CN114772952B

CN114772952B - Macrocrystalline fused magnesia as well as preparation method and preparation device thereof

Info

Publication number: CN114772952B
Application number: CN202210423059.6A
Authority: CN
Inventors: 张世东
Original assignee: Individual
Current assignee: Individual
Priority date: 2022-04-21
Filing date: 2022-04-21
Publication date: 2023-03-21
Anticipated expiration: 2042-04-21
Also published as: CN114772952A

Abstract

The invention discloses macrocrystalline fused magnesia as well as a preparation method and a preparation device thereof. The preparation method comprises the following steps: preparing magnesite, carrying out primary selection, and optionally carrying out pretreatment; pressing the obtained material into material balls; calcining the material balls at high temperature, and cooling and crystallizing to obtain the macrocrystalline fused magnesia. The invention only needs one-time calcination, and does not need filler and transfer raw materials in the calcination process, thereby shortening the calcination time, reducing the energy consumption and improving the quality of the large-crystal fused magnesia.

Description

Macrocrystalline fused magnesia as well as preparation method and preparation device thereof

Technical Field

The invention relates to the technical field of refractory materials, in particular to macrocrystalline fused magnesia as well as a preparation method and a preparation device thereof.

Background

The magnesite can be calcined and melted at different temperatures to produce light-burned magnesia, heavy-burned magnesia and electric-fused magnesia, the main components of which are magnesia. The three products have the same basic chemical components except for different magnesia contents caused by different calcining temperatures and magnesite impurity contents, but have obvious differences in many physical and chemical properties.

The light burned magnesium is mainly used for animal feed and crop fertilizer, building material and decorative material, plastics, paint and adhesive, etc. The reburning magnesium is mainly used as refractory material in metallurgical industry for making magnesia brick, magnesia-chrome brick, magnesia-alumina brick, silicon-magnesia brick, metallurgical sand, metallurgical powder, etc. Fused magnesia is a stable basic magnesia refractory material, is an excellent high-temperature electrical insulating material, is an important raw material for manufacturing high-grade magnesia bricks, magnesia carbon bricks and unshaped refractory materials, and is widely applied to the fields of metallurgy, building materials, glass, petrifaction, cement, national defense and the like.

At present, light-burned magnesium is prepared by calcining at about 700 ℃ to 1100 ℃ in one step, and heavy-burned magnesium is prepared by calcining at about 1650 ℃ to 1800 ℃ in one step. The preparation process of the fused magnesia comprises two steps of calcination, and specifically comprises the steps of firstly carrying out light burning on magnesite to obtain light burning magnesium, and then smelting, melting and recrystallizing the light burning magnesium in an electric arc furnace to form the fused magnesia.

Therefore, the fused magnesia causes the defects of raw material waste, large energy consumption and long process time in the two-time calcining process. Therefore, a preparation method with low cost, short process flow and good product quality is needed.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides large-crystal fused magnesia and a preparation method and a device thereof. The method only needs one-time calcination, does not need filler and raw material transfer in the calcination process, shortens the calcination time, reduces the energy consumption, and improves the quality of the fused magnesia, thereby completing the invention.

In order to achieve the above object, the present invention provides, in a first aspect, a method for preparing macrocrystalline fused magnesia, comprising the steps of:

step 1, preparing magnesite, carrying out primary selection, and optionally carrying out pretreatment;

step 2, pressing the materials obtained by primary selection into material balls;

and 3, calcining the material balls at high temperature, and cooling and crystallizing to obtain the macrocrystalline fused magnesia.

In step 1 of the invention, the content of the primary selected magnesium oxide is more than 43 percent, and/or the pretreatment comprises screening and grinding.

In the step 2 of the invention, the obtained powder is pressed together with an additive, preferably pressed into pellets, the additive is preferably one or more of inorganic additives and/or organic additives, and the mass ratio of the additive to the powder is (1-20): 100.

