Liquid soils

The cleaning process proceeds by one of three primary mechanisms solubilization, emulsification, and roll-up [229]. In solubilization the oily phase partitions into surfactant micelles that desorb from the solid surface and diffuse into the bulk. As mentioned above, there is a body of theoretical work on solubilization [146, 147] and numerous experimental studies by a variety of spectroscopic techniques [143-145,230]. Emulsification involves the formation and removal of an emulsion at the oil-water interface the removal step may involve hydrodynamic as well as surface chemical forces. Emulsion formation is covered in Chapter XIV. In roll-up the surfactant reduces the contact angle of the liquid soil or the surface free energy of a solid particle aiding its detachment and subsequent removal by hydrodynamic forces. Adam and Stevenson s beautiful photographs illustrate roll-up of lanoline on wood fibers [231]. In order to achieve roll-up, one requires the surface free energies for soil detachment illustrated in Fig. XIII-14 to obey... 

Liquid soil can be removed by dkect emulsification and solubiLkation as well as by roU-up. Oils that are more readily emulsified or solubilked are removed more rapidly and more completely. 

Un chien Ajufhihyon) de 31 Kil. reijoit le 8 mars cc. 1,6 de liquide (soil... 

Lebeau et al. (2002) investigated the sorption of cadmium by viable microbial cells that were free or immobilized in alginate beads by incubating the bacteria in a liquid soil extract medium at pH 5 7 and Cd concentrations of 1 to 10 mg L-1. The percentage of Cd biosorbed reached a maximum (69%) at low Cd concentrations and neutral pH. Thus, the effectiveness of bacteria, inoculated into metal-contaminated soils, would largely depend on the concentration of the metal and its distribution between the biomass and the medium. 

Liquid silicone rubber (LSR), 22 584 Liquid silicon, properties of, 22 484t Liquid soaps, 22 748 Liquid soil detergency, 8 422-423 Liquid—solid chromatography, adsorption, 1 610-611... 

A first step in deciding on an analytical procedure to use or a species to look for is to understand that the species of interest may be in one of four soil compartments (see Figure 6.3) the solid (both inorganic and organic), the liquid (soil solution), the gaseous (soil air), or the biological (living cells). It is also important to remember that molecules and ions can move between compartments and interconvert between species. 

Detergency, or the power of a detergent product to remove soil, depends on the ability of surfactants to lower the interfacial tension between different phases. This can be explained for a typical case where removal of liquid soil is aided by surfactant adsorption onto the soil and substrate surfaces from the cleaning bath (Figure 2) using Young s equation,... 

Figure 2. Liquid soil removal from substrate in the presence of surfactants.

The procedures employed for the liquid, soil, water and air samples are described and discussed below. 

Both in situ and ex situ chemical oxidation technologies are commercially available for the treatment of liquids, soils, and sludges containing hydrocarbons and other oxidizable contaminants. 

Hexadecane Studies. Figure 2 also indicates that the removal of low viscosity liquid soils such as hexadecane (Cj6) is difficult to monitor with this spectroscopic approach because of the rapidity of removal. The run performed with surfactant-free water, however, indicates that a stable C16-water interface is achieved after 5 minutes. The somewhat hydrophobic ZnSe surface of the IRE can be considered a reasonable model of the polyester fabric surface. Water alone cannot completely clean the C16 from the surface, indicating a significant adhesion energy of hydrocarbon to the ZnSe. 

The importance of a surfactant - rich phase, particularly a lamellar one, to detergency performance was noted for liquid soils such as C16 and mineral oil (3.6). Videomicroscopy experiments indicated that middle phase microemulsion formation for C12E04 and Cjg was enhanced at 30 °C, while at 18 °C, oil - in - water, and at 40 °C, water - in - oil microemulsions were found to form at the oil - bath interface (3.6). A strong temperature dependence of liquid soil removal by lamellar liquid crystals, attributed to viscosity effects, has been noted for surfactant - soil systems where a middle - phase microemulsion was not formed (10). 

