The use of batch type centrifugal gravity concentrators has been accepted by industry for the past 10 years with many units having been installed across the globe. The main objective behind installing these units is to remove gold lock-up within grinding circuits. However, the handling of the high-grade concentrates that are produced has become the no.1 concern for many mining companies.

Falcon Concentrators Inc. looked at this in detail and has developed a flowsheet that eliminates the downstream difficulties and security risks by using continuous concentrators within the grinding circuit. The process remains the same within the grinding circuit, but the concentrate treatment is somewhat different yet easy to understand and implement.

This report examines the details of installing the Falcon C continuous concentrators within grinding circuits and looks at the advantages for such a circuit.

Falcon has been involved with gravity concentration for the last 13 years, having designed two distinct ranges of equipment; a semi-continuous Falcon SB range for installation into grinding circuits and the recently released Falcon C range for pre-concentration and scavenging in a wide range of mineral industries.

Metallurgical and efficiency data from a recent evaluation on a Falcon C40 concentrator on Pittsburgh No.8 seam coal is presented at mass throughput capacity values in excess of 100 tonnes/hour.  The particle separation density for 1mm x 75 micron coal was about 1.60 with relatively high efficiency (EP = 0.12).  Typical ash and sulfur rejection values of 85% and 70%, respectively, were achieved while recovering 85% of the combustible material.

An introductory paper describing the theory and principle behind gravity "bowl" concentrators. Falcon applications in African gold recovery and an initial pilot campaign at Kleinkopje Colliery are presented.

The Falcon Model "C" concentrator is discussed in its ability to treat fine coal in relation to several other enhanced gravity separators as well as spiral concentrators and flotation columns. The relatively high g-forces supplied by the Falcon units give it the ability to achieve more efficient, low gravity cut points on fine coal while demonstrating operational simplicity.

A discussion about the ability of the Falcon C40 to reject ash and sulfur to clean fine coal streams with results and operating experience derived from processing many different coal samples and feed characteristics over a one year period. Good metallurgical results and mechanical availability as well as accurate C10 to C40 scale up is confirmed.

This paper discusses the results of tests conducted with a Falcon C10 unit on several Illinois coals. The Falcon is shown to be very effective at cleaning both ash and sulfur from coal samples in the 28 x 325 size fraction. The ash content of a 100 x 325 Illinois No.5 coal sample was reduced from 18% to 8% with a high combustible recovery of 97% and a total sulfur rejection of 45%. The separation performance achieved on size fractions between 28 x 325 was found to be better or equal to that achieved by release analysis, indicating the possibility of eliminating the need for relatively expensive froth flotation for treating these size fractions. The effects of critical operating parameters of the Falcon on separation performance is also investigated and optimized.

An overview of coal preparation stressing the challenges of economically processing and cleaning fine coal streams with comparisons between conventional and new technology. Falcon is highlighted as being very effective for cleaning fine streams and holds much promise for future preparation plants.

This paper identifies the drawbacks of traditionally recognized surface-based separation processes for cleaning fine coal streams and discusses the merits and recent promising developments in enhanced gravity separators. It describes the basic working principles of several new generation gravity separators including Falcon and provides a review of the advantages and limitations of each for fine coal processing. Topics addressed in this paper include separation performance, unit capacity and process economics

Introductory coal washing results using a lab scale batch Falcon concentrator are investigated. The paper discusses the sharp decrease in flotation efficiency in the presence of high-ash middling particles and the advantages of a gravity based process. The Falcon demonstrates effective treatment of Pittsburgh coals and warrants production scale testing.