Pilot-scale study of deep cone thickener for phosphatic clay dewatering

The disposal of phosphatic clay is a formidable task due to their fine size and low self-weight consolidation of the clay particles. It takes several years for waste clay slurry to thicken from about three per cent to 20 per cent solids by gravity settling. A more efficient and cost-effective dewatering/consolidation process for phosphatic clay is of great interest to the Florida phosphate industry. The present study was conducted to investigate on the pilot-scale the feasibility of Deep Cone Thickening (DCT) process to thicken the phosphatic clay waste to a paste, without filtration, for mine backfilling or surface stacking. A 2 t/h Deep Cone™ paste thickener was employed at the South Fort Meade mine of Mosaic Company to investigate the effects of key operating parameters, including feed rate, sand addition rate, flocculant type and dosage, bed depth, etc. 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 per cent and 98 per cent, respectively with a residence time of as low as two hours. The highest clay content and total solids content in the paste were more than 25 per cent and 35 per cent, respectively, with a clay:sand ratio of 2:1.