A process for producing high-strength alpha gypsum powder using discarded ceramic gypsum molds

Abstract

The invention belongs to the field of waste gypsum recycling, and specifically relates to a process for producing high-strength alpha gypsum powder by using waste ceramic gypsum molds. The process specifically comprises the following steps: after crushing, grinding and screening the recycled waste ceramic gypsum molds to remove impurities, water is added to prepare slurry of a certain concentration, and then primary crystallization and secondary crystallization are respectively performed, and the slurry after crystallization is centrifuged and dried to obtain high-strength alpha gypsum powder, wherein yttrium oxide is used as a crystallization agent in the secondary crystallization, which can promote the growth rate of alpha-gypsum crystals in the gypsum slurry, and can stabilize the generated alpha-gypsum crystals so that the crystal form will not be transformed after dehydration and cooling, so as to form 99.5% alpha-hemihydrate gypsum, and realize industrialized production.

Description

Technical Field

[0001] The invention belongs to the field of waste gypsum recycling, and in particular relates to a process for producing high-strength alpha gypsum powder by utilizing waste ceramic gypsum molds. Background Art

[0002] When α-hemihydrate gypsum mold is used, it will go through a long-term hydration process of water absorption and dehydration. A supersaturated solution of dihydrate gypsum will appear to form dihydrate gypsum crystal nuclei → dihydrate gypsum crystal nuclei continue to grow → dihydrate gypsum crystallizes → SO4 -2 and Ca +2 Continue to dissolve and diffuse to the surface of dihydrate gypsum crystals → eventually dihydrate gypsum is basically formed and cannot be used. These gypsums that cannot be used anymore are waste gypsum.

[0003] At present, all ceramic production areas directly discard the waste gypsum, and the amount is extremely large. In the ceramic production area of ​​Dehua, Fujian alone, more than 50,000 tons of waste gypsum are produced each year. The liquid phase high-strength α-hemihydrate gypsum production process can be used to make waste gypsum into high-strength or even ultra-high-strength α-gypsum crystal particles. However, after dehydration and cooling by this process, the crystal form of the gypsum is reversed, and stable α-hemihydrate gypsum cannot be obtained. The final α-hemihydrate gypsum is less than 30%, so it cannot be used industrially and needs further improvement. Summary of the invention

[0004] The purpose of the present invention is to overcome the disadvantages of the prior art and provide a process for producing high-strength alpha gypsum powder by using waste ceramic gypsum molds.

[0005] The present invention adopts the following technical solution:

[0006] A process for producing high-strength alpha gypsum powder by using waste ceramic gypsum molds, specifically comprising the following steps:

[0007] Step 1, crushing, grinding and screening the recycled waste ceramic plaster mold to remove impurities;

[0008] Step 2, adding the waste gypsum powder obtained in step 1 into a premixing tank, adding water, and mixing at a temperature of 55-65° C. to form a slurry with a concentration of 25-35%;

[0009] Step 3, pumping the slurry into the first crystallization tank three times by using a slurry pump for the first crystallization;

[0010] Step 4, pumping the mixture obtained in step 3 into a second crystallization tank, adding yttrium oxide, and performing secondary crystallization at 135° C. and 0.32 MPa. When the material level in the second crystallization tank reaches 88-92%, standing for 10-20 minutes;

[0011] Step 5, sending the gypsum slurry discharged from the second crystallization tank into a centrifugal separator, removing water from the slurry, and then sending it into a dryer for drying to obtain high-strength α gypsum powder.

[0012] Furthermore, in step 4, the weight ratio of the added amount of yttrium oxide to the slurry is 0.1-1:1000.

[0013] Furthermore, in step 3, the first crystallization environment of the slurry is as follows: reaction temperature 100-160°C, reaction pressure 0.3-0.5MPa, reaction time 10-20min; the weight ratio of the added amount of the crystallization agent to the slurry is 0.1-1:1000.

[0014] Furthermore, the crystal-changing agent is yttrium oxide.

[0015] Furthermore, in step 5, when the centrifuge is working, the temperature of the slurry is not lower than 105° C., and the moisture content of the material after centrifugal separation is not higher than 8%.

[0016] Furthermore, in step 5, the drying temperature is 100-120° C., and the moisture content of the obtained high-strength α gypsum powder does not exceed 0.2%.

