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The Upgrading of Primary Gold Gravity Concentrates
A.R. Laplante; McGill University, Montreal
April 28th, 2000
Knelson Concentrators have had a profound impact on the practice of gold recovery by gravity, with many successful installations worldwide. As the technology matured, so did the design of primary recovery circuits, the most common option being bleeding of primary cyclone underflow to feed a screen ahead of a 30" Knelson Centre Discharge. Important design considerations have been discussed in Laplante et al. (1994). The Knelson has the virtue of producing very little concentrate mass, which in principle should make downstream processing easy. However, the first author has evaluated many gold rooms, and it has become apparent that most designs (of the wet processing section) have serious flaws, and that in many cases adequate retrofit would prove very difficult, generally because of lack of head room. In all fairness to designers, the gold room design problem is a difficult one, despite the small mass treated (typically 1 t/d), because of the unique properties of Knelson concentrates, which are very seldom characterized at the design stage (i.e. rheology, settling rates, size distribution, tramp iron content). There is little literature on the topic, and no generally accepted practice.
In this contribution, the authors examine how Knelson concentrates are produced (i.e. the gold room feed), what wet processing in gold rooms should achieve, flowsheet design and circuit layout, with particular emphasis on the addition of a scavenging stage to maximize recovery (at which point experimental work will be presented). Different processing alternatives are discussed briefly.
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