A waste incineration fly ash geopolymer composite material and a preparation method thereof

Abstract

The present application relates to the technical field of solid waste treatment and resource utilization, and discloses a waste incineration fly ash geopolymer composite material and a preparation method thereof, which is made of waste incineration fly ash, apatite group minerals, zero-valent iron powder, persulfate and an alkali activator. The preparation method comprises the following steps: mixing the waste incineration fly ash, the apatite group minerals, the zero-valent iron powder and the persulfate to obtain a composite powder; performing frequency conversion mechanical-chemical synergistic activation on the composite powder, wherein the activation process comprises a low-temperature activation stage and a high-energy pulse activation stage; and finally mixing the activated powder with the alkali activator, pouring and forming, and curing. Through the time sequence regulation of mechanical energy input, the present application step by step drives the reduction reaction and the oxidation reaction in the same system, solves the compatibility problem of the reducing agent and the oxidizing agent, synergistically degrades different types of persistent organic pollutants, stabilizes the heavy metals, and resources the fly ash to prepare a geopolymer material with mechanical properties.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste treatment and resource utilization, and in particular to a waste incineration fly ash geopolymer composite material and a preparation method thereof. BACKGROUND

[0002] Waste incineration is one of the main technical means for modern municipal solid waste reduction and harmless treatment, but the fly ash generated by waste incineration is a hazardous waste. The fly ash of waste incineration is rich in heavy metals such as lead and cadmium, and also adsorbs persistent organic pollutants such as polychlorinated aromatic hydrocarbons (PCDD / Fs) and polycyclic aromatic hydrocarbons (PAHs). These pollutants are chemically stable, have high toxicity and biological enrichment, and if not properly disposed of, will pose a long-term threat to the ecological environment and human health.

[0003] The current mainstream disposal method for waste incineration fly ash is to carry out safe landfill after cement-based solidification / stabilization. This method mainly reduces the leaching toxicity of heavy metals through physical encapsulation and adsorption of cement hydration products, but has limited chemical degradation effect on polychlorinated organic pollutants such as dioxins.

[0004] In order to degrade the organic pollutants in fly ash, chemical methods have been used. For example, using strong oxidizing agents such as persulfate to generate free radicals can effectively oxidize and decompose polycyclic aromatic hydrocarbons; and using zero-valent iron as a reducing agent can achieve the reduction and dechlorination degradation of dioxins. However, the degradation of dioxins and polycyclic aromatic hydrocarbons requires opposite redox environments. Direct addition of oxidizing agents and reducing agents in the same system will cause the two to react with each other and be consumed, resulting in low degradation efficiency of the target pollutants, and it is difficult to simultaneously treat multiple persistent organic pollutants in a single process. Therefore, developing a technology that can simultaneously and efficiently degrade multiple persistent organic pollutants, stabilize heavy metals, and realize resource utilization of fly ash in a one-step process is a technical problem that needs to be solved in the field. SUMMARY

[0005] The technical problem solved by the present application is that the existing waste incineration fly ash treatment technology cannot simultaneously degrade persistent organic pollutants with different chemical properties, stabilize heavy metals, and realize resource utilization of the product in a single process. In particular, the chemical environment required for the dechlorination degradation of dioxins is different from that required for the oxidative degradation of polycyclic aromatic hydrocarbons, and reducing agents and oxidizing agents are prone to ineffective reactions in the same system, resulting in low treatment efficiency.

[0006] To solve the above problems, the present application provides the following technical solutions:

[0007] In a first aspect, the present application provides a waste incineration fly ash geopolymer composite material.

[0008] The composite is made of raw materials including 100 parts of waste incineration fly ash, 3-10 parts of apatite group minerals, 1-5 parts of zero-valent iron powder, 1-5 parts of persulfate, and an alkali activator prepared by mixing 30-50 parts of sodium silicate solution and 10-25 parts of sodium hydroxide solution.

[0009] The waste incineration fly ash, the apatite group minerals, the zero-valent iron powder and the persulfate are subjected to a frequency conversion mechanical-chemical synergistic activation treatment including a low-temperature activation stage and a high-energy pulse activation stage before being mixed with the alkali activator.

[0010] By using the above technical solution, the technical solution realizes the degradation of organic pollutants, the stabilization of heavy metals and the geological polymerization of the material matrix in the waste incineration fly ash in a single process through specific raw material combination and preparation process. The technical principle of the scheme is that different chemical reactions in the system are controlled by time through a frequency conversion mechanical-chemical process:

[0011] 1. Low-temperature activation stage: lower mechanical energy input is mainly used to break up agglomerates, increase the specific surface area of reactants and update the surface of zero-valent iron to expose active sites. This energy level is conducive to the reduction and dechlorination reaction of dioxin chlorinated organic matter by zero-valent iron, and is insufficient to trigger large-scale decomposition of persulfate, thereby avoiding premature consumption between reducing agent and oxidizing agent.

[0012] 2. High-energy pulse activation stage: the instantaneous input of high energy generates local high temperature at the particle collision point, effectively triggering the decomposition of persulfate to generate active sulfate radicals (SO4 - ). The radicals can oxidize and decompose polycyclic aromatic hydrocarbons with stable chemical properties.

[0013] The timing control of the above energy input realizes the step-by-step driving of reduction reaction and oxidation reaction in the same reactor, solves the compatibility problem of reducing agent and oxidizing agent, and synergistically degrades different types of persistent organic pollutants.