In step 3 of the invention, the high temperature is more than 2200 ℃, preferably more than 2500 ℃, and the pellets are calcined at high temperature for one time; preferably, nitrogen or inert gas is introduced in a staged manner in the cooling crystallization process; preferably, the pellets are placed in a graphite crucible of a preparation device, and are calcined and cooled for crystallization.

In a second aspect, the present invention provides macrocrystalline fused magnesia produced according to the method of the first aspect.

In a third aspect, the present invention provides an apparatus for producing macrocrystalline fused magnesia, preferably for carrying out the method of the first aspect for producing macrocrystalline fused magnesia of the second aspect. The device comprises a lower cavity, a middle cylinder and an upper cover plate, wherein preferably, the bottom of the middle cylinder is connected with the top of the lower cavity.

The macrocrystalline fused magnesia as well as the preparation method and the preparation device thereof have the beneficial effects that:

(1) The method provided by the invention adopts staged introduction of nitrogen or inert gas, so that the temperature is rapidly reduced, the magnesium oxide and impurities in a molten state are effectively layered, and the quality of the fused magnesia can be improved;

(2) The method provided by the invention can obtain high-grade macrocrystalline fused magnesia without screening high-purity magnesite, thereby increasing the utilization rate of magnesite;

(3) The device provided by the invention can form a rapid cooling gradient for magnesium oxide in a molten state, so that the quality of macrocrystalline fused magnesia is improved, and the device can be used for producing macrocrystalline fused magnesia in different batches and has a wide application range.

Drawings

FIG. 1 is a schematic structural view of an apparatus for preparing macrocrystalline fused magnesia according to the present invention;

FIG. 2 is a photograph of a macrocrystalline fused magnesia prepared in example 1 of the present invention;

the reference numerals in fig. 1 are as follows:

1-lower cavity, 2-bottom guard plate, 3-graphite crucible, 4-middle cylinder, 5-lower heat insulation cage, 6-upper heat insulation layer, 7-upper cover plate, 8-air inlet, 9-air outlet, 10-lifting device, 11-electrode bar, 12-support plate.

Detailed Description

The following detailed description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings, will make the advantages and features of the invention easier to understand by those skilled in the art, and thus will clearly and clearly define the scope of the invention.

It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrases "comprising 8230; \8230;" comprise 8230; "do not exclude the presence of additional identical elements in any process, method, article, or apparatus that comprises the element.

At present, the preparation process of fused magnesite generally comprises two steps of calcining, firstly, magnesite is lightly calcined in a rotary calciner or a light-calcined kiln to obtain light-calcined magnesium; then transferring the light-burned magnesium to an electric arc furnace to be smelted, melted and crystallized to form the fused magnesia. Therefore, the raw materials are wasted in the transfer process, and the two times of calcination cause low production process efficiency, high energy consumption and serious environmental pollution.

In order to solve the problems, the invention provides a preparation method of large-crystal fused magnesia. The method only needs one-time calcination, and does not need filler and transfer raw materials in the calcination process, thereby shortening the calcination time, reducing the energy consumption and improving the quality of the large-crystal fused magnesia.

In a first aspect, the present invention provides a method for preparing macrocrystalline fused magnesia, which mainly comprises the following steps:

step 1, preparing magnesite, carrying out primary selection, and optionally carrying out pretreatment.

Magnesite and anhydrous carbonate minerals such as calcite and dolomite have similar crystal structures and similar cation radiuses, can form wide isomorphism, have similarity in physical properties and are often closely symbiotic or mixed together.

Therefore, the magnesite is firstly primarily selected to remove impurities in the magnesite, so that the grade of the magnesite is improved.

In one embodiment of the present invention, in step 1, the primary selected magnesium oxide content is greater than 43%, and/or

The pre-treatment comprises sieving and grinding, preferably grinding the magnesite into a powder.

For example, magnesite may be initially selected to have a magnesium oxide content greater than 43%, preferably greater than 45%, more preferably greater than 46%, and then screened and ground after initial selection.

