For utilisation of micro-fines concentrate, the Indian iron makers are shifting their focus from sinter intensive blast furnace operation to pellet oriented operation in combination of other smelting technologies. Adoption of suitable pelletisation technology of varying capacity is being increased to encourage meeting specific needs with respect to availability and type of iron ore fines/concentrate in the country.

The Indian hematite iron ore concentrate has high LOI because of the presence of kaolinite, goethite and gibbsite even after beneficiation process. As this ore is in fragile nature, the blaine number of pellet feed material is high. To maximise the iron values from the slimes and tailings, flotation process is to be adopted next. This provides the hydrophobic characteristic on the surface of the particles, which has negative impact on pelletisation.

With this project and others, it is a challenging task to handle as the iron ore concentrate has high LOI, high baine and hydrophobic surface particles. It needs to improve the heating cycle of induration segment of the present pelletisation technology through fundamental studies.

Challenges

The production of steel in India was low, the selective mining was adopted to take high-grade iron ore to meet the required specification of steel plants and sponge iron plants. Gradually, the demand of ore increases and the quality of grade depletes.

The washing and beneficiation concept were implemented. As all the separation equipment were imported to meet the need of the process, the performance did not match because of the ore characteristics. As a result,
the overall productivity as well as the quality of the product came down.

Solution

As the clay minerals (mostly kaolinite) create problem in the iron ore processing and scrubbing techniques are used to remove the clay minerals before processing for upgradation. Most of the clay particles present in the ore are below 75 microns. In general, it coats on the surface of the particles. If the particle size is below 30 mm, drum scrubber is used otherwise for below 10 mm size, screw scrubber is used.

This screw scrubber is designed by CSIR-IMMT, Bhubaneswar and transferred to Swagat Urithene Ltd, Hyderabad, to implement commercially with maximum capacity of 200TPH. Around 80 per cent of clay particles are getting removed by using this technique and simultaneously, the hydrodynamics of downstream equipment is being easily controlled.

Outcomes

To improve the dewatering system, CSIR-IMMT has developed column thickener to improve the settling rate of particles in comparison with conventional thickener. In this process, both gravity and magnetic techniques are implemented to make synergic effect for settling of the particles. As its aspect ratio (length/diameter) is high, it needs small space in comparison of conventional thickener.

The patent was taken and transfer of technology to commercial level is underway. To maximise the recovery from lean grade ores like BHQ/BHJ/BGQ, slimes, tailings, CSIR-IMMT has developed the process by combination of reduction roasting followed by conventional beneficiation. CSIR-IMMT is providing a complete technology package of beneficiation, pelletisation, DRI and smelting processes.