[0014] At the same time, the apatite group minerals in the system release phosphate ions during the mechanical-chemical activation and subsequent hydration process. The ions react in situ with heavy metal ions such as lead and cadmium in the fly ash to form stable apatite-like mineral phases, achieving chemical fixation of heavy metals.

[0015] In addition, the mechanical-chemical process stimulates the pozzolanic activity of the fly ash. The activated powder undergoes a geological polymerization reaction under the action of the alkali activator to form a dense, high-strength three-dimensional aluminosilicate network structure. The structure endows the final product with mechanical properties, which can be used as building materials. The dense physical structure also physically encapsulates the chemically fixed heavy metals, reducing the leaching risk of pollutants.

[0016] Preferably, the apatite group mineral is phosphate rock powder or hydroxyapatite. Phosphate rock powder is widely available and low in cost, while hydroxyapatite has higher reactivity, both of which can effectively provide the phosphate ions required for stabilizing heavy metals.

[0017] Preferably, when the apatite group mineral is hydroxyapatite, it is prepared by a wet chemical precipitation method, specifically including:

[0018] (1) under the condition that the pH value is 10-11, a diammonium hydrogen phosphate solution is added dropwise into a calcium nitrate solution to react, obtaining a suspension;

[0019] (2) the suspension is aged, filtered, washed and dried to obtain the hydroxyapatite.

[0020] Preferably, the concentration of the sodium hydroxide solution in the alkali activator is 8-14 mol / L, and the modulus of the sodium silicate solution is 2.5-3.0. Within this parameter range, the alkali activator can provide suitable alkalinity and soluble silicon source for the geopolymerization reaction, promoting the formation of a high-strength geopolymer matrix.

[0021] In a second aspect, the present application provides a preparation method of a waste incineration fly ash geopolymer composite material, which adopts the following technical solution:

[0022] The preparation method includes the following steps:

[0023] (a) mixing waste incineration fly ash, an apatite group mineral, zero-valent iron powder and persulfate to obtain a composite powder;

[0024] (b) performing frequency-variable mechanical-chemical synergistic activation on the composite powder to obtain an activated composite powder, the activation process including a low-temperature activation stage and a subsequent high-energy pulse activation stage;

[0025] (c) mixing the activated composite powder in step (b) with an alkali activator to obtain a slurry;

[0026] (d) casting and forming the slurry and performing curing.

[0027] By adopting the above technical solution, the preparation method of the present application realizes comprehensive treatment of waste incineration fly ash through an integrated process flow. The core lies in the frequency-variable mechanical-chemical synergistic activation process in step (b), which makes different types of chemical reactions in the system occur step by step under their respective suitable conditions through time sequence control of mechanical energy input.

[0028] In the low-temperature activation stage, lower energy input preferentially promotes the reduction and dechlorination reaction of zero-valent iron; then in the high-energy pulse activation stage, instantaneous high-energy input is used to trigger the oxidation reaction of persulfate.

[0029] The step-by-step driving strategy effectively avoids the direct reaction and loss of the reductant and the oxidant in the mixed state, so that the two can synergistically act in the same system to degrade different types of organic pollutants. At the same time, the entire activation process also improves the reaction activity of the fly ash, which is beneficial to the subsequent geopolymerization reaction.

[0030] Preferably, the synergistic activation in step (b) is carried out in a planetary ball mill, and the ball-to-material mass ratio is (15-25):1. Further, the rotation speed of the low-temperature activation stage is 250-350 rpm, and the duration is 75-150 min; the high-energy pulse activation stage includes running at a rotation speed of 500-700 rpm, then pausing, and repeating the running and pausing process.

[0031] By adopting the above technical solution, the specific process parameters are the specific ways to realize the aforementioned step-by-step driving strategy. In the planetary ball mill, the set ball-to-material ratio and rotation speed can provide enough energy for particle grinding, dispersion, and surface renewal of zero-valent iron in the low-temperature stage, but not enough to trigger the decomposition of persulfate; while in the high-energy pulse stage, the higher rotation speed can provide the transient energy required to trigger the oxidation reaction. The alternating mode of running and pausing is beneficial to controlling the system temperature and avoiding overheating.

[0032] Preferably, in the high-energy pulse activation stage, the rotation speed is 500-700 rpm for 3-5 min, the pause is 1-2 min, and the process is repeated 4-6 times.

[0033] By adopting the above technical solution, the running-pause cycle of the high-energy pulse stage is quantified, which can realize the control of the total input energy, is beneficial to the effective activation of persulfate, while avoiding energy waste, and makes the entire activation process stable and controllable.

[0034] Preferably, in step (d), the curing temperature is 20-70℃, and the time is 6-24h.

[0035] By adopting the above technical solution, curing under this temperature and humidity condition is beneficial to the full performance of the geopolymerization reaction, so as to form a dense matrix with mechanical properties and low permeability, which effectively physically encapsulates heavy metals.

[0036] In summary, the present application includes at least one of the following beneficial technical effects:

[0037] 1. The present application realizes the efficient and synergistic degradation of different types of organic pollutants in the same system by adopting a variable-frequency mechanical-chemical activation process. The method preferentially drives the reduction and dechlorination reaction of zero-valent iron through a low-speed activation stage, and then triggers the oxidation reaction of persulfate through a high-energy pulse stage, avoiding the ineffective consumption of reducing agents and oxidizing agents, and improving the overall removal effect of persistent organic pollutants.

