Lili Liu

The dramatic increase in sewage sludge production requires researchers to develop and explore more commercially viable ways for alleviating current environmental and socioeconomic challenges connected with its routine management. It has been established that sewage sludge can be processed to fabricate various valuable products or as fuels for electricity generation. In this research, kaolin (calcined from coal gangue) and sewage sludge were successfully used to prepare porous ceramic bricks without any additives. The effect of sewage sludge on the microstructure, phase composition, and mechanical properties of kaolin-sewage sludge ceramic bricks was investigated. The results show that the kaolin-sewage sludge ceramic bricks are mainly composed of mullite (3Al₂O₃·2SiO₂), sillimanite (Al₂SiO₅), aluminum phosphate (AlPO₄), hematite (Fe₂O₃) as well as a small amount of quartz (SiO₂). The ceramic bricks present a typical porous structure, and the number and size of micropores increases noticeably with the increase of sewage sludge content. The sintering shrinkage rate and porosity of ceramic bricks increased significantly with the increase of sewage sludge content, which is mainly attributed to the increase of liquid phase proportion and high temperature volatilization. Sewage sludge can significantly improve the mechanical properties of kaolin-sewage sludge ceramic bricks. When the sewage sludge content is 30 wt.%, the ceramic bricks present the maximum compressive strength and flexural strength and high porosity (32.74%). The maximum sintering shrinkage rate and porosity are 12.17% and 40.51%, respectively.

Due to the complexity of components and high hazard of emissions, thermochemical conversions of plastics among waste-integrated circuits (ICs) are more favorable compared with the common treatment options of electronic waste (E-waste), such as chemical treatment and burning. In this study, the waste random-access memory, as the representative IC, was used to investigate the thermal degradation behaviors of this type of E-waste, including a quantitative analysis of pyrolysis characteristics and non-isothermal kinetics. The results show that the pyrolysis of the ICs can be divided into three different decomposition stages. The pyrolysis temperature and gas atmosphere play an important role in the pyrolysis reaction, and the heating rate greatly affects the rate of the pyrolysis reaction. The non-isothermal kinetic parameters and reaction mechanisms of ICs are determined using the Friedman method, Coats and Redfern (CR) method, and Kissinger method. The results show that the actual average activation energy of the pyrolysis reaction of ICs should be between 170 and 200 kJ·mol⁻¹. The optimally fitting model for the ICs pyrolysis is the three-step parallel model consisting of the random nucleation model (A_m) and reaction order model (C_n).

A tunable and efficient strategy was adopted to synthesize highly porous nano-structured CuO−carbonized composites (Cu_xO@C) using Cu₃(BTC)₂ as a sacrificial template. The as-synthesized CuO nanocomposites exhibited hollow octahedral structures, a large surface area (89.837 m² g⁻¹) and a high proportion of Cu₂O active sites distributed on a carbon frame. Based on DFT calculations, both the Cu atoms on the surface (Cu_S) and oxygen vacancy (O_V) exhibited strong chemical reactivity. On the perfect CuO (111), the Cu_S transferred charge to O atoms on the surface and SO₂ molecules. A strong adsorption energy (−1.41 eV) indicated the existence of the chemisorption process. On the oxygen-deficient CuO (111), the O₂ preferably adsorbed on O_V and then formed SO₃ by bonding with SO₂, followed by the cleavage of the O−O bond. Furthermore, the CuO nanocomposites exhibited an excellent ratio of S/Cu in SO₂ removal experiments compared with CuO nanoparticles produced by coprecipitation.

Vitrification has attracted much attention as an efficient method for solidifying heavy metals in hazardous solid wastes, but its effect is limited when hazardous solid wastes contain chlorides. Aiming at fly ash, a normal chlorine-containing solid waste, a novel process of chlorination melting and glass curing was developed to completely realize the harmlessness of heavy metals. Melting temperature, time, and auxiliary agent were adequate to realize the harmlessness, and their influence on the migration and transformation of Cl, Na, Pb, and Zn and the leaching of slag were studied. The results showed that the majority of Cl, Na, Pb, and Zn in the fly ash had been transferred to the soot, and the residual part in the slag had been solidified in glass by controlling the process conditions. Under the optimized conditions (12 wt.% CaO and 5 wt.% SiO₂ was added, the N₂ flow ratio was at 1 L/min, and the melting temperature was 1300 °C for 2 h), the leaching index was determined, including the acid dissolution ratio, the Pb and Zn content of the water leaching solution, and the acid leaching solution, which all met the requirements of the relevant standards. Furthermore, the novel process provided a simple and efficient approach for the disposal of other similar solid wastes containing chlorides and heavy metals.

