Coupled microwave hydrothermal dechlorination and geopolymer preparation for the solidification/stabilization of heavy metals and chlorine in municipal solid waste incineration fly ash

To improve the degradation efficiency of persistent organic pollutants (POPs) in municipal solid waste incineration fly ash (MSWIFA), as well as to overcome the difficulties of subsequent hydrothermal liquid and hydrothermal slag treatment, a two-step treatment strategy of microwave hydrothermal degradation coupled with geopolymer immobilization was proposed. Results showed that the optimal process parameters for microwave hydrothermal dechlorination were a temperature of 220 °C, a time of 1 h, and NaOH addition of 10 wt%. Microwaves accelerated the OH^- mediated hydrolysis reactions and promoted the breaking of CCl bonds, leading to dechlorination. The compressive strength of the 20 % MSWIFA-based geopolymers reached 75.79 MPa, and the immobilization rate of the heavy metals (HMs) and Cl^- surpassed 90 %. Alkaline environment provided by microwave hydrothermal promoted the formation of Ca(OH)₂, which subsequently formed Friedel's salt (3CaO•Al₂O₃•CaCl₂•10H₂O) with Cl^- in the geopolymer. The charge density difference and density of states (DOS) of Friedel's salt were analyzed by first-principles calculations, confirming that the existence of strong interactions between Ca-s, Al-p, O-p, and Cl-p states was the chemical mechanism of Cl^- immobilization. The Friedel's salt and HMs were encapsulated by geopolymers with dense silica-alumina tetrahedral frameworks, achieving the solidification/stabilization (S/S) of HMs and Cl^-. This work provided a new approach for the environmentally sound and resourceful treatment of MSWIFA.

Resource utilization of municipal solid waste incineration fly ash - cement and alkali-activated cementitious materials: A review

The increase in municipal solid waste (MSW) production has led to an increase in MSW incineration fly ash (MSWIFA) production. MSWIFA contains toxic and harmful substances such as heavy metals and dioxins, which can cause harm to the environment if not treated properly. Only a few MSWIFAs will be landfilled directly, and the rest will need to be treated by other methods. The treatment of MSWIFA can be divided into three types: separation, stabilization/solidification (S/S), and thermal treatment, which are either not fully developed or too costly. Resource utilization is a sustainable means of treating MSWIFA. MSWIFA is used in the production of cement and alkali-activated cementitious materials as a means of resource utilization with significant advantages. This can alleviate the consumption of nature and reduce greenhouse gas emissions in conventional cement production. Compared with MSWIFA cement, MSWIFA alkali-activated cementitious material can be achieved with almost no consumption of natural resources, which is worthy of further research to realize the large-scale application of MSWIFA. At the end of the paper, the perspective of separation of dioxins from MSWIFA, co-processing of MSWI ash, and production of "MSWIFA green materials" is presented.

Exploiting in-situ solid-state NMR spectroscopy to probe the early stages of hydration of calcium aluminate cement

We report a high-field in-situ solid-state NMR study of the hydration of CaAl₂O₄ (the most important hydraulic phase in calcium aluminate cement), based on time-resolved measurements of solid-state ²⁷Al NMR spectra during the early stages of the reaction. A variant of the CLASSIC NMR methodology, involving alternate recording of direct-excitation and MQMAS ²⁷Al NMR spectra, was used to monitor the ²⁷Al species present in both the solid and liquid phases as a function of time. Our results provide quantitative information on the changes in the relative amounts of ²⁷Al sites with tetrahedral coordination (the anhydrous reactant phase) and octahedral coordination (the hydrated product phases) as a function of time, and reveal significantly different kinetic and mechanistic behaviour of the hydration reaction at the different temperatures (20 °C and 60 °C) studied.

Preparation of red mud-based geopolymer materials from MSWI fly ash and red mud by mechanical activation

A novel method to activate red mud was proposed in this study. Municipal solid waste incineration fly ash (MSWIFA) and red mud were utilized to prepare red mud-based geopolymer materials (RGM). The hydration characteristics of RGM were studied by X-ray diffraction, scanning electronic microscopy, and Fourier transform infrared spectroscopy. The long-term stability and physical properties of RGM were tested by freeze-thaw cycle, European Community Bureau reference (BCR) and unconfined compressive strength (UCS) tests. Results showed that mechanical activation can not only effectively activate red mud, but also effectively improve the reaction of MSWIFA and red mud. When 14% sodium silicate was added to the binder, the UCS reached 12.75 MPa at 28 days. In the RGM, aluminosilicate was effectively activated by mechanical activation and reacted with calcium ion to form complex hydration products. The activator reacts adequately with activated aluminum to form a high-strength geopolymer. The freeze-thaw cycles and BCR test results also showed that the RGM had long-term stability and the characteristics satisfied the requirements of MU10 fly ash bricks. This study demonstrated that RGM may be utilized in cement composites.

A new NMR crystallographic approach to reveal the calcium local structure of atorvastatin calcium

We combine experimental and computational determination of ⁴³Ca solid-state NMR parameters (chemical shift tensors, quadrupolar coupling tensors, and Euler angles) to constrain the structure of the local calcium–ligand coordination environment.

A 43Ca and 13C NMR study of the chemical interaction between poly(ethylene-vinyl acetate) and white cement during hydration

(43)Ca and (13)C NMR methods were used to study the chemical interaction of poly(ethylene-vinyl acetate) (PEVAc) admixture in commercial-grade white cement. From (43)Ca NMR it is shown both that PEVAc induces modest changes in the hydrated cement structure, and that hydrated commercial cement is significantly more complex than models that have been used for its structure in past work. The (13)C NMR results show that the PEVAc hydrolysis occurs early in the cement hydration acceleration period, with a rate well-fit by an exponential decay using a time constant of 6±1 days.