Purification by Reverse Osmosis

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

8.4.3.5 Distillation

Distillation (including vacuum distillation) is at least conceptually simple. It

removes all but volatile contaminants. In practice, some contaminants will cause

foaming, and evaporator maintenance is often a problem. If laundry waste or other

waste-containing detergents are to be evaporated, it may be necessary to add an

antifoaming compound. Although these are sometimes effective, they often

degrade with heat faster than the detergents or other compounds causing the

foaming. Few evaporators take the product to dryness, as this often creates a scale

build-up. If the evaporator bottoms are removed as a solution, they must be

solidified, usually with some increase in volume.

8.4.3.6 Purification by Reverse Osmosis

This process is highly effective on relatively pure water streams. The water is

passed through a semipermeable membrane by mechanical pressure, leaving

contaminants behind. The result is generally 80% to 99% of the influent water

released as pure water, with the remainder containing all of the contaminants.

Reverse osmosis has the advantage over ion exchange in that it will remove non-

ionic contaminants although these often shorten the life of the membrane. It is

much more energy-efficient than distillation and requires much less equipment for

the same volume of water treated. It is sometimes used as a "polishing" technique

to further treat relatively clean water.

8.4.3.7 Solidification

Solidification is often a last-resort treatment because, while the other treatments

described reduce the volume of solid waste requiring disposal, solidification

increases it. Nevertheless, it is useful for some waste. Portland cement is the most

common solidification medium for water solutions, aqueous suspensions, and

resins. However, there are other proprietary materials, including some especially

for oils and other organic compounds.

8.4.3.8 Solvent Extraction

Solvent extraction is used exclusively with organic solvents and involves mixing

the solvent with an immiscible aqueous solution in which the contaminant is

soluble. In this way, the contaminant is transferred to the aqueous solution for

further treatment. (Solvent extraction may also be used in the other mode, in which

the contaminant is transferred to the organic solvent solution, but this has fewer

applications in waste management.) The organic solution is usually recycled.

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