High-quality oxidized pellets are the basis to achieve high-efficiency utilization of vanadium–titanium magnetite (VTM) ores. Bentonite was used as a binder of VTM. The main phase composition of VTM is titanomagnetite and ilmenite. When the amount of bentonite is 1%, the compressive strength and dropping strength of VTM pellets can meet the requirements. To improve metallurgical properties, the pellets need to be roasted. The best conditions for roasting are as follows: calcination temperature of 1523 K and a calcination time of 20 min. The consolidation mechanism, phase transformation, and crystal structure transformation of VTM in the process of oxidation roasting are also explained.

Manganese and iron oxides catalysts supported on silicalite-1 and titanium silicalite-1 (TS-1) are synthesized by the wet impregnation method for the selective catalytic reduction (SCR) of NO_x with NH₃ (NH₃-SCR), respectively. The optimized catalyst demonstrates an increased NO_x conversion efficiency of 20% below 150 °C, with a space velocity of 18,000 h⁻¹, which can be attributed to the incorporation of Ti species. The presence of Ti species enhances surface acidity and redox ability of the catalyst without changing the structure of supporter. Moreover, further researches based on in situ NH₃ adsorption reveal that Lewis acid sites linked to Mn⁴⁺ on the surface have a huge influence on the improvement of denitration efficiency of the catalyst at low temperatures.

A series of CeO_x catalysts supported by commercial porous cordierite ceramics (CPCC) and synthesized porous cordierite ceramics (SPCC) from fly ash were prepared for selective catalytic reduction of NO_x with ammonia (NH₃-SCR). A greater than 90% NO_x conversion rate was achieved by the SPCC supported catalyst at 250–300 °C when the concentration of loading precursor was 0.6 mol/L (denoted as 0.6Ce/SPCC), which is more advantageous than the CPCC supported ones. The EDS mapping results reveal the existence of evenly distributed impurities on the surface of SPCC, which hence might be able to provide more attachment sites for CeO_x particles. Further measurements with temperature programmed reduction by hydrogen (H₂-TPR) demonstrate more reducible species on the surface of 0.6Ce/SPCC, thus giving rise to better NH₃-SCR performance at a low-temperature range. The X-ray photoelectron spectroscopy (XPS) analyses reveal that the Ce atom ratio is higher in 0.6Ce/SPCC, indicating that a higher concentration of catalytic active sites could be found on the surface of 0.6Ce/SPCC. The in situ diffused reflectance infrared fourier transform spectroscopy (DRIFTS) results indicate that the SCR reactions over 0.6Ce/SPCC follow both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms. Hence, the SPCC might be a promising candidate to provide support for NH₃-SCR catalysts, which also provide a valuable approach to recycling the fly ash.

The present study firstly proposed a method of integrated utilization of sewage sludge (SS) and coal gangue (CG), two waste products, for cement clinker products with the aim of heat recovery and environment protection. The results demonstrated that the incremental amounts of SS and CG addition was favorable for the formation of tricalcium silicate (C₃S) during the calcinations, but excess amount of SS addition could cause the impediment effect on C₃S formation. Furthermore, it was also observed that the C₃S polymorphs showed the transition from rhombohedral to monoclinic structure as SS addition was increased to 15 wt %. During the calcinations, most of trace elements could be immobilized especially Zn and cannot be easily leached out. Given the encouraging results in the present study, the co-process of sewage sludge and coal gangue in the cement kiln can be expected with a higher quality of cement products and minimum pollution to the environment.

Waste heat recovery from high temperature slags represents the latest potential way to remarkably reduce the energy consumption and CO₂ emissions of the steel industry. The molten slags, in the temperature range of 1723–1923 K, carry large amounts of high quality energy. However, the heat recovery from slags faces several fundamental challenges, including their low thermal conductivity, inside crystallization, and discontinuous availability. During past decades, various chemical methods have been exploited and performed including methane reforming, coal and biomass gasification, and direct compositional modification and utilization of slags. These methods effectively meet the challenges mentioned before and help integrate the steel industry with other industrial sectors. During the heat recovery using chemical methods, slags can act as not only heat carriers but also as catalysts and reactants, which expands the field of utilization of slags. Fuel gas production using the waste heat accounts for the main R&D trend, through which the thermal heat in the slag could be transformed into high quality chemical energy in the fuel gas. Moreover, these chemical methods should be extended to an industrial scale to realize their commercial application, which is the only way by which the substantial energy in the slags could be extracted, i.e., amounting to 16 million tons of standard coal in China.