A green and multi-win strategy for coal fly ash disposal by CO2 fixation and mesoporous silica synthesis.

Coal combustion provides plenty of energy, along with enormous coal fly ash (CFA) and CO2 emission. CFA could be recycled for mesoporous silica synthesis, but expensive templates are usually needed. In this work, we proposed a multi-win strategy using CO2 as the precipitator and template. Mesoporous silica powders, with a maximum specific surface area of 355.45 m2/g, a pore volume of 0.73 cm3/g, and an average pore size of around 7.67 nm, were synthesized. The influences of silicon concentration, CO2 flow rate, and ultrasound were investigated. In addition, the Na2CO3 by-product was produced with a purity of over 92 %. By averagely calculating, 1 ton CFA could generate 285 kg mesoporous silica and 1.02 t crude Na2CO3. Around 433 kg of CO2 could be absorbed. Therefore, multi-goals of CFA disposal, CO2 storage, and valuable silica materials production were realized, and the study could pave the way for large-scale industrial applications.

Characteristics, application and modeling of solid amine adsorbents for CO2 capture: A review.

In recent years, global warming has become an important topic of public concern. As one of the most promising carbon capture technologies, solid amine adsorbents have received a lot of attention because of their high adsorption capacity, excellent selectivity, and low energy cost, which is committed to sustainable development. The preparation methods and support materials can influence the thermal stability and adsorption capacity of solid amine adsorbents. As a supporting material, it needs to meet the requirements of high pore volume and abundant hydroxyl groups. Industrial and biomass waste are expected to be a novel and cheap raw material source, contributing both carbon dioxide capture and waste recycling. The applied range of solid amine adsorbents has been widened from flue gas to biogas and ambient air, which require different research focuses, including strengthening the selectivity of CO2 to CH4 or separating CO2 under the condition of the dilute concentration. Several kinetic or isotherm models have been adopted to describe the adsorption process of solid amine adsorbents, which select the pseudo-first order model, pseudo-second order model, and Langmuir isotherm model most commonly. Besides searching for novel materials from solid waste and widening the applicable gases, developing the dynamic adsorption and three-dimensional models can also be a promising direction to accelerate the development of this technology. The review has combed through the recent development and covered the shortages of previous review papers, expected to promote the industrial application of solid amine adsorbents.

Recycling municipal solid waste incineration fly ash in super-lightweight aggregates by sintering with clay and using SiC as bloating agent.

Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste and requires proper treatments. Sintering of MSWI fly ash for the production of lightweight aggregate (LWA) is a promising treatment technology, while the dependence on natural bloating clay to produce high quality LWA has limited its wide application. In this study, by using SiC as a bloating agent, normal clay could be used to produce super-lightweight aggregate (bulk density <500 kg/m3) with MSWI fly ash. Effects of SiC addition amount, sintering temperature and duration on LWA performance were studied. The results showed that LWA with SiC addition of 0.1-0.5 wt% had significant expansion at sintering temperature of 1120 °C-1160 °C. The optimal conditions were 0.3 wt% SiC addition and sintering at 1120 °C for 30 min, and the bulk density could reach 212 kg/m3 with other properties meeting the LWA standard (GB/T 17431.1-2010). Further, the heavy metal leaching toxicity was significantly decreased after sintering and met the MSWI fly ash utilization standard (HJ 1134-2020). The X-ray diffraction results revealed the formation of a complex diopside-based phase after sintering. This study provides a new approach for recycling MSWI fly ash in LWA without dependence on specific clay resources, and makes this technology wider applicability.

Effect of microbially induced calcium carbonate precipitation treatment on the solidification and stabilization of municipal solid waste incineration fly ash (MSWI FA) - Based materials incorporated with metakaolin.

Microbially induced calcium carbonate precipitation (MICP) has been considered as a potential treatment method for the solidification and stabilization of municipal solid waste incineration fly ash (MSWI-FA).The main obstacle for MICP treatment of MSWI-FA is the harsh environment which causes the bacteria fail to maintain their urease activity effectively, thus decreases the solidification effect and material properties. Currently, there is no research on blending metakaolin (MK) as a protective carrier for the bacteria into the MSWI-FA. The effect of the MICP process on the curing properties of MSWI FA-based cementing materials in the MK and MSWI-FA reaction system is largely unknown. In this study, different mixing ratios of MK were used to adjust the Ca/Si/Al ratio in the mixture, and the properties of the cementing material (MSWI-FA mixed with MK and water) and the MICP-treated material (MSWI-FA mixed with MK and bacterial solution) were investigated. This study contributes to find suitable additives to promote effect of MICP on the solidification of MSWI-FA and the improvement of material properties. The results showed when the mixing ratio of MSWI FA was 90 wt %, the MICP treatment was able to increase the compressive strength of the samples up to 0.99 Mp, and the compressive strength of samples reached 1.46 MPa, when the mixing ratio of MSWI FA was 80 wt %. Though the metakaolin did not show inhibitory effect on the urease activity, the compressive strength of the MICP-treated samples did not further show a significant increase when the mixture of MK was increased from 20 wt% to 30 wt%. Further investigation suggested that MICP activities of bacteria utilizing calcium sources could have an impact on the formation/deformation of calcium-containing hydration products in the reaction system, thus affecting the mechanical and chemical properties of MSWI based materials. MICP treatment is effective in the immobilization of certain heavy metals of MSWI FA, especially for Pb, Cd and Zn. This research shows the potential of using MICP to treat the MSWI fly ash, meanwhile, it is necessary to find suitable reaction system with the proper additives in order to further improve the properties of the MSWI FA based material in terms of mechanical performance.

