Method for preparing hydraulic cementing material from waste incineration fly ash

Abstract

The invention discloses a method for preparing a hydraulic cementing material from waste incineration fly ash. The method comprises the following specific steps: firstly, fully reacting CO2 with fly ash in a water phase in a high-pressure reaction kettle to obtain treated fly ash slurry; and mixing the treated fly ash slurry with cement to replace part of cement, thereby obtaining the water-hardened cementing material. And after the curing time is up, the heavy metal leaching and compressive strength of the prepared hydraulic cementing material exceed those of a hydraulic cementing material prepared from untreated fly ash under the same addition amount. According to the method, the strong alkaline characteristic of the waste incineration fly ash is fully exerted, water phase pretreatment replaces part of cement to prepare a hydraulic cementing material to synergistically cure heavy metal in the fly ash, and the purpose of treating waste with waste is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of solid waste resource utilization, and in particular to a method for preparing a hydraulic cementitious material by utilizing fly ash from garbage incineration. Background Art

[0002] Domestic waste incineration fly ash (referred to as fly ash) is mainly produced from the flue gas purification system and heat recovery system in the incineration system. Its output is usually 3-10% of the mass of the incinerated waste. It contains harmful heavy metals and highly toxic dioxins, etc. It is a hazardous solid waste and must be treated and disposed of harmlessly. At present, the main method for treating fly ash in various countries is direct landfill after cement solidification / stabilization. On the one hand, this method will occupy a large amount of precious land resources and greatly increase the disposal cost. In addition, the harmful heavy metals and dioxins in the fly ash can easily penetrate into the soil and groundwater, causing secondary pollution to the environment. On the other hand, this harmless treatment wastes fly ash resources to a large extent.

[0003] At the same time, greenhouse gas emissions have caused many environmental and ecological problems. Among the gases with greenhouse effect, CO2 accounts for three quarters, so to weaken the greenhouse effect, we must first reduce CO2 emissions. my country's annual CO2 release ranks first in the world, so for my country, the problem of controlling CO2 emissions needs to be solved urgently.

[0004] At present, fly ash is treated as waste and then directly landfilled after solidification or stabilization; the other is to realize resource utilization. So far, the resource utilization of fly ash is mainly reflected in the following aspects: as part of the raw material for cement production, but the chloride content in fly ash is high, resulting in a decrease in cement quality; as a road construction material, but there is an adverse effect on the strength of the roadbed, and there is a problem of heavy metal leaching; as an auxiliary cementitious material to replace part of the cement in the preparation of concrete, it can save cement and improve some properties of concrete to a certain extent.

[0005] The current mainstream research is to prepare fly ash into a cementitious material and then adsorb CO2. Since it is a reaction between gas and solid phases, the reaction rate is slow, the CO2 adsorption amount is low, and the temperature at which the adsorption reaction occurs is difficult to carry out at room temperature, resulting in high energy consumption. Therefore, it is necessary to develop a low-energy synergistic method for treating fly ash and CO2. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing hydraulic cementitious materials using fly ash from garbage incineration, while solving the problem of increasing greenhouse gas emissions year by year and excessively high toxicity of heavy metal leaching from fly ash that does not meet landfill standards.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing a hydraulic cementitious material using fly ash from garbage incineration, comprising the following steps:

[0008] S1. Mix fly ash and water at room temperature with a liquid-to-solid ratio L / S of 1-5 mL / g;

[0009] S2, transferring the solid-liquid mixture in step S1 to a high-pressure reactor, and charging CO2 gas into the reactor for reaction;

[0010] S3, after the reaction is completed, the pre-treated fly ash slurry is obtained, and P·C42.5 grade cement is added according to the preset water-binder ratio, stirred until the slurry becomes thin, and then transferred to the mold;

[0011] S4, drying, and curing and shaping in a sealed state;

[0012] S5. Take out the hydraulic cementitious material after solidification and cure it at room temperature for 28 days to obtain a hydraulic cementitious material test block.

[0013] Preferably, the fly ash in step S1 is fly ash from a grate furnace or a fluidized bed waste incineration, and the CaO content in the fly ash is not less than 25%.

[0014] Preferably, the operating parameters of the high-pressure reactor in step S2 are: temperature 40-60° C., rotation speed 800 rpm, and time 3 h.

[0015] Preferably, in step S2, CO2 gas at a pressure of 2±0.05Mpa is filled.

[0016] Preferably, the water-to-binder ratio w / b in step S3 is 0.4-0.45.

[0017] Preferably, the curing temperature in step S4 is 60° C. and the curing time is 48 hours.

[0018] Preferably, the fly ash content in the hydraulic binder in step S5 is not higher than 20%.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention utilizes the acidic characteristics of CO2 aqueous solution to pretreat fly ash in an aqueous phase. The treated fly ash can directly replace part of cement to prepare hydraulic cementitious materials without drying. The strength does not significantly decay within a certain addition range, and the leaching of heavy metals also meets the standards, thereby realizing "turning waste into treasure and treating waste with waste".

