Physicochemical principles

Physicochemical principles governing the various flotation processes are esiamially identical, even though there can be significant differences in the actual mechanics used in their application. Besic principles involved in flotation are discussed below with appropriate examples. 

In die recent past, a number of excellent reviews and bouks have appeared on the physicochemical aspects of flotation.1-1 Only a brief overview of the mechanistic aspects are inclnded here and for more details readers should consult the above references. 

Electrostatic properties of the solid surfaces generally result either from the preferealial dissolution of the lattice ions, as in Ibe case of silver indide. or from the hydrolysis of the surfaces followed by the pH-dependent dissociation of the surface hydroxyls as in the case of silica 1 

FIGURE 16.3 1 Schematic diagram or the diffuse double layer—Stem s mndel. 

I 15 and rf are, respectively, the adsorption densities of sodium and barium counterions under conditions 

In the case of an inorganic species, r can be assumed to be equal fo its diameter in the hydrated or dehydrated form as the case nay be. Even though a similar assumption has been made in the past with respect to surfactants, it must be noted tiiat in this case r can vary anywhere from the cross-sectional diameters of the molecule (For flat adsorption on particles) to the diameter of a partially coiled mokcuk or even that of a folly extend molecule (for surface mkellization). the driving force for adsorption, 

The success of selective flotation depends primarily on the differences in dm hydrophoincity of the qtecies or particles that ate to be floated. Except for a small fraction, ctflUgends are gnmally faydtophilk and therefore, to impart hydrophobicity, surfactants that selectively will associate with or a tb on them are added to the system. These surfactants, generally called collectors, have at least one polar head and one hydrophobic tail in their molecular stmemre. Collectors adsorb on minerals with their hydrophobk tail nimed toward the bulk solution, thereby making the minerals hydrophobk. Typical examples of collectors used in practice include long-chain amines for quartz, potash, and anionic complexes such as fertocyanide and short-chain xanthates for base metal sulfides. 

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An elementary introduction to chemistry is given in Chapter 3 this serves only to provide background and for more advanced consideration reference will be necessary to specific text books, e.g. as listed in the Bibliography. A brief discussion of the relevance of physicochemical principles to hazard identification is given in Chapter 4. Relevant toxic and flammable properties, and summaries of appropriate precautions to cater for them during handling, use and disposal, are provided in Chapters 5 and 6, respectively. Reactive hazards are discussed in Chapter 7. The special problems with cryogenic materials and chemicals under pressure, typified by compressed... 

Hazards can often be foreseen from basic physicochemical principles, as summarized below. 

Aqueous environments will range from very thin condensed films of moisture to bulk solutions, and will include natural environments such as the atmosphere, natural waters, soils, body fluids, etc. as well as chemicals and food products. However, since environments are dealt with fully in Chapter 2, this discussion will be confined to simple chemical solutions, whose behaviour can be more readily interpreted in terms of fundamental physicochemical principles, and additional factors will have to be considered in interpreting the behaviour of metals in more complex environments. For example, iron will corrode rapidly in oxygenated water, but only very slowly when oxygen is absent however, in an anaerobic water containing sulphate-reducing bacteria, rapid corrosion occurs, and the mechanism of the process clearly involves the specific action of the bacteria see Section 2.6). 

There are two basic classes of mathematical models (see Fig. 5.3-18) (1) purely empirical models, and (2) models based on physicochemical principles. 

T. Austad, K. Veggeland, I. Fjelde, and K. Taugbol. Physicochemical principles of low tension polymer flood. In Proceedings Volume, volume 1, pages 208-219.7th Eapg Impr Oil Recovery Europe Symp (Moscow, Russia, 10/27-10/29), 1993. 

The fluid mosaic model conveniently describes how the constituent molecules are ordered, and it correctly describes, in first order, some of the membrane s properties. However, it does not give explicit insight into why the biological membrane has a particular structure, and how this depends on the properties of the constituent molecules and the physicochemical conditions surrounding it. For this reason, only qualitative and no quantitative use can be made of this model as it pertains to permeation properties, for example. It is instructive to review the physicochemical principles that are responsible for typical membrane characteristics. In such a survey, it is necessary to discuss simplified cases of self-assembly first, before the complexity of the biological system may be understood. The focus of this quest for principles will therefore be more on the level of the molecular nature of the membrane, rather than viewing a... 

