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Item Optimisation of the mineral grading wind sifter separator for coal beneficiation(University of the Witwatersrand, Johannesburg, 2024) Alade, Jimmy Joanah; Bada, SamsonThe concept of wind sifting for particle separation has been successfully implemented for various concentration purposes. Diverse configurations based on this concept have been fabricated over many decades. It has been used in recycling, agriculture, electronic waste sorting, furniture, food and beverages, and mineral processing industries to some extent. The approach’s effectiveness stems from the capability of separating lighter particles from heavier ones. This study utilised an optimised version of the wind-sifter that was designed and fabricated by the author during his master's degree. The drawback experienced while testing the first prototype wind-sifting separator led to this investigation. This study used a computer simulation technique (the Lagrangian particle tracking method). This resulted in observing the effectiveness of the separation process in the newly designed separator. The design of the new separator was made flexible in its mode of operation by fabricating detachable collecting bins to the separator assembly. This means the optimised separator can be operated with or without the coal collecting bins, unlike the prototype version, which could only run with its bins. The design of the separator was done with the aid of Autodesk Inventor, and simulation was carried out using Star-CCM+TM computer software. The simulation tests were performed for different particle sizes (−6.7+3.35 mm), (−3.35+1.0 mm) and (−1.0+0.2 mm) at different airstream velocities. The optimal airstream velocities from the previous study (at a cut point of 1.6 g/cm3) were also used in this study when the separator was run with its bins. These airstream velocities were 6.0 to 4.0 m/sec, 4.2 to 2.0 m/sec and 1.7 to 1.0 m/sec for the (−6.7+3.35 mm), (−3.35+1.0 mm) and (−1.0+0.2 mm) particle sizes, respectively. A simulation was used to determine the airstream velocity ranges of the separator without collecting bins. These were 10.5 to 9.0 m/sec for the (−6.7+3.35 mm), 7.0 to 5.0 m/sec for the (−3.35+1.0 mm) and 3.5 to 2.5 m/sec for the (−1.0+0.2 mm) particles. For the –1.0 mm size faction, three particle size distributions (–1.0+0.1 mm), (–1.0+0.15 mm) and (–1.0+0.2 mm) were simulated. The best airstream velocities of 1.7 m/sec and 3.5 m/sec were achieved, respectively, for the closed and opened bins. The results of the simulation study led to the fabrication of the optimised wind sifter used in this study. From the sink and float test conducted on two sets of feed-coal (coal A and coal B), the extent to which the separator could beneficiate coal was determined. The sink and float analysis revealed that coal A has a higher ash content than coal B. Coal A, at (−1.0+0.2 mm) size iii fraction, has an ash content of 4.29% at 1.3 relative density (RD). This is followed by the (−3.35+1.0 mm) particle size with 5.55% ash content and the (−6.7+3.35 mm) size fraction with an ash content of 5.89%. At an RD of 1.5, coal A has a specific ash content of 16.65%, and coal B has an ash content of 13.56% for the (−6.7+3.35 mm) fraction. Upon separating with the wind sifter, the clean coal products from coal A have a higher ash content compared to those from coal B. Running the separator without the bins, clean coal products with cumulative ash content ranging from 22.42% to 19.44% for the (−6.7+3.35 mm), 24.61% to 21.43% for the (–3.35+1.0 mm) and 27.54% to 22.51% for the (–1.0+0.2 mm) fractions were obtained. For the particle size of (−6.7+3.3 mm) and with the bins closed, a clean coal product of 20.21% was obtained from coal A (feed coal with 37.38% ash content). A coal product with 19.55% ash content was obtained from coal B (from feed coal of 26.65% ash). A second-stage test conducted on a first-stage coal product of 23.48% ash content yielded a coal product of 21.79% ash and 80% yield for coal A at (6.7+3.35 mm). This trend was also observed for other first-stage products at the three particle sizes used in this study. The Ep values obtained from this separator ranged between 0.035 and 0.16, with the Ep values increasing as the airstream velocity was reduced. For the (6.7+3.35 mm) fraction, Ep values (Probable Error of Separation) of 0.035, 0.095, and 0.16 were obtained at 6.0, 5.0, and 4.0 m/sec air velocities, respectively. Overall, the cleanest coal product with 16.73% ash and 26.70 MJ/kg was obtained in this study from coal A at bin 2. According to the study’s results, the separator was highly adaptable. The separator could also be used for upgrading and pre- concentrating other minerals in the mineral processing industry.