In the present invention, the magnesite screening method is not particularly limited. For example, magnesite can be screened by flotation. The main process of the flotation method comprises the steps of firstly carrying out reverse flotation by using a collector dodecylamine cation and a foaming agent No. 2 oil (the main component is terpineol), then carrying out direct flotation by using inhibitor water glass, sodium hexametaphosphate, a collector fatty acid and a foaming agent sodium oleate, and screening magnesite with the magnesium oxide content of 44-47.5%.

In the invention, the magnesite is ground into powder of 3-280 meshes, preferably 10-150 meshes, which can help to obtain more compact and uniform pellets, so that the magnesite is easier to calcine and saves energy.

The specific process is that the magnesite is finely ground by a ball mill and graded by a grader, powder with the grain diameter of 3-280 meshes is collected by a dust collector and then enters a ball pressing system, and powder with the grain diameter not satisfying is returned to the ball mill to be continuously ground until the grain diameter of the powder is between 3-280 meshes.

And 2, pressing the material obtained in the step 1 into material balls.

In a preferred embodiment of the present invention, in step 2, the powder obtained in step 1 is pressed together with the additive, and preferably the powder and the additive are mixed and then pressed into pellets.

In the present invention, the pellets have a diameter of 10 to 50mm, preferably 20 to 40mm, which facilitates the calcination of the pellets and significantly shortens the melting time of the pellets.

Preferably, the additive is one or more of an inorganic additive and/or an organic additive,

the inorganic additive is preferably at least one of magnesium oxide, magnesium chloride and carbon, and the organic additive is preferably at least one of bio-based material, resin and paraffin.

In the invention, the additive is decomposed into water vapor and carbon monoxide (or carbon dioxide) at high temperature, so that holes are generated in the pellets, and the pellets are prevented from bursting; and simultaneously, oxygen in the air is absorbed in the decomposition process, so that the impurities, namely ferrous oxide, are prevented from being completely oxidized, and the quality (color) of the macrocrystalline fused magnesia is prevented from being damaged.

Preferably, the mass ratio of the additive to the powder is (1-20): 100.

According to researches, the mass ratio of the additive to the powder is more than 20, the pellets are easy to collapse when the additive is decomposed during pellet calcination, so that the pellets are bonded, a longer calcination time is required, and meanwhile, the generated water vapor and carbon monoxide (or carbon dioxide) have a certain flame retardant effect, so that the pellets are not completely calcined. When the mass ratio of the additive to the powder is less than 1 to 100, the effect of the additive is not significant, and therefore the mass ratio of the additive to the powder is (1 to 20): 100, preferably (5 to 15): 100, more preferably (10 to 15): 100, for example, 12.

More preferably, the additive is a mixture of a bio-based material and a resin; and/or the mass ratio of the bio-based material to the resin is (5-13): 1.

The bio-based material is a novel material which is prepared by taking renewable biomass, including crops, trees and other plants and residues and inclusions thereof as raw materials and adopting biological, chemical and physical means and the like.

In the present invention, the bio-based material is preferably konjac glucomannan and/or hydroxyethyl cellulose. The resin is preferably a phenolic resin and/or a diphenolylpropane glycidyl ether.

Researches show that when the bio-based material and the resin are selected from the materials, the bio-based material and the resin can be well bonded with powder, and meanwhile, the stability of material ball melting can be ensured in the calcining process, and local collapse is avoided.

Meanwhile, when the mass ratio of the bio-based material to the resin is (5-13): 1, preferably (6-11): 1, a relatively uniform pellet can be easily formed at one time, and the pellet does not locally collapse during the calcination process.

In the present invention, the high temperature is 2200 ℃ or higher, preferably 2500 ℃ or higher, preferably 2600 to 3400 ℃, more preferably 2800 to 3200 ℃; the calcination time is 6-15 h, preferably 8-12 h, under which the pellets can be completely melted and the magnesium carbonate is completely converted into magnesium oxide.

Preferably, the pellets are calcined at a high temperature without feeding and multiple times of calcination, so that the temperature stability and the pellet calcination uniformity can be ensured.

