阅读说明：本技术 一种镁渣制备活性氧化镁的方法及镁水泥的制备方法 (Method for preparing active magnesium oxide from magnesium slag and method for preparing magnesium cement ) 是由 肖学英 文静 李颖 董金美 郑卫新 常成功 张志宏 于 2020-05-08 设计创作，主要内容包括：本发明公开了一种镁渣制备活性氧化镁的方法及镁水泥的制备方法,该镁渣制备活性氧化镁的方法,包括在400～800℃煅烧温度下煅烧镁渣,获得煅烧产物；其中,镁渣是煅烧提锂工艺的副产镁渣,镁渣中还包含硼酸镁杂质。前述镁渣制备镁水泥的方法,包括在400～800℃煅烧温度下煅烧镁渣,获得煅烧产物；将煅烧产物、氯化镁和水混合,养护后得到镁水泥。本发明提供的镁渣制备活性氧化镁的方法以含有较多杂质离子的提锂镁渣作为原料,经过调节煅烧条件获得了活性较高的氧化镁产物,并进一步利用该氧化镁制备镁水泥,实现了将大量废弃的低价值副产物转化成实用工业原料的目的。(The invention discloses a method for preparing active magnesium oxide from magnesium slag and a method for preparing magnesium cement, wherein the method for preparing the active magnesium oxide from the magnesium slag comprises the steps of calcining the magnesium slag at the calcining temperature of 400-800 ℃ to obtain a calcined product; wherein the magnesium slag is a byproduct magnesium slag of a calcination lithium extraction process, and the magnesium slag also contains magnesium borate impurities. The method for preparing the magnesium cement by the magnesium slag comprises the steps of calcining the magnesium slag at the calcining temperature of 400-800 ℃ to obtain a calcined product; and mixing the calcined product, magnesium chloride and water, and curing to obtain the magnesium cement. The method for preparing the active magnesium oxide from the magnesium slag provided by the invention takes the lithium-extracted magnesium slag containing more impurity ions as a raw material, obtains a magnesium oxide product with higher activity by adjusting the calcining condition, and further prepares magnesium cement by using the magnesium oxide, thereby realizing the purpose of converting a large amount of waste low-value byproducts into practical industrial raw materials.)

1. The method for preparing the active magnesium oxide from the magnesium slag is characterized by comprising the steps of calcining the magnesium slag at the calcining temperature of 400-800 ℃ to obtain a calcined product; wherein the magnesium slag is a byproduct magnesium slag of a calcination lithium extraction process, and the magnesium slag comprises magnesium hydroxide, magnesium oxide and magnesium borate.

2. The method according to claim 1, wherein the mass fraction of magnesium oxide in the calcined product is 66% to 85%, and the activity of magnesium oxide is 55% to 75%.

3. The method according to claim 2, wherein the calcination temperature is 600 to 800 ℃, and the activity of magnesium oxide in the calcined product is greater than or equal to 70%.

4. The method according to claim 1, wherein the activity of magnesium oxide in the calcined product increases with the increase of the calcination temperature in the calcination temperature range of 400 to 650 ℃; in the calcining temperature range of 650-800 ℃, the activity of the magnesium oxide in the calcined product is reduced along with the increase of the calcining temperature.

5. A method according to any one of claims 1 to 4, wherein the particle size of the magnesium slag is 100 mesh or less.

6. The method according to claim 5, characterized in that the calcination time of the magnesium slag is less than or equal to 60 min.

7. A method for preparing magnesium cement is characterized by comprising the following steps:

a method for preparing active magnesium oxide from the magnesium slag according to any one of claims 1 to 6;

and mixing the calcined product with magnesium chloride and water according to the mass ratio of 8.5-10: 1: 14-16, and curing to obtain the magnesium cement.

8. The method for preparing magnesium cement according to claim 7, wherein the compressive strength of the magnesium cement after the hydration hardening is less than or equal to 104.2 MPa.

9. The method for producing magnesium cement according to claim 8, wherein the calcination temperature is 600 to 800 ℃, and the mass ratio of the calcined product to the magnesium chloride is 8.5 to 9: 1.

10. A method of producing magnesia cement according to any one of claims 7 to 9, wherein the curing process is maintained in a closed environment.