[0017] From the above description of the present invention, it can be seen that compared with the prior art, the beneficial effects of the present invention are as follows: the present application limits the method for processing waste ceramic gypsum molds, uses yttrium oxide as a crystal-transforming agent, and performs two crystal-transforming operations on the recycled gypsum slurry. Among them, the use of yttrium oxide as a crystal-transforming agent can promote the growth rate of α-gypsum crystals in the gypsum slurry, and can stabilize the generated α-gypsum crystals so that they will not undergo crystal transformation after dehydration and cooling, so as to form 99.5% α-hemihydrate gypsum and realize industrial production. DETAILED DESCRIPTION

[0018] The present invention is further described below through specific implementation modes.

[0019] A process for producing high-strength alpha gypsum powder by using waste ceramic gypsum molds, specifically comprising the following steps:

[0020] Step 1, crushing, grinding and screening the recycled waste ceramic plaster mold to remove impurities;

[0021] Step 2, adding the waste gypsum powder obtained in step 1 into a premixing tank, adding water, and mixing at a temperature of 55-65° C. to form a slurry with a concentration of 25-35%;

[0022] Step 3, pumping the slurry into the first crystallization tank three times with a slurry pump for the first crystallization, wherein the reaction temperature is 100-160° C., the reaction pressure is 0.3-0.5 MPa, and the reaction time is 10-20 min; the weight ratio of the added amount of yttrium oxide to the slurry is 0.1-1:1000;

[0023] Step 4, pumping the mixture obtained in step 3 into a second crystallization tank, adding yttrium oxide, and performing secondary crystallization at 135° C. and 0.32 MPa. When the material level in the second crystallization tank reaches 88-92%, standing for 10-20 minutes, wherein the weight ratio of the added amount of yttrium oxide to the slurry is 0.1-1:1000;

[0024] Step 5, sending the gypsum slurry discharged from the second crystallization tank into a centrifuge, and under the action of hot air, maintaining the temperature of the slurry not lower than 105°C, removing water from the slurry so that the moisture content of the slurry is not higher than 8%, and then sending it into a dryer and drying it at a temperature of 100-120°C to obtain high-strength α gypsum powder with a moisture content not exceeding 0.2%.

[0025] Example 1

[0026] A process for producing high-strength alpha gypsum powder by using waste ceramic gypsum molds, specifically comprising the following steps:

[0027] Step 1, crushing, grinding and screening the recycled waste ceramic plaster mold to remove impurities;

[0028] Step 2, adding the waste gypsum powder obtained in step 1 into a premixing tank, adding water, and mixing at a temperature of 55° C. to form a slurry with a concentration of 35%;

[0029] Step 3, pumping the slurry into the first crystallization tank three times by a slurry pump for the first crystallization, wherein the reaction temperature is 100° C., the reaction pressure is 0.3 MPa, and the reaction time is 20 min; the weight ratio of the added amount of yttrium oxide to the slurry is 0.1:1000;

[0030] Step 4, pumping the mixture obtained in step 3 into a second crystallization tank, adding yttrium oxide, and performing secondary crystallization at 135° C. and 0.32 MPa. When the material level in the second crystallization tank reaches 88%, standing for 10 minutes, wherein the weight ratio of the added amount of yttrium oxide to the slurry is 1:1000;

[0031] Step 5, sending the gypsum slurry discharged from the second crystallization tank into a centrifuge, and under the action of hot air, maintaining the temperature of the slurry not lower than 105°C, removing water from the slurry so that the moisture content of the slurry is not higher than 8%, and then sending it into a dryer and drying it at a temperature of 100°C to obtain high-strength α gypsum powder with a moisture content not exceeding 0.2%.

