183

conducted. Sands 1, 2, 5,10, and 12 were used to provide a broad range of TOC
and clay content in the batch sorption tests. The mass of the foundry sand was
maintained constant (2 g), and the zinc concentration was varied between 10 and
75 mg/L. The initial pH was adjusted to 2.6. The tumbling time was set at 10 hrs,
which was found to be sufficient to ensure equilibrium (Fig. 7.1).
Sorption isotherms from the batch sorption tests are shown in Fig. 7.9.
The isotherms exhibit some non-linearity, particularly at lower concentrations.
Fits of the linear and Freundlich isotherm models are summarized in Table 7.4.
Method 1 corresponds to fits of the linear model with a non-zero intercept. A
zero-intercept was forced for Method 2. Comparable fits were obtained with the
Freundlich model and the linear model with a non-zero intercept.
Partition coefficients obtained from the batch sorption tests were
compared to those obtained from the batch kinetic tests for Sands 1, 10, and 12.
For Sands 2 and 5, the partition coefficients were estimated using Eqs. 7.2,
which was developed using data from the batch kinetic tests. In general, the
partition coefficients from the batch kinetic tests and those predicted by Eq. 7.2
are comparable to the partition coefficients obtained from the batch sorption tests
(Fig. 7.10). Therefore, partition coefficients estimated using Eq. 7.2 should be
reliable for a relatively broad range of concentrations.