In a preferred embodiment of the present invention, in step 3, nitrogen or an inert gas is introduced during the cooling crystallization.

In the prior art, large-crystal fused magnesia is formed by natural cooling for 6 to 8 days in the environment. However, in this process, the cooling time is long, the utilization rate of the apparatus is reduced, oxygen and water vapor in the environment are contacted in the cooling crystallization process, and at a high temperature, ferrous oxide is easily oxidized into ferric oxide, which deteriorates the quality (color) of the macrocrystalline fused magnesia.

It is found through research that nitrogen or inert gas is introduced in the cooling crystallization process, so that gasified impurities can be removed, oxygen is removed, and oxidation of ferrous oxide is reduced, thereby the macrocrystalline fused magnesia is white (similar to white).

Preferably, nitrogen or inert gas is introduced in a staged manner; more preferably, the time for introducing nitrogen or inert gas in each stage is increased in sequence.

Researches show that in the cooling crystallization process, the purity, the crystal grain size and the structure compactness of the macrocrystalline fused magnesia obtained by suddenly reducing the cooling temperature can be greatly improved.

The invention adopts the step-by-step introduction of nitrogen or inert gas, so that the temperature is sharply reduced, the magnesium oxide and impurities in a molten state are effectively layered, the magnesium oxide crystals are rapidly precipitated under the impurities, and the impurities are precipitated in the final stage, thereby improving the quality of the large-crystal fused magnesia.

Preferably, the first stage is to continuously introduce nitrogen or inert gas for 12 to 18 hours, preferably 14 to 15 hours, stop and stand for 10 to 17 hours, preferably 13 to 15 hours; in the second stage, nitrogen or inert gas is continuously introduced for 16 to 20 hours, preferably 17 to 18 hours, then the reaction is stopped, and the mixture is kept stand for 16 to 19 hours, preferably 17 to 18 hours; the third stage is to continuously introduce nitrogen or inert gas for 24 to 36 hours, preferably 28 to 32 hours, stop and stand to room temperature.

Wherein, adopt above-mentioned stage time of ventilating, can guarantee to provide quick cooling gradient for the magnesium oxide crystal for impurity scatters on the grain boundary of macrocrystalline fused magnesia at last, improves macrocrystalline fused magnesia's purity and article looks.

In a preferred embodiment of the present invention, in step 3, the pellets are placed in a graphite crucible, and are calcined and cooled for crystallization.

Specifically, the apparatus used in step 3 may include:

the lower cavity is provided with a graphite crucible and a bottom protection plate at the bottom of the graphite crucible; optionally, a supporting plate fixedly connected with the lower cavity body is further arranged;

the bottom of the middle cylinder is connected with the top of the lower cavity, a heat insulation cage is arranged in the middle cylinder, and the graphite crucible is positioned inside the heat insulation cage; and

the bottom of the upper cover plate is connected with the top of the middle cylinder, and the upper cover plate is provided with an electrode bar, an air inlet and an air outlet.

In the first aspect, by using the method, high-grade macrocrystalline fused magnesia can be obtained without sieving high-purity magnesite, so that the utilization rate of the magnesite is increased.

In a second aspect, the present invention provides macrocrystalline fused magnesia. The macrocrystalline fused magnesia is produced according to the method for producing macrocrystalline fused magnesia according to the first aspect.

In a third aspect, the present invention provides an apparatus for producing macrocrystalline fused magnesia, preferably for carrying out the method of the first aspect for producing macrocrystalline fused magnesia of the second aspect. As shown in fig. 1, the device may mainly comprise a lower chamber 1, an intermediate cylinder 4 and an upper cover plate 7.

Wherein, the lower cavity 1 is provided with a graphite crucible 3, a bottom protection plate 2 at the bottom of the graphite crucible 3 and a support plate 12 fixedly connected with the lower cavity 1.