[0038] 2. The present application realizes the dual stabilization of chemical fixation and physical encapsulation of heavy metals, significantly reducing the environmental leaching risk of pollutants. The apatite family minerals in the system react in situ with heavy metals such as lead and cadmium to form stable mineral phases, achieving chemical fixation; the subsequent formation of high-strength and dense polymer matrix physically encapsulates the solidified heavy metal products, further improving the long-term reliability of the solidification / stabilization effect.

[0039] 3. The present application converts waste incineration fly ash into geopolymer composite materials with mechanical properties, realizing the resource utilization of hazardous waste. The mechanical-chemical activation enhances the pozzolanic activity of fly ash, enabling it to participate in the geopolymerization reaction as a main raw material. The prepared composite material can be used as a building material. This method replaces the traditional landfill disposal method, reducing land occupation and environmental pollution, and has economic and environmental benefits. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 Comparison chart of organic pollutant degradation effect; wherein figure a) is the degradation effect comparison of dioxin (PCDD / Fs) in different samples; figure b is the degradation effect comparison of polycyclic aromatic hydrocarbons (PAHs) in different samples;

[0041] Figure 2 Heavy metal leaching toxicity test result chart of the final product of example 1;

[0042] Figure 3 Comparison chart of mechanical property test results of each sample at 28 days of age;

[0043] Figure 4 Comparison chart of heavy metal leaching toxicity test results of each sample; wherein, figure a) is the comparison of lead (Pb) leaching concentration, figure b) is the comparison of cadmium (Cd) leaching concentration, figure c) is the comparison of zinc (Zn) leaching concentration, and figure d) is the comparison of chromium (Cr) leaching concentration;

[0044] Figure 5 Part of the sample compressive strength development with age line chart. DETAILED DESCRIPTION

[0045] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0046] The main raw materials and reagents used in the following examples and comparative examples are as follows, and the reagents not specifically described are commercially available analytical pure or higher grade products.

[0047] The waste incineration fly ash was taken from a domestic waste incineration power plant, which was the original fly ash collected by a bag-type dust collector without any pretreatment.

[0048] The phosphate ore powder was prepared by grinding a natural apatite mineral, and the main component was fluorapatite (CAS No.: 1306-05-4) with a particle size of less than 75 μm.

[0049] Hydroxyapatite (HAP) was prepared according to the method of Preparation Example 1.

[0050] Zero-valent iron powder (ZVI) was an industrial grade reduced iron powder with an average particle size of 45 μm.

[0051] The sodium silicate solution was an industrial grade liquid with a molar ratio (modulus) of silicon dioxide to sodium oxide of 2.5 or 3.0.

[0052] Preparation Example 1:

[0053] The present preparation example provides a method for preparing hydroxyapatite, which comprises the following steps:

[0054] A 0.5 mol / L calcium nitrate (Ca(NO3)2) solution and a 0.3 mol / L diammonium hydrogen phosphate ((NH4)2HPO4) solution were prepared respectively. Under vigorous stirring, the diammonium hydrogen phosphate solution was slowly added to the calcium nitrate solution at a rate of about 5 mL / min, while using ammonia water to continuously adjust the pH value of the mixed solution to be stable between 10 and 11. After the addition was completed, the reaction was continued to be stirred at room temperature for 2 h to allow it to be fully aged. After the stirring was stopped, the obtained white suspension was allowed to stand for aging for 12 h, and then was filtered. The filter cake was washed with deionized water for multiple times until the pH value of the filtrate after washing was close to neutral. The washed filter cake was placed in an oven at 105°C for drying for 12 h. Finally, the dried block material was ground and passed through a 200 mesh sieve to obtain hydroxyapatite powder with the chemical formula of Ca 10 (PO4)6(OH)2, which was sealed and stored for use.

[0055] Example 1:

[0056] The embodiment provides a preparation method of a waste incineration fly ash geopolymer composite material, and comprises the following steps:

[0057] (1) 100 parts of waste incineration fly ash, 3 parts of phosphate ore powder, 1 part of zero-valent iron powder and 1 part of potassium persulfate are added into a planetary ball mill according to mass fraction, and the ball-to-material mass ratio is set to 15:1.

[0058] (2) A variable-frequency mechanical-chemical program is started, and the total time is set to 90 min. The program comprises the following steps: first, low-temperature activation is performed at a speed of 250 rpm for 75 min; then, high-energy pulse activation is performed, that is, the speed is 500 rpm for 3 min, the speed is paused for 2 min, and the high-energy pulse process is repeated for 5 times.

[0059] (3) An alkali activator is prepared by mixing 8 mol / L of a sodium hydroxide solution and a sodium silicate solution with a modulus of 3.0, wherein the sodium silicate solution is 50 parts, and the sodium hydroxide solution is 10 parts, and the mixture is cooled to room temperature after mixing.

[0060] (4) The composite powder obtained in step (2) is added to the alkali activator prepared in step (3), and is stirred in a mechanical stirrer for 15 min and then cast.

[0061] (5) The mold with the slurry is placed in an environment with a temperature of 20 ℃ and a relative humidity of not less than 95% for curing for 24 h, and then demolding is performed to obtain a sample.

