Hydrophobicityand collectorless flotation of inorganic materials |
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| Institution: | 1. School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, China;2. Fuyang normal university, Fuyang, 236037, China;3. National Key Laboratory of Science and Technology on Aerospace Intelligence Control, Beijing Aerospace Automatic Control Institute, Beijing, 100854, China;4. College of Computer and Information Sciences, Fujian Agriculture and Forestry University, Fuzhou 350002, China;1. Division of Biotechnology, National Centre for Disease Control, 22 Sham Nath Marg, Delhi, 110054, India;2. Division of Zoonosis, National Centre for Disease Control, 22 Sham Nath Marg, Delhi, 110054, India;3. Department of Biosciences, Jamia Millia Islamia University, New Delhi, 110025, India;1. College of Energy and Power Engineering, Jiangsu Province Key Laboratory of Aerospace Power System, Nanjing University of Aeronautics and Astronautics, Nanjing, 210016, China;2. Faculty of Engineering, Computing and Science, Swinburne University of Technology, Jalan Simpang Tiga, 93350 Kuching, Sarawak, Malaysia;3. Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM), State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Nanjing Tech University, No. 5 Xin Mofan Road, Nanjing 210009, China;1. CNR-NANOTEC, Via G. Amendola 122/D, Bari, Italy;2. Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Via Elce di Sotto 8, Perugia 06123, Italy |
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| Abstract: | Hydrophobicity and floatability of solids have been analyzed from the standpoint of properties of solid-water and solid-water vapors interfaces, chemical bonds, bulk properties, crystal structure of the solid, and reactivity of the solid with water. Although the hydrophobicity results from complex interactions in the solid-water-air system, simple equations and rules for predicting hydrophobicity and floatability are presented. The applicability of the Gaudin-Miaw-Spedden theory which states that molecular and sheet crystals, if their structure is controlled by the residual bonds across their basal planes, are floatable was confirmed. It was also shown that elements and compounds with different degrees of ionic-covalent and metallic-nonmetallic characters of bonds in the absence of residual bonds can be either hydrophilic, hydrophobic, or change their properties from hydrophobic to hydrophilic and vice versa. For some materials, hydrophobidty was found to be time-dependent. Decreasing hydrophobicity occurs with the oxidation and hydroxylation of the surface (oxides, metals), while increasing hydrophobicity takes place due to non-dissociative adsorption of water vapors on the surface (noble metals). Increased hydrophobicity can also be due to the formation of hydrophobic species such as sulfur species on the surface of Sulfides. It was demonstrated that the potential hydrophobicity of solids, expressed as the contact angle formed between the three involved (solid, water, and air) phases, can be evaluated from the Hamaker constants.This work supplements the Gaudin-Miaw-Spedden theory by showing that not only molecular crystals (paraffin, I2, S8, As4O6, As2S2) and non-ionic sheet crystals (MoS2, Sb2S3, talc, graphite, As2S3, boric acid, BN) but also elements and crystalline compounds without residual bonds can be hydrophobic and floatable. A partial list of such materials includes Hg, Ge, Si, SiC, AgI, CaF2, and diamond (whose hydrophobidties are already well known) as well as BaSO4, FeTiO3, In, and Sn (whose hydrophobidties have been established in this work). It was also demonstrated that the hydrophobidty of some solids changes as a result of reaction of the surface with constituents of the air. |
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