Fourth generation gravity separation using the Reflux Classifier

• Fourth generation Reflux Classifier investigated for the first time. • New fluidisation based on slow rotating rake to develop dense medium zone. • Step change increase in upgrade of tin achieved using a single stage separation. The Reflux Classifier achieves powerful synergy between an upper system of inclined channels and lower fluidised bed arrangement, delivering gravity separation in a single stage of separation. This paper is concerned with the step-change improvement in gravity separation utilising the latest in a series of improvements. The laminar-shear separation mechanism led to the introduction of closely-spaced inclined channels, nominally 6 mm, solving a previously intractable problem in concentrating metallurgical coal. The more recent shift to a spacing of 3 mm, and even 1.8 mm has delivered a further step change in the separation of gangue minerals from dense minerals. In this new work, we have introduced changes to the lower fluidised bed, removing the fluidisation distributor and installing a slow-moving rake with water addition. This change produced a much more robust fluidisation boundary condition, removing the vagaries of the minimum fluidisation condition, producing a stronger dense medium effect, hence significant step change in gravity separation performance well beyond anything that was previously possible. This step change in performance reveals a direct pathway from a feed grade of 0.32 wt% tin to a significant recovery of the tin at a grade higher than 40 wt%.