[0021] 2. The present invention is carried out in an aqueous system, with rapid processing, large CO2 adsorption capacity, low temperature reaction, low energy consumption, and water in the reaction process participates in the preparation of subsequent hydraulic cementitious materials, without wastewater discharge.

[0022] 3. The present invention gives full play to the strong alkalinity of waste incineration fly ash, and uses aqueous phase mineralization CO2 to directly prepare cementitious materials for synergistic solidification of heavy metals in fly ash, thus achieving the synergistic treatment of CO2 adsorption, fly ash resource utilization, and heavy metal disposal, which has multiple meanings such as green, economical, and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a compressive strength diagram of the Zhenjiang hydraulic cementitious material test block prepared in Example 1 of the present invention after curing for 7 days and 28 days.

[0024] Figure 2 It is a compressive strength diagram of the Yangquan hydraulic cementitious material test block prepared in Example 2 of the present invention after curing for 7 days and 28 days. DETAILED DESCRIPTION

[0025] The present invention provides a method for preparing a hydraulic cementitious material by utilizing fly ash from garbage incineration, comprising the following steps:

[0026] S1. Mix fly ash and water at room temperature with a liquid-to-solid ratio L / S of 1-5 mL / g;

[0027] Preferably, the fly ash in step S1 is fly ash from a grate furnace or a fluidized bed waste incineration, and the CaO content in the fly ash is not less than 25%.

[0028] S2, transferring the solid-liquid mixture in step S1 to a high-pressure reactor, and charging CO2 gas into the reactor for reaction;

[0029] Preferably, the operating parameters of the high-pressure reactor in step S2 are: temperature 40-60° C., rotation speed 800 rpm, and time 3 h.

[0030] Preferably, in step S2, CO2 gas at a pressure of 2±0.05Mpa is filled.

[0031] S3, after the reaction is completed, the pre-treated fly ash slurry is obtained, and P·C42.5 grade cement is added according to the preset water-binder ratio, stirred until the slurry becomes thin, and then transferred to the mold;

[0032] Preferably, the water-to-binder ratio w / b in step S3 is 0.4-0.45.

[0033] S4, drying, and curing and shaping in a sealed state;

[0034] Preferably, the curing temperature in step S4 is 60° C. and the curing time is 48 hours.

[0035] S5. Take out the hydraulic cementitious material after solidification and cure it at room temperature for 28 days to obtain a hydraulic cementitious material test block.

[0036] Preferably, the fly ash content in the hydraulic binder in step S5 is not higher than 20%.

[0037] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0038] Example 1: Zhenjiang grate furnace fly ash was selected as the fly ash raw material of this method, Zhonglian brand composite silicate cement P·C42.5 (conforming to national standard GB175-2007) was used as the standard cement sample, ash samples were prepared according to national standard GB / T 202-2008, and the ash chemical composition was tested by XRF. The results are shown in Table 1.

[0039] Table 1 Chemical composition of Zhenjiang grate furnace fly ash and P·C42.5 standard cement

[0040]

[0041]

[0042] (1) From the XRF characterization, it can be seen that Zhenjiang grate furnace fly ash is a kind of fly ash with high calcium and high chloride content, and also contains a considerable amount of sodium and potassium salts.

[0043] (2) The hydraulic cementitious materials were prepared by using the CO2-treated Zhenjiang fly ash slurry and P·C42.5 cement. The compressive strength after curing for 7 and 28 days was as follows: Figure 1 As shown, the specific proportions of hydraulic cementitious materials are shown in Table 2.

[0044] Table 2 Zhenjiang hydraulic cementitious materials production ratio

[0045]

[0046] Combination Figure 1 , among the hydraulic cementitious material test blocks with a curing time of 7 days, the compressive strength of the hydraulic cementitious material test blocks treated with 5% and 10% CO2 is higher than that of pure P·C42.5 cement. When 5% is added, the compressive strength increases by 10MPa, and when 10% is added, the compressive strength increases by 5.1MPa, which meets the strength requirements of 42.5 cement (the basis for judgment is: "General Portland Cement" (GB 175-2007)). With the increase of curing time, the compressive strength of the test blocks cured for 28 days has increased, especially the test blocks with 5% and 10%, the compressive strength reaches 54.9Mpa and 52Mpa respectively, which is far higher than the strength requirements of 42.5 cement. The raw materials in the hydraulic cementitious material test blocks have a decreasing compressive strength trend with the increase of fly ash content, but it is still higher than the strength requirements of 32.5 cement, and has strong practicality as a whole.

[0047] (3) The heavy metal leaching detection method of Zhenjiang grate furnace ash and Zhenjiang cementitious material adopts HJ / T299-2007 "Solid waste leaching toxicity leaching method sulfuric acid and nitric acid method", and the results are shown in Table 3 below.

