IRON ORE FLOTATION

Economically Important Iron-Bearing Minerals Name Crystal System Chemical Fromula Specific Gravity Iron Content Magnetite Cubic FeO.Fe2O3 4.97-4.18 72.4 Hematite Hexagonal-rhombohedral Fe2O3 4.9-5.3 70.0 Martite 4.8-5.3 Geathite Rhobohedral Fe2O3.H2O 4.0-4.4 62.9 Limonite Mixed, chiefly geothite 2Fe2O3.3H2O 3.6-4.0 60.0 Siderite FeCO3 3.0-3.88 48.2 Pyrite FeS2 4.95-5.17 46.6 The most important minerals are the oxides. Upon firing, all minerals will be converted to the most suitable Fe2O3 form.

Impurities Slag-forming Deleterious impurities Acidic: silica (SiO2) and alumina (Al2O3) Basic: lime (CaO) and magnesia (MgO) Deleterious impurities Sulfur, phosphorus, and other metallic oxides Most ores have an excess of SiO2 and Al2O3; ash of coke used for fuel is composed of these oxides. Therefore, a basic flux, e.g. Limestone, must be added. Most other impurities, especially sulfur and phosphorus, impart undesirable properties to steel.

Market Specifications-1 The average iron content of ores and agglomerated products has steadily increased, Grade of marketable ores are based not only on chemical analysis but also on the structural quality (particle size) Marketable ores; coarse ore (+10 mm), sinter (-6+0.150 mm), pellets. Pellets have provided the most substantial technical and economical advantages.

Market Specifications-2 Hematite, lump grade: 62.5% Fe Pellets for blast furnace charge: 65% Fe and <5% SiO2 Pellets for direct reduction: <67% and <2% SiO2+Al2O3 Sulfur can be reduced to the desired level during iron making, but this cases extra cost. Phosphorus/iron weight ratio < 0.002

Concentration Methods Magnetic separation Low intensity (0.05-0.15 Tesla) High intensity (1.2-2.2 Tesla) Magnetic roastig: Roasting (600-800 °C) in reducing environment to convert hematite to magnetite. Gravity separation Sedimentation Spirals Heavy media Jigging

Flotation-1 Used for Direct flotation Reverse Flotation non-magnetic iron ores As a final concentration stage to improve concentrate grade Direct flotation Iron oxide is floated Anionic reagents, such as petroleum sulfonates or fatty acids, are most commonly used Reverse Flotation Flotation of gangue, mainly silica Cationic collectors at pH 11-12 Use organic depressants (starch or guar gum) to depress iron minerals Activation of silica by Ca2+ and use of anionic collectors

Flotation-2 Separation of apatite Flotation of iron minerals at pH 6.5 using anionic collector Use flourosilisic acid and sodium silicate to depress apatite Reverse flotation of apatite at pH 8.5 Depress iron minerals by organic depressants

Tilden Concentrator Flowsheet