The federal Bureau of Mines is conducting research on maintaining an adequate supply of minerals to meet national needs, while minimizing undesirable environmental effects through pollution abatement. Storage and disposal of the slimes from processing phosphate rock have been continuing problems. Their slow settling rate has hampered recycling of processing water and required that large land areas be set aside as storage ponds. This research quantifies some of the slimes' colloidal properties. Electrophoretic mobilities were determined on a sample of Florida phosphatic clay wastes converted to the sodium cationic form, from ph 2 to ph 13. A maximum in the mobilities occurred near ph 11 which also corresponded to a minimum in viscosity of the slimes. Waste mobilities increased when sodium chloride was added. Electrophoretic mobilities were also determined on two additional waste samples converted to the sodium, calcium, and aluminum cationic forms, and on samples of attapulgite, kaolinite, and montmorillonite clays--the predominant clay minerals present in these wastes, at ph values of about 4, 6-7, and 10. The trend in electrophoretic mobility versus ph was similar for all samples, but magnitude of the mobility was greatly affected by mineral composition and cationic form of the samples. Research at the Tuscaloosa Research Center is carried out under an agreement between the Bureau of Mines, U.S. Department of the Interior, and the University of Alabama.