Abstract
Dewatering of various types of fine wastes has been a subject of intense research for many years due to the economic and environmental impacts of their disposal. These wastes include fine phosphatic clays generated by phosphate mining, tailings from the kaolin industry, red mud from processing alumina, and many other and chemical processing wastes. For instance, the phosphate industry in Florida generates an estimated 100,000 tons per day of phosphatic waste clay. This waste containing 3 to 5% solids has historically been pumped to large, above-ground holding ponds, where water is decanted through spillways as the solids slowly consolidate under the impact of gravity to a 15-18% solids level. At this solids content, the ponds slowly dehydrate and form a crust on their surface, which hinders further surface evaporation. Without additional physical efforts to dewater the mass, it may take several decades for the clay to consolidate to a solids content of 25-35%. Because these clay ponds occupy up to 40% of the mined area, they represent a considerable economic penalty to the industry and limit the re-use of tens of thousands of acres of central and north Florida land. This conventional practice also ties up tremendous amounts of water and causes loss of water through evaporation. The economic impact of this conventional disposal practice, coupled with the difficulty of obtaining new mining permits due to this issue, has prompted the mining industry to seek new methods for rapid dewatering of the waste clays.
In this report, the results of laboratory as well as pilot-plant testing of a novel process using hydrocyclones as a rapid dewatering device, as well as sand/clay mixing, are discussed. Results indicate that up to 80% of the water could be recovered and recycled back to the plant in a few minutes. A soil of more than 45% solids content and 1:1 sand/clay ratio could be produced and used to fill mine cuts for land reclamation. The technical, economical, and practical aspects of this process are presented.
Hassan El-Shall - University of Florida