The 5 Main Steps in Processing Diamond Ore
Diamonds mined in major diamond mining countries such as Russia, Botswana, South Africa and Canada are mostly destined for the jewellery market and the remainder for industrial use. Industrials feature in the fabrication of various drilling tools such as diamond drill bits or cutting equipment such as diamond saws.
Diamonds are generally found in rock known as kimberlite. Kimberlite contains other heavy minerals such as garnets and chrome diopsides, along with small amounts of diamonds. The origins of the word “diamond” imply “invincibility”, a reference to its extreme hardness.
Here are the main steps in processing diamond ore. A number of these processes use equipment from Multotec:
The first step in kimberlite ore processing is crushing. This process reduces large run-of-mine lumps into smaller pieces, making them easier to handle, and releases or liberates the diamonds to be recovered in subsequent steps. Crushing is done in stages to “gently” free the diamonds from the kimberlite rock and produce a target size, usually less than 25 mm, for further processing. You don’t want the pieces to be too small, because you don’t want to crush the diamonds!
Ore is sized using vibrating screens after each crushing stage. Wet screening is usually preferred as the ore from the mine is already wet and wet processing eliminates the need for dust control. The choice of the correct screen panels is crucial to achieve efficient screening.
Scrubbing is used to wash and break down clay lumps present in the ore. Once the ore is scrubbed it is wet screened to remove unwanted fine material less than 1 mm in size. Diamonds below this size are of little value and are discarded. Collectively, the process of crushing, scrubbing and screening prepares the ore for the concentration process, where dense media separation is used.
The heavy minerals, including diamonds, are separated from waste material based on their density differences in a dense media separation process. In this process, ore is mixed into a ferrosilicon slurry, then fed to a dense media cyclone, where the heavy minerals are separated from the waste. The heavy minerals sink and exit the bottom of the cyclone to a sinks screen, and the waste floats and exits the top of the cyclone to a floats screen. The ferrosilicon is recovered for reuse with a magnetic separator. The density of the ferrosilicon is maintained using densifying cyclones. The diamonds in the concentrate are recovered downstream in the recovery process. Modern flowsheets now incorporate x-ray sorters to concentrate ore larger than 10 mm and thus replace dense media separation for this feed size.
Finally, in the last step, the diamonds are recovered in various ways:
- On belts or vibrating tables coated with a specially formulated grease that only the diamonds stick to. The grease is melted and the raw diamonds recovered.
- By x-ray sorting, which identifies diamonds as they fluoresce or by their atomic mass.
We guarantee that Multotec Canada’s diamond ore processing equipment is adapted to every step in processing. Contact our team for more information on our products!