[0032] Example 2

[0033] A process for producing high-strength alpha gypsum powder by using waste ceramic gypsum molds, specifically comprising the following steps:

[0034] Step 1, crushing, grinding and screening the recycled waste ceramic plaster mold to remove impurities;

[0035] Step 2, adding the waste gypsum powder obtained in step 1 into a premixing tank, adding water, and mixing at a temperature of 65° C. to form a slurry with a concentration of 25%;

[0036] Step 3, pumping the slurry into the first crystallization tank three times by a slurry pump for the first crystallization, wherein the reaction temperature is 160° C., the reaction pressure is 0.5 MPa, and the reaction time is 10 min; the weight ratio of the added amount of yttrium oxide to the slurry is 1:1000;

[0037] Step 4, pumping the mixture obtained in step 3 into a second crystallization tank, adding yttrium oxide, and performing secondary crystallization at 135° C. and 0.32 MPa. When the material level in the second crystallization tank reaches 92%, standing for 20 minutes, wherein the weight ratio of the added amount of yttrium oxide to the slurry is 1:1000;

[0038] Step 5, sending the gypsum slurry discharged from the second crystallization tank into a centrifuge, and under the action of hot air, maintaining the temperature of the slurry not lower than 105°C, removing water from the slurry so that the moisture content of the slurry is not higher than 8%, and then sending it into a dryer and drying it at a temperature of 120°C to obtain high-strength α gypsum powder with a moisture content not exceeding 0.2%.

[0039] Example 3

[0040] A process for producing high-strength alpha gypsum powder by using waste ceramic gypsum molds, specifically comprising the following steps:

[0041] Step 1, crushing, grinding and screening the recycled waste ceramic plaster mold to remove impurities;

[0042] Step 2, adding the waste gypsum powder obtained in step 1 into a premixing tank, adding water, and mixing at a temperature of 60° C. to form a slurry with a concentration of 30%;

[0043] Step 3, pumping the slurry into the first crystallization tank three times with a slurry pump for the first crystallization, wherein the reaction temperature is 130° C., the reaction pressure is 0.4 MPa, and the reaction time is 15 min; the weight ratio of the added amount of yttrium oxide to the slurry is 0.65:1000;

[0044] Step 4, pumping the mixture obtained in step 3 into a second crystallization tank, adding yttrium oxide, and performing secondary crystallization at 135° C. and 0.32 MPa. When the material level in the second crystallization tank reaches 90%, standing for 15 minutes, wherein the weight ratio of the added amount of yttrium oxide to the slurry is 0.72:1000;

[0045] Step 5, the gypsum slurry discharged from the second crystallization tank is sent to a centrifuge, and under the action of hot air, the temperature of the slurry is maintained at not less than 105°C, and the water in the slurry is removed so that the moisture content of the slurry is not higher than 8%, and then sent to a dryer and dried at a temperature of 110°C to obtain high-strength α gypsum powder with a moisture content not exceeding 0.2%.

[0046] Comparative Example 1

[0047] A process for producing high-strength alpha gypsum powder by using waste ceramic gypsum molds, specifically comprising the following steps:

[0048] Step 1, crushing, grinding and screening the recycled waste ceramic plaster mold to remove impurities;

[0049] Step 2, adding the waste gypsum powder obtained in step 1 into a premixing tank, adding water, and mixing at a temperature of 60° C. to form a slurry with a concentration of 30%;

[0050] Step 3, pumping the slurry into the first crystallization tank three times with a slurry pump for the first crystallization, wherein the reaction temperature is 130° C., the reaction pressure is 0.4 MPa, and the reaction time is 15 min; the weight ratio of the added amount of magnesium sulfate to the slurry is 0.65:1000;

[0051] Step 4, pumping the mixture obtained in step 3 into a second crystallization tank, adding magnesium sulfate, and performing secondary crystallization at 135° C. and 0.32 MPa. When the material level in the second crystallization tank reaches 90%, standing for 15 minutes, wherein the weight ratio of the added amount of magnesium sulfate to the slurry is 0.72:1000;

[0052] Step 5, sending the gypsum slurry discharged from the second crystallization tank into a centrifuge, and under the action of hot air, maintaining the temperature of the slurry not lower than 105°C, removing water from the slurry so that the moisture content of the slurry is not higher than 8%, and then sending it into a dryer and drying it at a temperature of 110°C to obtain gypsum powder with a moisture content not exceeding 0.2%.

