The effects of the mechanical-chemical stabilization process for municipal solid waste incinerator fly ash on the chemical reactions in cement paste.

A water extraction process can remove the soluble salts present in municipal solid waste incinerator (MSWI) fly ash, which will help to increase the stability of the synthetic materials produced from the MSWI fly ash. A milling process can be used to stabilize the heavy metals found in the extracted MSWI fly ash (EA) leading to the formation of a non-hazardous material. This milled extracted MSWI fly ash (MEA) was added to an ordinary Portland cement (OPC) paste to induce pozzolanic reactions. The experimental parameters included the milling time (96h), water to binder ratios (0.38, 0.45, and 0.55), and curing time (1, 3, 7 and 28 days). The analysis procedures included inductively coupled plasma atomic emission spectroscopy (ICP/AES), BET, mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) imaging. The results of the analyses indicate that the milling process helped to stabilize the heavy metals in the MEA, with an increase in the specific surface area of about 50times over that of OPC. The addition of the MEA to the OPC paste decreased the amount of Ca(OH)2 and led to the generation of calcium-silicate-hydrates (C-S-H) which in turned increased the amount of gel pores and middle sized pores in the cement. Furthermore, a comparison shows an increase in the early and later strength over that of OPC paste without the addition of the milled extracted ash. In other words, the milling process could stabilize the heavy metals in the MEA and had an activating effect on the MEA, allowing it to partly substitute OPC in OPC paste.

Mechanochemically induced synthesis of anorthite in MSWI fly ash with kaolin.

The process of mechanical milling has been found to effectively stabilize heavy metals in municipal solid waste incinerator (MSWI) fly ash, as well as to restrain the evaporation of heavy metals during thermo-treatment. This method is adopted in this study and the composition and degree of amorphization adjusted to improve the efficiency of crystalline anorthite synthesis. Different milling times (1, 5, 10 and 20 h) and different sintering temperatures (900, 950, 1000, 1100, 1200 and 1300 °C) are utilized. The extracted fly ash and kaolin (KEFA) were mixed to simulate an anorthite composite. The experimental results indicate that the degree of amorphization of the KEFA increased as the milling time increased. Furthermore, the synthesis of crystalline anorthite increased as the degree of amorphization increased. The milling process allowed a reduction in the synthesization temperature from 1300 °C to 950 °C. The heavy metals are sealed in during the liquid sintering phase, which reduces the amount of heavy metals released from the sintered specimens.

Direct observation of charge ordering in magnetite using resonant multiwave x-ray diffraction.

Charge disproportion at octahedral Fe sites in magnetite was observed at low temperature using two inversion-symmetry related three-wave resonant x-ray diffraction, 022-311 and 002-̅3̅1, near the iron K edge. Both of the three-wave cases involve the (002) forbidden-weak reflection. The self-normalized three-wave to two-wave (002) diffraction intensity ratio automatically cancels the self-absorption effect and leads to direct determination of charge disproportion for magnetite below 120 K. This approach provides a more direct and effective way for extracting charge-ordering information.