Florene A.T. and Atwood D., Physicochemical Principles of Pharmacy 2nd Edn., Macmillan Press, London, 1988. 

Schulman S. G. (1977) Fluorescence and Phosphorescence Spectroscopy Physicochemical Principles and Practice, Pergamon Press, Oxford. 

Florence AT, Attwood D. Physicochemical Principles of Pharmacy, 2nd edn. London MacMillan Press, 1988. 

The aim of this book is to introduce to the principles and applications of a branch of chemistry called surface and colloid chemistry. Most science students are taught physicochemical principles pertaining to gases, liquids, and solids. The matter around us is recognized to be made of these three states of matter. However, in university chemistry textbooks, seldom more than a chapter is devoted to the science of surface and colloid chemistry. At technical schools worldwide, the same is the case, in general. However, in the realm of applications of physico-chemical technology, the science of surface and colloid chemistry is one of the most important. Common examples of the principles at work in this field are ... 

V.G. Babak, M. J. Stebe, A review on highly concentrated emulsions Physicochemical principles of formulation, J. Disp. Sci. Technol. 23 (2002) 1-15. 

Fourth, and finally, Rausser and Small seem to have assumed, like so many scientists until recendy, that organisms have evolved only to retain biologically active NPs, as if organisms were doing the hrst stage of a screening trial on behalf of humans. As explained in Chapter 5, the Screening Hypothesis, based on well-established physicochemical principles, postulates that most NPs are simply members of the NP library that the natural world has made. Like individual chemicals in the libraries of synthetic chemicals made by humans, most of the chemicals will possess no potent biomolecular activity. 

Our object has been to enumerate all sets of steps corresponding to possible direct mechanisms. Insight into how to choose the elementary steps themselves can often be obtained from physicochemical principles and experimental surface examination as well as from rate data. This information will also throw light on the most likely mechanisms from among those generated. 

Attwood, D.A. and Florence, A.T. (1998). Physicochemical Principles of Pharmacy, Third Edition, Palgrave, New York. 

The physicochemical principles governing the "softening", or glass transition of the encapsulating matrices have been studied by Karel and his co-workers (1983) and most recently by Levine and Slade (1986). These studies have shown that the release occurs when the glassy, impermeable structure undergoes a transition to a more mobile rubbery state. (Figure 1)... 

At its inception, Emeleus and Sharpe adopted what they described as a broad definition of inorganic chemistry. As they indicated, the subject depends very much for its existence on the application of physical and physicochemical principles to chemical phenomena. One of their aims was the integration of structural, kinetic, and thermodynamic data with descriptive chemistry. All this and more has, I am quite sure, been achieved. Inorganic chemistry has certainly not become any less broad over the intervening years. 

Classes of Estimation Methods Table 1.1.1 summarizes the property estimation methods considered in this book. Quantitative property-property relationships (QPPRs) are defined as mathematical relationships that relate the query property to one or several properties. QPPRs are derived theoretically using physicochemical principles or empirically using experimental data and statistical techniques. By contrast, quantitative structure-property relationships (QSPRs) relate the molecular structure to numerical values indicating physicochemical properties. Since the molecular structure is an inherently qualitative attribute, structural information has first to be expressed as a numerical values, termed molecular descriptors or indicators before correlations can be evaluated. Molecular descriptors are derived from the compound structure (i.e., the molecular graph), using structural information, fundamental or empirical physicochemical constants and relationships, and stereochemcial principles. The molecular mass is an example of a molecular descriptor. It is derived from the molecular structure and the atomic masses of the atoms contained in the molecule. An important chemical principle involved in property estimation is structural similarity. The fundamental notion is that the property of a compound depends on its structure and that similar chemical stuctures (similarity appropriately defined) behave similarly in similar environments. 

The HPLC methods for the determination of TCs in food samples can be divided into four groups according to the physicochemical principle used for sample cleanup or according to the type of detection ... 

Hunt, C.A., MacGregor, R.D. and Siegel, R.A. (1986) Engineering targeted in vivo drug delivery. I. The physiological and physicochemical principles governing opportunities and limitations. Pharm. Res., 3, 333-344. 

Florence A.T., and D.A. Attwood. 1998. Buccal and sublingual absorption. In Physicochemical principles of pharmacy. 3rd ed., 392. Basingstoke, UK MacMillan Press. 

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