GB1573454A - Process for concentrating iron in iron ore - Google Patents

Description

(54) IMPROVEMENTS IN AND RELATING TO A PROCESS FOR CONCENTRATING IRON IN IRON ORE (71) We, HAZEN RESEARCH, INC., a Corporation organised and existing under under the laws of the State of Colorado, United States of America, of 4601 Indiana Street, Golden, Colorado, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a process for concentrating iron in iron ore.

The increasing necessity to use low grade iron ores for making steel, because of the depletion of high grade ores and economic factors, has created a demand for reducing the costs in producing steel from iron ore.

According to the present invention there is provided a process for concentrating a nonmagnetic low-grade iron ore which comprises converting iron oxide in the ore into iron carbide, and separating the iron carbide from gangue by subjecting the treated ore to a magnetic separation step.

In general, finely particulate iron oxides or concentrates are preferred. Conversion of iron oxide into iron carbide via reduction to iron will in general be effected by a gaseous mixture in a fluidized bed at a temperature of not more than about 7050C with a preferred temperature range from about 480 to 6500C.

The CO/CO2 and hydrogen to water vapour ratios of the gases are maintained at levels insufficient for oxidation of iron carbide to occur.

The iron carbide produced is a mixture of carbides of formulae Fe2C and Fe3C, with Fe C predominating.

A process embodying the invention will now be described, by way of example.

A fluidized bed unit oi a conventional type can be used in which a finely-divided feed material on a grate or other perforate support is fluidized by upwardly flowing gases which can include or consist entirely of the reactant gases. Auxiliary equipment will usually include heating and temperature control and monitoring equipment, heat exchangers, scrubbers, cyclones, gas cycling equipment, and other conventional equipment.

As used herein, the term "hydrogen bearing gas" includes hydrogen gas alone, and the term "carbon containing material" includes carbon alone.

An iron ore concentrate is fed to the fluidized bed unit where it is carburized.

Iron oxides are first reduced in the fluidized bed to iron and the iron is then converted to iron carbide in a continuous process, the reducing and carburizing gases being used together. In order to prevent sticking, caused by the transient presence of metallic iron, the temperature is preferably maintained below about 7050C at all times, and more preferably in the range of from about 480 to 6500C.

Hydrogen is preferably used as the reducing gas, although carbon monoxide or hydros carbon gases or mixtures of hydrogen with CO and hydrocarbon gases can be used.

Hydrogen is preferred as the reducing gas because the water produced can be easily removed from the unit off-gas, thus permitting recycling of the balance of the gas without the need for extensive complicated and expensive chemical systems for removing the oxidation producrs of carbon which are formed when carbon containing reducing gases are used.

The preferred carburizing gas is propane, although carbon monoxide or other hydrocarbon gases,- or solid carbon, can be used, with the lower alkyl hydrocarbon gases being preferred. A wide range of carbonaceous materials can be used, so long as they supply carbon to form iron carbide.

By balancing of the ratios of the hydrogen and carbon bearing materials, it is possible to restrict the hydrogen to a reducing function and the carbon to a carburizing function.

This can readily be done by maintaining the quantity of hydrogen bearing gases in excess of the quantity of carbon bearing gases.

Because of the equilibria which occur in hydrogen-carbon-oxygen gas systems, the required hydrogen-carbon ratios will automatically require that methane be present in the gas system. The quantity of methane present will be a function of the carbon to hydrogen ratio, as well as the temperature and pressure conditions.

Further details of the process for converting iron oxide into iron carbide and thereafter into steel are described and claimed in our copending patent application no. 47131/76 (Serial No. 1 573 453).

The carbon content in the product will vary with the percentage of iron oxide in the feed material. Lower grade ores with lower iron contents will automatically yield products with lower carbon contents.

The volume of hydrogen in the hydrogencarbon monoxide reducing and carburizing mixture should exceed the volume of carbon monoxide, the preferred amount of hydrogen being over about 60 percent by volume of the carbon monoxide present.

