Question

The following flowsheet shows a typical arrangement of cyclones that you would see in the mining industry. Ore consisting of gangue (sand) plus valuable minerals enters as the feed to A from the upstream crushers. The cyclones all have the same geometry.

For example, in the gold mining industry, the aim is to achieve very small ore particles, e.g. < 50\mu m, so the gold crystals are exposed on the outer surface. Later these particles are placed into in a downstream solution of cyanide which dissolves (leaches out) the exposed gold from the ore [so note to yourself: keep gold rings and jewellery away from cyanide solutions].

Describe what might be the purpose of each of the three cyclones and why they are connected as they are. Also state where the two outlets from the flowsheet might go to next.

Give your answer in the context of the above example. Note: there is no need to describe the answer in terms of grade efficiency curves, simply give a qualitative explanation of what is happening.

             

Answer 1

Solution

Cyclone A is performing a rough separation of the recycled material and fresh feed. The finer overflow from A leaves to cyclone C where it is separated again to improve the cut. The fines leaving in the overflow of cyclone C will be the material going to cyanide leaching (cyanidation).

Cyclone B receives the heavier underflow from A. The heavier material from B will be the larger of the large particles that initially entered. These particles are too big and will likely be recycled back to the crushers, or some other unit operation to reduce their size. They will then likely be returned back to this flowsheet for another attempt at separating them based on size.

The overflow from B and underflow from C are midsize particles from the broad central area of the size distribution curves. These are particles that may be the right size for cyanidation or particles that are too large and require size reduction. Either way, they are recycled over and over through the cyclones until they leave in an appropriate stream.