Dioxin emission and distribution from cement kiln co-processing of hazardous solid waste.

Cement kiln collaborative disposal technology can not only dispose of hazardous waste but also provide energy for the cement industry. However, the addition of hazardous waste may promote the formation of dioxins in cement kilns. In this study, typical hazardous solid wastes, such as solidified fly ash, electroplating sludge, and industrial residue, were co-processed in a cement kiln with different feeding positions and different feeding amounts. The concentrations of dioxins in the flue gas, clinker, and precalciner furnace slag were investigated. The effect of adding mixed hazardous solid waste on the formation of dioxin was also studied. The results showed that the concentration of dioxin in the flue gas without added hazardous waste was 1.57 ng/m3, and the concentration varied from 1.03 to 6.49 ng/m3 after the addition of hazardous waste. In addition, the concentration of dioxin in the flue gas and solid samples increased substantially when the co-processing ratio doubled. The large amount of Cu in solidified fly ash promoted the formation of dioxins, while the higher S content in the electroplating sludge suppressed the formation of dioxins. Compared with the addition of single hazardous waste, the concentration of dioxin in precalciner furnace slag increases by about 300%. Furthermore, the distributions of isomers in the clinker and precalciner furnace slag were similar. 1,2,3,4,6,7,8-HpCDD and OCDD accounted for a large proportion of the mass concentration, and the contribution rate ranged from 48.7 to 82.0%. Most importantly, correlation analysis showed that the concentration of dioxin was closely related to the copper content, hazardous waste types and additive proportion, with correlation coefficients of 0.79, 0.83, and 0.89, respectively. This study provides a basis for exploring the high environmental benefits of disposing of hazardous solid waste by co-processing in cement kilns.

Modification of activated carbon using urea to enhance the adsorption of dioxins.

Activated carbon is commonly used to remove dioxins from flue gas via adsorption. Improving the targeted adsorption capacity of activated carbon for dioxins can reduce the consumption of adsorbents and help achieve emission standards for target pollutants. Here, commercial coal-based activated carbon was used as a raw material and modified by urea impregnation along with treatment at high temperature under a nitrogen atmosphere. It was found that modification with urea effectively improved the pore structure of activated carbon while incorporating a certain amount of nitrogen. The best modification effect was achieved at a modification temperature of 600 °C, an impregnation ratio of urea to activated carbon of 1:1, and with high-temperature treatment for 2 h. The mesopore volume of the modified activated carbon (AC600) reached 0.38 cm3/g, accounting for 57.58% of the total pore volume. With an impregnation ratio of urea to activated carbon of 1:1, high-temperature treatment for 2 h, and a modification temperature of 800 °C, a certain amount of nitrogen was introduced into the carbon rings to form a modified activated carbon (AC800) rich in pyridine and pyrrole groups (atomic percentage = 4.84%). The activated carbon modified by urea and the unmodified activated carbon were subsequently selected for dioxin adsorption experiments using a dioxin generation and adsorption system. AC600 showed the highest adsorption efficiency for dioxins, reaching 97.65%, based on toxicity equivalents. Although AC800 has poor pore properties, it has more pyridine and pyrrole groups than AC600. Consequently, the efficiency of AC800 at adsorbing low-concentration dioxins reached 85.24% based on toxicity equivalents. Overall, this study describes two mechanisms for effectively modifying activated carbon with urea based on (1) optimizing the pore structure of activated carbon and (2) incorporating nitrogen.

Fast determination of two atractylenolides in Rhizoma Atractylodis Macrocephalae by Fourier transform near-infrared spectroscopy with partial least squares.

Rhizoma Atractylodis Macrocephalae (RAM) is a commonly used food and traditional Chinese medicine (TCM), which traditionally strengthens the spleen, benefits vital energy, eliminates dampness, and promotes hidroschesis. Its primary effective constituents are polysaccharides and volatile oil, whose main components are atractylenolide I and III. Fourier transform near-infrared spectroscopy (FT-NIR) is widely used in TCM research. However, determination of atractylenolides in RAM using FT-NIR has not been described. In this study, a new method for the determination of atractylenolides I and III in RAM by NIR was established. The spectral characteristics of atractylenolides I and III were obtained by second derivative multiple scattering correction, and its chart to the original absorbance spectra. Additionally, in combination with the partial least squares (PLS) algorithm, the calibration process was performed for the quantitation of the samples. The root mean square error of cross-validation of the PLS models for atractylenolides I and III was 0.0387 and 0.0358, and the determination coefficient of quantitative models was 96.63 and 96.16, respectively. This study demonstrated that NIR spectroscopy can be used to analyze quickly and efficiently the contents of atractylenolides I and III in RAM.