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CN-121591219-B - Method for preparing low-calcium silicate by using fly ash and coal gangue

CN121591219BCN 121591219 BCN121591219 BCN 121591219BCN-121591219-B

Abstract

The invention provides a method for preparing low-calcium silicate by utilizing fly ash and coal gangue, which relates to the technical field of building materials, and comprises the steps of taking a sodium silicate solution as a raw material, increasing the concentration of SiO 2 of the sodium silicate solution to 130-200 g/L, adjusting the modulus to 2-3.5, preheating a diluted solution, reacting with lime milk, controlling the mole ratio of SiO 2 /CaO, stirring for 1-6 hours, standing and curing for 0.5-12 hours, introducing CO 2 gas to carbonize until the pH value is reduced to 8.5-9.8, filtering, washing and drying to obtain the low-calcium silicate, optionally adding an auxiliary agent consisting of hydroxyapatite nanowires, mesoporous silica, nano cerium oxide and the like before carbonization, buffering the pH reduction and improving the structure, and the obtained low-calcium silicate has lower Ca/Si mole ratio, better water content and excellent performance and is suitable for the fields of papermaking fillers and the like.

Inventors

  • YE WENSHENG
  • ZHANG ZHANJUN
  • GAO PEIJUN
  • ZHAO FAN

Assignees

  • 鄂尔多斯市蒙泰铝业有限责任公司

Dates

Publication Date
20260512
Application Date
20260128

Claims (7)

  1. 1. A method for preparing low-calcium type calcium silicate by using fly ash and/or coal gangue, which is characterized by comprising the following steps: (1) Providing a sodium silicate stock solution and a silicon supplementing raw material, wherein the sodium silicate stock solution is from an alkaline desilication process of coal ash and/or coal gangue, and the silicon supplementing raw material is the coal ash and/or the coal gangue; (2) Mixing the sodium silicate stock solution with a silicon supplementing raw material, adding alkali, heating to 95-100 ℃ for reaction for 2-6 hours, and filtering to obtain a solution A, wherein the concentration of SiO 2 in the solution A is 130-200 g/L, the concentration of Na 2 O is 50-75 g/L, and the modulus is 2.0-3.5; (3) Adding deionized water into the solution A to dilute the solution A until the concentration of SiO 2 is 50-160 g/L, and preheating the solution A to 75-95 ℃; (4) Preparing lime milk, wherein the concentration of the lime milk is 40-150 g/L; (5) Mixing the preheated solution A with lime milk, wherein the mol ratio of SiO 2 to CaO is 2:1-12:1, and stirring and reacting for 1-6 hours at 75-95 ℃ to obtain reaction slurry; (6) Standing and curing the reaction slurry at 75-95 ℃ for 0.5-12 hours to obtain cured slurry; (7) Introducing CO 2 gas into the cured slurry until the pH of the system is reduced to 8.5-9.8, so as to obtain carbonized slurry; (8) Filtering the carbonized slurry, washing a filter cake with hot water, and then drying to obtain the low-calcium silicate.
  2. 2. The method for preparing low-calcium silicate by using fly ash and/or gangue according to claim 1, wherein the alkali concentration is adjusted in the step (2) by adding sodium hydroxide or sodium hydroxide solution.
  3. 3. The method for preparing low-calcium silicate by using fly ash and/or coal gangue according to claim 1, wherein the SiO 2 content of the silicon-supplementing raw material in the step (2) is 45% -52%, and the raw material is dried and ground, and the flow rate of CO 2 gas is 0.4-0.5L/min and the stirring speed is 150 rpm in the step (7).
  4. 4. The method for preparing low-calcium silicate by using fly ash and/or gangue according to claim 1, wherein in the step (7), the carbonization process is performed by monitoring the pH value with an on-line pH meter, and stopping aeration when the pH is lowered to 9.2, 9.8 or 8.5.
  5. 5. The method for preparing low-calcium silicate by using fly ash and/or coal gangue according to claim 1, wherein the washing in the step (8) is repeated by using hot deionized water at 60 ℃ until no white precipitate is generated by dropwise adding 0.1M silver nitrate solution after the washing solution is acidified by dilute nitric acid, which indicates that chloride ions are removed, and the drying in the step (8) is carried out for 12 hours at 105 ℃, and the washing solution is ground and sieved by a 200-mesh sieve.
  6. 6. The method for preparing low-calcium silicate by using fly ash and/or coal gangue according to claim 1, wherein the method further comprises the step of adding an auxiliary agent between the steps (6) and (7), wherein the addition amount of the auxiliary agent is 3% -5% of the mass of the solution A, the auxiliary agent is stirred for 30 minutes at 150: rpm, the auxiliary agent preparation raw materials comprise 10 parts of hydroxyapatite nanowires, 3 parts of mesoporous silica, 1 part of nano cerium oxide, 2 parts of sodium polyacrylate and 1 part of polyvinylpyrrolidone by weight, and the preparation method of the auxiliary agent comprises the steps of preserving the heat of the hydroxyapatite nanowire powder and the mixed solution A containing the mesoporous silica and the nano cerium oxide for 6 hours at the pH of 10.0, 130 ℃ and 0.3: MPa, cooling, shearing, dispersing and spray drying.
  7. 7. The method for preparing low-calcium silicate by using fly ash and/or coal gangue according to claim 6, wherein the air inlet temperature of spray drying is 200 ℃, the air outlet temperature is 90 ℃, the feeding pump speed is 6 mL/min, and the compressed air flow rate is 600L/h.