Results have shown that the carburizing is highly successful in producing iron carbide directly from iron oxides when operated at temperatures of about 545-6350C using hydrogen to water vapour ratios of from 5 to 1, to 8 to 1 and CO/CO2 ratios of from about 1 to 1, to 5 to 1. Successful carburizing can be effected at a temperature of from about 480 to 6500C with a hydrogen to water vapour ratio of about 2.5 to 1 to about 8 to 1, and a CO/CO2 ratio of about 1 to 1 up to about 4 to 1. Under these conditions, 1 to 70 percent by volume of methane will be present in gas systems containing the prescribed amounts of hydrogen, water vapour, CO, and CO2. Iron carbide has not been produced outside these ranges.

The carburizing step enables the iron in low grade, non-magnetic ores to be separated from the gangue. As the iron carbide produced from non-magnetic ores is magnetic, it is only necessary to carburize a non-magnetic ore, such as oxidized taconites, to convert the iron oxide therein into iron carbide and to subject the treated ore to magnetic separation to separate the resulting magnetic iron carbide from the gangue. The iron carbide recovered can then be reduced to steel.

By means of the described process the iron content of low-grade non-magnetic iron ore can be enriched by separating out the gangue. Thus further processing of the ore can be carried out more economically.

WHAT WE CLAIM IS: - 1. A process for concentrating a nonmagnetic low-grade iron ore which comprises converting iron oxide in the ore into iron carbide, and separating the iron carbide from gangue by subjecting the treated ore to a magnetic separation step.

2. A process according to claim 1, in which the iron oxide is converted into iron carbide in a fluidized bed using a mixture of hydrogen bearing gas and a carbon containing material.

3. A process for concentrating a nonmagnetic low-grade iron ore substantially as hereinbefore described.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. gas system. The quantity of methane present will be a function of the carbon to hydrogen ratio, as well as the temperature and pressure conditions. Further details of the process for converting iron oxide into iron carbide and thereafter into steel are described and claimed in our copending patent application no. 47131/76 (Serial No. 1 573 453). The carbon content in the product will vary with the percentage of iron oxide in the feed material. Lower grade ores with lower iron contents will automatically yield products with lower carbon contents. The volume of hydrogen in the hydrogencarbon monoxide reducing and carburizing mixture should exceed the volume of carbon monoxide, the preferred amount of hydrogen being over about 60 percent by volume of the carbon monoxide present. Results have shown that the carburizing is highly successful in producing iron carbide directly from iron oxides when operated at temperatures of about 545-6350C using hydrogen to water vapour ratios of from 5 to 1, to 8 to 1 and CO/CO2 ratios of from about 1 to 1, to 5 to 1. Successful carburizing can be effected at a temperature of from about 480 to 6500C with a hydrogen to water vapour ratio of about 2.5 to 1 to about 8 to 1, and a CO/CO2 ratio of about 1 to 1 up to about 4 to 1. Under these conditions, 1 to 70 percent by volume of methane will be present in gas systems containing the prescribed amounts of hydrogen, water vapour, CO, and CO2. Iron carbide has not been produced outside these ranges. The carburizing step enables the iron in low grade, non-magnetic ores to be separated from the gangue. As the iron carbide produced from non-magnetic ores is magnetic, it is only necessary to carburize a non-magnetic ore, such as oxidized taconites, to convert the iron oxide therein into iron carbide and to subject the treated ore to magnetic separation to separate the resulting magnetic iron carbide from the gangue. The iron carbide recovered can then be reduced to steel. By means of the described process the iron content of low-grade non-magnetic iron ore can be enriched by separating out the gangue. Thus further processing of the ore can be carried out more economically. WHAT WE CLAIM IS: -

1. A process for concentrating a nonmagnetic low-grade iron ore which comprises converting iron oxide in the ore into iron carbide, and separating the iron carbide from gangue by subjecting the treated ore to a magnetic separation step.

2. A process according to claim 1, in which the iron oxide is converted into iron carbide in a fluidized bed using a mixture of hydrogen bearing gas and a carbon containing material.

3. A process for concentrating a nonmagnetic low-grade iron ore substantially as hereinbefore described.