BENEFICATION OF SOUTH CAROLINA SILLIMANITE SCHISTS *

Abstract

AbstractLaboratory batch and pilot‐plant tests have demonstrated that the South Carolina sillimanite schists are amenable to beneficiation by recognized mineral‐dressing methods. Flotation tests on a number of small samples indicate that the schists containing prismatic sillimanite respond more readily to treatment than those containing fibrous sillimanite.Batch testing of the small samples was supplemented by continuous trial runs in the laboratory pilot plant on a schist from the Pelzer, South Carolina, area. The schist, containing 17% prismatic sillimanite, was ground to 20‐mesh and concentrated by a combination of tabling and flotation supplemented by magnetic separation of the concentrates. In an average test, 82% of the sillimanite was recovered in concentrates which contained 99% sillimanite and 1.04% total ferric oxide.The concentrates were tested at the Electrotechnical Laboratory of the Bureau of Mines, Norris, Tennessee, for refractory properties. Standard‐size brick made from the concentrates met A.S.T.M. and the more severe Navy reheat‐test specifications for super‐duty refractories.Summary of Testing of Sillimanite ConcentratesThe beneficiated South Carolina concentrate was tested at the Electrotechnical Laboratory of the Bureau of Mines at Norris, Tennessee. Standard‐size brick that were power pressed and then fired five hours at 1600°C. showed only a slight volume change, thus meeting the A.S.T.M. and the more severe Navy reheat specifications for superduty refractories. All types of commercial as well as experimental refractories have been tested at the Electrotechnical Laboratory. Brick made from South Carolina sillimanite had the highest load resistance of any alumina‐silica refractories tested except electric‐furnace cast corundum‐mullite block.After firing, the brick were mottled brown in color. Acid leaching of the concentrates removes some of the iron compounds on the surfaces of the grains and improves the color. Brick made from acid‐leached sillimanite may be of value in glasshouse refractories.