Solidification and immobilization of MSWI fly ash through aluminate geopolymerization: Based on partial charge model analysis.
This study presents an integrated synopsis of the solidification and immobilization mechanisms of fly ash-based geopolymers. A rational analysis of the ion reactions involved in geopolymerization was conducted using the partial charge model (PCM). The following conclusions were obtained: (1) heavy metal cations cannot be immobilized as counter cations through exchange with Na+; (2) isomorphous substitution of heavy metals in the geopolymer can be expected from the condensation reaction between the hydrolyzed heavy metal species and aluminosilicate; (3) the hydrolyzed species condensation could result in solidification and immobilization and be promoted by aluminates; and (4) a geopolymer with the highest immobilization and solidification efficiency can be obtained at an intermediate pH value. The partial charges on the framework of Si, Al, and O in the primary building blocks of aluminosilicate and heavy metal-doped aluminosilicate were confirmed through XPS and29Si NMR spectroscopy analyses. The effects of activator dosage and types on fly ash-based geopolymers were also investigated, and the results verify the PCM analysis. A geopolymer with the highest strength was produced at an intermediate alkaline dosage. Silicate or aluminate introduced into the activator improved the strength and immobilization efficiency, and aluminate exhibited better performance. Heavy metals bound to the exchangeable or acid-soluble fraction were transformed into aluminosilicate species during geopolymerization.
School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China; Beijing Key Laboratory of Resource-oriented Treatment of Industrial Pollutants, China.
Lei
L
Zheng
School of Environment, Tsinghua University, Beijing 100084, China; Key Laboratory for Solid Waste Management and Environment Safety (Tsinghua University), Ministry of Education of China, Beijing 100084, China.
Wei
W
Wang
State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China. Electronic address: gaoxb@craes.org.cn.
Xingbao
X
Gao
D000538:Aluminum Silicates / Q000737:chemistry; D060729:Coal Ash / Q000737:chemistry*; D019245:Compressive Strength; D009682:Magnetic Resonance Spectroscopy; D019216:Metals, Heavy / Q000737:chemistry; D056951:Photoelectron Spectroscopy; D011108:Polymers / Q000737:chemistry*; D012037:Refuse Disposal / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
D000538:Aluminum Silicates; D060729:Coal Ash; D019216:Metals, Heavy; D011108:Polymers; C049037:aluminosilicate
Aluminate; Immobilization mechanism; MSWI fly ash based geopolymer; Partial charge model; Solidification