1. Containing Fluid at Waste Sites
It is often desirable to have a liquid-proof barrier for containing a large body of liquid of liquid-containing material. For example, landfills and surface impoundments are two types of impoundments in which the fill volume may be hazardous wastes that contain toxic liquids. Some sort of barrier is necessary to prevent leakage that would contaminate the environment.
Membrane liners are one type of barrier often used for containing fluid waste. These liners are made from large sheets of flexible material such as plastic. In addition to being flexible, the liner material is selected to resist deterioration as a result of contact with the waste.
The liner is placed in a suitable excavated depression in the earth and is constructed to define the bottom and sides of the impoundment as an impermeable barrier. Generally, to form the liner, sheets of the material are seamed together at the site to form one or more continuous layers. In some installations, double liners are installed, with a layer of material such as sand between them.
One problem with such liners, however, is that installation practices and operational factors may lead to punctures or separated seams, and thus leaks in the liner. After hazardous waste has been introduced, such leaks are difficult to repair. Existing methods include draining the impoundment or using a cofferdam to access the leak, retrofitting the impoundment with a new liner, or applying a thick layer of sealant on the bottom. These repair methods may endanger workers and are generally unreliable and expensive.
The formation of a sealing layer over the impoundment liner is one means of inhibiting leakage if punctures exist. A slurry consisting of clay particles mixed with water is pumped into the impoundment. By the action of gravity, the clay particles fall toward the bottom of the impoundment to the top surface of the liner. This treatment is not always effective and the cost is prohibitive. The clay layer must be allowed to form over the entire liner because there is no means for selecting where a seal is to be made. At the bottom of the impoundment, this layer must be several centimeters thick to ensure an effective seal. Sealing the side walls of the impoundment is especially difficult because the particles tend to fall downward and the layer must be substantially thicker to protect against wave action and prevent the clay layer from sloughing to the bottom.
2. Applications of Electrophoresis
Electrophoresis can be described as an electrokinetic phenomenon that involves the motion of suspended solid particles through a stationary liquid under the influence of an applied electric field. Electrophoresis has been applied in various arts since the early part of this century.
One of the first practical uses of electrophoresis was electrophoretic coating of various materials. Examples are the use of aqueous emulsions for coating the inner surface of food cans with lacquers and the use of nonaqueous media for coating metals with resin.
It is well known that clay particles may carry an electrical charge and may be used as the particles in electrophoretic motion. This characteristic of clay particles has been applied to cake a mud fluid onto a porous well wall during drilling. Another application involves methods for de-watering clay suspensions so that the clay can be used for commercial purposes.