Can pre-concentration become a key savior for the mining industry and help in lowering metal production costs?
Pre-concentration is a way to reduce the quantity of ore requiring higher cost downstream processing, i.e. grinding in particular. By using a low cost method to pre-concentrate mineral-bearing particles into a smaller volume, one can attain significant cost savings in overall energy consumption and operational expenses. A previous blog “Remote Sensing of Ore Grades” discussed a new pre-concentration method under development.
Pre-concentration is nothing new and has been around for many years but is generally limited in the techniques available. Hence many ore types are not amenable to it..unfortunately. The main methods being used are:
Ore sorting can be done using automated optical, electrical, or magnetic susceptibility sensors to separate ore particles from waste particles. The different sensor types can include colour recognition, near infrared radiation sensors, x-ray fluorescence, x-ray transmission, radiometric, or electromagnetic sensing. The sensors can determine if a particle contains valuable mineral or waste, thereby sending a signal to activate air jets to deflect material into ore and waste bins.
Density or specific gravity difference is another property that some pre-concentration methods can rely on. Gravity based systems such as dense media separation (DMS), jigs, or centrifugal concentrators are currently in production use.
Another simple pre-concentration method used is scrubbing, whereby simply washing away fines may remove some deleterious materials prior to final processing.
Pre-concentration can provide several benefits to an operation:
-If done underground or at remote mine site, the net ore hoisting and ore transport costs can be reduced.
-If the pre-concentration rejects can be used as mine backfill, this can reduce backfilling costs.
-Processing of higher grade pre-concentrated mill feed can reduce total energy costs and ultimately reduce the cash cost of metal produced.
-Grinding costs can be reduced if waste particles are harder than the ore particles and they can be removed beforehand.
-Minimizing waste through the process plant will reduce the quantity of tailings that must be disposed of.
-Lowering operating costs may potentially allow lowering of the cutoff grade and increasing mineral reserves.
-Higher head grades would increase metal production without needing an increase in plant throughput.
Not all ore types are amenable to pre-concentration and therefore a rigorous testing program is required. In most cases the pre-con method would be relatively obvious to the metallurgical engineer but testing is still required to measure performance. Testing is required to determine the amount of waste rejection that can be achieved without incurring significant ore loss during the process. Generally one can produce a higher quality final product if one is willing to reject more ore with the waste, so it becomes a trade-off of recovery versus total processing cost.
Fine particles from the primary and secondary crushing stages might require bypassing the pre-con circuit. If this bypassed material is sent for downstream processing, one may need to examine crushing systems that minimize fines generation to avoid too much material bypassing the pre-con circuit.
One must also decide if the pre-con system should reject waste particles from the material stream or reject ore particles from the stream since the overall recovery and product quality will be impacted depending on which approach is used.
My bottom line is that the mining industry is continually looking for ways to improve costs and pre-concentration may be a great way to do this. Every process plant design should at least take an initial look at it to see if is feasible for their ore type. While the existing pre-concentration methods have their limitations, future technologies may bring in new ways to pre-concentrate and so this is probably an area where research dollars would be well spent.