EXPERIMENTAL METHODS

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impurities is more difficult to purify than the same so-

lution containing a lower concentration of impurities.

This study examines the effects of freezing rate and

impurity concentration only. Mixing intensity was not

studied because it is an artifact of the mechanical de-

sign and geometry of the freezing device.

To study the effects of freezing rate and impurity

concentration, we built a bench-scale freeze concen-

trator (see Fig. 2). This device can freeze a sample at a

predetermined constant freezing rate. To eliminate the

force of gravity on the migration of particles away from

the freezing front, a 30-cm-long by 5-cm-diameter

Plexiglas tube is made to travel horizontally. A small

reservoir located at the end of the tube is used to col-

lect any excess pinkwater produced by the expansion

of the sample during freezing. The temperature of the

refrigerated collar at the entrance to the freezing cham-

ber is adjusted to obtain different freezing rates.

EXPERIMENTAL METHODS

Pinkwater

The pinkwater was obtained from the equalization

tank at the treatment facility located at McAlester Army

Ammunition Plant (AAP) in McAlester, Oklahoma.

Four 1-L samples were collected in brown glass bottles,

refrigerated, packed in dry ice, and shipped to CRREL.

The contents of these bottles were then mixed to ob-

tain a homogeneous starting solution. We analyzed