CONTRIBUTION OF FREEZING AND THAWING METHODS TO CONDITIONING OF SLURRY OF COLLOIDAL SOLID PARTICLES.

As pre-treatment technique for conditioning slurries prior to dewatering, effectiveness of freezing and thawing methods was examined by using ferric hydroxide slurry and sludge from waterworks. Slurries contained in vertical columns were frozen in a freezer operated at minus 30 degree C for various refrigeration times and also in a refrigerating bath controlled in a range from minus 5 to minus 76 degree . The relations between the temperature of the slurry and the time were measured. The size distributions of particulate flocs before and after the freezing were measured by an image analyzer. It was demonstrated that the floc particles considerably increased in size and also decreased in the ratio of the perimeter to the projected areas after freezing and thawing opearations. Dewaterability of the conditioned slurries was discussed in terms of the sedimenation tests, the constant pressure filtration tests and the capillary suction time.