Adsorption on Solid Particles

A gas-particle partition coefficient, Kp, is commonly used to describe the distribution of a SOC between the gas and particle phase. It is defined as the ratio of the SOC in particles (in units such as ng pg 1) to that in the gas phase (in units such as ng m 3). In essence, it is the fraction of the mass of total suspended particulate matter (TSP) that is the SOC of interest divided by the SOC gas-phase concentration. This gas-particle partition coefficient, which has units of m3 pig, can be calculated from the following  

F (from /liter-associated material) is the concentration of the SOC in air that is in the particle phase, in ng m 3, A (from the use of an adsorbent to collect the gas) is the gas-phase concentration in ng m 3, and TSP is the concentration of total suspended / articles, in pg m 3. (Note that this is the definition in common usage today however, some earlier papers (e.g., Yamasaki et al., 1982 Pankow, 1987) defined Kp as the inverse, i.e., as equal to /((TSP) F.) Because measurements of F, TSP, and A are difficult to make in an artifact-free manner and because equilibrium may not always hold in the atmosphere (see later), the quantity (F TSP) A is often referred to as the measured partition coefficient, in contrast to the true, ther- 

Pankow (1987) showed that this assumption of a linear Langmuir isotherm is consistent with the pioneering work of Junge (1977) on the adsorption of SOCs on particles. The fraction of the total SOC in the atmosphere adsorbed on aerosol particles, denoted / , was hypothesized by Junge to be related to the surface area (ST, cm2 per cm3 of air) of the TSP and the saturation vapor pressure of the SOC by 

In this case pL is the saturation vapor pressure of the adsorbing gas at that temperature and c is a constant characteristic of the compound and the temperature. 

As discussed in detail by Pankow (1987) and Pankow and Bidleman (1992), the Junge approach can be reduced to an expression of the form 

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The presence of copolymer and surfactant together alters the rheological properties of solutions, adsorption on solid particles, solubility, and stability of colloidal dispersions. The solution properties are mainly influenced by... 

For adsorption on flocculated particles, the polymer was added in a drop-by-drop-wise manner from a burette containing a 50 cc solution to a 50 cc solution containing the solids. Flocculation was performed in an unbaffled vessel, 58 ram in diameter. Agitation was achieved with a 3-bladed propeller, 35 mm in... 

Figure 23-6. upper right). In gas-solid adsorption chromatography, analyte is adsorbed directly on solid particles of stationary phase (Figure 23-6, upper left). 

The formation of multilayer structure can be carried out by several ways 1) adsorption on liquid/liquid interface - Langmuir-Blodgett films [5,6] 2) adsorption on solid/liquid interface - alternate adsorption of oppositely charged polyelectrolytes (PE) and surfactants on flat surfaces or spherical particles [7,8], To control the process of multilayer systems formation, it is necessary to under-... 

For example, in the presence of strongly binding natural organic ligands in water (especially at pH > 6), metals such as Cu, Ni, and Cd remain in solution, decreasing their extent of adsorption onto solid particles (e.g., goethite). On the contrary, with weaker ligands (even in excess), and more acidic pH, the metal ions prefer to adsorb onto soil or sediment particles. 

In gas chromatography (GC), a gaseous solute (or the vapour from a volatile liquid) is carried by the gaseous mobile phase. In gas-liquid partition chromatography, the stationary phase is a non-volatile liquid coated on the inside of the column or on a fine support. In gas-solid adsorption chromatography, solid particles that adsorb the solute act as the stationary phase. 

Scheutjens-Fleer (SF) Theory. A conceptual model for the effects of NOM on colloidal stability can be developed by using existing theoretical and experimental investigations of polymer and polyelectrolyte adsorption on solid surfaces and of the effects of macromolecules on colloidal stability. The modeling approach begins with the work of Scheutjens and Fleer for uncharged macromolecules, termed here the SF theory (3-5). This approach has been extended to the adsorption of linear flexible strong polyelectrolytes by van der Schee and Lyldema (6), adapted to weak polyelectrolytes (7-9), and applied to particle-particle interactions (8, 10). 

The adsorption from aqueous solution of surfactants with two hydrophilic and two hydrophobic groups (gemini surfactants, Chapter 12) onto oppositely charged sites on solid particle surfaces—cationic geminis onto clay particles (Li, 2000), anionic geminis onto limestone particles (Rosen, 2001)—results in one hydrophilic group oriented toward the solid surface and the second oriented toward the aqueous phase. The solid particles are dispersed in both cases. 

