X-ray transmission (XRT) sorting has been introduced into the minerals industry in 2006 and has found various applications in diamonds, industrial minerals, and metal ore processing since. The technology offers planar projection of the atomic density of single particles similar to the principle known from airport scanners, but being capable of treating up to 150 tph per metre working width.
In 2010, a pilot operation using a belt-type sensor-based sorter went into production at the Mittersill mine to treat the faction 16-28 mm. After an optimisation phase, the results were superseding expectations and therefore in 2012 a bigger production plant was set up. Two x-ray based sorters are in parallel operation since. One is treating the finer fraction 16-30 mm while the other is treating the coarser fraction 30-60 mm after the secondary crushing stage. The XRT sorters are operated with the objective to reject barren waste before it enters the mill and flotation plant. 105,000 tpa of waste material area rejected per year and can be sold as aggregates for road construction. This means that about 22% of the run-of mine ore are rejected at an early stage with a waste reject grade lower than 0.03 wrt %WO3.
The installation has not only led to lower specific operating costs but also led to reduced tailings disposal in an environmentally sensitive area. This allows the mine to reduce its headgrade which allows for a longer mine life. Alternatively it is possible to produce more tungsten concentrate, which is delivered to the smelter.
This article will introduce the technological principle of XRT-based sorting and will discuss the flow-sheet of Mittersill mine. Experiences that have led to the current plant design are described as well as the impact it has on the operation.
This paper was presented at IMPC 2014