Copyright © 2019 by the International Astronautical Federation (IAF). All rights reserved. Differences in the electrostatic properties of materials can be exploited for both the sizing and enrichment of minerals. In this study, the motion of silica particles falling through an electrostatic field was investigated to characterise a custom free-fall electrostatic separator. The motion was affected by varying the magnitude of the electrostatic field and the spacing of the electrodes. SiLibeads (spherical silica) were sized and tribocharged in a borosilicate glass beaker and fed into the separator. Fourteen electrostatic field strengths each generated at three different electrode spacings (75 mm, 150 mm, and 225 mm) were studied. The percentage of particles reporting to each electrode was measured. Analyses of the results indicate that the expected linear increase in the field strength does not increase proportionally the amount of material reporting to each electrode, indicating that additional underlying parameters must be characterised. Further, an analysis of the variance between the measurements indicates that there are almost no significant effects on the separator's operation due to changing either the field strength or electrode spacing. However, two statistically unique operating conditions were identified. The measurements collected at a field strength of 0.04 kV/mm with a 75-mm spacing were unique relative to other field strengths at that spacing and may indicate an optimal operating condition. Further, the data collected at each electrode spacing with a constant electric field strength of 0.06 kV/mm were also found to be unique. This implies that there may be a performance dependence on electrode spacing in addition to the field strength. Further analysis and experimentation are required to draw more detailed conclusions.