This invention relates generally to iron ore benefication and particularly to froth flotation for concentrating fine-grained iron ore.
Iron ore is an important mineral commodity because it is the primary source of iron, the metal most widely used by man. World production of iron ore in 1977 was estimated at 840 million tons, and an estimated 350 million tons was shipped in international trade.
The United States is the world's fourth largest producer of iron ore and is a major importer. Imports supply about one-third of the primary iron required by the U.S. steel industry. In contrast, imports supplied less than 5 percent of U.S. demand in 1953.
The decline in U.S. production was due to several factors. During World War II, it became apparent that U.S. reserves of high-grade ore would be seriously depleted by the 1950's. To secure additional supplies of ore, U.S. companies began an intensive search for deposits in foreign countries. These efforts were highly successful; large investments were made, and imports began in the early 1950's. Because most U.S. ore was relatively low grade and comparatively costly to produce, the increasing availability of low-cost, high-grade foreign ore became an important means of combating growing competition from the reconstructed steel industries of Europe and Japan. Of course, any technology which would enable low grade U.S. ore to be processed economically would be desirable because such technology would cut down U.S. dependance on foreign imports. A low grade ore which is present in great abundance in the United States is taconite. The term taconite was originally applied to the hard, fine-grained, banded iron-bearing formation of the Mesabi range. The term is now often used to describe similar rocks in other areas, such as "low grade deposits of the taconite type." If magnetite is the principal iron mineral, the rock is called magnetic taconite; if hematite is the principal iron mineral, the rock is called hematite taconite, oxidized taconite or non-magnetic iron ore. Because hematite taconite is non-magnetic, magnetic concentration of the iron oxide in the ore is not used because it is expensive and inefficient. Furthermore, because of the small grain size of the iron oxide components of both hematite taconite and magnetic taconite, these ores are difficult to float by known direct flotation techniques.
At this point, it should be noted that "direct" flotation is a process in which the iron oxide itself is floated away from the gangue or silica. Grinding of fine grained ores such as taconite produces a great deal of slime; and the physical and chemical properties of fine grained ores makes it difficult to process by froth flotation.
In addition, indirect flotation such as cationic flotation of fine grained ores is characterized by low recovery rates. Thus there is simply no effective procedure for concentrating such ores.
As would be expected, the literature is replete with various procedures for concentrating iron ores. Representative of such procedures are those described in U.S. Pat. Nos. 3,779,380 and 3,292,780.
U.S. Pat. No. 3,779,380 to Bishop describes ore beneficiation and particularly froth flotation applied to iron ore. The beneficiation process described enables direct flotation of the iron oxide. This process, however, is not as efficient when dealing with fine grained ores as is the present process.
U.S. Pat. No. 3,292,780 to D. W. Frommer et al. describes a process for improving flotation of iron ores by selective flocculation and flotation. In the process, the ore is ground, the iron oxides are selectively flocculated with starch while the silicate gangues are dispersed with sodium silicate. The fine silicates are removed by desliming and the coarse silicates are removed by cationic amine flotation. A commercial operation based on the above process is in operation in North America for processing a fine grained iron ore. The process is a technical success for treating fine-grained iron ore; however, the process has its drawback due to additional loss of iron in the slimes and hence a reduction in the iron unit recovery.
It would, of course, be desirable to provide a process for processing fine-grained iron oxide by a direct flotation of iron oxides without desliming.
Accordingly, it is an object of the invention to provide a particularly effective flotation agent, one that will allow the recovery of a maximum amount of iron from low grade iron ores.
Another object of the present invention is to process the fine grained iron oxides in ores such as taconite to recover maximum iron oxides in a direct flotation of iron oxides.
Another object of the invention is the provision of a direct flotation of iron oxides without desliming to reduce iron losses.