[0062] Example 2:

[0063] The embodiment provides a preparation method of a waste incineration fly ash geopolymer composite material, and comprises the following steps:

[0064] (1) 100 parts of waste incineration fly ash, 6 parts of hydroxyapatite prepared in preparation example 1, 3 parts of zero-valent iron powder and 3 parts of sodium persulfate are added into a planetary ball mill according to mass fraction, and the ball-to-material mass ratio is set to 20:1.

[0065] (2) A variable-frequency mechanical-chemical program is started, and the total time is set to 120 min. The program comprises the following steps: first, low-temperature activation is performed at a speed of 300 rpm for 100 min; then, high-energy pulse activation is performed, that is, the speed is 600 rpm for 5 min, the speed is paused for 2 min, and the high-energy pulse process is repeated for 4 times.

[0066] (3) An alkali activator is prepared by mixing 12 mol / L of a sodium hydroxide solution and a sodium silicate solution with a modulus of 2.5, wherein the sodium silicate solution is 40 parts, and the sodium hydroxide solution is 18 parts, and the mixture is cooled to room temperature after mixing.

[0067] (4) The composite powder obtained in step (2) is added to the alkali activator prepared in step (3), and after stirring in a mechanical stirrer for 10 min, it is poured into a mold for molding.

[0068] (5) The mold with the slurry is placed in an environment with a temperature of 60°C and a relative humidity of not less than 95% for curing for 12 h, and then demolded to obtain a sample.

[0069] Example 3:

[0070] The present embodiment provides a preparation method of a waste incineration fly ash geopolymer composite material, comprising the following steps:

[0071] (1) 100 parts of waste incineration fly ash, 10 parts of phosphate rock powder, 5 parts of zero-valent iron powder and 5 parts of potassium persulfate are added into a planetary ball mill, and the ball-to-material mass ratio is set to 25:1.

[0072] (2) A variable frequency mechanical-chemical program is started, and the total time is set to 180 min. The program includes: first, low-temperature activation at a speed of 350 rpm for 150 min; then high-energy pulse activation is performed, running at a speed of 700 rpm for 5 min, pausing for 1 min, and repeating the high-energy pulse process for a total of 6 times.

[0073] (3) An alkali activator is prepared by mixing a 14 mol / L sodium hydroxide solution with a sodium silicate solution with a modulus of 2.5, wherein the sodium silicate solution is 30 parts and the sodium hydroxide solution is 25 parts, and then cooled to room temperature after mixing.

[0074] (4) The composite powder obtained in step (2) is added to the alkali activator prepared in step (3), and after stirring in a mechanical stirrer for 5 min, it is poured into a mold for molding.

[0075] (5) The mold with the slurry is placed in an environment with a temperature of 70°C and a relative humidity of not less than 95% for curing for 6 h, and then demolded to obtain a sample.

[0076] Comparative Example 1:

[0077] Compared with Example 1, the difference is that the waste incineration fly ash, phosphate rock powder, zero-valent iron powder and potassium persulfate are simply dry mixed in a stirrer, without the variable frequency mechanical-chemical activation step, and the rest are the same.

[0078] Comparative Example 2:

[0079] Compared with Example 1, the difference is that step (2) does not use a variable frequency program, but continuously runs at a constant high speed of 600 rpm for 20 min, and the rest are the same.

[0080] Comparative Example 3:

[0081] The difference compared with Example 1 is that potassium persulfate is not added in the composite functional additive, and the rest is the same.

[0082] Comparative Example 4:

[0083] The difference compared with Example 1 is that zero-valent iron powder is not added in the composite functional additive, and the rest is the same.

[0084] Comparative Example 5:

[0085] Different from the technical solution of Example 1, the present comparative example uses the traditional water washing method for pretreatment: the fly ash is water washed, filtered and dried, then only the water washed fly ash is used as the raw material, without adding any composite functional additive, and the same alkali activator and subsequent steps as in Example 1 are used to prepare the sample.

[0086] Test Example 1:

[0087] The experimental steps are as follows:

[0088] (1) Take about 10 g of the original waste incineration fly ash, the composite powder of step (2) of Example 1, and the composite powder sample of step (2) of Comparative Example 2, respectively, and dry them in an oven at 105°C to constant weight.

[0089] (2) Weigh the dried sample, and add 13 C 12 labeled PCDD / Fs mixed internal standard and deuterated PAHs mixed internal standard to it, then place the sample in a Soxhlet extractor for continuous hot extraction for 24 h with toluene as the solvent.

[0090] (3) Concentrate the extract to about 2 mL by rotary evaporation, and purify it by a multi-layer composite silica gel column, which is filled with neutral silica gel, basic silica gel, neutral silica gel, acidic silica gel, neutral silica gel and anhydrous sodium sulfate from bottom to top.

[0091] (4) First, wash the purification column with n-hexane and discard the washing liquid, then elute it with a mixed solvent of n-hexane and dichloromethane, and collect the target components of PCDD / Fs and PAHs respectively.

[0092] (5) Rotary evaporate each component eluent collected to near dryness, add 13 C 12 labeled injection standard, and make up with n-nonane or toluene for instrument analysis.

