Coal Preparation » Gravity Separation
This project explored the impact of various clay minerals on the stability and efficiency of Dense Medium Cyclones (DMC) used in coal processing, particularly at lower relative densities. Clays, once considered contaminants, are now recognised for their dual role in altering the medium's rheological properties and contributing to non-magnetic stabilisation. This project aimed to evaluate these effects through laboratory and pilot plant experiments by analysing plant samples from four mines and creating simulated media to replicate real-world DMC conditions.
Laboratory tests revealed that double-layer clays, such as bentonite, increased medium viscosity and decreased settling rates, while single-layer clays, like kaolinite, showed lower viscosities and faster settling. Pilot plant experiments, conducted at CSIRO's DMC facility, utilised a 150mm cyclone to investigate the effects of clay type, medium density (relative density, RD), magnetite grade, and non-magnetic content (non-mag) on key performance indicators: Ep (separation efficiency), d50 (cut point), and pressure.
Results highlighted that medium density (RD) significantly affects all key variables, with higher RD improving separation efficiency. Double-layer clays negatively impacted efficiency by increasing Ep but slightly reduced d50 due to their stabilising effect. Magnetite grade and non-magnetic content also influenced d50 and pressure but to a lesser extent.
The project underscores the critical importance of medium density and clay mineralogy in maintaining DMC stability. Effective management of medium density and clay proportions is essential for optimising DMC performance and achieving efficient separation.