.5 yuan/bottle NaNO₃ AR500g Guangdong/Guanghua 10.6 yuan/bottle Mg(NO₃)₂ 6H₂O AR500g Guangdong/Guanghua 19.6 yuan / bottle Al(NO₃)₃ 9H₂O AR500g Guangdong/Guanghua 17.9 yuan/bottle NaAlO₂ AR500g Tianjin/Damao 20 yuan/bottle

Calculated by the reaction equation of the present invention:

To prepare 194g of Mg ₂ Al(OH) ₆ (OH) _x (NO ₃ ) _1-x ·nH ₂ O, a total of 20.07+3.28+1.2=24.55 yuan is required.

Calculated by the traditional preparation method reaction equation:

To prepare 194g of Mg ₂ Al(OH) ₆ (OH) _x (NO ₃ ) _1-x ·nH ₂ O, a total of 20.07+13.4+3.6+1.8=38.87 yuan is required.

Cost saving (38.87-24.55)/38.87=36.8%

Similarly, calculations for 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 O The process is the same as above, and the calculation results are shown in Table 4.

Table 4 The present invention compares with traditional preparation method cost

rust inhibitor Cost of the invention (yuan) Traditional preparation method (yuan) save costs(%) 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)。

Images