Coal Preparation

Economic Effect of Low Amounts of Non-Magnetics in the Correct Medium

Coal Preparation » Gravity Separation

Published: November 16Project Number: C23046

Get ReportAuthor: Michael O’Brien and Bruce Firth | CSIRO

This project has developed a methodology by which the economic loss incurred in a plant when processing a coal through a Dense Medium Cyclone (DMC), operating with a correct medium relative density less than 1.4, when the non-magnetics concentration in the correct medium is varied due to plant stoppages, feed changes, clay breakdown or bleed valve setting changes can be determined. The genesis for the project came from several previous ACARP projects which examined the effect of the non-magnetic material concentration in the magnetite medium. The results of those projects showed that instability can occur with mediums that contain less than 20% by weight of non-magnetic material with a particle size less than 0.200 mm and with a correct medium relative density (RD) below 1.4.

The concentration the of non-magnetics in the medium can depend on the feed rate to the plant, the amount of clays in the feed, the breakdown of particles in the DMC circuit and the setting of the bleed to the magnetic separator. Sherritt, in ACARP C20045, found that if everything else was held constant and the feed rate to the plant changed then the amount of non-magnetics in the correct medium is directly proportional to the feed rate.

The use of a model to describe the washability of a coal was considered for this project as it would allow a quantitative description of the washability with a limited number of variables and facilitate the calculation of coal recovery when a partition curve was applied to it. Washability curves relate the mass and ash value of a density separated coal fraction to the density at which the corresponding separation was made. Only two basic relationships are required to characterise washability, the first relates ash value to relative density, and the second defines the distribution by mass % of the relative density fractions.

Two models were developed that described the ash value to relative density relationship and the distribution by mass % of the relative density fractions for the 39 Australian washability's provided by Armstrong that covered the "good" the "bad" and the "ugly" range of washability's over six categories.

An e-newsletter has also been published for this project, highlighting its significance for the industry.


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