Beneficiation of phosphate in the southeastern United States generates a slurry of finely divided clay wastes that are impounded to allow the particulates to settle. The aggregation of phosphatic clay slime wastes and slimes produced from potash beneficiation by microbial processes was studied using several bacterial species known to produce polymeric substances. Experiments included flocculation activity of whole cells in the presence of phosphatic clays, observation of clay flocculation rates by polymers derived from these organisms, and clarity of polymer-flocculated clay suspensions. The polymer-producing organisms exhibited little capacity for flocculating phosphate and potash clay slimes. Fungal spores of cladosporium cladosporioides (isolated from a phosphate clay waste impoundment), when agitated with clay slime for several days, caused the clay to form pellets. Separation of the clay- fungal pellets from the process water might be possible using a screening technique. Studies with c. Cladosporioides included the determination of suitable energy substrates and supplements for growth, absorption studies of a pigment produced by the organism, determination of the time required for bioflocculant production by the organism, and an elucidation of the conditions required for the pelletization of clay slimes by the fungus.