A pilot-scale Deep Cone thickener (DCT) from Dorr-Oliver EIMCO has been employed at a phosphate mine in central Florida to investigate the effects of key operating parameters, including feed rate, sand addition rate, flocculant dosage, and bed depth on waste clay thickening performance. The pilot-scale field testing successfully demonstrated the simultaneous production of an underflow paste product and a clear overflow water stream. Typical overflow water recovery and underflow solids recovery were more than 88% and 98%, respectively with a residence time of about 2 hours. The highest clay content and total solids content in the paste were higher than 25% and 35%, respectively, when the flotation sand tailing was added to the clay slurry at a clay/sand ratio of 2:1 by weight.