Technical Field

The invention relates to the technical field of magnesium cement preparation, in particular to a method for preparing active magnesium oxide and magnesium cement from magnesium slag.

Background

Lithium is an indispensable important raw material of modern high-tech products, the lithium mainly exists in lithium-containing ores and salt lake brine, and the lithium resource of the salt lake brine in China accounts for 80% of the total lithium resource in China. The current process for extracting lithium carbonate from salt lake brine produces a large amount of magnesium slag as a by-product (including magnesium oxide and magnesium hydroxide), and the yield of the magnesium slag even far exceeds the yield of lithium products. Meanwhile, the separation difficulty of each impurity ion in the magnesium slag is very high, so that the low-grade lithium-extracting magnesium slag has very limited application, and the large accumulation of the magnesium slag causes great waste of resources and serious pollution to the environment. Lithium salt production enterprises urgently need a process capable of actively recycling magnesium slag byproducts and improving the grade of magnesium slag.

Disclosure of Invention

Light-burned Magnesium oxide is one of the raw materials for preparing ternary system of Magnesium cement (also called Magnesium oxysulfide, abbreviated as MOC). The light-burned magnesia comprises active magnesia and inactive magnesia, and is a general term for magnesite calcination products. The invention obtains active magnesium oxide by calcining magnesium slag of a lithium extraction process, and then further researches the optimal proportion of magnesium cement prepared by using the active magnesium oxide.

The invention provides a method for preparing active magnesium oxide from magnesium slag, and a preparation method of magnesium cement is obtained on the basis of the active magnesium oxide.

The invention provides a method for preparing active magnesium oxide from magnesium slag, which comprises the steps of calcining the magnesium slag at the calcining temperature of 400-800 ℃ to obtain a calcined product; wherein the magnesium slag is a byproduct magnesium slag of a calcination lithium extraction process, and the magnesium slag comprises magnesium hydroxide, magnesium oxide and magnesium borate.

Furthermore, the mass fraction of the magnesium oxide in the calcined product is 66-85%, and the activity of the magnesium oxide is 55-75%.

Further, the calcination temperature is 600-800 ℃, and the activity of magnesium oxide in the calcined product is greater than or equal to 70%.

Further, in the calcining temperature range of 400-650 ℃, the activity of magnesium oxide in the calcined product is increased along with the increase of the calcining temperature; in the calcining temperature range of 650-800 ℃, the activity of the magnesium oxide in the calcined product is reduced along with the increase of the calcining temperature.

Furthermore, the granularity of the magnesium slag is below 100 meshes.

Further, the calcination time for calcining the magnesium slag is less than or equal to 60 min.

The invention also provides a preparation method of the magnesium cement, which comprises the following steps: the steps of the method for preparing the active magnesium oxide by the magnesium slag; and mixing the calcined product with magnesium chloride and water according to the mass ratio of 8.5-10: 1: 14-16, and curing to obtain the magnesium cement.

Further, the compressive strength of the magnesium cement after hydration hardening is less than or equal to 104.2 MPa.

Further, the calcination temperature is 600-800 ℃, and the mass ratio of the calcined product to the magnesium chloride is 8.5-9: 1.

Further, the curing process is maintained in a closed environment.

The preparation method of the active magnesium oxide provided by the invention takes the magnesium slag of the calcination lithium extraction process containing more impurity ions as a raw material, obtains a magnesium oxide product with higher activity by adjusting the calcination conditions, and further utilizes the magnesium oxide to prepare magnesium cement, thereby realizing the purpose of converting a large amount of waste low-value byproducts into practical industrial raw materials.

Drawings

The above and other aspects, features and advantages of embodiments of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is an XRD spectrum of magnesium slag used in the examples of the present invention. (ii) a

FIG. 2 is a thermogravimetric analysis map of magnesium slag in the example of the present invention;

FIG. 3 is an XRD test pattern of the calcined product of examples 1 to 5 of the present invention;

FIG. 4 is a graph showing the effect of calcination temperature on the activity of a calcined product;

FIG. 5 is a graph showing the comparison of the compressive strengths of the magnesium cement test pieces in examples 6 to 21.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical application to thereby enable others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated.

