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我国生活垃圾的年产量逐渐增加。根据国家统计年鉴数据[1],我国生活垃圾的年产量从2015年的1.91×108 t增长到2020年的2.35×108 t。目前,生活垃圾的处理方式主要有填埋和焚烧2种。其中,焚烧法具有降低垃圾体积、消灭病原体、分解有害物质和回收能量等优势,是生活垃圾的重要处理方式[2]。但在垃圾焚烧过程中,垃圾中的重金属在炉膛中挥发,然后富集到飞灰中[3]。因此,垃圾焚烧飞灰被归类为危险废物,随着垃圾焚烧技术的推广应用,其处理处置已经引起了广泛关注。
目前,垃圾焚烧飞灰的处理方法主要有填埋[4]、水泥固化[5]、螯合剂稳定[2]、烧结[6]、熔融[7]等。其中,通过高温热处理法将垃圾焚烧飞灰转化成高附加值的微晶玻璃,既可以实现其无害化处理,又可制备高附加值产品,被认为是一种比较有潜力的方法。目前,利用垃圾焚烧飞灰制备微晶玻璃主要以纯化学试剂或自然资源作为辅料对垃圾焚烧飞灰进行成分调控,并引入一定量的晶核剂来促进结晶最后得到微晶玻璃产品。李保庆等[8]以垃圾焚烧飞灰和废玻璃为主要原料,以SiO2、Na2CO3、CaO、Al2O3、MgO为辅助原料制备了微晶玻璃。当烧结温度为1 030 °C时,微晶玻璃的机械性能最优,其密度为2.81 g∙cm−3、抗弯强度为83.78 MPa、显微硬度为7.40 GPa。PONSOT等[9]利用垃圾焚烧飞灰、粉煤灰、煤脱硫渣、硅溶胶、废玻璃和高岭土为原料制备微晶玻璃,混合原料在1 050 ℃下直接烧结后得到的微晶玻璃具有最优的物理机械性能,其密度为1.80 g∙cm−3,抗弯强度为(38.20±5.40)MPa。刘汉桥等[10]将垃圾焚烧飞灰和废玻璃以3∶1的比例混合并引入3%晶核剂TiO2,通过熔融烧结法制备了微晶玻璃,在850 ℃下烧结得到性能最优的微晶玻璃,其密度为2.62 g∙cm−3,抗弯强度为90.44 MPa,耐酸碱性分别为97.30%、99.10%。在上述的研究中,虽然制得的微晶玻璃具有优良的物理化学性能,但是纯化学试剂和晶核剂的使用提高了废物基微晶玻璃的成本。而利用具有成分互补特点的固体废弃物作为配料,实现全废物基飞灰微晶玻璃的研究少有报道。
在CaO-Al2O3-SiO2微晶玻璃系统中,SiO2是主要的玻璃网络形成氧化物,能增强玻璃网络的连接程度。CaO是主要的玻璃网络外体氧化物,可以提供游离氧,打破玻璃网络结构,促进玻璃的析晶,与SiO2的作用相反。吴春丽等[11]研究了CaO/SiO2比对不锈钢渣CaO-Al2O3-SiO2微晶玻璃性能的影响。结果表明,微晶玻璃的主晶相为硅灰石,性能在CaO/SiO2比为0.72时达到最优,其密度为3.11 g∙cm−3,显微硬度为6.49 GPa,吸水率为0.11%,耐酸性为96.51%,耐碱性为99.02%。汪振双等[12]研究了CaO/SiO2比对粉煤灰CaO-Al2O3-SiO2微晶玻璃性能的影响。微晶玻璃的主晶相为副硅灰石,次晶相为钙长石,当CaO/SiO2比为0.33时,微晶玻璃性能最优,其密度为2.87 g∙cm−3,抗压强度为105.28 MPa,抗弯强度为45.62 MPa。张雪峰等[13]研究了CaO/SiO2比对复合尾矿微晶玻璃性能的影响。结果表明,微晶玻璃的主晶相为普通辉石相,CaO/SiO2比的减小对样品力学性能和密度的影响不大,当CaO/SiO2比等于0.32时,微晶玻璃的性能最优,其抗折强度为169.20 MPa,密度为2.92 g∙cm−3,耐酸碱性分别为95.00%和98.00%。由此可见,碱度对不同固体废物基微晶玻璃性能的作用机制并不相同。因此,研究碱度对全废物基微晶玻璃性能的影响很有必要。
因此,本研究以垃圾焚烧飞灰为主原料,优势配伍具有成分互补特点的粉煤灰和废玻璃作为辅料,通过熔融烧结法制备了CaO-Al2O3-SiO2系统微晶玻璃。对不同碱度基础玻璃的析晶动力学和析晶机理进行了分析,并且研究了碱度和烧结温度对垃圾焚烧飞灰基微晶玻璃的晶相转变、机械物理性能、微观结构以及重金属浸出毒性的影响
利用生活垃圾焚烧飞灰制备全废物基微晶玻璃
Preparation of entirely waste-based glass-ceramics from municipal solid waste incineration fly ash
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摘要: 生活垃圾焚烧飞灰被划定为危险废物,随着垃圾焚烧发电技术的推广应用,其处理处置引起了广泛关注。以垃圾焚烧飞灰为主原料,通过优势配伍粉煤灰和废玻璃,制备了全废物基CaO-Al2O3-SiO2系统微晶玻璃。重点研究了烧结温度与碱度(CaO/SiO2)对微晶玻璃的晶相演变、机械物理性能和微观结构的影响,以及不同微晶玻璃的析晶机理。结果表明,当碱度在0.48-0.70时,基础玻璃的结晶方式都为三维整体结晶,但碱度的升高可以降低基础玻璃的结晶活化能。所有微晶玻璃中的晶相为钠长石、硅灰石和钙铝黄长石,不受烧结温度和碱度变化的影响。当碱度为0.56(GC2)时,抗压强度随烧结温度的升高在总体上呈现增加的趋势,但显微维氏硬度却逐渐降低。随着碱度的增加,抗压强度先增加然后降低,当碱度为0.56时,最大值为553.77 MPa,显微维氏硬度逐渐升高,当碱度为0.70时,其最大值为5.89 GPa。此外,典型重金属的毒性浸出测试结果表明,微晶玻璃的重金属浸出浓度远低于规定的浸出阈值,对环境无潜在风险。该研究结果可为垃圾焚烧飞灰资源化利用提供参考。