Synergistic influence of diatomite and MoS2 nanosheets on the self-alkali-activated cementation of the municipal solid waste incineration fly ash and mechanisms

Investigation of waste alkali-activated cementing material using municipal solid waste incineration fly ash and dravite as precursors: Mechanisms, performance, and on-site application

The proper treatment of municipal solid waste incineration fly ash (MSWIFA) is a crucial concern due to its hazardous nature and potential environmental harm. To address this issue, this study innovatively utilized dravite and black liquor to solidify MSWIFA. The semi-dry pressing method was employed, resulting in the production of waste alkali-activated cementing material (WACM). This material demonstrated impressive compressive and flexural strength, reaching 45.89 MPa and 6.55 MPa respectively, and effectively solidified heavy metal ions (Pb, Cr, Cu, Cd, and Zn). The leaching concentrations of these ions decreased from 27.15, 10.36, 8.94, 7.00, and 104.4 mg/L to 0.13, 1.05, 0.29, 0.06, and 12.28 mg/L, respectively. The strength of WACM increased by 3 times compared to conventionally produced materials. Furthermore, WACM exhibited excellent long-term performance, with acceptable heavy metal leaching and minimal mechanical degradation. Experimental and theoretical analyses revealed the heavy metal solidification mechanisms, including chemical binding, ion substitution and physical encapsulation. Finally, the on-site application of WACM confirmed its feasibility in meeting both environmental and strength requirements.

Characterization and stabilization of incineration fly ash from a new multi-source hazardous waste co-disposal system: field-scale study on solidification and stabilization

The multi-source hazardous waste co-disposal system, a recent innovation in the industry, offers an efficient approach for hazardous waste disposal. The incineration fly ash (HFA) produced by this system exhibits characteristics distinct from those of typical incineration fly ash, necessitating the use of adjusted disposal methods. This study examined the physicochemical properties, heavy metal content, heavy metal leaching concentration, and dioxin content of HFA generated by the new co-disposal system and compared them with those of conventional municipal waste incineration fly ash. This study investigated the solidification and stabilization of HFA disposal using the organic agent sodium diethyl dithiocarbamate combined with cement on a field scale. The findings revealed significant differences in the structure, composition, and dioxin content of HFA and FA; HFA contained substantially lower levels of dioxins than FA did. Concerning the heavy metal content and leaching; HFA exhibited an unusually high concentration of zinc, surpassing the permitted emission limits, making zinc content a critical consideration in HFA disposal. After stabilization and disposal, the heavy metal leaching and dioxin content of HFA can meet landfill disposal emission standards when a 1% concentration of 10% sodium diethyldithiocarbamate (DDTC) and 150% silicate cement were employed. These results offer valuable insights into the disposal of fly ash resulting from incineration of mixed hazardous waste.

Study on the relation between macro-mechanical properties and micro-structure of geopolymers with different activator modulus

The fly ash-based geopolymer (FABG) containing slag has distinct advantages in field applications. In this work, given that the activator modulus is a significant parameter affecting the properties of FABG, the influence mechanism of activator modulus (SiO2/Na2O from 1.1 to 1.5) on the macro-mechanical properties and micro-structure composition of FABG containing slag is explored. According to the experimental results, the early product of FABG containing slag is mainly C-A-S-H gel, and N-(C)-A-S-H gel with high cross-linking degree is formed at a later stage. Both C-A-S-H and N-A-S-H gels are distinguished in reaction products by using 29Si NMR. The Si/Al ratio of N-A-S-H gel and C-A-S-H gel decreases with the increase of modulus, resulting in an increase of MCL in C-A-S-H. Appropriate activator modulus can effectively activate slag and fly ash to yield more gels and form a more uniform and dense micro-structure, resulting in a lower threshold pore size and macroporosity, and an associated increase of the material strength. Meanwhile, the gel amount has a positive effect on the strength development in the FABG.