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Characterization of naturally aged cement-solidified MSWI fly ash
Bing Du1, Jiantao Li1, Wen Fang1
1Key Laboratory for Solid Waste Management and Environment Safety, School of Environment, Tsinghua University, Beijing, PR China.
Waste Management (New York, N.Y.)
|November 21, 2018
Summary
Long-term aging of cement-solidified municipal solid waste incineration fly ash (MSWI-FA) significantly reduces soluble salts but leaves heavy metals like lead in potentially leachable forms. Further research is needed to understand the environmental risks of aged MSWI-FA.
Area of Science:
- Environmental Science
- Geochemistry
- Materials Science
Background:
- Solidification/stabilization (S/S) is a common treatment for municipal solid waste incineration fly ash (MSWI-FA).
- Understanding the long-term physicochemical characteristics of aged MSWI-FA is crucial for environmental risk assessment.
- Cement-solidified MSWI-FA aged for 6 years (FA-6) was studied to evaluate its properties after natural aging.
Purpose of the Study:
- To investigate the physicochemical characteristics of naturally aged cement-solidified MSWI-FA.
- To determine the distribution and leaching behavior of heavy metals and inorganic salts in aged MSWI-FA.
- To identify the controlling mineral phases for heavy metal immobilization and release.
Main Methods:
- Analysis of elemental and mineral composition, microstructure, and thermogravimetric properties of FA-6.
- Investigation of leaching characteristics for inorganic salts, anions, and heavy metals (Cd, Cr, Cu, Pb, Zn).
- Application of pH-dependent leaching tests combined with the geochemical model LeachXS to determine heavy metal chemical forms.
Main Results:
- Soluble salt content in FA-6 decreased by over 92% compared to fresh MSWI-FA.
- Significant proportions of Pb (100%), Cd (100%), and Zn (58%) were found in the non-mineral phase of FA-6, indicating potential environmental risk.
- Lead leaching concentration (4007.37 μg/L) exceeded landfill limits (250 μg/L), with Pb5(PO4)3Cl and Pb2(OH)3Cl identified as controlling phases.
Conclusions:
- Natural aging significantly reduces soluble salts in cement-solidified MSWI-FA but may not fully immobilize heavy metals.
- The non-mineral phase and specific mineral phases like smithsonite control the leaching of heavy metals, posing potential environmental risks.
- Understanding the geochemical behavior of aged MSWI-FA is essential for safe disposal and management strategies.
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