China
Africa
Explore chapters and articles related to this topic
Protection of groundwater resources quality and quantity in mining areas
Published in Vladimír Strakoš, Vladimír Kebo, Radim Farana, Lubomír Smutný, Mine Planning and Equipment Selection 1997, 2020
Another example of influence of mining activity on an important water resource is the area south of the Karvina town center, where iodine-bromine water is being retained for the Darkov spa. Fossil iodine-bromine Miocene water detected more than 100 years ago in former coal-detecting deposit boreholes is retained for balneological purposes from arenaceous interbeds in the lutaceous facies of Lower Baden (cover of productive Upper Baden). These water-bearing arenaceous layers are developed in the depth range of −161 to −335 m below sea level. The coffer of the boreholes made between 1931 (Helena) and 1943 (Jan II, Novy pramen and Vilemina) is, under the conditions of aggressive chemical composition of retained water (significant content of NaCl, permeation by gaseous CH4, mineralization of ca 17–28 gl−1), probably on the very limit of service life.
Kekulé Structure
Published in Mihai V. Putz, New Frontiers in Nanochemistry, 2020
Marina A. Tudoran, Mihai V. Putz
After years of studies, scientists determine that there are a series of problems which arise in the Kekulé theory for benzene. First is represented by the low reactivity of benzene, meaning that benzene does not react with alkenes and bromine water, as it should. Another problem is referring to the carbon-carbon bond length, more precisely, the symmetrical characteristic of a molecule in Kekulé form with all six carbon-carbon bonds with the same length, even if in general the single and the double bond have different length. Also, the hydrogenation enthalpies are in question, due to the fact that based on the actual chemical name of the Kekulé structure, cyclohexa-1,3,5-triene, and based on the fact that cyclohexene (with 1 double bond) has the values of its hydration enthalpy equal with 120 kJ/mol, benzene (with 3 double bonds) should have a hydrogenation enthalpy equal with 360 kJ/mol while the experimentally measured value is 152 kJ/mol, less than the expected value.
Properties of Coal
Published in A. Williams, M. Pourkashanian, J. M. Jones, N. Skorupska, Combustion and Gasification of Coal, 2018
A. Williams, M. Pourkashanian, J. M. Jones, N. Skorupska
Usually only the total sulfur is determined, but methods are available for ascertaining the amount present in each of the three forms (BS1016m 106.4.2 1996, 106.5; ISO 157: 1996). A simple, standard method of determining the total sulfur present is the Eschka method. In this, the air-dried coal is mixed with the Eschka (MgO + Na2CO3) mixture, and the mixture is heated until all the coal has been oxidized. Oxides of sulfur from the combustion of the coal and of any pyrites present react with the alkaline Eschka mixture (containing BaC12) to form sulfates and sulfites. When oxidation is complete, the residue is mixed with water, and any sulfites present are oxidized to sulfates by the addition of a little bromine-water. The barium sulfate is formed and weighed. The total amount of sulfur in the coal on a wt% basis is calculated. Where the amounts of sulfur present as pyrites and as sulfates are known, the organic sulfur is found by subtracting these from the total sulfur.
Mechanism of sulfur removal from coal by microwave assisted acetic acid-hydrogen peroxide system
Published in Journal of Sulfur Chemistry, 2023
Sidan Cheng, Mei Li, Shiyong Xu, Ning Ding, Jinsong Yue, Hui Li
Sulfur components and substrates in coal samples have different response effects to microwave due to different dielectric constants. The sulfur group is activated prior to the coal matrix. Microwave assisted desulfurization can remove more sulfur content without significant changes in the coal matrix [5,6]. Yang et al. [7] demonstrated that the desulfurization rate of coal samples treated with acetic acid and hydrogen peroxide could reach 22.62%. Tang et al. [8] found that acetic acid-hydrogen peroxide produced more hydroxyl radicals assisted by microwave than hydrogen peroxide alone, which benefit to sulfur removal. Mu et al. [9] found that bromine water could effectively remove organic sulfur in coal with the assistance of microwave, and sulfur-containing bonds were broken in the microwave field. Finally, sulfur-containing substances were oxidized by HBrO to soluble sulfate and removed.
Enhancing surface performance of wool using reduced ionic liquid
Published in The Journal of The Textile Institute, 2022
Zhe Jiang, Yiyi Zhang, Qiang Wang, Ping Wang, Yuanyuan Yu, Man Zhou, Ende Li
The oxidation of bromine solution on the wool surface makes the osmotic pressure inside and outside the wool fiber inconsistent, thereby forming bubbles (Wakelyn, 1972). The more complete the scale layers on the wool surface, the larger the bubbles. The Allwörden reaction test images are shown in Figure 2. In the untreated wool fiber, the surface formed a large number of vesicles in bromine water, covering almost the entire wool fiber. After the treatment for 1 min, the number and volume of the vesicles were slightly reduced. When the treatment time extended to 3 min, the number and volume of the vesicles were markedly decreased. Besides, there were no bubbles in some places. The vesicles were hardly observed on the wool surface after the treatment for 5 min. The result demonstrated that the ionic liquid effectively modifies the wool surface.
Understanding oxidative addition in organometallics: a closer look
Published in Journal of Coordination Chemistry, 2022
Nabakrushna Behera, Sipun Sethi
Binuclear oxidative addition reactions of metal complexes having d7-, d8- and f3-systems have been illustrated. In each case the driving force for the reaction is associated with the increased stability of the product at its higher oxidation state. Halpern, in his 1970s Accounts of Chemical Research article, described oxidative addition reactions of pentacyanocobaltate(II) with a variety of substrates such as hydrogen, bromine, water, peroxide, methyl iodide, etc. (Scheme 8) [19]. In each case a single molecule breaks into two groups and links to two different metal centers, in accord with reaction type ‘B’ in Scheme 1. Scott and co-workers reported the reactions of halogens (Cl2, Br2, I2) with two equivalents of uranium(III) complex 20 to afford corresponding uranium(IV) halide complexes 21-23 (Scheme 9) [7, 20]. These reactions are formally type ‘B’ oxidative additions.