The case for wet processing iron ore
For a high-grade iron ore deposit, that is, greater than 62 per cent, a dry crushing and sizing process is sufficient to achieve the required product quality and size fraction as lump ore, sponge ore or sinter fines.
Other deposits with lower ore quality, less than 58 per cent, could use selective mining and blending methods to achieve nominated grade targets. However, today’s quality restrictions for sinter fines and concentrate for pellets often mean advanced processing, such as washing, separation and concentrating, is required.
Depending on the ore type, quality and its degree of degradation, a washing and classifying plant can increase the iron content by two to five per cent, while reducing the silica, alumina, titanium oxide, sulfur and phosphorous content through removal of fines below 0.063 mm by washing. For example, decreasing the alumina content reduces the blast furnace coke consumption level while increasing the productivity and reducing the consumption of flux.
While some iron ore companies are already marketing these ‘green’ iron ore pellets, others have only just commenced development of advanced processing systems for their production sites.
A major hurdle that needs to be overcome when choosing beneficiation is the related capital investment and operational costs associated with the core equipment required - infrastructure development and increases in water usage and power consumption can be significant.
Further, given the remote locations of most operations in Australia, securing the required volumes of power and fresh water for wet processing can also be very difficult to achieve. Another important influencing factor is water and tailings management, with its associated costs and risks.
While there are a number of washing technologies available on the market today, the capital and operating costs of many of these systems may result in less than optimal economics.
The most commonly used machines are scrubber drums, log washers or screw washers. These systems clean the material using the shearing stress created by a mechanical action, such as the rotation of a drum.
In contrast, other washing technologies operate with impact stress. They use impact or compressive forces to clean the material. In these machines, either hydraulic or mechanical energy is applied.
In both cases, infrastructure costs and huge increases in power and water can weaken the case for wet processing. However, thanks to significant technological advances in the area of wet processing, highly efficient systems do exist.
For example, an innovative hydraulical washing technology that uses high pressure water jets to clean the material has demonstrated its ability to save approximately 50 per cent water and ten per cent energy compared to the traditional washing systems. Due to its modular and mobile structure, it also reduces capital and operational costs.
Through a thorough evaluation of the technologies available, iron ore producers have an opportunity to determine the best solution for their project and improve their bottom lines.