Description

Method for preparing low-calcium silicate by using fly ash and coal gangue Technical Field The invention relates to the technical field of building materials, in particular to a method for preparing low-calcium silicate by using fly ash and coal gangue. Background Fly ash and gangue are bulk solid wastes generated in the coal exploitation and utilization process, and the stockpiling of the fly ash and the gangue occupies land and can cause dust emission and groundwater pollution. In the recycling of solid waste, sodium silicate solution can be extracted by treating fly ash or coal gangue by an alkaline method, and then sodium hydroxide is recovered by lime milk causticization, and meanwhile, a calcium silicate byproduct is generated. However, the calcium silicate produced by the traditional process is mainly a high-calcium product with a SiO 2/CaO molar ratio of about 1:1, and has low bulk density, high water content, coarse granularity, general whiteness and high pH value. In practical application scenes, for example, a solid waste treatment center of a certain power plant, the calcium silicate has low bulk density, the transportation and stacking cost accounts for more than 30% of the product value, the economic transportation radius is usually not more than 100 km, meanwhile, when the calcium silicate is used as a papermaking filler or a polymer material additive, the calcium silicate needs to be additionally added with an acid agent for neutralization until the pH value is less than 10, the treatment cost is increased by about 15-20%, and the high-value application of the calcium silicate is severely limited. Therefore, developing a method for directly producing low-calcium silicate to increase the density of the product and reduce the water content and pH value is an urgent need in the industry. Disclosure of Invention The invention aims to provide a method for preparing low-calcium silicate by using fly ash and coal gangue, which solves the problems of low product bulk density, high water content, large granularity, overhigh pH value and the like caused by high-calcium silicate in the prior art, and has the advantages of high product transportation and stacking cost, short economic application radius and technical bottlenecks of increased cost and limited applicability caused by additional alkali reduction treatment in high-value application fields (such as papermaking and high-grade filling), and the specific technical scheme of the invention is as follows: the invention provides a method for preparing low-calcium silicate by using fly ash and coal gangue, which comprises the following steps: (1) Providing a sodium silicate stock solution and a silicon supplementing raw material, wherein the sodium silicate stock solution is from an alkaline desilication process of coal ash and/or coal gangue, and the silicon supplementing raw material is the coal ash and/or the coal gangue; (2) Mixing the sodium silicate stock solution with a silicon supplementing raw material, adding alkali, heating to 95-100 ℃ for reaction for 2-6 hours, and filtering to obtain a solution A, wherein the concentration of SiO 2 of the solution A is 130-200 g/L, the concentration of Na 2 O is 50-75 g/L, and the modulus is 1.79-4.13; (3) Adding deionized water into the solution A to dilute the solution A until the concentration of SiO 2 is 50-160 g/L, and preheating the solution A to 75-95 ℃; (4) Preparing lime milk, wherein the concentration of the lime milk is 40-150 g/L; (5) Mixing the preheated solution A with lime milk, wherein the mol ratio of SiO 2 to CaO is 2:1-12:1, and stirring and reacting for 1-6 hours at 75-95 ℃ to obtain reaction slurry; (6) Standing and curing the reaction slurry at 75-95 ℃ for 0.5-12 hours to obtain cured slurry; (7) Introducing CO 2 gas into the cured slurry until the pH of the system is reduced to 8.5-9.8, so as to obtain carbonized slurry; (8) Filtering the carbonized slurry, washing a filter cake with hot water, and then drying to obtain the low-calcium silicate. Further, the alkali concentration is adjusted in the step (2) by adding sodium hydroxide or sodium hydroxide solution. Further, the SiO 2 content of the silicon supplementing raw material in the step (2) is 45-52%, and the silicon supplementing raw material is dried and ground, and in the step (7), the flow rate of CO 2 gas is 0.4-0.5L/min, and the stirring speed is 150 rpm. Further, in step (7), the carbonization process monitors the pH value by an online pH meter, and stops aeration when the pH drops to 9.2, 9.8 or 8.5. Further, the washing in the step (8) is repeatedly performed by adopting hot deionized water at the temperature of 60 ℃ until no white precipitate is generated by dropwise adding 0.1M silver nitrate solution after the washing solution is acidified by dilute nitric acid, which indicates that chloride ions are removed, and the drying in the step (8) is performed for 12 hours at the temperature of 105 ℃, and the washing solu