Characteristics of powder charging behavior via forced triboelectric charging on an inclined chute

This study presents a novel method for selective charging of powders by dry triboelectric forced charging utilized as the first stage of material sorting in an electric field. In forced triboelectric charging, a high voltage is applied to the copper chute in which particles are charged during their transportation. In this research, the effect of the operating parameters of the chute, including mass flow rate, angle of inclination, and length, on the specific particle charge of limestone powders was investigated. In addition, the behavior of the charged particles in an electrostatic sorter was analyzed by evaluating their charge distribution after sorting. The results reveal that as the length of the chute increases, the specific charge asymptotically approaches a saturation value, which is determined by the high voltage applied. Furthermore, for a given chute length, the high voltage influences the amount and the sign of the specific particle charge, including a high voltage value at which the particles are neutral on average, i.e., the so-called point of zero net charge (PZNC). This PZNC is of particular interest for sorting out a target component from a powder mixture. However, if the mass flow rate is increased above a certain value, the specific charge decreases as the number of particle wall contacts is reduced due to stratification. Bipolar charge distributions were observed for all investigated high voltages, with the distribution width increasing with particle size to the power of 2.1. The modal value of the charge distribution shifts according to the difference in voltage applied to the PZNC.