Outline of the Factors Influencing Single Cell Design

In general, the contractor is responsible for the engineering design of the cell, while the customer is responsible for the design of the separation system. This involves the selection of both chemical collectors, depressants and frothers and also the solution pH. The principles underlying these have been thoroughly discussed earlier.

In addition, the degree of pretreatment required to liberate the desired component from the waste, prior to the flotation separation, has to be decided. Obviously the two parties to the project have to interact and this is done in the first instance through laboratory and pilot plant trials, followed if possible by a large-scale plant trial.

The contractor's responsibility is to provide, within economic constraints, equipment in which dispersed bubbles of a specified size will be generated in the pulp, to achieve efficient bubble interception with particles of a specified density and size distribution. The fundamental considerations underlying this have been discussed earlier. There are two main types of equipment, which employ very different techniques for bubble-particle contact.

Mechanical sub-aeration cells In these cells the pulp is stirred vigorously by a centrally located agitator, on of whose functions is simply to prevent solids settling. In most cells the central agitator also induces air down an annulus surrounding its shaft and disperses the air radially as bubbles into the pulp. The intense turbulence generated by the agitator favours a high rate of bubble-particle collision, but also if the turbulent intensity is too high then previously attached particles may detach from the bubble surface.

The flow pattern in these cells divides into an intense inner region in the vicinity of the impeller, and a much larger less turbulent outer region in the bulk of the cell. In the relatively quiescent outer region the bubble-particle aggregates rise to form a froth. The cell design provides a sufficient depth between the pulp/froth interface and the overflow weir to permit drainage of some entrained solids. In commercial cells the froth can be removed by mechanical scrapers so froth mobility at the overflow is not usually a serious concern.

Finally, a class of cells should be mentioned in which specific attention is paid to achieving a high degree of bubble-particle contact without subsequent detachment. One example of this class of intensive cell, pumps the feed through a venturi nozzle which induces air under pressure into the low pressure region at the venturi throat. This causes bubbles to form which appear to nucleate on the solid particles.

Column cells In these cells particle-bubble interception occurs under low turbulent conditions essentially through particles settling under gravity meeting rising bubbles. The bubbles are introduced at the bottom of the collection zone through a sparger, and the feed particle suspension near the top of the collection zone. The low approach velocities of fine particles settling slowly and bubbles rising against down-flowing water reduce the interception rates, thus requiring more possible contacting opportunities, leading to very deep collection zones.

At the top of the collection zone a froth bed forms, which itself may be deep with bed depths of over 1 m being reported. The column cells produce very high purity products, achieved largely by the displacement of entrained water after adding wash water to the upper froth surface.

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.

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