Intensive Cells Design

flotation bank, it is possible to achieve high recoveries of a floatable material.

In recent times, a number of flotation machines have been introduced which seek to reduce the residence time, by using new ways to bring about the contact between particles and bubbles. These are referred to as intensive flotation cells. Although the way in which the air is introduced - and the bubbles are made - differs from one type to another, they share a common feature. The collision between particles and bubbles does not take place within a liquid with a low number concentration of bubbles, or with a low gas hold-up. Rather, the air is introduced in such a way that contact is made in a device with a high air void fraction - a high ratio of gas volume to a given liquid volume. Once contact has been made, the bubbly mixture, which resembles a dense foam, passes to another vessel where the bubbles can disengage from the liquid, bearing their load of floatable particles to the supernatant froth layer.

The formation of bonds between bubbles and particles after collision is an essential step in flotation, and the topic has received much attention in flotation theory and practice. It has not always been appreciated that phenomena which take place in the froth phase above the liquid can also have a large effect on overall flotation performance. While the yield or recovery of floatable material obviously requires an efficient mechanism for contacting particles and bubbles, the grade or purity of the product is largely determined by froth-phase phenomena. When a continuous cloud of bubbles, whose surface contains selectively adsorbed hydrophobic particles, rises upwards through the froth-liquid interface, some of the liquid is trapped between the bubbles and is entrained into the froth layer. This liquid is the same composition as the main liquid in the flotation cell, so the concentration of gangue or waste particles in the liquid in the froth is approximately the same as in the liquid layer from which it arose, at least in the first instance. The presence of nonselective particles in the entrained water will reduce the grade of the concentrate product. While the bubbles are rising in the froth, the liquid layers between bubbles are draining, and gangue particles are carried downward, returning to the pulp layer. Over the last 20 years, it has become commonplace to apply clean water to the top of the froth layer, causing a continuous downward flow through the froth which tends to wash out the entrained gangue. With froth washing, flotation products of very high grade can easily be produced. (This assumes that the valuable material is completely liberated from the gangue by grinding. Any gangue which is locked into valuables will generally float with the latter, thereby reducing the concentrate grade.)

The main objectives in the design of froth flotation equipment are always the same: to produce a device capable of achieving high grades and recoveries, with small size, minimum capital and operating costs, ease of operation and maintenance. To meet these objectives, many new cells have been tried over the years. This review will concentrate on the limited range of such cells which can genuinely be described as intensive, in that the contact time between bubbles and particles is very short, and the flotation cells are correspondingly quite small relative to the throughput. These are the air-sparged hydrocyclone (ASH), the Jameson cell, and the Ekof cell.

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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