Effect of freeze-thaw process on partitioning of contaminants in ferric precipitate

The primary interest of this work was to determine the processing conditions which will provide the most water removal from the precipitate after freezing and thawing. The work examined the effect of variables such as freezing time, freezing temperature, and pre-treatment steps, e.g. agitation or concentration, on the freeze thaw process of ferric precipitates. The extent of dewatering of freeze thawed samples was not significantly affected by freezing rate or curing time, provided the floe was completely frozen. However, a pre-concentration step was found to produce a more concentrated residual. The relatively low degree of structure within the ferric floes makes them particularly suitable for freeze-thaw conditioning. Only a slight increase in leach out of contaminant from the floe was observed. Thus, the experiments indicate that this is a very simple and effective method of dewatering precipitates, which does not require the use of additional additives. (C) 2003 Elsevier Ltd. All rights reserved.