E BAAWUAH1, C KELSEY2, J R KELLY3, J ADDAI-MENSAH4 AND W SKINNER5
Comminution continues to be the most capital intensive unit operation in mineral processing. The fundamental purpose of comminution is to liberate the valuable minerals so that they can be economically concentrated into saleable products.
Declining ore quality characterised by lower grade and increased complexity requires significant energy consumption for comminution. Low grade magnetite ores are typically fine-grained and require fine to ultrafine grinding (P80 ~ 30 - 40 μm) to enhance its liberation from the typically siliceous gangue matrix. Historically, this has been achieved using multi-stage crushing and grinding technologies, which require high energy consumption with low energy efficiency. This motivated innovations in energy efficient technologies for comminution. Such technology has been developed in the IMPTEC super-fine crusher. It is an innovative, dry (with the potential to be operated wet), media free, energy efficient crusher that can to reduce 10 mm feed particles to 19 – 30 μm with very low recycle load.
In this study, the mineralogical and physicochemical characteristics of crushed magnetite ore using the IMPTEC super-fine crusher have been investigated in comparison with those of rod milling. The super-fine crusher generated higher liberated magnetite minerals in the – 300 + 212 μm and < 45 μm size fractions compared to rod mill. Both comminution devices generated large low-grade hematite and goethite middlings. However, the rod mill produced higher locked/unliberated hematite and goethite compared to that of the super-fine crusher. Quartz mineral had the highest liberation irrespective of the comminution device used.
The super-fine crusher generated higher entrapment of other minerals within the silica matrix compared to the rod mill.
The breakage mechanism of the super-fine crusher which is predominantly through high compression with shear, generated improved mineral liberation in the coarse size fractions compared to the predominant abrasion and attrition breakage mechanisms of rod milling. The higher mineral liberation generated by the rod mill is potentially due to the prolonged batch milling of the ore compared to the single pass open circuit of the super-fine crusher.