Even the simplest detersive system is surprisingly complex and heterogeneous. It can nevertheless be conceptually resolved into simpler systems that are amenable to theoretical treatment and understanding. These simpler systems are represented by models for substrate-sohd soil and substrate-liquid soil. In practice, many soil systems include solid-liquid mixtures. However, removal of these systems can generally be analyzed in terms of the two simpler model systems. Although these two systems differ markedly in behavior and structure, and require separate treatment, there are certain overriding principles that apply to both. 

A second principle applying to these model systems is derived from their colloidal nature. With the usual thermodynamic parameters fixed, the systems come to a steady state in which they are either agglomerated or dispersed. No dynamic equilibrium exists between dispersed and agglomerated states. In the solid-soil systems, the particles (provided they are monodisperse, i.e., all of the same size and shape) either adhere to the substrate or separate from it. In the liquid-soil systems, the soil assumes a definite contact angle with the substrate, which may be anywhere from 0° (complete coverage of the substrate) to 180° (complete detachment). The governing thermodynamic parameters include pressure, temperature, concentration of dissolved... 

Pano-drench [Morton], TM for a liquid soil-treatment concentrate containing 0.6% cya-no(methylmercuri)-guanidine. 

Repellent finishes are important components of many protective textiles. Apphca-tions for repellent textiles range from medical textiles to raincoats. The low surface energies provided by repellent finishes can keep solid and liquid soils from adhering to treated fiber surfaces. Finishes based on hydrocarbon and silicone chemistries can yield water repellent textiles, while fluorochemicals are necessary to achieve the low surface energies needed for dry soil and oil repellency. "... 

Fig. 1-1. Transport processes in solid-liquid soil reactions—Nonactivated processes 1. Transport in the soil solution, 2. Transport across a liquid film at the solid-liquid interface, 3. Transport in a liquid-filled micropore. Activated processes 4. Diffusion of a sorbate at the surface of the solid, 5, Diffusion of a sorbate occluded in a micropore, 6. Diffusion in the bulk of the solid.

Liquid soil is usually removed by roll-up, emulsification, direct solubilization, and possibly formation of microemulsion or liquid crystalline phases. The oil emulsification capability of the surfactant solution and the oil-water interfacial tension are relevant physicochemical parameters. 

Removal of Liquid Soil Removal of liquid (oily) soil by aqueous baths is accomplished mainly by a roll-back or roll-up mechanism in which the contact angle that the liquid soil makes with the substrate is increased by adsorption of surfactant from the cleaning bath. 

Figure 6-3 illustrates the situation of a liquid soil adhering to a substrate in the presence of air. The reversible work to remove the liquid oily soil O from the substrate, the work of adhesion Wa (equations 6.12 and 6.13) is given by the expressions... 

When surfactants of the proper structure are present in the bath, they will adsorb at the substrate-bath (SB) and liquid soil-bath (OB) interfaces in such a fashion (i.e., with the hydrophilic group oriented toward the aqueous bath) as to reduce jSB and Job, with consequent reduction in the work to remove the soil from the substrate. Reduction in ySB will also cause a decrease in cos 0 and an increase in 0, resulting in the observed roll-back of the liquid soil. Many investigators of oily soil removal,... 

FIGURE 10-1 Contact angle at the bath-liquid soil-substrate junction. 

If the contact angle is 180°, the bath will spontaneously completely displace the liquid soil from the substrate if the contact angle is less than 180° but more than 90°, the soil will not be displaced spontaneously but can be removed by hydraulic currents in the bath (Figure 10-2) (Schwartz, 1972). When the contact angle is less than 90°, at least part of the oily soil will remain attached to the substrate, even when it is subjected to the hydraulic currents of the bath (Figure 10-3) (Schwartz, 1971, 1972), and mechanical work or some other mechanism (e.g., solubilization, see below) is required to remove the residual soil from the substrate. 

---