The inventor of the invention provides a method for preparing active magnesium oxide by using magnesium slag based on the difficult problem of difficult reutilization of a large amount of chlorine-containing magnesium slag generated by extracting lithium from a salt lake, and researches magnesium cement and a preparation method thereof on the basis of the active magnesium oxide.

The method for preparing the active magnesium oxide by the magnesium slag comprises the following steps: calcining the magnesium slag at the temperature of 400-800 ℃ to obtain a calcined product.

The magnesium slag is a byproduct magnesium slag of a lithium extraction process by a calcination method, and the main phases in the magnesium slag are magnesium oxide, magnesium hydroxide and magnesium borate. Before calcination, the magnesium slag is ball-milled to be below 100 meshes, so that heat transfer is uniform.

The magnesium slag calcining time is less than or equal to 60min, the highest activity can be achieved only by 1h, and compared with 3-6 h or even longer calcining time required by other processes, the magnesium slag calcining time is very good in energy consumption saving effect.

In the calcining process: mg (OH)₂The reaction formula for the pyrolysis to produce MgO is:

CaCO at a calcination temperature of more than 700 DEG C₃Has been completely decomposed to generate CaO and CO₂The reaction formula is as follows:

the magnesium borate is not decomposed within the range of 400-800 ℃.

Finally, in the calcined product, the mass fraction of the magnesium oxide is 66-85%, and the activity of the magnesium oxide is 55-75%.

In the calcining temperature range of 400-650 ℃, the activity of magnesium oxide in the calcined product is increased along with the increase of the calcining temperature; in the calcining temperature range of 650-800 ℃, the activity of the magnesium oxide in the calcined product is reduced along with the increase of the calcining temperature, and at 650 ℃, the activity of the magnesium oxide reaches 75%. Preferably, the calcination temperature is 600-800 ℃, and the activity of the magnesium oxide in the calcined product under the condition is more than or equal to 70%.

The active magnesium oxide has the advantages of smaller grain diameter, large specific surface, obvious lattice distortion, active physicochemical property and stronger reaction capability with other substances compared with the common magnesium oxide. The activity of magnesium oxide is the property of magnesium oxide, and the difference mainly comes from the lattice distortion, defects, dislocation and unsaturated valence bonds of magnesium oxide crystals. In the ternary system of magnesium cement, 518 phase (5Mg (OH) in magnesium cement₂·MgCl₂·8H₂O) and 318 phase (3Mg (OH)₂·MgCl₂·8H₂O) is the major structural phase, and the amount of 518 phase formation and crystal morphology are believed to be the supports for the strength of the magnesium cement.

The invention also provides a method for preparing magnesium cement by using the magnesium slag, which comprises the steps of calcining the magnesium slag at the calcining temperature of 400-800 ℃ to obtain a calcined product (namely the method for preparing the active magnesium oxide); and mixing the calcined product with magnesium chloride and water according to the mass ratio of 8.5-10: 1: 14-16, and curing to obtain the magnesium cement.

The amount of the calcined product in the ratio of the amounts of the foregoing substances is calculated from the total amount of the calcined product, not the content of active magnesium oxide in the calcined product. The proportion is selected under the condition that the quantity ratio of the substances is more than 5:1:13, so as to ensure the fluidity and the consistency of the cement paste, and the proportion is lower than the quantity ratio of the substances, so that a 518 strength phase of the magnesium cement is not easy to form in a hydration product, and the strength is reduced; above the amount ratio of this substance, the cement paste is too thick to be easily constructed, and also causes waste of raw materials, resulting in an increase in preparation cost.

The compressive strength of the cured magnesium cement after hydration hardening is less than or equal to 104.2 MPa.

The curing process is kept in a closed environment, because the magnesium cement hardened body exists in the form of densely interwoven short rod-shaped crystals in the closed curing environment, the formation and growth of a 518 phase in the magnesium cement are facilitated.

When the mass ratio of the calcined product to the magnesium chloride is in the range of 8.5-9: 1, the compressive strength increases with the extension of the curing period, and the phenomenon of shrinkage does not occur. Therefore, the ratio of the amount of the calcined product to the amount of the magnesium chloride is preferably in this range.