In the invention, the graphite crucible 3 is used for filling the material balls at one time, and the filling is not required to be continuously carried out in the calcining process, so the specification of the graphite crucible can be determined according to the actual quantity of the fused magnesia to be produced (the specification of the graphite crucible is different from 1# to 2500#, and the graphite crucibles with different specifications can be purchased or customized). In order to further protect the safety of the graphite crucible, the large-crystal fused magnesia prepared by the invention with a thickness of 10-20 mm can be constructed in the graphite crucible.

In the invention, a layer of coke or carbon block can be laid on the uppermost layer of the material ball to be used as an ignition agent or a combustion improver.

Since both the thermal conductivity and the electrical resistance of graphite are affected by temperature, for example, the resistivity is a negative value below 700 to 900K and a positive value above 900K, the thermal conductivity reaches a maximum value at a certain temperature, and the rest of the thermal conductivity is reduced, that is, the graphite has good thermal conductivity with anisotropy, the bottom protective plate 2 of the present invention is preferably graphite.

In a preferred embodiment of the present invention, the surface of the backplate 2 has a convex structure, and the convex structure is circular or polygonal.

In the present invention, the size of the bottom protection plate 2 is larger than that of the graphite crucible 3 and smaller than that of the support plate 12, that is, the graphite crucible 3 is completely placed on the bottom protection plate 2, and the bottom protection plate 2 is completely placed on the support plate 12. The bottom protective plate 2 is arranged to be a convex structure, and preferably, the convex structure is arranged unevenly, so that the graphite crucible 3 and the bottom protective plate 2 are in point contact, and the graphite crucible is cooled rapidly in the cooling process. For example, the projections are cylindrical with a height of 3 to 6mm and a diameter of 10 to 15 mm. The cylinder of this size both keeps graphite crucible's stability while, can make nitrogen gas or inert gas's interlude circulation again to realize the all-round cooling to graphite crucible.

In the present invention, the support plate 12 mainly functions to support the graphite crucible 3 and the bottom protection plate 2. The support plate 12 includes a steel frame for supporting, a metal plate disposed on the steel frame, and a heat insulating layer on the upper surface of the metal plate. The thickness of the heat insulation layer is 15-30 mm graphite.

In a preferred embodiment of the invention, an overflow channel is also provided in the lower chamber 1.

The overflow port channel is arranged to ensure the safety of the device, and whether liquid flows out or not is observed through the overflow port, so that whether the graphite crucible is intact or not is judged, and the normal operation of reaction is ensured.

Wherein, the bottom of the middle cylinder 4 is connected with the top of the lower cavity 1, a heat insulation cage is arranged in the middle cylinder 4, and the graphite crucible 3 is positioned in the heat insulation cage.

In a preferred embodiment of the present invention, the lower cavity 1 is connected to the middle cylinder 4 by a clamping groove or a bolt, so as to ensure that the lower cavity 1 can be separated from the middle cylinder 4, thereby facilitating the filling and discharging.

In a preferred embodiment of the invention, the insulation cage comprises a supporting steel frame and an insulation layer arranged inside the steel frame.

Wherein, set up thermal-insulated cage and can be in the ball melting stage, the stable temperature in the holding device can avoid the ball that melts earlier can not be because of the continuous heat dissipation cooling of device and the condensation crystallization.

Preferably, the thermal insulation cage is a split thermal insulation cage, which comprises an upper layer thermal insulation cage 6 and a lower layer thermal insulation cage 5, wherein, when the upper layer thermal insulation cage and the lower layer thermal insulation cage are closed, the top end of the lower layer thermal insulation cage 5 is higher than the bottom end of the upper layer thermal insulation cage 6.

Preferably, the lower ends of the upper and lower

thermal insulation cages

6 and 5 have annular protrusions protruding outward.

More preferably, the annular raised outer dimension of the upper insulation cage 6 is equal to the inner dimension of the lower insulation cage 5. Therefore, the upper and lower layers of heat insulation cages can be well contacted with each other, and the temperature of the melting process is kept.

More preferably, the internal dimensions of the lower insulating cage 5 are less than or equal to the dimensions of the bottom shield 2.

