Dry coal beneficiation of high-ash South African coal utilising a wind sifter separator

Clean Coal Technology Research Group, School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Private Bag X3, Wits 2050, Johannesburg, South Africa.

^* Corresponding author: alade.jimme@gmail.com

Abstract

Beneficiation of high-ash South African coal is challenging, especially in water-scarce regions, amid increasingly stringent environmental regulations. Traditional wet methods, although effective, are unsustainable due to excessive water consumption and high waste slurry generation. Accordingly, this study focusses on evaluating a wind sifter separator for the dry beneficiation of high-ash run-of-mine (ROM) coal, classified into three particle size distributions (PSD's): (-6.7+3.35 mm), (-3.35+1 mm), and (-1+0.2 mm). By applying aerodynamic principles, the wind sifter separates coal based on density and size variations, which provides an alternative to water-based techniques. The wind sifter separator was able to reduce the ash content of the feed coal (37.4 wt. % ash) to 16.7%, with mean probable error (Ep) values of 0.035 to 0.16, depending on airstream velocity. The separator demonstrated operational flexibility by performing efficiently with and without bin collection. The results obtained indicate substantial ash removal while maintaining significant clean coal recovery, offering a viable dry beneficiation solution for water-limited regions. When compared to conventional wet beneficiation and other dry techniques, the achieved balance between ash reduction and energy (or combustible matter) recovery underscores its competitive performance. Furthermore, its design suggests potential uses beyond coal, such as pre-concentration and upgrading of other minerals, which makes it a promising breakthrough for sustainable mineral processing.