[0053] Comparative Example 2

[0054] A process for producing high-strength alpha gypsum powder by using waste ceramic gypsum molds, specifically comprising the following steps:

[0055] Step 1, crushing, grinding and screening the recycled waste ceramic plaster mold to remove impurities;

[0056] Step 2, adding the waste gypsum powder obtained in step 1 into a premixing tank, adding water, and mixing at a temperature of 60° C. to form a slurry with a concentration of 30%;

[0057] Step 3, pumping the slurry into the first crystallization tank three times by a slurry pump for the first crystallization, wherein the reaction temperature is 130° C., the reaction pressure is 0.4 MPa, and the reaction time is 15 min; the weight ratio of the added amount of succinic acid to the slurry is 0.65:1000;

[0058] Step 4, pumping the mixture obtained in step 3 into a second crystallization tank, adding succinic acid, and performing secondary crystallization at 135° C. and 0.32 MPa. When the material level in the second crystallization tank reaches 90%, standing for 15 minutes, wherein the weight ratio of the amount of succinic acid added to the slurry is 0.72:1000;

[0059] Step 5, sending the gypsum slurry discharged from the second crystallization tank into a centrifuge, and under the action of hot air, maintaining the temperature of the slurry not lower than 105°C, removing water from the slurry so that the moisture content of the slurry is not higher than 8%, and then sending it into a dryer and drying it at a temperature of 110°C to obtain gypsum powder with a moisture content not exceeding 0.2%.

[0060] The gypsum powder prepared in Examples 1-3 and Comparative Examples 1-2 was tested accordingly to obtain the following data, see Table 1 for details.

[0061] Table 1

[0062] project Tensile strength after drying / MPa Compressive strength after drying / MPa α-Gypsum crystal conversion rate / % Example 1 7.0 56 99.5 Example 2 7.0 55 99.6 Example 3 7.2 58 99.8 Comparative Example 1 2.9 24 35.6 Comparative Example 2 3.2 27 42.5

[0063] It can be seen from the above table that the present application limits the treatment method of waste ceramic gypsum molds, uses yttrium oxide as a crystal-transforming agent, and performs two crystal-transforming operations on the recovered gypsum slurry. Among them, the use of yttrium oxide as a crystal-transforming agent can promote the growth rate of α-gypsum crystals in the gypsum slurry, and can stabilize the generated α-gypsum crystals so that they will not undergo crystal transformation after dehydration and cooling, so as to form 99.5% α-hemihydrate gypsum and realize industrial production.

[0064] The above description is only a preferred embodiment of the present invention, and therefore cannot be used to limit the scope of implementation of the present invention. That is, equivalent changes and modifications made according to the application scope of the present invention and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A process for producing high-strength alpha gypsum powder using discarded ceramic gypsum molds, characterized in that: The specific steps include: Step 1, crushing, grinding and screening the recycled waste ceramic plaster mold to remove impurities; Step 2, adding the waste gypsum powder obtained in step 1 into a premixing tank, adding water, and mixing at a temperature of 55-65° C. to form a slurry with a concentration of 25-35%; Step 3, pumping the slurry into the first crystallization tank three times by using a slurry pump for the first crystallization; Step 4, pump the slurry obtained in step 3 into the second crystallization tank, add yttrium oxide, and perform secondary crystallization at 135° C. and 0.32 MPa. When the material level in the second crystallization tank reaches 88-92%, stand for 10-20 minutes; Step 5, sending the gypsum slurry discharged from the second crystallization tank into a centrifugal separator, removing water from the slurry, and then sending it into a dryer for drying to obtain high-strength α gypsum powder; In step 3, the first crystallization environment of the slurry is as follows: reaction temperature 100-160°C, reaction pressure 0.3-0.5MPa, reaction time 10-20min; the weight ratio of the added amount of the crystallization agent to the slurry is 0.1-1:1000; the crystallization agent is yttrium oxide.

2. The process for producing high-strength α-gypsum powder by using waste ceramic gypsum molds according to claim 1, characterized in that: In step 4, the weight ratio of the added amount of yttrium oxide to the slurry is 0.1-1:1000.

3. The process for producing high-strength α-gypsum powder by using waste ceramic gypsum molds according to claim 1, characterized in that: In step 5, when the centrifuge is working, the temperature of the slurry is not lower than 105° C., and the moisture content of the material after centrifugal separation is not higher than 8%.

4. The process for producing high-strength alpha gypsum powder using waste ceramic gypsum molds according to claim 1, characterized in that: In step 5, the drying temperature is 100-120° C., and the moisture content of the obtained high-strength α gypsum powder does not exceed 0.2%.