Figure 4. Illustration of local equilibrium assumption in leaching from a CDF

ERDC TN-DOER-C16

July 2000

leaching procedure may be necessary if the full lift thickness is dewatered prior to placement of the

next lift. Sequential batch leaching of aerobic, aged sediment can be used to simulate leaching of

the surface crust in a CDF (Brannon, Myers, and Tardy 1994).

Ionic strength. Sequential batch leaching of freshwater sediments usually yields a desorption

isotherm such as shown in Figure 5 (Brannon, Myers, and Tardy 1994). This is what is known as

a classical desorption isotherm. Its key feature is a single distribution coefficient that is constant

throughout the sequential leaching procedure. A commonly observed feature of desorption iso-

therms for metals in freshwater sediments is that they do not go through the origin, but intercept the

ordinate at some other point. The intercept indicates the amount of metal in geochemical phases

that is resistant to aqueous leaching which is generally tied up by acid volatile sulfides in the

sediment.