Redeposition

In contrast to the sulfide ores, the lateritic ores were formed over long periods of time as a result of weathering of exposed nickel-containing rocks. The lateritic weathering process resulted in nickel solutions that were redeposited elsewhere in the form of oxides or siUcates. One type of laterite is nickeliferous limonitic iron laterite (Ee, Ni)O(OH) which consists primarily of hydrated iron oxide in which the nickel is dispersed in soHd solution. 

Oxygen is a prime factor in the corrosion of system materials and the release, activation, and redeposition of activated corrosion products. 

Ink particle redeposition on cellulose fibers can reduce deinked paper brightness. Should larger ink particles redeposit on fibers, visible ink specks may result. Sodium siUcate is often added to the pulper to act as a dispersant and reduce this redeposition (6,14). Up to 5% based on dry paper weight may... 

Synthetic fabrics can also be finished to achieve a number of specific characteristics (199). For example, increased electrical conductivity can improve the antistatic character of polyester. Similarly, finishes that improve hydrophilic character also improve properties related to soil release and soil redeposition (199,200). 

Various hydrophilic finishes have been used in connection with soil release and soil redeposition during laundering. These finishes can impart a degree of antistatic protection to the treated materials however, the main functions of these finishes are to release soil and to prevent the redeposition during laundering. 

Much of the work that led to elucidating the role of budders as calcium sequestering agents in detergency was done in connection with redeposition studies (34). 

Sodium carboxymethylceUulose, NaCMC, greatly reduces redeposition in cotton-washing systems based on synthetic surfactants. It is effective at remarkably low concentrations of ca 1% of the standard washing compositions used at ca 0.1 to 0.2% in the bath. Thus, ca 0.001—0.002%, or 10—20 ppm NaCMC is sufficient to significantly inhibit redeposition. 

Solid Soil Type and Size. Different soHd soils differ greatly in ease of removal and redeposition behavior. These differences can be traced to particle size and soil—substrate bonding. The effect of particle size variation on detergency has been studied with soil removal and redeposition techniques. 

As might be expected, large differences in the removabiUty of soHd particulate soil are due to differences in the chemical nature of the particle surface. Thus, kon oxides, lampblacks, and clays, all of the same particle size, differ greatly in thek redeposition behavior and the manner in which they are removed. 

Redeposition of sod can be estimated simultaneously with net sod removal (detergency) by including a white swatch with the soded swatches. It also can be estimated separately by adding a measured amount of sod to a fresh wash bath, then treating the white swatch ia this standard-sod bath. The former method is, superficially at least, more reaUstic. The latter method, however, is frequently of greater value ia development work because both the quantity and composition of the sod are known and can be controlled. 

In afterscouting, most often a synthetic tanning agent is used to prevent redeposition of dye on unptinted areas and to improve wetfastness properties of the print. 

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