[0093] (6) The content of PCDD / Fs was analyzed by isotope dilution-high resolution gas chromatography / high resolution mass spectrometry (HRGC / HRMS) and the total toxicity equivalent (I-TEQ) was calculated according to HJ 77.4-2008; the total content of PAHs was analyzed by gas chromatography-mass spectrometry (GC-MS) according to GB / T 36197-2018.

[0094] The experimental results are shown in Table 1 and Figure 1

[0095] Table 1: Test results of the content of organic pollutants in each sample

[0096] Test object PCDD / Fs content (ng I-TEQ / kg) Total PAHs content (mg / kg) Raw waste incineration fly ash 850.3 155.7 Example 1 composite powder 47.9 16.4 Comparative example 2 composite powder 286.5 78.2

[0097] The test results show that the variable frequency mechanical chemical method of Example 1 can effectively degrade persistent organic pollutants in fly ash.

[0098] There is a high concentration of PCDD / Fs (850.3 ng I-TEQ / kg) and PAHs (155.7 mg / kg) in the original waste incineration fly ash. After the variable frequency mechanical chemical synergistic treatment adopted in Example 1, the contents of PCDD / Fs and PAHs in the powder are significantly reduced to 47.9 ng I-TEQ / kg and 16.4 mg / kg, respectively, and the degradation rates are 94.4% and 89.5%, respectively. This result confirms that the combination of the composition and process of the present application can effectively destroy and remove these two types of organic pollutants with different chemical properties.

[0099] Comparative Example 2 uses constant high-speed ball milling, although it also achieves a certain degradation of pollutants (PCDD / Fs degradation rate of 66.3%, PAHs degradation rate of 49.8%), but its effect is far inferior to Example 1. The internal reason is that under the input of continuous high-energy mechanical force, the reducing agent zero-valent iron and the oxidizing agent persulfate are activated simultaneously and indiscriminately. These two active substances with opposite properties directly and non-selectively react in the system, leading to the consumption of each other, thereby reducing their effective concentrations for degrading target pollutants (zero-valent iron degrades PCDD / Fs, and persulfate degrades PAHs).

[0100] The variable frequency program of the present application controls energy input by time sequence, including two stages of low-temperature activation and high-energy pulse. The energy input in the low-temperature activation stage is mainly used to update the surface of zero-valent iron and promote its reduction function, and this energy level is not enough to trigger the decomposition of persulfate. In the subsequent high-energy pulse stage, the instantaneous high-energy input produces local high temperature, triggering the decomposition of persulfate to generate active species to degrade PAHs. This distinction of energy input in time suppresses the ineffective reaction between the reducing agent and the oxidizing agent, which is the technical basis for achieving the synergistic degradation of the two pollutants. ​

[0101] Test Example 2

[0102] The experimental procedure is as follows:

[0103] (1) The final cured sample prepared in Example 1 was crushed using a jaw crusher and passed through a sieve with a mesh size of 5 mm.

[0104] (2) 100 g of the treated sample was weighed out and operated in accordance with HJ 557-2010. Sulfuric acid / nitric acid was used as the leaching agent. The amount of acid was adjusted during the oscillation process so that the pH value of the liquid was 5.0 ± 0.05 at the end of the leaching. The liquid-solid ratio was kept at 10 L / kg.

[0105] (3) The sample was placed on a horizontal oscillator and continuously oscillated at a speed of 110 r / min at a temperature of (23 ± 2) °C for 8 h.

[0106] (4) After the oscillation was completed, it was left to stand for 16 h, and then the leaching liquid was pressure-filtered using a microporous filter membrane with a pore size of 0.45 μm.

[0107] (5) Part of the filtrate was taken and the concentrations of lead (Pb), cadmium (Cd), zinc (Zn), and chromium (Cr) in the leaching liquid were detected using inductively coupled plasma mass spectrometry (ICP-MS) in accordance with HJ 700-2014.

[0108] The experimental results are shown in Table 2 and Figure 2 .

[0109] Table 2 Concentrations of heavy metals in the leaching liquid of the final product:

[0110] Heavy metal to be tested Example 1 leaching solution concentration (mg / L) GB 16889-2008 limit value (mg / L) Lead (Pb) 0.038 0.25 Cadmium (Cd) 0.0016 0.015 Zinc (Zn) 0.17 2 Chromium (Cr) 0.065 1.5

[0111] The leaching toxicity test results show that the cured product prepared in Example 1 has an effective stabilization effect on heavy metals. The concentrations of Pb, Cd, Zn, and Cr in the leaching liquid are 0.038 mg / L, 0.0016 mg / L, 0.17 mg / L, and 0.065 mg / L, respectively, which are significantly lower than the limit values specified in the Standard for Pollution Control on the Landfill Site for Domestic Waste (GB 16889-2008).

[0112] The low leaching concentration of heavy metals in the product is attributed to the dual action mechanism of chemical fixation and physical encapsulation. In terms of chemical fixation, the phosphate rock powder in the composite powder releases phosphate ions (PO4 3- ) during mechanical activation and subsequent hydration reactions. These ions react with lead ions (Pb 2+ ) and chloride ions (Cl -) reaction, generating extremely stable chloro-apatite pyromorphite (Pb5(PO4)3Cl) in situ. Other divalent metal ions such as cadmium and zinc can also be fixed by isomorphous substitution into the apatite lattice.