In the invention, the lower heat insulation cage 5 can be stably placed on the bottom protection plate 2 or sealed with the bottom protection plate 2 by utilizing the annular bulge of the lower heat insulation cage 5, and the upper heat insulation cage 6 can be accommodated in the lower heat insulation cage 5 by utilizing the annular bulge of the upper heat insulation cage 6 to form a stable heat insulation space, thereby being beneficial to melting of material balls.

Preferably, the upper insulation cage 6 comprises at least one layer of insulation and the lower insulation cage 5 comprises at least two layers of insulation. More preferably, 2 layers of 10-20 mm graphite are laid in the upper heat insulation cage, and 3 layers of 10-20 mm graphite are laid in the lower heat insulation cage.

Wherein, because in the melting process, need not to continue to add the material ball, guarantee the stability of temperature around graphite crucible 3 promptly and can make the material ball melt fast, keep the stability of electric current simultaneously, avoid the short circuit, and upper portion temperature is less than lower part temperature a little, does benefit to the upward migration of gaseous state impurity.

In a more preferred embodiment of the invention, the upper insulation cage 6 is fixed to the upper cover plate 7 and the lower insulation cage 5 is connected by a lifting device 10.

In the invention, the lower heat insulation cage 5 can move up and down through the lifting device 10, so that in the cooling crystallization process, the lower heat insulation cage 5 is lifted through the lifting device 10, and the lower heat insulation cage 5 is positioned at the bottom of the upper cover plate 1, thus the cooling space is an inner cavity of the whole device, the cooling space is enlarged, and the graphite crucible can be cooled by using nitrogen or inert gas more conveniently.

Wherein, the middle cylinder 4 is externally provided with a fixed bracket for fixing the whole device.

According to the invention, the bottom of the upper cover plate 7 is connected with the top of the middle cylinder 4, and the upper cover plate is provided with an electrode rod 11, an air inlet 8 and an air outlet 9.

Specifically, the upper cover plate 7 can fix the electrode bar 11 and the lifting device of the lower-layer heat insulation cage 5, and can also be used for heat preservation and heat insulation to avoid heat loss.

The invention also comprises an electrode lifting device, a transformer and accessories thereof, structures and equipment such as high-voltage control, low-voltage control, a large-current circuit and the like, and can be installed by adopting a conventional scheme according to actual conditions to realize basic functions.

In the present invention, the electrode rods 11 are three graphite electrode rods. The three graphite electrode rods form a triangle, wherein the size of the triangle changes along with the change of the specification of the graphite crucible, and the three graphite electrode rods move up and down by using the electrode lifting device, so that the three graphite electrodes can be inserted into the material balls of the graphite crucible.

Preferably, the exhaust port 9 is communicated with an exhaust system, so that the gas in the device can be extracted and exhausted in real time; the exhaust system extracts the gas and then carries out recovery processing.

More preferably, a dust bag for recycling is installed at the outlet of the exhaust system, and fine material particles or dust are adsorbed and recycled by the dust bag to prevent the fine material particles or dust from being directly discharged into the air.

More preferably, the waste gas is introduced into a water cooling system before entering the dust removal bag, the gas is cooled by the water cooling system, and then the gas is introduced into the dust removal bag; after the cooling water exchanges heat with the waste gas, the temperature is increased, and the cooling water can be used for heating.

In a preferred embodiment of the present invention, the lower cavity 1, the middle cylinder 4 and the upper cover plate 7 are all built with linings of 10-50 mm in thickness, and the linings are made of fused magnesia (which can be macrocrystalline fused magnesia prepared by the present invention), so that the safety of the device can be ensured.

In a preferred embodiment, the outer surface of the intermediate cylinder 4 is covered with a thermoelectric power generation sheet assembly for converting heat on the outer surface of the intermediate cylinder 4 during cooling crystallization into electric energy.

In this embodiment, thermoelectric generation piece subassembly hot junction and cold junction have the temperature difference with the surface and the external environment contact of middle barrel 4 respectively to form the thermoelectric force at thermoelectric generation piece subassembly both ends, thereby turn into the electric energy with heat energy, and can be through the outside output electric energy of wire, supply power to other circuits.

