Soap flotation of calcite with particular reference to the upgrading of Caversham Sandstone

Abstract

The Caversham sandstone forms a large deposit, several hundred feet thick extending over an area of the East coast of the Dunedin district. It is also found outcropping in the Lookout Point area. The high carbonate content of the deposit (40 - 65%) has caused attention to be focussed on the sandstone as a possible source of calcium carbonate. Some time prior to 1865 calcination was attempted in a sandstone quarry near the Kaikorai Valley while in 1865 specimens containing up to 68% carbonate were reported(20). The favourable location of the deposit in relation to the Milburn Lime and Cement Company's cement works at Burnside make it of economic interest to this Company as a potential raw material for cement manufacture. Before the sandstone could be used for this purpose considerable upgrading of the carbonate content would be necessary and modifications to its natural mineral content would be desirable. The two possible methods of doing this are: ( 1) to lightly grind the sandstone and size it to determine whether any of the constituents concentrate in particular size fractions (2) to float the carbonates with an anionic collector and modify the silicate, and perhaps the iron distribution, with a cationic collector. Froth flotation is widely used to produce cement raw materials of the correct chemical composition (2) and in all cases fatty acids or their derivatives are used as anionic collectors. This thesis attempts to explain the action of the more important fatty acids as collectors for calcite and to show how these reagents act as collectors for the carbonate minerals of the Caversham sandstone.