[0113] At the physical encapsulation level, fly ash undergoes geopolymerization in the presence of alkali activators, forming a dense three-dimensional aluminosilicate network structure. This process encapsulates the chemically immobilized heavy metal mineral phases and a small amount of unreacted heavy metal ions within the gel network. This dense matrix structure constitutes a physical barrier that prevents the migration of heavy metals to the external environment. It is this synergistic mechanism of chemical immobilization and physical encapsulation that ensures the long-term stability of heavy metals in the solidified body, effectively controlling their environmental risks.

[0114] Test Example 3:

[0115] The experimental procedure is as follows:

[0116] (1) The components prepared in Examples 1-3 and Comparative Examples 1-5 were prepared into 40mm x 40mm x 160mm sample prisms according to the requirements of GB / T 17671, with three prisms prepared for each group.

[0117] (2) After molding, the sample with the mold was placed in a standard curing oven for 24 hours, then removed and continued to be cured in an environment with a temperature of (20±1) °C and a relative humidity of not less than 95% until the 28-day age.

[0118] (3) After the curing period, the samples were removed. First, the flexural strength test was performed on a flexural strength testing machine, and the load at the time of fracture was recorded.

[0119] (4) The two segments of the broken block formed after the flexural test were used as the samples for the compressive strength test, and the test was performed on a compressive strength testing machine, and the maximum pressure at the time of sample failure was recorded.

[0120] (5) According to the standard formula, the flexural strength and compressive strength of each group of samples were calculated, and the arithmetic mean of the three samples was taken as the result.

[0121] The experimental results are shown in Table 3 and Figure 3 .

[0122] Table 3: 28-day mechanical property test results of each sample:

[0123] Test object Compressive strength (MPa) Flexural strength (MPa) Example 1 38.7 6.9 Example 2 43.1 7.8 Example 3 41.5 7.5 Comparative example 1 5.4 1.2 Comparative example 2 25.8 4.6 Comparative example 3 35.2 6.3 Comparative example 4 36.1 6.5 Comparative example 5 19.3 3.7

[0124] The mechanical property test data show that the solidified bodies prepared in Examples 1-3 have high compressive strength and flexural strength. The 28-day compressive strength of Examples 1-3 is more than 38MPa, and the flexural strength is close to 7MPa, showing the application potential of the material as a building material.

[0125] Comparative Example 1 was not mechanically chemically activated, and its 28-day compressive strength was only 5.4 MPa, indicating that the original activity of the fly ash raw material was extremely low and could not support effective geopolymerization reaction. This confirms that mechanical chemical activation is a necessary step to activate the fly ash pozzolanic activity, which serves to destroy the inert glass structure on the surface of the fly ash particles, increase the specific surface area, and provide more active sites for subsequent reactions.

[0126] Comparative Example 2 used constant high-speed activation, and although its strength was significantly improved compared to Comparative Example 1, it was still significantly lower than Examples 1-3. This shows that the variable frequency mechanical chemical process used in the present application can more effectively optimize the particle morphology and grading of the composite powder by controlling the energy input, avoiding problems such as particle agglomeration or reduced amorphization caused by excessive grinding, and is conducive to forming a hardened structure that is more tightly packed and has fewer defects.

[0127] Comparative Example 5 used a traditional water washing method to pretreat fly ash, and although the mechanical properties were better than those of Comparative Example 1 by removing inhibitory salts, the strength was still lower than that of the examples of the present application. At the same time, the water washing method produces waste liquid containing high concentrations of chloride salts and heavy metals, constituting secondary pollution, increasing the complexity of the process and environmental costs, and not meeting the principles of efficient and low-carbon resource utilization of solid waste.

[0128] In summary, the technical solution of the present application, through the synergistic effect of the variable frequency mechanical chemical activation process and the composite additive, not only realizes the in-situ, one-step treatment of pollutants, but also effectively activates the material properties of fly ash. The activated high-activity powder can undergo sufficient geopolymerization reaction under alkaline activation conditions, forming a more dense and uniform aluminosilicate geopolymer network structure.

[0129] Test Example 4:

[0130] The experimental steps are as follows:

[0131] (1) The final cured samples (cured for 28 days) prepared in Examples 1-3 and Comparative Examples 1-5 were respectively taken, crushed using a jaw crusher, and then passed through a 5 mm sieve.

[0132] (2) 100 g of each group of samples was weighed, and horizontal oscillation leaching was performed according to HJ 557-2010. Sulfuric acid / nitric acid was used as the leaching agent, and the amount of acid was adjusted during the oscillation process so that the liquid pH value at the end of the leaching was 5.0±0.05, and the liquid-solid ratio was 10 L / kg.

[0133] (3) The samples were continuously oscillated at a speed of 110 r / min for 8 h at (23±2) ℃, and then statically placed for 16 h.

[0134] (4) The leaching liquid was pressure-filtered using a 0.45 μm microporous filter membrane.

[0135] (5) Take the filtrate, according to HJ 700-2014, using inductively coupled plasma mass spectrometry (ICP-MS) to detect the concentration of lead (Pb), cadmium (Cd), zinc (Zn), chromium (Cr) in the leaching solution.

