Radial and axial mixing of particles in a dry batch ball mill

• Main Author: Chibwana, Clement
• Format: Others
• Language: en
• Published: 2006
• Subjects: radial mixing; axial mixing; mixing kinetics; eye position; near shell position
• Online Access: http://hdl.handle.net/10539/1526

Student Number : 0401422G - MSc dissertation - School of Chemical and Metallurgical Engineering - Faculty of Engineering === Mixing is an important operation that is carried out in food, paint, pharmaceutical and mineral processing industries. Ball mills are one of the many mixing vessels used in a mineral processing industry. During grinding, the mill’s efficiency depends on particle presentation to the grinding media and the adequate utilisation of the applied forces to effect breakage of particles (ore). Utilisation of applied forces is affected by how well particles and grinding media are mixed. The study of charge mixing is important as it affects the mill’s production rate and accelerates media wear, thus relevant to the cost reduction for the milling process. The kinetics of mixing in a batch ball mill were quantified both radially and axially. Experiments were conducted in a laboratory batch ball mill and two experimental programs were used to study the mixing process. Radial mixing of particles was observed to increase with increasing mill speed. For a mill used in this study, mixing of particles at Nc=90% took almost half the total time taken at Nc=75% to reach completion. A simplified mathematical model is presented, which can be used to predict the radial mixing of particles in a ball mill. Axial mixing of particles was observed to be affected by both the charge system used and segregation of particles from the grinding media. It took a minute for mixing to reach 80% completion for a mill used in the experiments. Mixing of particles was faster in a steel balls/plastic powders charge system than in a glass beads/quartz charge system. The distribution of particles in a batch mill was observed to vary along the axis of the mill. The centre of the mill was overfilled with particles, U>1, while the regions near the mill ends were underfilled, U<1. The opposite was true for the grinding media. The data reported was based on measurements of particle distribution along the mill as affected by different charge systems. The work presented in this thesis is a contribution to the continuing research on mixing of particles in ball mills.