Biodrying with the hot-air aeration system for kitchen food waste.

Biodrying is a promising method that produces bio-stabilized output with minimum pretreatment requirements. In this study, a hot-air supply system was added to the traditional biodrying process for kitchen waste, which showed significant reduction in moisture content in 5 days (maximum reduction of 37.45%). A series of experiments was conducted to optimize the hot-air biodrying system utilizing different aeration rates, temperatures, and mixing ratios of feedstock to bulking agents. The results showed that a 65 °C aeration temperature led to the highest water removal rate and low volatile solids consumption rate, with the biodrying index reaching 4.9 g water per gram of volatile solids. On the other hand, evaluation of the overall biodrying efficiency based on the weight loss and bio-stabilization showed that intermittent aeration temperature at 55 °C performed best, offering suitable conditions for water evaporation and bio-degradation. In combination with a flow rate of 0.8 L/kg*min and 1:1 mixing ratio, these conditions resulted in the maximum volatile solids consumption of 26.26% in 5 days. The volatile solids consumption and 34.47% water removal rate of the trial had contributed to a total of 64.13% weight loss. The weight loss was even higher than that of a conventional biodrying system which was conducted for more than 14 days.

Manufacture of alkali-activated and geopolymer hybrid binder (AGHB) by municipal waste incineration fly ash incorporating aluminosilicate supplementary cementitious materials (ASCM).

The treatment and disposal of municipal solid waste incineration fly ash (MSWI FA) faces many challenges, such as landfill space occupation, high costs and potential environmental threats. In this study, coal fly ash (CFA), metakaolin (MK) and silica fume (SF) were used as aluminosilicate supplementary cementitious materials (ASCM), and mixed with MSWI FA as precursors for the synthesis of alkali-activated and geopolymers hybrid binder (AGHB). The results show that this alkali-activated technology efficiently immobilized the heavy metals in MSWI FA, and the ASCM contributes to the compressive strength enhancement of the AGHB. The highest compressive strength of the synthesized products that mixed MSWI FA with CFA and MK as precursors, reached 5.34 and 9.06 MPa, respectively. The compressive strength of the ASCM synthesized by mixing MSWI FA and SF in the mass ratio of 70:30 with the alkali activator modulus of 1.6 M could reach 11.2 MPa after 28 d of curing, which met the quality standard of MU10 (NY/T 671-2003) for load-bearing brick.The leaching concentrations of Hg and Pb were reduced from 0.15 to 3.96 mg/L to less than 0.003 and 0.107 mg/L, which were below the limit established by the Chinese standard (GB 8978-1996). The research provides the technical parameters of the optimization conditions on the synthesis of MSWI FA-based AGHB, for the resource utilization of MSWI FA and reduction of the environmental risk.

A review on the applications of microbially induced calcium carbonate precipitation in solid waste treatment and soil remediation.

Improper disposal and accumulation of solid waste can cause a number of environmental problems, such as the heavy metal contamination of soil. Microbially induced calcium carbonate precipitation (MICP) is considered as a promising technology to solve many environmental problems. Calcium-based solid waste can be utilized as an alternative source of calcium for the MICP process, and carbonate-based biominerals can be used for soil remediation, solid waste treatment, remediation of construction concrete, and generation of bioconcrete. This paper describes the metabolic pathways and mechanisms of microbially induced calcium carbonate precipitation and highlights the value of MICP for solid waste treatment and soil remediation applications. The factors affecting the effectiveness of MICP are discussed and analyzed through an overview of recent studies on the application of MICP in environmental engineering. The paper also summarizes the current challenges for the large-scale application of this innovative technology. In prospective study, MICP can be an effective alternative to conventional technologies in solid waste treatment, soil remediation and CO2 sequestration, as it can reduce negative environmental impacts and provide long-term economic benefits.

Insights into the Critical Role of Abundant-Porosity Supports in Polyethylenimine Functionalization as Efficient and Stable CO2 Adsorbents.

The emerging polyethylenimine (PEI)-functionalized solid adsorbents have witnessed significant development in the implementation of CO2 capture and separation because of their decent adsorption capacity, recyclability, and scalability. As an indispensable substrate, the importance of selecting porous solid supports in PEI functionalization for CO2 adsorption was commonly overlooked in many previous investigations, which instead emphasized screening amine types or developing complex porous materials. To this end, we scrutinized the critical role of different commercial porous supports (silica, alumina, activated carbon, and polymeric resins) in PEI impregnation in this study, taking into account multiple perspectives. Hereinto, the present results identified that abundant larger pore structures and surface functional groups were conducive to loading a considerable amount of PEI molecules. Various supports after PEI functionalization had great differences in adsorption capacities, amine efficiencies, and the corresponding optimal temperatures. In addition, more attention was paid to the role of porous supports in long-term stability during the consecutive adsorption-regeneration cycles, while N2 and CO2 purging as regeneration strategies, respectively. Especially, CO2-induced degradation due to urea species formation was specifically recognized in a SiO2-based adsorbent, which would induce serious concerns in CO2 cyclic capture. On the other side, we also confirmed that adopting conventional porous supports, for example, HP20, could achieve superior adsorption performance (above 4 mmol CO2/g) and cyclic stability (around 1% loss after 30 cycles) rather than the ones synthesized through complex approaches, which ensured the availability and scalability of PEI-functionalized CO2 adsorbents.