Present and Future Trends

Traditionally, flotation machine design closely follows the trend of comminution machines in mineral-processing plants. Due to economic considerations in the processing of low grade ores, the present comminution machines such as crushers, semi-autogous, autogenous and ball mills are designed for very high capacities. The Cadia Hill Mine in New South Wales, Australia, which treats a copper-gold ore at the rate of 2100 tonnes per hour, utilizes a 12 m diameter SAG mill (with a 20 MW motor) and two 6.5 x 11 m ball mills (each with a 8.75 MW motor). To be compatible with the comminution circuit, large capacity 150 m3 flotation cells are used in the rougher circuit.

At present, cells are large as 300 m3 are being designed by various manufacturers. Installation of large cells has many advantages:

1. reduction in capital costs;

2. reduced size of plants;

3. reduced power consumption;

4. reduced maintenance;

5. easy control;

6. reduced reagent consumption.

However, with increase in cell size, the problem of machine design and metallurgical scale-up becomes more acute. The scale-up features that may have been tolerated on smaller cells are not applicable to larger cells. The simple similitude considerations used in terms of dimensionless numbers (power number, Froude number, air flow number, Reynolds number) are not sufficient to design large machines. The development and evaluation costs rapidly increase with cell size, which calls for a more rational and fundamental basis in cell design. Extensive research at the Julius Kruttschnitt Mineral Research Centre in Brisbane has shown that bubble surface area flux or Sb is an important criterion for metallurgical scale-up, which will gain more prominence in the future and will be considered as a parameter in conjunction with other important dimensionless numbers used in machine design and scale-up.

An increase in cell sizes also requires more effective froth transportation due to the increase in travel time of bubble-particle aggregates which results in high drop-back and low froth recovery. To address the problem of froth transportation and stability in large cells, new design features such as internal launders, double launders, high capacity launders, booster cones, froth crowders, cross-launders and beehive launders are emerging. More work will be carried out by cell manufacturers and researchers to understand froth transportation and froth recovery. The effect of the interactions of different launder designs, froth crowders and cell-operating parameters such as impeller speed, air rate and froth depth will be the subject of further investigation for better cell design and optimization of cell operation.

The design differences of various cells marketed by different manufacturers are in fact differences in impeller/stator mechanisms and air input systems (either self-induced or forced air type through a standpipe with a solid shaft or through a hollow shaft). However, the design of tanks is similar for different cell types, and resembles the cylindrical design of the old Maxwell cells. The launder and froth crowding devices in different designs are tailor-made to suit different applications.

The large new flotation cells are equipped with integrated control systems. The recent trend of installation of a few large cells in a circuit will see more control instrumentation like air flow control, variable speed drive for speed control, as well as online measurement equipment for monitoring bubble size, superficial gas velocity, gas hold-up and bubble surface area flux, which will be used for better cell performance optimization. Froth vision equipment will also gain prominence for better control of froth in the large flotation cells.

The development of flotation cells will continue as more and more fine particle processing will be necessary in future. The large flotation machines will have to be designed to generate very small bubbles and a high degree of microturbulence for effective bubble-particle collision to remain competitive against other novel technologies like high intensity pneumatic cells. Entrainment will be a major issue in concentrators, which will need refinement of froth-washing technologies in mechanical flotation cells.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment