Abstract: A process of the type employing freezing and thawing of metal hydroxide sludge to effect phase separation by gravity settling of solids to permit removal of the purified water, and a preferred system for carrying out the process. Commercially available refrigeration equipment, suitably modified and adjusted to operate in the freezing of sludge in sheets and breaking the sheets into relatively small pieces, is utilized in order to minimize the costs of hardware end controls. The frozen sludge particles are deposited in a melt tank containing a quantity of sludge which has previously been frozen and thawed.