[0048] Table 3 Heavy metal leaching of Zhenjiang raw ash and Zhenjiang hydraulic cementitious material test blocks at 7d and 28d

[0049]

[0050]

[0051] The hydraulic cementitious material test blocks prepared by this method performed excellently in terms of heavy metal leaching. The leaching of heavy metal elements measured in the hydraulic cementitious material test blocks was reduced compared with the original ash, especially in the Cr, Cu, Zn, and Pb elements. At the same time, the heavy metal leaching of the prepared hydraulic cementitious material met the standards.

[0052] Example 2: Yangquan fluidized bed fly ash and Zhonglian composite silicate cement P·C42.5 (in compliance with national standard GB175-2007) were selected as test samples, ash samples were prepared according to national standard GB / T 202-2008, and the ash chemical composition was tested using XRF. The results are shown in Table 4.

[0053] Table 4 Chemical composition of Yangquan fluidized bed and P·C42.5 standard cement

[0054]

[0055] (1) XRF characterization shows that Yangquan fluidized bed fly ash is a fly ash containing high calcium silicon-aluminum compounds.

[0056] (2) The hydraulic cementitious materials were prepared by using the CO2-treated Zhenjiang fly ash slurry and P·C42.5 cement. The compressive strength after curing for 7 and 28 days was as follows: Figure 2 As shown in Table 5, the specific proportions for making the hydraulic cementitious material test blocks are shown in Table 5.

[0057] Table 5 Yangquan water hard gelling material production ratio

[0058]

[0059] Combination Figure 2The compressive strength of all hydraulic cementitious materials mixed with fly ash is lower than that of the test blocks made of pure cement, indicating that Yangquan fluidized bed fly ash has a certain negative effect on the formation of hydraulic cementitious materials, but the test blocks mixed with 5% still meet the 42.5 cement strength requirement, indicating that it still has practical value. The 28-day compressive strength trend is very similar to that of Zhenjiang hydraulic cementitious materials, and the additions of 5% and 10% are both higher than the pure standard cement test blocks. At the same time, all hydraulic cementitious material test blocks meet the 32.5 cement strength requirement, indicating that this method can turn fly ash into treasure and has strong practicality.

[0060] (3) The heavy metal leaching detection method for Yangquan fluidized bed raw ash and Yangquan hydraulic cementitious materials adopts HJ / T299-2007 "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid and Nitric Acid Method", and the results are shown in Table 6 below.

[0061] Table 6 Heavy metal leaching from Yangquan raw ash and Yangquan hydraulic cementitious materials for 7 days

[0062]

[0063] The hydraulic cementitious material prepared by this method has excellent performance in heavy metal leaching, especially significantly reducing the Zn and Pb elements. Although the leaching concentration of some elements is higher than that of the original ash, the heavy metal leaching of the prepared hydraulic cementitious material meets the standards.

[0064] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a hydraulic cementitious material using fly ash from garbage incineration, characterized in that: The following steps are involved: S1. Mix fly ash and water at room temperature with a liquid-to-solid ratio of 1-5 mL / g; S2, transferring the solid-liquid mixture in step S1 to a high-pressure reactor, and charging CO2 gas into the reactor for reaction; S3, after the reaction is completed, the pre-treated fly ash slurry is obtained, and P·C42.5 grade cement is added according to the preset water-binder ratio, stirred until the slurry becomes thin, and then transferred to the mold; S4, drying, and curing and shaping in a sealed state; S5. Take out the hydraulic cementitious material after solidification and cure it at room temperature for 28 days to obtain a hydraulic cementitious material test block.

2. The method for preparing hydraulic cementitious materials by using fly ash from garbage incineration according to claim 1, characterized in that: The fly ash in step S1 is fly ash from a grate furnace or a fluidized bed waste incineration, and the content of CaO in the fly ash is not less than 25%.

3. According to the method for preparing hydraulic cementitious materials using waste incineration fly ash as described in claim 1, the operating parameters of the high-pressure reactor in step S2 are: temperature 40-60°C, rotation speed 800rpm, and time 3h.

4. According to the method for preparing hydraulic cementitious materials using waste incineration fly ash as described in claim 1, CO2 gas with a pressure of 2±0.05Mpa is filled in step S2.

5. According to the method for preparing hydraulic cementitious material by using waste incineration fly ash as claimed in claim 1, the water-binder ratio in step S3 is 0.4-0.

45.

6. According to the method for preparing hydraulic cementitious materials using waste incineration fly ash as claimed in claim 1, the curing temperature in step S4 is 60°C and the curing time is 48 hours.

7. According to the method for preparing hydraulic cementitious material by using fly ash from garbage incineration as claimed in claim 1, the fly ash content in the hydraulic cementitious material in step S5 is not higher than 20%.

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