Gravity separation has been an important method of gold recovery for thousands of years. There is no doubt that it is an economical, pollution-free method, especially when compared to cyanidation. It is still extensively used in the world and has experienced a resurgence in popularity because of the advent of the Knelson Concentrator. It can be expected that gold recovery by gravity separation will continue to play an important role, especially for small and middle sized gold mines.
In most of the gold gravity circuits, primary gold concentrates with 0.2 to 5% gold are produced by Knelson Concentrators or jigs. There is a trend of replacing jigs by Knelson Concentrators. The primary concentrate is accumulated and treated daily by a shaking table to produce a concentrate with a gold content of 40-80% for smelting. The tabling operation is labour intensive, a security risk, and expensive, especially when the primary concentrates are produced with the Knelson Concentrator. Exploiting the use of the Knelson Concentrator as a cleaner to replace or supplement shaking tables promises to be very attractive.
For the third stage (smelting), the high grade of the furnace feed is obtained at the cost of recovery during tabling. Smelting is expensive, cannot separate silver from gold, as well as having environment problems due to the release of sulphur dioxide. Intensive cyanidation is not suitable for many gold mines because of the small quantity of the concentrate produced, typically 1 tonne per day, making its operation difficult to justify. Therefore, chlorination, an alternative which can treat high grade gold gravity concentrates to produce very pure gold and separate silver, is a promising alternative.
In many gold mine sites, for the primary stage of upgrading, there is a trend for jigs to be replaced by the Knelson Concentrator; for the secondary stage, upgrading is likely to remain gravity, but tabling will be supplemented or replaced by Knelson Concentrators.