Adsorption from solutions onto solid surfaces is important in many industrial practices, such as dye or organic contaminant removal, edible oil clarification by activated carbon, and ion exchange, where the adsorption of ions from electrolyte solutions is carried out. Adsorption from solution is also used in analytical chemistry in various chromatography applications. On the other hand, surfactant, polymer and biological material adsorption on solids, to modify the surface of solid particles in stabilizing dispersions, are also very important industrial fields. 

The nature of surfactant adsorption on solid surfaces depends on the polarity and solubility of the surfactant. Thus, when an aqueous surfactant solution is in contact with non-polar coal particles, adsorption layers are formed which have polar groups oriented towards the aqueous phase. In contrast, surfactant solutions in oils (hydrocarbons, vegetable oil oxidation products etc.) in contact with polar materials or powders (carbonates, silicates) the polar groups are on the solid phase surface. 

In the case of dextran (0.1-1%) and amyiopectin (0.05%) the potentiometric measurements do not indicate any interaction with NaDS, the activity of NaDS solutions is the same with and without these polymers. An amylose solution of 0.025% was turbid and it did not clear up even in the presence of 20 mmoLkg" NaDS. However, the potentiometric measurements showed binding of NaDS according to a Langmuir isotherm with a saturation value of 0.27 mmol/g amylose. The binding of NaDS on amylose is regarded as an adsorption on solid amylose particles and not as an interaction between them in solution. It is concluded that the investigated polysaccharides do not interact with NaDS in aqueous solution. 

In simimary, the adsorption of surfactants on colloidal particles is influenced by the EDL and it affects the EDL. Surfactant molecules compete with simple ions from the background electrolyte for adsorption in the Stern layer (Dimov et al. 2002), yet the interaction between adsorbed surfactant molecules introduces additional complexity to the problem of EDL formation. Detailed introduction into the surfactant adsorption on solid surfaces is, e.g., given by Myers (1999, Chap. 9) and Holmberg et al. (2002, Chap. 17). 

N.K. Dimov, V.L. Kolev, P.A. Kralchevsky, L.G. Lyutov, G. Broze, A. Mehreteab, Adsorption of ionic surfactants on solid particles determined by zeta-potential measurements Competitive binding of counterions. J. Colloid Inhriace Sci. 256(1), 23—32 (2002). doi 10.1006/jcis.2001. 

Quite often, the individual test method, while stimulating field conditions accurately, will not give reproducible results because of variables such as surface preparation, velocity and adsorption of inhibitors on solid particles, and other factors, some of which are indeterminate. Several investigators have reported the use of statistical methods in the evaluation of test results. 

The latex adsorption work is the only recent study examining the surface properties of xanthan gum. However, it must be stressed that it was carried out on solid particles and not on liquid interfaces. The reports claiming that the gum has surface activity and that it can stabilize emulsions did not consider the adsorption properties of the gum. The surface activity of the gum is not very clear from its structure, but it is possible that some of it is derived from conformational changes induced by heat treatment [176]. 

The adsorption of HMI on solid particles was investigated [11] using two different latex dispersions, namely polystyrene (PS) and polymethylmethacrylate (PMMA). Both lattices have a narrow particle size distribution with PS having a diameter of 321 nm and polydispersity index of 0.03 and PMMA having a diameter of 273 nm and polydisper-sity index of 0.05. The results are shown in Figure 15.5, which shows the amount of adsorption F in pmol/m versus HMI concentration (pmol/dm ). 

An important factor that is not taken into account in the DLVO theory is adsorption, on the particle s surface, of long polymeric chains. The adsorption of a non-ionic polymer or a polyelectrolyte on the solid surface can cause, not only a modification of the zeta potential, but also a critical difference between the value of the zeta potential and the state of dispersion. Steric repulsion is associated with the obstmction effect of these polymers that are capable to form a sufficiently thick layer to prevent the particles from approaching one another in the distanee of influence of the Van der Waals attractive forces. Steric stabihzation will therefore depend on the adsorption of the polymeric dispersant and the thickness of the layer developed. Several interpretation models for stabilization by steric effect have been put forward. They rely either on a statistical approach, or on the thermodynamics of solutions. Steric stabilization is particularly useful in organic, fairly non-polar or non-polar environments, as in the case of tape casting (see section 5.4.3). 

This equation has the same form of that obtained for solid diffusion control with D,j replaced by the equivalent concentration-dependent diffusivity = pDpj/[ pn]Ki l - /i,//i)) ]. Numerical results for the case of adsorption on an initially clean particle are given in Fig. 16-18 for different values of A = = 1 - R. The upt e curves become... 

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