Float process

The response of any given feed to sink-float processing can be accurately established in the laboratory by testing with various heavy hq-uids. The hquids generally used for this purpose are listed in Table 19-12. These halogenated hydrocarbons are mutually miscible, which enables the preparation of almost any pulp density attainable in a commercial plant. Heavy-hquid test work provides the basis for specifying the optimum screen size for the preparation of the feed. 

Chemical Additives The use of chemical additives in sink-float processing is not common except for the use of lime to prevent oxidation and decomposition of the medium. A small amount of clay is sometimes added to improve the kinetic stability of the suspension. 

Costs Because sink-float processing is applied to relatively coarse particles and is a single-pass operation, capital and operating costs are usually considerably lower than would be required for a flotation or a gravity mill of the same capacity. A large flow of water is required for feed preparation and for media recovery, but almost total recoveiy for recirculation is possible. A minimum of two job-trained operators per shift is generally required by law, but these would be able to attend several separators at almost any feed rate. 

Dense-medium separators (sink and float processes)... 

FIG. 107. The principle of sheet glass manufacture by the float process (Pilkington, 1969). 

The current process of heavy media separation (HMS sometimes called dense media separation) is the most widely used sink-float process today and is very efficient at reducing the acid-insoluble content of magnesite however, it is not as effective at reducing the lime content. This means that magnesite undergoing HMS can have a much higher insoluble content than that of lime and still achieve a chemical purity equivalent to that of direct-haul ore. The practical limit for the lime content is approximately 6wt%, while the limit for acid-insoluble material can be as high as 20 wt%. 

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