The Jameson Cell

The Jameson Sotation cell was invented by Professor Graeme Jameson at the University of Newcastle, Australia, in 1986. It was developed to a practical reality at Mount Isa Mines, Mount Isa, Queensland, and was licensed to MIM Holdings of Brisbane in 1989. To date, there are 187 installations worldwide, in 19 countries. The cell is used for roughing, scavenging and cleaning, and also for removing oil haze from solvent extraction liquors. The distribution by field of use is coal 37%; copper 29%; other minerals 17%; and solvent extraction 17%.

In this cell, contact between particles and bubbles takes place in a dense foam which is produced in a vertical downcomer, as depicted in Figure 2. The pulp is introduced to the top of the downcomer as a confined liquid jet, and air is entrained into the feed and broken up into fine bubbles by the jet. A dense foam with a high void fraction is created in the

Figure 2 Schematic of the Jameson cell. The height overall is approximately 2-3 m. The cross-sectional area of the cell is directly proportional to the desired feed flow rate.

downcomer, creating a very favourable environment for collision of particles and bubbles. In fact, because of the high void fraction, of the order 50-60% by volume, the pulp is distributed in the form of thin liquid films between the bubbles, and collection occurs by migration of particles within the thin films, which are not much thicker than the diameter of the particles.

The dense mixture of bubbles and pulp discharges at the base of the downcomer, and the bubbles disengage from the pulp, rising into the froth layer. The bubble-free pulp discharges as tailings from the bottom of the cell. The froth behaves like that on top of a flotation column, in that grade and recovery can be strongly inSuenced by the froth depth and the application of washwater, and the upward superficial air velocity Jg. From the point of view of collection, the downcomer operates best when the ratio of air rate to feed rate is less than one-to-one on a volume basis.

The froth is treated much as in conventional columns. Washwater is usually applied if a high grade product is required. As with columns, when the air rate is altered, both steps in the Sotation process - particle/bubble contact and froth entrainment - are affected. Thus an increase in air rate may cause an increase in recovery because more bubble surface area is created on which to capture particles, and because changes in the ratio of bubble to particle sizes will affect the probability of collision. At the same time, there may be an increase in entrainment of the gangue into the froth which may lead to a decrease in grade, unless steps are taken to remove the entrained gangue by changes in froth depth and wash-water rate. Thus the optimum performance of the cell is related to the air superficial velocity, Jg. The key features of the cell are:

1. The contacting environment is highly intensive, so that only short residence times are required. The total cell residence time is 1-2 min; the residence time in the downcomer is around 10 s. A short column is therefore produced which is ideal for retrofit, or installation in cramped headroom. The Soor area is, however, similar to that required by conventional columns for the same throughput.

2. The bubbles formed by the impinging jet are very small, offering enhanced carrying capabilities for fine concentrate particles.

3. Air is drawn in from the atmosphere and no air compressor or blower is needed.

4. In the cleaning zone, with the use of washwater, the levels of concentrate grade approach the maximum levels possible.

The size of bubbles produced in the flotation cell is an important determinant of cell capacity. The mass of particles which can be carried out on the surface of the bubbles is dependent on the gas-liquid interfacial area. For a given gas flow rate, the interfacial area is inversely proportional to the bubble size, so there is an advantage in making small bubbles. However, it must be kept in mind that in the disengagement zone, the buoyancy of the bubbles must be sufficient to lift particles of the largest size in the pulp to the surface of the liquid. The best compromise appears to be to make bubbles in the range 0.35-1 mm. Bubble sizings on full scale operating cells and test cells show that the Jameson cell produces an arithmetic mean bubble diameter of the order of 300-600 |im, while the Sauter (volume-to-surface) mean diameter, dvs, is of the order 360-950 |im. These sizings compare very favourably with conventional columns where the Sauter mean bubble size is typically 2-3 mm.

Some general operating characteristics of the Jameson cell are now discussed.

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