Superior product size distribution
Grinding performance of an IsaMill™ is fundamentally different from alternative grinding technologies. The short residence time, plug flow, attrition grinding and patented product separator combine to produce a product size distribution that cannot be matched.
The IsaMill™ operates by stirring fine media at high speed (over 20m/s tip speed). The fine media and high disc speed increases the probability of media and particle collisions, as well as the energy of these collisions. The IsaMill™ breaks particles using both attrition and abrasion breakage modes. Particles are chipped repeatedly to produce a fine sized product at relatively low power consumptions.
Grinding performance of an IsaMill™ is fundamentally different from a ball mill. The impact mechanism and long residence times in ball mills combined with inherent inefficiencies of cyclones results in indiscriminate grinding and poor size distributions. This leads to slimes generation, higher reagent consumption and energy wastage.
In contrast, the IsaMill™ produces a different size distribution. Sequential grinding in the IsaMill™ doesn't flatten the size distribution, it sharpens it, even in open circuit. This remarkable characteristic has crucial implications for energy efficiency and downstream processing – the grinding enegy is focussed on the coarse particles that need it, not wasted creating ultrafines. There are four reasons for this:
- The small media size which favours attrition grinding.
- Each ore particle has to pass through eight consective grinding chambers (the grinding discs), ensuring no short circuiting.
- Particles have to escape the high centripetal forces of the product separator (20m/s tip speed) before leaving the mill (this is why IsaMills™ do not need to be closed circuited with cyclones).
- The high power intensity means that all of the above happens in a short residence time. Typical average residence time in an IsaMill™ is only 90 seconds, leaving little opportunity for overgrinding.
The product separator of the IsaMill™ is one of its key advantages. The eight consecutive grinding chambers and high tip speed of the separator means that the mill constantly delivers sharp sizing performance. There are no screens or trommels to fail or block, any particle that leaves the mill must escape the same centrifugal forces.
A further advantage of this mechanism is that it allows the IsaMill™ to use a wide range of natural media. Even if a portion of the media degrades early, it can exit the mill without blocking screens, with the remaining competent media retained for grinding. In contrast, mills closed by fine screens are limited to using only the most competent media.