As part of its objective to expand the body of mineral information as a basis for new technology, the Bureau of Mines conducted research on the fundamental behavior exhibited by phosphate clay waste in settling ponds. A semiempirical equation used to describe the compaction of ceramic powders in a single-acting die was applied to aqueous phosphatic clay waste and attapulgite slurries. This equation, v* = a1e-k1/p + a2e-k2/p, was found to describe the compaction of an attapulgite gel and a phosphate slime gel by a moving screen. V* is the ratio of the compaction achieved at a given pressure, p, to the compaction achieved at a pressure sufficient to remove all space between particles. The constant a1 represents the fraction of compaction achieved at low pressure by rearrangement of flocs to higher packing density, and a2 represents the fraction of compaction achieved at higher pressure resulting from removal of voids within flocs. K1 and k2 are constants determined from the experimental data. Both the low-pressure and high-pressure compaction mechanisms were observed in the compaction of the clays. These two compaction mechanisms offer an explanation for the observation that impounded slimes initially dewater rapidly and then dewater at a much slower rate.