Iron ore flotation

    When is mentioned the iron ore flotation must be mentioned two cases: sulphide and non sulphide ores. The first group usually involves pyrite flotation. At the beginning of the last century pyrite was used as the main source to produce sulphuric acid and froth flotation was used to concentrate them. Nowadays, this is not practiced and pyrite is recovered by flotation only when precious metals are hosted in the crystal structure of pyrite, but if there is not precious metals into pyrite, its flotation must be avoided. This is the typical case of polymetallic ore flotation. To float pyrite is not complicated and be practiced at natural pH when there is auriferous pyrite or at residual pH after recovering base metals such as lead, copper and zinc. Pyrite flotation needs a collector like potassium amyl xanthate (PAX) and a frother such as methyl isobutyl carbinol (MIBC). Some gold operations practice pyrite flotation and the concentrate is leached employing cyanide.

    The other case is more complicated and involves oxidized iron minerals (e.g. hematite, siderite) which are recovered to produce steel. Its recovery usually is related to low grade iron ores which has silicates as gangue. So, such ores must be processed to separate the iron oxides from the sterile material. In such flotation the oxides can be floated by using anionic collectors or a reverse flotation process is employed when silica is floated from the iron oxide by using cationic collectors.

    Oxide iron flotation employs three types of reagents: collectors, which cause attachment between solids and bubbles. Frothers, which are used to create air bubbles by changing surface tension and valuable particles, are skimmed from the flotation machine. And antifoams, which can react with particle surface in the pulp to maintain minerals from remaining in the froth. Instead, particles fall and don’t float.

    Some oxide iron ores must be ground to specific size in order to obtain liberation from the gangue. Thus, is reduced the presence of gangue or slimes which can affect the flotation process. Sometimes, the problem can be minimized by employing desliming steps before flotation. But, that step is added to the flotation cost. Iron ores usually contains a huge amount of silicates and its presence has been found to have a negative effect on the quality of the iron and complicates the process for the production of iron. Then, it is important that the silicate content of the enriched iron mineral can be reduced as much as can be possible.

    Essentially, iron ore flotation employ two types of collectors: anionic and cationic, the difference between them is related to which mineral want be floated and which sinks. This can be determined by testworks which allow obtaining relations between iron minerals and gangue, and of course the type of collector used. By employing anionic collectors, fined sized crystalline iron minerals (e.g. siderite) are recovered away from siliceous particles (e.g. quartz). In the other case, using cationic collectors, the siliceous mineral is floated with iron minerals or sometimes flotation of iron minerals is avoided. In the latter case, tailings contain iron minerals.