Surface potential minerals equation

Abstract This chapter first explains the natural flotability of some minerals in the aspect of the crystal structure and demonstates the collectorless flotaiton of some minerals and its dependence on the h and pH of pulp. And then the surface oxidation is analysed eletrochemically and the relations of E to the composition of the solutions are calculated in accordance with Nemst Equation. The E h-pH diagrams of several minerals are obtained. Thereafter, electrochemical determination such as linear potential sweep voltammetry (LPSV) and cyclic voltammetry (CV) and surface analysis of surface oxidation applied to the sulphide minerals are introduced. And recent researches have proved that elemental sulfur is the main hydrophobic entity which causes the collectorless flotability and also revealed the relation of the amount of sulfur formed on the mineral surfaces to the recoveries of minerals, which is always that the higher the concentration of surface sulphur, the quicker the collectorless flotation rate and thus the higher the recovery. 

The Poisson-Boltzman (P-B) equation commonly serves as the basis from which electrostatic interactions between suspended clay particles in solution are described ([23], see Sec.II. A. 2). In aqueous environments, both inner and outer-sphere complexes may form, and these complexes along with the intrinsic surface charge density are included in the net particle surface charge density (crp, 4). When clay mineral particles are suspended in water, a diffuse double layer (DDL) of ion charge is structured with an associated volumetric charge density (p ) if av 0. Given that the entire system must remain electrically neutral, ap then must equal — f p dx. In its simplest form, the DDL may be described, with the help of the P-B equation, by the traditional Gouy-Chapman [23-27] model, which describes the inner potential variation as a function of distance from the particle surface [23]. 

Equation 3.7 points out that the variation in the electric field strength (-dy/dx) is related to the second power of the inverse of the thickness of the double layer times /, while Equation 3.8 shows that / decays exponentially with respect to distance (jc) from the surface (Fig. 3.23). A plot of ln( // (/0) versus x produces a straight line with slope k, which is the inverse of the double layer thickness. The assumption ij/0 < 25 mV is not applicable to all soil minerals or all soils. Commonly, clay minerals possess more than 25 mV in surface electrical potential, depending on ionic strength. The purpose of the assumption was to demonstrate the generally expected behavior of charged surfaces. 

Note that variably charged soil mineral surfaces do not exactly obey the Nernst equation. The assumption is only valid at approximately one pH unit above or belov the PZC or at approximately 25 mV of surface electrical potential. The assumption is only used for demonstration purposes. Since H+ and OH are considered to be potential determining ions (PDIs), Equation 3.15 can be rewritten as... 

Soils are composed of inorganic and organic minerals with surfaces possessing sites capable of producing chemical or physical bonds with compounds or minerals dissolved in water (see Chapter 3). These solute-mineral surface reactions regulate the potential of chemicals in the soil-water environment to become mobile. Such chemicals include plant nutrients, pesticides, and/or other synthetic organics making up soil-water pollutants. The potential of chemical species to move in the soil-water system depends on the potential of soil to conduct water and on the potential of solution minerals to react with soil minerals. In the case of a nonreactive chemical species (nonreactive solute), its mobility in the soil system will be equal to that of water. However, the mobility of a reactive solute would be less than that of water. The rate of downward movement of a chemical species (e.g., a monovalent cation X+) can be predicted by the equation... 

Surface complexation models of the solid-solution interface share at least six common assumptions (1) surfaces can be described as planes of constant electrical potential with a specific surface site density (2) equations can be written to describe reactions between solution species and the surface sites (3) the reactants and products in these equations are at local equilibrium and their relative concentrations can be described using mass law equations (4) variable charge at the mineral surface is a direct result of chemical reactions at the surface (5) the effect of surface charge on measured equilibrium constants can be calculated and (6) the intrinsic (i.e., charge and potential independent) equilibrium constants can then be extracted from experimental measurements (Dzombak and Morel, 1990 Koretsky, 2000). 

An extension of the Langmuir equation (equation (6.3)) has been proposed for phosphate adsorption to soils and metal oxides in order to relate adsorption to the electrostatic potential of mineral surfaces and to the bulk solution characteristics, such as pH, electrolyte concentration, temperature and competing ions (Barrow et al., 1980 Barrow, 1983, 1985, 1993 Bolan et al., 1986) ... 

As seen from Equation 1.7, the electro-osmotic flow depends on the dielectric constant and viscosity of pore fluid, as well as the surface charge of the solid matrix represented by the zeta potential (the electric potential at the junction between the fixed and mobile parts in the double layer). The zeta potential is a function of many parameters, including the types of clay minerals and ionic species that are present, as well as the pH, ionic strength, and temperature. If the cations and anions are evenly distributed, an equal and opposite flow occurs, causing the net flow to be zero. However, when the momentum transferred to the fluid in one direction exceeds the momentum of the fluid traveling in the other direction, electro-osmotic flow is produced. 

Electrostatic field of the mineral surface forces these ions to move in opposite directions and therewith disrupts the uniformity of their distribution. Oppositely charged ions of the solutions distance one from another, at which their total charge becomes adequate with the electrostatic potential at the point X. That is why volume density of the salt charge in the electrostatic field a (x) 0 and, according to Boltzmann equation (2.101), has value... 

Although the positive and negative charges are equated in these minerals, there exist free valemces at the crystal surfaces. These, as well as the ionic potential, i.e. the ratio of charge to ionic radius, determine the stability of these minerals when exposed to atmospheric agents. 

The present chapter highlights recent developments in photocatalysis that are pertinent to its potential process applicability in water treatment for organic contaminants specifically, (i) mechanism understanding, intermediates and stoichiometry of the overall process (ii) its generality for complete contaminant destruction (mineralization) (iii) some specific contaminant classes of interest (chlorinated aromatics, surfactants, herbicides and pesticides) (iv) kinetics (equations, surface vs. bulk reactions) (v) influence of additional oxidants (vi) use of solar vs. artificial illumination (vii) different catalysts and catalyst s forms (suspended vs. immobilized) (viii) photoreactor design (ix) comparison with other techniques using oxidants and light, with care to the evaluation of efficiency and economics. 

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