Abstract: Municipal solid waste incineration fly ash was categorized as hazardous waste and its management had drawn widespread attention with the promotion and application of waste-to-energy technology. An entirely waste-based glass-ceramic of CaO-Al2O3-SiO2 system was synthesized from municipal solid waste incineration fly ash, coal fly ash and waste glass. The effect of sintering temperature and basicity (CaO/SiO2) on the crystal phase transition, physical-mechanical performance and microstructure of the glass-ceramics and the crystallization kinetic of parent glasses were investigated. The results indicated that all the parent glass exhibited three-dimensional bulk crystallization when basicity was in range of 0.48-0.70, the increase of basicity decreased the crystallization activation energy of parent glass. The coexisting crystal phases in the glass-ceramics were anorthite, wollastonite and gehlenite and the type of crystal phases was not affected by sintering temperature and basicity. When basicity was 0.56 (GC2), the compressive strength increased in general with the increase of sintering temperature but the microhardness exhibited the opposite trend. With the increase of basicity, the compressive strength increased firstly and then decreased, its maximum value was 553.77 MPa when basicity was 0.56, the microhardness increased and its maximum value was 5.89 GPa when basicity was 0.70. In addition, the toxic leaching test results of typical heavy metals showed that the leaching concentrations of heavy metals in glass-ceramics were far below limitation and there was no potential risk to the environment. The results of this study can provide theoretical and data support for the resource utilization of municipal solid waste incineration fly ash.
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表 1 原材料的化学成分
Table 1. Chemical compositions of raw materials
% 供试样品 CaO SiO2 Al2O3 MgO Na2O Cl SO3 其他 垃圾焚烧飞灰 42.80 1.92 0.54 0.82 12.10 24.5 7.43 9.89 粉煤灰 2.45 51.10 37.30 0.67 0.21 0.06 0.68 7.53 废玻璃 10.4 69.20 1.44 3.79 12.90 0.08 0.35 1.84 表 2 不同混合比例原料的化学成分
Table 2. Chemical compositions of raw materials under various mixing ratios
% 样品编号 CaO SiO2 Al2O3 MgO Na2O GC1 18.96 39.32 13.68 1.66 8.18 GC2 20.18 35.05 15.42 1.35 7.50 GC3 21.40 30.78 17.17 1.05 6.83 表 3 不同碱度微晶玻璃的结晶峰温度(Tp/℃)和析晶动力学参数(Ec, n)
Table 3. Crystallization temperatures (Tp/℃) and crystallization kinetic parameters (Ec, n) of glass-ceramics with various basicity
样品编号 加热速率/(℃∙min−1) Ec /(kJ∙mol-1) n 5 10 15 20 GC1 910 927 940 948 245.10 3.90 GC2 926 960 960 970 204.44 4.59 GC3 940 961 984 982 199.49 7.08 表 4 微晶玻璃的重金属浸出浓度
Table 4. The heavy metal leaching concentrations of the resultant glass-ceramics
样品 重金属浸出浓度 (mg∙L−1) Cd Cr Cu Ni Pb Zn GC2-850 ℃ 2.52 ND ND 0.97 1.96 0.01 GC2-900 ℃ 2.36 ND ND 1.43 3.13 ND GC2-950 ℃ 2.44 ND ND 1.30 1.30 ND GC2-1000 ℃ 2.54 ND ND 1.30 2.74 ND GC2-1050 ℃ 2.59 ND ND 1.23 2.59 ND GC1-950 ℃ 2.75 ND ND 0.41 0.75 ND GC3-950 ℃ 2.47 ND ND 1.23 2.56 ND 毒性阈值a 5.0 1.0 - - 5.0 - 毒性阈值b 5.0 1.0 100 10 5.0 100 注:ND表示未检测出;a US EPA TCLP 阈值;b中国国家标准《危险废物鉴别标准 浸出毒性鉴别》(GB 5085.3–2007)。 -
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