Evaluation of a recycling process for printed circuit board by physical separation and heat treatment.
Printed circuit boards (PCBs) from discarded personal computer (PC) and hard disk drive were crushed by explosion in water or mechanical comminution in order to disintegrate the attached parts. More parts were stripped from PCB of PC, composed of epoxy resin; than from PCB of household appliance, composed of phenol resin. In an attempt to raise the copper grade of PCB by removing other components, a carbonization treatment was investigated. The crushed PCB without surface-mounted parts was carbonized under a nitrogen atmosphere at 873-1073 K. After screening, the char was classified by size into oversized pieces, undersized pieces and powder. The copper foil and glass fiber pieces were liberated and collected in undersized fraction. The copper foil was liberated easily from glass fiber by stamping treatment. As one of the mounted parts, the multi-layered ceramic capacitors (MLCCs), which contain nickel, were carbonized at 873 K. The magnetic separation is carried out at a lower magnetic field strength of 0.1T and then at 0.8 T. In the +0.5mm size fraction the nickel grade in magnetic product was increased from 0.16% to 6.7% and the nickel recovery is 74%. The other useful mounted parts are tantalum capacitors. The tantalum capacitors were collected from mounted parts. The tantalum-sintered bodies were separated from molded resins by heat treatment at 723-773 K in air atmosphere and screening of 0.5mm. Silica was removed and 70% of tantalum grade was obtained after more than 823K heating and separation. Next, the evaluation of Cu recycling in PCB is estimated. Energy consumption of new process increased and the treatment cost becomes 3 times higher comparing the conventional process, while the environmental burden of new process decreased comparing conventional process. The nickel recovery process in fine ground particles increased energy and energy cost comparing those of the conventional process. However, the environmental burden decreased than the conventional one. The process for recovering tantalum used more heat for the treatment and therefore the energy consumption increased by 50%, when comparing with conventional process. However, the market price for tantalum is very large; the profit for tantalum recovery is added. Also the environmental burden decreased by the recycling of tantalum recovery. Therefore, the tantalum recovery is very important step in the PCB recycling. If there is no tantalum, the consumed energy and treatment cost increase in the new process, though the environmental burden decreases.
Department of Systems Innovation, The University of Tokyo, Hongo Bunkyo-ku, Tokyo 113-8656, Japan. Electronic address: tfujita@sys.t.u-tokyo.ac.jp.
Toyohisa
T
Fujita
Dowa Eco-System Co. Ltd., Tokyo 101-0021, Japan.
Hiroyuki
H
Ono
Department of Systems Innovation, The University of Tokyo, Hongo Bunkyo-ku, Tokyo 113-8656, Japan.
Gjergj
G
Dodbiba
Aita University, Akita 010-8502, Japan.
Kunihiko
K
Yamaguchi
D004853:Epoxy Resins / Q000737:chemistry; D005557:Formaldehyde / Q000737:chemistry; D006358:Hot Temperature; D007220:Industrial Waste / Q000032:analysis* / Q000191:economics; D010636:Phenols / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D059027:Recycling / Q000191:economics / Q000379:methods*; D012037:Refuse Disposal / Q000191:economics / Q000295:instrumentation / Q000379:methods*; D013635:Tantalum / Q000737:chemistry* / Q000191:economics
D004853:Epoxy Resins; D007220:Industrial Waste; D010636:Phenols; D011108:Polymers; D005557:Formaldehyde; D013635:Tantalum; C011529:phenol-formaldehyde resin
Evaluation; Heat treatment; Physical separation; Printed circuit board; Recycling