This centrifugal concentrator can recover fine particles of free gold. The pulp is screened in order to avoid coarse particles such as 4 mm or more. The material in slurry form is fed centrally to the bottom of a ribbed inner cone rotating at a high speed. Centrifugal force causes the first feed to fill the bottom rib with solids and the next higher slightly larger diameter rib with solids and the next higher slightly larger diameter rib and subsequent ones are sequentially filled in few seconds. After that all the feed moves upward as thin film over the conical surface of the sand filled ribs and out. Compaction of solids trapped in the ribs of the cone is prevented by adding water through a series of holes in the cone wall. In this way, the trapped solids are fluidized.
The Knelson concentrator employs the principles of hindered settling and centrifugal force. A central perforated cone containing horizontal ribs is rotated in order to get a centrifugal force of 60g (g is gravity acceleration). The cone is surrounded by a pressurized water jacket that forces water through holes to keep the bed of heavy particles fluidized. In this way, the force of the water acts against the centrifugal force of the rotating cone.
If there are free gold particles or particles transporting gold in the film of slurry that is passing over the fluidized solids trapped in the ribs of the cone, they will penetrate the fluidized bed under enhanced gravity situation and displace lighter particles of similar volume trapped in the rib. This process is repeated several times until saturate the ribs with heavy particles. In other words, this is a trading process that exchange light particles for heavy particles.
Cut away schematic of a Knelson Centrifugal Concentrator
The pressure and flow of fluidization water controls the concentrate bed and porosity and hence the capacity to select what minerals will or will not into the concentrate. Many operator think that lower pressures are employed for lo specific gravity gangue material and vice versa. Also higher pressure will be used for coarse particles due to more water will be needed to clean the concentrate bed.The flowsheet can include a Knelson concentrator in the primary grinding circuit in order to recover the gold present in the underflow due to this stream contains heavy particles and the problem of fine particles of gangue is minimized. The Knelson can be used to as rougher and cleaner units and the last cleaning stage is performed in shaking tables, typically a Gemini table has proved to be very efficient.
By using a Knelson Concentrator can be recovered fine free gold/electrum particles from the grinding circuit. The ratio of concentration for gold in a hydrocyclone is a good way to estimate if gravity concentration is possible. Normally if the gold is concentrating to the underflow, then it must be as a free gold bearing alloy. When a pilot scale testing is possible, we can confirm many design parameters and flowsheet options. A big plant will determine the effect of a gravity circuit on the plant gold distribution. In this way, the gravity circuit must improve the plant payment for gold. The method of handling gravity concentrate is plant dependent. Plants with gold treatment or with significant gravity gold production may include a smelting stage in order to get a gold ingot.
Jigs and Knelson Concentrator | Spiral, Cones and Centrifugal Concentrators | Effect of Particle Size on Knelson Concentrator Performance | Applicability of the Knelson Concentrator | How to Study the Performance of the Knelson Concentrator | Overload of the Knelson Concentrator | Recovery of Fine Gold Using a Knelson Concentrator Operation Mechanism of the Knelson Concentrator | Using the Knelson to Retreat Table Tails | Using the Knelson Concentrator to Evaluate Gold Gravity Circuits |