Flocculation procedures, effect

Procedure. Initially, the flocculation procedure adopted was to add polymer to the clay suspension, stir rapidly for 15 seconds to ensure good mixing and then to flow the treated suspension through a 3 m length of coiled 1 mm diameter tubing. Tube flow is known to be an effective method of applying shear to a suspension and hence promoting orthokinetic flocculation (12). 

Figure 5. Effect of different flocculation procedures, using polymer A and a kaolin concentration of 140 mg/1. Procedures 1) Rapid mixing only, 2) Rapid mixing and tube flow (as in Figure 1) 3) Rapid mixing and slow...

The complexity of the mixtures made it impossible to define the chemical composition so the commercial preparations were divided into four groups (Table 8.2) on the basis of a series of sophisticated chemical assay procedures. Caramel colorants must be compatible with the food products in which they are used, which usually means the absence of flocculation and precipitation in the food. These undesirable effects result from charged macromolecular components of caramel which react with the food. Hence the net ionic charge of the caramel macromolecules at the pH of the intended food product is the prime determinant of compatibility. Caramel colorants are used in a variety of foods (Table 8.2) but over 80% of the caramel produced in the US is used to color soft drinks particularly colas and root beers. 

The choice of chemical is usually based on trial-and-error procedures hence, demulsifier technology is more of an art than a science. In most cases a combination of chemicals is used in the demulsifier formulation to achieve both efficient flocculation and coalescence. The type of demulsifiers and their effect on interfacial area are among the important factors that influence the coalescence process. Time-dependent interfacial tensions have been shown to be sensitive to these factors, and the relation between time-dependent interfacial tensions and the adsorption of surfactants at the oil-aqueous interface was considered by a number of researchers (27, 31-36). From studies of the time-dependent tensions at the interface between organic solvents and aqueous solutions of different surfactants, Joos and coworkers (33—36) concluded that the adsorption process of the surfactants at the liquid-liquid interface was not only diffusion controlled but that adsorption barriers and surfactant molecule reorientation were important mecha-... 

Flocculation. Flocculation is the least costly procedure to concentrate non-hlgh-level waste. The principles are unspecific adsorption of radionuclides on a carrier, such as Fej 03(07) or calcium phosphate, or cocrystallization with a suitable crystalline precipitate, such as strontium with CaCOa. The sludge has to be collected by settling or filtering and is handled as the radioactive waste concentrate. This technique, because of its rather poor decontamination effect, is suitable only for LLW. Usually, the concentrate has a high water content. 

The purification of surfactants has to be performed in a way that addresses their specific effects on interfacial properties. Thus, chemical purification procedures, such as recrystallisation, distillation, flocculation, and washing with organic solvents, are important steps (Czichocki et al. 1981) but usually do not lead to a sufficient purity, i.e. surface-chemical purity. Therefore, efficient purification methods are based on interfacial principles. 

Data on grain size distribution of the various strata is important to the overall site characterization and provides information related to other properties and behavior, such as permeability and water flow. Two main concerns are testing procedures and texture (grain size) classification systems. At present, there is no universally accepted classification system and testing methods can be quite different. The presence of significant biogenous materials, effects of flocculation due to salts, and the fact that some deep-sea clays are extremely fine-grained, requires that special procedures be considered. 

Cleanup procedures vary considerably depending on both the mycotoxin(s) and the commodity to be analyzed. For many commodities slurries of freshly precipitated iron(III) hydroxide and copper(II) carbonate have proved effective in removing co-extractives. Flocculation of impurities with aqueous lead acetate or zinc acetate has also been used. Some mycotoxins can be adsorbed onto silica gel and/or florosil and subsequently eluted. Indeed, a range of commercially available prepared columns, such as Sep-Pak, have proved very convenient as a cleanup stage for crude extracts of mycotoxins before subsequent analysis. 

Sometimes the effect of the detention time is so strong that the overflow rate can be ignored and the scale-up is based on the so-called second order test procedure (as the flocculation process usually follows a second order reaction model ). The required detention time is determined by testing the residual solids concentrations in the supernatant under the conditions of mild shear. 

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