More preferably, the cold end of the thermoelectric generation chip assembly is coated with heat conductive silicone grease, so that the cooling time can be shortened.

In another preferred embodiment, the outer surface of the middle cylinder 4 and/or the lower part of the support plate 12 are further provided with a water cooling system for reducing the cooling time in the cooling crystallization process.

In the invention, the water cooling system comprises a cooling pipeline and a driving device. The driving device is used for blowing cooling water into the cooling pipeline and providing power for the circulating flow of the cooling water.

For example, the cooling pipeline can comprise a plurality of spiral coils connected in parallel, so that the stroke of cooling water in each spiral coil is reduced, the overall flow rate of the cooling water is increased, and the cooling effect is improved.

Alternatively according to the invention, the cooling ducts may be vertical ducts, comprising an upper collar at the top and a lower collar at the bottom; a plurality of vertical pipes are arranged between the upper annular pipe and the lower annular pipe and can be arranged in parallel.

The operation of the manufacturing apparatus of the present invention is described in detail below with reference to fig. 1:

before the furnace starts to work, the lower cavity is firstly moved out, the material balls are filled in the graphite crucible, and are compacted and compacted, then a layer of coke or carbon block is paved on the uppermost layer of the material balls, and the paving range of the coke or carbon block is within the triangular range formed by the three graphite electrode rods, so that a circuit forms a loop after arcing. And then the lower cavity and the middle cylinder are connected by a clamping groove or a bolt, so that the lower cavity and the middle cylinder are fixedly installed. And closing the air inlet of the upper cover plate, opening the air outlet, and descending the three graphite electrode rods to enable the three graphite electrode rods to be inserted into the material ball. Then entering into an arc starting stage and a melting stage in sequence. And finally, opening an air inlet in a cooling stage, lifting a lower-layer heat insulation cage, introducing nitrogen or inert gas in a staged manner until the temperature is cooled to room temperature, separating the lower cavity and the middle barrel by utilizing a clamping groove or a bolt, moving out the lower cavity, and crushing the magnesium lump in the graphite crucible to obtain the macrocrystalline fused magnesia.

According to the invention, the device can form a rapid cooling gradient for magnesium oxide in a molten state, so that the quality of large-crystal fused magnesia is improved. The device can produce different batches of large-crystal fused magnesia and has wide application range.

For further understanding of the present invention, the technical solutions of the present invention are described below with reference to the following examples, and the scope of the present invention is not limited by the following examples.

Example 1

Primarily selecting 300kg of magnesite with the magnesium oxide content of 44-47.5%; grinding magnesite into powder of 10-150 meshes;

adding 33kg of hydroxyethyl cellulose and 3kg of phenolic resin into the powder, uniformly mixing and pressing into material balls with the diameter of 20-40 mm.

The pellets are placed in a graphite crucible 3 (specification # 400) of the apparatus for preparation of the present invention, and the pellets are compacted and compacted, and then a layer of coke is laid on the uppermost layer of the pellets.

The clamping groove is used for connecting the lower cavity 1 and the middle barrel 4, so that the lower cavity and the middle barrel are fixedly installed.

The air inlet 8 of the upper cover plate 7 is closed, the air outlet 9 is opened, and the three graphite electrode rods are descended to be inserted into the material ball.

The calcination was continued for about 9h at 3200 deg.C.

After the calcining and sintering, opening the air inlet 8, lifting the lower-layer heat insulation cage 5, continuously introducing nitrogen for about 15 hours, stopping, and standing for about 14 hours; then continuously introducing nitrogen for about 18 hours, stopping introducing the nitrogen, and standing for about 18 hours; and finally, continuously introducing nitrogen for about 32 hours, stopping introducing the nitrogen, and standing to room temperature.

