Surface charge recovery

Fig. XIII-9. The dependence of the flotation properties of goethite on surface charge. Upper curves are potential as a function of pH at different concentrations of sodium chloride lower curves are the flotation recovery in 10 M solutions of dodecylammo-nium chloride, sodium dodecyl sulfate, or sodium dodecyl sulfonate. (From Ref. 99.)...

The results indicate that persistence of organosilicone surfactants in the parent molecule form will be limited on typical soil media and in aqueous environments. Reduced recovery was considered to be a result of abiotic degradation and/or strong sorption processes. Losses were most significant on solid media exhibiting extreme pH values and were also enhanced in the presence of clay substrates. Studies on clays indicated that pH, potential for intercalation and surface charges are important factors in the removal process. 

Surfactant adsorption on solids from aqueous solutions plays a major role in a number of interfacial processes such as enhanced oil recovery, flotation and detergency. The adsorption mechanism in these cases is dependent upon the properties of the solid, solvent as well as the surfactant. While considerable information is available on the effect of solid properties such as surface charge and solubility, solvent properties such as pH and ionic strength (1,2,3), the role of possible structural variations of the surfactant in determining adsorption is not yet fully understood. 

The removal of PhCs by NF membranes occurs via a combination of three mechanisms adsorption, sieving and electrostatic repulsion. Removal efficiency can vary widely from compound to compound, as it is strictly correlated to (a) the physicochemical properties of the micro-pollutant in question, (b) the properties of the membrane itself (permeability, pore size, hydrophobicity and surface charge) and (c) the operating conditions, such as flux, transmembrane pressure, rejections/recovery and water feed quality. 

They concluded that the surface charge of HS controlled their recovery, and any carrier component decreasing the effective surface charge of HS led to a sorption increase. Furthermore, the cross-flow rate influenced recovery dramatically, which supports the idea that either sorption to membrane or permeation through it is responsible for losses. Finally, other channel components play a minor role. The authors recommendations were to use 0.005 M TRIS-buffer (pH 9.1) as a carrier solution (recovery of about 85-90%) and use a regenerated cellulose membrane with a 5-kDa cutoff as the accumulation wall. 

For serum replacement (6), the latex is confined in a cell with a uniform-pore-size Nuclepore filtration membrane. Distilled, deionized water is pumped through the latex until the conductance of the effluent stream is about the same as that of the distilled, deionized water. This serum replacement removes the adsorbed emulsifier and solute electrolyte quantitatively and allows recovery of the serum in a form suitable for further analysis however, it does not+replace the Na+ and K counterions of the surface groups with Vl ions. To do this, dilute hydrochloric acid (ca. 10 N) is pumped through the latex, followed by distilled, deionized water to remove the excess acid. The latex is then titrated conductometrically to determine the surface charge. 

The surface charge of the solid particles has been reported to play an important role in the recovery process. Maximum recovery is achieved when the particles exhibit net zero surface charge.(13-15) Lai and Fuerstenau (16) have reported that ultrafine (0.1 pm) alumina particles can be extracted from... 

Figure 4 Schematic diagram of the role of surface charge in the oil displacement process. High surface charge density results in high oil recovery, while low surface charge density results in low oil yields.

Figure 10.35. Flotation of geothite with 10" M solutions of dodecylammonium chloride (open squares), sodium dodecyl sulfate (open circles) and sodium dodecyl sulfonate (filled circles), illustrating the dependence of flotation recovery on surface charge (after ref. (8))...

High surface charge density -Low interfacial tension -Low interfacial viscosity -High electrical repulsion between oil droplets and sand -High recovery... 

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