Polycyclic aromatic hydrocarbons (PAHs) are the predominant chemical compounds in coal tar (CT). Extensive published data indicate their carcinogenic effects both on humans, in industrial workers, and on animals. However, there is a trend toward using CT as a medication for skin diseases, dermatitis, and psoriasis. But how safe is the use of CT for humans? This review systematizes data on the carcinogenic effects of PAHs on humans, their concentrations in coal tar, and the degree of exposure to carcinogenic factors during skin disease therapy.
This paper presents the results of a study assessing the impact of drainage and subsequent rewetting processes on the accumulation and specific features of the vertical activity distribution of Cs-137, Am-241, Pb-210, U-234, and U-238 in the peat deposit of an ombrotrophic boreal bog (exemplified by the Ilas bog complex in the Arkhangelsk oblast). The data obtained indicated an extremely low level of radioactive contamination in the studied areas. It was demonstrated that hydromelioration of peat deposits led to changes in activity levels and redistribution of the test series of technogenic and natural radionuclides, which was expressed in the shift and localization of their concentration zone toward the peatland surface. It was established that the transformation of the hydrological regime of the deposits during the drainage of ombrotrophic bog areas enhanced the binding of radionuclides by peat sediments, including due to changes in physicochemical conditions.
A comprehensive study of the calorific characteristics of composite biofuels based on birch phloem has been conducted. The lower heating values of composites with varying compositions, including brown coal, oil-containing waste, and pine needles, were measured calorimetrically. Linear relationships between the calorific characteristics and the composition of the composite (e.g., bast content) were identified. Verification calculations of the combustion heat of composites with a component ratio of 1 : 1 were performed using empirical formulas by Dulong, Mendeleev, Wondraczek, Nivel, and Given, followed by conversion to lower heating values based on experimentally measured moisture and ash content. The results indicated that the smallest deviations between calculated values and experimental data for combustion heat could be achieved using Dulong’s formula.
Air purification from volatile organic compounds (VOCs) remains a serious problem of maintaining public health and environmental safety due to their toxic properties and widespread use in various fields of industrial production. In the presented work, the kinetic patterns of acetone vapor adsorption processes with commercially activated carbon AG-3 and its nitric acid–modified analogues were studied. To obtain modified adsorbent samples, the initial activated carbon AG-3 was treated with 2 M, 4 M, and 6 M aqueous solutions of nitric acid at a temperature of 100°C for 2 h. The reaction mixture was then cooled to room temperature and washed with distilled water until the neutral pH of the filtrate was reached. The obtained samples were dried at 110°C until a constant mass was obtained. To evaluate the acidic properties of the surface of semiconductor adsorbents, the adsorption of pyridine from its solutions in octane was studied using UV spectrometry. The results showed that the sorbent samples obtained by treatment of the initial industrial activated carbon AG-3 with a 2 M aqueous solution of nitric acid had the highest acidity. A further increase in the concentration of nitric acid led to a decrease in the acidic properties of the adsorbent and the specific surface area of the modified samples. The processes of acetone vapor adsorption were studied at room temperature and atmospheric pressure using the gravimetric method. The kinetic data obtained was analyzed using the Yelovich and Morris–Weber pseudo-first and pseudo-second order models. It was found that acid modification of the adsorbent significantly increased its capacitance characteristics, but it had little effect on the rate of acetone vapor adsorption. At the same time, the activated carbon image modified with a 2 M HNO3 solution also showed the best results. Kinetic investigation has shown that, in all cases, the process of acetone vapor absorption under consideration was best described by a pseudo-second-order model, which indicated the limiting nature of the stage of chemisorption of adsorbate molecules on the adsorbent surface. At the same time, the use of the Morris–Weber model also showed a good agreement between experimental and calculated results, which indicated the possible influence of diffusion processes on the rate of acetone vapor adsorption as the number of free centers on the adsorbent surface decreased. The results obtained indicate that it is impossible to control the conditions of acid modification of carbon adsorbents in order to increase the effectiveness of their practical application.
The article considers the effect of exposure time and nominal value of PAN fiber on its structural properties during thermal stabilization. Three optimal modes were selected for each fiber rating, which can significantly increase the uniformity and completeness of stabilization, ensure a minimum concentration of residual nitrogen, and form a fiber structure that meets the requirements for a precursor to produce high-quality carbon fiber.
