India’s Iron ore resources are estimated at 28.5 billion tonnes, distributed between Haematite at 17.9 and Magnetite at 10.6 billion tonnes. Though, both numbers are impressive at first glance; here’s a staggering fact: while 45% of the haematite resources are classified as reserves, a meager 0.2% of magnetite receives the same recognition. This peculiarity inspired this article which elucidates magnetite and its role in the steel industry.
Magnetite is a black/brownish black, naturally occurring iron oxide, represented chemically as Fe3O4. It is magnetic in nature – hence the name – a property that has been applied extensively while dealing with the mineral. Being a source of iron, it is the starting material for many iron & steel producers around the world. Another application of magnetite, which should be of interest to this industry, is its use as a heavy media in coal washeries, to separate out higher grades of coal from lower ones. However, other materials may also be used for this purpose.
In a world perspective, magnetite has greater importance in several countries compared to India. China, the world’s largest steel producer, uses magnetite as the major raw material. Taconite, the principle iron ore in America, contains magnetite as the iron bearing material.Appreciable deposits are found in Australia and many European countries, especially Sweden. Other small deposits may be found across countries around the world.
In India, over 90% of magnetite is found in the southern states of Karnataka (73%), Andhra Pradesh (14%) and Tamil Nadu (5%). Rajasthan in the west accounts for another 5%. The balance is scattered over Goa, Kerela, Maharashtra, Odisha, Jharkhand, Assam, Nagaland & Meghalaya.
Mining & Beneficiation
Like haematite, magnetite is not found in such high grades so as to be used as DSO. The ore is beneficiated for magnetite recovery. Magnetite ores have mere 15-40% iron content and as such, cannot be used directly for iron making. It has to be beneficiated to concentrate the iron bearing material. For this purpose, the magnetic nature of the mineral is employed. The entire process involves the crushing and grinding of ores to powder form, exposing it to a magnet for separation followed by other agglomeration processes for value addition and onward utilization. Most miners of magnetite ore install a beneficiation and Pelletisation line at the mining site for direct sales as feeding material.
A lot of Power is used up in the beneficiation process of magnetite, representing the bulk of the costing. Continuous research aims at reducing this factor, which would allow overall costs of using magnetite to come down, thus making it more competitive.
Value for Money
An obvious question here is why anyone would explore magnetite ores as it is of extremely low grade and involves high costs of beneficiation. However, magnetite attracts premium rates in comparison to its peer haematite because post-beneficiation, it has a high & consistent iron content concentration of 68% and a low associated gangue. On the other hand, the iron content of high grade haematite may vary between 60-65%. This rewards the buyer during steelmaking in the form of lower energy and carbon consumption, which more than compensates for the extra costing. Also, magnetite is used for high cleanliness steel as it has practically no P or S associated with it. Thus, it should not be surprising to know that magnetite is often tagged as the ‘superior ore’.
Also, countries which have magnetite deposits as the dominant iron source consider it as a viable raw material.
The Pelletisation Makeover
Magnetite during the firing stage of Pelletisation is oxidized into haematite. Here, it is essential to understand that both, magnetite and haematite, are oxides of iron, the latter containing more oxygen for each unit of Fe (higher oxidation state). In the first instance, this fact would prompt you to try and avoid haematite formation to the maximum possible extent, so as to deter association of more oxygen, which have to only be consequently removed during iron-making in a blast furnace or a DRI furnace/kiln. However, the oxidation during Pelletisation is imperative for the ore’s further use. A metallurgical explanation is the higher reducibility of haematite compared to magnetite. All factors remaining constant, the amount of reduction haematite would undergo is significantly greater than that of magnetite. In other words, haematite forms iron much faster than magnetite.
Another advantage of magnetite pelletisation is that it does not require any fuel to be added to the powder mix. Usually, coal fines, grinded petro coke, coke oven fines etc are part (around 1%) of the pellet mix so as to ensure homogeneous hardening of pellet during firing. But magnetite upon oxidation to haematite releases considerable energy which eliminates the requirement of an external fuel. As a leading steel producer in the country put it, “we as an integrated steel plant utilize the coke fines generated in our ovens and during storage, in our pellet plant. However, if magnetite were to be available, the stand alone pellet plants, mainly the ones using Chinese technology & equipment, would be the most benefitted as they would then not be forced to raise temperatures and would prevent the oft encountered breakdowns.” In the middle-east, plants use a mix of haematite fines and magnetite (30-35%) for pellet making in order to exploit this advantage, whilst also obtaining higher quality pellets.
Magnetite in India
The huge amount of magnetite present in India has already been stated in the introduction. However, after speaking to most major steel producers in the country, it can be safely claimed that none of them mine or purchase magnetite for their production. The major reason is the abundant availability of haematite in India, which can be used as a direct feed. The plentiful haematite aside, another reason for absence of magnetite in the Indian scenario is that even regional distribution does not warrant its use. The south, which holds most of the magnetite, is also blessed with sufficient haematite in Karnataka and Goa.
But, it is not true that magnetite in India is to date untouched.
The Kudremukh Iron Ore Company: a history of magnetite usage in India
Though magnetite has no presence on the Indian scene today, the same hasn’t always been the case. KIOCL Ltd had been allotted mines in Kudremukh, Karnataka and mined magnetite ore from here for 25 years, with a Pelletisation facility at Mangalore, around 100 kms from the mines. But, following a Supreme Court of India verdict in 2005, which stated that the mines were part of a National Park, KIOCL was banned from mining at Kudremukh. This was a setback for the thriving company. At the time, most had written off KIOCL as a thing of the past. However, the turnaround of the company, its adaptation of its beneficiation & pelletisation facility to suit haematite ore and its current success and growth is a corporate wonder.
Many say the use of magnetite is inevitable; if not today, then maybe years, surely decades later when the DSO grade haematite has been exhausted. Barring the high cost of beneficiation, magnetite scores over haematite on prime factors such as iron content and impurity levels and that beneficiated magnetite is superior to haematite is an established fact.
But, also of concern is the distribution of magnetite in the country. The largest concentration, in Karnataka, is mostly in a region which is ecologically sensitive. The Western Ghats, considered a ‘biodiversity hotspot’ and identified as a World Heritage Site, is an important location in efforts of conservation and sustenance of environment. Also, ban on industrial activity here & there in the region is recurring news. It is for the future to unfold how the balance between nature and industry is struck.