Characterization of heavy metals solidification during hydrothermal synthesis of tobermorite from incineration fly ash
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摘要:
城市生活垃圾焚烧飞灰的环境安全利用处置已成为当前环境管理部门和行业部门亟待解决的问题。为降低焚烧飞灰中重金属对环境的潜在风险，以水洗飞灰为原料水热合成托贝莫来石，探讨Ca与(Si+Al)的摩尔比〔以Ca/(Si+Al)表示〕对水热产物的晶相组成、微观形貌和表面官能团的影响，研究水热过程中重金属（Hg、Ni、Pb、Zn和Cr）的浸出浓度、浸出率、液相迁移率、形态分布和环境风险的变化。结果表明：Ca/(Si+Al)对水热产物的类型具有重要影响，Ca/(Si+Al)的增加有利于抑制沸石类结构的生成，促进托贝莫来石的形成。随着托贝莫来石的形成，水热产物中5种重金属的毒性浸出浓度和浸出率逐渐降低，相较于水洗飞灰，在最佳比例为1.10的条件下水热产物中重金属的浸出浓度分别下降99.5%、99.0%、99.4%、88.9%和63.7%，浸出率低至0.25%、0.08%、0.01%、0.01%和2.73%，同时重金属向液相的迁移率仅为1.41%、4.28%、0.29%、0.05%和0%，表明大部分重金属均稳定地存在于固相产物中，而不是迁移至水热液中。这归因于托贝莫来石的形成增加了5种重金属残渣态的占比，降低了重金属的迁移性。风险评价指数（risk assesssment code，RAC）结果显示，最佳比例条件下水热产物中5种重金属的RAC均低于10%，达到环境低风险水平。综上，水热合成托贝莫来石是一种稳定焚烧飞灰中重金属很有前景的方法，为富含重金属的危险废物的安全处置和回收利用提供了一种可行的替代方案。
Abstract:The environmentally safe utilization and disposal of municipal solid waste incineration fly ash is an urgent problem that needs to be addressed by environmental management and industry departments. To mitigate the potential risk of heavy metals in incineration fly ash to the environment, the effects of Ca/(Si+Al) (molar ratio) on the crystalline phase composition, microscopic morphology, and surface functional groups of hydrothermally synthesized tobermorite using washed fly ash were investigated. Additionally, the changes in leaching concentration, leaching rate, liquid-phase mobility, morphological distribution, and environmental risk of heavy metals (Hg, Ni, Pb, Zn, and Cr) during the hydrothermal process were examined. The results demonstrated that Ca/(Si+Al) had a significant impact on the type of hydrothermal products, higher Ca/(Si+Al) molar ratio was favorable for inhibiting the formation of zeolite-like structures and promoting the formation of tobermorite. As tobermorite formed, the toxic leaching concentrations and leaching rates of the five heavy metals in the hydrothermal products gradually decreased. Compared to washed fly ash, the leaching concentrations of heavy metals in the hydrothermal products under the optimal ratio (1.1) condition decreased by 99.5%, 99.0%, 99.4%, 88.9%, and 63.7%, respectively, while the leaching rates reached as low as 0.25%, 0.08%, 0.01%, 0.01%, and 2.73%. Moreover, the migration of heavy metals to the liquid phase was limited to 1.41%, 4.28%, 0.29%, 0.05%, and 0%, indicating that most heavy metals were stably present in solid-phase products rather than migrating to the hydrothermal liquid. This was attributed to the formation of tobermorite, which increased the proportion of the five heavy metal residue states and decreased heavy metal mobility. The risk assessment code (RAC) results revealed that RAC of the five heavy metals in the hydrothermal products under the optimal ratio conditions was less than 10%, reaching an environmentally low-risk level. In summary, hydrothermal synthesis of tobermorite was a promising method for stabilizing heavy metals in incineration fly ash, providing a viable alternative for the safe disposal and recycling of hazardous wastes rich in heavy metals.
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Key words:
- waste incineration fly ash /
- tobermorite /
- harmless /
- hydrothermal treatment /
- leaching toxicity
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图 8 水热过程中重金属向液相的迁移率
Figure 8. Mobility of heavy metals to liquid phase during hydrothermal processes
图 9 WFA和水热产物的BCR形态分析
Figure 9. BCR morphological analysis of WFA and hydrothermal products
表 1 WFA的化学组成
Table 1. Chemical composition of WFA
元素 占比/% 元素 占比/% Ca 78.9 K 0.90 Si 2.80 Ti 1.35 Al 1.29 Fe 2.40 Cl 1.50 Zn 1.78 S 4.19 Na 0.59 
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表 2 WFA和水热产物中的重金属浓度
Table 2. Heavy metal contents of WFA and hydrothermal products
mg/kg 样品 Hg Ni Pb Zn Cr WFA 17.7 27.8 857.7 4 818.2 76.9 WHT-1 5.9 13.3 308.0 2 420.4 55.7 WHT-2 7.9 15.1 455.0 2 890.5 58.8 WHT-3 10.9 15.9 521.9 3 099.0 69.3
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表 3 WFA和水热产物中的重金属浸出浓度和浸出率
Table 3. Heavy metal leaching concentrations and leaching rates of WFA and hydrothermal products
样品 浸出浓度/(mg/L) 浸出率/% Hg Ni Pb Zn Cr Hg Ni Pb Zn Cr WFA 0.210 0.103 0.325 0.198 0.545 11.86 3.71 0.38 0.04 7.09 WHT-1 0.027 0.011 0.038 0.062 0.291 4.49 0.83 0.12 0.03 5.22 WHT-2 0.019 0.002 0.017 0.073 0.226 2.43 0.15 0.04 0.03 3.85 WHT-3 0.003 0.001 0.002 0.022 0.189 0.25 0.08 0.01 0.01 2.73 GB 5085.3—2007中浓度限值 0.10 5.00 5.00 100 15
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表 4 WFA和水热产物的RAC评价结果
Table 4. Results of RAC evaluation of WFA and hydrothermal products
% 样品 Hg Ni Zn Pb Cr WFA 44.68 13.56 0.57 2.03 6.52 WHT-1 1.55 4.23 0.11 0.07 5.48 WHT-2 1.34 5.03 0.07 0.05 3.72 WHT-3 1.04 0.95 0.04 0.04 2.40
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