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Citation - WoS: 198
Citation - Scopus: 210
Physical and Chemical Interactions in Coal Flotation
(Elsevier Ltd., 2003) Polat, Mehmet; Polat, Hürriyet; Chander, Subhash
Coal flotation is a complex process involving several phases (particles, oil droplets and air bubbles). These phases simultaneously interact with each other and with other species such as the molecules of a promoting reagent and dissolved ions in water. The physical and chemical interactions determine the outcome of the flotation process. Physical and chemical interactions between fine coal particles could lead to aggregation, especially for high rank coals. Non-selective particle aggregation could be said to be the main reason for the selectivity problems in coal flotation. It should be addressed by physical (conditioning) or chemical (promoters) pretreatment before or during flotation. Although the interactions between the oil droplets and coal particles are actually favored, stabilization of the oil droplets by small amounts of fine hydrophobic particles may lead to a decrease in selectivity and an increase in oil consumption. These problems could be remedied by use of promoters that modify the coal surface for suitable particle-particle, droplet-particle and particle-bubble contact while emulsifying the oil droplets. The role of promoters may be different for different types of coals, however. They could be employed as modifiers to increase the hydrophobicity of low rank coals whereas their main role might be emulsification and aggregation control for high rank coals. In this paper, a detailed description of the various phases in coal flotation, their physical and chemical interactions with each other in the flotation pulp, the major parameters that affect these interactions and how these interactions, in turn, influence the flotation process are discussed.
Citation - WoS: 20
Citation - Scopus: 23
Electrostatic Charge on Spray Droplets of Aqueous Surfactant Solutions
(Elsevier Ltd., 2000) Polat, Mehmet; Polat, Hürriyet; Chander, Subhash
Electrostatic charges on individual spray droplets were measured using a refined form of the Millikan oil drop method. The measurement system consisted of three main sections; a droplet generation cell, a settling column and a charge measurement chamber. The trajectories required for calculation of charge were determined using a high-speed motion analyzer coupled to a long-focal-length microscope. Charges on droplets were manipulated by the addition of surface-active agents into the spray solution. Droplet charge was a function of the type and concentration of the surfactant added. For ionic surfactants, it showed a maximum at low surfactant concentrations, decreased with further surfactant addition and was constant after the CMC. The charge on cationic surfactants was always more than that observed with the anionic surfactants. Nonionic surfactants displayed a steady increase in droplet charge with increasing concentration. The charges were lower compared to the ionic surfactants. (C) 2000 Elsevier Science Ltd. Electrostatic charges on individual spray droplets were measured using a refined form of the Millikan oil drop method. The measurement system consisted of three main sections; a droplet generation cell, a settling column and a charge measurement chamber. The trajectories required for calculation of charge were determined using a high-speed motion analyzer coupled to a long-focal-length microscope. Charges on droplets were manipulated by the addition of surface-active agents into the spray solution. Droplet charge was a function of the type and concentration of the surfactant added. For ionic surfactants, it showed a maximum at low surfactant concentrations, decreased with further surfactant addition and was constant after the CMC. The charge on cationic surfactants was always more than that observed with the anionic surfactants. Nonionic surfactants displayed a steady increase in droplet charge with increasing concentration. The charges were lower compared to the ionic surfactants.
Citation - WoS: 39
Citation - Scopus: 43
Adsorption of Peo/Ppo Triblock Co-Polymers and Wetting of Coal
(Elsevier Ltd., 1999) Polat, Hürriyet; Chander, Subhash
The adsorption characteristics of PEO/PPO/PEO triblock co-polymers on coal were investigated using surface tension and contact angle measurements. Although these surfactants have been widely used as wetting agents, it was observed that they increased the hydrophobicity of coal at concentrations below about 10-6 M. Surface tension studies were carried out to explain the reasons for this behavior. The surface tension versus concentration profiles displayed three distinct regions. In region I, surface tension decreased linearly and monomers were proposed to be the dominant species. This region extended to a surfactant concentration of about 10-6 M. In region II, a transition region between regions I and III, dimers, trimers, etc., were considered to form. In region III, micelles formed and surface tension was independent of concentration. The concentration at which monomers associate to form dimers, etc., is referred to as the critical association concentration (cac). The contact angle of coal increased when concentration was raised from low values to the cac. It decreased when the reagent concentration was above the cac. Finally, at concentrations above the cmc, the wetting of coal was complete and contact angle was zero.

Chemistry / Kimya

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