Solid suspensions, adsorption

Batch tests (i. e., tests on individual waste materials) are conducted with the provided solid suspensions (e.g., soils such as Woodburn, Sagehill, and Olyic, as well as two bottom sediment samples) prepared with previously air-dried solids (i. e., soils and bottom sediments), ground to a uniform powdery texture for mixing with the eluates from the 24-h batch leaching test of the different SWMs/COMs. The concentrations of eluates in solution were designed to evaluate the capability of different environmental solids to adsorb available contaminants. The solid particles were fully dispersed with the aqueous phase to achieve complete adsorption. Common practice is to use a solid solution ratio of 1 g 4 ml [ 1 ], together with proper tumbling of the samples at a constant temperature (e.g., at least 24 h in a constant temperature environment of 20°C). 

At the beginning, the electric double layer at the solid-aqueous electrolyte solution interface was characterized by the measurements of the electrokinetic potential and stability of dispersed systems. Later, the investigations were supported by potentiometric titration of the suspension, adsorption and calorimetric measurements [2]. Now, much valuable information on the mechanism of the ion adsorption can be obtained by advanced spectroscopic methods (especially infrared ATR and diffuse spectroscopy) [3], Mosbauer spectroscopy [4] and X-ray spectroscopy [5]. Some data concerning the interface potential were obtained with MOSFET [6], and AFM [7]. An enthalpy of the reaction of the metal oxide-solution systems can be obtained by... 

Sample of solid suspension in the supernatant, collected after the attainment of adsorption equilibrium, was transferred to the thermostated microelectrophoresis celt. The velocity U for at least 10 particles was measured at the two stationary levels and the average value taken the polarity of electrodes was reversed after each velocity measurement. For a spherical particle, the following equation is satisfied ... 

Fundamental investigation of the system at the molecular level. This requires investigations of the structure of the solid/liquid interface, namely the structure of the electrical double layer (for charge-stabiUsed suspensions), adsorption of surfactants, polymers and polyelectrolytes and conformation of the adsorbed layers (e.g., the adsorbed layer thickness). It is important to know how each of these parameters changes with the conditions, such as temperature, solvency of the medium for the adsorbed layers, and the effect of addition of electrolytes. 

The role of surfactants in stabilizing solid suspensions is, again, one of great academic and technological importance. Because of the vast literature available concerning the fundamental and practical aspects of the subject, its pursuit will be left to the interested reader. Suffice it to say that the nature of the surfactant to be used (its adsorption properties, electrical charge characteristics, rheological properties in solution, etc.) should always be considered early in preliminary formulation processes. 

In eertain eases, the primary proeess objeetive is to keep solid partieles in suspension. Areas of applieation involve eatalytie reaetions, erystallization, preeipitation, ion exehange, and adsorption. Axial flow and pitehed-blade turbines are best suited in providing the essential flow patterns in a tank to keep the solids in suspension. The suspended solid is eharaeterized by two parameters ... 

Of special interest in liquid dispersions are the surface-active agents that tend to accumulate at air/ liquid, liquid/liquid, and/or solid/liquid interfaces. Surfactants can arrange themselves to form a coherent film surrounding the dispersed droplets (in emulsions) or suspended particles (in suspensions). This process is an oriented physical adsorption. Adsorption at the interface tends to increase with increasing thermodynamic activity of the surfactant in solution until a complete monolayer is formed at the interface or until the active sites are saturated with surfactant molecules. Also, a multilayer of adsorbed surfactant molecules may occur, resulting in more complex adsorption isotherms. 

Adsorption on Kaolinite. For kaolinite, the polymer adsorption density is strongly dependent on the solid/liquid ratio, S/L, of the clay suspension. As S/L increases, adsorption decreases. This S/L dependence cannot be due totally to autocoagulation of the clay particles since this dependence is observed even in the absence of Ca2+ at pH 7 and at low ionic strength where auto-coagulation as measured by the Bingham yield stress is relatively weak (21). Furthermore, complete dispersion of the particles in solvent by ultra-sonication before addition of... 

