Metals Adsorption From Bioleaching Solution of Printed Circuit Board

Adsorption of Metals from Bioleaching Solution of Printed Circuit Board

Len Foong KOONG, Gordon MCKAY, John BARFORD

The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong

Printed Circuit Boards (PCB) are used to physically support and electrically connect electronic components via copper conductive pathways. They are composed of polymers, glass fiber, solder and metals, most of which are hazardous to the environment if not disposed or treated carefully. In the last two decades electrical and electronic products have become more affordable and better, due to the rapid innovation of the industry. As a result, the product life becomes shorter and more electronic waste is generated, adding stress to the environment, landfill space and public health. Thus it has become of great interest to improve the recycling of waste PCBs. The current technology first removes recoverable components via manual or robotic disassembly line; the materials on the scrapped PCBs are then recycled by mechanical separation, pyrometallurgy or hydrometallurgy. Bioleaching of PCBs is gaining more attention recently as a more environmental friendly and cheaper treatment for PCBs. Researchers have found that the mixture of bacteria Acidithiobacillus Ferrooxidans (A. ferrooxidans) and Acidithiobacillus Thiooxidans (A. thiooxidans) can effectively leach out metals from PCBs, notably copper, nickel, zinc, lead and tin. As the culture mixture produces sulfuric acid, lead and tin will precipitate as sulfate salts. However there is still a need to recover the remaining metals from the bioleaching solution. Two types of adsorbents: synthetic compound NH2-MCM-41 and commercially available Chitosan are used in the single and binary components isotherm studies. NH2-MCM-41, a type of mesoporous silica grafted with aminopropyl groups and known for its heterogeneity of surface functional group is used to compare with the selectivity (binary components studies) and capacity of Chitosan (single components studies) which contains primary amine as functional group. Ultimately it is our goal to separate the metals individually to make downstream recovery easier.