Attention towards beneficiatingfine coal currently sentto tailings has grown recently, motivated bythe need for improved plant yield, and improved environmental management (Mercuri et al., 2014). Historically, the major obstacles preventing feasible beneficiation of hydrocyclone overflow include firstly, the need to process low pulp density feed at a high volumetric rate, and secondly, the high level of ash rejection necessary in order to produce a saleable coal product. Previously the first obstacle has led to prohibitive capital cost and hence long pay-back times, while the second has led to significant risk in delivering product with a satisfactory calorific value via the mineral matter and moisture, and a robust separation performance. To overcome these challenges, advancements in fine particle beneficiation technology are required. One emerging technology, the Reflux Flotation Cell (RFC), offers a unique two-stage solution to rapidly separate and clean fine coal particles from low pulp density tailings. The first stage facilitates as a rougher to quickly concentrate the fine coal, and reduce the flotation footprint by a factor of five or more by enhancing the throughput rate per unit vessel area. The second stage facilitates the cleaning of the recovered coal to deliver a low ash coal product from the first stage product through an effective distribution of fluidization wash water. The RFC utilizes a system of inclined channels to enhance the bubble-liquid segregation rate through a novel application of the Boycott effect (Boycott, 1920), thus enabling significantly higher gas and liquid fluxes, and bubble surface area fluxes per unit vessel area compared to conventional flotation devices (Jiang et al., 2014). Bubbles entering the inclined channels located below the vertical compartment encounter an effective increase in vessel area, thus allowing entrained bubbles to rise to the top of the channels and return, or reflux, back to the vertical compartment and avoid their loss to the tailings. This phenomenon has shown to deliver high flotation throughput capacity, achieving feed fluxes of up to a ten times greater than used in conventional flotation (Dickinson et al., 2015). Furthermore, exceptional cleaningand slimes rejection has beendemonstrated throughthe application of uniformfluidization wash water delivered downwards through the RFC plenum chamber that formally encloses the top of the system (Galvin et al., 2014).
展开▼