[0136] The experimental results are shown in Table 4 and Figure 4

[0137] Table 4: Heavy metal concentration (mg / L) in the leaching solution of each sample:

[0138] Test object Lead (Pb) Cadmium (Cd) Zinc (Zn) Chromium (Cr) Example 1 0.038 0.0016 0.17 0.065 Example 2 0.031 0.0013 0.15 0.058 Example 3 0.045 0.0021 0.23 0.071 Comparative example 1 15.6 0.95 38.4 4.3 Comparative example 2 0.19 0.008 0.88 0.45 Comparative example 3 0.041 0.0017 0.19 0.069 Comparative example 4 0.043 0.0019 0.2 0.066 Comparative example 5 1.15 0.032 4.7 1.8

[0139] The test results show that the Pb, Cd, Zn, Cr leaching concentrations of samples 1-3 are much lower than the standard limit value of GB 16889-2008, indicating that the technical scheme of the present application can realize the stable solidification of heavy metals under different parameter combinations.

[0140] Comparative Example 1 is not mechanically activated, and its heavy metal leaching concentration is extremely high, proving that direct mixing of fly ash raw materials cannot form an effective solidification matrix, and mechanical chemical activation is a prerequisite for forming a dense polymer structure to achieve physical encapsulation.

[0141] Comparative Example 2 uses constant high speed, and although its leaching concentration is lower than the standard, it is still significantly higher than the examples, indicating that the frequency conversion program of the present application helps to form a geopolymer matrix with higher quality and denser structure, thereby improving the effect of physical encapsulation.

[0142] Comparative Examples 3 and 4 respectively lack oxidizing agent and reducing agent, but their heavy metal leaching concentrations are close to the results of the examples. This phenomenon shows that zero-valent iron and persulfate are mainly used for the degradation of organic pollutants in this technical scheme, and do not play a decisive role in the solidification of heavy metals. The solidification of heavy metals mainly depends on other components in the system.

[0143] Comparative Example 5 uses the traditional water washing method, and its leaching concentration is greatly over-standard and much higher than the examples. This shows that the water washing method can only remove part of the water-soluble heavy metals, while the present application realizes the in-situ chemical fixation of heavy metals by introducing apatite minerals into the system. During the reaction, phosphate ions react with lead ions to form minerals such as chlorapatite and lead ore with stable chemical properties. This chemical fixation mechanism fundamentally reduces the activity and migration ability of heavy metals, and its effect is much better than simple physical water washing.

[0144] Therefore, the test results confirm that the present application realizes the efficient and stable solidification of heavy metals by combining the chemical fixation effect of apatite minerals with the physical encapsulation effect of mechanically activated geopolymer.

[0145] Test Example 5: ​

[0146] The experimental procedure is as follows:

[0147] (1) The samples of Example 1, Comparative Example 1 and Comparative Example 2 were selected for testing. Comparative Example 1 represents the baseline without activation, Comparative Example 2 represents the conventional mechanical chemical method, and Example 1 represents the present application.

[0148] (2) According to GB / T 17671, each component was used to prepare a plurality of test prisms with a size of 40 mm x 40 mm x 160 mm.

[0149] (3) After all the test prisms were demolded after 24 h of curing in a standard curing box (temperature (20 ± 1) °C, relative humidity ≥ 95%), they were continuously cured under the same conditions.

[0150] (4) Three test prisms were taken from each group when the age reached 3 days, 7 days, 14 days and 28 days, respectively, and their compressive strengths were tested according to GB / T 17671.

[0151] (5) The average compressive strength at each age was recorded.

[0152] The experimental results are shown in Table 5 and Figure 5 .

[0153] Table 5 Compressive strength (MPa) of each sample at different ages:

[0154] Curing age (days) Example 1 Comparative example 1 Comparative example 2 3 18.2 1.1 10.5 7 29.5 2.6 18.3 14 35.1 3.9 22.9 28 38.7 5.4 25.8

[0155] The compressive strength test data at different ages show that the sample of Example 1 exhibits a high strength (18.2 MPa) at an early age (3 days) and the strength has developed to 29.5 MPa at 7 days, close to 75% of its final strength. This indicates that the variable frequency mechanical chemical procedure of the present application generates a large amount of high-reactivity aluminosilicate precursors through effective activation of the composite powder. These precursors can rapidly undergo geopolymerization under alkali activation to quickly form a gel network structure with load-bearing capacity, so the strength of the material develops rapidly.

[0156] The strength of the sample of Comparative Example 1 develops extremely slowly, with a 28-day strength of only 5.4 MPa. This confirms that the fly ash raw material without mechanical chemical activation treatment has very low pozzolanic activity, and the degree and rate of geopolymerization are severely insufficient, which cannot form effective structural strength.

[0157] Comparative Example 2 used constant high rotation speed treatment, and its strength development rate and final strength were between Example 1 and Comparative Example 1. Although the conventional high-energy ball milling could also stimulate the activity of part of the fly ash, its strength development process was significantly slower than Example 1. This may be because the continuous high-energy input can not only destroy the particles, but also may cause excessive crushing of the particles or agglomeration, forming a particle size distribution that is not optimal, affecting the filling efficiency of the subsequent geopolymer gel and the compactness of the microstructure. The variable frequency program of the present application can more finely regulate the crushing and activation process of the particles by combining low-temperature activation with high-energy pulses, producing precursors with more reasonable particle size distribution and higher surface activity, thereby making the geopolymerization reaction more efficient and complete.

[0158] Based on the results of Test Examples 1-5, the present technical solution simultaneously achieves the harmless and resource utilization of waste incineration fly ash through an integrated processing flow.

