There are numerous reasons why it is beneficial to introduce washing of raw iron ore reserves to increase efficiencies in steel production and maximise revenues from the material and these are outlined in detail here with specific reference to experience in the Indian market.
Why wash iron ore?
The fundamental reason for the use of iron ore reserves is to extract the iron from the ore for further processing. Within the steel production market in India there are various production methods used to achieve this – sponge iron production, blast furnaces, sinter plants and pelletisation plants.
These types of systems require different material grades and particle sizes. In blast furnaces the feed is normally +10mm and ‘lump’ material. This is in contrast to sinter plants where the feed is usually -10mm and pelletisation generally requires complete crushing to below 500 micron or 0.5mm. In each of these processes the requirement is to achieve a high FE grade value and low values for unwanted contaminants within the feed material.
It is generally the case that steel producers look for FE values of 62% in the ore feed to allow for cost effective processing. The processing of iron ore involves the material being introduced to a furnace or kiln in order to burn off the unwanted contaminants. The end result of this process is a product known as Ore Oxide (Fe2O3), which is then used for steel production. If the FE value of the ore feed is much less than 62% it is generally felt that cost effective production is not viable – you need higher quantities of the ore feed in order to produce the amount of ore oxide required, which takes up space in the kiln, thus increasing production costs.
Reducing contaminants essential
Another unwanted contaminant within raw iron ore is Silica. The problem here relates to the fact that Silica requires extremely high temperatures in order for it to be burned off. Therefore, the more silica that exists in the raw material, the more energy is used in producing the ore oxide.
Finally, steel producers are also keen to minimise the quantity of Alumina in the raw feed as a percentage of the total as it creates waste build up inside the kilns. The resulting cleaning and maintenance of the kilns is another very expensive process and one which steel producers are keen to reduce.
It is very important to highlight the importance of a focus on the reduction of the presence of contaminants within the feed material in any iron ore washing operation. The presence of contaminants such as alumina and silica have a negative effect on the steel production process as they are a direct cause of high production costs. By reducing the presence of these contaminants in the feed material, the processing of the iron ore becomes viable as a result of
the cost reduction that is a direct result of washing. The reduction of contaminant levels within the feed can often be overlooked as people focus solely on the increase in Fe value that washing can bring. The reduction in the level of contaminants within the feed has a direct positive impact on the Fe grade of the material, and therefore is an important consideration for anyone looking into an ore washing plant.