2015 Volume 56 Issue 1 Pages 140-148
When recycling important rare metals (such as tantalum) from the printed circuit boards of waste electronic equipment, electronic devices must first be delaminated from the boards. The devices are then separated into individual device types. We previously developed a double-tube pneumatic separator for practical use in the separation process. One of the features of this equipment is the introduction of orifices in a pneumatic separation column, and experiments and an airflow simulation were conducted to clarify its effect. This study investigated the effects of the length of the distance between the orifices (separation room) and the airflow rate on the airflow velocity profile in the separation room and the separation characteristics of tantalum capacitors and quartz resonators focusing on the length of the separation room in the separation column. The results suggested that the separation column could be divided into four typical zones where the velocity profiles changed toward the top of the column: (1) high velocity zone where floating particles were forced to accelerate, (2) maintaining a relatively uniform velocity profile, (3) changing to a more uniform velocity profile, and (4) changing to a velocity profile with a slightly higher velocity around the column center. The main reason for the formation of zones (2)–(4) was that the internal airflow in the column had yet to become a fully developed turbulent flow. In these zones, there was relatively little difference between the velocity at the column center and that around the center to form a uniform velocity profile. Therefore, there was possibly a high-accuracy separation based on the difference in particle density. We defined these zones as ‘separation zones’. Under the experimental conditions used, and applying the optimum separation velocity for the airflow, which was estimated by performing a floating–falling experiment on each electronic device, it transpired that a high separation efficiency was obtained when the separation room was longer than 300 mm. In addition, when using 4% less than the optimum airflow rate, if the length of the separation room was 300–500 mm, that is the length of the separation zone was 50–250 mm, separation could also be achieved with high efficiency.