Leoni et al. [365,370] conclude that the extraction of insecticide from waters by adsorption on Tenax yields results equivalent to those by the liquid-liquid procedure when applied to waters that do not contain solid matter in suspension. For waters that contain suspended solids that can adsorb some insecticides in considerable amounts, the results of the two methods are equivalent only if the water has previously been filtered. In these instances, therefore, the analysis will involve filtered water as well as the residue of filtration. 

Polychlorotrifluoroethylene (PCTFE) is ordinarily prepared by emulsion polymerization. A polymer suitable for thermal processing requires coagulation, extensive washing, and postpolymerization workup. Coagulation to provide a filterable and washable solid is a slow, difficult process and removal of surfactant is an important part of it. Complete removal may be extremely difficult depending on the extent of adsorption to the polymer particles. Consequently we set out to develop a suspension polymerization process, which would be surfactant-free and afford an easily isolated product requiring a minimum of postreaction workup. 

The partition coefficients for different LAS homologues (Table 5.4.2) are higher in the marine environment due to the higher ionic strength that promotes sorption of anionic surfactants [14] and an increase in the partition coefficient with the alkylic chain length has been observed (Table 5.4.2). The evolution of the concentration of the various homologues of LAS in solids in suspension (cf. Fig. 5.4.2) is similar to that found in water and, in the process of adsorption, an increase can be observed in line with the chain length, as commented on previously. 

The concentrations of LAS found in water and fluvial sediments show great variability (see Chapter 6.3). The values found in water (0— 600 p,gL 1) [7-10] and in sediments (0-600 p-gg-1) [7,9,11,12] show the pronounced affinity of the compound for the solid phase. The partition coefficients of LAS observed in fluvial sediments range from 100 to 2600 L kg-1 [9], The maximum concentrations have been detected close to urban centres in which untreated wastewater is discharged, and a rapid rate of decrease is observed as one moves downstream from these [9,13]. Some authors have found dilution to be the main factor responsible for decreasing concentrations along the course of a river towards the sea [9,13,14], but others consider biodegradation to be the most efficient process [9,15], while Rapaport and Eckhoff [16] hold adsorption onto solids in suspension to be a major factor for LAS removal from river water. 

Titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy are two techniques which have seldom been applied to study reactions at the solid-liquid interface. In this paper, we describe these two techniques and their application to the investigation of salicylate ion adsorption in aqueous goethite (a-FeOOH) suspensions from pH 4 to 7. Evidence suggests that salicylate adsorbs on goethite by forming a chelate structure in which each salicylate ion replaces two hydroxyls attached to a single iron atom at the surface. 

Modifications of surface layers due to lattice substitution or adsorption of other ions present in solution may change the course of the reactions taking place at the solid/liquid interface even though the uptake may be undetectable by normal solution analytical techniques. Thus it has been shown by electrophoretic mobility measurements, (f>,7) that suspension of synthetic HAP in a solution saturated with respect to calcite displaces the isoelectric point almost 3 pH units to the value (pH = 10) found for calcite crystallites. In practice, therefore, the presence of "inert" ions may markedly influence the behavior of precipitated minerals with respect to their rates of crystallization, adsorption of foreign ions, and electrokinetic properties. 

The transport of disulfoton from water to air can occur due to volatilization. Compounds with a Henry s law constant (H) of <10 atm-m /mol volatilize slowly from water (Thomas 1990). Therefore, disulfoton, with an H value of 2.17x10" atm-m /mol (Domine et al. 1992), will volatilize slowly from water. The rate of volatilization increases as the water temperature and ambient air flow rate increases and decreases as the rate of adsorption on sediment and suspended solids increases (Dragan and Carpov 1987). The estimated gas- exchange half-life for disulfoton volatilization from the Rhine River at an average depth of 5 meters at 11 °C was 900 days (Wanner et al. ] 989). The estimated volatilization half-life of an aqueous suspension of microcapsules containing disulfoton at 20 °C with still air was >90 days (Dragan and Carpov 1987). 

Negative adsorption occurs when a charged solid surface faces an ion in an aqueous suspension and the ion is repelled from the surface by Coulomb forces. The Coulomb repulsion produces a region in the aqueous solution that is depleted of the anion and an equivalent region far from the surface that is relatively enriched. Sposito (1984) characterized this macroscopic phenomenon through the definition of the relative surface excess of an anion in a suspension, by... 

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