The compressive strength of the magnesia cement test piece made of the calcination product with the age of 7 days and the temperature of 700 ℃ is slightly lower than that of the magnesia cement test piece made of the calcination product with the age of 600 ℃ and 800 ℃, but the compressive strength still increases along with the increase of the calcination temperature. Along with the increase of age, the compressive strength of the test piece fluctuates, but the compressive strength of the magnesium cement test piece prepared by the calcined product at 800 ℃ increases along with the increase of age.

H is taken as the main experiment index of the compressive strength of the test piece₂O and MgCl₂When the quantity ratio of the substances is 14, the compressive strength of the test piece is strongest; the calcining temperature of the magnesium slag is 800 ℃.

In the actual process, magnesium chloride and water can be prepared into a magnesium chloride solution (equivalent to H) with the Baume degree of 21.9-28.3 DEG Be₂O and MgCl₂The ratio of the calcined product to the magnesium chloride is 14-16: 1), and then mixing the calcined product with the magnesium chloride solution. The conversion relation between the baume degree and the mass fraction of the concentration of the magnesium chloride solution is as follows according to the baume degree:

baume-1.4342 +0.98 × MgCl₂Mass fraction of solution × 100

The method for preparing active magnesium oxide and magnesium cement using magnesium slag according to the present invention will be described below with reference to specific examples, and it will be understood by those skilled in the art that the following examples are only specific examples of the method for preparing active magnesium oxide and magnesium cement using magnesium slag according to the present invention, and are not intended to limit the entirety thereof.

The embodiment of the invention adopts the magnesium slag of the process of extracting lithium from salt lake brine by a calcining method of national ann's science and technology development limited company in Qinghai, and the specific process refers to Chinese patent (CN). Firstly, the magnesium slag is analyzed and tested:

the results of X-ray fluorescence analysis (XRF for short) and chemical composition analysis of the magnesium slag are shown in tables 1 and 2:

table 1 XRF analysis data of magnesium slag

TABLE 2 XRF chemical composition analysis data of magnesium slag

As can be seen from the combination of tables 1 and 2, the magnesium slag contains more than 1% of Mg²⁺，Cl^-And B₂O₃And Ca²⁺，Al³⁺，Fe²⁺，K⁺，Li⁺，Na⁺，SO₄ ^2-And SiO₂The content is less than 0.5 percent.

FIG. 1 is an X-ray diffraction (XRD) pattern of magnesium slag. As can be seen from the figure, the main phase composition in the magnesium slag is MgO, Mg (OH)₂And Mg₃B₂O₆The XRD analysis result is similar to the content information of the chemical components, the content of the magnesium hydroxide is 70.88 percent, the content of the magnesium oxide is 8.32 percent, and the content of the magnesium borate is 20.79 percent.

Mg in magnesium slag₃B₂O₆Stable in nature, Mg (OH)₂The pyrolysis temperature is in the range of 340 ℃ to 490 ℃, and Mg is in the range of 400 ℃ to 800 ℃₃B₂O₆The presence state remains stable, Mg (OH)₂Gradually decomposing with increasing temperature to form MgO, so that a certain amount of Mg is present in the calcined product₃B₂O₆。

Thermogravimetric analysis (TG for short) and micro-quotient thermogravimetric analysis (DTG for short) are carried out on the magnesium slag, and the obtained map is shown in figure 2. According to thermogravimetry mapping, the mass change of the sample is small before 200 ℃, which shows that the phase in the calcined magnesium slag has stable property before 200 ℃; the mass change is more obvious between 307 ℃ and 358.6 ℃, the mass change is 21.67 percent, the maximum endothermic temperature is 348.2 ℃, and the mass change is partially Mg (OH)₂The pyrolysis loses the bound water to produce MgO. The sample quality tends to be stable above 500 ℃, the quality change at 550-1150 ℃ is only 2.49 percent, and the partial quality loss is assumed to be CaCO₃Caused by pyrolysis, then calcining CaCO in the magnesium slag₃The content of (B) is 5.65%, and it can be seen from chemical analysis that CaCO was contained in the magnesium slag before calcination₃The content is not more than 0.8 percent, so the mass change of 550-1150 ℃ is mainly caused by the thermal decomposition of other impurities in the magnesium slag. When the heating was completed, the mass residual ratio was 74.05%.

First, example for preparing activated magnesium oxide