The lower cavity 1 and the middle cylinder 4 are separated by using a clamping groove, the lower cavity 1 is moved out, the magnesium lump in the graphite crucible 3 is crushed, white macrocrystalline fused magnesia is obtained, the magnesium oxide crystal grains are uniform, the size of the magnesium oxide crystal grains is approximately between 10 and 30mm, and a real object photo of any one of the macrocrystalline fused magnesia is shown in figure 2.

The obtained macrocrystalline fused magnesia has the determination that the magnesia content is about 98.31 percent, the iron oxide and ferrous oxide content is about 0.44 percent, the alumina content is about 0.10 percent, the silica content is about 0.30 percent, the calcium oxide content is about 0.80 percent, the ignition loss is about 0.05 percent, and the bulk density is about 3.50g/cm ³ 。

Comparative example 1

The preparation is carried out as in example 1, except that after the continuous energization calcination is carried out for 9 hours at 3200 ℃, the air inlet 8 is opened, the lower-layer heat insulation cage 5 is lifted, the lower-layer heat insulation cage is naturally cooled for a period of time, then the lower cavity 1 and the middle cylinder 4 are separated, the lower cavity 1 is removed, the lower cavity is naturally cooled, the magnesium lumps in the graphite crucible 3 are crushed after the lower cavity is cooled to the room temperature, and the light red crystalline fused magnesia is obtained. The magnesia content of the resulting magnesite was determined to be about 92.4%, the iron oxide content was determined to be about 1.85%, the alumina content was determined to be about 1.21%, the silica content was determined to be about 2.08%, the calcium oxide content was determined to be about 2.31%, the burn-off was determined to be about 0.15%, and the bulk density was determined to be about 3.27g/cm ³ 。

The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to limit the invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention.

Claims

1. A method for preparing macrocrystalline fused magnesia is characterized by comprising the following steps:

step 1, preparing magnesite, carrying out primary selection, and carrying out pretreatment, wherein the pretreatment comprises screening and grinding, and the magnesite is ground into powder;

step 2, pressing the obtained material into material balls;

step 3, calcining the material balls at high temperature, and cooling and crystallizing to obtain macrocrystalline fused magnesia;

in the step 2, the process is carried out,

the powder obtained in the step 1 and the additive are pressed together, the powder and the additive are mixed firstly and then pressed into material balls,

the mass ratio of the additive to the powder is (1-20) to 100;

the additive is a mixture of a bio-based material and a resin; the mass ratio of the bio-based material to the resin is (5-13): 1;

in the step 3, the process is carried out,

the high temperature is above 2200 ℃;

calcining the pellets at high temperature for the first time;

nitrogen or inert gas is introduced in a staged manner in the cooling crystallization process, the first stage is stopped after 12 to 18h of continuous introduction, and the mixture is kept stand for 10 to 17h; the second stage is that the mixture is continuously introduced for 16 to 20h, then the mixture is stopped, and the mixture is kept still for 16 to 19h; and the third stage is that the reaction is stopped after continuously introducing the mixture for 24 to 36h, and the mixture is kept stand to room temperature.

2. A process according to claim 1, characterised in that in step 1 magnesite is subjected to a preliminary selection, and magnesite with a magnesium oxide content of more than 43% is selected.

3. The method according to claim 1, wherein the high temperature is 2500 ℃ or higher in step 3.

4. The method as claimed in claim 3, wherein the high temperature in step 3 is 2600 to 3400 ℃.

5. The method according to claim 1, wherein in the step 3, the first stage is stopped after continuously introducing for 14 to 15h, and the mixture is left for 13 to 15h; in the second stage, the mixture is continuously introduced for 17 to 18h and then is stopped, and the mixture is kept stand for 17 to 18h; and the third stage is that the reaction is stopped after continuously introducing the mixture for 24 to 36h, and the mixture is kept stand to room temperature.

6. The method as claimed in any one of claims 1 to 5, wherein in step 3, the pellets are placed in a graphite crucible, calcined and cooled for crystallization.

7. The method according to claim 6, wherein in step 3, the preparation apparatus used comprises, in addition to the graphite crucible: lower cavity, middle barrel and upper cover plate.