Forced Migration of Nonsoluble and Soluble Metallic Pollutants ahead of a Liquid−Solid Interface during Unidirectional Freezing of Dilute Clayey Suspensions

To test whether suspended and dissolved forms of metallic pollutants in water can be simultaneously separated by freezing, we subjected water initially at 0 °C and containing (0.69−1.03) × 10-2 mol of dissolved lead nitrate and 0.83−1.68 g of suspended clay (Na−montmorillonite) per kilogram of suspension to unidirectional freezing. Less suspended and dissolved forms of lead remained behind the freezing interface as compared to that in the initial suspension. The greatest reduction of total lead behind the freezing interface was obtained when the pH was between 5 and 9 and when −2 °C cooling was used: i.e., for a mean rate of freezing front advance on the order of 1 μm s-1.