[0159] The data of Test Example 1 proves the effective degradation of organic pollutants by the variable frequency mechano-chemical method. Through time-controlled energy input, this method promotes the reduction and dechlorination of PCDD / Fs by zero-valent iron in the low-temperature activation stage, and then triggers the oxidative decomposition of PAHs by persulfate in the high-energy pulse stage. This mechanism solves the problem of mutual consumption of oxidizing agents and reducing agents in a constant high-energy field, making the degradation rates of PCDD / Fs and PAHs reach 94.4% and 89.5%, respectively, which is significantly better than the effect of constant rotation speed treatment.

[0160] Test Examples 2 and 4 systematically verify the environmental safety of the products. The leaching concentrations of heavy metals of all example products are far below the limits of GB 16889-2008. The analysis of the comparative examples shows that the stable solidification of heavy metals is not dependent on the organic matter degradation system, but is due to the chemical fixation induced by apatite minerals, and the physical encapsulation barrier formed by the geopolymerization reaction. This chemical fixation mechanism makes the heavy metals in situ transform into stable mineral-like phases, which is much better than the traditional water washing pretreatment method of Comparative Example 5.

[0161] Test Examples 3 and 5 prove the material value of the products from two dimensions of final performance and development process. The 28-day compressive strength of the example solidified bodies all exceeds 38 MPa, which has the mechanical basis for use as building materials. The strength development curve (Test Example 5) shows that the example samples exhibit rapid strength growth in the early stage of reaction, which indicates that the variable frequency mechano-chemical process not only activates the fly ash, but also optimizes the particle size distribution and reactivity of the powder, promoting the geopolymerization reaction to be more rapid and more complete, and finally forming a more compact microstructure. This explains why its mechanical properties are better than those of samples that are not activated (Comparative Example 1) or activated by constant rotation speed (Comparative Example 2).

[0162] In summary, the core of the present application is a variable frequency mechanical chemical procedure. The procedure cooperatively drives chemical reactions of different mechanisms in a single process step through accurate regulation of reaction energy, degrades persistent organic pollutants, and activates inorganic substrates. The subsequent geopolymerization reaction not only gives the product high mechanical strength, but also forms a dense matrix that becomes a second barrier to stabilize heavy metals, ultimately converting highly contaminated waste incineration fly ash into an environmentally safe and valuable material.

[0163] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications, changes, omissions, substitutions and adaptations can be made by those skilled in the art without departing from the application, which is defined by the following claims and their equivalents.

Claims

1. A polymer composite material for waste incineration fly ash, characterized in that, Made from raw materials comprising the following parts by weight: Waste incineration fly ash: 100 portions; Apatite group minerals: 3-10 parts; Zero-cost iron powder: 1-5 parts; Persulfate: 1-5 parts; Alkali activator, wherein the alkali activator is composed of 30-50 parts of sodium silicate solution and 10-25 parts of sodium hydroxide solution; The waste incineration fly ash, apatite group minerals, zero-valent iron powder and persulfate are pre-treated with frequency conversion mechanical and chemical synergistic activation, which includes a low-temperature activation stage and a high-energy pulse activation stage, before being mixed with the alkaline activator. The rotation speed during the low-temperature activation stage is 250–350 rpm, and the duration is 75–150 min. The high-energy pulse activation phase includes running at a speed of 500-700 rpm, then pausing, and repeating this running and pausing process.

2. The waste incineration fly ash-polymer composite material according to claim 1, characterized in that, The apatite group minerals are phosphate rock powder or hydroxyapatite.

3. The waste incineration fly ash-polymer composite material according to claim 2, characterized in that, When the apatite group mineral is hydroxyapatite, it is prepared by the following steps: (1) Under the condition of pH value of 10-11, diammonium hydrogen phosphate solution is added dropwise to calcium nitrate solution to carry out the reaction and obtain a suspension; (2) The suspension is aged, filtered, washed and dried to obtain the hydroxyapatite.

4. The waste incineration fly ash-polymer composite material according to claim 1, characterized in that, The concentration of the sodium hydroxide solution is 8–14 mol / L; and / or the modulus of the sodium silicate solution is 2.5–3.

0.

5. A method for preparing a polymer composite material from waste incineration fly ash according to any one of claims 1-4, characterized in that, Includes the following steps: (a) A composite powder is obtained by mixing waste incineration fly ash, apatite group minerals, zero-valent iron powder and persulfate; (b) The composite powder is subjected to frequency conversion mechanical and chemical synergistic activation to obtain activated composite powder. The activation process includes a low-temperature activation stage and a subsequent high-energy pulse activation stage. (c) The activated composite powder from step (b) is mixed with an alkaline activator to obtain a slurry; (d) The slurry is poured into shape and cured.

6. The preparation method according to claim 5, characterized in that, The synergistic activation described in step (b) is carried out in a planetary ball mill with a ball-to-material mass ratio of (15-25):

1.

7. The preparation method according to claim 5, characterized in that, During the high-energy pulse activation phase, the pulse is run at 500-700 rpm for 3-5 minutes, paused for 1-2 minutes, and the process is repeated 4-6 times.

8. The preparation method according to claim 5, characterized in that, The curing temperature in step (d) is 20–70°C, and the curing time is 6–24 hours.

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